U.S. patent application number 11/593817 was filed with the patent office on 2008-05-08 for method of forming a gear.
Invention is credited to Yahya Hodjat, Roger Lawcock, John Roes, Joel Wright.
Application Number | 20080105021 11/593817 |
Document ID | / |
Family ID | 39358554 |
Filed Date | 2008-05-08 |
United States Patent
Application |
20080105021 |
Kind Code |
A1 |
Hodjat; Yahya ; et
al. |
May 8, 2008 |
Method of forming a gear
Abstract
A method of forming a gear comprising gripping a blank to be
spun formed in a spin forming machine, spin forming a gear having
helical teeth disposed on an inner surface, and ejecting the gear
by simultaneous extension and rotation of an ejector member and
thereby rotation of the gear being ejected.
Inventors: |
Hodjat; Yahya; (Oxford,
MI) ; Lawcock; Roger; (Burlington, CA) ;
Wright; Joel; (Kitchener, CA) ; Roes; John;
(Strathroy, CA) |
Correspondence
Address: |
THE GATES CORPORATION
IP LAW DEPT. 10-A3, 1551 WEWATTA STREET
DENVER
CO
80202
US
|
Family ID: |
39358554 |
Appl. No.: |
11/593817 |
Filed: |
November 7, 2006 |
Current U.S.
Class: |
72/82 |
Current CPC
Class: |
B21D 53/28 20130101;
B21D 22/16 20130101; B21H 5/025 20130101 |
Class at
Publication: |
72/82 |
International
Class: |
B21H 5/00 20060101
B21H005/00 |
Claims
1. A method of forming a gear comprising: gripping a blank to be
spun formed in a spin forming machine; spin forming a gear having
helical teeth disposed on an inner surface; and ejecting the gear
by simultaneous extension and rotation of an ejector member and
thereby rotation of the gear being ejected.
2. The method as in claim 1 further comprising trimming excess
material from the gear.
3. The method as in claim 1 further comprising heat treating the
gear.
4. The method as in claim 1 further comprising case hardening the
gear.
5. The method as in claim 1 further comprising cutting the gear
into two or more gears.
6. The method as in claim 1 further comprising spin forming a part
on an outer surface of the gear.
Description
FIELD OF THE INVENTION
[0001] The invention relates to a method of spin forming a gear
having teeth on a radially inward oriented surface.
BACKGROUND OF THE INVENTION
[0002] Annulus gears are an integral part of most automotive
transmissions and are also used for many other industrial
applications. These gears are required to have very accurate
dimensions as well as a hardened structure to be able to transfer
power efficiently without generating noise and without failing
under the application loads.
[0003] Conventional methods of manufacturing annulus gears include
broaching, shaper cutting, or grinding the gears. Each of these are
very expensive processes with long cycle times, namely because each
tooth is made individually.
[0004] Representative of the art is U.S. Pat. No. 3,777,345 to
Brown which discloses a toothed tool for finish forming, by
rolling, a cylindrical or helical work gear, said tool having, in
the flanks of its teeth, serrations extending perpendicular to the
axis of the tool which define flutes in the tooth flanks and
intervening lands, the flutes on each tooth flank extending
alternately from the tip towards the root and from the root towards
the tip and extending along part only of the length of the tooth
flank and being so disposed that corresponding flutes on successive
tooth flanks are disposed helically on the circumference of the
tool.
[0005] What is needed is a method of spin forming a gear having
teeth on a radially inward oriented surface. The present invention
meets this need.
SUMMARY OF THE INVENTION
[0006] The primary aspect of the invention is to provide a method
of spin forming a gear having teeth on a radially inward oriented
surface.
[0007] Other aspects of the invention will be pointed out or made
obvious by the following description of the invention and the
accompanying drawings.
[0008] The invention comprises a method of forming a gear
comprising gripping a blank to be spun formed in a spin forming
machine, spin forming a gear having helical teeth disposed on an
inner surface, and ejecting the gear by simultaneous extension and
rotation of an ejector member and thereby rotation of the gear
being ejected.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The accompanying drawings, which are incorporated in and
form a part of the specification, illustrate preferred embodiments
of the present invention, and together with a description, serve to
explain the principles of the invention.
[0010] FIG. 1 is a cross sectional view of a blank.
[0011] FIG. 2 is a cross-sectional view of a spun formed part.
[0012] FIG. 3 is a cross-sectional view of a trimmed spun part.
[0013] FIG. 4 is a cross-sectional view of the forming mandrel
assembly.
[0014] FIG. 5 is a detail of FIG. 4.
[0015] FIG. 6 is a detail of the mandrel assembly.
[0016] FIG. 7 is a cross-sectional view of FIG. 2 with an overspun
portion.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0017] FIG. 1 is a cross sectional view of a blank. The first step
in manufacturing an annulus gear is spinning a blank, also known in
the art as flow forming, on a mandrel. The blank 10 may either
comprise a tube or a round flat blank stamped from sheet (plate)
metal. The blank material can be chosen from a variety of micro
alloys or alloy steels, although for lower load applications carbon
steels or low carbon steels can also be used. Some of the blank
materials that can be used include, but are not limited to,
designated European steel grades including HLB 22, HLB 27, and
27MnV6. Various US steel grades are applicable as well.
[0018] FIG. 2 is a cross-sectional view of a spun formed part. Part
20 comprises teeth 21 disposed on a radially inward inner surface.
In this embodiment teeth 21 are helical for use in transmissions
and the like or any application requiring a helical gear. Teeth 21
have an angle .alpha. to a rotational axis. Angle .alpha. may be
any required by a user. In this embodiment angle .alpha. is
approximately 20.degree.. Teeth 21 may also be straight cut as
required by a user.
[0019] Skirt 22 is an artifact of the spin forming process. Skirt
22 may be removed or further shaped in a subsequent trimming step.
Trimming may be accomplished by cutting or other suitable process
known in the art.
[0020] FIG. 3 is a cross-sectional view of a trimmed spun part.
After spinning, the extra material around the gear skirt 22 is
trimmed to the desired shape 220 and the gear is ready for heat
treatment. For example, lugs 221 may be stamped or cut in the part
depending upon the desired service.
[0021] Portion 223 is also removed by trimming to axially
"daylight" teeth 21. Removal of portion 223 may or may not be
required depending upon the intended service for the finished
gear.
[0022] Different practices recommended for the heat treatment
process to achieve the required hardness with minimal dimensional
distortions include heat treating the core and carburizing the
case, heat treating the core and carbo-nitriding the case and
through hardening. The heat treatment process utilizes a through
hardening process where the material is hardened all the way
through its core to a hardness of 30 to 40 Rockwell C (but other
hardnesses can be chosen). A case hardening is also used where a
layer of about 0.75 mm (0.030'') thick on the surface is hardened
to a hardness of about 60 Rockwell C (but other hardnesses can also
be chosen). This process, which is a known art, gives the part the
proper strength and ductility throughout its cross section in
addition to a hardened case or skin.
[0023] After heat-treating, the part is finished using known
machining methods to the tolerances required for transmission
applications and to remove the distortion caused by heat treating.
The average amount of distortion caused by heat treatment is about
0.2 mm (0.008'') for parts that are about 150 to 200 mm (6 to 8
inches) in diameter. The tolerances for annulus gears are usually
very tight and are usually in the hundredths of millimeters range.
The finishing process comprises diamond broaching where a broach
tool comprising tool steel and covered with diamond particles
embedded in chromium or nickel is used. The diamond broach moves by
advancing axially for a distance of about 2 to 6 mm, for example,
and then axially retracting a lesser distance of about 1 to 3 mm,
for example. The oscillating or pulsing action allows the ground
and shaved material to be washed away by the coolant/lubricant in
the machine allowing a better, faster, and more accurate broaching
operation. The amount of material that is removed is about 0.25 mm
which is mostly the result of heat treatment distortion.
[0024] Another method that can be used for finishing is hard
broaching where a broach needle made of tool steel is forced into
the grooves with both axially linear and rotational movement to
thereby broach the gear surfaces 21.
[0025] FIG. 4 is a cross-sectional view of the forming mandrel
assembly. A tail stock 101 and headstock 102 cooperatively engage
and grip blank 10. For reference purposes, FIG. 4 depicts the blank
in a mandrel after it has been fully spun formed 20 (see FIG.
2).
[0026] The tail stock 101 and headstock 102 are pressed together by
a hydraulic cylinder 1010 to grip and rotate the blank. The end of
headstock 102 comprises a toothed die 105. Teeth 21 are formed on
the outer surface of die 105 as the blank material is spun formed
into the die.
[0027] The headstock 102 and tailstock 101 rotate the blank.
Rotation of the headstock 102 is caused by rotation of spindle 103
which also contains the non-rotating ejector shaft 108 within.
Spindle 103 is rotated by a motor 200 which is connected to the
spindle by a belt drive 201 or any other suitable drive known in
the art.
[0028] As the blank rotates a roller 104 (or two or more rollers)
are radially pressed to the blank to form part 20, see FIG. 5. The
ejector shaft 108 and ejector cylinder 1080 do not rotate, instead
only the spindle 103, head stock 102 and tail stock 101 rotate.
[0029] Once the part 20 is formed it is ejected from the die.
Ejector shaft 108 engages part 20 by extension of ejector cylinder
1080. As the ejector cylinder 1080 is axially extended, pin 106 in
shaft 108 engages a slot 107 in portion 1070. This causes the
ejector shaft 108 and part 20 to rotate, for example, through
approximately 20.degree. as shaft 108 extends. Simultaneously, tail
stock 101 is retracted to allow ejection. Rotation of part 20 as it
is ejected causes teeth 21 to disengage and to be pressed clear of
die 105. The rotation angle (or amount of rotation) of shaft 108
substantially matches the angle of the helical gears formed in part
20 to facilitate ejection.
[0030] Spinning can be performed on an individual part or a
plurality of parts simultaneously. In the case where they are
formed simultaneously a single toothed blank is formed in a part as
described herein. The intermediate part is then removed from the
mandrel and cut to make individual annulus gears. Namely, the
formed intermediate part is an elongated version of part 20 as
described herein. The elongation is determined as a function of the
number of gears to be cut from the formed intermediate part. For
example, if three formed gears are desired, the intermediate part
has a length totaling the combined length of the three gears to be
cut therefrom.
[0031] Furthermore, the gear can either be flow formed individually
or in combination with other rotating parts of the transmission in
a stacked assembly manner to reduce the number of separate parts
required.
[0032] FIG. 7 is a cross-sectional view of FIG. 2 with an overspun
portion. A formed gear 20 either before or after heat-treating and
finishing can be placed on other flow or spin forming tooling and
another component 500 can then be spun over the part 20. Namely,
flow forming of an overlaid component 500 is accomplished on the
outer surface 222 of the otherwise spun formed part 20. In this
case, to assure a permanent lock between the part 20 and the outer
component 500, one of many engagement portions 501, i.e., grooves,
splines, blind ended screw threads, and so on can be spun formed,
broached or machined on the outside surface 222. In the
alternative, component 500 may be cast in place on surface 222 of
part 20. In another alternative component 500 may be made
separately and then pressed onto surface 222 of part 20. In either
of the foregoing alternatives, the engagement portions 501 may or
may not be used depending on the service conditions for the
finished component.
[0033] FIG. 5 is a detail of FIG. 4. Roller 104 comprises an outer
surface 1040. Surface 1040 comprises a shape suitable to form the
outer surface 222 of the gear 20. One, two, three, or more shaping
rollers 104 may be used simultaneously, although the preferred
arrangement is three rollers located in 120 degree arrangement. The
three roller configuration avoids creation of any out-of-roundness
as the part is being spun formed. Rollers 104 may be moved
vertically and horizontally in the "x" or "y" direction during the
spin forming process.
[0034] FIG. 6 is a detail of the mandrel assembly. Pin 106 is
guided by slot 107 as part 20 is ejected. As the part is ejected is
rotates in direction "R". Once the part 20 is ejected a new blank
10 can then be placed in position and the process repeated. Ejector
shaft 108 is guided within and slides within head stock 012.
[0035] Although a form of the invention has been described herein,
it will be obvious to those skilled in the art that variations may
be made in the construction and relation of parts without departing
from the spirit and scope of the invention described herein.
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