Abstract:
A set of tooling for a progressive forming machine comprising die and tool units having internal complementary cavity portions for receiving a workpiece, one of said units being arranged to slide a limited distance along its axis and to be biased by a spring force towards the other unit when the units are mounted in the forming machine, the units each having an end face with a smooth surface finish adapted to press against the smooth surface finish of the end face of the other unit, the end face area of one of the units being relatively small compared to its major cross-sectional area whereby a high contact pressure between the end faces is obtained for a given spring bias force such that extrusion/cooling oil coating a workpiece received in the cavity portions is restrained from leakage from the cavity portions across said end faces during a hydrostatic trapped extrusion of the workpiece in the die and tool units whereby the die and tool units are capable of shaping the workpiece to a degree beyond limits of conventional cold-forming processes.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to metal cold-forming and, in particular, machine arrangements and methods for achieving a high reduction in area of a workpiece. 
       PRIOR ART 
       [0002]    Cold-forming machines are typically used to mass produce shaped parts starting with a cutoff of round metal wire. Blanks or workpieces are sheared from a length of wire after straightening from a coil, positioned in successive stationary dies, and struck by reciprocating tools to change their shape into intermediate and, eventually, finished products. These forming operations can include upsetting where the diameter of the wire blank is increased or extrusion where the diameter is reduced or both upsetting and extrusion. Usually, extrusions are accomplished in a stationary die rather than a reciprocating tool. This technique can be problematic where the workpiece is long, i.e. being several times its diameter in length. In these circumstances, the workpiece can tend to stick in the die. The knockout pin used to eject the workpiece from the die, as a result of the area reduction, is relatively small in cross-section. The greater the length of the workpiece compared to its cross-section, the more acute is the problem of ejecting the workpiece from the die. The knockout pin besides being reduced in diameter must be increased in length in relation to the workpiece length and becomes prone to breakage. 
         [0003]    Among the challenges to be met has been the economical, high volume production of pointed parts, especially long pointed parts, where the reduction in area approaches at least 95% and where secondary operations off the cold former are to be avoided. 
       SUMMARY OF THE INVENTION 
       [0004]    The invention involves cold-forming methods and machinery for the economical production of metal parts characterized by a high reduction in area and long length or other substantial change in form while avoiding secondary machining operations. The invention is disclosed in the context of a multi-die progressive former, generally known in the art, and a unique arrangement of dies and tools and related instrumentalities. In preferred embodiments, a long, high carbon steel part is pointed with a reduction in area of about 95% in a net shape or near net shape process. At an intermediate station in the disclosed embodiments, the tooling is arranged to perform a novel closed cavity consequent hydrostatic extrusion process. The tooling and method achieves, in high carbon steels for example, area reductions to levels previously generally considered impractical or unobtainable. Use of the hydrostatic extrusion station can be followed by successive forming stations that together can approach or reach a total of 95% reduction in area. This degree of area reduction effectively results in a pointed workpiece. Alternatively, a workpiece can be pointed following the hydrostatic extrusion stage by pulling the workpiece to neck down the area to be pointed and thereafter further extruding it to a final point. Still another pointing method that can follow the unique hydrostatic extrusion step is a pinch pointing process. In this method, once the workpiece is preliminarily reduced in area by the hydrostatic extrusion, it is pinch formed with a flash that can be sheared off or can be broached off by further disclosed techniques. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  depicts a series of workstations in a progressive multi-die forming machine in accordance with a first embodiment of the invention; 
           [0006]      FIG. 2  illustrates tooling areas of the workstations of  FIG. 1  on an enlarged scale; the right side of the images are before the end of the workstroke and the left side are at the end of the workstroke; 
           [0007]      FIG. 3  illustrates additional details of a machine set up in conformity to  FIGS. 1 and 2 ; 
           [0008]      FIG. 4  is a fragmentary vertical section through the third workstation of the machine illustrated in  FIG. 3 ; 
           [0009]      FIG. 5  depicts a series of workstations in a progressive multi-die forming machine in accordance with a second embodiment of the invention; 
           [0010]      FIG. 6  illustrates tooling areas of the workstations of  FIG. 5  on an enlarged sale; the right side of the images are before the end of the workstroke and the left side are at the end of the workstroke; 
           [0011]      FIG. 7  illustrates additional details of a machine set up in conformity to  FIGS. 5 and 6 ; 
           [0012]      FIGS. 8A ,  8 B, and  8 C illustrate operations of the tooling at the fifth workstation of the machine depicted in  FIG. 7 ; 
           [0013]      FIG. 9  illustrates a series of workstations in progressive multi-die forming machine in accordance with a third embodiment of the invention; 
           [0014]      FIG. 10  illustrates tooling areas of the workstations of  FIG. 9  on an enlarged scale; 
           [0015]      FIG. 11  illustrates a series of workstations in a progressive multi-die forming machine in accordance with a fourth embodiment of the invention; and 
           [0016]      FIG. 12  illustrates tooling areas of the workstation of  FIG. 11  on an enlarged scale. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0017]    Referring to  FIG. 3 , a cold-forming machine  10  includes a die breast or bolster  11  and a slide or ram  12  guided for reciprocation towards and away from the die breast. U.S. Pat. No. 4,898,017, the disclosure of which is incorporated herein by reference, details the general arrangement and is an example of a machine useful in practicing the present invention. The illustrated machine  10  has five forming stations WS 1 -WS 5  downstream of a cutoff station  13 . It is conventional to arrange the cutoff station  13  and successive workstations WS 1 -WS 5  in a common horizontal plane each with an equal spacing from adjacent ones of these stations. This permits a generally conventional mechanical transfer device to move a workpiece  15  progressively from one station to the next in a known manner. 
         [0018]      FIG. 3  illustrates certain details of the machine while enlarged details of the forming tools are illustrated in  FIGS. 1 and 2 . The workstations of  FIG. 2  are superposed with the same workstations in  FIG. 1  but are much enlarged. The details of  FIG. 2  are split views with the left side showing the parts at the finished position of the tool. The right side of the details in  FIG. 2  shows the workpiece or blank received in the die prior to the actual forming operation. The slide  12  is reciprocated in a horizontal plane by a suitable motor and drive system well known in the art. 
         [0019]    Ahead of the cutoff station  13  is an auxiliary wire drawer, through which a straightened wire from a coil is fed and drawn to a precise diameter for feeding into the forming machine  10 . A phosphate and bonderlube coating is drawn into the outside surface of the wire during the drawing process. At a plane indicated at  14 , the cutoff station  13  shears a precise length and, therefore, volume of drawn wire for forming a part or workpiece  15 . The sheared end surfaces of the workpiece  15  will be irregular and without the coating due to the shearing operation. Before the slide  12  completes a forming blow, each workpiece  15  has been transferred to the next succeeding workstation. Forward motion of the slide causes a tool at a workstation to insert the workpiece into a die. 
         [0020]    In the first workstation WS 1 , the workpiece  15  is inserted into a die  18  and pressed on both ends by a die kickout pin  19  and tool pin  20 . The terms die and tool as used herein will often mean an assembly of a case and an insert in the case. The die and tool cases and inserts are typically cylindrical. Die and tool cavities and kickout pins are, likewise, typically cylindrical or, at least, round in cross-section. The ends of the die and tool pins  19 ,  20  that contact the workpiece  15  may be flat but preferably have a 3° point to displace material from the center of the workpiece ends to remove the surface variations developed at the sheared faces. 
         [0021]    At the second workstation WS 2 , the forming blow forms a radius on the circumference of the end of the workpiece  15  which end, ultimately, will be greatly reduced in area. This radius squeezes the raw uncoated end of the blank or workpiece  15  so that a round and coated surface will be provided for first contact with an extrusion tool in the subsequent workstation WS 3 . A small corner radius is formed on the same workpiece end to remove any sharp edges or flash burrs. The operation at this second workstation WS 2  is a form of trapped extrusion where the workpiece  15  is totally enclosed in the die  21  before the workpiece is deformed in the work stroke. 
         [0022]    In the disclosed embodiments of the invention, the point end of the workpiece  15  is formed in the tool; this technique of “reverse forming” is typically not done in cold-forming processes. Pointing the workpiece  15  while it is partially in the tool and partially in the die requires precise alignment and control between the tool and die. Any significant misalignment would result in non-uniformity of the workpiece, with scraping or metal shaving as it enters a misaligned tool. 
         [0023]    The reverse forming process begins with insertion of the workpiece  15  into the die  21 , stopping on a kickout pin  22  that is held stationary during the forming workstroke. As the heading slide  12  advances, a tool  23  contacts the die  21  to create a closed cavity. The die  21  is arranged to slide in a die holder  24 . In one example, a cluster of five nitrogen gas springs  26  (one of which is shown in  FIG. 3  at WS 2 ) are provided to develop a total of 560 lbs. initial spring force. The springs  26  bias the die  21  towards the heading slide  12  while enabling the die to be pushed back with the advancing tool  23  as the workpiece is forced into the tool cavity to produce the required shape. The volume of the workpiece  15  in relation to the die  21  is such that the die is slightly underfilled. Overfilling the die  21  can result in metal flashing between the tool  23  and die where the die spring force is exceeded. It will be understood that the die kickout pins and tool pins at the various workstations are operated by cams in a known manner to assure that the workpiece is ejected from the respective die or tool after the workstroke is completed. 
         [0024]    At the third workstation WS 3 , a reverse forming process, again, begins with a tool  33  inserting the workpiece  15  into a die  31 , the workpiece stopping on a kickout pin  32  that is held stationary during the forming workstroke. As the heading slide  12  further advances, the tool  33  contacts the die  31  to create a closed cavity for forming the part. The die  31  slides in a holder  34 , being spring biased towards the heading slide  12  and pushed back with the advance of the tool  33  as the material is forced into the tool cavity to trap extrude the required shape defined by the tool. A tangential slot  35  on the die, working with a pin  43  serves to limit axial motion of the die  31  on the die breast to the short distance required for the trap extrusion at this station. By way of example, C1055 steel has been successfully extruded to an 80% reduction in area in this single workstation WS 3 . Normally, reverse forming by extruding into a tool has previously been limited to approximately 55% reduction in area. Extrusions greater than 55% reduction in area typically result in a workpiece beginning to upset into flash between the tool and die. 
         [0025]    The disclosed reverse forming process allows parts with long shank lengths (e.g. lengths of about 3 or more diameters) and smaller point diameters to be successfully formed. The majority of the blank or workpiece  15  remains inside the die  31  with only a short length of the workpiece inside the tool  33 . This allows ejection of the workpiece  15  from the die  31  to be proportionately robust, with a full workpiece diameter kickout pin  32 . A small diameter tool kickout pin  37  in the tool  33  requires very little force and short kickout distance to eject the workpiece from the tool. The longer length of the workpiece  15  that is inside the die  31  will tend to make the workpiece stay in the die and, therefore, avoid the need for high kickout forces from the tool pin  37 . By comparison, conventional trap extrusion forming inside the die would require a proportionately small diameter kickout pin equal to the extruded reduced diameter, with a kickout stroke longer than the overall part length. Such kickout pins are subject to high breakage rates due to length to diameter ratio, and the larger workpiece diameter being kicked out by a small diameter kickout pin. 
         [0026]    The process performed at the third workstation WS 3 , in accordance with the invention, involves an adaptation of hydrostatic extrusion. To accomplish this “consequent hydrostatic extrusion” process, the interface between the die  31  and tool  33  is maintained at a contact pressure adequate to contain the hydrostatic medium which in this case, is liquid cold-forming extrusion/cooling oil. This can be achieved by arranging a tool insert  36  to protrude 0.05 mm to concentrate the closing force on the small diameter face of the insert against the opposing face of a die insert  38 . The diameter of the tool and die insert end faces are substantially less than the diameters of the end profiles of the tool and die cases. The workpiece  15  is coated by flooding with the extrusion oil from a dispenser nozzle  41  ( FIG. 4 ) as it enters the die  31 . Prior to reception of the workpiece  15  into the die, the kickout pin  32  is frictionally held with its end flush with the face of the die insert  38  so as to exclude any significant volume of oil between the workpiece  15  and end of the kickout pin when it enters the die. The kickout pin  32  is closely fitted to the bore of the die  31  so as to restrict fluid loss around the pin in the forming blow. 
         [0027]    It has been found that the tail portion of the workpiece  15  also swells up tight to the die bore to restrict oil loss. When the oil seal is properly maintained, the workpieces  15  extrudes to the required shape without swelling up to the tool and die insert diameters, except for the tail portion of the workpiece near the kickout pin  32 . When workpieces are hydrostatically extruding properly as a consequence of the extrusion/cooling oil being confined in the cavity mutually formed in the die insert  38  and tool insert  36 , the end of the workpiece remains slightly rounded from underfill, without flashing around the die kickout pin  32 . Additionally, the part of the workpiece  15  received in the tool  33  remains about 0.04 mm smaller than the tool and die diameter due to the enclosed hydrostatic oil pressure (with the workpiece having its major diameter nominally about 3.12 mm along its major length). The oil cushion trapped around the workpiece  15  keeps the majority of its body from contacting the cavity surfaces of the tool and die inserts  36 ,  38 , thereby reducing the friction between these forming inserts and the workpiece. It has been found that the workpieces will not extrude properly if the oil application is insufficient or if the tool or die faces, indicated at  39  and  40 , are marred so as to prevent a tight oil seal at their interface. These imperfect conditions result in the blank not extruding, but swelling up tight against the tool and die insert surfaces, and flashing around the die kickout pin  32 . The added forming pressure may also cause failure of the die kickout pin  32 . 
         [0028]    The extrusion lengths of the workpieces  15  at the third workstation WS 3  are held consistent by stopping the extrusion against the tool knockout pin  37 . The end shape of the parts extruded with the disclosed process are unique with a uniform dome shaped end surface. Traditional high reduction trap extrusions have an irregular hollow or cupped end surface. 
         [0029]      FIG. 4  is a somewhat schematic view of the third workstation WS 3  taken in a vertical plane through the center of the die holder. A pivotal lever  46  has an upper forked end  47  that presses against the rear of the die  31 . A lower end  49  of the lever  46  is engaged by an operating rod  51  connected to a piston of a nitrogen gas spring  52 . The gas spring  52  is located below its respective workstation WS 3  in a machine area permitting a relatively large spring to exist and enabling its high pressure to be multiplied by the long length of the lower end  49  of the lever  46  compared to the length of the upper end  47  measured from a fulcrum  53 . By way of example, the spring  52  and lever  46  can develop 3,200 lbs. of force on the sliding die  31 . By comparison, the forming load for the illustrated extrusion is calculated at about 3,000 lbs. Thus, the sliding die spring force is at least equal to the forming load at this workstation WS 3 . The high pressure lever  46  is capable of developing forces many times greater than the multiple nitrogen springs at the second workstation WS 2 , the latter of which being limited in potential force by the restrictions of the diameter of the die case. 
         [0030]    At the subsequent workstation WS 4 , a second extrusion is performed to further reduce the end diameter formed in the preceding die  31 . At this fourth station WS 4 , a 35% reduction in area open extrusion of the workpiece  15  into a tool  56  is accomplished. Generally, an open extrusion involves a lighter forming load whereby the body of the workpiece  15  may be unsupported in the open space between a tool  56  and an opposing die  57  without upsetting. 
         [0031]    The workpiece  15  is transferred to the fifth workstation WS 5  for finish forming. A tool  61  forms an upset head on the workpiece  15  while further reducing the point end diameter. The point end area at this station is reduced by approximately 45%. The 45% reduction is the normal maximum for point forming while upsetting. The die  62  is of the sliding type biased forwardly by a high pressure lever  46  like that shown in  FIG. 4 . The limited die slide action is accommodated at the fifth station of  FIG. 3  by a pin  63  and slot  64 . The disclosed process has successfully formed parts to a full form finish shape with smooth end surfaces. 
         [0032]    Referring now to  FIGS. 5-8 , inclusive, a second process for reducing the area of or pointing a workpiece is disclosed. In this process, a multi-die cold former  70  has six workstations. The machine  70  has the general arrangement of the earlier described machine  10  and the same is true of machines associated with other processes and equipment disclosed below in connection with  FIGS. 9-12 . 
         [0033]    The first three workstations are arranged essentially the same as those described above in connection with the cold-forming machine  10  shown in previous  FIGS. 1-4 . Where appropriate, the same numerals have been used to designate the same or like parts in the respective machines  10 ,  70 . The process involves a reduction in area extrusion, a subsequent reduction by pulling, followed by a combination upset and extrusion step to finish the part. Detail of the forming tools used in the presently described “pulling” process is shown in  FIGS. 5 and 6 . In  FIG. 6 , the enlarged details are split views with the right side showing a workpiece at a respective die prior to the forming operation and the left side showing the parts at the fully advanced position of the respective tools. At the third workstation WS 3 , the trap extrusion forms a reduced stem  71  on the end of a workpiece to be pointed. 
         [0034]    At the fourth workstation WS 4 , the end of the stem  71  is upset into a bulb-shape  78  for gripping in the subsequent pulling station WS 5 . The forming operation at the fourth station WS 4  uses a sliding tool  73  with tool segments or inserts  74  for forming a small bulb-shaped upset on the reduced stem  71 . The tool segments  74  can be four in number and are disposed at the front of a tool case  76 . The segments  74  are allowed to move within the tool case  76  to close together during the upsetting motion and to open to allow clearance for the upset bulb  78  to be ejected from the tool cavity mutually formed by the segments. A plurality of nitrogen gas springs  77  (one such spring is shown in  FIG. 7  at the fourth workstation WS 4 ) bias the tool case towards the die. The combined spring pressure is adequate for holding the segments  74  closed against one another for a relatively small upsetting load. A circumferential indent formed by the segments  74 , may be added at the base of the bulb  78  to facilitate a uniform break off of the bulb or slug. 
         [0035]    At the fifth workstation WS 5 , the upset bulb  78  is pulled apart from the remainder of the workpiece to thereby reduce or neck down the area of the stem beneath the bulb  78 . At this workstation WS 5 , a front pusher sleeve  81  ( FIGS. 8A-C ) of a tool assembly  80  slips over the upset bulb  78  formed at the preceding station and pushes on a tapered shoulder of the workpiece behind the bulb so as to insert the workpiece into a die  83 . A spring loaded plunger  84  in the die  83  receives the opposite end of the workpiece and retracts, holds and extends during operations at this station. Two opposed pivoting gripper inserts  86 , extending radially through slots in the pusher sleeve  81  close on the reduced neck of the workpiece  72  as the gripper inserts enter the die case  83 , shown by the transition between  FIGS. 8B and 8C . The grippers  86  are biased open apart from one another by leaf springs  85 . A tool kickout mechanism of conventional construction is timed to hold the pusher sleeve  81  stationary while the heading slide  12  and the tool assembly  80  with its grippers  86  pull away from the die  83 . The tool kickout travel causes the pusher sleeve  81  to lag and allow the upset bulb  78  to be pulled by the grippers  86  away from the tapered shoulder  82  ultimately breaking off the bulb or slug. 
         [0036]    At the sixth workstation WS 6 , a tool  87  forms an upset head on the workpiece  72  while further reducing the point end diameter. 
         [0037]    Referring now to  FIGS. 9 and 10 , there is shown a point forming process involving a combination of extrusion and pinch trim. The process of  FIGS. 9 and 10  utilizes substantially the same initial steps and tooling as the first three workstations in the preceding two disclosed forming processes. These steps are followed by a pinch pointing technique involving a formed sideways upset with flash and then followed by a sideways trimming operation to remove the flash. More specifically, at a fourth workstation WS 4  a tool case  91  carries segments or inserts  92  that upset a point shape with flash  93 . The segments  92  are allowed to move within the tool case  91  to close together during the upsetting and to open to allow clearance for the part to be ejected. A small insert  94  inside the split inserts  92  is a stop to hold the shoulder of the part at the forming position within the inserts. The small insert  94  has a central slot to allow the flash  93  to pass and the part to be ejected. 
         [0038]    The plane of the drawings at the fifth workstation WS 5  in  FIGS. 9 and 10  is rotated 90 degrees from that of the fourth workstation WS 4 . A slide  95  in a tool case  90  is driven sideways as the tool case approaches the opposing die causing the flash  93  to be sheared from the workpiece. At the sixth station WS 6  the part is upset and further pointed. 
         [0039]    The process depicted in  FIGS. 11 and 12  is the same as that described in reference to  FIGS. 9 and 10  except for the operation conducted in the fifth workstation WS 5 . Here, the flash  93  upset produced at the fourth workstation WS 4  is removed with a broaching tool  96 . Broaching or cutting blades  97  are pivotally mounted within the tool  96 . Pusher pins  98  mounted in a die  99  engage and rotate the broaching blades  97  to remove the flash  93  produced in the earlier workstation WS 4 . At the last workstation WS 6  the part is upset and further pointed as previously described. 
         [0040]    While the invention has been shown and described with respect to particular embodiments thereof, this is for the purpose of illustration rather than limitation, and other variations and modifications of the specific embodiments herein shown and described will be apparent to those skilled in the art all within the intended spirit and scope of the invention. Accordingly, the patent is not to be limited in scope and effect to the specific embodiments herein shown and described nor in any other way that is inconsistent with the extent to which the progress in the art has been advanced by the invention.