Abstract:
An impact cutoff device for a progressive high speed cold former having a low mass rigid cutter carriage, a torsion spring for carriage return, and an articulated, oil lubricated and dampened carriage drive block on a pivoting drive lever serving to reduce impact induced vibration otherwise leading to fatigue failure and wear of the various cutter parts and consequent loss of cutoff accuracy and quality.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to blank cutoff apparatus for progressive cold forming machines. 
       PRIOR ART 
       [0002]    For cutting wire and bar stock, it is common to use enclosed circular sleeves as cutter blades, one movable with a cutter carriage (cutter) and the other fixed (quill). Reducing the diametrical clearance in the cutter blades is known to improve the quality of cutoff as well as to maintain control of the blank after it has been sheared. 
         [0003]    With minimal clearance between the cutting or shearing blades and the wire, and because the wire shears at the very beginning of the shearing motion, there is minimal distance for a cutter carriage to accelerate to a significant velocity. Thus, most high velocity cutter mechanisms accelerate a driving member to the desired velocity prior to engaging the cutter carriage. 
         [0004]    Prior art impact blank cutoff devices have often been complicated, have required a high level of maintenance, and have exhibited early wear. 
       SUMMARY OF THE INVENTION 
       [0005]    The invention provides an impact cutoff device for a progressive high speed cold former that is simple, reliable, and durable in design. The device is characterized by a low mass rigid cutter carriage, a torsion spring for carriage return, and an articulated, oil lubricated and dampened carriage drive block on a pivoting drive lever. These features reduce impact induced vibration otherwise leading to fatigue failure and wear of the various cutter parts and consequent loss of cutoff accuracy and quality. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a diagrammatic isometric view of selected components of a progressive cold forming machine and the impact cutoff device of the invention; 
           [0007]      FIG. 2  is an enlarged cross-sectional view of a drive lever area of the inventive cutoff device; 
           [0008]      FIG. 3  is a view similar to  FIG. 2  showing a drive lever block aligned with a lower face of the cutter carriage at the instant of impact; 
           [0009]      FIG. 4  shows the drive lever and associated components in their respective positions where the cutter carriage is at the end of its stroke to deliver a cut blank to a transfer pickup station; 
           [0010]      FIG. 5 , in a view like  FIG. 1 , shows a cutter carriage biasing torsion spring retracted for removal of a cutter cassette or pack; 
           [0011]      FIG. 6  is an isometric view of the cutter cassette of the invention; 
           [0012]      FIG. 7  is an isometric view of the cutter carriage; and 
           [0013]      FIG. 8  is an isometric view of a base of the cutter cassette. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0014]    A progressive cold forming machine is schematically illustrated at  10  in  FIG. 1 . For clarity, only a few selected components of the machine  10  are illustrated. A series of die stations  11  of a bolster  12  are evenly spaced in a horizontal array. A ram or slide, not shown, reciprocates towards and away from the bolster while carrying a horizontal array of punches or tools on centers corresponding to the die stations  11 . As is customary, a transfer device (not shown) transfers a blank from one die station  11  to a successive one as the blank is progressively formed into a finished or nearly finished part. A cutoff device  13  of the invention is adjacent a first one of the die stations  11 . The cutoff device  13  receives round wire and shears it into separate blanks of uniform length. The transfer device in a known manner picks up a sheared blank and moves it to the first die station. With reference to  FIGS. 6-8 , the cutoff device  13  includes a cutter pack or cartridge  14 . The cutter pack  14  includes an elongated vertically oriented cutter carriage  16  with an upper body  17  of rectangular cross-section and a lower rod  18  integral and symmetrical with the body  17 . The rod  18  has coaxial cylindrical sections at opposite ends and the narrow intermediate zone  19 . The lower end of the intermediate zone  19  terminates at a pair of shoulders  21  symmetrically disposed on opposite sides of the rod  18  in a common imaginary plane perpendicular to the axis of the rod. A lower end face  22  of the rod  18  is flat and perpendicular to the longitudinal axis of the rod  18 . The cutter carriage  16  is precisely guided for vertical translation in a mounting plate assembly  23  by horizontally adjustable guide bars  24  and a cover plate  26 . A cutter blade  27 , in the form of a cylindrical sleeve, is carried in an upper part of the rectangular carriage body  17 . Similarly, a cutter blade  28 , configured as a cylindrical sleeve, is carried on the mounting plate assembly  23 . The guide bars  24  are horizontally adjustable to bring the cutter blade  27 ,  28  into horizontal alignment and a stop bolt  29  is adjustable to bring the cutter blades into vertical registration at a lowermost position of the carriage  16  in the mounting plate assembly  23  where the cutter blades register with one another and the lead end of the wire stock is received. Adjacent faces of the cutter blades  27 ,  28  locate the plane of shear in the blank. 
         [0015]    The cutoff device  13  is operated by a cam  31  which, as is customary, rotates in timed relation to the cycle of the machine  10 . The cam  31  oscillates a pivotal drive lever  32  which, in turn, causes the cutter carriage  16  to reciprocate thereby causing the cutter blades  27 ,  28  to sever a blank from a wire supply. The drive lever  32  with a sleeve bearing  33  pivots on a pin  35  ( FIG. 2 ). The cam  31 , as it rotates, pivots the drive lever  32  by contact with a cam follower  34  on the lever. It will be seen that the axii of rotation of the cam  31 , the cam follower  34 , and the drive lever  32  are parallel. 
         [0016]    The drive lever  32  is biased by springs  36  to maintain the follower  34  in contact with the profile of the cam  31 . The lever  32  includes an extension  37  carrying a striker block assembly  38  that engages the lower face  22  of the carriage rod  18 . The pair of compression springs  36  bear against the extension  37  to keep the cam follower  34  in contact with the cam  31 . The striker block assembly  38  includes a block body  39  saddled on a cylindrical pin  41  having an axis parallel to the pivot pin  35  of the drive lever  32 . 
         [0017]    The pin  41  rests in a transverse slot  42  in the lever extension  37 . The block body  39  has a slot  43  of cylindrical section providing a fit over the pin  41 . A circular striker or impact disk  44  is assembled in a shallow bore in the top of the block body  39 . A compression spring  46  resiliently biases the block body  39 , clockwise about the pin  41  in the FIGS., so that a lower face  47  of the block body  39  rests against an adjacent surface of the extension  37  when the disk  44  is not engaging the lower end face  22  of the carriage rod  18 . 
         [0018]    An oil lubrication circuit delivers oil to a top face of the striker disk  44 . The circuit includes passages  51  drilled in the lever pin  35 , an oil groove around this pin, passages  52  drilled in the extension  37  and respective aligned holes  53 ,  54  in the pivot pin  41  and striker disk  44 . A branch  56  of the lubrication circuit delivers lubrication oil through a pivot pin  57  to a lower slotted face of an articulated support plate  58  supporting the drive lever biasing springs  36 . The plate  58  pivots on the pin  57  to avoid eccentric loading on the springs  36 . 
         [0019]      FIG. 2  illustrates the position of the drive lever  32  at the beginning of a cutoff cycle. A gap  61  exists between the impact disk  44  and lower end face  22  of the carriage rod  18 . The cam  31  accelerates the drive lever  32  to the position in  FIG. 3  where the impact disk  44  strikes the carriage rod  18 . By way of example, but not limitation, the speed of the impact disk  44  is preferably at least 1.5 meters/second and, more preferably, is at least 2 meters/second. The impact causes the cutter carriage  16  to assume the speed of the impact disk  44 . 
         [0020]    Nearly instantaneously, depending on the clearance between the wire stock and the cutter blades  27 ,  28 , the cutter blades begin to shear the wire at the plane between them. The carriage mounted cutter  27  continues to move at a high speed at least until a blank is sheared from the wire supply. Typically, this occurs when the carriage cutter  27  has moved a small fraction of the diameter of the wire. 
         [0021]    As illustrated in  FIG. 3 , the striker block assembly  38  is proportioned, when its lower face  47  is seated against the extension  37 , so that the face of the impact disk  44  is aligned with the lower end face  22  of the carriage rod  18  at the time of their initial contact. The impact disk upper surface and end face  22  remain parallel and in full contact while the drive lever  32  pivots further under control of the cam  31 . This parallelism is maintained by pivotal motion of the striker block assembly  38  relative to the lever  32  and compression of the biasing spring  46 . As the drive lever  32  returns to the position of  FIG. 2 , the spring  46  returns the striker block assembly  38  to its illustrated position. 
         [0022]    Pivoting of the block body  39  permits the full face of the impact disk  44  to remain in contact with the carriage rod end face  22  thereby minimizing contact pressure and wear between these surfaces. The high forces developed during actual shearing of the wire stock borne by these surfaces occurs when they are at or adjacent a plane perpendicular to the line of motion of the cutter carriage  16  and which extends through the axis of the drive lever pin  35 . This geometry minimizes relative sideways movement between the impact disk  44  and carriage rod  18  thereby reducing wear of these elements. 
         [0023]    Lubricating oil present between the impact disk  44  and carriage rod  18  from the lubrication oil circuit through the lever  32  also reduces frictional wear. The oil at this interface, additionally, dampens the shock of the impact between the impact disk  44  and rod end surface  22 . 
         [0024]    A torsion spring  66  serves to bias the cutter carriage  16  towards its lowermost position where the carriage cutter blade  27  is in alignment with the stationary cutter blade  28  in the mounting plate assembly  23 . The spring  66  is supported in a bushing (not shown) adjacent each of its ends fixed to the frame of the machine  10 . The torsion spring  66  has a torque arm  67  fixed on an end of the spring adjacent the drive lever  32 . The torque arm is forked at a distal end so as to provide two tangs  68  that bear against the rod shoulders  21 . The torsion spring  66  maintains the lower end face  22  of the cutter carriage rod  18  in engagement with the impact disk  44  of the striker block assembly  38  of the drive lever  32  through all but the most retracted part of the pivotal stroke of the drive lever. The torsion spring  66  avoids the tendency of a coil spring to exhibit a surge or shockwave when it sustains a sudden impact force. As a result, the torsion spring  66  is less susceptible to fatigue failure. 
         [0025]      FIG. 5  illustrates a manner of releasing the torsion spring force from the carriage  16 . A pneumatic cylinder actuator  71  is coupled to an arm  72  fixed on an end of the torsion spring  66  opposite the end to which the torque arm  67  is fixed. When a piston rod of the actuator  71  is extended, the torque arm  67  is raised to enable the cutter pack or cartridge  14  to be removed from the cutoff station. In normal operation, as shown in  FIG. 1 , the actuator arm  72  twists the torsion spring  66  to hold the torque arm  67  against the rod shoulders  21 . 
         [0026]    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.