U.S. patent application number 11/107126 was filed with the patent office on 2005-09-29 for method and apparatus for braking and advancing a welding wire.
This patent application is currently assigned to Illinois Tool Works Inc.. Invention is credited to Hennecke, Peter, Huismann, Gerd.
Application Number | 20050211689 11/107126 |
Document ID | / |
Family ID | 30000074 |
Filed Date | 2005-09-29 |
United States Patent
Application |
20050211689 |
Kind Code |
A1 |
Huismann, Gerd ; et
al. |
September 29, 2005 |
Method and apparatus for braking and advancing a welding wire
Abstract
A method and apparatus for providing welding-type power include
a wire feeder that provides wire to an arc and a power supply that
provides power to the arc. A reversible wire feed motor moves the
wire to and away from the arc. A controller controls the reversible
wire feeder motor to reverse at least once per process cycle,
and/or controls the power source to provide a desired mean arc
current, and/or controls the reversible motor in response to short
detection and short clearing, and/or controls the reversal
frequency in response to pool oscillation frequency. A wire feed
motor output is slaved to an average of the reversible motor
output. The controller may include various control modules, such as
a mean arc current control module, and/or a short detection
feedback circuit. The reversible motor is a stepper motor, that
incrementally turns in a series of steps having a given angle in
another embodiment. The controller includes a step size output and
the given angle is varied in response to the step size output.
Inventors: |
Huismann, Gerd; (Hamburg,
DE) ; Hennecke, Peter; (Am Silberg, DE) |
Correspondence
Address: |
CORRIGAN LAW OFFICE
5 BRIARCLIFF CT
APPLETON
WI
54915
US
|
Assignee: |
Illinois Tool Works Inc.
|
Family ID: |
30000074 |
Appl. No.: |
11/107126 |
Filed: |
April 15, 2005 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11107126 |
Apr 15, 2005 |
|
|
|
10200863 |
Jul 23, 2002 |
|
|
|
Current U.S.
Class: |
219/137.71 |
Current CPC
Class: |
B23K 9/1006 20130101;
B23K 9/0735 20130101; B23K 9/124 20130101; B23K 9/125 20130101 |
Class at
Publication: |
219/137.71 |
International
Class: |
B23K 009/10 |
Claims
1. A welding-type power source, comprising: a wire feeder disposed
to provide wire to an arc; a power supply disposed to provide power
to the arc; a braking wire feed motor, disposed to move the wire to
and away from the arc, and to superimpose movement of the wire onto
the movement from the wire feed motor; and a controller, connected
to the power supply and the wire feeder, and including a braking
wire feeder control module connected to the braking wire feeder
and, wherein the braking wire feeder control module includes a
braking motor output having a value determined at a frequency of at
least once per process cycle and further including a wire feed
motor output slaved to an average of the reversible motor
output.
2. The welding-type power source of claim 1, wherein the controller
includes a mean arc current control module.
3. The welding-type power source of claim 1, further comprising a
short detection feedback circuit, providing an input to the
controller.
4. (Cancelled.)
5. The welding-type power source of claim 1, including a buffer
disposed between the wire feed motor and the braking motor, wherein
the controller includes a buffer feedback module and the wire feed
motor output is responsive to the buffer feedback module.
6. The welding-type power source of claim 1 further comprising a
buffer disposed between the wire feed motor and the braking motor;
and wherein the controller includes a buffer feedback module and a
wire feed motor output responsive to the buffer feedback
module.
7. The welding-type power source of claim 1, wherein the braking
motor is a stepper motor, whereby the motor incrementally turns in
a series of steps having a given angle.
8. The welding-type power source of claim 7 wherein the controller
includes a step size output and the given angle is varied in
response to the step size output.
9-10. (canceled)
11. A welding-type power source, comprising: a wire feeder disposed
to provide wire to an arc including a wire feed motor for moving
the wire to the arc; a power supply disposed to provide power to
the arc; a braking wire feed motor, disposed to move the wire to
and away from the arc and to superimpose movement of the wire onto
the movement from the wire feed motor; a buffer disposed between
the wire feed motor and the braking motor; and a controller,
connected to the wire feeder, and including a braking wire feeder
control module connected to the braking wire feeder and, wherein
the braking wire feeder control module includes a braking motor
output, and including a mean arc current control module having an
arc current control output responsive to mean arc current and
connected to the power supply, and including a buffer feedback
module and a wire feed motor output responsive to the buffer
feedback module.
12. The welding-type power source of claim 11, further comprising a
short detection feedback circuit, providing an input to the
controller.
13. (canceled)
14. A welding-type power source, comprising: a wire feeder disposed
to provide wire to an arc, including a wire feed motor for moving
the wire to the arc; a power supply disposed to provide power to
the arc; a braking wire feed motor, disposed to move the wire to
and away from the arc and to superimpose movement of the wire onto
the movement from the wire feed motor; a controller, connected to
the power supply and the wire feeder, and including a braking wire
feeder control module connected to the braking wire feeder and,
wherein the braking wire feeder control module includes a braking
motor output, and the controller includes a wire feed motor output
slaved to an average of the braking motor output; and a short
detection feedback circuit, providing an input to the
controller.
15. (canceled)
16. The welding-type power source of claim 14, including a buffer
disposed between the wire feed motor and the braking motor, wherein
the controller includes a buffer feedback module and the wire feed
motor output is responsive to the buffer feedback module.
17. The welding-type power source of claim 16, wherein the braking
motor is a step motor, whereby the motor incrementally turns in a
series of steps having a given angle.
18. A welding-type power source, comprising: a wire feeder,
includes a wire feed motor for moving the wire to the arc, disposed
to provide wire to an arc; a power supply disposed to provide power
to the arc; a braking wire feed motor, disposed to move the wire to
and away from the arc whereby movement of the wire is superimposed
onto the movement of the wire from the wire feed motor; a
controller, connected to the power supply, and including a braking
wire motor output connected to the braking wire feeder and,
including a wire feed motor output slaved to an average of the
braking motor output.
19. The welding-type power source of claim 18, including a buffer
disposed between the wire feed motor and the braking motor, wherein
the controller includes a buffer feedback module and the wire feed
motor output is further responsive to the buffer feedback
module.
20. (canceled)
21. A welding-type power source, comprising: a wire feeder includes
a wire feed motor for moving the wire to the arc, disposed to
provide wire to an arc; a power supply disposed to provide power to
the arc; a braking wire feed motor, disposed to move the wire to
and away from the arc whereby movement of the wire is superimposed
onto the movement from the wire feed motor; a buffer disposed
between the wire feed motor and the braking motor; and a
controller, connected to the power, supply, and including a braking
wire feeder control module connected to the braking wire feeder,
and having a buffer feedback input, and having and a wire feed
motor output responsive to the buffer feedback input and connected
to the wire feeder.
22. The welding-type power source of claim 21, wherein the braking
motor is a step motor, whereby the motor incrementally turns in a
series of steps having a given angle.
23. The welding-type power source of claim 22 wherein the
controller includes a step size output and the given angle is
varied in response to the step size output.
24-30. (canceled)
31. A method of providing welding-type power, comprising: feeding
wire to the arc; providing power to the arc; reversing the
direction of the wire while continuing to feed wire toward a
welding torch, at least once per process cycle for a plurality of
consecutive cycles; providing a wire feed motor for moving the wire
to the arc; providing a braking motor to superimpose movement of
the wire onto the movement from the wire feed motor; buffering wire
from the superimposition; and controlling a speed of the wire feed
motor output in response to the buffering.
32. The method of claim 31, further comprising controlling the
power in response to mean arc current.
33. The method of claim 31, further comprising detecting when the
arc has shorted and controlling the power and the direction of the
wire in response thereto.
34. The method of claim 33, further including: providing a wire
feed motor for moving the wire to the arc; providing a braking
motor that superimposes movement of the wire onto the movement from
the wire feed motor; and slaving the speed of the wire feed motor
to an average speed of the braking motor.
35. The method of claim 34, including storing wire from the
reversing and controlling the speed of a wire feed motor in
response to the storing.
36. (canceled)
37. The method of claim 31, further comprising reversing the
direction of the wire incrementally turns in a series of steps
having a given distance.
38. The method of claim 37, further comprising varying the given
distance in response to control parameters.
39-40. (canceled)
41. A method of providing welding-type power, comprising: feeding
wire to the arc; providing power to the arc; reversing the
direction of the wire; controlling the power in response to mean
arc current; providing a wire feed motor for moving the wire to the
arc; providing a braking motor that superimposes movement of the
wire onto the movement from the wire feed motor; and slaving the
speed of the wire feed motor to an average speed of the braking
motor.
42. The method of claim 41, further comprising detecting when the
arc has shorted and controlling the power and the direction of the
wire in response thereto.
43. (canceled)
44. The method of claim 42, including storing wire from the
reversing and controlling the speed of a wire feed motor in
response to the storing.
45. The method of claim 42, further comprising reversing the
direction of the wire incrementally turns in a series of steps
having a given distance.
46. A method of providing welding-type power, comprising: feeding
wire to the arc; providing power to the arc; reversing the
direction of the wire while continuing to feed wire toward a
welding torch; detecting when the arc has shorted and controlling
the power and the direction of the wire in response thereto;
providing a wire feed motor for moving the wire to the arc;
providing a braking motor to superimpose movement of the wire onto
the movement from the wire feed motor; buffering wire from the
superimposition; and controlling a speed of the wire feed motor
output in response to the buffering.
47. (canceled)
48. The method of claim 46, further comprising reversing the
direction of the wire incrementally turns in a series of steps
having a given distance.
49. The method of claim 48, further comprising varying the given
distance in response to control parameters.
50-51. (canceled)
52. A method of providing welding-type power, comprising: feeding
wire to the arc with a wire feed motor; providing power to the arc;
reversing the direction of the wire with a braking motor that
superimposes movement of the wire onto the movement from the wire
feed motor; and slaving the speed of the wire feed motor to an
average speed of the braking motor.
53. The method of claim 52, further comprising reversing the
direction of the wire incrementally turns in a series of steps
having a given distance.
54. The method of claim 53, further comprising varying the given
distance in response to control parameters.
55-56. (canceled)
57. A method of providing welding-type power, comprising: feeding
wire to the arc; providing power to the arc; reversing the
direction of the wire; buffering wire from the reversing; and
controlling a speed of the wire feed motor output in response to
the buffering.
58-59. (canceled)
60. A system for providing welding-type power, comprising: means
for feeding wire to the arc including a wire feed motor for moving
the wire to the arc; means for providing power to the arc; and
means for reversing the direction of the wire, including a braking
motor that superimposes movement of the wire onto the movement from
the wire feed motor, while continuing to feed wire toward a welding
torch at least once per process cycle for a plurality of
consecutive cycles, connected to the means for feeding; and means
for slaving the speed of the wire feed motor to an average speed of
the braking motor, connected to the wire feed motor.
61. The system of claim 60, further comprising means for
controlling the power in response to mean arc current, connected to
the means for providing.
62. The system of claim 61, further comprising means for detecting
when the arc has shorted and for controlling the power and the
direction of the wire in response thereto, connected to the means
for feeding.
63. (canceled)
64. The system of claim 60, including means for storing wire from
the reversing, connected to the means for feeding, and means for
controlling the speed of a wire feed motor in response to the
storing, connected to the means for providing.
65. The system of claim 60, further comprising: means for buffering
wire from the reversing, connected to the means for feeding; and
means for controlling a speed of the wire feed motor output in
response to the means for buffering.
66. The system of claim 60, further comprising means for varying a
distance of reversal in response to control parameters, connected
to the means for feeding.
67-68. (canceled)
69. A system for providing welding-type power, comprising: means
for feeding wire to the arc including a wire feed motor and a
braking motor; means for providing power to the arc; means for
reversing the direction of the wire, disposed adjacent the wire;
means for controlling the power in response to mean arc current,
connected to the means for providing; and means for slaving the
speed of the wire feed motor to an average speed of the braking
motor, connected to the means for feeding.
70. The system of claim 69, further comprising means for detecting
when the arc has shorted, connected to the wire, and means for
controlling at least one of the power and the direction of the wire
in response thereto, connected to at least one of the means for
feeding and the means for providing.
71. (canceled)
72. The system of claim 70, including means for storing wire from
the reversing, connected to the means for feeding, and means for
controlling the speed of a wire feed motor in response to the
storing, connected to the means for feeding.
73. A system for providing welding-type power, comprising: means
for feeding wire to the arc; means for providing power to the arc;
means for reversing the direction of the wire while continuing to
feed wire toward a welding torch, connected to the wire; means for
detecting when the arc has shorted and controlling at least one of
the power and the direction of the wire in response thereto,
connected to at least one of the means for feeding and the means
for providing; and means for buffering wire from the reversing,
connected to the means for feeding, and means for controlling a
speed of the wire feed motor output in response to the buffering,
connected to the means for providing.
74. (canceled)
75. The system of claim 73, wherein the means for reversing
includes means for reversing the direction of the wire
incrementally turns in a series of steps having a given distance,
connected to the wire.
76. The system of claim 75, further means for comprising varying
the given distance in response to control parameters, connected to
the means for reversing.
77-78. (canceled)
79. A system for providing welding-type power, comprising: means
for feeding wire to the arc; means for providing power to the arc;
means for reversing the direction of the wire with a braking motor
that superimposes movement of the wire onto the movement from the
means for feeding, adjacent the wire; and means for slaving the
speed of the wire feed motor to an average speed of the braking
motor, connected to the means for feeding.
80. The system of claim 79, further comprising means for reversing
the direction of the wire incrementally turns in a series of steps
having a given distance, connected to the means for reversing.
81. The system of claim 80, further comprising means for varying
the given distance in response to control parameters, connected to
the means for reversing.
82-83. (canceled)
84. A system for providing welding-type power, comprising: means
for feeding wire to the arc; means for providing power to the arc;
means for reversing the direction of the wire, disposed adjacent
the wire; means for buffering wire from the reversing, disposed
between the means for feeding and the means for reversing; and
means for controlling a speed of the means for feeding in response
to the buffering, connected to the means for feeding.
85-86. (canceled)
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to the art of
welding. More specifically, it relates to welding using a short
circuit process.
BACKGROUND OF THE INVENTION
[0002] There are many different arc welding processes used for
numerous welding applications. While different processes share some
characteristics, such as using an electric arc and/or current flow
to provide the heat for the weld, different processes have
characteristics that render them desirable for particular
applications.
[0003] MIG welding is a widely used process that gives high heat
input into the wire electrode and the workpiece, and thus can give
high deposition rates. However, the process can be unstable and
control of the arc length can be difficult. The MIG process is
often performed as a short circuit welding.
[0004] Another known welding process is called controlled short
circuit welding, or short circuit welding. Short circuit welding is
often performed as a MIG process. Generally, short circuit welding
includes a short circuit state, wherein the welding wire is
touching the weld pool thus creating a short circuit, and an arc
state, wherein an arc is formed between the welding wire and the
weld pool. During the arc state the wire melts, and during the
short circuit state the molten metal is transferred from the end of
the wire to the weld puddle.
[0005] Disadvantages of short circuit welding relate to the
transitions between states, and instability of the process.
Transition from the short circuit state to the arc state was
typically caused by providing sufficient current to "pinch" off a
droplet. The pinching off at high current can result in a violent
disintegration of the molten metal bridge producing excessive weld
spatter. Instability also results from the weld pool being pushed
away.
[0006] Many attempts in the prior art were made to create a stable
short circuit welding power supply, such as those shown in U.S.
Pat. Nos. 4,717,807, 4,835,360, 4,866,247, 4,897,523, 4,954,691,
4,972,064, 5,001,326, 5,003,154, 5,148,001, 5,742,029, 5,961,863,
6,051,810 and 6,160,241. These patents generally disclose
complicated control schemes that fail to control the process to
provide a stable and effective weld. They include control schemes
that try to control the deposition of material and/or predict or
cause a transition to the subsequent state based on the total
energy put into the weld, the length of the stick out, total watts,
time of the preceding state, etc.
[0007] These schemes share a common failure: they attempt to
control both the energy of the weld and the transition between
states using output current or power. This necessarily entails a
sacrificing of one control goal (either energy to the weld or state
transition) for the sake of the other. The net result is that the
control schemes do not perform well at either controlling the
energy into the weld or controlling the transition.
[0008] Another short circuit welding control system is disclosed in
U.S. Pat. No. 6,326,591. This system adequately controls the energy
into the weld, but it does not provide independent control of the
transitions between states.
[0009] The present inventors have published descriptions of a
controlled short circuit welding process where mechanical movement
of the wire (advancing and retracting) is used to control the
transition between welding states. The short circuit state is
entered by advancing the wire until the wire touches the weld pool.
The arc state is entered by retracting the wire until the wire does
not touch the weld pool, and an arc forms. This system allows a
typical output control to be used to control the energy delivered
to the weld. By separating control of the transitions from control
of energy, the system allows for better control of each.
[0010] A controlled short circuit welding system requires the
capability of advancing and retracting the wire. The inventors have
disclosed in the literature the use of a stepper motor to control
the wire movement. A stepper motor adequately provides for short
term advancing and retracting of the wire.
[0011] However, a stepper motor does not necessarily provide
adequate feeding of the wire over the long term. Accordingly, a
system that provides for advancing and retracting of the wire, and
long term feeding of the wire, is desirable.
[0012] One problem with controlled short circuit welding arises
when the wire is retracted. The wire from the source is feeding
toward the weld, and has momentum in that direction. The retracting
motor moves the wire in the opposite direction. With nothing to
compensate for the opposing forces, the wire might not feed in a
smooth and efficient manner. Accordingly, a controlled short
circuit welder that compensates for the reversal of the wire is
desirable.
[0013] Another problem with controlled short circuit welding is
that the prior art has not fully taken advantage of the process
control made possible by the mechanical control of the state
transitions. Thus, a controlled short circuit welder that provides
for electrical control of the arc for the purpose of controlling
heat into the weld, and not for causing transitions from one state
to another, is desirable.
[0014] The prior art has not adequately addressed the needs of
short circuit welding at lower currents with thicker wires. The
difficult to implement control schemes, in particular, make it
difficult to weld with thicker wire, such as 2.4 mm diameter wire,
e.g., at low currents, such as less than 100 amps. Accordingly, a
controlled short circuit welding process that may be used at low
currents relative to the wire diameter is desirable.
SUMMARY OF THE PRESENT INVENTION
[0015] According to a first aspect of the invention a welding-type
power source, or a method of welding, includes a wire feeder that
provides wire to an arc and a power supply that provides power to
the arc. A reversible wire feed motor moves the wire to and away
from the arc. A controller controls the reversible wire feeder
motor to reverse at least once per process cycle, and/or controls
the power source to provide a desired mean arc current, and/or
controls the reversible motor in response to short detection and
short clearing, and/or controls the reversal frequency in response
to pool oscillation frequency.
[0016] According to a second aspect of the invention a welding
system, or a method of welding, includes a wire feeder having a
wire feed motor for providing wire to the arc and a power supply
that provides power to the arc. A reversible wire feed motor moves
the wire to and away from the arc whereby movement of the wire is
superimposed onto the movement of the wire from the wire feed
motor. A controller controls the power, the reversible wire motor,
and the wire feed motor output is slaved to an average of the
reversible motor output.
[0017] The controller includes various control modules, such as a
mean arc current control module, and/or a short detection feedback
circuit, in alternative embodiments.
[0018] A wire feed motor that moves the wire to the arc is included
in one embodiment. The reversible motor superimposes movement of
the wire onto the movement from the wire feed motor, and/or
controls the wire feed motor to feed wire at an average speed of
the reversible motor.
[0019] A buffer is between the wire feed motor and the reversible
motor, and the controller receives feedback from the buffer, and
controls the wire feed motor in response thereto in another
embodiment.
[0020] The reversible motor is a stepper motor that incrementally
turns in a series of steps having a given angle in another
embodiment. The controller includes a step size output and the
given angle is varied in response to the step size output.
[0021] The controller includes a frequency module is responsive to
at least one control parameter, such as pool oscillation frequency
in one alternative embodiment.
[0022] Other principal features and advantages of the invention
will become apparent to those skilled in the art upon review of the
following drawings, the detailed description and the appended
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a diagram of a welding system, in accordance with
the present invention;
[0024] FIG. 2 is a torch with a buffer and reversible motors in
accordance with the present invention;
[0025] FIG. 3 is a cross-sectional view of the torch of FIG. 2;
[0026] FIG. 4 is a detailed cross-sectional view of a buffer in
accordance with the present invention;
[0027] FIG. 5 is a cross-sectional view of a weld cable used as
part of a buffer in accordance with the present invention; and
[0028] FIG. 6 is a wave form of a process cycle in accordance with
the preferred embodiment.
[0029] Before explaining at least one embodiment of the invention
in detail it is to be understood that the invention is not limited
in its application to the details of construction and the
arrangement of the components set forth in the following
description or illustrated in the drawings. The invention is
capable of other embodiments or of being practiced or carried out
in various ways. Also, it is to be understood that the phraseology
and terminology employed herein is for the purpose of description
and should not be regarded as limiting. Like reference numerals are
used to indicate like components.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0030] While the present invention will be illustrated with
reference to a particular welding system using particular
components, it should be understood at the outset that the
invention may also be implemented with other systems, components,
and modules, and be used in other environments.
[0031] Generally, the present invention is a method and apparatus
for controlled short circuit welding that includes mechanical
control of transitions between the arc and short circuit states. In
one embodiment the process includes a pulse mode. Control of energy
to the weld is effected using the output current or voltage
magnitude, wave shape, time, etc. Thus, the transitions are caused
to occur, and current can be coordinated with, the transitions to
reduce spatter, instability, or other undesirable features, by, for
example, changing the current as the transition occurs, or in
anticipation of the transition.
[0032] Mechanical control of the states is performed by advancing
and retracting the wire at the arc. An advance followed by a
retraction defines one process cycle. (Process cycle, as used
herein, includes one cycle of the states of the process such as an
arc state followed by a short circuit state, or an arc state,
followed by a short circuit state, followed by a pulse state, etc.)
The advancing and retracting are, in the preferred embodiment,
accomplished using a pair of motors disposed on either side of the
wire, opposite one another and near (or mounted on) the torch. The
motors are, in various embodiments stepper motors, servo motors,
planetary drive motors, zero backlash motors, gearless motors, or
replaced with a linear actuator. The pair is disposed one after the
other in one embodiment.
[0033] Stepper motors are used in the preferred embodiment, and the
number, and angle or size of the step is controlled to control the
length of wire advanced or retracted.
[0034] The preferred embodiment includes a wire feed motor mounted
near the source of wire, such as a reel of wire, that drives the
wire to the torch (although other embodiments omit this motor). As
the reversible motors retract the wire (and the wire feed motor
continues to feed the wire) a buffer is provided to account for the
increase in wire between the wire feed motor and the reversible
motors. Similarly, when the reversible motors advance the wire,
wire is withdrawn from the buffer. The reversible motors move the
end of the wire in addition to the movement from the wire feed
motor, or they superimpose motion onto motion imposed by the wire
feed motor. The speed of the wire feed motor is slaved to the
average speed of the reversible motors, so that, on average, they
both drive the same length of wire, in the preferred
embodiment.
[0035] The buffer may be anything that stores and returns the extra
wire, or provides an increased wire path length between the source
and the torch. The buffer of the preferred embodiment includes a
wire liner about the wire for at least a portion of the distance
from the source to the torch. The liner is disposed in a tube that
is wider, and the liner can bend and flex within the tube, thus
increasing the length of wire/in a given length of tube. The tube
is mounted to a hollow shaft, and the wire passes through the
shaft. The shaft is fixed in one position. Thus, as the wire is
retracted, the wire moves relative to the tube and shaft (or the
tube and shaft may be said to move relative to the wire). The shaft
could be mounted to slide along the axis of the wire, and thus move
relative to the tip of the torch, thereby increasing the length of
the wire path between the tip (arc end) of the torch and the wire
source end of the torch.
[0036] Alternatively, the liner may be mounted to the shaft, and
the wire moves relative to the liner. The liner is compressible,
such as a coil spring, so that as the wire retracts, the spring
compresses, in the preferred embodiment. Sensors may be provided
that sense the amount of wire in the buffer, or the tension of the
wire, and the process controlled (average wire feed speed e.g.) may
be controlled in response thereto.
[0037] A controller is provided that causes the motors to reverse
at least once per process cycle in the preferred embodiment, and
controls the current output based on mean arc current (average
current during the arc state only, or a function thereof), power,
energy, voltage, or other welding output parameters. Feedback may
include one or more of short detection, buffer feedback, tension
feedback, pool oscillation, in addition to traditional welding
parameters. Alternatives include reversing less frequently than
once per cycle. One alternative provides for repeated reversals
during the weld (i.e., not merely at the conclusion of the weld),
but not once per cycle.
[0038] For example, the braking at the end of the arc cycle can
feed forces between wire and droplet, which may disrupt the liquid
bridge without retracting action. This is particularly present with
lower wire diameters and higher short circuiting frequencies. The
droplet has the speed of the wire before braking. This kinetic
energy can be enough for disrupting the liquid path. In this case,
no retracting is needed.
[0039] The control may include controlling heat, penetration and/or
bead formation by controlling the advancement of the wire into the
weld pool. The relative time in arc state and short state (arc
balance) may be set by the user (as may be the time in the pulse
state if it is used). Control of parameters such as polarity
(balance), gas mixtures etc. may be done in coordination with the
relative arc/short times (or other parameters).
[0040] Referring now to FIG. 1, a welding system 100 includes, in
accordance with the preferred embodiment, a power supply 102, a
wire feeder 104, a controller 106 and a torch 108, and a supply
line 112 which feeds welding current, gas, water, control, and
current for motors to torch 108, that cooperate to provide welding
current on weld cables 105 and 107 to a workpiece 110. Power supply
102, wire feeder 104 and controller 106 may be commercially
available welding system components, such as a Miller Invision
456.RTM. power supply, and a modified Miller XR.RTM. wire feeder.
Power supply, as used herein, includes any device capable of
supplying welding, plasma cutting, and/or induction heating power
including resonant power supplies, quasi-resonant power supplies,
etc., as well as control circuitry and other ancillary circuitry
associated therewith. Power source, or source of power, as used
herein, includes the power circuitry such as rectifiers, switches,
transformers, SCRs, etc. that process and provide the output power.
Wire feeder, as used herein, includes the motor or mechanism that
drives the wire, the mounting for the wire, and controls related
thereto, and associated hardware and software. It can include a
motor near the source of wire that pushes the wire to the weld,
and/or motor(s) near the torch that pulls the wire into the line
and to the contact tip, or pulls the wire back from the contact
tip. Wire path as used herein, includes the path the wire takes
from the wire source to the torch or power supply, and may include
through a liner, a buffer, etc.
[0041] Controller 106 is part of wire feeder 104 and power supply
102 in this embodiment. Controller 106 also includes control
modules adapted for the present invention, such as a reversible
wire feeder control module to control the reversible motors, a mean
arc current module, and the control module for the mechanical
control of the arc states. Controller, as used herein, includes
digital and analog circuitry, discrete or integrated circuitry,
microprocessors, DSPs, etc., and software, hardware and firmware,
located on one or more boards, used to control a device such as a
power supply and/or wire feeder. Control module, as used herein,
may be digital or analog, and includes hardware or software, that
performs a specified control function. For example, a mean arc
current control module controls the output to provide a desired
mean arc current.
[0042] FIG. 2 shows torch 108 in more detail. Torch 108 includes,
in addition to the features of prior art torches, a pair of motor
housings 203 and 205 have motors disposed within to drive the wire
to or from the weld, and a buffer 201 to take up wire 209 when it
is retracted, and provide wire 209 when it is advanced. Buffer, as
used herein, includes components used to take up the wire when the
wire direction is reversed and provide wire when the wire is
advanced. The end of the wire at the arc is shown as 207. The motor
housings and buffer are adjacent to the torch in the preferred
embodiment, and near the torch in other embodiments. Adjacent the
torch, as used herein, includes abutting, touching or part of the
torch, directly or through a housing. Near the torch, as used
herein, includes much closer to the torch than the source of wire,
such as more than 75% of the way from the source to the torch. One
embodiment provides that a handheld torch includes a small spool of
wire mounted on the torch.
[0043] FIG. 3 is a cross-sectional view of the torch of FIG. 2,
taken along lines A-A. A pair of motors 301 and 302 are preferably
stepper motors (although they may be other motors) and drive the
wire and are disposed adjacent to the wire, and directly opposite
one another, on opposite sides of the wire, thereby substantially
equalizing forces on the wire. In alternative embodiments they are
disposed one following the other, or on the same side of the wire.
Directly opposite one another, as used herein, includes at
substantially the same position along a wire path. Disposed
adjacent the wire, as used herein, includes being close enough to
the wire to push or pull the wire. Drive the wire, as used herein,
includes one or both of moving the wire toward the torch and moving
the wire away from the torch.
[0044] Buffer 201 may also be seen on FIG. 3, and is shown in more
detail on FIG. 4, and includes a shaft 401 mounted on a support
403. Shaft 401 has a hollow axis, through which wire 209 passes.
Weld cable 105 (FIGS. 1 and 5) is comprised of an outer tube 501
and a liner 503, with wire 209 disposed therein. The outer diameter
of line 503 is substantially smaller than the inner diameter of
tube 501, to allow for wire length to be taken up or stored by
liner 503 flexing within tube 501. Liner 503 is preferably a coil
spring that allows for compression and expansion to further buffer
the wire. Storing a length of wire, as used herein, includes taking
up wire when the wire direction is reversed. Substantially more
than an outer diameter of the liner, as used herein includes enough
room to move and flex. Wire liner, as used herein, includes a tube
in which the wire can easily move. Tube 501 is mounted to shaft 401
so that wire 209 moves with respect to shaft 401.
[0045] A sensor can be included that senses the amount of wire
taken up by buffer 201. Examples of such sensors include a wheel
with an encoder that is turned as the wire moves past it, or a
linear transformer, with the liner being comprised of a ferrite or
magnetic material. The controller includes a buffer feedback input
that receives the feedback, and provides a wire feed motor output
that is responsive to the buffer feedback. Tension in the wire can
also be sensed and used to control the process.
[0046] Control of the process from an electrical standpoint is
easier since process control is performed using mechanical control
of the wire position. Therefore, the welding current becomes an
independent process parameter, totally opposite to the conventional
MIG process.
[0047] One desirable control scheme uses mean arc current (average
current during the arc state, or a function thereof) as the control
variable. This allows better control of the melting and heat to the
weld, and reduces spatter and instability, compared to prior art
control schemes. It is possible to use mean arc current to control
the heat, since arc current is not used to cause the transition
from arc to short (or the opposite). The control of the states can
be coordinated with the current control. For example, if a state
transition is to occur at a time T1, the current transition can
occur shortly before that, so as to avoid disrupting the weld pool.
Another control feature is to allow the user to set relative arc
and short time, or balance between EP and EN.
[0048] One desirable arc waveform is shown in FIG. 6, and includes
an arc current waveform with three segments--an initial high
current segment, an intermediate current segment, and a low current
segment. The low current segment is entered into prior to the short
forming, thereby enhancing a smooth transition to the short circuit
state.
[0049] Because the welding current becomes an independent process
parameter, the current can be set to the value, which directs the
process into the wanted situation by physical determined behavior.
For a low spatter material transfer, the forces onto the liquid
have to be low, when the cross section of the electrical conductor
is low. Therefore, the currents have to be low during those phases.
During the middle part of the short circuit state, where larger
cross section of the electrical conductor is present, high forces
can be used to move liquids. Also, high currents during the middle
part of the short circuit state are possible. During the arc phase,
the current can be used for movement of the liquid and determining
the melting rate.
[0050] The present invention may be used with known control
schemes, but implement them in a more desirable fashion by
eliminating the need for current levels to cause transitions. For
example, schemes using either arc length or stick-out as a control
variable can be implemented easily because the stepper motors allow
stick-out to be measured precisely. Because the transitions are
caused mechanically, the arc length may be redetermined each
process cycle.
[0051] The present invention may be implemented with a variety of
processes, including but not limited to electrode positive,
electrode negative, alternating polarity, ac mig, mig brazing, hard
facing, and welding with thick wire at low currents. For example,
welding on a 2.4 mm wire may be performed at 100 amps, or even 35
or fewer amps with the present invention. Prior art systems
required more current on thick wire to cause the short to clear and
to enter the arc state. The present invention doesn't rely on
current to clear the short, so thick wire and low current may be
used.
[0052] The control preferably ties the speed of the wire feed motor
to the average speed of the stepper motors, so that the wire feed
speed follows the process speed. Averaging speed over 20-30 process
cycles (about 500 msec.) provides for effective control.
[0053] Pool oscillation frequency can be found by monitoring the
distance the wire travels until a short is created, or an arc is
created. One control scheme provides that the state transitions are
timed to coincide with the natural frequency of pool oscillation.
The controller includes a frequency module and a pool oscillation
feedback circuit that effect this control scheme. A short detection
feedback circuit may be used as part of the control loop.
[0054] Numerous modifications may be made to the present invention
which still fall within the intended scope hereof. Thus, it should
be apparent that there has been provided in accordance with the
present invention a method and apparatus for controlled short
circuit welding that fully satisfies the objectives and advantages
set forth above. Although the invention has been described in
conjunction with specific embodiments thereof, it is evident that
many alternatives, modifications and variations will be apparent to
those skilled in the art. Accordingly, it is intended to embrace
all such alternatives, modifications and variations that fall
within the spirit and broad scope of the claims.
* * * * *