U.S. patent application number 11/615559 was filed with the patent office on 2007-05-10 for electric arc welder system with waveform profile control for cored electrodes.
This patent application is currently assigned to LINCOLN GLOBAL, INC.. Invention is credited to Russel K. Myers, Badri K. Narayanan, Patrick T. Soltis, Elliot K. Stava.
Application Number | 20070102406 11/615559 |
Document ID | / |
Family ID | 34935271 |
Filed Date | 2007-05-10 |
United States Patent
Application |
20070102406 |
Kind Code |
A1 |
Stava; Elliot K. ; et
al. |
May 10, 2007 |
ELECTRIC ARC WELDER SYSTEM WITH WAVEFORM PROFILE CONTROL FOR CORED
ELECTRODES
Abstract
An electric arc welder for creating a welding process in the
form of a succession of AC waveforms between a particular type of
cored electrode, with a sheath and core, and a workpiece by a power
source comprising an high frequency switching device for creating
the individual waveforms in the succession of waveforms, each
waveform having a profile is formed by the magnitude of each of a
large number of short current pulses generated at a frequency of at
least 18 kHz where the profile is determined by the input signal to
a wave shaper controlling the short current pulses; a circuit to
create a profile signal indicative of the particular type of
electrode; and a select circuit to select the input signal based
upon the profile signal whereby the wave shaper causes the power
source to crate a specific waveform profile for the particular type
of cored electrode.
Inventors: |
Stava; Elliot K.; (Sagamore
Hills, OH) ; Myers; Russel K.; (Hudson, OH) ;
Narayanan; Badri K.; (Euclid, OH) ; Soltis; Patrick
T.; (Shaker Heights, OH) |
Correspondence
Address: |
FAY SHARPE / LINCOLN
1100 SUPERIOR AVENUE
SEVENTH FLOOR
CLEVELAND
OH
44114
US
|
Assignee: |
LINCOLN GLOBAL, INC.
1200 Monterey Pass Road
Monterey Park
CA
91754
|
Family ID: |
34935271 |
Appl. No.: |
11/615559 |
Filed: |
December 22, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10834141 |
Apr 29, 2004 |
7166817 |
|
|
11615559 |
Dec 22, 2006 |
|
|
|
Current U.S.
Class: |
219/130.5 |
Current CPC
Class: |
B23K 9/092 20130101;
B23K 9/1068 20130101; B23K 9/1043 20130101 |
Class at
Publication: |
219/130.5 |
International
Class: |
B23K 9/10 20060101
B23K009/10 |
Claims
1. An electric arc welder, comprising: means for identifying a
particular type of electrode used in a given welding process; means
for selecting a particular waveform profile according to an
identified electrode type; a power source operative to provide a
succession of waveforms between an electrode and a workpiece
according to a wave shape signal; and means for providing the wave
shape signal to the power source at least partially according to
the selected particular waveform profile; wherein the selected
waveform profile causes a sheath and a core of the identified
electrode to melt at about the same rate.
2. The welder of claim 1, wherein the means for identifying the
particular type of electrode comprises a reading device that
automatically identifies a particular type of electrode used in a
given welding process and provides a corresponding electrode type
input to the means for selecting a particular waveform.
3. The welder of claim 1, wherein the means for selecting a
particular waveform profile comprises: a lookup component receiving
an electrode type input from the means for identifying the
particular type of electrode and generating a profile output
according to the electrode type input and a welding process
setpoint; a select component receiving the profile output from the
lookup component and selecting a particular stored waveform profile
according to the profile output.
4. The welder of claim 1, wherein the means for providing the wave
shape signal comprises a waveform generator receiving a selected
particular waveform profile and providing a wave shape signal to
the power source at least partially according to the selected
particular waveform profile.
5. The welder of claim 1, further comprising a profile control
component for setting at least one profile parameter of an
individual waveform, the parameters selected from the class
consisting of frequency, duty cycle, up ramp rate and down ramp
rate.
6. The welder of claim 5, further comprising a magnitude circuit
for adjusting the individual waveform to set total current, voltage
and/or power without substantially affecting the general fixed
profile.
7. The welder of claim 1, wherein the selected waveform profile has
a leading edge and a ramp portion at the leading edge to control
melting of the sheath.
8. The welder of claim 1, wherein the electrode has an outer
diameter and the selected waveform profile controls the arc length
between the electrode and the workpiece to about 1.5 times the
outer diameter of the electrode or less.
9. The welder of claim 1, wherein the power source provides a
succession of AC waveforms between the electrode and the workpiece
according to the wave shape signal.
10. An electric arc welder, comprising: a power source operative to
provide a succession of waveforms between an electrode and a
workpiece according to a wave shape signal; a reading device that
identifies a particular type of electrode used in a given welding
process; means for selecting a particular waveform profile
according to the identified electrode type; means for providing the
wave shape signal to the power source at least partially according
to the selected particular waveform profile; a profile control
component for setting at least one profile parameter of an
individual waveform, the parameters selected from the class
consisting of frequency, duty cycle, up ramp rate and down ramp
rate; and a magnitude circuit for adjusting the individual waveform
to set total current, voltage and/or power without substantially
affecting the general fixed profile.
11. The welder of claim 10, wherein the selected waveform profile
causes a sheath and a core of the identified electrode to melt at
about the same rate.
12. The welder of claim 10, wherein the selected waveform profile
has a leading edge and a ramp portion at the leading edge to
control melting of the sheath.
13. The welder of claim 10, wherein the electrode has an outer
diameter and the selected waveform profile controls the arc length
between the electrode and the workpiece to about 1.5 times the
outer diameter of the electrode or less.
14. The welder of claim 10, wherein the power source provides a
succession of AC waveforms between the electrode and the workpiece
according to the wave shape signal.
15. An electric arc welder, comprising: a power source operative to
provide a succession of waveforms between an electrode and a
workpiece according to a wave shape signal; a reading device that
identifies a particular type of electrode used in a given welding
process; means for selecting a particular waveform profile
according to the identified electrode type; means for providing the
wave shape signal to the power source at least partially according
to the selected particular waveform profile; a data store with
addressable data blocks each indicative of a specific cored
electrode; a select component with a number of stored waveform
signals for setting a given waveform profile in the means for
providing the wave shape signal; and an output component to output
a special data block to select a given waveform signal upon
selecting the address for the identified electrode type.
16. The welder of claim 15, wherein the waveforms are AC waveforms
individually comprising a positive portion with a first shape and
having a first time, and a negative portion with a second shape and
having a second time, wherein one of the first and second shapes is
greater in magnitude than the other of the shapes, and wherein the
time of the shape with the greater magnitude is substantially less
than the time of the other shape.
17. The welder of claim 15, further comprising a set point storage
device including a plurality of data blocks individually indicative
of a specific wire feed speed set point, wherein the select
component is responsive to both the data block outputted from the
data store and the set point storage device.
18. The welder of claim 15, wherein the given waveform profile
causes the sheath and core to melt at about the same rate.
19. The welder of claim 15, wherein the output component outputs
the special data block to select the given waveform signal upon
selecting the address according to the particular cored electrode
and according to a wire feed speed of the welding process.
20. The welder of claim 15, wherein the electrode has an outer
diameter and the selected waveform profile controls the arc length
between the electrode and the workpiece to about 1.5 times the
outer diameter of the electrode or less.
Description
REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of, and claims priority
to and the benefit of, co-pending U.S. patent application Ser. No.
10/834,141, filed Apr. 29, 2004, entitled ELECTRIC ARC WELDER
SYSTEM WITH WAVEFORM PROFILE CONTROL FOR CORED ELECTRODES, the
entirety of which is hereby incorporated by reference.
[0002] The present invention relates to the art of electric arc
welding and more particularly to an electric arc welder with
waveform profile control for cored electrodes used in pipeline
welding, primarily off-shore pipeline welding.
INCORPORATION BY REFERENCE
[0003] The present invention is directed to an electric arc welder
system utilizing high capacity alternating circuit power sources
for driving two or more tandem electrodes of the type used in seam
welding of large metal blanks, such as pipelines. It is preferred
that the power sources use the switching concept disclosed in Stava
U.S. Pat. No. 6,111,216 wherein the power supply is an inverter
having two large output polarity switches with the arc current
being reduced before the switches reverse the polarity.
Consequently, the term "switching point" is a complex procedure
whereby the power source is first turned off awaiting a current
less than a preselected value, such as 100 amperes. Upon reaching
the 100 ampere threshold, the output switches of the power supply
are reversed to reverse the polarity from the D.C. output link of
the inverter. Thus, the "switching point" is an off output command,
known as a "kill" command, to the power supply inverter followed by
a switching command to reverse the output polarity. The kill output
can be a drop to a decreased current level. This procedure is
duplicated at each successive polarity reversal so the AC power
source reverses polarity only at a low current. In this manner,
snubbing circuits for the output polarity controlling switches are
reduced in size or eliminated. Since this switching concept is
preferred to define the switching points as used in the present
invention, Stava U.S. Pat. No. 6,111,216 is incorporated by
reference. The concept of an AC current for tandem electrodes is
well known in the art. U.S. Pat. No. 6,207,929 discloses a system
whereby tandem electrodes are each powered by a separate inverter
type power supply. The frequency is varied to reduce the
interference between alternating current in the adjacent tandem
electrodes. Indeed, this prior patent of assignee relates to single
power sources for driving either a DC powered electrode followed by
an AC electrode or two or more AC driven electrodes. In each
instance, a separate inverter type power supply is used for each
electrode and, in the alternating current high capacity power
supplies, the switching point concept of Stava U.S. Pat. No.
6,111,216 is employed. This system for separately driving each of
the tandem electrodes by a separate high capacity power supply is
background information to the present invention and is incorporated
herein as such background. In a like manner, U.S. Pat. Nos.
6,291,798 and 6,207,929 disclose further arc welding systems
wherein each electrode in a tandem welding operation is driven by
two or more independent power supplies connected in parallel with a
single electrode arc. The system involves a single set of switches
having two or more accurately balanced power supplies forming the
input to the polarity reversing switch network operated in
accordance with Stava U.S. Pat. No. 6,111,216. Each of the power
supplies is driven by a single command signal and, therefore,
shares the identical current value combined and directed through
the polarity reversing switches. This type system requires large
polarity reversing switches since all of the current to the
electrode is passed through a single set of switches. U.S. Pat. No.
6,291,798 does show a master and slave combination of power
supplies for a single electrode and discloses general background
information to which the invention is directed. For that reason,
this patent is also incorporated by reference. An improvement for
operating tandem electrodes with controlled switching points is
disclosed in Houston U.S. Pat. No. 6,472,634. This patent is
incorporated by reference.
[0004] The present invention relates to coordination of a specific
waveform profile for an AC waveform, which profile is coordinated
with a particular cored electrode used in welding, such as pipeline
welding. Such welding normally uses DC positive or DC negative,
especially when using a cored electrode. There is one exception
where a cored electrode has been tried. In the prior art, a cored
electrode has been suggested for use in conjunction with a STT
waveform which waveform can be positive or negative. In an
illustration the process alternates between STT positive and a STT
negative. This concept is not AC, but is shown in Stava U.S. Pat.
No. 6,051,810, which is incorporated by reference herein as
background information.
BACKGROUND OF INVENTION
[0005] Welding applications, such as pipe welding, often require
high currents and use several arcs created by tandem electrodes.
Such welding systems are quite prone to certain inconsistencies
caused by arc disturbances due to magnetic interaction between two
adjacent tandem electrodes. A system for correcting the
disadvantages caused by adjacent AC driven tandem electrodes is
disclosed in Stava U.S. Pat. No. 6,207,929. In that prior patent,
each of the AC driven electrodes has its own inverter based power
supply. The output frequency of each power supply is varied so as
to prevent interference between adjacent electrodes. This system
requires a separate power supply for each electrode. As the current
demand for a given electrode exceeds the current rating of the
inverter based power supply, a new power supply must be designed,
engineered and manufactured. Thus, such system for operating tandem
welding electrodes require high capacity or high rated power
supplies to obtain high current as required for pipe welding. To
decrease the need for special high current rated power supplies for
tandem operated electrodes, assignee developed the system disclosed
in Stava U.S. Pat. No. 6,291,798 wherein each AC electrode is
driven by two or more inverter power supplies connected in
parallel. These parallel power supplies have their output current
combined at the input side of a polarity switching network. Thus,
as higher currents are required for a given electrode, two or more
parallel power supplies are used. In this system, each of the power
supplies are operated in unison and share equally the output
current. Thus, the current required by changes in the welding
conditions can be provided only by the over current rating of a
single unit. A current balanced system did allow for the
combination of several smaller power supplies; however, the power
supplies had to be connected in parallel on the input side of the
polarity reversing switching network. As such, large switches were
required for each electrode. Consequently, such system overcame the
disadvantage of requiring special power supplies for each electrode
in a tandem welding operation of the type used in pipe welding;
but, there is still the disadvantage that the switches must be
quite large and the input, paralleled power supplies must be
accurately matched by being driven from a single current command
signal. Stava U.S. Pat. No. 6,291,798 does utilize the concept of a
synchronizing signal for each welding cell directing current to
each tandem electrode. However, the system still required large
switches. This type of system was available for operation in an
Ethernet network interconnecting the welding cells. In Ethernet
interconnections, the timing cannot be accurately controlled. In
the system described, the switch timing for a given electrode need
only be shifted on a time basis, but need not be accurately
identified for a specific time. Thus, the described system
requiring balancing the current and a single switch network has
been the manner of obtaining high capacity current for use in
tandem arc welding operations when using an Ethernet network or an
internet and Ethernet control system. There is a desire to control
welders by an Ethernet network, with or without an internet link.
Due to timing limitation, these networks dictated use of tandem
electrode systems of the type using only general synchronizing
techniques.
[0006] Such systems could be controlled by a network; however, the
parameter to each paralleled power supply could not be varied. Each
of the cells could only be offset from each other by a
synchronizing signal. Such systems were not suitable for central
control by the internet and/or local area network control because
an elaborate network to merely provide offset between cells was not
advantageous. Houston U.S. Pat. No. 6,472,634 discloses the concept
of a single AC arc welding cell for each electrode wherein the cell
itself includes one or more paralleled power supplies each of which
has its own switching network. The output of the switching network
is then combined to drive the electrode. This allows the use of
relatively small switches for polarity reversing of the individual
power supplies paralleled in the system. In addition, relatively
small power supplies can be paralleled to build a high current
input to each of several electrodes used in a tandem welding
operation. The use of several independently controlled power
supplies paralleled after the polarity switch network for driving a
single electrode allows advantageous use of a network, such as the
internet or Ethernet.
[0007] In Houston U.S. Pat. No. 6,472,634, smaller power supplies
in each system are connected in parallel to power a single
electrode. By coordinating switching points of each paralleled
power supply with a high accuracy interface, the AC output current
is the sum of currents from the paralleled power supplies without
combination before the polarity switches. By using this concept,
the Ethernet network, with or without an internet link, can control
the weld parameters of each paralleled power supply of the welding
system. The timing of the switch points is accurately controlled by
the novel interface, whereas the weld parameters directed to the
controller for each power supply can be provided by an Ethernet
network which has no accurate time basis. Thus, an internet link
can be used to direct parameters to the individual power supply
controllers of the welding system for driving a single electrode.
There is no need for a time based accuracy of these weld parameters
coded for each power supply. In the preferred implementation, the
switch point is a "kill" command awaiting detection of a current
drop below a minimum threshold, such as 100 amperes. When each
power supply has a switch command, then they switch. The switch
points between parallel power supplies, whether instantaneous or a
sequence involving a "kill" command with a wait delay, are
coordinated accurately by an interface card having an accuracy of
less than 10 .mu.s and preferably in the range of 1-5 .mu.s. This
timing accuracy coordinates and matches the switching operation in
the paralleled power supplies to coordinate the AC output
current.
[0008] By using the internet or Ethernet local area network, the
set of weld parameters for each power supply is available on a less
accurate information network, to which the controllers for the
paralleled power supplies are interconnected with a high accuracy
digital interface card. Thus, the switching of the individual,
paralleled power supplies of the system is coordinated. This is an
advantage allowing use of the internet and local area network
control of a welding system. The information network includes
synchronizing signals for initiating several arc welding systems
connected to several electrodes in a tandem welding operation in a
selected phase relationship. Each of the welding systems of an
electrode has individual switch points accurately controlled while
the systems are shifted or delayed to prevent magnetic interference
between different electrodes. This allows driving of several AC
electrodes using a common information network. The Houston U.S.
Pat. No. 6,472,634 system is especially useful for paralleled power
supplies to power a given electrode with AC current. The switch
points are coordinated by an accurate interface and the weld
parameter for each paralleled power supply is provided by the
general information network. This background is technology
developed and patented by assignee and does not necessarily
constitute prior art just because it is herein used as
"background."
[0009] As a feature of the system in Stava U.S. Pat. No. 6,207,929,
two or more power supplies can drive a single electrode. Thus, the
system comprises a first controller for a first power supply to
cause the first power supply to create an AC current between the
electrode and workpiece by generating a switch signal with polarity
reversing switching points in general timed relationship with
respect to a given system synchronizing signal received by the
first controller. This first controller is operated at first
welding parameters in response to a set of first power supply
specific parameter signals directed to the first controller. There
is provided at least one slave controller for operating the slave
power supply to create an AC current between the same electrode and
workpiece by reversing polarity of the AC current at switching
points. The slave controller operates at second weld parameters in
response to the second set of power supply specific parameter
signals to the slave controller. An information network connected
to the first controller and the second or slave controller contains
digital first and second power supply specific parameter signals
for the two controllers and the system specific synchronizing
signal. Thus, the controllers receive the parameter signals and the
synchronizing signal from the information network, which may be an
Ethernet network with or without an internet link, or merely a
local area network. The invention involves a digital interface
connecting the first controller and the slave controller to control
the switching points of the second or slave power supply by the
switch signal from the first or master controller. In practice, the
first controller starts a current reversal at a switch point. This
event is transmitted at high accuracy to the slave controller to
start its current reversal process. When each controller senses an
arc current less than a given number, a "ready signal" is created.
After a "ready" signal from all paralleled power supplies, all
power supplies reverse polarity. This occurs upon receipt of a
strobe or look command each 25 .mu.s. Thus, the switching is in
unison and has a delay of less than 25 .mu.s. Consequently, both of
the controllers have interconnected data controlling the switching
points of the AC current to the single electrode. The same
controllers receive parameter information and a synchronizing
signal from an information network which in practice comprises a
combination of internet and Ethernet or a local area Ethernet
network. The timing accuracy of the digital interface is less than
about 10 .mu.s and, preferably, in the general range of 1-5 .mu.s.
Thus, the switching points for the two controllers driving a single
electrode are commanded within less than 5 .mu.s. Then, switching
actually occurs within 25 .mu.s. At the same time, relatively less
time sensitive information is received from the information network
also connected to the two controllers driving the AC current to a
single electrode in a tandem welding operation. The 25 .mu.s
maximum delay can be changed, but is less than the switch command
accuracy.
[0010] The unique control system disclosed in Houston U.S. Pat. No.
6,472,634 is used to control the power supply for tandem electrodes
used primarily in pipe seam welding and disclosed in Stava U.S.
Pat. No. 6,291,798. This Stava patent relates to a series of tandem
electrodes movable along a welding path to lay successive welding
beads in the space between the edges of a rolled pipe or the ends
of two adjacent pipe sections. The individual AC waveforms used in
this unique technology are created by a number of current pulses
occurring at a frequency of at least 18 kHz with a magnitude of
each current pulse controlled by a wave shaper. This technology
dates back to Blankenship U.S. Pat. No. 5,278,390. Shaping of the
waveforms in the AC currents of two adjacent tandem electrodes is
known and is shown in not only the patents mentioned above, but in
Stava U.S. Pat. No. 6,207,929. In this latter Stava patent, the
frequency of the AC current at adjacent tandem electrodes is
adjusted to prevent magnetic interference. All of these patented
technologies by The Lincoln Electric Company of Cleveland, Ohio
have been advances in the operation of tandem electrodes each of
which is operated by a separate AC waveform created by the waveform
technology set forth in these patents. These patents are
incorporated by reference herein. However, these patents do not
disclose the present invention which is directed to the use of a
unique implementation of waveform technology to create a specific
waveform for use in welding using an AC current and a cored
electrode.
[0011] When using the waveform technology as so far described for
off-shore welding or welding on pipelines, the welding process
generally used solid welding wires with a shielding gas. In this
type of process, DC welding as described, together with STT welding
has been the normal practice. When cored electrodes are used, the
core can be formed of alloy material to make the weld metal. Such
processes generally required DC welding using cored electrodes.
Consequently, in the past cored or solid wire using a DC process
with external shielding gas has been the normal practice,
especially for off-shore welding and pipeline welding. The DC
welding presented little problems of uneven burn back of the sheath
and core. The electrodes were cored for alloying. The need for
controlled strength and hardness combined with low diffusible
hydrogen limits made it difficult to use AC welding. These DC
welding processes have been used in the field and are the
background to which the present invention is directed. There has
been no use of cored electrodes and AC welding because the AC
waveforms were not tailored to any particular cored electrode. The
burn rate for the sheath and core could not be controlled.
THE INVENTION
[0012] The present invention is used with a cored electrode having
a special constructed AC waveform generated between the cored
electrode and workpiece, which special AC waveform is outputted in
succession to constitute the welding process. By using the present
invention the waveform in the AC welding process is controlled in a
unique manner that adjusts several profile parameters and also the
energy profile of the individual sections of the waveform. The
waveform is coordinated with a specific cored electrode so the
sheath and core burn back at the proven rate. AC welding could not
be used successfully for a cored electrode. The creation of a
special profile for the waveform effects the overall welding
process in a unique manner that accurately controls the process
using waveform technology of the type pioneered by The Lincoln
Electric Company of Cleveland, Ohio. By using the present
invention, the welding process is controlled to effect several
characteristics, such as penetration into the base metal, the melt
off rate of the electrode, the heat input into the base metal, and
the welding travel speed as well as the wire feed speed while using
AC welding with a cored electrode. In addition, the arc welding
current and/or arc welding voltage waveform is generated to
essentially "paint" a desired waveform for coordination with a
given cored electrode to effect the mechanical and metallurgical
properties of the "as welded" weld metal resulting from the welding
process. The invention selects the profile of an AC waveform for a
given electrode. By having the ability to accurately control the
exact profile of the AC waveform, this invention is made
possible.
[0013] In the past DC welding was the norm. In the past DC welding
of pipeline was normal. To use AC welding so the heat would be
controlled or adjusted there was still a need for shielding gas
which could blow away in high winds. To reduce heat the wire feed
speed had to be reduced. AC welding could control heat, but could
not be used with cored electrodes. The invention allows use of
cored electrodes with AC welding and when using a cored electrode,
reducing the problems of high winds.
[0014] When coordinating various welding waveforms, sometimes
called wave shapes, with specific cored electrodes, an improvement
in the welding process both in welding speed and improved
mechanical and metallurgical properties is obtained. The actual
electrode is combined with the unique profile controlled AC
waveforms to produce the required welding results heretofore
obtainable by only DC welding. By coordinating the desired welding
wire and a specific exactly controlled general AC profile of an
individual waveform in a succession of waveforms constituting the
welding process, the welder using the present invention can produce
heretofore unobtainable weld results. This provides a unique AC
welding process usable in off-shore welding and pipeline
welding.
[0015] In accordance with the present invention there is provided
an electric arc welder for creating a succession of AC waveforms
between a cored electrode and a workpiece by a power source
comprising an high frequency switching device such as an inverter
or its equivalent chopper for creating individual waveforms in the
succession of waveforms constituting the welding process. Each of
the individual waveforms has a precise general profile determined
by the magnitude of each of a large number of short current pulses
generated at a frequency of at least 18 kHz by a pulse width
modulator with the magnitude of the current pulses controlled by a
wave shaper. The polarity of any portion of the individual AC
waveform is determined by the data of a polarity signal. A profile
control network is used for establishing the general profile of an
individual waveform by setting more than one profile parameter of
the individual waveform. The parameters are selected from the class
consisting of frequency, duty cycle, up ramp rate and down ramp
rate. Also included in the welder control is a magnitude circuit
for adjusting the individual waveform profile to set total current,
voltage and/or power for the waveform without substantially
changing the set general profile. This concept of the invention is
normally accomplished in two sections where the energy is
controlled in the positive polarity and in the negative polarity of
the generated waveform profile.
[0016] In accordance with another aspect of the present invention
there is provided a method of electric arc welding by creating a
succession of AC waveforms between a cored electrode and a
workpiece by a power source comprising an high frequency switching
device for creating individual waveforms in the succession of
waveforms constituting the weld process. Each of the individual
waveforms has profile determined by the magnitude of each of a
large number of short current pulses generated at a frequency of at
least 18 kHz by a pulse width modulator with the magnitude of the
current pulses controlled by a wave shaper. The method comprises
determining the plurality of any portion of the individual waveform
by the data of a plurality signal, establishing the general profile
of an individual waveform by setting more than one profile
parameter of an individual waveform, the parameters selected from
the class consisting of frequency, duty cycle, up ramp rate and
down ramp rate and adjusting the waveform to set the total
magnitude of current, voltage and/or power without substantially
changing the set profile.
[0017] In the past, the off-shore and pipe welding was normally
limited to a single polarity using a gas shielded metal wire. Such
shielding is difficult to control in windy conditions often
experienced in off-shore and pipeline welding. Consequently, there
is a substantial need for a welding process using self shielding
electrodes such as FCAW-SS wire technology. The sheath on the
electrode and the inner flux core must be melted at the same rate
while maintaining the same wire feed speed without introducing
undesirable arc instability. Furthermore heat can not be adjusted.
Consequently, there is a desire for an AC waveform so the duty
cycle of either the negative or positive portion of the waveform is
controlled to adjust the melting rate and heat to the weld pool
during the welding operation. All of these difficulties have
generally limited the use of AC welding with a cored, self shielded
electrode. The advantage of AC welding with the advantage of cored
self shielding was not obtainable on a consistent basis. The
waveforms, especially when developed by waveform technology, have
to be different for each different cored electrode. Thus, the use
of a standard AC arc welder with cored electrode having self
shielding capabilities has not been available in the past. The
present invention allows the use of cored self shielding electrodes
with AC welding, which combination is novel and is accomplished to
optimize the actual welding result by correlating the waveform and
a specific electrode.
[0018] The invention accomplishes AC welding with cored self
shielding electrodes to achieve superior productivity and
mechanical properties by lowering the heat input per unit of
deposition and by shortening the arc length to reduce atmospheric
contamination. This has not been accomplished before in pipeline
welding. The invention allows the use of a welding operation
involving AC waveforms in a manner that can accomplish a short arc
length to prevent atmospheric contamination. Furthermore, by using
a self shielding electrode, the atmospheric wind can not blow away
the shielding gas as is experienced in FCAW-G welding. The
invention is the development of a new welding system making
possible the use of cored electrodes. This is accomplished with an
AC arc welding power source. The benefits of both a cored electrode
and AC welding are obtained. The AC power source, in accordance
with the invention, is capable of generating a wave shape of
virtually any form and is not limited to simply an AC sine wave or
square wave. The AC waveform has a specific profile that is
coordinated with an exact cored electrode to optimize the waveform
profile for the electrode being used in the welding process. In
accordance with an aspect of the invention, the waveform has an
unbalanced relationship so that the positive and negative polarity
portions of the welding process heat and deposit molten metal in a
different manner to optimize the AC welding process. By using the
present invention, the constituents of the core material of the
electrode is selected to achieve optimum results for the weld
metal, in terms of metallurgical and mechanical properties of the
"as welded" material. In other words, the electrode core chemistry
is modified to take advantage of the various AC waveforms produced
by the AC arc welding power source by coordinating the waveforms
with the chemistry of the core. This has never been accomplished
before and allows the use of cored electrodes with self shielding
capability in off-shore pipeline welding. Different polarity
portions of the waveform produce different welding results for a
given electrode in terms of heat input to the work, melt off rate
of the electrode and the metallurgical and mechanical properties of
the weld deposit. By using an AC welding power source as described,
in conjunction with a tubular electrode of the self shielding type,
superior welding results are achieved. The self shielded electrode
does not require additional shielding gas and therefore results in
additional savings in the welding process. Furthermore, the power
source uses waveform technology where the profile of the waveform
can be created. The profile can be selected based upon both the
specific construction of the cored electrode and the wire feed
speed of the welding process. Consequently, a distinct advantage of
the invention is the ability to control the actual waveform of the
AC welding process by the specific cored electrode used and the set
point of the welder. Thus, the invention provides significant
benefits in the quality of the weld and also increases welding
speed. Consequently, the production rate using the present
invention is increased.
[0019] The invention furthermore benefits application in the field
of cross country pipeline welding, as well as off-shore welding of
pipelines or other structures. In the pipe welding industry, it is
well known that the weld quality and welding speed or production is
of essence. In cross country and off-shore pipeline construction
projects, it is well known that such projects normally include high
hourly costs for the construction equipment. This is especially the
case on off-shore pipeline projects, where the ships used for
constructing the pipeline normally lease at a cost of millions of
dollars per day. Consequently, the welding of the pipeline must be
done as quickly as possible with a minimum of repairs to minimize
the cost factor in the process. Consequently, the AC welding
process and the tubular cored electrode significantly benefit the
industry in terms of producing high quality welds at a faster
speed.
[0020] A broad aspect of the present invention is the tailoring or
coordinating of accurately profiled waveforms of an AC welding
process with the exact chemistry and composition of the electrode.
Thus, a given electrode is identified to provide an identification
signal. This signal is used to select the exact coordinated AC
waveform from many waveforms stored in the power source. This
concept of selecting the profile of the AC waveform to match a
specific cored electrode has not been heretofore used. This process
allows AC welding of a pipeline with a cored, self shielded
electrode.
[0021] In accordance with the present invention there is provided
an electric arc welder for creating a welding process in the form
of a succession of AC waveforms between a particular type of cored
electrode with a sheath and core and a workpiece by a power source.
The power source comprises a high frequency switching device for
creating the individual waveforms in the succession of waveforms
constituting the welding process. Each waveform has a profile that
is formed by the magnitude of the large number of short current
pulses generated at a frequency of at least 18 kHz, where the
profile is determined by the input signal to a wave shaper
controlling the short current pulses. The invention involves a
circuit to create a profile signal indicative of a particular type
electrode and a select circuit to select the input signal based
upon the profile signal indicative of a specific electrode. In this
manner, the wave shaper causes the power source to create a
specific waveform profile for a particular type of cored electrode.
By coordinating the exact waveform with a particular cored
electrode, a cored electrode is usable in an AC waveform welding
process. This process was not generally obtainable in the past.
[0022] In accordance with another aspect of the present invention
there is provided a method of welding with a specific cored
electrode having a sheath and core. The method comprises using a
waveform with a specific profile tailored for welding with a
specific cored electrode, creating a series of these selected
waveforms to provide a welding process and welding with the
electrode using this selected welding process. In accordance with a
limited aspect of the invention the created waveform is an AC
waveform. Furthermore, the waveform can have a different shape for
the positive polarity and the negative polarity. In this manner,
the one polarity involves a relatively low current for a longer
period of time. This maintains the arc length relatively short to
reduce the amount of exposure to the atmosphere during the welding
process. In this modification of the invention, the waveform is an
AC waveform so that the profile of the selected waveform of the
method is accurately controlled.
[0023] The primary object of the present invention is the provision
of an electric arc welder, wherein the waveform is created by
waveform technology and is developed for a particular cored
electrode so that an off-shore pipeline welding process can be
accomplished using FCAW-SS process.
[0024] Another object of the present invention is the provision of
a method, wherein waveform technology is used to generate waveforms
coordinated with a particular cored electrode.
[0025] Yet another object of the present invention is the provision
of a welder and method, as defined above, which welder and method
results in a relatively short arc length and is used in high wind
conditions for off-shore pipeline welding and pipeline welding in
general.
[0026] Still a further object of the present invention is the
provision of an electric arc welder and method, as defined above,
wherein the AC waveform has a low heat polarity portion to obtain a
short arc length.
[0027] Still another object of the present invention is the
provision of a welder and method, as defined above, which welder
and method utilizes a cored electrode that can be operated DC
positive, DC negative, but preferably AC.
[0028] Another object of the present invention is the provision of
an electric arc welder and method, as defined above, which welder
and method can be used for AC open root welding and combines self
shielding electrodes with an AC waveform that is tailored to the
particular electrode.
[0029] Still a further object of the present invention is the
provision of an electric arc welder and method, as defined above,
which welder and method utilizes both the identification of a
particular electrode and the wire feed speed to select the desired
tailored waveform.
[0030] Another object of the present invention is the provision of
an electric arc welder that has the capabilities of accurately
controlling the profile of the waveform so the profile of the
waveform can be coordinated with a given electrode, especially a
cored electrode.
[0031] Yet another object of the present invention is the provision
of an electric arc welder and method, as defined above, which
welder and method allow coordination between a self shielded
electrode and a waveform of the programmable power source, either
DC or AC. In this manner, a waveform is programmed into the power
source so superior results are accomplished when using the
corresponding, matched cored electrode.
[0032] Still a further object of the present invention is the
provision of an electric arc welder utilizing waveform technology,
which welder is capable of having a waveform that is tailored made
for a specific cored electrode. This is especially advantageous for
a self shielded electrode when used in an AC welding process.
[0033] Yet another object of the present invention is the provision
of an electric arc welder and method, as defined above, which
welder and method has a waveform coordinated with a self shielded
electrode so that the sheath and core melts at substantially the
same rate.
[0034] Yet a further object of the present invention is the
provision of an electric arc welder using waveform technology
wherein the general profile of the individual waveforms
constituting the AC welding process is accurately controlled to a
given profile that will produce a weld with desired mechanical and
metallurgical properties with a specific cored electrode.
[0035] Another object of the present invention is the provision of
an electric arc welder, as defined above, which electric arc welder
generates a precise controllable and changeable general profile for
the waveform of an AC welding process to thereby adjust the weld
speed, deposition rate, heat input, mechanical and metallurgical
properties and related characteristics to improve the quality and
performance of the welding process.
[0036] These and other objects and advantages will become apparent
from the following description taken together with the accompanying
drawings.
BRIEF DESCRIPTION OF DRAWINGS
[0037] FIG. 1 is a block diagram of a welding system that can be
used to perform the present invention;
[0038] FIG. 2 is a wiring diagram of two paralleled power sources,
each of which include a switching output and can be used in
practicing the invention;
[0039] FIG. 3 is a cross sectional side view of three tandem
electrodes of the type controllable by the power source disclosed
in FIGS. 1 and 2;
[0040] FIG. 4 is a schematic layout in block form of a welding
system for three electrodes using the disclosure in Houston U.S.
Pat. No. 6,472,634 and Stava U.S. Pat. No. 6,291,798 and where one
of the three power sources is used in forming a precise tailored
waveform by the program as shown in FIG. 17;
[0041] FIG. 5 is a block diagram showing a single electrode driven
by the system as shown in FIG. 4 with a variable pulse generator
disclosed in Houston U.S. Pat. No. 6,472,634 and used for
practicing the present invention;
[0042] FIG. 6 is a current graph for one of two illustrated
synchronizing pulses and showing a balanced AC waveform for one
tandem electrode;
[0043] FIG. 7 is a current graph superimposed upon a polarity
signal having logic to determine the polarity of the waveform as
used in a welder that can practice the present invention as shown
in FIGS. 17, 21 AND 27;
[0044] FIG. 8 is a current graph showing a broad aspect of a
waveform with a profile controllable by the present invention to be
optimum for a given cored electrode and outputted by the welder
shown in FIGS. 21 and 27;
[0045] FIGS. 9 and 10 are schematic drawings illustrating the
dynamics of the weld puddle during concurrent polarity
relationships of tandem electrodes;
[0046] FIG. 11 is a pair of current graphs showing the waveforms on
two adjacent tandem electrodes that can be generated by a
background system;
[0047] FIG. 12 is a pair of current graphs of the AC waveforms on
adjacent tandem electrodes with areas of concurring polarity
relationships, where each waveform can be coordinated with a given
electrode;
[0048] FIG. 13 are current graphs of the waveforms on adjacent
tandem electrodes wherein the AC waveform of one electrode is
substantially different waveform of the other electrode to limit
the time of concurrent polarity relationships;
[0049] FIG. 14 are current graphs of two sinusoidal waveforms for
adjacent electrodes operated by a background system to use
different shaped waveforms for the adjacent electrodes;
[0050] FIG. 15 are current graphs showing waveforms at four
adjacent AC arcs of tandem electrodes shaped and synchronized in
accordance with a background aspect of the invention;
[0051] FIG. 16 is a schematic layout of a known software program to
cause switching of the paralleled power supplies as soon as the
coordinated switch commands have been processed and the next
coincident signal has been created;
[0052] FIG. 17 is a block diagram of the program used in the
computer controller of the welder to control the actual profile of
the waveform using the disclosure and concepts shown in FIGS. 1-16,
so a welder performs in accordance with the preferred embodiment of
the present invention, as shown in FIGS. 21 AND 27;
[0053] FIG. 18 is a schematically illustrated waveform used in
explaining the implementation of the present program shown in FIG.
17;
[0054] FIG. 19 is a side elevational view with a block diagram
illustrating the use of the preferred embodiment of the present
invention;
[0055] FIG. 20 is an enlarged cross-sectioned pictorial view taken
generally along line 20-20 of FIG. 19;
[0056] FIG. 21 is a block diagram disclosing the preferred
embodiment of the present invention;
[0057] FIG. 22 is a graph of the current, voltage or power curve
showing the waveform used in the welding process when implementing
the invention as shown in FIG. 21;
[0058] FIG. 23 is a graph similar to the graph of FIG. 22
illustrating certain modifications in the created waveform capable
of being obtained when using the preferred embodiment of the
present invention;
[0059] FIG. 24 is an enlarged, schematic view representing a cored
electrode where the sheath and core are melted at a different
rate;
[0060] FIG. 25 is a view similar to FIG. 24 illustrating the
disadvantage of a failure to employ the present invention for
welding with cored electrodes;
[0061] FIG. 26 is a view similar to FIGS. 24 and 25 showing the
operation of a welding process using the present invention as
illustrated in FIG. 21; and,
[0062] FIG. 27 is a block diagram showing a welder similar to the
welder shown in FIG. 21 using a modification of the preferred
embodiment of the invention where a fixed cored electrode activates
a given waveform to be outputted from the waveform generator.
PREFERRED EMBODIMENT
[0063] Referring now to the drawings wherein the showings are for
the purpose of illustrating a preferred embodiment of the invention
only and not for the purpose of limiting same, a background system
for implementing the invention is shown in detail in FIGS. 1, 2, 4,
5 and 16. FIGS. 2 and 6-15 describe prior attributes of the
disclosed background welding systems. The welder described in FIGS.
17 and 18 is used to construct the precise profile of the waveforms
used in the wave shaper or waveform generator as a profile tailored
for a specific electrode shown in FIG. 20. These
electrode-determined profiles are used in practicing the invention
described by use of FIGS. 19-27.
[0064] Turning now to the background system to which the present
invention is an improvement and/or an enhancement, FIG. 1 discloses
a single electric arc welding system S in the form of a single cell
to create an alternating current as an arc at weld station WS. This
system or cell includes a first master welder A with output leads
10, 12 in series with electrode E and workpiece W in the form of a
pipe seam joint or other welding operation. Hall effect current
transducer 14 provides a voltage in line 16 proportional to the
current of welder A. Less time critical data, such as welding
parameters, are generated at a remote central control 18. In a like
manner, a slave following welder B includes leads 20, 22 connected
in parallel with leads 10, 12 to direct an additional AC current to
the weld station WS. Hall effect current transducer 24 creates a
voltage in line 26 representing current levels in welder B during
the welding operation. Even though a single slave or follower
welder B is shown, any number of additional welders can be
connected in parallel with master welder A to produce an
alternating current across electrode E and workpiece W. The AC
current is combined at the weld station instead of prior to a
polarity switching network. Each welder includes a controller and
inverter based power supply illustrated as a combined master
controller and power supply 30 and a slave controller and power
supply 32. Controllers 30, 32 receive parameter data and
synchronization data from a relatively low level logic network. The
parameter information or data is power supply specific whereby each
of the power supplies is provided with the desired parameters such
as current, voltage and/or wire feed speed. A low level digital
network can provide the parameter information; however, the AC
current for polarity reversal occurs at the same time. The "same"
time indicates a time difference of less than 10 .mu.s and
preferably in the general range of 1-5 .mu.s. To accomplish precise
coordination of the AC output from power supply 30 and power supply
32, the switching points and polarity information can not be
provided from a general logic network wherein the timing is less
precise. The individual AC power supplies are coordinated by high
speed, highly accurate DC logic interface referred to as
"gateways." As shown in FIG. 1, power supplies 30, 32 are provided
with the necessary operating parameters indicated by the
bi-directional leads 42m, 42s, respectively. This non-time
sensitive information is provided by a digital network shown in
FIG. 1. Master power supply 30 receives a synchronizing signal as
indicated by unidirectional line 40 to time the controllers
operation of its AC output current. The polarity of the AC current
for power supply 30 is outputted as indicated by line 46. The
actual switching command for the AC current of master power supply
30 is outputted on line 44. The switch command tells power supply
S, in the form of an inverter, to "kill," which is a drastic
reduction of current. In an alternative, this is actually a switch
signal to reverse polarity. The "switching points" or command on
line 44 preferably is a "kill" and current reversal commands
utilizing the "switching points" as set forth in Stava U.S. Pat.
No. 6,111,216. Thus, timed switching points or commands are
outputted from power supply 30 by line 44. These switching points
or commands may involve a power supply "kill" followed by a switch
ready signal at a low current or merely a current reversal point.
The switch "ready" is used when the "kill" concept is implemented
because neither of the inverters are to actually reverse until they
are below the set current. This is described in FIG. 16. The
polarity of the switches of controller 30 controls the logic on
line 46. Slave power supply 32 receives the switching point or
command logic on line 44b and the polarity logic on line 46b. These
two logic signals are interconnected between the master power
supply and the slave power supply through the highly accurate logic
interface shown as gateway 50, the transmitting gateway, and
gateway 52, the receiving gateway on lines 44a, 46a. These gateways
are network interface cards for each of the power supplies so that
the logic on lines 44b, 46b are timed closely to the logic on lines
44, 46, respectively. In practice, network interface cards or
gateways 50, 52 control this logic to within 10 .mu.s and
preferably within 1-5 .mu.s. A low accuracy network controls the
individual power supplies for data from central control 18 through
lines 42m, 42s, illustrated as provided by the gateways or
interface cards. These lines contain data from remote areas (such
as central control 18) which are not time sensitive and do not use
the accuracy characteristics of the gateways. The highly accurate
data for timing the switch reversal uses interconnecting logic
signals through network interface cards 50, 52. The system in FIG.
1 is a single cell for a single AC arc; however, the invention is
not limited to tandem electrodes wherein two or more AC arcs are
created to fill the large gap found in pipe welding. However, the
background system is shown for this application. Thus, the master
power supply 30 for the first electrode receives a synchronization
signal which determines the timing or phase operation of the system
S for a first electrode, i.e. ARC 1. System S is used with other
identical systems to generate ARCs 2, 3, and 4 timed by
synchronizing outputs 84, 86 and 88. This concept is schematically
illustrated in FIG. 5. The synchronizing or phase setting signals
82-88 are shown in FIG. 1 with only one of the tandem electrodes.
An information network N comprising a central control computer
and/or web server 60 provides digital information or data relating
to specific power supplies in several systems or cells controlling
different electrodes in a tandem operation. Internet information 62
is directed to a local area network in the form of an Ethernet
network 70 having local interconnecting lines 70a, 70b, 70c.
Similar interconnecting lines are directed to each power supply
used in the four cells creating ARCs 1, 2, 3 and 4 of a tandem
welding operation. The description of system or cell S applies to
each of the arcs at the other electrodes. If AC current is
employed, a master power supply is used. In some instances, merely
a master power supply is used with a cell specific synchronizing
signal. If higher currents are required, the systems or cells
include a master and slave power supply combination as described
with respect to system S of FIG. 1. In some instances, a DC arc is
used with two or more AC arcs synchronized by generator 80. Often
the DC arc is the leading electrode in a tandem electrode welding
operation, followed by two or more synchronized AC arcs. A DC power
supply need not be synchronized, nor is there a need for accurate
interconnection of the polarity logic and switching points or
commands. Some DC powered electrodes may be switched between
positive and negative, but not at the frequency of an AC driven
electrode. Irrespective of the make-up of the arcs, Ethernet or
local area network 70 includes the parameter information identified
in a coded fashion designated for specific power supplies of the
various systems used in the tandem welding operation. This network
also employs synchronizing signals for the several cells or systems
whereby the systems can be offset in a time relationship. These
synchronizing signals are decoded and received by a master power
supply as indicated by line 40 in FIG. 1. In this manner, the AC
arcs are offset on a time basis. These synchronizing signals are
not required to be as accurate as the switching points through
network interface cards or gateways 50, 52. Synchronizing signals
on the data network are received by a network interface in the form
of a variable pulse generator 80. The generator creates offset
synchronizing signals in lines 84, 86 and 88. These synchronizing
signals dictate the phase of the individual alternating current
cells for separate electrodes in the tandem operation.
Synchronizing signals can be generated by interface 80 or actually
received by the generator through the network 70. Network 70 merely
activates generator 80 to create the delay pattern for the many
synchronizing signals. Also, generator 80 can vary the frequency of
the individual cells by frequency of the synchronizing pulses if
that feature is desired in the tandem welding operation.
[0065] A variety of controllers and power supplies could be used
for practicing the system as described in FIG. 1; however,
preferred implementation of the system is set forth in FIG. 2
wherein power supply PSA is combined with controller and power
supply 30 and power supply PSB is combined with controller and
power supply 32. These two units are essentially the same in
structure and are labeled with the same numbers when appropriate.
Description of power supply PSA applies equally to power supply
PSB. Inverter 100 has an input rectifier 102 for receiving three
phase line current L1, L2, and L3. Output transformer 110 is
connected through an output rectifier 112 to tapped inductor 120
for driving opposite polarity switches Q1, Q2. Controller 140a of
power supply PSA and controller 140b of PSB are essentially the
same, except controller 140a outputs timing information to
controller 140b. Switching points or lines 142, 144 control the
conductive condition of polarity switches Q1, Q2 for reversing
polarity at the time indicated by the logic on lines 142, 144, as
explained in more detail in Stava U.S. Pat. No. 6,111,216
incorporated by reference herein. The control is digital with a
logic processor; thus, A/D converter 150 converts the current
information on feedback line 16 or line 26 to controlling digital
values for the level of output from error amplifier 152 which is
illustrated as an analog error amplifier. In practice, this is a
digital system and there is no further analog signal in the control
architecture. As illustrated, however, amplifier has a first input
152a from converter 150 and a second input 152b from controller
140a or 140b. The current command signal on line 152b includes the
wave shape or waveform required for the AC current across the arc
at weld station WS. This is standard practice as taught by several
patents of Lincoln Electric, such as Blankenship U.S. Pat. No.
5,278,390, incorporated by reference. See also Stava U.S. Pat. No.
6,207,929, incorporated by reference. The output from amplifier 152
is converted to an analog voltage signal by converter 160 to drive
pulse width modulator 162 at a frequency controlled by oscillator
164, which is a timer program in the processor software. The shape
of the waveform at the arcs is the voltage or digital number at
lines 152b. The frequency of oscillator 164 is greater than 18 kHz.
The total architecture of this system is digitized in the preferred
embodiment of the present invention and does not include
reconversion back into analog signal. This representation is
schematic for illustrative purposes and is not intended to be
limiting of the type of power supply used in practicing the present
invention. Other power supplies could be employed.
[0066] A background system utilizing the concepts of FIGS. 1 and 2
are illustrated in FIGS. 3 and 4. Workpiece 200 is a seam in a pipe
which is welded together by tandem electrodes 202, 204 and 206
powered by individual power supplies PS1, PS2, PS3, respectively.
The power supplies can include more than one power source
coordinated in accordance with the technology in Houston U.S. Pat.
No. 6,472,634. The illustrated embodiment involves a DC arc for
lead electrode 202 and an AC arc for each of the tandem electrodes
204, 206. The created waveforms of the tandem electrodes are AC
currents and include shapes created by a wave shaper or wave
generator in accordance with the previously described waveform
technology. As electrodes 202, 204 and 206 are moved along weld
path WP a molten metal puddle P is deposited in pipe seam 200 with
an open root portion 210 followed by deposits 212, 214 and 216 from
electrodes 202, 204 and 206, respectively. As previously described
more than two AC driven electrodes as will be described and
illustrated by the waveforms of FIG. 15, can be operated by the
invention relating to AC currents of adjacent electrodes. The power
supplies, as shown in FIG. 4, each include an inverter 220
receiving a DC link from rectifier 222. In accordance with Lincoln
waveform technology, a chip or internal programmed pulse width
modulator stage 224 is driven by an oscillator 226 at a frequency
greater than 18 kHz and preferably greater than 20 kHz. As
oscillator 226 drives pulse width modulator 224, the output current
has a shape dictated by the wave shape outputted from wave shaper
240 as a voltage or digital numbers at line 242. Output leads 217,
218 are in series with electrodes 202, 204 and 206. The shape in
real time is compared with the actual arc current in line 232 from
Hall Effect transducer 228 by a stage illustrated as comparator 230
so that the outputs on line 234 controls the shape of the AC
waveforms. The digital number or voltage on line 234 determines the
output signal on line 224a to control inverter 220 so that the
waveform of the current at the arc follows the selected profile
outputted from wave shaper 240. This is standard Lincoln waveform
technology, as previously discussed. Power supply PS1 creates a DC
arc at lead electrode 202; therefore, the output from wave shaper
240 of this power supply is a steady state indicating the magnitude
of the DC current. The present invention does not relate to the
formation of a DC arc. To the contrary, the present invention is
the control of the current at two adjacent AC arcs for tandem
electrodes, such as electrodes 204, 206. In accordance with the
invention, wave shaper 240 involves an input 250 employed to select
the desired shape or profile of the AC waveform. This shape can be
shifted in real time by an internal programming schematically
represented as shift program 252. Wave shaper 240 has an output
which is a polarity signal on line 254. In practice, the polarity
signal is a bit of logic, as shown in FIG. 7. Logic 1 indicates a
negative polarity for the waveform generated by wave shaper 240 and
logic 0 indicates a positive polarity. This logic signal or bit
controller 220 directed to the power supply is read in accordance
with the technology discussed in FIG. 16. The inverter switches
from a positive polarity to a negative polarity, or the reverse, at
a specific "READY" time initiated by a change of the logic bit on
line 254. In practice, this bit is received from variable pulse
generator 80 shown in FIG. 1 and in FIG. 5. The background welding
system shown in FIGS. 3 and 4 uses the shapes of AC arc currents at
electrodes 204 and 206 to obtain a beneficial result, i.e. a
generally quiescent molten metal puddle P and/or synthesized
sinusoidal waveforms compatible with transformer waveforms used in
arc welding. The electric arc welding system shown in FIGS. 3 and 4
have a program to select the waveform at "SELECT" program 250 for
wave shaper 240. The unique waveforms are used by the tandem
electrodes. One of the power supplies to create an AC arc is
schematically illustrated in FIG. 5. The power supply or source is
controlled by variable pulse generator 80, shown in FIG. 1. Signal
260 from the generator controls the power supply for the first arc.
This signal includes the synchronization of the waveform together
with the polarity bit outputted by the wave shaper 240 on line 254.
Lines 260a-260n control the desired subsequent tandem AC arcs
operated by the welding system of the present invention. The timing
of these signals shifts the start of the other waveforms. FIG. 5
merely shows the relationship of variable pulse generator 80 to
control the successive arcs as explained in connection with FIG.
4.
[0067] In the welding system of Houston U.S. Pat. No. 6,472,634,
the AC waveforms are created as shown in FIG. 6 wherein the wave
shaper for arc AC1 at electrode 204 creates a signal 270 having
positive portions 272 and negative portions 274. The second arc AC2
at electrode 206 is controlled by signal 280 from the wave shaper
having positive portions 282 and negative portions 284. These two
signals are the same, but are shifted by the signal from generator
80 a distance x, as shown in FIG. 6. The waveform technology
created current pulses or waveforms at one of the arcs are
waveforms having positive portions 290 and negative portions 292
shown at the bottom portion of FIG. 6. A logic bit from the wave
shaper determines when the waveform is switched from the positive
polarity to the negative polarity and the reverse. In accordance
with the disclosure in Stava U.S. Pat. No. 6,111,216 (incorporated
by reference herein) pulse width modulator 224 is generally shifted
to a lower level at point 291a and 291b. Then the current reduces
until reaching a fixed level, such as 100 amps. Consequently, the
switches change polarity at points 294a and 294b. This produces a
vertical line or shape 296a, 296b when current transitioning
between positive portion 290 and negative portion 292. This is the
system disclosed in the Houston patent where the like waveforms are
shifted to avoid magnetic interference. The waveform portions 290,
292 are the same at arc AC1 and at arc AC2. This is different from
the present invention which relates to customizing the waveforms at
arc AC1 and arc AC2 for purposes of controlling the molten metal
puddle and/or synthesizing a sinusoidal wave shape in a manner not
heretofore employed. The disclosure of FIG. 6 is set forth to show
the concept of shifting the waveforms. The same switching procedure
to create a vertical transition between polarities is used in the
preferred embodiment of the present invention. Converting from the
welding system shown in FIG. 6 to an imbalance waveform is
generally shown in FIG. 7. The logic on line 254 is illustrated as
being a logic 1 in portions 300 and a logic 0 in portions 302. The
change of the logic or bit numbers signals the time when the system
illustrated in FIG. 16 shifts polarity. This is schematically
illustrated in the lower graph of FIG. 6 at points 294a, 294b. Wave
shaper 240 for each of the adjacent AC arcs has a first wave shape
310 for one of the polarities and a second wave shape 312 for the
other polarity. Each of the waveforms 310, 312 are created by the
logic on line 234 taken together with the logic on line 254. Thus,
pulses 310, 312 as shown in FIG. 7, are different pulses for the
positive and negative polarity portions. Each of the pulses 310,
312 are created by separate and distinct current pulses 310a, 312a
as shown. Switching between polarities is accomplished as
illustrated in FIG. 6 where the waveforms generated by the wave
shaper are shown as having the general shape of waveforms 310, 312.
Positive polarity controls penetration and negative polarity
controls deposition. The positive and negative pulses of a waveform
are different and the switching points are controlled so that the
AC waveform at one arc is controlled both in the negative polarity
and the positive polarity to have a specific shape created by the
output of wave shaper 240. The waveforms for the arc adjacent to
the arc having the current shown in FIG. 7 is controlled
differently to obtain the advantages illustrated best in FIG. 8.
The waveform at arc AC 1 is in the top part of FIG. 8. It has
positive portions 320 shown by current pulses 320a and negative
portions 322 formed by pulses 322a. Positive portion 320 has a
maximum magnitude a and width or time period b. Negative portion
322 has a maximum magnitude d and a time or period c. These four
parameters are adjusted by wave shaper 240. In the illustrated
embodiment, arc AC2 has the waveform shown at the bottom of FIG. 8
where positive portion 330 is formed by current pulses 330a and has
a height or magnitude a' and a time length or period b'. Negative
portion 332 is formed by pulses 332a and has a maximum amplitude d'
and a time length c'. These parameters are adjusted by wave shaper
240. In accordance with the invention, the waveform from the wave
shaper on arc AC1 is out of phase with the wave shape for arc AC2.
The two waveforms have parameters or dimensions which are adjusted
so that (a) penetration and deposition is controlled and (b) there
is no long time during which the puddle P is subjected to a
specific polarity relationship, be it a like polarity or opposite
polarity. This concept in formulating the wave shapes prevents long
term polarity relationships as explained by the showings in FIGS. 9
and 10. In FIG. 9 electrodes 204, 206 have like polarity,
determined by the waveforms of the adjacent currents at any given
time. At that instance, magnetic flux 350 of electrode 204 and
magnetic flux 352 of electrode 206 are in the same direction and
cancel each other at center area 354 between the electrodes. This
causes the molten metal portions 360, 362 from electrodes 204, 206
in the molten puddle P to move together, as represented by arrows
c. This inward movement together or collapse of the molten metal in
puddle P between electrodes 204 will ultimately cause an upward
gushing action, if not terminated in a very short time, i.e. less
than about 20 ms. As shown in FIG. 10, the opposite movement of the
puddle occurs when the electrodes 204, 206 have opposite
polarities. Then, magnetic flux 370 and magnetic flux 372 are
accumulated and increased in center portion 374 between the
electrodes. High forces between the electrodes causes the molten
metal portions 364, 366 of puddle P to retract or be forced away
from each other. This is indicated by arrows r. Such outward
forcing of the molten metal in puddle P causes disruption of the
weld bead if it continues for a substantial time which is generally
less than 10 ms. As can be seen from FIGS. 9 and 10, it is
desirable to limit the time during which the polarity of the
waveform at adjacent electrodes is either the same polarity or
opposite polarity. The waveform, such as shown in FIG. 6,
accomplishes the objective of preventing long term concurrence of
specific polarity relationships, be it like polarities or opposite
polarities. As shown in FIG. 8, like polarity and opposite polarity
is retained for a very short time less than the cycle length of the
waveforms at arc AC1 and arc AC2. This positive development of
preventing long term occurrence of polarity relationships together
with the novel concept of pulses having different shapes and
different proportions in the positive and negative areas combine to
control the puddle, control penetration and control deposition in a
manner not heretofore obtainable in welding with a normal
transformer power supplies or normal use of Lincoln waveform
technology.
[0068] In FIG. 11 the positive and negative portions of the AC
waveform from the wave shaper 240 are synthesized sinusoidal shapes
with a different energy in the positive portion as compared to the
negative portion of the waveforms. The synthesized sine wave or
sinusoidal portions of the waveforms allows the waveforms to be
compatible with transformer welding circuits and compatible with
evaluation of sine wave welding. In FIG. 11, waveform 370 is at arc
AC1 and waveform 372 is at arc AC2. These tandem arcs utilize the
AC welding current shown in FIG. 11 wherein a small positive
sinusoidal portion 370a controls penetration at arc AC1 while the
larger negative portion 370b controls the deposition of metal at
arc AC1. There is a switching between the polarities with a change
in the logic bit, as discussed in FIG. 7. Sinusoidal waveform 370
plunges vertically from approximately 100 amperes through zero
current as shown in by vertical line 370c. Transition between the
negative portion 370b and positive portion 370a also starts a
vertical transition at the switching point causing a vertical
transition 370d. In a like manner, phase shifted waveform 372 of
arc AC2 has a small penetration portion 372a and a large negative
deposition portion 372b. Transition between polarities is indicated
by vertical lines 372c and 372d. Waveform 372 is shifted with
respect to waveform 370 so that the dynamics of the puddle are
controlled without excessive collapsing or repulsion of the molten
metal in the puddle caused by polarities of adjacent arcs AC1, AC2.
In FIG. 11, the sine wave shapes are the same and the frequencies
are the same. They are merely shifted to prevent a long term
occurrence of a specific polarity relationship.
[0069] In FIG. 12 waveform 380 is used for arc AC1 and waveform 382
is used for arc AC2. Portions 380a, 380b, 382a, and 382b are
sinusoidal synthesized and are illustrated as being of the same
general magnitude. By shifting these two waveforms 90.degree.,
areas of concurrent polarity are identified as areas 390, 392, 394
and 396. By using the shifted waveforms with sinusoidal profiles,
like polarities or opposite polarities do not remain for any length
of time. Thus, the molten metal puddle is not agitated and remains
quiescent. This advantage is obtained by using the present
invention which also combines the concept of a difference in energy
between the positive and negative polarity portions of a given
waveform. FIG. 12 is illustrative in nature to show the definition
of concurrent polarity relationships and the fact that they should
remain for only a short period of time. To accomplish this
objective, another embodiment of the present invention is
illustrated in FIG. 13 wherein previously defined waveform 380 is
combined with waveform 400, shown as the sawtooth waveform of arc
AC2 (a) or the pulsating waveform 402 shown as the waveform for arc
AC2(b). Combining waveform 380 with the different waveform 400 of a
different waveform 402 produces very small areas or times of
concurrent polarity relationships 410, 412, 414, etc. In FIG. 14
the AC waveform generated at one arc is drastically different than
the AC waveform generated at the other arc. This same concept of
drastically different waveforms for use in the present invention is
illustrated in FIG. 14 wherein waveform 420 is an AC pulse profile
waveform and waveform 430 is a sinusoidal profile waveform having
about one-half the period of waveform 420. Waveform 420 includes a
small penetration positive portion 420a and a large deposition
portion 420b with straight line polarity transitions 420c. Waveform
430 includes positive portion 430a and negative portion 430b with
vertical polarity transitions 430c. By having these two different
waveforms, both the synthesized sinusoidal concept is employed for
one electrode and there is no long term concurrent polarity
relationship. Thus, the molten metal in puddle P remains somewhat
quiescent during the welding operation by both arcs AC1, AC2.
[0070] In FIG. 15 waveforms 450, 452, 454 and 456 are generated by
the wave shaper 240 of the power supply for each of four tandem
arcs, arc AC1, arc AC2, arc AC3 and arc AC4. The adjacent arcs are
aligned as indicated by synchronization signal 460 defining when
the waveforms correspond and transition from the negative portion
to the positive portion. This synchronization signal is created by
generator 80 shown in FIG. 1, except the start pulses are aligned.
In this embodiment of the invention first waveform 450 has a
positive portion 450a, which is synchronized with both the positive
and negative portion of the adjacent waveform 452, 454 and 456. For
instance, positive portion 450a is synchronized with and correlated
to positive portion 452a and negative portion 452b of waveform 452.
In a like manner, the positive portion 452a of waveform 452 is
synchronized with and correlated to positive portion 454a and
negative portion 454b of waveform 454. The same relationship exists
between positive portion 454a and the portions 456a, 456b of
waveform 456. The negative portion 450b is synchronized with and
correlated to the two opposite polarity portions of aligned
waveform 452. The same timing relationship exists between negative
portion 452b and waveform 454. In other words, in each adjacent arc
one polarity portion of the waveform is correlated to a total
waveform of the adjacent arc. In this manner, the collapse and
repelling forces of puddle P, as discussed in connection with FIGS.
9 and 10, are diametrically controlled. One or more of the positive
or negative portions can be synthesized sinusoidal waves as
discussed in connection with the waveforms disclosed in FIGS. 11
and 12.
[0071] As indicated in FIGS. 1 and 2, when the master controller of
switches is to switch, a switch command is issued to master
controller 140a of power supply 30. This causes a "kill" signal to
be received by the master so a kill signal and polarity logic is
rapidly transmitted to the controller of one or more slave power
supplies connected in parallel with a single electrode. If standard
AC power supplies are used with large snubbers in parallel with the
polarity switches, the slave controller or controllers are
immediately switched within 1-10 .mu.s after the master power
supply receives the switch command. This is the advantage of the
high accuracy interface cards or gateways. In practice, the actual
switching for current reversal of the paralleled power supplies is
not to occur until the output current is below a given value, i.e.
about 100 amperes. This allows use of smaller switches.
[0072] The implementation of the switching for all power supplies
for a single AC arc uses the delayed switching technique where
actual switching can occur only after all power supplies are below
the given low current level. The delay process is accomplished in
the software of the digital processor and is illustrated by the
schematic layout of FIG. 16. When the controller of master power
supply 500 receives a command signal as represented by line 502,
the power supply starts the switching sequence. The master outputs
a logic on line 504 to provide the desired polarity for switching
of the slaves to correspond with polarity switching of the master.
In the commanded switch sequence, the inverter of master power
supply 500 is turned off or down so current to electrode E is
decreased as read by hall effect transducer 510. The switch command
in line 502 causes an immediate "kill" signal as represented by
line 512 to the controllers of paralleled slave power supplies 520,
522 providing current to junction 530 as measured by hall effect
transducers 532, 534. All power supplies are in the switch sequence
with inverters turned off or down. Software comparator circuits
550, 552, 554 compare the decreased current to a given low current
referenced by the voltage on line 556. As each power supply
decreases below the given value, a signal appears in lines 560,
562, and 564 to the input of a sample and hold circuits 570, 572,
and 574, respectively. The circuits are outputted by a strobe
signal in line 580 from each of the power supplies. When a set
logic is stored in a circuit 570, 572, and 574, a YES logic appears
on lines READY.sup.1, READY.sup.2, and READY.sup.3 at the time of
the strobe signal. This signal is generated in the power supplies
and has a period of 25 .mu.s; however, other high speed strobes
could be used. The signals are directed to controller C of the
master power supply, shown in dashed lines in FIG. 16. A software
ANDing function represented by AND gate 584 has a YES logic output
on line 582 when all power supplies are ready to switch polarity.
This output condition is directed to clock enable terminal ECLK of
software flip flop 600 having its D terminal provided with the
desired logic of the polarity to be switched as appearing on line
504. An oscillator or timer operated at about 1 MHz clocks flip
flop by a signal on line 602 to terminal CK. This transfers the
polarity command logic on line 504 to a Q terminal 604 to provide
this logic in line 610 to switch slaves 520, 522 at the same time
the identical logic on line 612 switches master power supply 500.
After switching, the polarity logic on line 504 shifts to the
opposite polarity while master power supply awaits the next switch
command based upon the switching frequency. Other circuits can be
used to affect the delay in the switching sequence; however, the
illustration in FIG. 16 is the present scheme.
[0073] As so far described in FIGS. 1-16, the welder, and control
system for the welder to accomplish other advantageous features is
submitted as background information. This description explains the
background, not prior art, to the present invention. This
background technology has been developed by The Lincoln Electric
Company, assignee of the present application. This background
description is not necessarily prior art, but is submitted for
explanation of the specific improvement in such waveform technology
welders, as accomplished by the welder described in FIG. 17. This
welder "paints" the exact profile of a waveform to be used in a
welding process. Thus, a precise waveform is obtained by use of
program 700. This waveform is coordinated with a specific cored
electrode.
[0074] The welder and/or welding system as shown in FIGS. 4 and 5,
is operated by control program 700 used to accurately set the exact
profile of a given waveform for use with a specific cored electrode
shown in FIGS. 19 and 20. Program 700 is illustrated in FIG. 17,
where welder 705 has a wave shaper 240 set to a general type of
weld waveform by a select network 250. The selected waveform is the
desired AC waveform to perform, by a succession of waveforms, a
given welding process. This waveform, in accordance with the
invention, is set to be used with a specific cored electrode.
Waveform control program 700 has a profile control network 710 to
set the exact, desired profile of the waveform and a magnitude
control circuit 712 to adjust the energy or power of the waveform
without substantially changing the set profile to be used for a
given cored electrode. This specific profile is stored in the
welder disclosed in FIGS. 21 and 28 for use when the corresponding
electrode is to be used in the welding process.
[0075] The program or control network 700 is connected to the wave
shaper 240 to control the exact general profile of each individual
waveform in the succession of waveforms constituting an AC welding
process. To accomplish this objective of accurate and precise
synergic setting of the waveform general profile, four separate
profile parameters are adjusted individually. The first parameter
is frequency set into the waveform profile by circuit 720 manually
or automatically adjusted by interface network 722 to produce a set
value on an output represented as line 724. This value controls the
set frequency of the waveform profile. Of course, this is actually
the period of the waveform. In a like manner, the duty cycle of the
waveform is controlled by circuit 730 having an adjustable
interface network 732 and an output line 734 for developing a value
to control the relationship between the positive half cycle and the
negative half cycle. This profile parameter is set by the logic or
data on line 734 from circuit 730. By the signal or data on line
724 and the data on line 734, the AC profile of the waveform is
set. This does not relate to the energy level of the individual
portions of the waveform, but merely the general fixed profile of
the waveform. To control the up ramp rate of the waveform there is
provided a circuit 742 having a manual or automatic adjusting
network 742 and an output signal on line 744 for setting the rate
at which the set profile of the waveform changes from negative to a
positive polarity. In a like manner, a down ramp circuit 750 is
provided with an adjusting interface 752 and an output line 754.
The magnitudes of the values on lines 724, 734, 744 and 754 set the
profile of the individual waveform. At least two of these parameter
profiles are set together; however, preferably all of the profile
parameters are set to define a waveform profile.
[0076] To control the profile of the waveform for the purposes of
the energy or power transmitted by each individual waveform in the
welding process, program 700 includes magnitude circuit or network
712 divided into two individual sections 760, 762. These sections
of the magnitude circuit control the energy or other power related
level of the waveform during each of the polarities without
substantially affecting the general profile set by profile control
network 710. Section 760 includes a level control circuit 770 which
is manually adjusted by an interface network 772 to control the
relationship between an input value on line 774 and an output value
on line 776. Level control circuit 770 is essentially a digital
error amplifier circuit for controlling the current, voltage and/or
power during the positive portion of the generated set waveform
profile. Selector 250a shifts circuit 770 into either the current,
voltage or power mode. Section 760 controls the energy, or power or
other heat level during the positive portion of the waveform with
changing the general profile set by network 710. In a like manner,
second section 762 has a digital error amplifier circuit 780 that
is set or adjusted by network 782 so that the value on input line
784 controls the level or signal on output line 786. Selector 250b
shifts circuit 780 into either the current, voltage or power mode.
Consequently, the digital level data on lines 776 and 786 controls
the current, voltage and/or power during each of the half cycles
set by profile control network 710.
[0077] In accordance with another feature of program 700, wave
shaper 240 is controlled by only magnitude control circuit 712 and
the profile is set by network or program 250 used in the background
system shown in FIGS. 4 and 5. Network 250 does not set the
profile, but selects known types of waveforms as will be explained
with the disclosure of FIGS. 21 and 28. The enhanced advantage of
program 700 is realized by setting all profile parameters using
circuits 720, 730, 740 and 750 together with the magnitude circuits
770, 780. Of course, a waveform controlled by any one of these
circuits is an improvement over the background technology. Program
700 synergically adjusts all profile parameters and magnitude
values during each polarity of the AC waveform so the waveform
corresponds to a specific cored electrode.
[0078] To explain the operation of program 700, two waveforms are
schematically illustrated in FIG. 18. Waveform 800 has a positive
portion 802 and a negative portion 804, both produced by a series
of rapidly created current pulses 800a. Waveform 800 is illustrated
as merely a square wave to illustrate control of the frequency or
period of the waveform and the ratio of the positive portion 802 to
the negative portion 804. These parameters are accurately set by
using program 700 to modify the type of waveform heretofore merely
selected by network 450. In this schematic representation of the
waveform, the up ramp rate and the down ramp rate are essentially
zero. Of course, the switching concept taught in Stava U.S. Pat.
No. 6,111,216 would be employed for shifting between positive and
negative waveform portions to obtain the advantages described in
the Stava patent. Second illustrated waveform 810 has a frequency
f, a positive portion 812 and a negative portion 814. In this
illustration, the up ramp rate 816 is controlled independently of
the down ramp rate 818. These ramp rates are illustrated as arrows
to indicate they exist at the leading and trailing edges of the
waveform during shifts between polarities. Program 700 relates to
physically setting the exact profile of the individual waveforms by
circuits 720, 730, 740 and 750. Several parameters of the waveform
are adjusted to essentially "paint" the waveform into a desired
profile. A very precise welding process using a set general profile
for the AC waveform is performed by a waveform technology
controlled welder using program 700. This program is used to
"paint" a waveform for each individual cored electrode so there is
a match between the AC waveform and the electrode used in the
welding process.
[0079] Program 700 in FIG. 17 is used to construct or create AC
waveforms that are optimized and specially tailored for each of
individually identified cored electrode such as electrode 910 shown
in FIGS. 19 and 20. A welder 900 has torch 902 for directing
electrode 910 toward workpiece W. An arc AC is created between the
end of electrode 910 and workpiece W. The electrode is a cored
electrode with sheath 912 and internal filled core 914. The core
includes flux ingredients, such as represented by particles 914a.
The purpose of these ingredients 914a is to (a) shield the molten
weld metal from atmospheric contamination by covering the molten
metal with slag, (b) combine chemically with any atmospheric
contaminants such that their negative impact on the weld quality is
minimized and/or (c) generate arc shielding gases. In accordance
with standard practice, core 914 also includes alloying
ingredients, referred to as particles 914b, together with other
miscellaneous particles 914c that are combined to provide the fill
of core 914. To optimize the welding operation, it has been
necessary to use solid wire with an external shielding gas.
However, in order to produce a weld with specific mechanical and
metallurgical properties, specific alloys are required, which can
be difficult to obtain in the form of a solid wire. Contamination
is difficult to prevent when using a welding process requiring
external shielding gas. It would be advantageous to therefore use a
self shielding cored electrode, so that the environment does not
affect the welding. Cored electrodes experience different burn back
rates for the sheath and core. All of these difficulties have
resulted in most pipeline welding to be done with a solid wire and
external shielding gas. To overcome these problems, STT welding was
developed by The Lincoln Electric Company of Cleveland, Ohio for
use in pipeline welding. Such welding employs a short circuit
process where surface tension transfers the molten metal. This
process did lower heat of the welding process, especially during
open root welding. The advantages of both welding with an AC power
source and cored electrodes were not obtainable because the welding
waveforms were not optimized for the specific cored electrode. The
present invention overcomes these difficulties by using a program
such as program 700 shown in FIG. 17 so a precise AC waveform is
generated for the welding operation and correlated specifically to
a given cored electrode. By providing a precisely profiled or
shaped waveform for an AC welding operation coordinated with a
given cored electrode the welding operation is optimized. It is now
possible to use an AC welding operation with a waveform accurately
profiled to accommodate a specific cored electrode.
[0080] Welder 900 is constructed in accordance with the present
invention for performing an AC welding operation using a cored
electrode so the welding operation is optimized for the particular
electrode. Details of welder 900 are shown in FIG. 21 where power
source 920 is driven by rectifier 920a. Electrode 910 is a cored
electrode with sheath 912 and core 914. Power source 920 of welder
900 has a storage device, unit or circuit 922 to create an
electrode identification signal in line 924 to identify a
particular electrode 910 being used in the welding process. Reading
device 921 identifies the particular electrode 910 passing by the
reading device as indicated at the top of FIG. 21. Thus, the signal
in line 924 identifies electrode 910. Device 921a manually tells
reading device 921 which particular electrode 910 is being used. In
other words, reading device 921 is set to the particular cored
electrode 910 to be used in the welding operation. This device is
manually adjusted to indicate a specific electrode. Electrode 910
can be identified by storage device 922 by a bar code or other
reading technique. The bar code is located on the spool or drum
containing electrode wire 910. In other words, device 921 either
automatically senses the identification of wire or electrode 910 or
receives manual input to indicate the electrode as indicated by
block 921a. A signal in 921b is directed to storage device 922
where a signal in data form is stored for all electrodes to be used
by welder 900. The signal on line 921b addresses a particular data
in storage device 922 corresponding with the specific cored
electrode. This data causes an electrode identification signal to
be applied to line 924. This signal 924 activates waveform look up
device 926 so the device outputs a profile signal in line 928. This
signal 928 instructs select circuit 250 to select a particular
stored profile which has been created by program 700 for a
particular cored electrode. Program 700 shown in FIG. 17 tailors
the stored waveforms to a specific electrode. The remainder of
power source 920 has been previously described. The profile signal
in line 928 selects a specific constructed or created waveform
stored in a memory associated with circuit 250. An AC welding
waveform tailored to the particular construction and constituents
of a particular cored electrode 910 is outputted in line 242. In
accordance with an alternative, the particular signal in line 928
is determined by the electrode and the wire feed speed. Device 930
has a set point that is outputted in line 932. Consequently, the
logic or data on lines 924 and 932 determine the profile select
signal in line 928. A desired stored profile in the memory of
waveform generator 250 is used. This profile is based upon the
particular electrode and/or the particular set point wire feed
speed.
[0081] A typical constructed AC waveform is illustrated in FIG. 22
where process curve 950 includes a series of waveforms comprising
positive section 952 and negative section 954. In accordance with
the invention, the waveforms are created by a large number of
individual pulses 960 created at a rate substantially greater than
18 kHz and created at the output line 224a of pulse width modulator
224. This controls the high switching speed inverter. In the
preferred embodiment of the invention, curve 950 has a positive
magnitude x and a negative magnitude y with the length of the
negative portion 954 indicated to be z. In order to control the
heat in the welding operation, duty cycle z is adjusted when the
waveform shown in FIG. 22 is constructed for a particular cored
electrode. The negative portion 954 of FIG. 22 controls the overall
heat input to the workpiece. The positive portion 952 contributes
more heat to the electrode and less heat to the workpiece.
Therefore, by changing the duty cycle, the overall heat into the
workpiece can be varied or controlled. In the present invention, an
AC welding process is created at the output of wave shaper or
waveform generator 240. The selected waveform is precisely adjusted
to optimize its use with a particular cored electrode 910. To
control the heat in the welding operation, the waveform has duty
cycle of z controlled by program 700. After the waveform has been
fixed, it is set into waveform generator 240 based upon the logic
from select circuit 250. Welder 900 is used to correlate a
particular AC waveform with a particular cored electrode to fix the
operation of the welding process dictated by the constituents
forming electrode 910.
[0082] The waveform used in practicing the invention is preferably
a square waveform as shown in FIG. 22; however, to control the
initial heating it is within the scope of the invention to provide
a non-square AC waveform shown in FIG. 23 wherein process curve 970
comprises waveforms, each having positive portion 972 and negative
portion 974. Each of these portions is formed by a plurality of
individual pulses 960 as explained with respect to curve 950 in
FIG. 22. These individual pulses 960 are created at a frequency
greater than 18 kHz and are waveform technology pulses normally
used in inverter type power sources. To reduce the rate of heating,
portions 972, 974 are provided with ramp portions 976, 977, 978 and
979. Other profiles are possible to optimize the AC welding using
the present invention.
[0083] A problem caused when using cored electrodes without
implementation of the present invention is illustrated in FIG. 24.
The welding process melts sheath 912 to provide a portion of molten
metal 980 melted upwardly around the electrode, as indicated by
melted upper end 982. Thus, the sheath of the electrode is melted
more rapidly than the core. This causes a molten metal material to
exist at the output end of electrode 910 without protective gas or
chemical reaction created by melting of the internal constituents
of core 914. Thus, arc AC melts the metal of electrode 910 in an
unprotected atmosphere. The necessary shielding for the molten
metal is formed when the sheath and core are melted at the same
rate. The problem of melting the molten metal more rapidly than the
core is further indicated by the pictorial representation of FIG.
25. Molten metal 990 from sheath 912 has already joined workpiece W
before the core has had an opportunity to be melted. It can not
provide the necessary shielding for the welding process. FIGS. 24
and 25 show the reason why AC welding using cored electrodes has
not been used for off-shore pipeline welding and other pipeline
welding.
[0084] The invention proposes the use of an AC waveform as
described above as a means to control the heat input when using a
cored electrode.
[0085] By using the present invention, the precise profile for the
AC waveform used in the welding process is selected whereby sheath
912 and core 914 melt at approximately the same rate. The failure
to adequately coordinate the melting of the shield with the melting
of the core would be a reason for rejecting the use of AC welding
with cored electrodes for pipeline welding. The advantage of the
invention is a process not needing external shielding gas. When
this occurs, shielding gas SG and other shielding constituents are
generated ahead of the molten metal from sheath 912. By using the
present invention this feature can be obtained by precisely
profiling the waveform for the welding operation using program 700.
In the past such coordination was not possible. Invention of
program 700 or like programs made the present invention possible.
These programs generate waveforms which are specifically tailored
for individual cored electrodes allowing cored electrodes to be
used in an AC welding process in a manner to protect the molten
metal against atmospheric contamination during the welding
operation.
[0086] When welding with a cored electrode, it is desired to have
the sheath and core melt at the same rate. This operation promotes
homogeneous mixing of certain core materials with the outer sheath,
such that the mixture of molten materials chemically resists the
effects of atmospheric contamination. Alloying elements required to
produce desired weld metal mechanical and metallurgical
characteristics are uniformly distributed in the weld metal. In
addition, the protective benefits derived from slag and/or
gas-forming constituents are optimized. This situation is
illustrated in FIG. 27. In contrast, FIG. 26 illustrates a
situation where the sheath has melted more rapidly than the core.
Molten metal 990 from sheath 912 has already joined workpiece W
before core 914 has had an opportunity to be melted. Metal 990 has
not been protected from the effects of atmospheric contamination to
the degree that it would have been if the unmelted core
constituents had actually been melted. Additionally, alloying
elements needed to achieve desired mechanical and metallurgical
characteristics may be missing from molten metal 990.
[0087] An alternative of the present invention is shown in FIG. 27
where select circuit 992 selects a waveform B in accordance with
the data in line 994a from block 994. This block has data
identifying a particular electrode A. The electrode has a
composition that is accommodated by waveform B in select circuit
992. A set point in line 996a from wire feed speed block 996 is
used to select waveform B so that waveform B is not only a waveform
for the electrode which is a primary aspect of the invention, but
electrode A with a particular set point. This adjusts the output of
waveform generator 240 to control the waveform of the AC welding
process to be tailored to the exact cored electrode A identified by
block 994. Electrode A is used to activate waveform B.
[0088] The basic aspect of the invention is creation of a waveform
to perform the desired operation when using a particular cored
electrode. By identifying the particular cored electrode and
activating its coordinated AC waveform, the desired welding process
is performed between the electrode and the workpiece. Various
analog and digital components are possible for performing the
present invention. The constituents of the core and the size of the
sheath determines the optimum waveform profile used in the AC
welding process. This invention is made possible by the use of a
program such as program 700 in FIG. 17 to precisely set and modify
the profile of the waveform being used in an electric arc welding
process of the type using waveform technology.
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