Differential pressure device for folding apparatus
United States Patent n 1 nu 3,875,784  
 Daniels Apr. 8, 1975 [54] DIFFERENTIAL PRESSURE DEVICE FOR 3.388.574 6/[968 lgnoffo 72/22 3.581.535 (lll ll Hlllkh&#39; .a 72/3]:  
 {75] Inventor: Dennis Daniels, Bcllcvue. Wash. Prim)? w. Lanhum [73] Assignee: U.S. Amada l.td.. Seattle. Wash. AMI shrill I.\&#39;umi1m&#39;M. J. Keenan [22 Filed: Mar 4&#39; I974 Agcnr. or Fn&#39;mSeed. Berry, Vernon (&#39;51 21 Appl No.: 448.037  
  I57] ABSTRACT 2% 72/320: n/Dlb 72/313 A folding apparatus is provided with a pivotal folding l 7 4 2 punch that moves past a work sheet supporting sur- 8] held of 1: face and an anvil. Hydraulically powered piston and LIDIG&#39; 8 cylinder mechanisms pull the anvil against the work sheet supporting surface while simultaneously pulling [56] f f (Med the punch about the anvil. Second hydraulic cylinder UNITED PATENTS and piston mechanisms provide a variable resistance 2.228.448 H194! Fatlur 72/3l9 force against the movement of the punch. 3 l)l)9 2()l ll/Whl Hansen 71/322 l 3.209.570 m/whs Hills 72m 6 Ualm- 3 Drawmg Fgures DIFFERENTIAL PRESSURE DEVICE FOR FOLDING APPARATUS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to numerically controlled, automatic folding machines and. more particularly. to means for adjusting the clamping pressure between the anvil and the work sheet supporting surface on such folding machines.  
 2. Description of the Prior Art In my earlier application. Ser. No. 186.062. filed Oct. 4. l97l. now US. Pat. No. 3.815.393. there is disclosed a sheet metal forming maching of the type having a work sheet supporting surface. At the end of the supporting surface and spaced therefrom is a movable anvil. A movable folding punch is pivotally mounted on the machine to pivot past the end of the anvil and the work sheet supporting surface to bend the sheet metal around the anvil. The clamping force between the anvil and the work sheet supporting surface is automatically provided by a pair of hydraulic cylinders and pistons. The cylinders are mounted on slides that are secured to the ends of the anvil and the piston rods are coupled by chains to the punch. Retraction of the piston rods first pulls the anvil down into engagement with the work sheet and then draws the punch up and around for the bending operation. Many different types of mechanisms could be provided for obtaining the combined clamping and punching action. but. for the purposees of this invention. it only need be understood that the greater the pull on the pivotable punch. the greater the clamping force.  
  sheet metal. of course. comes in many different thicknesses and degrees of ductility. and the same machine will be required to fold thick V4 inch) steel plates and 1/32 inch aluminum sheets. lfthe clamping load is designed for tough steel. the anvil will press the steel with a large force to prevent slippage during bending. However. this same clamping force is then also applied on soft aluminum sheet prior to the punch beginning its bending action. In such a case. the clamping pressure may be too great. leaving an impression in the aluminum due to the excessive clamping force.  
 SUMMARY OF THE INVENTION It is an object of this invention to provide a variable differential pressure device for varying the clamping force on a work sheet in a pivotable. punch-type folding machine.  
  It is another object of this invention to provide an automatic folding machine in which the clamping force can be readily varied. dependent upon the type of work sheet being folded.  
  Basically. the invention employs hydraulically powered resistance means that oppose the force tending to pivot the punch about the anvil. Control means are provided for varying the amount of the resistance force. In the preferred embodiment. the resistance force is provided by a pair of hydraulic cylinder and piston mechanisms. the piston rods being operatively connected to the ends of the folding punch. A variable pressure relief valve is in the hydraulic line discharging from the cylinder when the punch is being moved about the anvil so that. by varying the relief pressure. the amount of resistance is determined.  
 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an isometric ofa preferred folding machine embodying the principles of the invention.  
  FIG. 2 is a vertical section of the folding machine shown in FIG. 1.  
  FIG. 3 is a preferred hydraulic schematic embodying the principles of the invention.  
 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As best shown in FIG. I. the folding apparatus includes a base frame 10 having side frames 12 and 14 and a work piece supporting surface 18. The work piece supporting surface is provided with adjustable stops 22 for moving a work sheet upwardly thereon. An anvil 23 is fixed at either end to a pair of slides 24 that ride in guides 25 mounted on the side frames 12 and 14. The anvil is movable upwardly a slight distance from the work piece supporting surface 18 so that a work sheet W can be moved beneath. The anvil can then be moved toward the supporting surface 18 to tightly clamp the work sheet during the folding operation.  
  Folding is accomplished by a pivotable punch 26 of the type described in my earlier application which is mounted to pivot about an axis 27.  
  The punch is simultaneously pivoted with additional clamping force being applied to the work sheet by a pair of hydraulic cylinders and pistons 30. For this purpose the cylinders are pivotally mounted by brackets 32 to the slides 24 which are coupled to the anvil 23. The piston rods 34 are coupled by chains 36 to the end of the punch by studs 38. As is readily apparent. retraction of the piston rods into the cylinders 30 first pulls the anvil 23 downwardly to clamp the work sheet and thence. with further retraction. draws the punch 26 about the end of the anvil to fold the work sheet. As is well known. the anvil is provided with a folding edge 23a to provide a crease in the work sheet.  
  For the purpose of providing a variable resistance against pivotable movement of the punch 26, a second set of cylinders and pistons 40 are provided. one on each side of the machine. Piston rods 42 are each coupled by a pivotable clevis 44 to the punch 26. As is readily apparent. movement of the punch in a counterclockwise direction. as shown in FIG. 2, will cause the piston rods 42 to be extended in the cylinders 40.  
  FIG. 3 illustrates a preferred hydraulic circuit for varying the amount of resistance force supplied by the piston rods 42. A pump P driven by a motor M delivers pressurized fluid to a solenoid-controlled, spring-biased valve 50. In the deenergized position. valve 50 directs fluid to line 51 to a three-way. spring-centered. solenoid-controlled valve 52. In the center position. the line 51 is connected to sump. Movement of valve 52 to the right directs line pressure from 51 to a line 53 and thence to the piston rod ends 34 of the cylinders 30. The piston rods 34 begin to retract but movement is resisted by piston rods 42, thus pulling the cylinders 30 and slides 24 downwardly to place an initial clamping force on the work sheet as described earlier. Fluid trapped in the piston rod ends of the cylinders 40 passes through lines 54 to a solenoid-operated valve 60 which. when energized. passes the fluid to a line 61 which is directed to sump through a pressure relief valve 62. This pressure relief valve is of any conventional type which can be adjusted to open to sump through a range of 5 to 500 psi. Assuming valve 62 is set to open at a pressure of (if) p.s.i.. for example. the punch 26 will be unable to pivot until such time as the clamping force exceeds the 60 psi. resistance force of the piston rods 42. Once this pressure is exceeded. additional clamping force is applied. dependent on the resistance to bending of the material of the work sheet. By changing the setting of valve 62. it can be readily seen that the initial clamping force can be easily varied from low forces for soft materials to large forces for tough materials.  
  The rate of punch movement is controlled by a flow restriction valve 70 and a two-way. spring-return solenoid valve 75. When valve 52 is to the right. retracting piston rods 34. valve 75 is moved to the left. causing fluid from the head ends of cylinders 30 to pass through check valve 72 and thence through the flow restriction valve 70. The valve 711 permits fluid to leave the cylinders at a controlled rate.  
  The piston rods 42 are retracted while simultaneously extending the piston rods 34 (and returning the punch} by moving the valve 52 to the left and valve 75 to the right. as shown in FIG. 3. In this position. line pressure front line 51 passes through valve 75. thence b through check valve 72 to lines 54. moving the piston rods 42 to the right. The movement of piston rods 42 to the right pulls the punch back down. causing the piston rods 34 to be extended through chains 36. Valve 72 opens only after a slight. predetermined pressure is reached. so that fluid moves piston rods 42 prior to piston rods 34. thus assuring tension in the chains 36.  
  While preferred embodiments of the invention have been illustrated and described. it should be understood that variations will be apparent to one skilled in the art without departing from the principles of the invention.  
  The embodiments of an invention in which a particular property or privilege is claimed are defined as follovvs:  
  l. A variable load applying apparatus for a fluidoperated folding machine of the type having a frame provided with a work sheet supporting surface. an anvil spaced from said work sheet supporting surface. to allow free movement of a work sheet beneath and having a folding edge. a punch mounted for pivotal movement past said work sheet supporting surface and folding edge to bend a work sheet clamped between the anvil and work sheet supporting surface. first powered means for moving the anvil toward said work sheet supporting surface for clamping a work sheet therebetween and for moving said punch to bend the work sheet. and wherein the clamping force is varied directly with the punch bending force. the improvement com prising:  
 means for providing a variable resistance force against movement of said punch so that initial movement of said first powered means effects a variable clamping force on the work sheet dependent on said resistance force. and  
 variable control means for determining the resistance force.  
  2. The apparatus of claim 1. said means for providing a variable resistance force including second powered means flexibly coupled to said punch.  
  3. The apparatus of claim I, said first powered means including flexible coupling means secured to opposite ends ofsaid punch, said second powered means including second flexible coupling means secured to opposite ends of said punch. said first and second powered means including hydraulic means for providing simultaneously opposed forces on said punch for controlling pivotal movement of the punch.  
  4. The apparatus of claim 3, said folding machine including transversely spaced. upright side frames having guide slots therein. said first powered means including cylinders and piston rods. linkage means pivotally securing each cylinder to said anvil. said flexible coupling means secured between the piston rods and said punch whereby retraction of said piston rods pulls said cylinders against said linkage means to push said anvil against said work piece supporting surface.  
  S. The apparatus of claim 2, said cylinders and piston rods coupled between the punch and said frame. said second powered means including force resistance means for providing a variable resistance force including hydraulic flow lines coupled to said cylinders. said control means including a pressure relief valve coupled to said hydraulic flow lines for relieving fluid pressure in said cylinders to extend the piston rods and thus allow movement ofthe punch. only after the resistance force exceeds a predetermined amount.  
  6. The apparatus of claim 5. said first powered means including primary cylinders and piston rods and bydraulic lines to said cylinders. said control means ineluding main control valve means for directing flow to said primary cylinders to begin moving the anvil against the work sheet and thence pivoting the punch at a con