U.S. patent application number 09/749766 was filed with the patent office on 2001-08-23 for laser hardened steel cutting rule.
Invention is credited to Christmas, Darryl L., Goossen, James C..
Application Number | 20010015348 09/749766 |
Document ID | / |
Family ID | 23379161 |
Filed Date | 2001-08-23 |
United States Patent
Application |
20010015348 |
Kind Code |
A1 |
Christmas, Darryl L. ; et
al. |
August 23, 2001 |
Laser hardened steel cutting rule
Abstract
The invention relates to surface hardening of steel workpieces
using laser beams and more particularly to laser hardening steel
cutting rules. The method comprises applying a first laser beam of
a first intensity and focused to a first focal point to a selected
surface area of the metal workpart and subsequently applying a
second laser beam having a second intensity and focused to a second
focal point to the selected surface area. Application of the first
laser beam heat treats the selected surface area to a predetermined
depth, thereby increasing the surface hardness. Application of the
second laser beam relieves internal stresses produced by the heat
treating while retaining the increased hardness.
Inventors: |
Christmas, Darryl L.;
(Woodstock, IL) ; Goossen, James C.; (Glenwood
City, WI) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
US
|
Family ID: |
23379161 |
Appl. No.: |
09/749766 |
Filed: |
December 28, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09749766 |
Dec 28, 2000 |
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09350999 |
Jul 12, 1999 |
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6218642 |
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Current U.S.
Class: |
219/121.85 |
Current CPC
Class: |
B23K 2103/04 20180801;
C21D 1/09 20130101; C21D 9/24 20130101 |
Class at
Publication: |
219/121.85 |
International
Class: |
B23K 026/00 |
Claims
What is claimed is:
1. A method of surface hardening a metal workpiece, comprising the
steps of: a first step of applying a first laser beam having a
first intensity and focused to a first focal point to a selected
surface area of said metal workpiece; and a second step of applying
a second laser beam having a second intensity and focused to a
second focal point to said selected surface area, wherein, in said
first step of applying said first laser beam to said selected
surface area, said selected surface area is heat treated to a
predetermined depth resulting in an increased hardness of said
selected surface area, and wherein, in said second step of applying
said second laser beam to said selected surface area, said selected
surface area is stress relieved of internal stresses produced by
said heat treating.
2. A method according to claim 1, wherein said first intensity of
said laser beam is greater than said second intensity of said laser
beam.
3. A method according to claim 2, wherein said first intensity of
said laser beam is about 500-550 watts and said second intensity of
said laser beam is about 80 watts less than said first intensity of
said laser beam.
4. A method according to claim 1, wherein said first focal point
has a distance less than said second focal point.
5. A method according to claim 4, wherein said first focal point
distance is about 0.010 inch and said second focal point is about
0.170 inch.
6. A method according to claim 1, wherein said metal workpiece is
passed through said laser beam having said first intensity during
said first step at a first predetermined feed rate and said metal
workpiece is passed through said laser beam having said second
intensity during said second step at a second predetermined feed
rate.
7. A method according to claim 6, wherein said first predetermined
feed rate is slower than said second predetermined feed rate.
8. A method according to claim 7, wherein said first predetermined
feed rate is about 125 feet per minute and said second
predetermined feed rate is about 155 feet per minute.
9. A method according to claim 1, wherein said laser beam having
said first intensity and said laser beam having said second
intensity are a continuous wave CO.sub.2 laser.
10. A method according to claim 1, wherein said laser beam having
said first intensity and said laser beam having said second
intensity are a YAG laser.
11. A method according to claim 1, wherein said heat treatment of
said selected surface area by said laser beam having said first
intensity results in a microstructure substantially of untempered
martensite, and wherein said selected surface area microstructure
remains substantially of untempered martensite after said stress
relief of said selected surface area by said laser beam having said
second intensity.
12. A method according to claim 1, wherein said increased hardness
of said selected surface area is at least 60 R.sub.c.
13. A method of surface hardening a steel cutting rule, comprising
the steps of: a first step of applying a first laser beam having a
first intensity and focused to a first focal point to a selected
surface area of said steel cutting rule; and a second step of
applying a second laser beam having a second intensity and focused
to a second focal point to said selected surface area, wherein, in
said first step of applying said first laser beam to said selected
surface area, said selected surface area is heat treated to a
predetermined depth resulting in an increased hardness of said
selected surface area, and wherein, in said second step of applying
said second laser beam to said selected surface area, said selected
surface area is stress relieved of internal stresses produced by
said heat treating but said increased hardness of said selected
surface area produced by said heat treating is retained.
14. A method according to claim 13, wherein said laser beam first
intensity is greater than said laser beam second intensity.
15. A method according to claim 14, wherein said laser beam first
intensity is about 500-550 watts and said laser beam second
intensity is about 80 watts less than said first intensity.
16. A method according to claim 13, wherein said laser beam first
focal point has a distance less than said laser beam second focal
point.
17. A method according to claim 16, wherein said laser beam first
focal point distance is about 0.010 inch and said laser beam second
focal point is about 0.170 inch.
18. A method according to claim 13, wherein said steel cutting rule
is passed through said first laser beam during said first step at a
first predetermined feed rate and said steel cutting rule is passed
through said second laser beam during said second step at a second
predetermined feed rate.
19. A method according to claim 18, wherein said first
predetermined feed rate is slower than said second predetermined
feed rate.
20. A method according to claim 19, wherein said first
predetermined feed rate is about 125 feet per minute and said
second predetermined feed rate is about 155 feet per minute.
21. A method according to claim 13, wherein said first laser beam
and said second laser beam are a continuous wave CO.sub.2
laser.
22. A method according to claim 13, wherein said first laser beam
and said second laser beam are a YAG laser.
23. A method according to claim 13, wherein said heat treatment of
said selected surface area by said first laser beam results in a
microstructure substantially of untempered martensite, and wherein
said selected surface area microstructure remains substantially of
untempered martensite after said stress relief of said selected
surface area by said second laser beam.
24. A method according to claim 13, wherein said increased hardness
of said selected surface area is at least 60 R.sub.c.
25. A method of surface hardening a steel cutting rule, comprising
the steps of: cleaning said steel cutting rule; applying a laser
beam absorbent substance to a selected surface area of said steel
cutting rule; drying said laser beam absorbent substance; applying
a first laser beam having a first intensity and focused to a first
focal point to said selected surface area of said steel cutting
rule; applying a second laser beam having a second intensity and
focused to a second focal point to said selected surface area; and
applying a corrosion inhibiting substance to said steel cutting
rule, wherein, in said step of applying said first laser beam to
said selected surface area, said selected surface area is heat
treated to a predetermined depth resulting in an increased hardness
of said selected surface area, and wherein, in said step of
applying said second laser beam to said selected surface area, said
selected surface area is stress relieved of internal stresses
produced by said heat treating but said increased hardness of said
selected surface area produced by said heat treating is
retained.
26. A hardened steel cutting rule obtained by the process
comprising the steps of: a first step of applying a first laser
beam having a first intensity and focused to a first focal point to
a selected surface area of a steel cutting rule; and a second step
of applying a second laser beam having a second intensity and
focused to a second focal point to said selected surface area.
27. A hardened steel cutting rule obtained by the process
comprising the steps of: applying a laser beam absorbent substance
to a selected surface area of a steel cutting rule; applying a
first laser beam having a first intensity and focused to a first
focal point to said selected surface area of said steel cutting
rule; and applying a second laser beam having a second intensity
and focused to a second focal point to said selected surface area.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to surface hardening of steel
workpieces. In particular, the present invention is a method of
hardening selected surface areas of steel cutting instruments, such
as cutting rules or knife blades, using laser beams to perform both
surface hardening and stress relief of the workpiece.
[0003] 2. Description of the Related Art
[0004] Typically, hardening of metals has been performed by
carburizing, induction heating and, more recently, laser
heat-treating. In conventional gas carburizing methods, a steel
workpiece is heated in an atmosphere of a selected gas. Materials
from the gas dissolve in the surface of the workpart becoming part
of the crystalline structure. For example, a steel workpart is
heated in an atmosphere of CO.sub.2 causing minute amounts of
carbon to be liberated on the surface of the hot metal and to
dissolve in the metal. A subsequent heat treatment to form a
martensitic microstructure on the surface produces a hard surface.
A martensitic microstructure is formed by heating the steel above
the critical temperature--the temperature at which the steel
changes phases from a ferrite or cementite microstructure to an
austenite microstructure--and rapidly cooling, or quenching, the
steel to form a new microstructure phase, martensite. Martensite is
the hardest of the steel microstructure phases.
[0005] However, the rapid cooling required to produce martensite
also induces internal stresses within the microstructure that make
the martensite brittle. Therefore, a subsequent tempering process
is required to relieve these internal stresses. Tempering typically
entails heating the steel to a temperature below the critical
temperature for several hours. Heating the steel below the critical
temperature avoids inducing a microstructure phase change back to
austenite, but also reduces some of the hardness of the martensite.
The hardness reduction is the result of some of the carbon
particles trapped in the martensite being released. Thus, the
microstructure before tempering appears as untempered martensite
and after tempering the microstructure appears as tempered
martensite.
[0006] Some drawbacks are present in surface hardening by
carburizing. One such drawback is that it is difficult to surface
harden only selected areas of the workpart. In order to only harden
selected areas, those surfaces not to be hardened must be masked.
The masking prevents those surfaces from being subjected to the gas
atmosphere, thereby preventing hardening of the masked surface. The
masking process is often difficult, time-consuming and unreliable
due to the intense heat of the carburizing process. Another
drawback of carburizing is controlling the depth of the hardened
surface. Carburizing typically requires post-processing machining,
such as grinding, in order to obtain the desired hardened case
depth. Carburizing also requires an additional tempering process
after the quenching process in order to stress relieve the part.
Such a stress relief process typically entails placing the
workpiece in an oven, often for a period of several hours. This
significantly increases both the cost and the amount of time to
process the workpiece.
[0007] Another known method of surface hardening steel workparts is
induction heating. In induction heating, the steel workpart is
placed within an induction coil. An electrical current is passed
through the induction coil which induces secondary currents to flow
along the surface of the workpart. The secondary current flow
causes the surface of the workpart to be preferentially heated. As
the electrical current in the induction coil is increased, the
surface of the workpart is heated above the critical temperature,
thus causing a microstructure phase change to austenite. When the
workpart is rapidly cooled, or quenched, a martensitic
microstructure is formed. Thus, when only a shallow surface of the
part is heated above the critical temperature and is rapidly
quenched, only the shallow surface is transformed into a
martensitic microstructure while the remainder of the part remains
unchanged. This shallow surface of martensite forms the hard
surface.
[0008] However, the rapid cooling induces internal stresses that
cause the steel part to become brittle. Therefore, a subsequent
tempering process is required to relieve the internal stresses.
[0009] Induction heating has some of the same drawbacks as
carburizing. Namely, it is difficult to harden only selected
surface areas and the steel workpart requires a post-hardening
tempering process that is costly and time-consuming.
[0010] Additionally, shallow hardened case-depths are difficult to
achieve with induction hardening. Typically, the case depth is
controlled during induction hardening by producing a higher
frequency current in the induction coil. However, common induction
heating machines present limitations on the highest frequency
available. Common induction heating machines have a frequency limit
of about 1 MHz. However, if a case depth of 0.004-0.006 was
desired, an induction machine frequency of approximately 10 MHz
would be required. Such a machine is costly and commonly only
available in Europe.
[0011] Induction heating has been the most common method of
producing steel cutting rules. Steel cutting rules produced by
induction heating generally provide good bendability properties,
thereby allowing the rules to be formed into a number of shapes.
However, induction heated rules generally have low durability
properties, thereby requiring frequent replacement. Additionally,
induction heated steel cutting rules require air or liquid
quenching during the heat-treating process which causes thin rules
to warp and further requires tempering to relieve internal
stresses. The tempering process typically lowers the surface
hardness previously obtained during the heat treating step.
Therefore, common induction hardened rules are typically hardened
to only about 55 R.sub.c.
[0012] Another known method of surface hardening is laser
heat-treatment. Various types of lasers are available for heat
treating workpieces, including continuous wave CO.sub.2 lasers.
Laser heat treatment using a CO.sub.2 laser typically entails
applying an absorbent substance, such as black oxide or phosphate
coatings, to the surface area of the part to be heated. This
coating reduces reflection of the laser beam and focuses the energy
of the laser beam to the area to be hardened. The laser beam is
then focused, via a lens or the like, which generates an intense
energy flux that rapidly heats the surface.
[0013] One distinct advantage of laser heat treatment is that the
laser beam may be controlled to heat the surface of the metal piece
above the critical temperature to a depth of only a few thousandths
of an inch or less. Controlling the depth of the heating to this
shallow level allows for self quenching. That is, no liquid or air
quenching is required. Self-quenching is accomplished by conduction
due to the mass and temperature disparity between the portion of
the workpart not heated by the beam and the small depth of the
surface heated above the critical temperature by the beam. The heat
on the surface is quickly transferred to the unheated portion
thereby quenching the heated surface. However, the self-quenching
process has been taught to be undesirable for thin parts such as
knife blades and therefore air or liquid quenching has been
particularly advisable. Air or liquid quenching is required due to
the insufficient mass of the part to facilitate the conduction. The
addition of such air or liquid quenching increases both the cost
and the processing time.
[0014] One such method of laser-treating steel workparts is
disclosed in U.S. Pat. No. 4,304,978. This patent teaches laser
heat treating a flat part, such as a knife or blade, by focusing a
laser beam perpendicular to the major flat surface of the part
using a cylindrical lens. The width of the beam is adjusted
according to the desired width of the part to be heated. The part
is then moved through the laser or the laser may be moved along the
part to heat the surface. U.S. Pat. No. 4,304,978 teaches that thin
parts, such as a knife blade, requires gas quenching to prevent
melting of the part. Therefore, one shortcoming of U.S. Pat. No.
4,304,978 is that the laser treated part, such as a knife blade, is
not self quenching.
[0015] Therefore, it is desirable to provide a method of hardening
a steel cutting rule or knife blade so as to obtain equivalent or
superior ductility properties as common induction heated rules, but
with superior wear resistance. It is also desirable that the method
provide for self quenching of the cutting rule or knife blade to
reduce processing time and cost.
[0016] Further, it is desirable to provide a method of stress
relieving the heat treated cutting rule that reduces the processing
time and cost without weakening the metal part.
SUMMARY OF THE INVENTION
[0017] The present invention addresses the foregoing shortcomings
of conventional steel hardening techniques by providing a method of
surface hardening metal workparts while maintaining the untempered
martensitic microstructure and relieving internal stresses, thereby
removing brittleness usually characterized with untempered
martensite but maintaining the hardness. Additionally, the present
invention provides self-quenching of thin workparts, such as
cutting rules or knife blades. The present invention accomplishes
the above while also producing hardened cutting rules with
comparable ductility properties to that of current cutting rules,
but with superior durability properties.
[0018] The present invention accomplishes the foregoing by
providing a process of surface hardening metal workparts by heat
treating and stress relieving the parts using laser beams. The
process entails first heat treating the parts using a
narrowly-focused laser beam and subsequently stress relieving the
parts using a laser beam of a lower intensity.
[0019] The heat treating process is controlled by adjusting the
laser beam intensity in order to obtain a desired case depth,
preferably a shallow case depth. The process does not require the
parts to be air or liquid quenched since the process results in
self-quenching of the parts.
[0020] Subsequent to the heat treating process a stress relief
process is performed. The stress relief process consists of
subjecting the part to the laser beam a second time, usually at a
lower intensity than that used in the heat treating process. The
stress relief process is controlled so as to only perform stress
relief and not to temper the microstructure of the parts. The
resultant microstructure after stress relief appears as untempered
martensite but without the brittleness usually accompanying
untempered martensite.
[0021] In one aspect of the invention, metal workparts are surface
hardened using laser beams to perform both heat treatment and
stress relief of the part. Prior to heat treating, a laser beam is
configured to obtain the desired hardness results. After
configuring the laser beam, a metal workpart is subjected to the
laser beam to perform the heat treatment process. The workpart is
preferably passed through the laser beam; however, the laser beam
may be traversed across the workpart surface. The heat treating
process is performed such that the parts are self-quenching. That
is, no air or liquid quenching is required. The heat treating
process forms a hard martensitic layer having a microstructure of
untempered martensite. Internal stresses created in the untempered
martensite layer make the untempered martensitic layer brittle,
thereby requiring stress relief.
[0022] Subsequent to the heat treating process the workpart is
stress relieved by being subjected to a laser beam a second time.
The laser beam is reconfigured to obtain the desired results for
performing stress relief. The workpart is then subjected to the
laser beam for stress relief either by passing through the laser
beam or by the laser beam traversing the surface of the part. The
resultant microstructure after stress relief appears as untempered
martensite. However, the internal stresses have been relieved.
Therefore, the hardness of the martensitic layer has been retained
but the brittleness has been eliminated.
[0023] In another aspect of the invention thin workparts such as
steel cutting rules or knife blades are surface hardened. The
process entails first heat treating and subsequently stress
relieving the cutting rule. Prior to the heat treating process, a
laser beam is configured to obtain the desired hardness results.
During the heat treating process the cutting rule is fed through
the laser beam vertically, in an upright position, such that only
the cutting tip of the cutting rule is subjected to the laser beam
for hardening. The tip of the cutting rule is hardened by the laser
beam to form a shallow hardened case of only a few thousandths of
an inch.
[0024] The cutting rule is subsequently stress relieved by being
subjected to the laser beam a second time. The laser is
reconfigured to obtain the desired results for performing stress
relief. The cutting rule is then passed through the laser beam,
thereby performing the stress relief. The microstructure of the
hardened surface after heat treatment but before stress relief
appears as untempered martensite. After being subjected to stress
relief, the microstructure maintains its appearance as untempered
martensite. However, the internal stresses have been relieved,
thereby eliminating brittleness.
[0025] The process may provide for additional steps such as
cleaning the cutting rule prior to the heat treatment process and
application of a corrosion inhibitor after the stress relief
process. Further, an additional step of applying a laser beam
absorbent substance to the surface area to be heat treated may be
required depending on the type of laser being used. For example, a
continuous wave CO.sub.2 laser beam would require a laser beam
absorbent substance, whereas a YAG laser would not require
application of the laser beam absorbent substance.
[0026] The resultant laser hardened cutting rule performs with the
bendability properties of known cutting rules. However, the
durability, wear-resistance, characteristics are greater than
commonly known cutting rules.
[0027] This brief summary has been provided so that the nature of
the invention may be understood quickly. More complete
understanding of the invention may be obtained by reference to the
following detailed description of the preferred embodiments thereof
in connection with the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is a top perspective view of a laser hardening
process according to the present invention.
[0029] FIG. 2 is a side perspective view of a laser hardening
process according to the present invention.
[0030] FIG. 3 is an enlarged view of a central laser processing
station.
[0031] FIG. 4A is an enlarged side view of the laser beam-cutting
rule interface.
[0032] FIG. 4B is an enlarged front view of the laser beam-cutting
rule interface.
[0033] FIG. 5 is an enlarged view of the interface shown in FIG.
4B.
[0034] FIG. 6A is a top view of a typical steel rule spring
coil.
[0035] FIG. 6B is a sectional view of a typical steel rule spring
coil.
[0036] FIG. 6C is a sectional view of a typical cutting rule after
having a beveled edge machined on one side.
[0037] FIG. 7 is a flow diagram for a laser hardening process.
[0038] FIG. 8 is a flow diagram for a laser hardening process.
[0039] FIG. 9A is a photograph of a cross-section of a steel
cutting rule before heat treating.
[0040] FIG. 9B is a photograph of a cross-section of a steel
cutting rule grain microstructure after laser heating but before
stress relief.
[0041] FIG. 10 is a photograph of a cross-section of a steel
cutting rule grain microstructure after being both laser heat
treated and stress relieved.
[0042] FIG. 11 is a photograph of a cross-section of a steel
cutting rule after being surface hardened by induction heating.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0043] Referring now to the drawings, a detailed description of the
preferred embodiments according to the present invention will be
described.
[0044] FIG. 1 is a top perspective view and FIG. 2 is a side
perspective view of a laser hardening process setup according to
one aspect of the present invention. As seen in FIG. 1 and FIG. 2,
a laser heat-treating process setup for laser hardening a steel
cutting rule contains a central laser processing station 1, a
start/finish station 2 and an intermediate takeup station 3.
Located between start/finish station 2 and central processing
station 1 are cleaning station 4, laser absorbent applying station
5, laser absorbent drying station 6, and corrosion inhibitor
applying station 7. Located along a path connecting start/finish
station 2, cleaning station 4, laser absorbent applying station 5,
drying station 6, central laser processing station 1 and takeup
station 3 are a means for guiding steel cutting rule 14 through the
various processing stations, such as guide rollers 11.
[0045] Start/finish station 2 and takeup station 3 provide a means
for retaining cutting rule 14 during the laser hardening process.
The function of stations 2 and 3 is to retain cutting rule 14,
whatever the form, during the laser hardening process and to
maintain tension in the cutting rule between stations 2 and 3
throughout the process. In the present embodiment, cutting rule 14
is in the form of a spring coil 16, therefore, a means compatible
for retaining spring coil 16 will be described. In the present
embodiment, start/finish station 2 and takeup station 3 preferably
contain a spindle 12 and drive motor 13 connected via a shaft or
the like. Spindle 12 contains a means for winding and unwinding
spring coil 16 such as slot 15. Drive motors 13 are preferably
common electrically driven motors. Drive motors 13 do not drive
cutting rule 14 during the laser hardening process. Rather drive
motors 13 maintain tension in cutting rule 14 between stations 2
and 3 during the laser hardening process by each applying an
opposing rotational force to their respective spindles. Drive
motors 13 are preferably controlled by a common programmable linear
controller (PLC) 33.
[0046] Cleaning station 4 provides a means for cleaning cutting
rule 14 at the initial stages of the laser hardening process.
Cleaning is sometimes necessary to remove dust and dirt particles
that may cause defects in the hardened surface. In the present
embodiment, cleaning station 4 preferably contains cleaning pads 17
connected to actuating device 18. Cleaning pads 17 are preferably
covered with a soft cloth material 19, such as cheesecloth or the
like. Actuating device 18 preferably actuates in a vise-like manner
applying a clamping force between cleaning pads 17.
[0047] Laser absorbent applying station 5 provides a means for
applying a laser beam absorbent substance, such as a water-soluble
ink or black oxide, to a selected surface area of cutting rule 14.
In the present embodiment, laser absorbent applying station 5
preferably contains an applicator 20, such as a roll-on applicator,
an ink reservoir 21, and a means for supplying the ink from ink
reservoir 21 to applicator 20, such as tube 22. Ink reservoir 21
preferably contains a water soluble ink 23 and is preferably
pressurized.
[0048] Drying station 6 provides a means for drying the laser
absorbent substance applied in station 5. In the present
embodiment, drying station 6 is preferably comprised of a series of
air nozzles 24. Air nozzles 24 supply compressed air 25 for drying
of the ink applied in the laser absorbent applying station 5.
[0049] Corrosion inhibitor applying station 7 provides a means for
applying a corrosion inhibiting substance 27, such as a rust
preventative oil, to the surface of cutting rule 14. In the present
embodiment cleaning station 4 is reconfigured as corrosion
inhibitor applying station 7 after the laser hardening process and
before the stress relief process. In station 7, cleaning pads 17
are removed and replaced by oil applying pads 26. Pads 26 are
soaked in a corrosion preventative oil such that when cutting rule
14 passes between pads 26, the oil is wiped onto the surface of
cutting rule 14. Station 7 also preferably contains an oil drip
system 37 for supplying additional oil to pads 26 during the
process. Drip system 37 preferably contains a pressurized oil
reservoir pressurized to cause oil to drip from an outlet in the
reservoir onto pads 26.
[0050] Central laser processing station 1 provides a means for
laser heat treating and laser stress relieving cutting rule 14. In
the present embodiment, central laser processing station 1
preferably comprises a laser beam producing device 8, a laser beam
focusing device 9, and drive motors 10a and 10b. Laser beam
producing device 8 is preferably a 1,000 watt continuous wave
CO.sub.2 laser beam producing mechanism. As a substitute for a
continuous wave CO.sub.2 laser, a YAG laser may be used or any
other type of laser that reaches a level of at least 500 watts
continuous wave may be used. Use of a YAG laser eliminates the need
for application of the water-soluble ink solution adding station,
i.e. stations 5 and 6. However, a YAG laser may create a safety
hazard, requiring special equipment not necessary for the use of a
continuous wave CO.sub.2 laser. Central laser processing station 1
may also contain a means for supplying an assist gas for
facilitating the laser heating process, such as assist gas nozzle
34. Assist gas nozzle 34 may provide a gas such as nitrogen to the
interface of the laser beam and the surface of the cutting rule
being hardened in order to facilitate the hardening process.
[0051] Laser beam focusing device 9 preferably comprises an optical
device 30 and an adjustable height optical device support 31. It
has been found that when optical device 30 is a plano/convex lens,
optimum laser hardening results are achieved. Optical support 31
preferably contains a linear translation mechanism 29 that provides
controlled vertical translation of optic 30. Vertical translation
of optic 30 provides a means for controlling the focal point of
laser beam 28 which will be described in more detail below.
Translation mechanism 29 is preferably a shaft having a sliding
frictional lock collar or other similar arrangement. Translation
mechanism 29 also preferably contains a means for measuring the
translation, such as a micrometer. Translation mechanism 29 may
also be a motorized translation device, such as a ball screw
actuator, and may also be computer controlled.
[0052] Drive motors 10a and 10b provide rotational power to drive
wheels 32. Drive wheels 32 provide a frictional force for feeding
cutting rule 14 through the laser hardening process stations. Drive
wheels 32 are preferably made of a substance such as rubber. Drive
motors 10a and 10b are preferably common electrically driven motors
synchronously controlled by a common programmable linear controller
33. Controller 33 provides a proper feed rate for performing both
the heat treating and stress relief processes on cutting rule
14.
[0053] Having obtained the processing stations setup according to
the foregoing, a description will now be made of the laser
hardening process for laser hardening a steel cutting rule. Prior
to performing the laser hardening process, central laser processing
station 1 is configured to obtain the desired laser hardening
results, and the steel cutting rule is prepared and installed in
the laser processing setup.
[0054] Referring now to FIGS. 3, 4a, 4b, and 5 a detailed
description will be made of the laser beam settings and adjustment
according to one aspect of the present invention.
[0055] As seen in FIG. 3, central laser processing station 1
comprises a laser beam producing device 8 and laser beam focusing
device 9. Laser beam producing device 8 is preferably a 1,000 watt
continuous wave CO.sub.2 laser that produces a D-mode laser beam
35. Laser beam focusing device 9 comprises optic 30 and adjustable
height optic support 31. Optic 30 is preferably a 11/2 inch
diameter, 5 inch focal length plano/convex optic and is connected
to optic support 31. Optic support 31 preferably contains a linear
translation mechanism 29 that provides a means for focusing laser
beam 28. In the present embodiment, translation mechanism 29
preferably contains a shaft and sliding collar having a frictional
lock and a means for measuring the translation, such as a
micrometer. Upon actuation of translation mechanism 29, optic 30
translates vertically along a Z axis, thereby providing for
adjustment of the focal point of laser beam 28. The focal point
reference origin O is preferably the cutting edge surface of
cutting rule 14. Utilizing cutting surface O as a reference, a
focal distance F may be obtained.
[0056] The laser beam power setting and focal point are first
established for the heat treating process. The power settings for
the heat treating process of the present embodiment preferably
comprise a laser beam power setting of between 500 to 550 watts.
The 50 watt range is used as a variable for adjusting the hardened
surface case depth. It should be noted that there is an almost
limitless number of options available to obtain a desired hardness
result. For example, the laser power setting and focal point may
each be independently varied to obtain a desired hardened surface
case depth. Additionally, the rate at which the workpart is fed
through the laser beam may also be varied in order to obtain a
desired result. Therefore, the laser power settings, focal point,
and feed rates described herein have been found to produce the
optimum results for the present invention. As seen in FIG. 4A, the
laser beam focal point referenced from surface O is optimally 0.010
inch as designated by dimension F. For the heat treating process
the laser beam dimensions L and W, as seen in FIGS. 4A and 5, are
approximately 11/4 inch and 0.010 to 0.012 inch, respectively. The
resultant beam has a substantially parabolic shape as denoted by P
in FIG. 4A.
[0057] After having obtained the laser hardening process
configuration and laser beam adjustments according to the
foregoing, a steel cutting rule raw material is prepared for the
laser hardening process. As seen in FIGS. 6A and 6B, the steel
cutting rule raw material commonly comes in a spring coil 16 form.
The cutting rule raw material commonly has a rectangular
cross-section, as seen in FIG. 6B. The preferred dimensions of the
steel cutting rule raw material according to the present embodiment
are a thickness T of 0.021 to 0.042 inches and a height H of two
inches or less. However, thicknesses up to 0.084 inch may also be
used. The preferred material for the cutting rule according to the
present embodiment is AISI 1050 spring steel. The preferred body
hardness of the raw material is 33-35 R.sub.c and has a grain
structure consisting mainly of tempered martensite with as much as
10-15% bianite. However, other material types and sizes may also be
utilized. As seen in FIG. 6C, a beveled edge 36 is machined on one
side of the steel cutting rule raw material. Beveled edge 36 may be
machined by common methods such as grinding or forming. Having
machined beveled edge 36, steel cutting rule coil 16 is now ready
for installation in the laser hardening process system.
[0058] As seen in FIG. 1, steel cutting rule coil 16 is installed
in start/finish station 2. Steel cutting rule coil 16 is installed
on spindle 12 with free end 37 on the innermost portion of coil 16
installed in slot 15 on spindle 12. The outermost free end 38 of
spring coil 16 is fed through the various processing stations and
into slot 15 of spindle 12 in intermediate takeup station 3. The
portion of steel cutting rule 14 initially fed through the
processing stations is not subjected to the laser hardening
process. Rather, it is excess material, known as lead, to be
discarded after the laser hardening process.
[0059] Upon commencing the laser hardening process, steel cutting
rule 14 is fed through the laser hardening process by drive motor
10a with drive motor 10b being idle. The speed of drive motor 10a
is controlled by programmable linear controller 33 and is
preferably set to a feed rate of about 125 feet per minute. It has
been found that a feed rate of 125 ft./min. coupled with the
previously described laser beam settings of 500-550 watts with a
0.010 focal distance from origin O provide the optimum laser
hardening results. However, as previously described, the feed rate
may be varied according to a desired hardness result. Drive motors
13 in stations 2 and 3 are also controlled by controller 33. Drive
motors 13 apply opposing rotational forces to their respective
spindles 12 to maintain tension in cutting rule 14 during the laser
hardening process.
[0060] The first step of the laser hardening process is to clean
the cutting rule in cleaning station 4. In the present embodiment
of the invention, steel cutting rule 14 passes between cleaning
pads 17 in cleaning station 4. Actuating device 18 supplies a
clamping force between pads 17 sufficient to supply wiping of steel
cutting rule 14 but not excessive such as to cause binding of steel
cutting rule 14. Steel cutting rule 14 is wiped clean by cloth 19
attached to cleaning pads 17. Although described in terms of the
present embodiment, alternate embodiments for cleaning station 4
may be used. For example, cutting rule 14 may be cleaned by air
curtains or a spray nozzle which dispenses a cleaning solution
rather than being wiped by cloth 19. After passing through cleaning
station 4 steel cutting rule 14 next passes through laser absorbent
applying station 5.
[0061] In laser absorbent applying station 5, a laser beam
absorbent substance such as a water-soluble ink or black oxide is
applied to a selected surface area of steel cutting rule 14. In the
present embodiment of the invention, a water-soluble ink solution
is applied to cutting edge O of steel cutting rule 14. The ink
solution is applied by an applicator 20, such as a roll-on or drip
applicator. Applicator 20 is connected to an ink reservoir 21
containing a water-soluble ink 23. Ink reservoir 21 is preferably
pressurized by an external pressure source, such as compressed air,
to a pressure of approximately 5 psi (pounds per square inch).
Pressurization of ink reservoir 21 is preferably sufficient to
cause the water-soluble ink 23 to flow to applicator 20 at a
desired rate in order to effect optimum application of the
water-soluble ink solution 23 to the selected surface of cutting
rule 14. Pressurization of ink reservoir 21 is preferably
controlled by programmable linear controller 33. As steel cutting
rule 14 passes through applying station 5, water-soluble ink
solution 23 is applied by applicator 20 to the selected surface
area of steel cutting rule 14 to be hardened. Although described in
terms of the present embodiment, alternate laser absorbent
materials and application methods may also be used. For example, a
black oxide or phosphate coating may be applied rather than ink.
Additionally, the laser absorbent material may be applied by an
alternate applying means such as a spray nozzle. After application
of the water-soluble ink solution, steel cutting rule 14 next
passes through drying station 6.
[0062] Drying station 6 contains a means for drying the laser
absorbent substance applied in station 5. In the present embodiment
of the invention, drying station 6 preferably contains a series of
air curtains 25. Air curtains 25 preferably comprise compressed air
supplied by a series of air nozzles 24. The air pressure supplied
to nozzles 24 is preferably regulated to approximately 80 psi and
is preferably controlled by programmable linear controller 33. The
air pressure supplied by nozzles 24 is preferably sufficient to dry
water-soluble ink solution 23 but insufficient to cause removal of
the ink solution from the surface. Alternate methods of drying the
laser absorbent substance may also be employed. For example, a heat
source may be applied to the laser absorbent substance in order to
dry it. After passing through drying station 6, steel cutting rule
14 next passes through central laser processing station 1.
[0063] Having obtained the laser power settings of 500-550 watts
and focal point of 0.010 inch from cutting edge surface O according
to the foregoing description, steel cutting rule 14 is heat treated
by passing steel cutting rule 14 beneath laser beam 28. The laser
beam intensity at the cutting rule surface is sufficient to cause a
shallow depth of the cutting rule surface to be heated above the
transformation temperature, thereby changing the phase of the steel
to austenite. After passing through laser beam 28 and being
transformed to austenite, the shallow surface area is rapidly
cooled by self-quenching, thereby transforming the steel phase to
martensite. The resulting martensite layer formed by the laser heat
treating process preferably has a hardness of at least 60 R.sub.c
and a case depth of about 0.004 to 0.006 inches. A shallow depth of
0.004 to 0.006 inch has been found to provide optimum surface
hardness and ductility properties. However, case depths between
0.001 to 0.010 may be obtained by varying the laser power settings,
focal point and feed rate. The hardened surface provides increased
wear resistance, thereby increasing the longevity of cutting rule
14 and reducing the cost of requiring frequent replacement of the
cutting rule. Furthermore, the hardened surface depth is shallow
enough that the cutting rule maintains its ductility properties,
thereby allowing the cutting rule to be bent or formed into a
number of shapes after being laser hardened.
[0064] FIG. 9A is a photograph of a cross-section of a steel
cutting rule prior to being subjected to the foregoing laser heat
treatment process. FIG. 9B is a photograph of a cross-section of a
steel cutting rule after being subjected to the foregoing laser
heat treatment process. As seen in FIG. 9B, the tip of the cutting
rule has been heated and contains a grain microstructure that has
an appearance of untempered martensite. The heat treated surface
area is depicted by the white area in the tip of the cutting rule.
It should be noted that the laser heat treatment process of the
present invention results in a uniform grain structure throughout
the heat treated tip area. In contrast, FIG. 11 is a photograph of
a cross section of a common induction hardened steel cutting rule
having a non-uniform heat treated tip. As seen in FIG. 11, a
grayish area in the middle of the heat treated tip has not been
heat treated, thereby resulting in a non-uniform heat treatment
process. This results in a lower surface hardness than that
achieved by the foregoing laser heat treatment process.
[0065] The hard untempered martensitic layer formed by the
foregoing laser heat treatment process contains internal stresses
that make the hardened surface brittle. In order to remove the
internal stresses, a stress relief process must be performed. The
stress relief process for the present invention is described in
more detail below. The next processing station after cutting rule
14 passes through laser processing station 1 for the heat treatment
process in intermediate takeup station 3.
[0066] In the present embodiment of the invention, intermediate
takeup station 3 winds steel cutting rule 14 back into the form of
a spring coil. This is accomplished by drive motor 13 in station 3
applying a rotational force to spindle 12, thereby causing steel
cutting rule 14 to wrap around spindle 12 forming coil 16. Although
described in terms of a coil winder, takeup station 3 may provide
for an alternate method to takeup the steel cutting rule after the
laser hardening process has been accomplished. After all of the
steel cutting rule has passed from station 2 to station 3, the
process is reversed to perform stress relief of the laser hardened
surface.
[0067] In the present embodiment of the invention, prior to
performing the stress relief, central laser processing station 1 is
reconfigured to perform the stress relief and cleaning station 4 is
reconfigured into corrosion inhibitor applying station 7.
[0068] Central laser processing station 1 is reconfigured by
adjusting the laser beam power setting and by adjusting the focal
point of the laser beam. The laser beam power setting for
performing the stress relief is preferably set to about 80 watts
below the power setting for the heat treating process. For example,
a power setting of 500 watts for heat treating would require a
power setting of about 420 watts for stress relief. The focal point
of the laser beam is adjusted by adjusting translation mechanism
29, thereby adjusting the distance of optic 30 from the laser
hardened surface O. The focal point of laser beam 28 for the stress
relief process is preferably set to 0.170 inch from cutting surface
O, thereby defining dimension F, as seen in FIG. 4A. It has been
found that the 80 watt power setting differential coupled with the
0.170 inch focal distance from cutting edge O provides for the
optimum stress relief results. However, as previously discussed,
the power settings, focal point and feed rate may be varied as
desired to achieve a desired result.
[0069] Cleaning station 4 is reconfigured into corrosion inhibitor
applying station 7 by removing cleaning pads 17 and installing
corrosion inhibitor applying pads 26 in place of cleaning pads 17.
Corrosion inhibitor applying pads 26 are preferably soaked in a
corrosion preventive oil prior to installation onto actuating
device 18. Corrosion inhibitor applying station 7 also preferably
contains a reservoir 39 of corrosion preventive oil and a means for
supplying the oil from the reservoir 39 to applying pads 26.
Reservoir 39 is also preferably pressurized similar to reservoir 21
in applying station 5 and the pressurization is preferably
controlled by programmable linear controller 33. The pressurization
is preferably controlled to provide a predetermined continuous drip
rate of the corrosion preventive oil from reservoir 39 to oil
applying pads 26. Supplying a continuous drip of oil from reservoir
39 to pads 26 ensures that pads 26 remain soaked with the oil and
thereby ensuring the oil is applied to cutting rule 14.
[0070] After having reconfigured stations 1 and 7, cutting rule 14
is prepared for the stress relief process. Free end 37 of cutting
rule 14, now contained on intermediate takeup station 3, is fed
through the processing stations and back onto spindle 12 in
start/finish station 2. Free end 37 is installed in slot 15 of
spindle 12 such that upon application of a rotational force by
drive motor 13 to spindle 12, cutting rule 14 is wound back into
the form of a coil 16.
[0071] Upon commencement of the stress relief process, steel
cutting rule 14 is fed through the processing stations by drive
motor 10b while drive motor 10a remains idle. Drive motor 10b is
preferably controlled by programmable linear controller 33 and is
set to provide a feed rate of about 155 feet per minute. It has
been found that a feed rate of 155 ft./min. coupled with the laser
settings of 80 watts below the heat treating power setting and a
0.170 focal distance, provide optimum stress relief results.
However, as mentioned, these variables may be adjusted in order to
achieve a desired result.
[0072] During the stress relief process steel cutting rule 14 first
passes through central laser processing station 1. The selected
surface area of steel cutting rule 14 which was previously hardened
during the heat treating step is now subjected to laser beam 28 a
second time to perform stress relief. Laser beam 28's intensity is
set such that only stress relief is performed while retaining the
previously hardened untempered martensite microstructure. One
objective of the present invention is to relieve the internal
stresses in the untempered martensite layer formed in the heat
treating step without substantially reducing the hardness of the
untempered martensite.
[0073] Typically, the stress relief process relieves internal
stresses by releasing some of the carbon particles trapped in the
microstructure when the untempered martensite was formed. The
release of these carbon particles from the microstructure reduces
the hardness of the untempered martensite and also changes its
microstructure appearance to tempered martensite. However, in the
present invention, the laser beam power setting and focal point are
established such that the internal stresses are relieved but the
microstructure retains its appearance as untempered martensite.
[0074] FIG. 10 is a photograph of a cross-section of a steel
cutting rule after being subjected to the foregoing stress relief
process. As seen in FIG. 10, the previously heat treated tip of the
cutting rule retains its appearance as untempered martensite.
However, since the internal stresses have been relieved, the
brittleness has been removed. The resultant steel cutting rule has
a surface hardness of at least 60 R.sub.c, about 5 R.sub.c higher
than conventional cutting rules, but has equivalent ductility
properties since the brittleness has been removed. After being
stress relieved in central laser processing station 1, steel
cutting rule 14 moves on to corrosion inhibitor applying station
7.
[0075] Upon entering corrosion inhibitor applying station 7, steel
cutting rule 14 passes between corrosion inhibitor applying pads
26. Pads 26 are preferably soaked in a corrosion preventive oil.
Actuating device 18 applies a clamping force between pads 26, such
that as cutting rule 14 passes between pads 26, corrosion
preventive oil is wiped onto the surface of cutting rule 14. As the
stress relief process proceeds, reservoir 39 is pressurized by an
external pressure source preferably to about 5 psi. The pressure is
sufficient to provide a continuous drip of oil contained within the
reservoir to be applied to pads 26, thereby maintaining saturation
of pads 26. Although the present embodiment employs a wipe-on
method of applying corrosion preventive oil, alternate methods such
as a spray or immersion bath application may also be employed.
[0076] Upon completion of the stress relief process, steel cutting
rule 14 is wound into the form of a spring coil 16 and is retained
in start/finish station 2. Spring coil 16 is then removed from
station 2 and is now ready for use in its final form.
[0077] In another aspect of the invention the foregoing laser
hardening process is utilized in laser hardening a metal workpart.
The metal workpart is not limited to the form of a steel cutting
rule but may be in any form such as a shaft or a flat plate. As
seen in FIG. 7, the metal workpart is surface-hardened by being
processed through central laser processing station 101. Central
laser processing station 101 may be similar to central laser
processing station 1 according to the foregoing description.
Central laser processing station 101 performs both a laser heat
treat process and a stress relief process similar to the foregoing
description. The laser beam configuration, such as the power
settings and focal point, are adjusted according to the foregoing
description in order to perform both the laser heat treatment and
the stress relief process on the metal workpart. The metal workpart
may be passed through central laser processing station 101 by means
such as a conveyor belt or other similar means or central laser
processing station 101 may be traversed across a stationary metal
workpart. The metal workpart is first heat treated by being
subjected to the laser beam, thereby forming a hard surface layer
having an appearance of untempered martensite. The metal workpart
is then stress relieved by being subjected to the laser beam a
second time similar to the foregoing description. After the stress
relief process, the metal workpart microstructure retains its
appearance as untempered martensite. However, internal stresses
have been relieved, thereby removing brittleness.
[0078] The metal workpart may also be subjected to additional
processing steps, such as cleaning station 104, laser beam
absorbent applying station 105, laser beam absorbent drying station
106 and corrosion inhibitor applying station 107, as seen in FIG.
8. Stations 104 through 107 as seen in FIG. 8 are similar to
stations 4 through 7 according to the foregoing description.
Accordingly, the metal workpart may be cleaned by methods such as a
dry cloth wipe, spray on cleaning solution or being subjected to an
air curtain. Also, a laser beam absorbent substance may be applied
to the surface area of the metal workpart depending on the type of
laser beam used in the laser hardening process. The laser beam
absorbent substance may be applied by various methods, such as roll
on or spray on application. Additionally, the laser beam absorbent
substance may require drying, such as being subjected to a series
of air curtains or a heat source. Further, a corrosion inhibiting
substance such as oil may be applied to the surface of the metal
workpart after being subjected to the stress relief process.
[0079] Although the present invention has been illustrated with
reference to certain preferred embodiments, it will be appreciated
that the present invention is not limited to the specifics set
forth therein. Those skilled in the art readily will appreciate
numerous variations and modifications within the spirit and scope
of the present invention, and all such variations and modifications
are intended to be covered by the present invention, which is
defined by the following claims.
* * * * *