Abstract:
Disclosed is an automatically equalizing press for sequential operations on opposite sides of a workpiece. The press is designed to allow a pair of punch-anvil combinations to work on opposing sides of the workpiece without substantially deforming the workpiece prior to the final, e.g. piercing, operation. One tool from each combination is mounted on a slide block which is capable of movement independent of the other slide block. The slide blocks are operable by fluid actuated pistons.

Description:
BACKGROUND OF THE INVENTION 
     Certain manufacturing processes call for operations on two legs of a single piece such as a workpiece having a U-shaped cross-section. The operations are designed to be along a common axis going through that U cross-section. Due to tolerances in the part, as well as the stiffness of the part, the machinery is designed to bring the tools in contact with each leg without deforming the leg prior to the operation, e.g. piercing. A variety of machinery or presses have been devised to alleviate some of the problems encountered in this area. That machinery has included various cylinder and piston combinations for moving opposed tooling against a central workpiece. This tooling, however, suffers from several drawbacks. Among the drawbacks are that the mechanisms for producing sufficient force for the piercing operations are not collinear with the tools themselves, e.g. the punches and anvils. Thus, as more forces are produced, the tools are subject to greater forces which can cant or cock the tooling relative to the desired line of operation. This results in greater tool wear with concomitant reduced tool life, as well as poorer performance due to inaccurate tool alignment, etc. Efforts to reduce some of the problems with unbalanced forces have been countered with larger more massive tools to resist the forces. This, however, can be self defeating in that the tools have to fit within limited space in the factory environment. 
     SUMMARY OF THE INVENTION 
     The present invention concerns tooling for operations, e.g. punching, on legs of a U-shaped workpiece whereby the tools, e.g. the punches and anvils, are autoequalized so that the punch will first contact the part, then will actuate anvil (die) into or towards the workpiece to prevent deformation of the workpiece prior to the operation itself. The tooling then allows the sequential operation on the other leg of the workpiece in a similar manner. 
     One component of the tooling, e.g. either punches or anvils, are mounted on independently reciprocal slide blocks. One of the slide blocks is actuated by fluid pressure against a connective portion. A certain amount of travel of the slide block will result in sufficient force to overcome a mechanical resistor, e.g. a spring, and cause the other component of tooling to draw closer to the first set of tooling. For example, movement of a punch mounted on a slide block will, at a point in travel, cause sufficient force to be generated to cause an anvil mounted on the tooling to travel towards the punch. The resistance of the spring and relative location of the punch and anvil are selected so that the punch and anvil arrive sequentially at the workpiece. The resistance is selected, however, so that the tool that first contacts the workpiece does not substantially deform the workpiece prior to the complementary tool contacting the workpiece. The independently reciprocating slide blocks are mounted within a T-slot of the tooling to resist canting forces generated by the non-collinear systems. 
     Among the advantages of the present invention are a more compact unit that better resists torquing or canting forces caused by non-collinear pistons with less resultant wear and higher accuracy. Further features and attributes of the present invention are explained in greater detail below. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of the dual pierce punch of the present invention with a representative workpiece in a centered position. 
     FIG. 2 is a end view of the present invention. 
     FIG. 3 is a top plan view of the dual pierce punch of the present invention in a partial cutaway in a centered position. 
     FIG. 4 is a side view of the present invention in cutaway at a first stage of operation. 
     FIG. 5 is a partial cross-sectional view of the invention in a further stage of operation. 
     FIG. 6 is a detail of the invention in the piercing operation. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Turning to FIG. 1, Base  3  is designed to be secured to the factory environment so as to properly locate the press to the workpiece. Base  3  may be mounted directly to a fixture station or mounted through an adaptor plate (not shown) such as when replacing a pre-existing piece of equipment. 
     Upon the base is mounted cylinder body  11 . The cylinder body is mounted for reciprocal movement along a single axis relative to base  3 . When viewing FIGS. 1,  3 ,  4 ,  5  and  6 , that axis would be Left to Right (and vice versa) on the page. Cylinder body  11  may be mounted via track rails  9  (FIG. 2) utilizing roller, ball, or other bearings as known to one of ordinary skill in the art. Preferably two track rails  9  containing bearings are used. The track rails  9  should be displaced towards the outer edges of the cylinder body  11 . Mounted centrally underneath the cylinder body  11  is an equalizer bar  1 . The equalizer bar  1  runs coaxial with the axis of movement of the cylinder body  11 . The equalizer bar  1  is integral with the cylinder body  11 , either being formed as one piece or rigidly attached. 
     On either end of the equalizer bar  1  is a spring  6  attached to an equalizer bracket  4  which in turn is attached to the base  3 . In preferred embodiment, the spring  6  is a nitrogen gas spring. The spring  6  serves to resist or retard the reciprocating movement of the cylinder body  11  and will help return it to center. One advantage of nitrogen springs is that they can be readily tuned to vary resistance. In the preferred embodiment, the nitrogen springs  6  are threaded to the equalizer bracket  4  and locked into proper displacement by jam nut  5 . 
     Mounted at the top of cylinder body  11  is tool post  21 . The operation of the press usually involves opposed punch and anvil (anvil will also be referred to in the application as dies). In the preferred embodiment, tool post  21  carries the dies  23  against which punches  25  operate. Conversely, tool post  21  could carry the punches and the slide blocks (discussed infra) in that embodiment would carry the die. 
     Running the length of cylinder body  11  is a cylinder which is co-axial with the direction of reciprocating movement of the cylinder body. End caps  18 A and  18 B seal off the ends of the cylinder, O-ring  16  helps ensure a fluid tight seal of the cylinder ends. 
     Placed within the cylinder are first and second pistons  2 A and  2 B, respectively. Polypak “B” type seals or piston rings  12  encircle the pistons to help maintain a fluid tight seal during movement within the cylinder. Pistons  2 A and  2 B are positioned so that the head or face of the piston  27 A and  27 B are facing towards the end caps  18 A and  18 B, respectively, of the cylinder. At the back of each of the pistons  2 A and  2 B and secured with the piston is a pin  13 A and B. Pin  13 A and B extends upwardly and is rigidly secured to the respective slide block  19 A and B. The slide blocks  19 A and B carry the complementary tooling  25 A and  25 B which cooperate with the tooling mounted on centerpost  21 . 
     As shown in FIG. 2, slide blocks  19 A and B travels in a T-slot  31  which runs the length of cylinder body  11 . Slide blocks  19 A and B have T-shaped rails  33  to fit within the T-slot to close tolerances. The use of a T-slot close to the center line where the punching actually occurs minimizes play within the tooling and allows the large forces generated during the actual piercing or punching operation to be accommodated on the large surface area of the T-slot. The T-slot allows for sufficient surface area to reduce side-to-side play, as well as play in an up and down direction. There are no bearings placed between the runner  3  of the slide block  19 A and B and the T-slot  33 , the surfaces themselves doing the bearing, except for conventional lubricant which is supplied to the surfaces on a routine basis. 
     Between the pistons  2 A and  2 B within the cylinder of cylinder body  11 , a spring  15  such as a nitrogen spring, mechanical spring, or other mechanical resistance unit is placed as shown in FIG.  1 . In the preferred embodiment, a nitrogen spring is used. This spring provides a biasing force to return the pistons  2 A and  2 B towards their rest positions against the respective end caps  18 . The spring  15  operates in an environment of atmospheric air. Since the volume of air is subject to being reduced when either piston  2 A or  2 B travels down the cylinder towards spring  15 , muffler  34  (see FIG. 2) provides venting to and from the ambient air from the cylinder during operation of the press. 
     Proximity switches  10  are mounted on the press. Proximity bracket  7  (FIG. 1) is rigidly secured to the base  3  via bolts. Slots  35  in bracket  7  allows for fine adjustment of the operation of the press once installed. Proximity plates  17  are mounted to the side of cylinder body  11  for further mounting of proximity switches  10 . Slots  35  in proximity plates  17  allow for fine adjustment of the placement of the proximity switch, once the press is installed. 
     Operation of the Press 
     In a typical use of the press, fluid is supplied under pressure through a fluid access port. In FIG. 1, ref. no.  37  designates the fluid access port for piston  2 B. Fluid is supplied to a space between piston  2 B and end cap  18 B. A similar port (not shown in FIG. 1 due to cutaway) on the left side supplies fluid between piston  2 A and end cap  18 A. FIG. 1 shows the press at rest, i.e., without fluid pressure. Piston  2 A is shown with a recess or counterbore  39 A into which fluid initially flows. As additional fluid is supplied, piston  2 A begins to move towards the center of the cylinder (to the right in drawings  1 ,  3 ,  4  and  6 ) causing a concomitant movement of pin  1   3 A and slide block  1   9 A. As a result, tool  25 A begins movement towards the tool post  21 . This stage of operation is represented by FIG.  4 . The tool  25 A comes into contact with the workpiece  41 A but not with sufficient force to distort the workpiece. 
     Upon movement of piston  2 A towards the center of the cylinder, an equal force is acting upon end cap  18 A (rigidly secured to cylinder body  11 ) biasing it to the left in FIGS. 1,  3 ,  4 ,  5  and  6 . Once the resistant force of nitrogen spring  6  is exceeded, the cylinder body  11  begins to move relative to the base  3  causing the tool post  21  to move towards tool  25 A. This stage of operation is shown in FIG.  5 . By adjustment of the force rate of spring  6 , the press can be adjusted so that tool  25 A and the tool on the post  21  do not deform leg  41 A of workpiece before the piercing operation. Tool  25 A and anvil  23 A are against workpiece  41 A and supporting it against deformities during the actual piercing operation. 
     Additional pressure supplied to the space between piston  2 A and  18 A supplies the force to complete the operation such as the piercing shown in FIG.  6 . Proximity switches  10  are adjusted so that once the proper travel of slide block  19 A and cylinder body  11  have occurred, the fluid pressure is released. Upon release of the fluid pressure, spring  15  returns the piston  2 A and cylinder body  11  to their original centered positions relative to each other and spring  6  returns body  11  to its original position relative to base  3 . To pierce the other leg  41 B of the workpiece, fluid pressure is supplied between piston  2 B and end plate  18 B to cause a mirror action movement of the cylinder body  11  and piston  2 B and their associated tooling. 
     Turning to FIG. 3, the slug removal system is shown. Stripper  45 A is compressed during the piercing operation when contacting the workpiece  41 A. Upon withdrawal of the punch  25 A from workpiece  41 A, gas springs  47 A and  49 A cause bar  45 A to extend relative to the punch helping to strip off any slugs and assist in cleaning workpiece  41 A. 
     The result is a compact dual pierce press that is able to bear considerable force along the axis of movement with reduced play and wear resulting in higher accuracy over extended periods of time. Likewise, the press is relatively easy to build, adjust and maintain. The use of independent pistons and slide blocks, in combination with the cylinder body, minimize clearances. Having pistons for both the slide blocks and a single bore also help equalize operation for each side.