Abstract:
A fluid jet cutting apparatus has a material supporting bed comprising a tank-like structure and containing a substance maintained in at least a partially frozen condition by refrigerant coils. The solidified surface of the substance provides a supporting surface for material to be cut and is reconstituted after a jet of cutting fluid passes therethrough.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates in general to apparatus for cutting sheet material and deals more particularly with improved high velocity fluid jet cutting apparatus for automated production cutting of limp sheet materials such as fabrics, plastic, paper, leather, rubber and the like. In an apparatus of the aforedescribed general type, a high pressure fluid jet, focused by a nozzle, functions as an omnidirectional cutting &#34;blade&#34; which produces a narrow kerf. Such apparatus is particularly suitable for cutting intricate shapes from multi-ply materials. The high pressure fluid jet stream travels at supersonic speed as it is ejected from the nozzle of the cutting tool and necessarily has considerable residual energy after passing through the material which has been cut. This residual energy poses a potential source of damage to the cutting apparatus and particularly to the means for supporting a material being cut. Heretofore, apparatus of the aforedescribed general type has been provided wherein the material supporting bed comprises a laminate of severable and self-healing materials that can be penetrated by the high velocity cutting jet. The self-healing material which may, for example, be a tar, putty, or fusible plastic material which flows together after the jet has passed through it is sandwiched between layers of the severable material. Apparatus of the aforedescribed general type is illustrated and described in U.S. Pat. No. 3,927,591 to Gerber, issued July 15, 1974 and assigned to the assignee of the present invention. The present invention is concerned with improvements in apparatus of the aforedescribed general type which includes a material supporting bed of self-healing material. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, apparatus for cutting sheet material comprises a material supporting bed which includes a tank having an open top and containing a substance which has a liquid state and a solid state. The exposed upper surface of the substance in its solid state constitutes a material supporting surface. A means within said tank maintains in a solid state at least a portion of the substance which defines the upper surface. A fluid jet cutting tool is supported above the upper surface and has a nozzle for discharging a jet of cutting fluid toward the upper surface. The apparatus also includes a means for moving the cutting tool relative to the upper surface. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a fragmentary perspective view of a fluid jet cutting apparatus embodying the invention. 
     FIG. 2 is a somewhat enlarged fragmentary sectional view taken along the line 2--2 of FIG. 1. 
     FIG. 3 is similar to FIG. 2 but shows another apparatus embodying the invention. 
     FIG. 4 is also similar to FIG. 2 but shows still another apparatus embodying the invention. 
     FIG. 5 is a fragmentary sectional view taken along the line 5--5 of FIG. 4. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Turning now to the drawing, a fluid jet cutting apparatus embodying the present invention and illustrated in FIG. 1 is indicated generally by the reference numeral 10. The apparatus 10 is particularly adapted for automated production cutting of sheet material and includes a material supporting bed indicated generally at 12. The bed generally comprises a tank 14 which is open at its top and contains a substance 16 which has a solid state and a liquid state and an exposed upper surface 18. The tank 14 also contains means for altering the physical state of the substance 16 to maintain in a solid state at least that portion of the substance which defines its upper surface 18. A lay-up of limp sheet material indicated at 20, which may comprise a single sheet or as many as several hundred sheets of woven or non-woven fabric or like material, is shown supported in vertically stacked relation by the solid surface 18. 
     The material 20 is cut by a high velocity fluid jet cutting mechanism, indicated generally at 22 which has a jet nozzle 24, and which is mounted above the bed 12 on a movable carriage assembly indicated generally by the numeral 26. The carriage assembly is supported for movement relative to the supporting bed 12 to move the nozzle 24 in longitudinal and transverse coordinate directions, as indicated by X and Y coordinate axes shown in FIG. 1. The carriage assembly moves in response to control signals received through a cable 28 from a programmable computer 30. The illustrated computer 30 reads digital data from a program tape 32 which defines contours of a cutting path. A high velocity fluid cutting jet emitted from the nozzle 24 impinges upon the lay-up 20, forms a kerf K therein, and moves in cutting engagement with the lay-up to cut patterns from it in response to the control signals transmitted by the computer 30. More specifically, the computer 30 transmits control signals to a drive motor 34 which drives a lead screw 36 to move the carriage assembly and the jet nozzle 24 longitudinally of the supporting bed 12 in one or the opposite X-coordinate direction. The computer 30 also transmits control signals to another drive motor 38 which drives a lead screw 40 to move the jet nozzle 24 relative to the carriage assembly 26 and transversely of the supporting bed 12 in one or the opposite Y-coordinate direction. 
     The tank 14 is generally rectangular and has a bottom wall 42, side walls 44, 44, and opposite end walls 46, 46, only one of which is shown in FIG. 1. Fluid inlet and outlet conduits indicated by the numerals 48 and 50, respectively, communicate with the interior of the tank 14, as shown in FIG. 2. Refrigerant coils indicated generally at 52 in FIG. 2 are located within the upper portion of the tank 14 below its upper edge and are connected to an exterior refrigeration unit 54. The substance 16, which may, for example, be water, is maintained at a level above the refrigerant coils 52. 
     A conventional hydraulically pressurized fluid jet cutting mechanism 22 is used to deliver a steady stream of cutting fluid under pressure to the jet nozzle 24. The mechanism 22 preferably includes an intensifier pump for delivering fluid under pressure to the nozzle and a pressure smoothing accumulator which smooths pressure pulsations from the pump so that fluid is supplied to the nozzle at substantially constant pressure, which may, for example, be in a range of from 10,000 psi to 100,000 psi. A typical nozzle may, for example, have a throat aperture in the range of 0.004 inches to 0.016 inches which produces an extremely fine high velocity fluid jet stream at the nozzle capable of penetrating and cutting through a multi-ply lay-up of cloth, plastic, leather or other material to be cut. Various cutting fluids may be used, however, it is preferable that the substance 16 also be used as a cutting fluid. Thus, when the substance 16 in the tank 14 is water it is preferable that water also be used as a cutting fluid. 
     Preparatory to cutting a lay-up of sheet material, the refrigeration unit 54 is operated to freeze the water 16 at least near its surface 18 whereby to form an ice bed for supporting the lay-up. This ice bed will support the material during lay-up or, if desired, a previously laid-up stack of material can be slid onto the ice surface. A layer of paper or plastic 53, such as polyethylene film, may be positioned between the lay-up and the ice surface 18. The jet nozzle 24 is positioned above the stationary lay-up 20 by the movable carriages 26 which moves in response to a selected taped program. The fluid jet emitted from the nozzle cuts through the lay-up and into or through the ice layer and may be absorbed in the water below the ice layer without backsplash. The thin kerf formed in the ice (less than 0.010 inch wide) supports the lay-up closely during tangent cuts and will quickly refreeze as the cutting jet moves on. Thus, the supporting bed 10 is entirely self-healing and normally requires no substantial maintenance other than that which may be required to maintain a constant level of water in the tank 14. The inlet and outlet conduits 48 and 50, respectively, facilitate maintenance of a constant liquid level within the tank 14. 
     Another fluid jet cutting apparatus embodying the present invention and indicated generally by the reference numeral 10a in FIG. 3 utilizes a supporting bed of &#34;spongy ice&#34; to support a lay-up of sheet material. Such spongy ice may be formed by agitating water during freezing or by the use of chemical additives in the water. The apparatus 10a shown in FIG. 3 is similar to the apparatus 10, previously described, however, it includes an air manifold 56 located within the tank and below the surface 18a. The manifold 56 is connected through a valve 58 to an external source of air under pressure, indicated at 60 and introduces air under pressure into the water to agitate the water during the refrigeration cycle. 
     A similar result may be attained without the requirement of special agitating apparatus by filling the tank with shaved ice flakes to form a supporting bed which has a surface consistency similar to that of packed snow. The advantage of using &#34;spongy ice&#34; or another substance having the consistency of packed snow is that the surface of such a substance will readily absorb the volume of water discharged by a fluid jet cutting apparatus performing a normal cutting operation without apparent disturbance of the surface. Such a surface can be readily reconstituted by refreezing or by the addition of water or shaved ice. Such a surface may also be reconstituted by scraping. 
     The supporting table concept of the present invention is particularly suitable for use on a cutting table adapted to cut long, wide lay-ups, that is lay-ups which may, for example, be six feet wide by 100 feet long. Such lay-ups are preferably compacted and held during the cutting operation to assure that all layers which comprise a lay-up are uniformly and accurately cut. An apparatus for cutting such long, wide lay-ups is illustrated in FIG. 4 and indicated generally by the reference numeral 10c. The apparatus 10c is similar in many respects to the apparatus 10 previously described and includes a cutting mechanism 22c, which has a jet nozzle 24c, and a tank 14c which contains refrigerant tubes 52c. The tubes are connected to an external refrigeration unit 54c for freezing a substance 16c and maintaining at least that portion of the substance which defines its surface 18c in a substantially solid state. A layer of paper or plastic 53c, which corresponds to the layer 53 in FIG. 2, may be positioned between the surface 18c and the layup 20c, substantially as shown in FIG. 4. 
     The peripheral walls of the tank 14c extend for some distance above the surface 18c, which, as shown, supports a long, wide lay-up of sheet material 20c. An elongated flap 62 made from relatively stiff metal or plastic is hinged along one longitudinally extending edge to each side wall 44c in vertically spaced relation to the surface 18c and extends inwardly from the side wall. A longitudinally spaced series of vacuum ports 64, 64 (one shown) are open through each side wall 44c between the surface 18c and an associated flap 62. An elongated vacuum manifold 66 connected to a suitable external vacuum source 68 is secured to each side wall 44c and communicates with the vacuum ports 64, 64 therein. Preferably, and as shown, each vacuum port 64 has an associated valve 70 movable between open and closed positions. In its open position each valve 70 exposes an associated valve port 64 so that the port communicates with the vacuum manifold 66. The valve 70, 70 may be arranged to operate in sequence in response to the motion of the carriage 16 in an X-coordinate direction or, if desired, each valve 70 may be provided with an individual operating motor (not shown) so that the various valves may be operated in response to a predetermined program in response to signals from an associated computer. 
     An inner marginal portion of each flap 62 overlies an associated upper marginal portion of the lay-up 20c substantially as shown in FIG. 4. When a vacuum is applied to the manifold 66, the flap 62 is drawn tightly down against the lay-up. Associated portions of the flap 62, the surface 18c and the inner surface of the associated side wall 44c cooperate with a vertical side of the lay-up 20c to form a vacuum chamber, indicated at 72, which communicates with the vacuum manifold 66 through the vacuum ports 64, 64 whereby vacuum is applied to the lay-up 20c. When valves are provided such as the valves 70, 70 vacuum may be applied locally to an area of the lay-up being cut by opening one or more valves in the immediate area laterally opposite the cut. If the lay-up comprises a porous material such as cloth, layers of plastic materials such as polyethylene film are preferably arranged in overlying and underlying relation to the lay-up to aid in the efficient compacting of the lay-up in response to applied vacuum. The application of vacuum through the vacuum chambers causes the hinged flaps 62, 62 to be drawn down against opposite marginal edges of the lay-up thereby clamping the lay-up against the surface 18c. The arrangement hereinbefore described provides a practical low cost construction and enables the use of a fluid jet cutting apparatus on long lay-ups such as encountered in furniture and apparel manufacturing, without the use of a large vacuum system.