U.S. patent application number 11/210060 was filed with the patent office on 2005-12-22 for sub-surface enhanced gear.
This patent application is currently assigned to Mikronite Technologies Group, Inc.. Invention is credited to Bredeson, Craig, Bringard, Robert, Hoffman, Steve E., Manning, Daniel.
Application Number | 20050279430 11/210060 |
Document ID | / |
Family ID | 46205682 |
Filed Date | 2005-12-22 |
United States Patent
Application |
20050279430 |
Kind Code |
A1 |
Hoffman, Steve E. ; et
al. |
December 22, 2005 |
Sub-surface enhanced gear
Abstract
An improved gear including a plurality of teeth defining a
surface, the teeth each having a substantially continuous first
subsurface stress layer located below the surface, and a second
subsurface stress layer located below the first subsurface stress
layer, the first subsurface stress layer comprising a thickness of
compressive residual stress.
Inventors: |
Hoffman, Steve E.;
(Englewood, NJ) ; Bredeson, Craig; (Eatontown,
NJ) ; Manning, Daniel; (Clifton, NJ) ;
Bringard, Robert; (Wilmington, NC) |
Correspondence
Address: |
DRINKER BIDDLE & REATH
ATTN: INTELLECTUAL PROPERTY GROUP
ONE LOGAN SQUARE
18TH AND CHERRY STREETS
PHILADELPHIA
PA
19103-6996
US
|
Assignee: |
Mikronite Technologies Group,
Inc.
Carlstadt
NJ
|
Family ID: |
46205682 |
Appl. No.: |
11/210060 |
Filed: |
August 23, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11210060 |
Aug 23, 2005 |
|
|
|
09965162 |
Sep 27, 2001 |
|
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Current U.S.
Class: |
148/586 |
Current CPC
Class: |
B23D 61/025 20130101;
B24B 31/0224 20130101; C21D 9/32 20130101; B23D 61/04 20130101;
B23D 65/00 20130101; C21D 7/04 20130101; B23D 61/021 20130101 |
Class at
Publication: |
148/586 |
International
Class: |
C21D 009/32 |
Claims
1. A gear including a plurality of teeth extending outward from a
body, each tooth being spaced apart from an adjacent tooth, the
portion of the body between adjacent teeth defining a bottom land,
each tooth having a tooth face and the top land, the tooth face
forming a tooth fillet at the juncture with the bottom land, the
top land, the bottom land and the tooth face defining a surface of
the gear, the gear comprising: a plurality of the teeth each having
a substantially continuous subsurface stress layer which extends
substantially under the tooth face and top land, the subsurface
stress layer having a thickness of compressive residual stress, at
least a portion of the layer of compressive residual stress being
formed by a process comprising the steps of: providing a high speed
centrifugal processing apparatus having an outer housing with a
central axis, and at least one inner vessel with a central axis;
placing the gear into the inner vessel; placing abrasive media into
the inner vessel; and rotating the inner vessel about its central
axis and about the central axis of the outer housing, the inner
vessel rotating at high speed relative to the outer vessel, the
high speed rotation causing the abrasive media to contact the
surface of the gear, the contact by the abrasive creating at least
a portion of the compressive residual stress in the gear.
2. A gear according to claim 1 wherein the thickness of the
compressive residual stress is non-uniform.
3. A gear according to claim 1 wherein the thickness of the
compressive residual stress is at least about 0.005 inches.
4. A gear according to claim 1 wherein the thickness of the
compressive residual stress is at least about 0.010 inches.
5. A gear according to claim 4 wherein the thickness of the
compressive residual stress is greater than about 0.012 inches.
6. A gear according to claim 1 wherein the subsurface stress layer
extends substantially under the tooth fillet.
7. A gear according to claim 1 wherein the subsurface stress layer
extends substantially under the tooth fillet and the bottom
land.
8. A gear according to claim 1 wherein magnitude of the compressive
residual stress is not uniform across the thickness.
9. A gear according to claim 1 wherein the compressive residual
stress is at least about 50 ksi.
10. A gear according to claim 1 wherein the compressive residual
stress is at least about 100 ksi.
11. A gear according to claim 1 wherein the compressive residual
stress is at least about 175 ksi.
12. A gear including a plurality of teeth extending outward from a
body, each tooth being spaced apart from an adjacent tooth, the
portion of the body between adjacent teeth defining a bottom land,
each tooth having a tooth face and the top land, the tooth face
forming a tooth fillet at the juncture with the bottom land, the
top land, the bottom land and the tooth face defining a surface of
the gear, the gear comprising: a plurality of the teeth each having
a substantially continuous first subsurface stress layer located
below the surface, and a second subsurface stress layer located
below the first subsurface stress layer, the first subsurface
stress layer comprising a thickness of compressive residual stress,
at least a portion of the layer of compressive residual stress
being formed by a process comprising the steps of: providing a high
speed centrifugal processing apparatus having an outer housing with
a central axis, and at least one inner vessel with a central axis;
placing the gear into the inner vessel; placing abrasive media into
the inner vessel; and rotating the inner vessel about its central
axis and about the central axis of the outer housing, the inner
vessel rotating at high speed relative to the outer vessel, the
high speed rotation causing the abrasive media to contact the
surface of the gear, the contact by the abrasive creating at least
a portion of the compressive residual stress in the gear.
13. A gear according to claim 12 wherein the thickness residual
compressive stress is at least about 0.005 inches.
14. A gear according to claim 12 wherein the thickness of the
residual compressive stress is greater than about 0.012 inches.
15. A gear according to claim 12 wherein the subsurface stress
layer decreases in magnitude through substantially the first layer
from a maximum at the surface.
16. A gear according to claim 12 wherein the residual compressive
stress is at least about 50 ksi.
17. A gear according to claim 12 wherein the gear includes a layer
below the surface that is carburized, and wherein the compressive
residual stress extends below the surface and the carburized
layer.
18. A method of increasing the compressive residual stress in a
gear comprising the steps of: providing a high speed centrifugal
processing apparatus having an outer housing with a central axis,
and at least one inner vessel with a central axis; placing a gear
into the inner vessel; placing abrasive media into the inner
vessel; and rotating the inner vessel about its central axis and
about the central axis of the outer housing, the inner vessel
rotating at a speed relative to the outer vessel so as to produce
acceleration of the media within the vessel in excess of 10 g's,
the high speed rotation causing the abrasive media to contact the
surface of the gear, the contact by the abrasive creating at least
a portion of the compressive residual stress in the gear.
19. A method of increasing the compressive residual stress
according to claim 18 wherein the accelerations are in excess of 15
g's.
20. A method of increasing the compressive residual stress
according to claim 18 wherein the inner vessel is rotated for at
least 6 minutes.
Description
RELATED APPLICATION
[0001] The present application is a continuation-in-part of U.S.
patent application Ser. No. 09/965,162, filed Sep. 27, 2001, which
is incorporated herein by reference in its entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to gears and, more
particularly, to an improved gear design with a sub-surface
enhanced layer of compressive residual stress.
BACKGROUND
[0003] Residual stress is a stress that exists within a part
without any external load, such as an applied force or thermal
gradient. These stresses are induced during the manufacturing
process, for example, due to working of the part, surface treatment
of the part or temperature changes during part formation. Residual
stresses within a part can be tensile or compressive. Most
conventional manufacturing processes tend to induce residual
tensile stresses into the component being fabricated.
[0004] It is well known that tensile stress tends to reduce the
mechanical performance of materials. For example, cracks that form
within a part tend to propagate more readily under the influence of
tensile residual stresses in the part. These stresses act upon the
crack causing the crack tip to extend through the part. Fatigue or
cyclic loading in the vicinity of the crack can accelerate the
crack propagation, which could lead to catastrophic failure of the
component. It is also known that residual tensile stresses can
cause corrosion in a part to propagate into cracking. Thus,
residual tensile stresses in a component are generally not
favorable.
[0005] One known way of reducing crack propagation in a component
is by inducing a compressive residual stress in the vicinity of a
crack tip. The compressive stress tends to inhibit crack growth,
thus improving the fatigue life of the component. However, to date,
the processes for introducing compressive residual stress in a part
have been limited to shot and hammer peening, and carburizing. The
drawback with peening processes is that they produce relatively
large, inconsistent compressive stress spots in the component.
FIGS. 1A-1D illustrate the effect of conventional peening on a
metallic surface. FIG. 1A schematically illustrates the granular
arrangement in a manufactured part. The grains are generally under
a tensile residual stress. As a shot hits the surface, it deforms
it locally, inducing compression into the material. See FIG. 1B.
The force of the shot causes localized plastic deformation,
resulting in a small area of subsurface residual compression.
[0006] Due to the size of the shots used in conventional shot
peening, the localized areas of compression are not consistent. As
such, the resulting product will generally include mixtures of
tensile and compressive residual stresses at the surface. See FIG.
1C. In the event that a crack develops in between shot peened
zones, those cracks can propagate.
[0007] In products that have tight internal radii, for example at
the root of a gear tooth and in notched materials (which is
generically shown in FIG. 1D), it is generally not possible for the
surface to be completely peened. As such, the very points where
there are high stress concentrations (e.g., notches and radiused
corners) are the same places where shot peening cannot reach and,
thus, cannot assist in reducing crack propagation.
[0008] Carburizing involves the addition of carbon to the surface
of low-carbon steels at temperatures generally between 850.degree.
C. and 950.degree. C. (1560.degree. F. and 1740.degree. F.). At
this temperature, the material is in its austenite crystalline
state, with a high solubility for carbon. Hardening is accomplished
when the high-carbon surface layer is subsequently quenched to form
martensite with a high-carbon martensitic outer surface. The result
is a carburized layer 1/8 to 1/2 mm thick. This surface provides
good wear and fatigue resistance. It is superimposed on a tough,
low-carbon steel core.
[0009] One of the problems with carburizing is that the high
temperature required to cause the material to go into its
absorptive austenite state also causes the steel to creep slightly.
As such, the net shape of the material changes. In parts that have
very critical size constraints carburizing may be unacceptable. In
products that mesh, such as gears, the slight variation in sizing
can produce noise and vibrations in the transmission.
[0010] Current gear manufacturing processes involve carefully
machined, ground, or hobbed gear teeth profiles with an outer
diameter known as an addendum circle, a pitch circle corresponding
to the preferred rolling point of the involutes, a clearance
circle, and a relief, with the base fillets of the teeth forming
the lowest dedendum circle. Tooth thickness and corresponding face
width (i.e., the flat face to flat face dimension), as well as the
top land, are all used to offset fatigue loads. However, sizing of
these components can be controlled only to a limited extent without
adversely affecting the performance of the part.
[0011] During operation, a gear goes through multiple phases of
loading as the gear teeth engage, transfer torque, and disengage.
Depending on the gearing arrangement, the mating of the teeth may
be through single or multiple points of contact (i.e., several
pairs of mating teeth.) In order for there to be multiple sets of
mating teeth engaging at the same time, there is, to at least some
degree, bending occurring in the teeth. Thus, the repeated
engagement and disengagement of the teeth causes fatigue loading on
the teeth. This loading typically produces the highest stress
concentration at the fillet located at the base of the teeth. This
is typically where cracks initiate in gears.
[0012] The face of the tooth above the pitch circle is the initial
contact point between the mating teeth. The first contact is a
sliding contact friction as the two mating gears engage at the
involutes and begin rolling. This pure slide is unavoidable. In
this area pitting, spalling, and case crushing are the typical
failure mechanisms. The greatest forces that are applied to the
teeth occur at the point of the involutes where the rolling contact
occurs. This rolling contact produces rolling contact fatigue.
[0013] As discussed above, shot peening cannot be used to surface
harden tight areas, such as splines, inside diameters, and deep
roots. Additionally because the shot impacts the surface in a
denting fashion, it distorts the surface. This deformity may
relieve cyclical fatigue issues, but may exacerbate rolling contact
fatigue by introducing pitting and void spaces which can facilitate
tensile loads in areas where yielding may occur. Additionally even
in areas of crack propagation that have been improved, the
introduction of dents or the failure to remove pits can create a
point where cracking can initiate.
[0014] Lapping of gear teeth is another process currently used to
strengthen teeth. Lapping is achieved in two different ways. In one
process, the gears are allowed to run against one another in a
friable abrasive slurry. The abrasive gradually refines the tooth
surface to reduce friction and failure origin points. However, the
abrasive does nothing to change the residual tensile
characteristics of the teeth at the fillet.
[0015] The second type of lapping occurs in a vibratory bowl with a
wet media in an acidic bath rubbing against the teeth. This type of
lapping offers similar surface and wear benefits, and can provide
some smoothing in the fillet area. However, this form of lapping
isn't nearly as controlled as intermeshing gear lapping, and
therefore can only be applied to achieve limited improvement before
exceeding reasonable time cycle constraints and permanently
deforming the desirable shape of the tooth face and flank.
[0016] A need, therefore, exists for an improved gear design that
minimizes cracking due to fatigue loads without adversely affecting
part performance.
SUMMARY OF THE INVENTION
[0017] The present invention relates to the a gear having an
improved layer of compressive residual stress. The gear including a
plurality of teeth extending outward from a body. Each tooth is
spaced apart from an adjacent tooth with the portion of the body
between adjacent teeth defining a bottom land. Each tooth having a
tooth face and the top land. The tooth face forming a tooth fillet
at the juncture with the bottom land. The top land, the bottom land
and the tooth face in combination define a surface of the gear.
[0018] A plurality of the teeth have a substantially continuous
subsurface stress layer which extends substantially under the tooth
face and top land. The subsurface stress layer has a thickness of
compressive residual stress. At least a portion of the layer of
compressive residual stress is formed by a high energy finishing
process. The high energy finishing process is performed in a high
speed centrifugal processing apparatus that has an outer housing
with a central axis, and at least one inner vessel with a central
axis. The gears are placed into the inner vessel along with an
abrasive media. The inner vessel is rotated about its central axis
and about the central axis of the outer housing. The inner vessel
is rotated at high speed relative to the outer vessel. The high
speed rotation causes the abrasive media to contact the surface of
the gear thereby creating at least a portion of the compressive
residual stress in the gear.
[0019] In one embodiment, the speed of the vessel is designed to
produce accelerations of the media within the vessel in excess of
about 10 g's. In a preferred embodiment, the accelerations are in
excess of 15 g's and more preferably about 30 g's.
[0020] The subsurface layer of compressive stress is at least about
0.005 inches. Preferably the thickness is about 0.010 inches and
more preferably about 0.012 inches.
[0021] The compressive residual stress created in the gear has a
maximum of at least about 50 ksi. Preferably the maximum
compressive residual stress is at least about 100 ksi and more
preferably at least about 175 ksi.
[0022] The foregoing and other features of the invention and
advantages of the present invention will become more apparent in
light of the following detailed description of the preferred
embodiments, as illustrated in the accompanying figures. As will be
realized, the invention is capable of modifications in various
respects, all without departing from the invention. Accordingly,
the drawings and the description are to be regarded as illustrative
in nature, and not as restrictive.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] For the purpose of illustrating the invention, the drawings
show a form of the invention which is presently preferred. However,
it should be understood that this invention is not limited to the
precise arrangements and instrumentalities shown in the
drawings.
[0024] FIGS. 1A-1D schematically illustrate the application of
conventional peening on a material surface.
[0025] FIG. 2A schematically illustrates the path of a media
particle as it interacts with the surface of a work piece in a
centrifugal processor.
[0026] FIGS. 2B and 2C schematically illustrate the resulting
residual compressive stress profile produced in a work piece using
a media mixture according to the present invention.
[0027] FIG. 3 schematically illustrates the resulting residual
compressive stress profile produced in a gear tooth in accordance
with the present invention.
[0028] FIG. 4 is a graph comparing the surface roughness between an
unprocessed bearing race and a processed bearing race.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] The present invention relates to a method and resulting gear
that has survival and operating benefits that have been established
through metallurgical, topographical, tribological, thermal,
chemical, and work translation evaluation. Each benefit is directly
attributable to the invention. The method uses a high-energy
centrifugal system operating at about 16 g's or higher (multiples
of gravitational force as calculated with the formula wr(n.times.n)
0.000341=g's where w=weight in pounds at sea level, r=radius in
feet, n=rpm). This measurement is taken at the center of the
operating vessel with total forces at the most distant radius point
increasing in a direct linear correlation.
[0030] It has been determined that centrifugal processors, such as
those available from Mikronite Technologies, Inc. and disclosed in
U.S. Pat. Nos. 5,355,638, 5,848,929, 6,599,176, 6,733,375 and
PCT/US03/21218, afford an almost perfect slide relationship between
the part being processed and the media in the processing vessel
that is used to modify the surface of the part. The forces imposed
on the media within a centrifugal processor are such that the media
contacts the work piece at an angle of incidence that is typically
not perpendicular to the work piece surface. This produces a
desirable slide relationship since it tends to reduce or eliminate
cumulative and inconsistent impact forces that plague the
uniformity of surface and sub-surface treatment in other high
compression processes such as hammering or peening. The sliding
signature of the media along the part surface produces a short (as
compared to the total length of the piece) substantially linear
scratch on the surface. The angle of incidence of the media results
in applied forces that are not only normal to the surface of the
part, but also parallel to the surface. In contrast, shot peening
and hammering are designed to apply a perpendicular or normal force
onto the material. Accordingly, these existing methods produce only
impact forces with localized, essentially point compression induced
in the part.
[0031] The scratching of the surface of a material in a high energy
centrifugal processor results in substantially entire surface
contact. Furthermore, the lateral or sliding motion of the media on
the surface produces molecular movement of the work piece material,
as opposed to simple crushing that is produced by peening. It has
been determined that when the movement of the media is highly
accelerated, the result is that the scratching produces a
substantially uniform and contiguous surface and sub-surface (i.e.,
layer) of residual compression in the work piece. FIG. 2A
schematically illustrates the surface layer compression that
results in a part subjected to centrifugal processing. An exemplary
trajectory T of a media M is shown. The media skips off the surface
at high speed, thus producing the highly desirable scratching and
sub-surface compression. The fluidized media environment created by
the centrifugal processor produces multidirectional scratches
across the entire surface of the work piece, which produces a
substantially uniform surface finish and sub-surface compression,
see FIG. 2B, and permits the application of compressive stress in
many remote regions, see FIG. 2C.
[0032] The centrifugal machine includes processing vessels into
which the gear is placed, along with a media material. The media is
preferably composed of a plurality of small granular or carrier
pellets with a surface coating of comparatively tiny hard abrasive
particles. The carrier pellets preferably have a size that permits
the largest inertial moment while at the same time not being too
large that they fail to reach all the points of the gear that need
to be processed. Testing has determined that the use of the
abrasive coated grains in high energy centrifugal machines produces
reduced depth penetration of the abrasive into the material (on the
order of less than 1/2 of the abrasive's size). Instead, the motion
created by the centrifugal processor creates a dynamic and
continuous sliding relationship between the gear and the coated
media. As such, the impingement is only a fraction of what it would
be if the media were directed orthogonal to the surface of the
gear. The result is a lap scratch of the surface. The size of the
abrasive and its lapping movement inhibits cumulative errors and
deep digs or depressions that typically result from shot peening.
Thus, the present invention reduces the problem of deformation that
is produced by shot peening, while still imparting equal or greater
compressive stress.
[0033] The depth of compressive stress at 16 g's energy has been
observed using XRT (X-ray Depth Profiling) testing to be in excess
of 0.012 inches, exceeding industry standards for shot peening. The
compressive residual stress also has been measured to over 175 k
psi, again exceeding standards of shot peening.
[0034] The gear is agitated in the centrifugal processor for a
sufficient time to remove topological anomalies. In doing so, the
present invention produces similar benefits as lapping. However,
since the present method does not require meshing gears, instead
using slide motion and much smaller media, it easily reaches the
root and imperfect fillet of the gear tooth and applies sufficient
force to induce a compressive residual stress while removing
fracture-inducing anomalies. The use of a high speed centrifugal
processor and media mixture discussed above produces a gear with
sub-surface stress and surface roughness reduction in less time and
completely different than conventional processes. In addition, the
small media does not deform the encoded shape of the involutes of
the tooth and, thus, does not negatively impact the proper rolling
tooth relationship, which is one of the major drawbacks to the use
of peening on gears.
[0035] The use of a high speed centrifugal processor applies far
greater forces on the gear and is able to reach areas of the gear
tooth that are not achievable by any conventional means. In
addition, because of the universal immersion and applied forces to
the gear, the processed gear becomes truly isotropic in nature.
Heretofore, the term "isotropic" has been limited to describing
regional areas where there was virtually identical surface
anomalies. However, the present invention provides a truly
isotropic gear since the loading and coverage of the abrasive media
is consistent over substantially the entire product. The resulting
compressive residual stress and refined topological surface extends
over substantially the entire gear surface, from the tip to the
root.
[0036] Also, because of the substantially continuous compressive
residual stress surface layer in the part (i.e., elimination of
tensile variations), the harmonics of the gear are preferentially
altered in a way unmatched by conventional processes.
[0037] Furthermore, the continuous compressive residual stress
surface layer has the effect of equalizing the electrical forces
that are common to distressed metals. As a result, the electrical
forces are essentially neutralized. Consequently, anodic corrosion
is now relatively remote or non-existent in the gear. This
translates into stability in impure environments, such as when the
gear is exposed to less than pure or contaminated lubricants. As
such, the present invention provides a unique pretreatment process
which results in a more even application of plasma and similar
coatings that are affected by electrical forces on the surface.
[0038] Even in lubricants that are specified correctly, when a part
is subjected to a load, the compression of the liquid results in
topical heat in the part. This issue is controlled by the gear
having a more accurate surface, free of radical highs and
compression zones. Additionally, forces of thermal behavior tend to
follow lines of uniformity in surface and subsurface structure.
Heat will conduct more evenly, and therefore with fewer tendencies
to anneal or distort, if the heat has a natural path leading to its
dissipation. The increased and consistent density in the gear made
in accordance with the present invention maintains heat effects on
the surface, thereby allowing the heat to disperse through
conduction into the oil and radiation to adjacent materials,
instead of propagating through the part. Accordingly, a gear made
in accordance with the present invention runs at a lower
temperature than conventional gears.
[0039] Tribologically, the isotropic surface has several benefits.
The nature of liquids is to find a condition of stable minimum
surface tension, which is generally a droplet in shape. Fluid
flowing over a surface tends to form a capillary or trough with the
fluid achieving a hydrodynamic barrier layer. The isotropic surface
imparted by the present invention has many small linear segmented
scratches corresponding to the abrasive size. These troughs cause
the fluid to spread. However, since the depth of the troughs is
consistent, there are no valleys in which the fluid gathers. Thus,
the layer that is formed is continuous and very thin, resulting in
a protective lubricated surface with minimum need to overcome
hydraulic forces.
[0040] Thus, the present invention provides a gear that has a
consistent layer of residual compressive stress on the surface of
the gear tooth, including in the area of the fillet. This is
schematically shown in FIG. 3. This compressive stress layer is at
least about 50 ksi and more preferably is at least about 100 ksi.
In one embodiment, the stress layer is at least about 175 ksi. The
thickness of the layer can also be varied depending on many
different factors, including the length of the processing time.
However, the layer is preferably at least about 0.005 inches in
thickness and more preferably is at least about 0.010 inches thick.
In one embodiment, the layer is at least about 0.012 inches
thick.
[0041] The present invention has applicability to various forms of
gears, including spur, helical, and herringbone.
[0042] In order to produce gears and other toothed or irregularly
shaped objects that cannot be traditionally hardened using peening,
a media mix is used in the centrifugal processor that provides the
necessary mass, hardness and abrasion to form the residual
compressive stress layer in the product. Suitable abrasives and
media mixes are described in co-pending application titled "Media
Mixture for Improved Compressive Stress in a Product," (Attorney
Docket No. 9436-36 US1), filed on ______, the disclosure of which
is incorporated herein by reference in its entirety.
[0043] Testing has also established that use of the high energy
centrifugal processors described above in combination with the
media can enhance even conventionally processed gears. For example,
as discussed above, one process for creating a layer of compressive
residual stress in a gear is to carburize the surface of the gear.
One drawback to carburizing is that the amount of compressive is
not as high as would be desired. Using the processing system
according to the present invention, conventionally carburized
products, including pinion gears, were produced that have
significantly increased compressive residual stress.
[0044] Referring to Test Protocol 1 shown below, a carburized
pinion gear was measured before and after application of the high
energy finishing process. Prior to application, the pinion had a
compressive residual stress at its surface of 122.7 ksi as measured
using X-ray diffraction. After application of the process according
to the present invention, the compressive residual stress was up to
204.3 ksi. That is a 66% increase. As shown in the chart, the
increase in compressive residual stress was consistently measured
down to a depth of 0.015 inches. On average, there was a 50%
increase in compressive residual stress through the depth.
[0045] Table 1A shows that the present invention produces a 67%
decrease in the surface roughness of the carburized pinion gear as
measured in terms of Ra. Ra is the Arithmetic Mean Deviation of the
roughness profile. This is a tremendous improvement in the surface
roughness of a conventional pinion gear. As shown the peaks on the
surface of a conventional carburized pinion gear were on average 34
.mu.in. When these high peaks break off during use of the pinion,
they tend to cause damage within the gearbox. The present invention
addresses this problem by significantly reducing the height of the
peaks, essentially evening out the surface. This minimizes damage
to the pinion gear and the gearbox.
[0046] Test Protocols 2-5 (shown below) were conducted on cutting
flutes made from different materials. These tests show similar
beneficial results as Test Protocol 1 discussed above.
[0047] Test Protocol 6 was performed on a bearing race made from
E52100 steel. Again there was an increase in the compressive
residual stress from 4% to 72.2%. Also shown in FIG. 4 is a chart
of the Ra on the surface of the bearing race. As can be readily
seen, the unprocessed part had significant variations over the
surface resulting in an Ra of 10.5 .mu.in. These variations result
in potential hot spots where faults (e.g. cracks) can start.
Furthermore, the variations in the surface contour generate
vibrations that result in vibratory loading on the race and
increased acoustic noise. The processed bearing race according to
the present invention had a significant decrease in the surface
roughness producing an Ra of 0.91 .mu.in.
[0048] Test Results
[0049] The present invention has been applied to several specimens.
The following summarizes the test results.
[0050] Test Protocol-1
[0051] Material--4140 Steel--Carburized Pinion Gear
[0052] Processing time--approximately 45 minutes at about 30
g's
[0053] Depth reading--surface to 0.015 inches
[0054] Location--measurement at same point but at different
depths
1TABLE 1 Compressive Residual Stress v. Depth - Pinion Gear Stress
(ksi) Depth Gear U Gear M Percentage (inches) (Unprocessed)
(Processed) Delta Increase 0 -122.7 -204.3 -81.6 66.5% 0.0005 -86.2
-124.6 -38.4 44.5% 0.001 -59.8 -95.7 -35.9 60.0% 0.002 -32.3 -59.8
-27.5 85.1% 0.004 -25.3 -37.6 -12.3 48.6% 0.007 -32.1 -42.7 -10.6
33.0% 0.01 -27 -43.3 -16.3 60.4% 0.015 -49.1 -51.4 -2.3 4.7%
[0055]
2TABLE 1A Ra on Surface - Pinion Gear Gear U Gear M Percentage
(Unprocessed) (Processed) Decrease 34 .mu.in 11 .mu.in 67.6%
[0056] Test Protocol-2
[0057] Material--Imported High Strength Steel 1/2 End Mill 2
Flutes--Solid carbide
[0058] Processing time--6 minutes at 30 g's
[0059] Depth reading--surface
[0060] Location inside flute, 3 measurements at same point, but at
different angles
3 TABLE 2 Unprocessed Processed Percentage Location (ksi) (ksi)
Increase 90.degree. -20 -40.48 39% 45.degree. -11.2 -32.66 190%
315.degree. -27.27 -39.36 44%
[0061] Test Protocol-3
[0062] Material--American High Strength Cobalt Steel 1/2 End Mill 2
Flutes--Square end
[0063] Processing time--6 minutes at 30 g's
[0064] Depth reading--surface
[0065] Location inside flute, 3 measurements at same point, but at
different angles
4 TABLE 3 Unprocessed Processed Percentage Location (ksi) (ksi)
Increase 90.degree. -95.11 -115.01 20% 45.degree. -46.6 -94.71 104%
315.degree. -125.03 -130.41 4%
[0066] Test Protocol-4
[0067] Material--American Solid Carbide {fraction (7/16)} End Mill
2 Flutes--Solid carbide
[0068] Processing time--6 minutes at 30 g's
[0069] Depth reading--surface
[0070] Location inside flute, 3 measurements at same point, but at
different angles
5 TABLE 4 Unprocessed Processed Percentage Location (ksi) (ksi)
Increase 90.degree. -79.89 -114.58 44% 45.degree. -114.48 -129.82
13% 315.degree. -16.25 -68.53 325%
[0071] Test Protocol-5
[0072] Material--American Hob Steel 2 Piece Test/(DP40PAZOWD,
057-1.degree.21'), M42 Tin
[0073] Coated
[0074] Processing time--8 minutes at 30 g's
[0075] Depth reading--surface
[0076] Location-1 measurement
6 TABLE 5 Unprocessed Processed Percentage Location (ksi) (ksi)
Increase 90.degree. -8.2 -17.7 115%
[0077] Test Protocol-6
[0078] Material--E52100 Steel--Bearing Race
[0079] Processing time--6 minutes at 30 g's
[0080] Depth reading--surface to 0.02 inches
[0081] Location--measurement at same point, but at different
depths
7TABLE 6 E52100 Steel - Bearing Race Unprocessed Processed Depth
Stress Depth Stress Percentage (inches) (ksi) (inches) (ksi)
Increase 0 -37.18 0 -57.95 55.8% 0.0005 -40.08 0.0006 -46.2 15.2%
0.001 -37.79 0.001 -39.3 4% 0.0019 -35.55 0.0021 -41.11 15.6%
0.0042 -32.08 0.004 -40.62 26.6% 0.0068 -29.4 0.0069 -30.81 4.8%
0.0104 -16.85 0.0098 -29.02 72.2% 0.0151 -14.79 0.015 -20.53 38.8%
0.02 -9.27 0.021 -12.93 39.5%
[0082] Accordingly, the present invention results in a gear that is
significantly different from conventional gears. The process
according to the present invention produces parts that have an
improved (increased) surface and sub-surface compressive residual
stress. This increased compressive residual stress helps to prevent
and/or reduce the propagation of cracking in the products. Also, as
discussed above, the process produces a gear with a very low
surface roughness. This results in reduced loading on the part,
including thermal loads, as well as reduced vibrations.
[0083] Although the invention has been described and illustrated
with respect to the exemplary embodiments thereof, it should be
understood by those skilled in the art that the foregoing and
various other changes, omissions and additions may be made therein
and thereto, without parting from the spirit and scope of the
present invention.
* * * * *