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(11) | EP 0 114 108 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Method for cold sizing a round workpiece having multiple diameters |
| (57) A method and apparatus (12) for cold sizing a round workpiece (14) having round surfaces
of cylindrical shapes that are coaxial about a central axis A of the workpiece and
have different diameters. A support (54, 55) rotatably mounts the workpiece (14) about
its central axis A between a pair of die assemblies (24a, 24b) which are spaced from
each other. Each die assembly (24a, 24b) includes a plurality of dies (56, 58, 60,
62) that are respectively aligned with the round surface (46, 48, 50, 52) of the workpiece
(14). Movement of the die assemblies in opposite directions as each other engages
sizing surfaces (66, 68, 70, 72) of the dies with the aligned round surfaces of the
workpiece to pressure size the workpiece surfaces. In one embodiment of the sizing
apparatus (12), the dies assemblies (24a, 24b) have elongated shapes and are moved
rectilinearly in a parallel relationship to each other to perform the sizing. Another
rotary embodiment of the sizing apparatus (12') includes rotary die assemblies (24a',
24b') mounted by associated spindles (85) whose rotation likewise pressure sizes the
round workpiece surfaces. Both embodiments of the sizing apparatus are disclosed as
including forming projections for forming projections for forming projections such
as splines (82) and/or helical thread (84) on the sized surfaces of the workpiece. |
TECHNICAL FIELD
[0001] This invention relates to a method and apparatus for cold sizing a workpiece having multiple diameters.
BACKGROUND ART
[0002] Round metal parts are conventionally accurately sized after an initial turning operation by a subsequent grinding operation in order to provide the required tolerance for the application for which the workpiece is to be utilized. For example, universal joints for vehicle drives conventionally include a joint member having four round surfaces of cylindrical shapes that are coaxial about a central axis of the joint member and have different diameters. The largest round surface is utilized with a seal to provide sealing of the joint, while the next largest round surface supports a bearing that mounts the joint. Both of the two smaller round surfaces are subsequently formed with projections, the larger one with splines utilized to rotatively couple the joint and the smaller one with a thread used in securing the joint in position. Grinding of these round surfaces on such joint members is both time consuming and costly but has been necessary in the past to provide the required roundness for accommodating the seal and bearing utilized as well as for providing the required roundness prior to the spline and thread forming.
[0003] A cooperable pair of movable tools has also been utilized in the past to cold form noncylindrical workpieces. See, for example, U.S. Patents 419,292, 446,934, 1,446,447, 1,469,174, 3,044,332, 3,466,918, 3,498,095, and 3,503,237 which disclose such forming.
[0004] Hot forming of an axle having round surfaces of cylindrical shapes with different diameters is disclosed by U.S. Patent 458,685 wherein a pair of straight tools are moved rectilinearly on opposite sides of the hot axle to provide the forming operation.
[0005] U.S. Patent 625,575 discloses a pair of straight tools that are moved rectilinearly to cold form a workpiece having a single cylindrical surface of a round shape.
[0006] Also, U.S. Patent 2,825,251 discloses a pair of tools used to perform forming by holding one of the tools stationary and moving the other one with the workpiece between the two tools.
DISCLOSURE OF INVENTION
[0007] An object of the present invention is to provide an improved method and apparatus for cold sizing a workpiece having a central axis and a plurality of round surfaces of cylindrical shapes that are coaxial about the central axis and have different diameters.
[0008] In carrying out the above object, the method is performed by mounting the workpiece for rotation about its central axis between a pair of die assemblies. Each of the die assemblies utilized includes a plurality of dies having sizing surfaces that extend parallel to the central axis of the workpiece respectively in alignment with the round surfaces of the workpiece. Movement of the die assemblies in opposite directions as each other engages the sizing surfaces of the dies with the round surfaces of the workpiece as the workpiece rotates about its central axis such that the sizing surfaces pressure size the round surfaces of the workpiece.
[0009] Pressure sizing of the workpiece can be performed by two different preferred ways in which the method is practiced. In one preferred practice of the method, the die assemblies are moved rectilinearly in opposite directions as each other and the dies thereof are provided with flat sizing surfaces that engage the round surfaces of the workpiece at diametrically opposite locations. In another preferred practice of the method, the die assemblies are rotated and the dies thereof have round sizing surfaces that engage the round surfaces of the workpiece at diametrically opposite locations.
[0010] In performing the method, it is also possible to continue the movement of the die assemblies in order to engage forming projections on the trailing end of one die of each die assembly with the aligned round surface of the workpiece to thereby form projections on this aligned round surface of the workpiece. Such projection forming can be utilized to provide splines on one of the round surfaces and can also be utilized to subsequently provide a helical thread on another round surface of the workpiece.
[0011] In the preferred practice-of the method disclosed, splines are formed on one of the round surfaces of the workpiece and a helical thread is formed on another round surface during successive operations after the initial sizing. It should be noted that only one round surface of the workpiece can be formed with projections at any given time due to the fact that the round surfaces have different speeds of circumferential movement for any given rate of workpiece rotation and the die assemblies can each only have a single speed at any given time due to their meshed relationship with the workpiece at the projections being formed. To perform sizing and subsequent projection forming of certain types of workpieces, a particular machine with which the apparatus is utilized may not have sufficient die length to permit the complete operation to be performed during a single movement of the die assemblies in opposite directions as each other. In such cases, the workpiece can be axially shifted to engage one of the round surfaces with forming projections on one die of each die assembly as the direction of movement is reversed.
[0012] It should be noted that during the initial sizing operation, sliding takes place between at least one of the round surfaces of the workpiece and the associated dies due to the difference in speeds thereof with the die assemblies moving only at a single speed. This is possible due to the fact that the sizing performed by the die assemblies initially only forms cylindrical shapes that do not present any interlocking relationship with the sizing surfaces of the dies of the die assembly. However, during subsequent forming of workpiece projections, the meshed relationship of the die projections and the workpiece projections being formed prevents forming of projections on more than one round surface of the workpiece at any given time as previously mentioned.
[0013] The object of the invention is also carried out by the apparatus that is utilized to cold size the workpiece. This apparatus includes a support for rotatably mounting the workpiece about its central axis and also includes a pair of die assemblies mounted for movement with the workpiece between the die assemblies. Each die assembly of the apparatus includes a plurality of dies respectively aligned with the round workpiece surfaces of different diameters. Each die has a sizing surface that extends parallel to the workpiece axis and engages the aligned round surface of the workpiece upon movement of the die assemblies as the workpiece rotates about its central axis such that the sizing surfaces pressure size the round surfaces of the workpiece.
[0014] In one preferred embodiment disclosed, the pair of die assemblies have elongated shapes and have dies with flat sizing surfaces. These elongated die assemblies are mounted for rectilinear movement in a parallel relationship to each other to perform the pressure sizing of the round surfaces of the workpiece by engagement therewith at diametrically opposite locations. A machine including lower and upper bases that define a work space therebetween is preferably utilized to mount the elongated die assemblies for their rectilinear movement in a parallel relationship to each other. Suitable slideways provided on the upper and lower.bases of the machine respectively mount the pair of elongated die assemblies for such rectilinear movement in the parallel relationship.
[0015] Another preferred embodiment of the apparatus includes a pair of rotary die assemblies having dies with round sizing surfaces. These rotary die assemblies are respectively mounted by a pair of spindles for rotary movement to perform the pressure sizing of the round surfaces of the workpiece at diametrically opposite locations. Each spindle is disclosed as including a clamp mechanism that clamps the rotary dies of the associated die assembly to perform the pressure sizing upon spindle rotation.
[0016] In both preferred embodiments of the apparatus, one of the dies of each die assembly includes a trailing end having projections for forming projections in the aligned round surface of the workpiece. Such projections can be provided on the trailing ends of different dies of each die assembly but at different locations along the length thereof in order to permit successive forming of the projections on different round surfaces of the workpiece such as the spline and thread froming previously discussed.
[0017] It should be mentioned that only a relatively small reduction takes place in the diameters of the round surfaces of the workpiece as the pressure sizing is performed. Such diameter reduction is always less than twenty thousandths of an inch and preferably less than ten thousandths of an inch. In the most preferred practice of the invention, the diameter reduction during the pressure sizing is only on the order of about four to six thousandths of an inch. This latter range in diameter reduction has been found to give accurate sizing of the round surfaces even with the relative sliding that takes place between the dies and certain of the round workpiece surfaces due to the different rates of speed as previously mentioned.
[0018] Also, it should be noted that the dies of each die assembly are disclosed as being separable from each other since this is the easiest and hence most economical way to manufacture the die assembly. However, in certain applications, it may be possible to utilize a die assembly wherein the dies are all made unitary with each other. Such unitary die assemblies would be more difficult to manufacture and hence more costly but, nevertheless, could be used to practice the invention.
[0019] The objects, features, and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings.
BRIEF DESCRIPTION OF DRAWINGS
[0020]
Figure 1 is a schematic front view of a machine including apparatus constructed in accordance with the invention to perform the cold sizing method thereof on a round workpiece;
Figure 2 is a sectional view taken along the direction of line 2-2 in Figure 1 to illustrate elongated die assemblies which are moved rectilinearily in opposite directions as each other to perform the cold sizing operation;
Figure 3 is a schematic view of another embodiment of apparatus constructed in accordance with the invention to perform the cold sizing method by rotary movement of a pair of rotary die assemblies;
Figure 4 is a sectional view taken along the direction of line 4-4 in Figure 3 to illustrate the construction of the rotary die assemblies;
Figure 5 is a view illustrating the workpiece after cold sizing thereof has been performed; and
Figure 6 is a view which illustrates the workpiece after projections in the form of splines and a thread have been formed on its two smallest round surfaces.
BEST MODES FOR CARRYING OUT THE INVENTION
[0021] With reference to Figure 1 of the drawings, a schematically illustrated machine is generally indicated by reference numeral 10 and includes apparatus 12 constructed in accordance with the present invention to cold size a round workpiece 14 at room temperature as is hereinafter more fully described. Machine 10 includes a lower base 16, an upper base 18, and a rear connecting portion 20 that cooperatively define a work space 22 in which the sizing apparatus 12 is located. Elongated lower and upper die assemblies 24a and 24b are respectively mounted on the lower and upper bases 16 and 18 by suitable slides 26 (Figure 2) that are movable along slideways 28 of the bases. These slideways 28 extend in a parallel relationship to each other as shown in Figure 1 such that operation of a schematically indicated drive mechanism 30 moves the die assemblies 24a and 24b in a parallel relationship to each other as illustrated by arrows 32. Drive mechanism 30 may be of any suitable type such as, for example, the one disclosed by United States Patent 3,793,866.
[0022] As seen in Figure 2, a pair of tool boxes 34 are respectively mounted on the pair of slides 26 above and below the workpiece 14. Each tool box 34 includes horizontal and vertical legs 36 and 38 for providing vertical and lateral support to dies of the die assemblies 24a and 24b as is hereinafter more fully described.
[0023] As illustrated in Figure 2, the round workpiece 14 is shown as the female member of a universal joint of the type used in vehicle drives. This universal joint member 14 has a central axis A and includes a cup shaped end 40 whose interior has grooves 42 for receiving balls that provide a coupling -thereof to a male joint member which is not shown. A shaft 44 of joint member 14 projects toward the left from its cup-shaped end 40 and includes round surfaces 46, 48, 50, and 52. These round surfaces have cylindrical shapes that are coaxial about the central axis A of the joint member 14 and have different diameters than each other. The largest diameter round suface 46 immediately adjacent the cup shaped end 40 of the joint member 14 is used to mount a seal that is used with the joint, while the next smaller round surface 48 receives a bearing that is utilized to mount the joint member during use. As is hereinafter more fully described, the round surface 50 which is just slightly smaller than the round surface 48 is ultimately provided with splines to couple the joint during use. The smallest round surface 52 is ultimately provided with a helical thread for receiving a suitable nut that secures the joint member in position during use.
[0024] As illustrated in Figure 2, apparatus 12 includes a workpiece support having a headstock center 54 and a tailstock center 55 that rotatably mount the workpiece 14 about its central axis A. Headstock center 54 is mounted in a suitable manner on the connecting portion 20 of the machine 10 illustrated in Figure 1, while the tailstock center 55 is mounted in a suitable manner on an unshown arm that projects forwardly from either the lower base 16 or the upper base 18 of the machine.
[0025] As illustrated in Figure 2, each of the pair of die assemblies 24a and 24b includes a plurality of dies 56, 58, 60, and 62 mounted on the associated tool box 34 for movement with the slide 26 on which the tool box is mounted. Unshown end clamps and/or unshown bolts secure the dies to the horizontal leg 36 of the tool box 34 and cooperate with bolts 64 that secure the dies to the vertical leg 38 of the associated tool box. Dies 56, 58, 60, and 62 have associated sizing surfaces 66, 68, 70, and 72 of a flat shape that extend parallel to each other and to the central axis A of the rotatably mounted workpiece 14 respectively in alignment with its round surfaces 46, 48, 50, and 42. Operation of the drive mechanism 30 moves the die assemblies 24a and 24b in opposite directions as each other as illustrated by arrows 32 to engage the sizing surfaces 66, 68, 70 and 72 at diametrically opposite locations with the round surfaces 46, 48, 50 and 52 of the workpiece 14 as the workpiece rotates about its central axis A. The spacing between the sizing surfaces on the lower and upper die assemblies 24a and 24b is such that the round workpiece surfaces 46, 48, 50, and 52 are pressure sized during the die assembly movement to provide accuracy in the roundness thereof as well as removal of surface defects.
[0026] It should be noted that during the sizing operation described above, only one of the workpiece surfaces and the aligned die engage each other in a rolling manner, while the other workpiece surfaces are engaged by their aligned dies in a combined rolling and sliding manner. Such sliding along with the rolling accommodates for the difference in speed of the different diameter surfaces and the fact that the die assemblies can only move at a single speed. The particular workpiece surface at which just rolling takes place depends upon the extent of friction. generated at the surfaces and the balancing of the resultant torques applied to workpiece 14.
[0027] After the initial sizing, the universal joint member 14 has the construction illustrated in Figure 5 where its round surfaces 46, 48, 50 and 52 are slightly smaller than the initial size. The reduction in size of the diameters of the round surfaces is very small as it is always less than twenty thousandths of an inch. Preferably, the reduction in the diameters of the round surfaces is less than ten thousandths of an inch and, most preferably, in the range of about four to six thousandths of an inch.
[0028] As illustrated in Figure 1, one of the dies 60 of each die assembly includes a trailing end 74 having projections 76 for forming projections in the aligned round surface 50 of the workpiece 14. Similarly, one of the dies 62 of each die assembly includes a trailing end 78 having projections 80 for forming projections in the aligned round surface 52 of the workpiece. As illustrated in Figure 6, the universal joint member 14 has its round surface 50 provided with projections in the form of splines 82 while the round surface 52 has its projections provided in the form of a helical thread 84. It should be noted that the projections can only be formed on a single round surface of the workpiece at any given time due to the difference in speeds of the different surfaces as previously discussed. Also, with certain machines, there may not be a sufficient stroke length of the die assemblies to provide the sizing and subsequent splining and threading operations. In such case, one or both of the projection forming operations can be performed during a reverse stroking of the die assemblies after first axially shifting the workpiece into alignment with dies having suitable projections for providing the required forming operations after the initial sizing.
[0029] After the complete operation, the drive mechanism 30 drives the die assemblies 24a and 24b out of engagement with the completed workpiece 14. This can be done by continuing the movement in the direction of arrows 32 in Figure 1 or, if no projections are formed, by reversing the direction for return stroking movement back to an end to end relationship of the die assemblies. Upon disengagement of the dies from the workpiece surfaces, the workpiece is removed from between the die assemblies for use or any further processing that may be necessary. If the workpiece removal is performed without any reversal, a return stroking movement must be performed prior to the next cycle.
[0030] With reference to Figures 3 and 4, another preferred embodiment of apparatus constructed in accordance with the invention to provice cold sizing of a round workpiece at room temperature is indicated generally by reference numeral 12' and includes a pair of rotary die assemblies 24a' and 24b' spaced on opposite sides of the workpiece 14. A pair of spindles 85 respectively support the pair of die assemblies 24a' and 24b' for rotation about associated axes B spaced on opposite sides of the workpiece axis A along which the workpiece 14 is rotatably mounted by the support provided by a headstock center 54 and tailstock center 55.
[0031] Each of the rotary die assemblies 24a' and 24b' includes a plurality of rotary dies 86, 88, 90, and 92 respectively aligned with the round surfaces 46, 48, 50, and 52 of the workpiece 14. These rotary dies each have an annular shape through whose center a shaft 94 of the associated spindle 85 extends along the axes B about which the rotary die assemblies are rotatively driven in any suitable manner. Rotary dies 86, 88, 90, and 92 have round sizing surfaces 96, 98, 100, and 102 that extend parallel to the central axis A of the workpiece 14 and engage the aligned round surfaces 46, 48, 50, and 52 of the workpiece upon rotary movement of the die assemblies 24a' and 24b' in the clockwise direction as illustrated by arrows 104 in Figure 3. Suitable notches 106 are provided in the dies to permit the axial positioning of the workpiece 14 therebetween in preparation for the sizing operation performed by the apparatus 12'.
[0032] A suitable drive mechanism, such as of the general type disclosed by U.S. Patent 4,045,988, drives the rotary spindles 24a' and 24b' of apparatus 12' to engage the round sizing surfaces 96, 98, 100, and 102 of the rotary dies with the aligned round surfaces 46, 48, 50, and 52 of the workpiece 14 as the workpiece rotates about its central axis A. Such engagement of the dies with the workpiece pressure sizes the round surfaces of the workpiece to provide accuracy in the roundness thereof as well as removing surface defects.
[0033] Sizing performed by the rotary sizing apparatus 12' of Figures 3 and 4 like the linear embodiment previously described only reduces the diameter of the round workpiece surfaces a very small extent which is always less than twenty thousandths of an inch. This diameter reduction with the rotary embodiment like the linear embodiment is preferably less than ten thousandths of an inch and, most preferably, in the range of four to six thousandths of an inch.
[0034] With reference to Figure 4, each of the die spindles 85 includes a flange 106 that engages the adjacent rotary die 92. A threaded portion 108 of each spindle 85 receives a nut 110 that engages the adjacent rotary die 86 to cooperate with the flange 106 in providing a clamp mechanism for clamping the rotary dies in a stacked relationship.
[0035] One of the rotary dies 90 of each rotary die assembly 24a' and 24b' includes a trailing end 112 provided with projections 114 for forming projections on the aligned round surface 50 of the workpiece 14. Like the embodiment of Figures 1 and 2, the projections formed on the round surface 50 are splines 82 as illustrated in Figure 6 when the workpiece is a universal joint member 14 of the type previously described. Likewise, one die 92 of each rotary die assembly has a trailing end 116 including projections 118 for forming projections on the round surface 52 of the workpiece 14. These projections 118 are in the form of the helical thread 84 illustrated in Figure 6 when the workpiece is a universal joint member 14 as previously discussed.
[0036] With the rotary embodiment 12' of the sizing apparatus, no return stroke in a reverse direction is necessary as with the linear embodiment of Figures 1 and 2. A reduced cycle time can thereby be achieved with the rotary sizing apparatus. Also, the rotary apparatus 12' like the linear apparatus only reduces the diameters of the workpiece surfaces a very small extend as previously described.
[0037] It should be appreciated that the invention can be carried out in its broadest practice by sizing of a workpiece having a plurality of round surfaces of different diameters without any subsequent projection forming. However, the apparatus and method disclosed have particular utility when constructed and utilized to perform subsequent projection forming such as the splines and/or thread previously discussed. Separate operations previously required can be eliminated by this single processing of the workpiece to thereby reduce its cost.
[0038] It should be appreciated that both embodiments 12 and 12' of the die assemblies can also be constructed with the dies thereof unitary with each. other rather than separable as shown. However, it is much easier and hence economical to manufacture the dies separate from each other which is the reason that such a construction is illustrated.
1. A method for cold sizing a workpiece having a central axis and a plurality of round
surfaces of cylindrical shapes that are coaxial about the central axis and have different
diameters, the method comprising: mounting the workpiece for rotation about the central
axis between a pair of_die assemblies each of which includes a plurality of dies having
sizing surfaces that extend parallel to the central axis of the workpiece respectively
in alignment with the round surfaces of the workpiece; and moving the die assemblies
in opposite directions as each other to engage the sizing surfaces of the dies with
the round surfaces of the workpiece as the workpiece rotates about the central axis
thereof-such that the sizing surfaces pressure size the round surfaces of the workpiece.
2. A method as in Claim 1 wherein the die assemblies are moved rectilinearly in opposite
directions as each other and have the dies thereof provided with flat sizing surfaces.
3. A method as in Claim 1 wherein the die assemblies are rotated and have the dies
thereof provided with round sizing surfaces.
4. A method as in Claim 1 wherein the movement of the die assemblies is continued
to engage forming projections on the trailing end of one die of each die assembly
with the aligned round surface of the workpiece to thereby form projections on said
aligned round surface of the workpiece.
5. A method for cold sizing a workpiece having a central axis and a plurality of round
surfaces of cylindrical shapes that are coaxial about the central axis and have different
diameters, the method comprising: mounting the workpiece for rotation about the central
axis between a pair of die assemblies each of which includes a plurality of dies having
flat sizing surfaces that extend parallel to the central axis and to each other in
respctive alignment with the round surfaces of the workpiece; moving the die assemblies
rectilinearly in a parallel relationship to each other in opposite directions to engage
the sizing surfaces of the dies with the round surfaces of the workpiece at diametrically
opposite locations as the workpiece rotates about the central axis thereof such that
the sizing surfaces pressure size the round surfaces of the workpiece; and thereafter
continuing the rectilinear movement of the die assemblies in opposite directions to
engage forming projections on a trailing end of one die of each die assembly with
one round surface of the workpiece to form projections on said one round surface of
the workpiece.
6. A method for cold sizing a workpiece having a central axis and a plurality of round
surfaces of cylindrical shapes that are coaxial about the central axis and have different
diameters, the method comprising: mounting the workpiece for rotation about the central
axis between a pair of die assemblies each of which includes a plurality of dies having
round sizing surfaces that extend parallel to the central axis in respective alignment
with the round surfaces of the workpiece; rotating the die assemblies to engage the
sizing surfaces of the dies with the round surfaces of the workpiece at diametrically
opposite locations as the workpiece rotates about the central axis thereof such that
the sizing surfaces pressure size the round surfaces of the workpiece; and thereafter
continuing the rotation of the die assemblies to engage forming projections on a trailing
end of one die of each die assembly with one round surface of the workpiece to form
projections on said one round surface of the workpiece.
7. Apparatus for colding sizing a workpiece having a central axis and a plurality of
round surfaces of cylindrical shapes that are coaxial about the central axis and have
different diameters, the apparatus comprising: a support for rotatably mounting the
workpiece about its central axis; a pair of die assemblies mounted for movement with
the workpiece therebetween; each die assembly including a plurality of dies respectively
aligned with the round surfaces of the workpiece; and each die having a sizing surface
that extends parallel to the workpiece axis and engages the aligned round surface
of the workpiece upon movement of the die assemblies as the workpiece rotates about
its central axis such that the sizing surfaces pressure size the round surfaces of
the workpiece.
8. Apparatus as in Claim 7 wherein the pair of die assemblies have dies with flat
sizing surfaces and are mounted for rectilinear movement in a parallel relationship
to each other to perform the pressure sizing of the round surfaces of the workpiece.
9. Apparatus as in Claim 7 wherein the pair of die assemblies have dies with round
sizing surfaces and are mounted for rotary movement to perform the pressure sizing
of the round surfaces of the workpiece.
10. Apparatus as in Claim 7 wherein one of the dies of each die assembly includes
a trailing end having projections for forming projections in the aligned round surface
of the workpiece.
11. Apparatus for cold sizing a workpiece having a central axis and a plurality of
round surfaces of cylindrical shapes that are coaxial about the central axis and have
different diameters, the apparatus comprising: a support for rotatably mounting the
workpiece about its central axis; a pair of elongated die assemblies mounted for rectilinear
movement in a parallel realtionship to each other on opposite sides of the workpiece;
each die assembly including a plurality of elongated dies respectively aligned with
the round surfaces of the workpiece; each die having a flat sizing surface that extends
parallel to the central axis of the workpiece and engages the aligned round surface
of the workpiece upon rectilinear movement of the die assemblies as the workpiece
rotates about its central axis such that the flat sizing surfaces pressure size the
round surfaces of the workpiece; and one die of each die assembly including a trailing
end having projections for forming, projections in the aligned round surface of the
workpiece.
12. Apparatus for cold sizing a workpiece having a central axis and a plurality of
round surfaces of cylindrical shapes that are coaxial about the central axis and have
different diameters, the apparatus comprising: a support for rotatably mounting the
workpiece about its central axis; a pair of rotary die assemblies mounted for rotation
on opposite sides of the workpiece about associated axes that extend parallel to the
central axis of the workpiece; each die assembly including a plurality of rotary dies
respectively aligned with the round surfaces of the workpiece; each die having a round
sizing surface that extends parallel to the central axis of the workpiece and engages
the aligned round surface of the workpiece upon rotary movement of the die assemblies
as the workpiece rotates about its central axis such that the round sizing surfaces
pressure size the round surfaces of the workpiece; and one die of each die assembly
including a trailing end having projections for forming projections in the aligned
round surface of the workpiece.