Abstract:
A method and apparatus for detecting a turned blank at a workstation in a progressive forging machine comprising simultaneously monitoring both the force on a tool in the workstation and the crank angle of the machine, determining a reference crank angle when the tool is subjected to a force at the workstation about to deliver a blow and a blank in the workstation is properly angularly aligned, operating the machine to forge blanks in a normal manner when a force on the tool at the workstation occurs substantially at the reference crank angle, and interrupting said normal manner when the force on the tool at the workstation occurs before said reference crankshaft angle to enable the blank being formed at the workstation to be separated from remaining blanks being forged in the machine.

Description:
[0001]    The invention relates to improvements in progressive forming machines and, in particular, apparatus for detecting angularly misaligned blanks at a workstation in which they are to be additionally formed. 
       BACKGROUND OF THE INVENTION 
       [0002]    Progressive forming machines typically shape a piece of round wire, hereinafter sometimes called a blank, into a desired shape by striking it with tools and forcing it into dies having configurations corresponding to intermediate and finally shaped blanks or parts. Depending on the character of the part, this forging process can involve separate forging blows performed at multiple successive work stations. Hex head or twelve point head bolts are examples of parts commonly produced in progressive forging machines that can suffer when a blank turns even slightly on its longitudinal axis when it is transferred from one work or forming station to another. Where the blank has a profile that is not both circular and concentric with its axis, rotation of the blank about its longitudinal axis can introduce enough misalignment to prevent the blank from being properly received and formed in a succeeding workstation. This unintended turning, even if relatively small, can result in a misshapen part. 
         [0003]    In a high production application, particularly where the unwanted turning of a blank occurs randomly and intermittently, a defective finished part may not be detected by the manufacturer. However, even a small number of defective parts mixed in with a large batch of good parts can cause significant problems for the ultimate user of the part. It can be expected that these problems and their associated costs will ultimately be traced back to the manufacturer resulting in customer dissatisfaction as well as ultimate financial loss to the manufacturer that far exceeds the value of the defective part. 
       SUMMARY OF THE INVENTION 
       [0004]    The invention provides a system to detect accidentally turned blanks at one or more workstations of a progressive forging machine. The system utilizes the inherent “go, no go” nature of the blank and tooling at the relevant station. Where the blank is properly aligned with the tooling in an angular sense, the blank will be smoothly received in the tooling. To the extent that the blank is angularly misaligned through accidental turning during the transfer process from station to station, it will resist entering the tooling. The system detects resistance of the blank in entering the tooling and interrupts regular operation of the machine to permit the misaligned blank to be removed from the stream of good product. 
         [0005]    In the preferred embodiment of the invention, misalignment between an inadvertently rotated blank at a particular work station is sensed by allowing the tooling to be displaced into its holder in response to forces imposed by the blank on the tool. Displacement, i.e. sliding, of the tool is detected by a proximity sensor which in turn communicates with the machine controller that can shut down the machine operation while the turned blank is removed manually or otherwise. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a diagrammatic side view of a multi-station forging machine in which the present invention is implemented; 
           [0007]      FIG. 2  is a diagrammatic plan view of the forging machine of  FIG. 1 ; 
           [0008]      FIG. 3A  is a fragmentary diagrammatic cross-sectional view of the machine taken at a vertical plane through the center of a workstation monitored for turned blanks in accordance with the invention; 
           [0009]      FIG. 3B  is a fragmentary view similar to  FIG. 3A  showing a blank with a polygonal cross-section properly oriented and inserted into a tool cavity of complementary shape; 
           [0010]      FIG. 3C  is a fragmentary view similar to  FIGS. 3A and 3B , but showing the blank in a condition where, because it has inadvertently turned, such as may occur in an imperfect transfer, it resists insertion into the complementarily shaped tool cavity; and 
           [0011]      FIG. 4  is a diagrammatic circuit showing various components of one form of control circuitry for the machine of  FIGS. 1 and 2 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0012]    Referring now to  FIGS. 1 and 2 , there is shown in side elevation and plan view, respectively, a progressive multistage forging machine  10  of generally conventional construction. An example of such a machine is shown in U.S. Pat. No. 4,898,017, the disclosure of which is incorporated herein by reference. The machine  10  is powered by an electric motor  11  that rotates a crankshaft  12  through a gear train indicated generally at  13  which is driven under the control of a clutch and brake assembly  14 . Rotation of the crankshaft  12 , through operation of a connecting rod  16 , causes a slide or ram  17  to reciprocate towards and away from a stationary die breast  18  as is understood by those skilled in the art. Each revolution of the crankshaft  12  causes the machine  10  to perform a forming cycle. The die breast  18  and slide  17  have a plurality of aligned tool mounting locations representing successive workstations  21   a  through  21   d  uniformly spaced in a common horizontal plane. 
         [0013]    Precise lengths of cylindrical wire stock, i.e. blanks  27 , are formed at a cutoff station  26  and from this station are transferred to successive workstations  21   a - 21   d  during a part of each machine cycle. A mechanical transfer device (not shown) known in the art, moves each blank  27  during this transfer movement from one station  21  to the next succeeding station  21 . Generally, a blank  27  being moved sequentially from station to station, has a cylindrical portion which is grasped by the fingers of the transfer mechanism. Typically, a forging machine is capable of producing forged parts of a wide variety of configurations. Frequently, these blanks or parts have areas with cross-sections that are not round and/or are not concentric about their longitudinal axis. For purposes of explanation, the longitudinal axis of a blank will ordinarily be understood to be the same as the central axis of its original cylindrical wire shape. There are frequently production jobs where it is important that the profile geometry of an accircular and/or eccentric blank, once formed in one station stay angularly aligned with the tooling in a subsequent station so that properly and accurately shaped parts can be reliably produced. Common examples of such parts are hex head and twelve point head bolts. From time to time, slippage or other mishandling of a blank  27  may occur during transfer of a blank from one station to the next and such slippage can involve some degree of turning, i.e. rotation of the blank about its longitudinal axis. Where the cross-sectional shape of a blank is not angularly aligned with the geometry of a subsequent tool, a misshapen or otherwise defective part is likely to be produced. It is therefore a desired goal of the present invention to detect such turned blanks so they can be separated from the product stream of good parts. 
         [0014]    The invention detects turned blanks  27  at a workstation such as the workstation  21   c  depicted in  FIGS. 3A-3C  by sensing a force resisting entry of a blank  27  into a cavity  28  of a tool  29 . This resistance occurs because a blank  27  being inadvertently turned does not freely slide into the cavity  28 . With reference to  FIGS. 3A-3C , a case  31  carrying the tool  29  is slidably supported in a bushing fixed in a tool holder  33  on the slide  17 . Compression springs  36  are carried in respective blind bores  37  in the case  31 . The bores  37  and springs  36  are parallel to a central axis  38  of the workstation  21   c.  The springs  36  are proportioned to be compressed between a plate  39  on which the holder  33  is mounted and the end of the bores  37  so that the springs  36  bias the case  31  forwardly towards the die breast  18 . A cross pin  41  fixed in the tool holder  33  is received in a tangential slot  42  in the wall of the case  31  and allows the case to move axially a limited distance corresponding to the width of the slot. The tool cavity  28  has an internal cross-section that is complementary to the external cross-section of the adjacent end of the blank  27  as it is presented to the workstation  21   c.  In the illustrated case, this cross-section is hexagonal, a form characteristic of a machine bolt and the result of a forming blow made in a preceding workstation  27   b.  In this station  21   c,  the blank  27  is to be further formed while its hex shape is precisely confined by the tool cavity  28 . For example, it may be desired to form a flange on the head of the blank  27  at the underside of the hex head. 
         [0015]      FIG. 3A  illustrates the slide  17  in a position approaching but spaced from front dead center, i.e. its position closest to the die breast  18 . In  FIG. 3A , the springs  36  bias the case  31  and, therefore, the tool  29 , to a forward position limited by bottoming of the pin  41  against one side of the tangential slot  42 . In  FIG. 3B , the slide  17  has moved close to the die breast  18 , although it is not yet at front dead center. It will be seen that the blank  27  has smoothly entered the tool cavity  28 , a result of being properly angularly oriented with respect to its longitudinal axis with the tool cavity. From this position of  FIG. 3B , the slide  17  can complete its stroke and the blank will be properly formed at this station. In  FIG. 3C , the blank is not properly angularly aligned with the tool cavity  28  and it will be seen by comparing this figure with that of  FIG. 3B  that the slide  17  has advanced to the same position as it is shown in  FIG. 3B . The misalignment of the blank  27  with the cavity  28 , however, prevents the blank from smoothly entering the cavity in a manner analogous to a “go, no go” gauge. The physical interference of the blank  27  and the tool  29  causes the tool and the case  31  in which it is fixed to retract against the force of the springs  36  relative to the holder  33 . 
         [0016]    A local flat or groove  46  on the case  31  is sensed by a proximity sensor  47  fixed in the holder  33  so that movement of the tool  29  and case  31  in the holder  33  results in a change in a signal from the proximity sensor  47 . That is to say, the proximity sensor  47  can detect movement of the tool  29  from the position illustrated in  FIGS. 3A and 3B  to the position illustrated in  FIG. 3C  relative to the holder  33 . 
         [0017]    Operation of the machine  10  can be controlled by a programmable logic controller (PLC)  51  ( FIG. 4 ) known in the art. In a customary manner, after the machine  10  has completed a number of start-up cycles, the machine finishes a blank  27  each time the crankshaft  12  makes a complete revolution. Various functions of the machine are timed by cams and other instrumentalities tied mechanically or electronically to the crankshaft  12 . In the present arrangement, the angular position of the crankshaft  12  going from 0° to 360° is monitored by a programmable rotary limit switch  52  known in the art. A resolver (not shown) signals the programmable rotary limit switch  52  of the precise angular position of the crankshaft  12 . When the machine  10  is set up for a production run of blanks different in configuration from a preceding run, and the turned blank monitoring feature of the present invention is to be used, the machine  10  can be run through a sufficient number of cycles to bring a blank  27  to the workstation  21   c  fitted with the proximity switch or sensor  47 . Assuming that the blank  27  is properly angularly aligned with the tool cavity  28 , the programmable rotary limit switch  52  can record the precise angle of the crankshaft  12  at which the tool  29  and case  31  are forced rearwardly in the tool holder  33  during a normal machine cycle. Thereafter, when full operation is initiated, the PLC  51 , working with the programmable rotary limit switch  52  can monitor or check for turned blanks  27  by determining that the blank  27  has prematurely caused displacement of the tool  29  and case  31  in the holder  33 . This can be done in accordance with the invention by relying on the turned blank  27  to not easily enter the complementarily shaped but not aligned tool cavity  28 . Interference between the blank  27  and tool  29 , owing to their angular misalignment, will result in the tool case  31  being displaced at an advanced point in the machine cycle, in particular, at an advanced angle of the crankshaft  12 , i.e. at an angle of displacement less than the angular displacement of the crankshaft  12  corresponding to  FIG. 3B . 
         [0018]    The machine  10  is thus controlled to interrupt the flow of regular production blanks  27  when the proximity switch or sensor  47  senses this premature or advanced displacement of the tool  29  and case  31 , measured by reference to the crankshaft angle. This control strategy is implemented, by way of example, with a hardwired logic circuit schematically shown in  FIG. 4 . 
         [0019]    Once the coil of a relay  54  is turned on, its own contact closes and maintains the coil energized as long as either of relay contacts  56  or  57  are closed. The relay  56  is controlled by the proximity sensor  47  and the relay  57  is controlled by the programmable rotary limit switch  52 . In order to initially energize relay  54 , a momentary reset signal is applied to the coil of the relay via a push button switch  55 . Once the relay  54  is “latched in” through its own contact and either relay  56  or  57  remain energized, a “no fault” signal remains applied to the PLC input (the PLC  51  monitors for the absence of a signal to determine that a fault or turned blank condition has occurred). 
         [0020]    The programmable rotary limit switch  52  and associated relay  57  hold the turned blank fault indicator relay  54  energized during a time period or portion of a machine cycle that the tool case  31  is ordinarily displaced by proper engagement of a blank  27  in the tool  29 . The relay  57  serves to maintain the fault indicating relay  54  on, i.e. latched in at this portion of a machine cycle. In contrast, the programmable rotary limit switch  52  turns off the relay  57  for a time period or segment of a machine cycle before normal displacement of the tool case  31  and the normal turn off of the related relay  56  to thereby create a check window and detect premature actuation of the proximity sensor  47 , assumed to be the result of a turned blank. 
         [0021]    As soon as neither relay  56  or  57  is energized, the power to the coil of relay  54  is removed and this relay de-energizes which action also opens its own contact. At the same time, the signal to the PLC  51  disappears which condition the PLC recognizes as a sensed turned blank (TBM fault) and the crankshaft  12  is stopped by the PLC with a signal to the clutch brake  14 . In the process of stopping the crankshaft  12 , even if either relay  56  or  57  are re-energized, relay  54  will not latch in again until a momentary signal is again reapplied to its coil via the reset push button  55 . 
         [0022]    A dashed outline  70  on  FIG. 4  encompasses the major system components that include the relay logic elements  54 ,  56 , and  57 , the PLC  51 , and the programmable rotary limit switch  52 . It is feasible for all three of these elements to be integrated into a common programmable device capable of handling all the control tasks within the necessary throughput time restraints. The same functions performed by these elements can be handled in the same basic way, only with more software and less hardware control. 
         [0023]    While, as disclosed, the crankshaft  12  can be stopped from cycling by the PLC  51  in the event that a turned blank fault signal is generated by a shut off of the relay  54  to enable a machine operator to manually retrieve the turned blank from the product stream, it is envisioned that the turned blank can be automatically retrieved after it is ejected from the machine and, in fact, with appropriate controls the turned blank could be withdrawn from the product stream of good parts without stopping the crankshaft  12 . 
         [0024]    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.