Abstract:
A machine, method and tooling to precision cold-form roller blanks for anti-friction bearings. The machine is a multistage progressive former using floating die cavities to enable simultaneous shaping of the ends of the roller with high accuracy and without flash. The tools and staged forming create an improved roller with an advantageous grain pattern and devoid of structural defects previously attributable to the presence of sheared end face material in the radiused corners of the blank and flash at its mid-section.

Description:
BACKGROUND OF THE INVENTION 
   The invention relates to the manufacture of cold-formed rollers and, in particular, to a process, machine and tooling that affords improvements in roller quality and reduction in manufacturing costs. 
   PRIOR ART 
   Rollers used in anti-friction bearings are commonly initially made in cold-forming machines. Traditionally, the cold-formed pieces are subsequently machined by grinding processes to achieve a desired precision shape and finish. Typically, grinding operations may involve several steps because the cold-formed part has significant flash and/or excess material as a result of the limitations and characteristics of traditional methods and tooling used in the cold-forming art. Grinding processes are expensive and significantly add to the cost of the finished roller. 
   SUMMARY OF THE INVENTION 
   The invention involves a cold-formed metal roller blank, that is relatively close to the net shape of a finish ground roller thereby greatly reducing machining or grinding costs and that has an improved grain structure which avoids premature bearing failure. The improved cold-formed part results from tooling elements that closely shape a part without flash and with a grain structure that follows the contours of the end edges of the roller and is axially uninterrupted thereby avoiding irregularities in the finished machined product. 
   The process involves multistage forming steps and unique tooling capable of producing accurate shapes at each station without the need or risk of flash. The tooling is configured to work a blank that is relatively small in diameter compared to prior art practice, into a part of substantially increased diameter. This technique assures that the material of the sheared end faces of the original blank are essentially excluded from the formed radiused corners between the zone of the rolling surface of the roller and the end faces of the roller. 
   The roller blank or workpiece is simultaneously formed at each end, at each station. The annular radiused corners at the ends of the workpiece are progressively accurately formed by filling the corresponding tool and die cavity areas at successive workstations without creating or risking flash at separation planes between the tool and die cavity parts. This flashless forming is accomplished by confining and shaping the mid-length of the blank with a floating die ring that eliminates the effects of friction at the sides of the workpiece which otherwise would inhibit material flow into the cavity corners and promote or require unwanted flash. At the last station, the workpiece is precision formed by closing the tool and die with a positive stop so that the tool geometry determines the final part shape independently of machine variables. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a roller blank made in accordance with the invention; 
       FIG. 2  is a photomicrograph of an axial cross-section of the blank of  FIG. 1 , acid etched to illustrate the grain pattern of the roller blank material; 
       FIG. 2A  is a photomicrograph similar to  FIG. 2  of the blank cross-section on an enlarged scale of a typical radiused corner of the blank; 
       FIG. 3  is a somewhat schematic plan view of tooling area of a multistation cold-forming or forging machine arranged to perform the process of the invention; 
       FIGS. 4A and 4B  are schematic sectional views of the first station of the machine of  FIG. 3  before and at front dead center of the slide, respectively; 
       FIGS. 5A and 5B  are schematic sectional views of the second station of the machine of  FIG. 3  before and at front dead center of the slide, respectively; 
       FIGS. 6A and 6B  are schematic sectional views of the third station of the machine of  FIG. 3  before and at front dead center of the slide, respectively; and 
       FIG. 7  is a side view of a finished roller made from the roller blank of  FIGS. 1 and 2 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  illustrates an example of a cold-formed roller blank  10  made in accordance with the present invention. The roller blank is of the barrel type, but it will be appreciated that certain principles of the invention are applicable to other roller styles including cylindrical and tapered rollers. The roller blank  10  made by the processes and tools disclosed hereinbelow can be produced to dimensional tolerances that are reduced to about 1/10 of that which is presently commercially accepted for subsequent finishing, typically by grinding after heat treatment. The roller blank  10  after heat treating and grinding is typically used with multiple identical pieces in anti-friction bearing assemblies as known in the art. 
   The roller  10  is formed in a multistation progressive cold-forming machine  11  illustrated in  FIG. 3  and of a type generally known in the industry. The forging machine  11  is depicted in a plan view of the tooling area in  FIG. 3 . The machine  11  includes a quill  12  that receives steel wire  13  at a cutoff station  14 , the center of which is represented by the center line  16 . The wire  13 , which is of a suitable steel such as AISI 52100, is very precisely fed in increments corresponding to the desired length of an initial workpiece or blank  10   a  to a shear or cutter  17  by feed apparatus known in the art. The machine  11  includes multiple progressive forming stations  21 - 23 , preferably three in number. The stations  21 - 23  are conventionally uniformly spaced from one another and from the cutoff station  14 . The forming stations  21 - 23  include die cases  26 - 28  fixed on a stationary die breast or bolster  29  and tool or punch cases  31 - 33  on a slide  34  that reciprocates towards and away from the die breast  29 . The slide  34  is shown at front dead center in  FIG. 3 . A conventional transfer mechanism, not shown, moves workpieces in steps from the cutoff station  14  to each of the forming stations  21 - 23  in timed relation to cyclical displacement of the slide  34  to and from the die breast  29 . 
   The following description of the formation of roller blanks  10  is made with reference to  FIGS. 3 ,  4 A, B.  5 A, B, and  6 A, B. The initial blank or workpiece  10   a  of predetermined diameter and precise length is produced by the shear  17  such that each end face  36 ,  37  of the blank  10   a  is a sheared surface having irregularities or unevenness inherent in the shearing process. The workpiece  10   a  is transferred to the first forming station  21  represented in  FIGS. 4A and 4B . Tool and die cavities  41 ,  42  are formed in respective inserts  43 ,  44 . These inserts or tooling elements  43 ,  44  and others shown in  FIGS. 3 and 4  with cross-hatching are formed of carbide or other suitable tooling material. Associated with the die cavity  42  is a floating die ring  46  including an insert  47 . These cavities  41 ,  42 , inserts  43 ,  44 , die ring  46 , and insert  47 , as well as others to be described, are annular or ring-like in form. As shown in  FIG. 3 , the floating die ring  46  is a cup-shaped body with a deep cylindrical skirt  48  and an integral end wall  49 . As indicated in  FIG. 3 , the floating die ring skirt  48  is telescoped over the die case  26  with minimal radial clearance between these elements, while allowing axial movement between them. The end wall  49  has a central aperture in which the die ring insert  47  is fixed. 
   The floating die ring  46  is resiliently biased to a forward position where its end wall  49  and insert  47  is spaced a limited distance from the die cavity  42  and the case  26  (as indicated in the right side of  FIGS. 4A and 4B ). The biasing force is provided by compression springs  51  (only one is seen in the plane of  FIG. 3 ) distributed symmetrically about the axis of the die cavity  42  (corresponding to the center line of the first station  21 ). The forward or extended position of the floating die ring  46  is determined by a tangential pin  52  received in a slot on the periphery of the floating die ring skirt  48 . 
   Referring to  FIGS. 4A and 4B , a work piece or initial blank  10   a  is received in the first station  21 . The right side of  FIGS. 4A and 4B  illustrate the beginning of the forming stages on the blank  10   a  which has been transferred from the cutoff station  14 . Prior to the instant in the machine cycle depicted at the right side of  FIGS. 4A and 4B , the blank has been held in position at this station by its ends  36 ,  37  with knockout or ejector pins  53 ,  54 , associated with the tool and die elements, respectively. These pins  53 ,  54  are yieldably held in their extended positions from the preceding machine cycle by friction drags, comprising belleville springs  57  and a friction shoe  58  thereby enabling the pins to grip the blank  18  when it is received from the transfer mechanism. Similar friction drags on the knockout pins at the subsequent stations  22 ,  23  are provided for the same purpose. In the illustrated arrangement, the tool and die cavities  41 ,  42  have blank radiused corner forming areas  59  with minimum diameters that in the illustrated example are smaller than the original diameter of the workpiece  10 a. The left sides of  FIGS. 4A and 4B  correspond to front dead center of the slide  34  and illustrate completion of the shaping of the workpiece at the first station. In the illustrated process, the workpiece or blank  10   b  has been partially extruded simultaneously and symmetrically at both of its ends and has been upset at its mid-section. The extrusion component of the forming process at this first station  21  results in substantially all of the material forming the original sheared end face  36 ,  37  to be displaced from the annular radiused corners  59  of the insert cavities  41 ,  42  which shape the rounded or radiused corners of the blank  10   b  between the ends of the blank and the sides of the blank. As shown, the radiused corners of the blank are produced by the complimentary-shaped corners  59  of the tool and die cavities  41 ,  42 . 
   The floating die ring  46  enables the material of the blank  10   b  to be fully driven into the corners  59  of the die cavity  42 . When the mid-length section of the blank  10   b  upsets, it is constrained to a desired size by the floating die ring  46 , and specifically the cylindrical interior surface of the insert  47 . Friction between the blank  10   a  and the wall of the floating ring insert  47  cannot significantly restrict displacement of blank material into the die cavity corners  59  because the floating ring  46 , by overcoming a relatively small force of the biasing springs  51 , can move with the blank stock and with the advancing tool cavity  41  so that substantially the full forging force is transmitted to the blank material in the area of the die cavity corners  59 . Thus, the effect of sidewall friction in the forming cavities of the die side of the tooling is effectively eliminated and the ends of the blank  10   b  can be formed symmetrically end-to-end essentially simultaneously. 
   The second die station  22 , represented at  FIGS. 5A ,  5 B, includes a floating die ring  61  similar in construction and function to the die ring  46  of the first station  21  and floating ring insert  60 . Associated with the floating die ring  61  are an integral cylindrical skirt  65 , springs  51  and a tangential pin  52  serving the same function as described before. Tool and die cavity inserts  62 ,  63  are mounted in respective cases  32  and  27 . 
   The first station die ring insert  47  establishes a diameter on the mid-length of the blank  10   b  (left side of  FIGS. 4A and 4B ) that is relatively close, e.g. a slip fit or a clearance fit, to the diameter of the internal cylindrical surface of the floating die ring insert  60  at the second station. The blank or workpiece  10   b  is transferred to the second station  22  and because its diameter is close to the diameter of the inside wall of the insert  60 , good alignment is maintained between the blank and tool elements of the second station  22 . At this station, the next blow of the slide  34  causes the blank  10   b  to upset near its ends to reduce the radius of its corners and to expand its diameter near these corners. The floating die ring  61 , as in the first station  21 , eliminates the effects of friction between the mid-section of the blank and the die cavity  64  of the floating ring insert  60  so that the blank  10   b  can be fully upset into the corners  66  of the tool and die cavities  67 ,  68  of inserts  62 ,  63  symmetrically, end-for-end and simultaneously. 
   At the third station  23 , seen in  FIGS. 6A ,  6 B, symmetrical cavities  81 ,  82  are formed in tool and die insert sets  83 ,  84  mounted in the respective tool and die cases  33 ,  28 . The right half of  FIGS. 6A and 6B  shows the start of the forming process and the left half of these figures shows the completed roller blank  10  developed at the end of the cold forming process. At this station  23 , as can be seen in a comparison of the right and left halves of  FIGS. 6A and 6B , the blank is formed by a combination of limited extrusion at its ends and upsetting along its mid-length. The shaping of the ends from the intermediate blank  10   b  received from the second station is somewhat limited but quite accurate. Upsetting of the mid-section of the blank  10  produces a final barrel shape. 
   The roller blank  10  produced at the third station  23  is very accurately formed for several reasons beyond the initial forming of its rounded corners as described in connection with the forming action at the first and second stations  21 ,  22 . First, radiused corners  88  of the tool and die cavities  81 ,  82  are not substantially different than those existing at the prior second station  22  so that relatively little shaping is required in these corner areas at this station. Secondly, a guide ring  90  fixed on the die case  28  is very closely fitted to the lead end of the tool case  33  so that when the tool case is received in the ring, both of these tool and die cases are precision aligned with one another. The guide ring  90  and lead end of the case  28  are cylindrical. 
   The relative lengths of the tool and die cases  33 ,  28  is made so that there is a slight interference between them in the direction of slide movement when the slide is at front dead center and faces  91 ,  92  of the die and tool cases are in contact. In this manner, the final shape of the roller blank  10  is accurately and repeatedly determined by the shape of the tooling, i.e. the cavities  81 ,  82  of the inserts  83 ,  84 . The tool insert  83 , at least, is recessed slightly from the plane of the tool case  33  so that there is no contact between the tool and die inserts  83 ,  84  in the front dead center position of the slide. 
   The accuracy of the cold-forming machine  10  in making the roller blanks is augmented by the technique of cooling the tooling with lubricant/coolant. Lubricant/coolant is circulated with a pump (not shown) through internal passages  94  in the tool and die cases  31 - 33 ,  26 - 28 , and floating die ring skirts  48 ,  65 . The coolant can be arranged to keep the temperature of the tools between room temperature and 140° F. The method of cooling the tooling elements improves the forming accuracy of the cold-forming machine because it essentially eliminates thermally induced dimensional variations in the tooling which can otherwise result in variations in the dimensional accuracy of the roller blank parts it is making. 
   Comparing the configuration of the original blank  10   a  with the finished shape  10 , it will be seen that the disclosed process departs from conventional practice in that a relatively large percentage of upset, i.e. change in diameter, is performed on the blank. This technique is helpful in removing irregularities out of the rounded or radiused corners of the blank  10 . 
     FIGS. 2 and 2   a  are photomicrographs of a longitudinally sectioned roller blank made according to the process and with the tooling and machine described hereinabove. The roller blank  10  has been etched to highlight its grain structure pattern.  FIG. 2A  is a view similar to  FIG. 2  on an enlarged scale showing the grain structure pattern of the roller blank  10  at a radiused corner surface  101  between the peripheral main surface  102  corresponding to the rolling surface and an end surface  103  of the roller  10 , the illustrated corner being typical of the other corners. In the illustrated example of the roller blank  10  particularly shown in  FIG. 2A , the radiused corner surface  101  blends smoothly with the main surface  102 . The grain pattern is characterized by smooth, uninterrupted lines that are parallel to the main surface  102  that extends along the major length of the roller blank and parallel to the annular radiused corner surfaces  101  at each end of the roller blank. The end faces  103  of the roller blank are generally perpendicular to its longitudinal axis which corresponds to the axis of rotation. The end faces  103 , on the scale of  FIGS. 2 and 2A  are somewhat irregular since they are the vestiges of the sheared end faces of the original or starting form of the roller blank. 
   The roller blank  10  is superior to prior art roller blanks for several reasons. The roller blank is manufactured to very precise dimensional tolerances, in some cases in the order of 1/10 of previously expected tolerances, so that it is near the net shape of the finished roller product thereby greatly reducing the amount of machining required to reach specified dimensions and rolling surface finish quality. Since the radiused corners are precisely formed to net shape (i.e. as ultimately used) or near net shape, the machining requirement in these areas is non-existent or minimal. 
   In the disclosed process, the tooling is arranged to exclude the material that forms the original sheared end faces from the radiused corners. The absence of this material from such corners is of great advantage because faults and irregularities ordinarily produced in the shearing process cannot exist in the radiused corners. Such faults and irregularities in the radiused corners of prior art rollers are known to initiate cracks and premature bearing failure when used in bearing assemblies. Still further, the disclosed roller blank avoids flash between a plane of separation between the tool and die cavity elements. Prior art processes and tooling frequently resulted in a flash ring being created on the periphery of the roller blank where the tool and die elements separate. This ring of flash required extra machining steps and resulted in discontinuous grain patterns at the finished rolling surface. Prior art bearing rollers are subject to premature failure adjacent the site of the flash created grain pattern discontinuity. 
   From the foregoing, it will be understood that the roller blank, because of its improved grain structure and accurate shape, is capable of reducing costs of anti-friction bearing manufacture and increasing bearing performance in service life. 
   A finished anti-friction metal roller  95  for an anti-friction bearing assembly, shown in  FIG. 7 , is made by machining the blank  10 , ordinarily after heat treatment by grinding a limited amount of material (e.g. 0.07 mm) from its annular main surface  102  and, optionally, from its end surface  103 . Suitable grinding equipment and techniques are well known in the industry. The axis of rotation of the roller is shown at  96 ; the ends  99  of the roller are in planes or substantially in planes perpendicular to the axis  96 , and a rolling surface  97  is concentrically disposed about the axis  96 . The grain structure pattern of the roller metal forming the rolling surface  97 , and the radiused corner surfaces  98  is parallel to such surfaces, being the result of grinding a small amount of material from the main side  102  of the blank  10 . By way of example, one commercial barrel-type roller blank made in accordance with the above description has a nominal major outside diameter of about 18 mm, a nominal length of about 17.5 mm and the radiused corner has a nominal radius of 2.04 mm. In another commercial example, a barrel-type roller blank has a nominal major diameter of 12 mm, a nominal length of 10 mm and the radiused corners have a nominal radius of 1.4 mm. Blanks of these two examples can be ground on the main surface to remote about 0.07 mm of material, for example, to form the peripheral rolling surface  97  and obtain acceptable commercial size and finish requirements. The end faces  99  of the finished roller can typically be left in their cold formed condition without machining, or can be ground as desired. 
   In various roller designs, the surface of the radiused corners, both in the cold formed state and in the finished or ground state of the roller, frequently is not tangent to the peripheral main formed surface or the peripheral finished rolling surface and/or is not tangent to a radial plane at its respective end face. For example, a radiused corner surface can intersect the peripheral formed main surface or the peripheral finished rolling surface, and/or a radial end surface at various different angles of, for example, 10, 20 or more degrees. An end surface, as originally cold formed, can be symmetrically indented around the roller axis and can be ground. 
   Ideally, when practicing the invention substantially all of the formed radiused corner surfaces will be devoid of material from the original sheared end face of the starting blank and the grain pattern immediately underlying this radiused corner surface will be parallel to such surface. The cold forming of the radiused corner surfaces of a blank to a precise shape and without material from the original irregular sheared end face of a starting blank in accordance with the invention enables the blank to be machined into a finished bearing roller ordinarily without the need to machine the radiused corners. 
   It should be evident that this disclosure is by way of example and that various changes may be made by adding, modifying or eliminating details without departing from the fair scope of the teaching contained in this disclosure. The invention is therefore not limited to particular details of this disclosure except to the extent that the following claims are necessarily so limited. As used herein, the term tooling and, alternatively, tools includes, separately and collectively, the tool and die inserts, the tool and die cases, and the floating die rings and inserts. In some applications, it may be desirable to integrate the tool cases and the inserts.