Method and apparatus for cutting sheets of material

Abstract: A cutting die (10), which has one or more blades (20) forming the perimeter of a ply to be cut from a sheet of material (14), has a resilient insert (40) placed within the blades to detach the ply from the material and from the cutting die (10) after the ply has been cut from the material (14) and has a hook-like appendage (28) extending from the perimeter of the blades to grip the material after the plies have been cut therefrom.

Description: This invention relates to a cutting die and also concernes a method and an apparatus using the cutting die for cutting plies for a composite article. Background Art Typically, a composite article is constructed of a plurality of plies. The plies are layered in register to conform to the plan shape of a finished article. The plies of some articles are cut from a resinous matrix preimpregnated composite sheet (called a prepreg). The cut plies are layered and cured in a molding die (usually at high temperature and pressure) to form the finished article. The prepreg sheets are supplied from a continuous roll. Each roll has a layer of paper positioned between each wrap thereof to prevent the wraps from sticking to one another. The prepreg plies may be cut into desired shapes by a computer controlled cutter. The computer controlled cutter cuts each ply from a sheet according to programmed instructions which detail each shape. Computerized cutting has several drawbacks; the process is generally slow as each ply is cut individually, and it is difficult to verify whether complete and proper cuts have been made because each cut ply remains within the prepreg waste (or "skeleton") after cutting. It is particularly important to have complete cuts passing through the prepreg to avoid manual intervention to cut the plies from the skeleton, and to allow automated machinery, which is used to stack the plies, to lift the cut plies from the skeleton without interference therefrom. Steel rule dies have been used to simultaneously cut a plurality of plies from a plurality of stacked prepreg sheets. Steel rule dies are generally comprised of a plurality of knife edges that are set into a backing board. The knife edges form the perimeter of a shape of a ply to be cut. The cutting process includes; unrolling a roll of prepreg to cut sheets therefrom, layering (or stacking) several sheets on top of one another, utilizing the steel rule die to cut the desired plies, separating each ply from the stacks thereof, marking each ply so that each ply may be properly placed (laid up) to form the article, and removing the paper from each ply prior to laying up each ply. Such a process is time consuming, labor intensive and prone to error. A cutting die according to the precharacterizing portion of independent claim 1 is disclosed in US-A-4,480,507 which concerns a punching unit for simultaneously cutting one or more wrappers from a tobacco leaf. A plurality of knife forms are fastened to a carrier. The interior of each knife form is filled out with a filling body. Expelling plunger means are provided to facilitate removal of the cut wrapper from the knife forms. Air suction means are used to deposit a tobacco leaf in stretched state on the knife forms. Disclosure of Invention In accordance with the invention there is provided a cutting die having one or more blades disposed thereon, said blades having knife edges forming a closed contour having a perimeter, said blades being adapted to cut a ply at the perimeter of the closed contour from a sheet of material, said die comprising detaching means disposed within said closed contour formed by said blades for detaching said ply from said cutting die and from said sheet after said ply has been cut, said die further comprising holding means disposed outside the perimeter of said closed contour to hold the sheet of material, characterized in that said holding means comprise appendages depending from said blades to hold the sheet of material after the ply has been cut. The improved cutting die cuts a plurality of plies reliably and efficiently. By the provision of the holding means it can be verified whether a ply is completely and properly cut from the sheet of material. Preferably, the detaching means comprises a resilient material, such as foam rubber, disposed within the closed contour defined by the blades and protruding above a plane formed by the knife edges of the blades. The cutting apparatus using the cutting die according to the invention includes a cutting board against which the cutting die cuts the plies. The cutting board may have a plurality of stakes extending therefrom to register the cut plies thereupon. The method of cutting using the cutting die according to the invention comprises the steps of: placing a sheet of material upon said cutting die, placing said sheet of material and die upon a cutting board, pressing said cutting die and cutting board together, said cutting die thereby cutting a ply from said sheet of material, and simultaneously separating said cutting die and cutting board, gripping said sheet of material about said perimeter by said blades, and detaching said ply from said sheet of material and from said cutting die. According to one embodiment the cutting die as well as the apparatus and method of cutting are conducive to automated laying up of the plies for each article. A paper backing layer is removed from the sheet of material before cutting. These and other features and advantages of the present invention will become more apparent in light of the detailed description of a best mode embodiment thereof, as illustrated in the accompanying drawing. Brief Description of Drawing Fig. 1 is a perspective view of a cutting die, a cutting board and a sheet of material before the material is cut, the cutting board and cutting die employing the features of the invention; Fig. 2 is a perspective view of the cutting board and cutting die of Fig. 1 after the sheet of material has been cut. Best Mode for Carrying Out the Invention Referring to Figs. 1 and 2, a cutting die 10 and cutting board 12 embodying the concepts of the present invention are shown. The cutting board and cutting die are used to cut plies 16 from sheets of material 14 such as prepreg (an interwoven graphite and fiberglass material which is impregnated by a polyimide resin system). The plies 16 are used to construct composite articles (not shown). One of ordinary skill in the art will readily appreciate that such a cutting board and cutting die may be utilized to cut materials other than prepreg. The cutting die 10 is comprised of a rigid backing board 18 which holds a plurality of blades 20 having knife edges 22. The blades, which are constructed of a steel banding material, are conventionally set within the backing board to form the perimeter 23 of the plies 16 to be cut. Generally, a separate blade is used to form each edge of the perimeter. The blades are either welded or brazed at their intersections 24 (i.e. at the corners of the perimeters) to close the perimeter. Some of the blades and their corresponding knife edges have portions 26 extending beyond the intersections of the blades. Such portions 26 have a hook-like appendage 28 having a curved inner surface 30. The appendage 28 helps the cutting die 10 grip the skeleton 32 of the material after cutting as will be discussed infra. Opposing corners 34 of the cutting die have blades which form a perimeter 36 that cuts a locating ply 38 as will be discussed infra. An insert 40 of closed cell, medium density, resilient material, such as a foam rubber is placed within the perimeter 23 of the blades. The insert protrudes above a plane formed by the knife edges 22. The insert protrudes above the plane of the knife edges a sufficient distance to ensure that the insert pushes the plies 16 from within the perimeter 23 of the blades 20 after cutting. The insert may include holes 42 to allow the insert to compress evenly. Additionally, the insert 40 is coated with a thin layer (not shown) of a release agent, such as tetraflouroethylene to minimize the possibility that a material (such as prepreg) sticks to the insert 40. The backing board 18 of the cutting die 10 has four, conventionally mounted, locating pins 44 extending therefrom as will be discussed infra. A plurality of clamps 46, each comprising a pivotally mounted band spring 48 and a mounting block 50, are disposed about the periphery of the backing board to hold a sheet of material as will be discussed infra. The cutting board is constructed of an extruded, molybdenum disulfide filled, nylon available from the Norton-Performance Plastics Company of Wayne, New Jersey under the tradename of Vekton®. The cutting board is relatively hard, wear resistant, and non-adherent so that it withstands repeated cutting and so plies cut thereon may be readily removed. A plurality of stakes 52 extend through the cutting board in approximate register with the position of the plies that are cut thereon as will be discussed infra. The cutting board has four notched portions 54, each notched portion adapted to receive a locating pin 44 therein to place the cutting die 10 in approximate register with the cutting board 12. In operation, the sheet of material 14 is placed upon the cutting die 10 over the knife edges 22. The material is then aligned (utilizing the locating pins 44 as a guide) on the cutting die and mounting blocks 50 so that the orientation of the fibers within the material meet the requirements of the article. The material is then secured to the mounting blocks (and the cutting die thereby) by pivoting the band springs 48 to clamp the sheet of material between the band springs 48 and the mounting blocks 50. After the sheet of material is secured, the cutting die is inverted and brought into contact with the cutting board. The locating pins 44 of the cutting die are located within the notches 54 of the cutting board so that the cutting board and cutting die and the stakes 52 of the cutting board and the perimeters 23 of the blades are in approximate register. Registration between the cutting board and cutting die is not exact to avoid consistently cutting in one place on the cutting board. Cutting in one place might score the board causing the material to stick within the board or fail to be fully cut. Both conditions are most undesirable. The cutting die and cutting board are then transported through a conventional roller press (not shown). The roller press presses the cutting board and die together thereby; forcing the knife edges 22 (including the portions 26 extending beyond the perimeter of the blades) through the material 14 to cut the plies 16 (including the locating plies 38) from the sheet of material, and compressing the insert 40. After the cutting board and cutting die pass through the roller press, the cutting die is lifted vertically above the cutting board (See Fig. 2). As the cutting die is lifted, the plies are separated from the perimeters 23 of the knife edges 22 of the cutting die and the skeleton 32 of the material by the insert 40. The inserts, which are no longer compressed, recovers their normal dimensions to protrude above the plane of the knife edges to force the cut plies out of the cutting die. The stakes 52 in the cutting board tend to grip the cut plies and hold them in register for further processing as will be discussed infra. During the pressing by the roller press, the hook-like appendage 28 penetrates the material 14. The material cut by the hook-like appendage tends to close about the curved inner portion 30 of the hook-like appendage. As a result, in conjunction with the normal friction between the perimeter of the blades and the skeleton, the skeleton 32 tends to adhere to the blades and is removed with the cutting die as the cutting die is lifted from the cutting board. The cut plies are left on the cutting board. Generally, the skeleton 32 is removed from the cutting die, and the cut plies, which are held in place by the stakes 52, are sent with the cutting board to be used in constructing a composite article. At another station (not shown) a computer controlled optical scanner (not shown) identifies the position of the locating plies 38 on the cutting board and then uses a data base to determine the position of the other plies 16. The computer may then control a robot (not shown) to pick up the plies and properly layer them to construct a preform of the composite article. Since each ply 16 is separated from the cutting die by the insert and from the skeleton 32 by the removal of the skeleton with the cutting die, it is simple to optically inspect whether a ply has been properly cut. Incomplete cuts may necessitate the stoppage of the assembly process thereby requiring manual intervention. Time and materials may be wasted and labor expenses may increase. Further, the invention facilitates automatic production of articles by permitting the use of automatic machines that are adapted to pick up and layer the cut plies.

Claims: Cutting die having one or more blades (20) disposed thereon, said blades (20) having knife edges (22) forming a closed contour having a perimeter (23), said blades (20) being adapted to cut a ply (16) at the perimeter (23) of the closed contour from a sheet of material (14), said die (10) comprising detaching means (40) disposed within said closed contour formed by said blades (20) for detaching said ply (16) from said cutting die (10) and from said sheet (14) after said ply (16) has been cut, said die (10) further comprising holding means disposed outside the perimeter (23) of said closed contour to hold the sheet of material (14), characterized in that said holding means comprise appendages (28) depending from said blades (20) to hold the sheet of material (14) after the ply (16) has been cut. Cutting die according to claim 1, characterized in that the appendages (28) are hook-like shaped. Cutting die according to claim 1, characterized by further comprising a plurality of clamps (46) disposed about said closed contour for holding and registering said sheet (14) against said blades (20). Cutting die according to claim 1, characterized by comprising further blades (20), said further blades having knife edges (22) forming at least one further closed contour having a perimeter (36), said further blades (20) being adapted to cut at least one further ply (38) at the perimeter (36) of said further closed contour from said sheet of material (14). Cutting die according to claim 1, characterized in that said detaching means (40) comprises resilient material disposed within the closed contour defined by said blades (20), said material protruding above a plane formed by knife edges (22) of said blades (20). Cutting die according to claim 5, characterized in that said resilient material is a foam rubber. Apparatus for cutting a ply from a sheet of material comprising a cutting die (10) according to claim 1, said apparatus being characterized by having a cutting board (12), said cutting board (12) and cutting die (10) being adapted to receive said sheet of material (14) therebetween and to be pressed together so that said blades (20) of said cutting die (10) cut said ply (16) from said material (14) against said cutting board (12). Apparatus according to claim 7, characterized in that said cutting die (10) has a plurality of pins (44) disposed about a periphery thereof, and said cutting board (12) has a plurality of notches (54) disposed within edges thereof, said pins (44) being adapted to be located within said notches (54) such that said cutting board (12) and said cutting die (10) are in approximate register. Apparatus according to claim 8, characterized in that said cutting board (12) further comprises a plurality of stakes (52) extending therefrom for gripping said ply (16) after said ply (16) is cut by said cutting die (10), said stakes (52) being in register with said perimeters of said cutting die (10) when said cutting die (10) and cutting board (12) are in said approximate register. Apparatus according to claim 9, characterized by comprising a plurality of further blades (20), said further blades having knife edges (22) forming at least one further closed contour having a perimeter (36), said further blades being adapted to cut at least one locating ply (38) at the perimeter (36) of said further closed contour from said sheet of material, after cutting of all plies (16,38) by the die (10) said at least one locating ply (38) being used to determine the position of the other ply (16). Apparatus according to claim 7, characterized in that said cutting board (12) further has a plurality of stakes (52) extending therefrom for gripping said ply (16) after said ply (16) is cut by said cutting die (10). Method for cutting a ply (16) from a sheet of material (14) utilizing a cutting die (10) according to claim 1, said method being characterized by comprising: placing a sheet of material (14) upon said cutting die (10), placing said sheet of material (14) and die (10) upon a cutting board (12), pressing said cutting die (10) and cutting board (12) together, said cutting die (10) thereby cutting a ply (16) from said sheet of material (14), and simultaneously separating said cutting die (10) and cutting board (12), gripping said sheet of material (14) about said perimeter by said blades (20), and detaching said ply (16) from said sheet of material (14) and from said cutting die (10). Method according to claim 12, characterized by further comprising removing a piece of backing material from said material (14) prior to placing said sheet of material (14) and die (10) upon said cutting board (12).

Inventors: FIDLER ALLAN H, MEMMOTT JAMES VAN WYCK, SINGER STEVEN D, FIDLER, ALLAN H., MEMMOTT, JAMES VAN WYCK, SINGER, STEVEN D.
Applicants: UNITED TECHNOLOGIES CORP, UNITED TECHNOLOGIES CORPORATION
Application year: 1989
Main classification: B26F1
IPC codes: B26F1, B26D7, B26D1