Apparatus For Roll Forming Workpieces

Abstract

Apparatus for forming toothed workpieces by rolling them in high pressure contact with a single forming die, the workpieces being held in precise relation with the die during at least the final stage of the rolling operation by locating members associated, respectively, with the workpiece and the basic machine, the locating members being in rolling contact during at least the final stages of the rolling operation.

Description

BACKGROUND OF THE INVENTION

This invention relates to apparatus for roll forming toothed workpieces and has particular application to the formation of parts, such as automotive transmission gears, which must meet unusually exacting standards for dimensional accuracy and quality of finish.

For many years, parts of this kind were manufactured by first hobbing a cylindrical blank to form the gear to a configuration closely approximating the final desired form and then forming the gear to final dimensions by shaving. While this system provided gears of adequate quality, satisfactory production rates could be achieved only by the use of a large number of bulky and expensive machines which required constant maintenance, attention and replacement of critical parts. Frequently the hobbing equipment introduced errors into the partially finished workpiece which were beyond the capacity of the shaving equipment or the production of an unacceptably high percentage of scrap parts.

In recognition of the deficiencies of the hobbing-shaving technique it has been proposed to substitute, for the final shaving operation, a roll finishing operation. Apparatus of this kind is disclosed in U.S. Pat. No. 3,362,059 owned by the Ford Motor Company and U.S. Pat. No. 3,533,258 owned by applicant's assignee. In general this type of apparatus comprises a pair of rotating dies, one of which rotates about a fixed axis and the other rotates about a laterally displaceable axis. The workpiece is rotatably mounted upon an axis which lies in the plane of the axes of the two dies and the axis of the workpiece is shifted laterally toward and away from the axis of the fixed axis die, the workpiece thus being engaged under high pressure at peripherally opposite points by the two dies. When the dies have reached the final rolling position the parts are rotated together during a short dwell period to finish the part to final dimensions after which the displaceable die is retracted and the workpiece is simultaneously retracted sufficiently to clear both dies and is then removed and replaced with an unfinished workpiece. This type of apparatus, particularly as disclosed and claimed in the aforesaid U.S. Pat. No. 3,533,258, has recently come into widespread use and for many operations has completely replaced the formerly used shaving equipment. Despite its many advantages and its excellent performance, this type of apparatus, nevertheless, is sufficiently expensive so that it is feasible only in environments where high production rates are the rule. Also it requires a pair of rolls or forming dies which are exactly matched and which must be installed with the utmost precision during initial setup of a machine and which must be operated through an expensive essentially zero backlash drive system to maintain the two dies in matched relation with the desired accuracy during operation.

SUMMARY OF THE INVENTION

With the foregoing considerations in mind it is the principal purpose and object of the present invention to provide improved apparatus for roll forming, particularly roll finishing, toothed workpieces which retain all of the performance advantages of prior rolling machines and yet which can be manufactured and sold at a cost which may be as little as 50 percent of the cost of prior machines.

It is also an object of the present invention to provide improved roll forming apparatus which eliminates the requirement for the manufacture of a pair of exactly matched dies heretofore necessary and which greatly simplifies the initial setup procedure thus further reducing operational costs.

In attaining these and other objects the present invention involves a significant departure from prior practice and provides an apparatus in which the roll forming is accomplished entirely by one die.

Heretofore, the performance of the rolling operation for high precision work by one die has been regarded as unattainable for the reason that the workpiece could not be held in position for final rolling except by an opposed force provided by a second opposed die in rolling contact with the workpiece at an area 180.degree. from the area of contact between the first die and the workpiece.

It has been established by extensive tests that in high precision work it is impossible, within the limits of practicality, to provide a workpiece support of sufficient rigidity to position the axis of the workpiece with the required precision during the rolling operation if the rolling operation is performed by one unopposed die.

In accordance with the present invention the workpiece is typically mounted for rotation on a workpiece support positioned between a pair of arbors, one of which is driven and carries a forming die or roll. The opposed arbor, which may be freely rotatable or driven, carries one or more pilot members having cylindrical surfaces which run in rolling contact with the cylindrical surfaces of corresponding pilot members carried by and rotatable with the workpiece support structure. As used herein, the terms "cylindrical" or "cylinder" include surfaces which are slightly crowned to avoid stress concentration. Since it is of critical importance that the axis of the workpiece be parallel with the axis of the forming die during rolling, the pilot members are preferably located as close as possible to the opposite ends of the workpiece to minimize cantilever or beam loads.

By virtue of this unique arrangement the workpiece support is subjected to no significant loads during rolling, the rolling loads being absorbed by the pilot members and the machine base.

In prior apparatus of the type using a pair of opposed dies to perform the rolling operation it was necessary, not only to manufacture the individual dies with the utmost care and precision, but also to match the dies substantially exactly to avoid the imposition of high localized stresses either on the dies or the workpiece during the rolling operation.

It was also necessary to set up the machine initially so that the two opposed dies were positionally matched substantially exactly and to employ an expensive drive mechanism to maintain this exact correlation during the rolling operation. All of these complexities are eliminated by the present invention.

Additional objects and advantages of the present invention will become apparent as the description proceeds.

DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a gear rolling apparatus constructed in accordance with the present invention;

FIG. 2 is a horizontal section taken along line 2-2 of FIG. 1 illustrating details of the workpiece support mechanism; and

FIG. 3 is an essentially central vertical section illustrating details of the workpiece feeding and discharging mechanism.

DESCRIPTION OF PREFERRED EMBODIMENTS

The rolling machine of the present invention comprises a rigid base structure indicated generally at 20 having a heavy rigid upwardly extending portion 22. The components 20 and 22 enclose or support all of the drive and control apparatus, which is essentially conventional and has been omitted as being unnecessary to an understanding of the invention.

Mounted on the base structure 20 is a lower spindle head assembly 24 comprising an adjustable base section 26 and a pair of upstanding arms 28 and 30 in which the spindle proper 32 is journaled. Supported for free rotation on the spindle 32 are a pair of identical pilot or backup members 34 and 36 having cylindrical peripheral pilot surfaces 38 and 40 respectively. If desired, the pilot surfaces may be formed on a single pilot member. Depending upon the desired mode of operation of the machine the lower spindle head 24 may be fixed in operation or may be coupled to a hydraulic cylinder carried within the base structure 20 which may elevate the spindle assembly during the rolling operation to establish the desired rolling pressure and the lower it to relieve the rolling pressure. An upper spindle head assembly, indicated generally at 42, is carried by the upper machine structure 22. The upper spindle head comprises a pair of arms 44 and 46 formed integrally with or suitably connected structure 22. Spindle proper 50, journaled in the arms 44 and 46, is driven by a suitable drive mechanism indicated at 52 to drive the forming roll or die 54 carried by the spindle at a suitable speed to perform the rolling operation. Preferably the upper spindle head incorporates means providing for size adjustment as well as taper and skew adjustment.

To minimize deflection of the system under rolling loads heavy tie bars 55 connect the structure adjacent to the upper and lower spindle heads.

Typically, the die 54 is provided with peripheral teeth which are conjugate to the teeth to be produced on the workpiece. One of several dies suitable for this application is disclosed in the aforesaid U.S. Pat. No. 3,362,059.

The workpiece W is positioned before, during and after the rolling operation on a fixture indicated generally at 56. The entire fixture assembly 56 is mounted for limited horizontal movement along suitable slideways 57 provided in the machine structure 22. The movement of the fixture is effected by a hydraulic cylinder 58, the piston rod 60 of which is connected to the fixture as at 62. The fixture assembly 56 includes a pair of laterally projecting arms 64 and 66 which carry a primary workpiece support and pilot assembly 68 and a secondary workpiece support and pilot assembly 70. The primary assembly 68 comprises a primary work support member 71 rotatably supported in preloaded precision bearing assemblies 72 and 74 carried by a housing 76 mounted for horizontal sliding movement between work holding and work releasing positions on suitable slideways 78 and the fixture arm 64. The primary work support assembly 68 is moved between its limit positions by the piston rod 80 of an air or hydraulic cylinder 82 carried by the end of arm 64. The secondary work support assembly 70 comprises a secondary work support member 84 rotatably supported on preloaded precision bearings 86 and 88 carried by the fixture arm 66.

The primary and secondary workpiece supports cooperate to straddle support the workpiece to position the workpiece with the utmost accuracy during the rolling operation, to maintain the axis of the workpiece in exact parallelism with the axis of the die 54, to hold the workpiece against axial movement, and, in cooperation with the pilot members 34 and 36, to transmit the rolling loads directly to the machine base 20 without loading the fixture assembly 56. To accomplish all of these objectives the primary work support member 70 is provided with a cylindrical extension 90 adapted to fit within minimum tolerance within a machined through bore 92 in the workpiece W. The projecting end of the extension 90 fits in close clearance relation within a socket 94 in the secondary work support member 84 to provide the required straddle support.

The primary and secondary work support members are provided with enlarged cylindrical portions 96 and 98, respectively, the cylindrical surfaces 100 and 102 of which are in rolling contact with the corresponding surfaces 38 and 40 of the pilot members 34 and 36 during the the cylindrical operation. Finally the end faces 104 and 106 of the cylindrical sections 96 and 98 are carefully finished to engage correspondingly finished surfaces 108 and 110 on the workpiece. The surface 106 on the secondary work support member provides the primary gauging surface against which the workpiece is urged by the secondary work support member by the cylinder 82. Thus, when the parts are in the position shown in FIG. 2 the workpiece is in the exact axial position required for rolling and is firmly held in this position throughout the rolling operation.

The apparatus of the present invention also comprises means for automatically feeding a series of workpieces to the machine and for discharging the finished workpieces to a convenient point of collection. This aspect of the invention will now be described with particular reference to FIG. 3.

Incoming workpieces are fed to a magazine 112 having a downwardly inclined chute portion 114 through which a series of workpieces passes by gravity. The lowermost workpiece passes for the lower end of the chute 114 onto an elevator 116 carried by the piston rod 118 of an air or hydraulic cylinder 120 suitably mounted in the magazine assembly 112. The cylinder moves the elevator 116 between a retracted position shown in FIG. 3 in alignment with the lower end of the work chute and an upper position in which the axis of the workpiece is aligned with the axes of the primary and secondary work support members when the fixture assembly 56 is advanced to the left as viewed in FIG. 3. When the fixture is so advanced, a roller 121 carried by an arm 122 mounted on a tie rod 124 extending between the ends of the fixture arms 64 and 66 contacts the lowermost workpiece in the chute 114 to restrain the flow of workpieces against downward movement while the elevator 116 is away from its retracted position. When the fixture assembly is retracted to the right as viewed in FIG. 3 roller 121 moves away from its holding position and permits the next workpiece to drop into the elevator 116.

Finished workpieces are delivered from the apparatus through a chute assembly 126 extending rearwardly and downwardly through the portion 22 of the machine. The upper side of the entrance portion of the chute is formed by an inclined surface of the work fixture 56, the surface being covered by a nylon plate 128. The lower portion of the entrance of the chute is formed by a plate 130 rockable about a pivot 132 between an inactive position shown in full lines in FIG. 3 and an active position shown in dotted lines. The plate 130 normally occupies its inactive position and is moved to its active position by a roller 134 carried by the fixture assembly which contracts an operating arm 136 rigidly connected to the plate 130. When the fixture is fully retracted following a completion of the rolling operation, the surface of the plate 128 is disposed in substantial alignment with the upper surface of the chute 126 and the plate 130 is moved to its active position. Accordingly, when the workpiece is released from the primary and secondary work support members it drops into the chute following a path which closely confines its movement to assure that the workpiece cannot become reengaged with the die 54 and cannot fall onto the lower pilot members 34 or 36 or the lower spindle mechanism.

The overall operation of the apparatus will now be considered, it being understood that fully automatic operation of the apparatus is effected by the use of conventional air or hydraulic circuits and control systems which per se form no part of the present invention and thus have been omitted as being unnecessary to an understanding of the invention.

Two modes of operation are contemplated. In the first, the workpiece is drawn laterally through the throat formed between the die 54 and the pilot members 34 and 36, the axis of which are fixed throughout the rolling operation. In the other mode of operation, the die 54 rotates about a fixed axis but the axis of the lower spindle head is raised during the operation to establish the desired rolling force and to assure penetration of the teeth of the die into the workpiece to the proper depth. At the completion of rolling, the lower spindle head is lowered to facilitate removal of the workpiece and the cycle is then repeated.

Considering the first mode of operation, let it be assumed that the magazine is supplied with one or more workpieces, on which embryo teeth have been formed by hobbing or an equivalent process, that one of the workpieces is in the elevator, that the fixture 56 is fully retracted to the right as viewed in FIG. 1 and that the primary work support assembly 68 is fully retracted, i.e., is moved to the left as viewed in FIG. 2. The work holding fixture is then advanced until the roller 121 contacts the lowermost workpiece in the chute. The elevator 116 is then raised to dispose the axis of the workpiece carried thereby in alignment with the axis of the primary and secondary work support members. The primary work support member is then advanced until the parts occupy the position shown in FIG. 2 at which time the workpiece is firmly clamped and supported between the primary and secondary work support members. The elevator is then lowered to the position shown in FIG. 1 and the fixture assembly is then retracted to the right as viewed in FIG. 1 permitting the next succeeding workpiece to fall into the elevator 116. As the workpiece is moved to the right, the embryo teeth of the workpiece contact the teeth of the driven die 54. The workpiece thus begins to rotate with the die. The initial retraction of the fixture is continued until the axis of the workpiece is approximately one-fourth inch from the common center line of the upper and lower spindle heads under token hydraulic pressure. This amount of offset is sufficient to provide positive clearance between the teeth of the prehobbed workpiece and the teeth of the die 54 and accordingly there is no working of the teeth on the workpiece by the teeth on the rolling die. At this point the pressure under which the fixture moves is substantially increased to force the workpiece laterally through the throat formed between the die 54 and the pilot rolls 34 and 36. This motion is continued until the axis of the workpiece is in the plane of the axes of the upper and lower spindle heads. A short dwell is provided at this point to permit completion of the rolling operation. During the dwell portion the teeth of the workpiece are formed to conform to the conjugate teeth on the die to form the teeth on the workpiece to final dimensional accuracy and with the requisite surface finish. During the final rolling operation the carefully machined surfaces 100 and 102 roll in contact with the similarly formed precision surfaces 38 and 40 on the pilot members carried by the lower spindle head assembly. It will be understood that surfaces 100 and 102 are out of contact with the teeth of the die 54. Since the surfaces 100 and 102 are concentric with the axis of the workpiece support member within very close limits, the axis of the workpiece is held at a constant distance from the axis of the die 54 to assure that the pitch diameter of the completed workpiece will be concentric with the bore of the workpiece within the limits defined by the fit of the workpiece on the work support member. Actual tests have established that this unique arrangement effectively corrects the eccentricity between the pitch line of the workpiece and the workpiece axis which may be introduced during hobbing of the parts.

As indicated above, the apparatus of the present invention is particularly suited for use in a production line and is capable of high production rates. In an essentially fully automated production line, parts will be delivered directly from the hobbing machine to the subject rolling apparatus. Occasionally the hobbing machine produces parts which are improperly formed and parts may be delivered to the rolling apparatus in which one or more teeth have not been formed at all. If such a part is forced into the final rolling position, the teeth of the die will be broken and the machine must be stopped for replacement of the die.

This danger is effectively eliminated by the apparatus of the present invention which in effect provides an automatic protective gauging device. Since only token hydraulic pressure is exerted on the fixture 56 as the workpiece is moved from the loading position to a position adjacent the rolling center line any abnormal tooth configuration of the workpiece such as partial hobbing, insufficient depth, etc., will result in the hesitation of the fixture as it moves the workpiece toward the final rolling position. An adjustable timer, which may be incorporated in the control circuit and preset to the length of time normally required to move the workpiece to the rolling position will interrupt this cycle and return the fixture to the loading position in the event the fixture does not complete its movement from the loading position to the final rolling position within the predetermined time. Preferably the timer is so connected as to discontinue operation of the entire machine when an improperly formed workpiece is presented to the machine.

The second mode of operation is the same as that previously described except that the lower spindle head is lowered as the workpiece is moved to final rolling position so that the surfaces of the pilot rolls 34 and 36 are out of contact with the surfaces 100 and 102. After the axis of the workpiece is aligned with the axes of the upper and lower spindle heads the lower spindle head is elevated to bring the pilot surfaces into contact and establish the desired rolling pressure which is continued during a short dwell period after which the lower spindle head is again retracted to its inactive position.

In either mode of operation, the work holding fixture 56 will be mounted to permit slight vertical deflections of the fixture to accommodate miscellaneous deflections in the machine and associated spindles. The desired mounting of the fixture can be effected for example by the installation of heavy springs in the mounting of the fixture.

From the foregoing it is apparent that the above-stated objects and advantages of the present invention have been attained by the provision of a machine which permits simplified tooling arrangements, effects a reduction in die costs, and which greatly simplifies initial setup of the apparatus and job changeover as well as protecting the relatively expensive dies and the machine from damage when improperly formed parts are presented to it. Also because of its unique construction the apparatus is particularly adapted to installation in a fully automated production line system. The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims

What we claim and desired to be secured by Letters Patent is:

1. Apparatus for roll forming a toothed workpiece comprising machine support structure, a toothed forming roll, means mounting said forming roll on said structure for rotation about a predetermined axis, backup means carried by said structure, a pair of workpiece support members mounted for coaxial rotation on said support structure about an axis essentially parallel to the axis of said forming roll and between said forming roll and said backup means, one of said members having an arbor adapted to extend through a central bore in said workpiece, the projecting end of said arbor being engageable with the other support member to provide a straddle support for said workpiece, means for shifting said one member axially to withdraw said arbor from said workpiece to permit the removal of said workpiece, and means on said work support members engageable with said backup means to hold the axis of said workpiece in predetermined relation with the axis of said roll.

2. The combination according to claim 1 wherein said backup means comprises at least one cylinder mounted for rotation about an axis essentially parallel with the axis of said forming roll, and said last-mentioned means comprises a second cylinder rotatable with one of said workpiece support members coaxially thereof.

3. Apparatus for roll forming toothed workpieces comprising of toothed forming roll, means supporting said forming roll for rotation about a predetermined axis, a first pair of cylindrical backup members mounted for rotation about a second axis essentially parallel to and spaced from said first axis, said cylindrical backup members being spaced apart a distance at least equal to the axial length of the teeth on said workpiece, a pair of workpiece support members mounted for coaxial rotation about an axis essentially parallel to the axis of said forming roll, one of said members having an arbor adapted to extend through a central bore in said workpiece, the projecting end of said arbor being engageable with the other support member to provide a straddle support for said workpiece, means for shifting said one member axially to withdraw said arbor from said workpiece to permit the removal of said workpiece from said apparatus, a second pair of cylindrical members carried, respectively, by said pair of workpiece support members at opposite sides of the teeth of said workpiece, each of said second pair of cylindrical members being adapted to run in rolling surface contact with one of said backup members to maintain the axis of said workpiece in predetermined relation with the axis of said forming roll at least as the workpiece is formed to final dimensions.

4. The combination according to claim 12 wherein said workpiece support members are mounted for movement laterally of a plane containing the axis of said roll and the axis of said backup members between a rolling station in which the axis of the workpiece is essentially aligned with the axes of the forming roll and the backup members and a loading position in which the axis of the workpiece is offset from said plane, and means to deliver a workpiece to said workpiece support members when the latter are displaced to said loading position.

5. The apparatus according to claim 3 wherein each of said second pair of cylindrical members has a radial face adapted to engage a radial face of said workpiece to restrain said workpiece against movement along its axis during rolling.