Patent Publication Number: US-7895926-B2

Title: Die cutting under vacuum through rollers

Description:
This application claims the benefit under 35 USC 119(e) of U.S. Application Ser. No. 60/701,995 filed Jul. 25, 2005 and claims priority to Canadian Application Serial No. 2,513,158 filed Jul. 25, 2005. U.S. Application Ser. No. 60/701,995 and Canadian Application Serial No. 2,513,158 are incorporated herein, in their entirety, by this reference to them. 
    
    
     FIELD 
     This specification describes one or more inventions that may relate to one or more of die cutting, steel rule or cavity dies, vacuum pre-compression in die cutting and roller presses. 
     BACKGROUND 
     The following background description is not an admission that any apparatus or method discussed below is prior art or part of the knowledge of people skilled in the art in any country. 
     U.S. Pat. No. 4,960,019 describes a stationary steel rule cutting die for cutting a fixed pattern in each of a plurality of stacked compressible material layers according to the shape of the steel rule die and including a vacuum system for reducing the stacked height of the compressible material layers prior to cutting. The die assembly includes an enclosure comprising an upper wall and collapsible side walls extending downwardly from the upper wall. A rigid annular structure is secured to the lower edge of the collapsible side walls. The enclosure is positioned over the stacked compressible material layers with an annular sealing surface defined on the lower peripheral edges of the rigid annular structure coacting with an upwardly facing, closed loop sealing surface defined on the steel rule cutting die to define a sealed chamber from which air is exhausted through the rigid annular structure to collapse the side walls of the enclosure and compress the material layers prior to cutting. 
     In U.S. Pat. No. 6,233,809, a cutting knife assembly has a baseboard with a generally planar surface. A cutting knife is detachably connected to the baseboard. The cutting knife extends in a perpendicular direction to the baseboard. The cutting knife circumscribes a knife cavity on the baseboard. At least one elongated cross member is affixed to the cutting knife and extends across the knife cavity. The cross member is mounted to the baseboard by a removable fastener. The cutting knife may then be easily removed from the baseboard and resecured. 
     U.S. Pat. Nos. 4,960,019 and 6,233,809 are incorporated herein, in their entirety, by this reference to them. 
     SUMMARY 
     It is an object of an invention described herein to improve on, or at least provide a useful alternative to, the prior art. It is another object of an invention described herein to provide a process or apparatus for cutting a material. The following summary is intended to introduce the reader to one or more of the inventions but not to define any invention. An invention may reside in any combination of one or more apparatus elements or process steps selected from the set of all apparatus elements and process steps described in any part of this document. 
     The inventors have observed that there is a need for a cost efficient method and apparatus for cutting low to medium quantities of material with high accuracy and material utilization, for example to produce automotive upholstery pieces for small manufacturers or limited production vehicles. Low to medium quantities may be, for example, the parts required in one material, for example cloth fabric or a vinyl laminate, for the interior of 1 to 20 automobiles. Some low volume work is being performed on machines that have some form of a computer controlled cutting head moving over a stationary sheet of material on a table. While these machines may be cost effective, the quality of the cut pieces is not as good as what may be obtained with dies. Some leather cutting is done by a roller press process. In this type of process, a sheet of leather is placed on a cutting pad which is a board made of a material, such as polypropylene, which is rigid enough to create a surface which can be cut against but soft enough to allow edges of the knives of dies to penetrate into it. Die cavities are placed on the leather by workers trained to get a good quantity and quality of cut pieces from irregularly shaped leather stock. This assembly is then sent through a roller press to cut the leather. While the cost of the roller press is sufficiently low for use in leather cutting, the process is not cost effective for cloth or vinyl work because the rate of production is comparatively low when compared to rates of production for cloth or vinyl cutting. Achieving higher throughput would require placing more layers of material under the dies with each pass. However, particularly with multiple layers of material, the rollers move or stretch the material as it is being cut causing the parts to grow in one direction or generally be inaccurately cut. 
     High volume automotive interiors are generally cut using steel rule type dies, cutting many layers of materials simultaneously in large presses. This process provides high quality parts, but the cost of a large press can only be recovered in high volume situations. 
     A process or apparatus described herein deals with these issues, in brief, by using a vacuum to compress multiple sheets of material against a set of dies before or while passing the material and dies through a roller press. The vacuum makes the die and material assembly more stable as it passes through the rollers and allows multiple layers to be cut accurately. Stability of the die and material assembly may be further enhanced by making the dies from narrow knife stock to create a low die and further optionally by installing braces vertically in some locations. Output may be further enhanced by placing the dies very close together or touching each other which is facilitated by using offset bevel steel for the knives of the die and removably mounting one or more dies to a die board which also aids in removing scrap pieces. Further optionally, in places where dies touch each other, parts of the outside side walls of the adjacent cavities may be ground to or near the point of the knife. Further optionally, the material and dies may be further pre-compressed by passing them through the roller press with the rollers set to a compressing, rather than cutting, separation distance. The process or apparatus thus provides a way to economically cut low to medium volumes of material accurately and economically or other uses or benefits, particularly where the same roller press can also be used part time for leather cutting. 
     In one aspect, an apparatus has a plurality of cavity dies attached to a die board. The dies and die board may be installed into, or be part of, an enclosure. The enclosure has or contains a cutting pad on the opposite side of the dies from the die board. The enclosure also has collapsible side walls and room for sheets of material, for example 1 to 6 sheets of material, to be placed in the enclosure between the dies and the cutting pad. A vacuum system can be attached in communication with the interior of the enclosure to create a vacuum in the enclosure, thus drawing the cutting pad and die board together and compressing any material between the dies and the cutting pad. The enclosure may be fed through a roller press to press the cutting pad against the dies so as to cut the material. One or more of the dies may have a brace or base plate through which it is attached to the baseboard. The dies may have offset bevel steel knives made of knife stock having a width of 32 mm or less or 20 mm or less, such that the die is 32 mm or less or 20 mm or less tall. One or more of the dies may be attached to the baseboard with quick release fasteners. The dies may be spaced from 0-1 mm apart from each other. 
     In another aspect, a process is described for producing pieces of material cut to a pattern from one or more, for example 1 to 6, sheets of material using cutting dies. The cutting dies are mounted on a die board in a pattern fitting within the perimeter of the sheets of material. The dies may touch adjacent dies or be spaced apart by 1 mm or less from adjacent dies at least along the controlling length or width of a nest or marker of dies. Sheets of material are placed on the dies. A cutting pad is placed over the sheets of material. The cutting pad is forced towards the die board, for example by a vacuum, to compress the sheets of material against the dies. The die board, dies, sheets of material and cutting pad are then passed through a roller press which forces the cutting pad into contact against the dies to cut the sheets of material. Optionally, one or more of the dies may be removed from the die board after cutting to assist in removing scraps of material from between adjacent dies. Further optionally, the sheets of material may be passed through the roller press to further pre-compress the material before cutting. 
     In other aspects, a quick release fastener, a die assembly with releasable dies and processes for mounting or removing dies or removing scrap from between dies are disclosed. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       One or more embodiments of one or more inventions will be described below with reference to the following figures. 
         FIG. 1  is a schematic representation of a die cutting apparatus being used to cut sheets of material. 
         FIG. 2  is a perspective view of several dies fastened to a die board resting on the bottom of an enclosure according to the apparatus of  FIG. 1 . 
         FIG. 3  is a perspective view of a section of a die board with a die fastened to the die board with a quick release fastener. 
         FIG. 3A  is a section view through a part of the die, die board and quick release fastener of  FIG. 3 . 
         FIG. 4  is an enlarged perspective view of a portion of the dies and die board of  FIG. 2  with a die removed to assist in removing scraps of cut material. 
         FIG. 5  is a perspective view of an enclosure containing dies according to  FIGS. 1 and 2  being fed through a roller press. 
     
    
    
     DETAILED DESCRIPTION 
     Various apparatuses or processes will be described below to provide an example of an embodiment of each claimed invention. No embodiment described below limits any claimed invention and any claimed invention may cover processes or apparatuses that are not described below. The claimed inventions are not limited to apparatuses or processes having all of the features of any one apparatus or process described below or to features common to multiple or all of the apparatuses described below. It is possible that an apparatus or process described below is not an embodiment of any claimed invention. The applicants, inventors and owners reserve all rights in any invention disclosed in an apparatus or process described below that is not claimed in this document and do not abandon, disclaim or dedicate to the public any such invention by its disclosure in this document. 
     Referring to part A of  FIG. 1 , a cutting assembly  10  has an enclosure  12 , a cutting pad  14 , a die board  16  and dies  18 . Dies  18  may be attached to the die board  16  by braces and fasteners as in U.S. Pat. No. 6,233,809. Optionally, dies  18  may be attached to die board  16  by making slots in the die board  16  to accept the dies  18 . When using slots in the die board  16 , the dies  18  may need to be spaced according to the limitations of router or laser slot cutting whereas using braces and fasteners to mount the dies  18  may allow for a closer spacing. In the embodiment illustrated, enclosure  12  incorporates cutting pad  14  and also has collapsible sides  20 , a bottom plate  22  and seals  24 . 
     Cutting pad  14  is made of a material, such as polypropylene, which is rigid enough to create a surface which may be cut against but soft enough to allow the dies  18  to penetrate it slightly. Die board  16  may be of any material, for example high density plastic, wood, or steel, suitable for transferring pressure from a press to the dies  18 . Optionally, cutting pad  14  may comprise two pads placed against each other in parallel. An outer pad is not penetrated by the dies  18  and so ensures that a seal or vacuum can be maintained. An inner pad is affixed to the underside of the outer pad, for example by adhesive tape or threaded fasteners. After many cuts, the inner pad may become eroded and need to be replaced. At such time, the inner pad is removed from the outer pad and replaced by a new inner pad. 
     Sides  20  may be of a rubber covered fabric or other flexible but generally gas impermeable material. Base plate  22  may be steel. Seals  24  may be fastened or bonded to sides  20  and attach to base plate  22 , for example magnetically, to enclose and seal a plenum  26  including space between the press board  14  and the die board  16 . An outlet  28  through a side  20  allows the plenum  26  to be connected to a vacuum source  30 , for example a vacuum pump, through hose  31 . Vacuum pump  30  is operable to create a partial vacuum in plenum  26  causing enclosure  12  to partially collapse and move press board  14  and die board  16  together to compress sheets of material  32  against dies  18  as shown in part B of  FIG. 1 . Cutting assembly  10  may then be fed through a roller press  34  as shown in part C of  FIG. 1 . Roller press  34  has conveyors  36  which force cutting assembly  10  through a pair of rollers  38 . Rollers  38  press the press board  14  against the die board  16  such that press board  14  is made to contact the tops, or knife edges, or dies  18 . The sheets of material  32  are cut by the dies  18 . Cut pieces  40  of material, shaped according to the patterns embodied by dies  18 , fall into the cavities of dies  18 . Scrap pieces  42  fall into spaces between dies  18 . The spaces within or between dies  18  may optionally have a layer of foam (not illustrated) placed in them as described in U.S. Pat. No. 4,960,019. 
     Optionally, assembly  10  can be passed through the roller press  34  in multiple passes to either further pre-compress the sheets of material  32  or to cut the sheets of material  32  in multiple passes. For example, during a first pass in a first direction, the rollers  38  may be set at a separation distance that further compresses the sheets of material  32  but does not cut them. The vacuum pump  30  may be on during this first pass such that there is only a limited rebound of the sheets of material  32  after the first pass, if any. The rollers  38  may then be moved closer together and the assembly passed through the rollers  38  a second time, optionally in a reverse direction. This second pass may cut the sheets of material  32 . For example, 6 plies of a fabric material might initially have a thickness of 35 to 40 mm when placed on the dies  18 . When the assembly  10  is assembled and vacuum source  30  turned on, the sheets of material  32  may compress, depending on the material, to for example 12 to 35 mm. A first pass through the roller press  34  with roller  38  set at a separation distance, less than the height of the assembly  10  but large enough to not cut the sheets of material  32 , may result in the sheets of material  32  having a thickness of 80 percent or less, or 60 percent or less, of their thickness before this pass, that is their thickness under vacuum alone. Stacks of a lesser number of sheets of material  32  involve correspondingly lesser thicknesses. The vacuum source may be left on continuously from before the first pass through roller press  34 , whether it is a cutting or compressing pass, until the sheets of material  32  have been fully cut. 
       FIG. 2  shows base plate  22  resting on a sheet of high density plastic  44  used to facilitate moving cutting unit  10  along skid tracks towards a roller press  34 . Die board  16  may be about 1-3 meter in width and 2-7 meters in length and have dies  18  across almost its entire area. A paper pattern (not shown) may be placed on die board  16  to aid in placing dies  18  according to a computer generated plot, printed on the paper pattern, of a best fit for dies  18  to minimize the amount of scrap produced from a piece of material of a given size. Dies  18  illustrated are removable dies attached to the die board  16  by fasteners through braces  54 , as described in U.S. Pat. No. 6,233,809 although other types of die  18  and die board  16  assemblies may be used. 
       FIGS. 3 and 4  show some dies  18  in larger detail. Dies  18  have a knife  50  having a knife edge  52  defining the shape of the periphery, or pattern, of a piece of material to be cut with the die  18 . The knife  50  is supported by braces  54  which also have holes  56  to facilitate using fasteners, for example screws  58 , to attach the dies  18  to die board  16 . Braces  54  are shown oriented horizontally although some braces  54  may optionally be made of a narrower material, oriented vertically, and located to strengthen areas of a die  18  under significant stress, for example where adjacent dies  18  touch each other or are very close together. 
     One or more dies  18  may also be fastened to die board  16  with quick release fittings  60 . As shown in  FIGS. 3 ,  3 A and  4 , quick release fitting  60  has cooperating elements or screws  74  that may be threaded into the die board  16  and cooperate with a bottom plate  62  and top plate  66 . Cooperating screws  74  have a shaft having a wide portion  76  which is the same diameter as the head of cooperating screw  74  and fits into an enlarged hole in brace  54  for example with an interference fit. The shaft also has a narrow section  78  between the head and the wide portion  76  of the shaft. Bottom plate  62  has a hole sized to fit over the head of cooperating screw  74  and guides  64  which hold the top plate  66  against the bottom plate  62  but allow the top plate  66  to slide horizontally. Top plate  66  has a slot  68  which is adapted to fit around narrow section  78  but not allow the head of a cooperating screw  74  to pass through the slot  68 . Slot  68  may also have a narrow opening such that top plate  66  snaps around the cooperating screw  74 . With top plate  66  slid so that the narrow section  78  of cooperating screw  74  is within slot  68 , the head of cooperating screw  74  can not pass through fitting  60  and so brace  54  is held in place. However, with top plate  66  slid away from cooperating screw  74 , the head of cooperating screw  74  can pass through fitting  60  allowing brace  54  and fitting  60  to be removed. Although this method and apparatus of mounting dies is described herein in combination with a roller press  34 , the same apparatus or process may be used to fasten dies  18  to die board  16  for use in other kinds of presses. 
     The knife  50  of die  18  may be relatively short compared to dies used in other applications. For example, knife  50  may be 32 mm tall or less or 20 mm tall or less, for example about 19 or 20 mm. The inventors have found that taller knives  50  are not necessary for economical low to medium volume cutting and may flex and so produce less accurate cut pieces in the method and apparatus of the invention. Knife edge  52  is offset to the outside of dies  18 . With this offset, and the short knife  50  being used to cut a limited, for example 6 or less, number of sheets, dies  18  can be placed very close together, for example at spacings of 1 mm or less or even touching at points of tangency with neighbouring dies  18 . Such small spacing may be required only between those dies  18  located along the controlling length or width of a set of dies  18 . Where die  18  spacing can be increased without increasing the length or width of a set of dies, a larger spacing may be used to reduce stress on the dies  18  and make scrap removal easier. Optionally, in places where adjacent dies  18  touch each other, the outside of the dies  18  may be ground down or otherwise removed to, or near to, knife edge  52  to reduce or remove the bevel on the outside of knife edge  52 . This allows parts of two adjacent dies  18  to be placed next to each other so as to create, in effect, a section of thick blade with a knife edge  52  in its center serving two adjacent dies  18 . 
     The small spacing along the controlling width or length, even compared to a slightly larger 3 mm spacing, produces a great reduction in scrap wastage. However, scrap pieces may be forced tightly into small inter die areas  70 , particularly if marker notches  72  in knife  50  angle into an inter die area  70 . Removing scrap from these areas is facilitated by attaching one or more dies  18  with the quick release fittings  60 . The quick release fittings  60  allow these dies  18  to be quickly removed between cuts, as shown in  FIG. 4 , to strip scrap from the inter die area  70 . Since not all dies  18  will have very small inter die areas  70  near them, and since removing one die  18  opens up the inter die spaces that the removed die  18  shares with stationary dies  18 , only some dies  18  need to be fitted with quick release fittings  60  or removed between cuts. Other dies  18  may be simply screwed to die board  16  and remain in place between cuts. 
     As shown in  FIG. 5 , a top part of the enclosure  12  including cutting pad  14  and sides  20  has been attached over base plate  22 . Seals  24  are within sides  20  and not visible. Die board  16 , dies  18  and a sheet of material placed over the dies  18  are not visible but located within enclosure  12 . A vacuum source  30 , not visible, is applying a partial vacuum to enclosure  12 . The resulting cutting unit  10  is being moved by conveyors  36  to the rollers  38  of a roller press  34 . Cutting unit  10  will emerge from the other side of roller press  34  with the sheet of material having been cut by the dies  18 . 
     The description above was of a sample embodiment or embodiments of one or more claims and not intended to limit or define the invention of any claim which may be carried out in various alternate embodiments.