Auto equalized dual pierce unit

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.

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.

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 18A
 and 18B 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 2A and 2B,
 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 2A and 2B are positioned so that the head or face of the
 piston 27A and 27B are facing towards the end caps 18A and 18B,
 respectively, of the cylinder. At the back of each of the pistons 2A and
 2B and secured with the piston is a pin 13A and B. Pin 13A and B extends
 upwardly and is rigidly secured to the respective slide block 19A and B.
 The slide blocks 19A and B carry the complementary tooling 25A and 25B
 which cooperate with the tooling mounted on centerpost 21.
 As shown in FIG. 2, slide blocks 19A and B travels in a T-slot 31 which
 runs the length of cylinder body 11. Slide blocks 19A 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 19A
 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 2A and 2B 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 2A and 2B 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 2A or 2B 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 2B. Fluid is supplied to a space between piston 2B and end cap
 18B. A similar port (not shown in FIG. 1 due to cutaway) on the left side
 supplies fluid between piston 2A and end cap 18A. FIG. 1 shows the press
 at rest, i.e., without fluid pressure. Piston 2A is shown with a recess or
 counterbore 39A into which fluid initially flows. As additional fluid is
 supplied, piston 2A 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
 13A and slide block 19A. As a result, tool 25A begins movement towards the
 tool post 21. This stage of operation is represented by FIG. 4. The tool
 25A comes into contact with the workpiece 41A but not with sufficient
 force to distort the workpiece.
 Upon movement of piston 2A towards the center of the cylinder, an equal
 force is acting upon end cap 18A (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 25A.
 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 25A and the tool
 on the post 21 do not deform leg 41A of workpiece before the piercing
 operation. Tool 25A and anvil 23A are against workpiece 41A and supporting
 it against deformities during the actual piercing operation.
 Additional pressure supplied to the space between piston 2A and 18A
 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 19A and cylinder body 11 have occurred, the fluid pressure
 is released. Upon release of the fluid pressure, spring 15 returns the
 piston 2A 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 41B of the workpiece,
 fluid pressure is supplied between piston 2B and end plate 18B to cause a
 mirror action movement of the cylinder body 11 and piston 2B and their
 associated tooling.
 Turning to FIG. 3, the slug removal system is shown. Stripper 45A is
 compressed during the piercing operation when contacting the workpiece
 41A. Upon withdrawal of the punch 25A from workpiece 41A, gas springs 47A
 and 49A cause bar 45A to extend relative to the punch helping to strip off
 any slugs and assist in cleaning workpiece 41A.
 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.