초록 ▼

Apparatus and method for forming curved needlepoint canvases from initially flat perforated sheet by applying pressure to a first side of the sheet, thus driving and deforming it into an aperture in a die, and by supporting the opposite side of the sheet during deformation with a pressure pad which

Apparatus and method for forming curved needlepoint canvases from initially flat perforated sheet by applying pressure to a first side of the sheet, thus driving and deforming it into an aperture in a die, and by supporting the opposite side of the sheet during deformation with a pressure pad which includes a recess into which the deformed sheet is driven.

대표청구항 ▼

1. In an apparatus for cold drawing a generally flat perforated plastic sheet, the apparatus including a die having a bore therein terminating in an aperture, first means for holding said sheet adjacent said aperture, and a punch having a curved contact surface, said punch being movable from a

1. In an apparatus for cold drawing a generally flat perforated plastic sheet, the apparatus including a die having a bore therein terminating in an aperture, first means for holding said sheet adjacent said aperture, and a punch having a curved contact surface, said punch being movable from a start position spaced from said sheet to a first position pressing a portion of said sheet into said aperture and forming a depression in said sheet, the improvement in combination therewith comprising: a pressure pad having an end surface with a recess in the center thereof, said pad having a first position inside said bore with said end surface adjacent said aperture and engaging and supporting said sheet while said punch is pressed downward, deforming said sheet into said recess said punch and pad being further movable to a second position, said punch pressing said sheet and pad together further into said bore and further deforming said sheet to have the shape of said contact surface while said pad remains engaging and supporting said deformed portion of said sheet, and drive means for moving said punch between said start, first and second positions, said punch further comprising on said contact surface a layer of material having durometer less than that of said sheet, said layer becoming embedded in perforations in said sheet when the punch is pressed to said first position, thereby establishing a mechanical coupling of said punch and sheet in the area of said embedded engagement. 2. Apparatus according to claim 1 wherein said contact surface comprises a hemispherical shape and said pad recess defines a circular arc having nominally the same radius as said hemispherical shape. 3. Apparatus according to claim 2 wherein said recess in said pressure pad had depth below said end surface of said pressure pad less than 50% of the radius of said contact surface, and said punch descends to said first position and forms said sheet fully into said recess while said pad is stationary and supports said sheet by engagement of said annular end surface, and said punch subsequently descends the remainder of the depth to said second position further drawing said sheet and simultaneously driving said pad downward the same distance as said punch moves between said first and second position. 4. Apparatus according to claim 2 wherein said punch further comprises a hemispherical-shaped layer of material having durometer less than that of said sheet secured on said hemispherical contact surface, said layer becoming embedded into perforations of said sheet when the punch is pressed to said first position, thereby establishing a mechanical coupling of said punch and sheet in the area of said embedded engagement. 5. Apparatus according to claim 4 wherein said layer is polyurethane having durometer in the range of 20 to 30. 6. Apparatus according to claim 2 wherein said die has a vertical bore defining a right cylinder whose diameter is the same as said aperture in the top end of said die, and said hemispherical contact surface of the punch has a radius nominally the same as said aperture. 7. Apparatus according to claim 1 wherein said first means is a frame comprising top and bottom parts separated by a space, said sheet being maintainable in a generally flat state in said space and being laterally movable in said space relative to said frame during said forming of said sheet. 8. Apparatus according to claim 7 wherein said top and bottom frames comprise generally square plates, each having a square central aperture the breadth of which is greater than the breadth of said die. 9. Apparatus according to claim 1 further comprising second means for releasably securing said punch to said die with said formed sheet therebetween. 10. Apparatus according to claim 1 wherein said die, punch, and pad comprise metal that is generally rigid. 11. Apparatus according to claim 1 wherein said pad is movable further downward to a third position separating said pad from said engagement with said sheet which remains between said punch and die, said drive means driving said pad to said third position after said punch and pad are driven to said second position. 12. Apparatus according to claim 11 further comprising means for coupling together said punch, die and formed sheet therebetween and means for heating said coupled punch, die and formed sheet to a temperature of approximately 212° F. for at least five seconds and then separating said punch, die and formed sheet. 13. Apparatus according to claim 1 wherein said sheet comprises thermoplastic. 14. Apparatus according to claim 1 wherein said sheet comprises thermoplastic formed as a mesh of two sets of parallel spaced ribs, one set perpendicular to the other with generally square shaped apertures between said ribs. 15. In a method of cold drawing a generally flat plastic sheet in which there are a plurality of spaced perforations, including the steps of positioning a punch with its contact surface on a first side of said sheet and an aperture of a die on the second opposite side of said sheet and pressing and deforming said sheet by said punch into said aperture, the improvement comprising the further steps of securing on said punch a layer of material having softer durometer than that of said sheet, supporting said second side of said sheet by an end surface of a pressure pad having a recess in said end surface, said recess having an inner wall conforming in shape to a contact surface of said punch, while urging said punch to press and deform a portion of said sheet into the recess and against said inner wall, thereby embedding said layer into perforations in said sheet when said sheet is pressed into said aperture and into and against said recess wall of said pad, thereby establishing a mechanical coupling between said punch and said sheet in the area of said embedded engagement, and thereafter urging said punch to press against and further deform said sheet while said inner wall remains in supporting engagement with said second side of said sheet and is moved as said punch further deforms said sheet. 16. A method according to claim 15 comprising the further step of separating said pad from said formed sheet, securing together said punch, die and formed sheet therebetween as a subassembly, submerging said subassembly in liquid at a temperature of approximately 212° F. for at least five seconds, removing said subassembly from said liquid and separating said formed sheet from said punch and die. 17. A method according to claim 15 wherein said liquid is water. 18. A method according to claim 15 wherein said punch defines a hemispherical shape, said recess in said pad defines a circular depression having radius slightly greater than the radius of said hemisphere, and said aperture has radius nominally the same as said hemisphere.