Patent Publication Number: US-3877334-A

Title: Method and apparatus for cutting sheet material with a fluid jet

Description:
[ 1 Apr. 15, 1975 United States Patent [191 Gerber METHOD AND APPARATUS FOR CUTTING SHEET MATERIAL WITH A FLUID JET CC CCU M 22 99 33 0000 :1 0a .lulu aae t a fle bb Ira eeh GGC 33. 777 999 111 II/ 389 [75] Inventor: Heinz Joseph Gerber, West Hartford, Conn.  
 Primary Examiner--J. M. Meister Attorney, Agent, or FirmMcCormick, Paulding &amp; Huber [73] Assignee: Gerber Garment Techology, Inc.,  
 East Hartford, Conn.  
 Nov. 23, 1973 [57] ABSTRACT A high velocity fluid cutting jet is utilized as a cutting [22] Filed:  
 Appl. No.: 418,548  
 tool to cut pattern pieces from limp sheet material. The limp material is spread on a support surface and is 9 76 6%m4C /37 w 00 7 .127 B 1 3JN-9Q195 y/0 4 30 8 3 .9 7 00 2 h H 3 7. 8 D2 u u c u n .3 &#34;e ms L C G m 5 m U hF N UN 5 55 dimension and the material cannot flutter or deflect away from the jet. A sharper and more accurate cut results.  
 [56] References Cited UNITED STATES PATENTS 3,495,492 2/1970 Gerber et a]. 83/925 CC 3,532,014 10/1970 83/177 Xv 21 Claims, 5 Drawing Figures PATENTED 1 19 5 3.877. 334  
 SHEET 3 BF 3 &#34;m w w m w&#34; wi i WP P l8 L62] VACUUM PUMP METHOD AND APPARATUS FOR CUTTING SHEET MATERIAL WITH A FLUID JET BACKGROUND OF THE INVENTION The present invention relates to the field of cutting and, more particularly, is concerned with the cutting of sheet materials such as limp fabrics, plastics, paper, leather, rubber and the like by means of a high velocity fluid cutting jet.  
  The use of high velocity fluid jets for cutting limp materials including clothing and upholstery fabrics has been contemplated in the past; however, the cutting jet has never actually attained complete acceptance or reached full development in the commercial field of cutting limp sheet material.  
  The fluid cutting jet has several advantages when compared, for example, to a mechanical cutting blade in that the jet never needs sharpening, it does not have to change elevation during a cutting operation and it is an omni-directional tool, that is, it has no specific orientation and hence a complete control axis is eliminated in an automatically controlled machine using the jet. Also, although a laser beam is similar to a cutting jet in these respects, the cutting jet offers the further advantage that it can penetrate through materials to much greater depths than the laser and without burning the materials.  
  Nozzles for the fluid cutting jets operate in a pressure range between 10,000 psi and 100,000 psi. The velocity of the fluids at these pressures varies between 1,000 feet per second and 3,000 feet per second but the quantity of fluid involved is minimal since the throat diameters of the nozzles from which the jets issue are in the order of 0.004 inches to 0.010 inches.  
  With such high velocities, the fluid jet may displace the material being cut or cause the material to flutter unless it is held rigidly. The cutting of limp sheet materials such as fabrics, plastics, paper and the like is especially prone to such a problem due to the fact that the materials are not capable of supporting themselves and are particularly weak when subjected to out-of-plane forces. The materials also tend to diffuse the jet by shreading and interfering with the jet and by capturing fluid which separates from the mainstream of the jet.  
  In accordance with the present invention, the problems associated with fluid-jet cutting operations are circumvented by compressing the materials into a hardened mass which can be more easily shattered by the fluid jet. In addition, apparatus employed to compress the material also aids in holding the material in place so that a more accurate cutting of the material along a desired path results.  
 SUMMARY OF THE INVENTION The present invention relates to a method and apparatus for cutting sheet material by means of a high velocity fluid cutting jet. A principal feature of the present invention is the compressing of the material being cut into a hardened mass to permit the fluid jet to pass through the material more easily and to hold the material in place for accurate cutting.  
  The cutting apparatus which carries out the method of the invention is comprised of supporting means defining a support surface on which the sheet material may rest while it is being cut. The cutting tool takes the form of a fluid jet nozzle, mounted above the support surface, and associated pumping equipment. The nozzle is constructed and oriented to direct a high velocity fluid jet toward the support surface so that impingement of the jet upon the sheet material performs the cutting function. Controlled drive means moves the tool and the sheet material relative to one another in directions parallel to the support surface to cause the jet emanating from the nozzle to translate along a desired line of cut on thematerial.  
  In accordance with the present invention, the sheet material being cut by the fluid jet is compressed at least in the region where the jet is operating. Compressive forces are applied to the sheet material in a direction generally normal to the plane of the material and the support surface on which it rests.  
  Various devices are employed to generate the compressive forces. A vacuum can be generated within the material by apparatus and in the manner described in U.S. Pat. No. 3,495,492 issued to the Assignee of the present invention. This patent also disclosesrollers and a travelling belt mounted on the rollers which rest upon the material and contribute to the compressive forces. Pressure can also be applied to the sheet material by the use of a powered roller as disclosed in U.S. Pat. No. 3,693,489 or by applying increased air pressure to an exposed surface of the sheet material as disclosed in U.S. Pat. No. 3,750,507, each of which patents issued to the Assignee of the present invention.  
  The various compressing means may also be used in combination to achieve maximum hardness within limp sheet material especially when the materials are spread in a multitiered layup on the support surface.  
 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a cutting apparatus comprising one embodiment of the present invention.  
  FIG. 2 is a transverse cross sectional view of the cutting apparatus as viewed along the sectioning line 2-2 in FIG. 1.  
  FIG. 3 is a cross-sectional view of the cutting apparatus similar to that in FIG. 2 and shows an alternate construction of the support bed on which the sheet material is spread.  
  FIG. 4 is a longitudinal cross-sectional view of a cutting apparatus comprising still another embodiment of the present invention.  
  FIG. 5 is a longitudinal cross-sectional view of a cutting apparatus comprising one further embodiment of the present invention.  
 DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates in a perspective view a cutting apparatus of the present invention. The apparatus, generally designated 10, is a numerically controlled cutting machine which is connected by means of a control cable 12 to a numerical controller (not shown) which generates all of the necessary cutting commands from a previously established or simultaneously generated cutting program. The cable 12 also transmits signals from the cutting machine to the controller to coordinate the sequencing of the program with the operation of the cutting machine.  
  The cutting apparatus 10 includes a vacuum holddown table 14 of the type disclosed in U.S. Pat. No. 3,495,492 referenced above. Basically, such a table has a porous, fluid permeable bed 16 defining a support surface on which the sheet material is placed in a spread condition. A vacuum or plenum chamber 18 in the lower portion of the table communicates through the porous bed 16 with the sheet material spread on the support surface. The vacuum chamber 18 is connected by means of a conduit 20 to a vacuum pump (not shown) which has a size sufficient to maintain a reduced pressure at the surface of the bed 16 below the sheet material. It is desirable to establish a plurality of vacuum zones throughout the table and to operate only the zone or zones over which the cutting tool is operating at a given time during a cutting operation. A zoned table is disclosed in US. Pat. No. 3,495,492.  
  The sheet material to be cut is placed on the surface of the porous bed 16 in a spread condition. To increase the productive output of the apparatus 10, a multitiered layup L is formed by placing many sheets of the material on top of one another. If the sheet material is air-permeable, the upper ply of the layup L may be covered with an impermeable overlay 22 such as a sheet of polyehtylene film. The film may also be spread over the uncovered portions of the bed 16. Such a film prevents leakage through the permeable layup and porous bed and enables the sheet material to be compressed more firmly into a hardened condition.  
  It has been fouond that by compressing limp sheet materials into a hardened condition, they react more uniformly to a cutting tool even though the individual characteristics of the material in the non-compressed condition are not changed. The materials, are, accordingly, described as being normalized by the compressive forces. The compressive forces produced by the vacuum table 14 are caused by atmospheric pressure, and at locations within the layup, the forces operate in a direction generally perpendicular to the plane of the material and the supporting surface of the bed 16.  
  The cutting tool of the present invention is comprised principally of a fluid jet nozzle 24 from which a high velocity fluid cutting jet emanates during a cutting operation. The nozzle 24 is connected directly to a Y- carriage 26 at a fixed elevation above the support bed 16. The Y-carriage is movable relative to the table 14 in the illustrated Y-direction and is supported on an X- carriage 28 which spans the table 14 in the Y-direction and is movable relative to the table in the illustrated X- direction.  
  The X-carriage 28 rests upon a pair of parallel racks 30 supported longitudinally along the edges of the table 14 by a series of brackets 32. An X-drive motor 34 mounted on the carriage 28 rotates two pinions (not shown) engaging the respective racks 30 at opposite sides of the table to translate the X-carriage 28 and Y- carriage 26 over the layup L in the X-direction. The motor 34 receives displacement command signals through the cable 12 from the controller in accordance with the cutting program.  
  The Y-carriage 26 is suspended over the work surface of the bed 16 on a guide rail 36 and a lead screw 38 mounted on the X-carriage. A Y-drive motor 40 rotates the lead screw 38 which is threadably engaged with the Y-carriage 26 to cause the carriage to translate back and forth on the X-carriage and over the work surface of the bed 16 in the Y-direction. Like the X- drive motor 34, the Y-drive motor 40 receives displacement commands from the controller in accordance with the cutting program. The drive motors 34, 40 and the carriages 26, 28 produce composite motions of the fluid jet nozzle 24 in the X- and Y-directions to permit the jet produced by the nozzle to translate progressively along a cutting path P defined by the periphery of a pattern piece to be cut from the layup L.  
  As best seen in FIG. 2, the jet nozzle 24 is mounted from the Y-carriage 26 to direct the fluid jet A toward the bed 16 along an axis generally normal to the plane of the sheet material and the support surface on which the material rests. A fluid pressurizing pump 50 is mounted at one end of the X-carriage 28 and is connected with the nozzle 24 on the Y-carriage 26 by means of a flexible hydraulic conduit 52 and a hydraulic intensifier 54.  
  The pump 50 has illustrated includes a small integral reservoir in which a pressurizing fluid is stored. The intensifier 54 is a pressure amplifier having small and large area pistons and also includes a fluid reservoir in which the cutting fluid, usually water, is stored. In one form of the invention, the pump produces an output pressure in the order of 3,000 psi and the pressurizing fluid is then energized throughout the hydraulic conduit 52 and in the pressure intensifier 54 on the Y- carriage 26. Within the intensifier 54 the pressurizing fluid energizes the cutting fluid by boosting it to a nozzle pressure in the range of 10,000 psi to 100,000 psi. The cutting fluid leaving the intensifier 54 at the elevated pressure passes through a connecting conduit 56 to the nozzle 24 and is discharged from the throat of the nozzle as the high velocity fluid cutting jet A. Typically, the nozzle has a throat aperture in the range of 0.004 inch to 0.010 inch so that the jet A is an extremely fine high velocity stream which is fully capable of penetrating multiple layers of limp fabric material even after the material has been compressed in a hardened condition by the vacuum generated within the bed 16.  
  The cutting action of the jet A at a cutting point on the layup is produced by having the jet effectively shatter or rip through the material. By compressing the limp material into a hardened condition with vacuum, the individual plies of the material cannot flutter or be displaced by the jet and collectively they are subjected, as a solid, to the full fracturing forces of the jet. A sharper cut results. Furthermore, since the vacuum holddown forces also prevent the sheet material from shifting, the contour of the cutting path followed by the jet as the nozzle is translated over the layup matches the programmed cutting path P more accurately.  
  One further and significant advantage achieved by combining the vacuum holddown system with the fluid cutting jet is that the overall thickness of the layup penetrated by the fluid jet is reduced and concomittantly the tendency to diffuse and weaken the jet as the material makes contact with and absorbs fluid at the outside surface of the jet. Accordingly, the cutting phenomenon exhibited by the jet in the upper plies of the layup L is substantially preserved for the lower plies and the same sharp and accurate cut is achieved throughout the depth of the layup.  
  The cross sectional view of FIG. 2 illustrates one embodiment of the table 14 which provides means for generating the vacuum within the layup L and for disposing of the fluid from the cutting jet after it&#39;cuts through the layup. The bed 16 as illustrated is comprised of a plurality of bristled mats arranged with the free or upwardly projecting ends of the bristles 58 in a common plane defining the support surface of the table. The mats rest upon a grating 60 which in turn rests upon a series of joists 62 extending laterally across the table 14 within the vacuum chamber 18. The joists 62 are fixed in the frame of the table 14 and, therefore, provide a rigid support for the grating 62 and the bristled mats of the bed 16.  
  A vacuum produced within the chamber 18 is also drawn within the region of the bristles 58 and at the supporting surface of the bed 16 by virtue of the communcation between the chamber 18 and the lateral edge 64 of the bristles. The vacuum or low pressure at the surface evacuates air from the layup L and draws the air horizontally through the bristles as viewed in FIG. 2. The air is then drawn out through the lateral edge 64 of the bristles down through the grating 60 and the joists 62 into the vacuum chamber 18 as illustrated by the arrows. The air is then taken from the vacuum chamber through the conduit 20 connected to the vacuum pump (not shown).  
  Precise zoning of the bed 16 so that only limited portions of the layup adjacent the cutting jet are compressed may be provided by placing partitions within the bristles and corresponding partitions forming subchambers within the vacuum chamber 18. Valves associated with the partitioned subchambers are, as de scribed in greater detail in U.S. Pat. No. 3,765,289 having the same assignee as the present application, operated sequentially by the motion of the X-carriage 28 and control the generation of vacuum in the partitioned zones of the bed 16. Only that portion of the layup being operated upon by the cutting jet is compressed at any given instant time in the cutting operation. lt has been found, however, that precise zoning of the bristles is not essential even though separate sub-chambers may be employed within the base of the bed. The resistance offered by the bristles to air flowing from adjacent zones is adequate to limit the total flow of air pulled through the vacuum chamber 18 to the vacuum pump.  
  The level of the vacuum generated within the layup is preferably greater than that previously employed with mechanical cutting tools such as illustrated in the above referenced U.S. Pat. No. 3,495,492. With a mechanical cutting tool, too much vacuum within the layup of sheet material can cause so much compression of the sheet material that the material will not permit a mechanical cutting blade to penetrate easily through the hardened material or translate along a cutting path through the material. Undue loading of the blade caused by too much compression causes excessive wear in the drive carriage and motors and can break the cutting blade. However, with a fluid cutting jet it is felt that the cutting operation is improved by greater compression, and vacuums or reduced pressures in the order of 20 inches of mercury are considered desirable.  
  The use of the vacuum table 14 with a fluid cuttingjet nozzle is particularly advantageous since the vacuum system also disposes of the spent cutting fluid. In FIG. 2, the vacuum chamber 18 receives all of the cutting fluid from the jet A because the fluid is drawn out of the porous bristle bed with the evacuated air. The chamber 18, therefore, serves as a collection chamber for the fluid and the vacuum pump connected with the chamber continually draws off the collected fluid.  
  To add further compressive forces to the sheet material in the layup L, a positive holddown pressure is applied externally to the layup by an air pressure chamber 70 suspended from the Y-carriage 26 immediately adjacent and surrounding the fluid nozzle 24. The chamber is formed by an inverted pan or shell having a large opening confronting the upper ply of the layup. The chamber. is closely spaced to the layup to prevent pressurized air withinthe chamber from escaping at a high rate under the edges of thepan. The escaping air could cause lifting of the upper ply of the layup or the polyethylene overlay 22 utilized with the vacuum system. The spacing between the chamber 70 and the layup may be controlled by the mounting structure supporting the chamber from the Y-carriage 26 or by mounting both the nozzle 24 and the chamber 70 on an auxiliary carriage at the projecting end of the Y- carriage 26 and moving the auxiliary carriage by means ofa servomotor along an axis normal to the plane of the sheet&#39;material on the support surface of the bed 16.  
  To supply a continuous flow of pressurized air to the chamber 70, an air pump 72 is mounted adjacent to the hydraulic pump 50 on one end of the X-carriage 28. The air pump 72 has a discharge port connected by means of a flexible fluid conduit 74 to an inlet aperture on the upper side of the chamber 70. The chamber, therefore, encloses a quantity of air at a pressure slightly above atmospheric pressure and generates a region of increased pressure locally around the fluid jet A during the cutting operation. As the jet A is moved along a cutting path P over the sheet material, the chamber 70 attached to the Y-carriage 26 moves in a corresponding manner with the jet.  
  It is contemplated that the air pressure chamber 70 may be used either in conjunction with the vacuum system or by itself to generate compressive forces normal to the plane of the sheet material in the layup L. Quite obviously, the combination of positive air pressure above the layup and the negative pressure or vacuum within the layup produces a greater hardening of the sheet material than either one of the pressures by themselves.  
  FIG. 3 illustrates another embodiment of the cutting machine 10 having a cutting table 14 in which the bed 16 is comprised of a metallic honeycomb 80. The honeycomb rests upon the grating 60 in the same manner as the bristled mats in FIG. 2 and defines the support surface on which the layup L of the sheet material is spread for the cutting operation. The cells of the honeycomb structure are most generally hexagonal in shape and are arranged with the axis of the cells extending perpendicular to the support surface for the sheet material and parallel to the fluid cutting jet A. The cells are open at both the top and bottom ends and, therefore, define passageways between the support surface and the vacuum chamber 18.  
  The vacuum system cooperates with the honeycomb bed to compress the layup of sheet material in essentially the same manner as the bristle bed in FIG. 2&#39;with one exception. Contrary to the bristles, the honeycomb 80 is only porous in the vertical direction since the cells define fluid passageways extending only from the support surface downwardly through the bed to the grating 60. Accordingly, lateral and longitudinal air flow in response to vacuum generated in the chamber 18 is not permitted and zoning, if desired, is greatly facilitated.  
  Nevertheless, the direct evacuation of air through the cells of the honeycomb 80 generates the same low pressure region on the support surface and within the layup to cause compressive forces to be applied normal to the sheet material. Further compressive forces produced by the pressure chamber 70 above the layup augment the vacuum-generated forces in the same manner as that described in connection with FIG. 2. Since the fluid jet A may not be entirely dissipated by the time it passes through the open honeycomb 80 and the grating 60, the floor of the vacuum chamber 18 absorbs any residual energy in the jet and the chamber again collects the fluid for discharge with the evacuated air.  
  FIG. 4 illustrates still another embodiment of the cutting machine employing a high velocity&#39;fluid cutting jet. The same reference numbers are used for previously defined elements. The fluid nozzle 24 is mounted on a Y-carriage 26 for lateral movement over the layup L of sheet material in substantially the same manner as that illustrated in FIGS. l3. The Y-carriage 26, however, is suspended from a stationary bridge 90 which straddles the layup. As in the embodiment of FIGS. 1-3, the hydraulic pump 50 delivers pressurizing fluid through the flexible conduit 52 to the intensifier 54 on the Y-carriage and the intensifier pressurizes the cutting fluid for discharge from the nozzle 24 as the fluid cutting jet.  
  Relative motion of the nozzle 24 and the sheet material in the Y-direction is produced by the Y-carriage 26 and associated drive motor. Relative motion of the nozzle and the material in the X-direction is produced by a pair of conveyors 92 and 94 placed in end-to-end relationship with an intervening gap between the conveyors registering with the fluid jet A. The conveyor 92 is formed by a pair of parallel rollers 96 and 98 extending under the layup L in the Y-coordinate direction and an endless conveyor belt 100 supported by the rollers 96 and 98. The conveyor 94 is constructed similarly by a pair of rollers 102 and 104 and a conveyor belt 106. Auxiliary conveyors 120 and 122 may be provided to move the layup L on and off of the conveyors 92 and 94.  
  It will be readily understood that the upper surfaces of the conveyor belts define a support surface on which the sheet material is spread. Servo drive motors (not shown) are connected to the rollers 96, 98, 102 and 104 to drive the belts 100 and 106 which move the sheet material back and forth in the X-direction relative to the cutting jet A. Composite motions of Y- carriage 26 and the conveyors 92 and 94 achieve relative movements of the nozzle and the layup which permit contoured cutting paths defined by the peripheries of the pattern pieces to be cut.  
  The gap between the two conveyors 92 and 94 is filled with a throatway 108 which supports the sheet material as it passes from one conveyor to the other. A slot extends in the Y-direction through the throatway and is aligned with the fluid jet A to permit the jet to pass into a vacuum chamber 110.  
  The chamber 110 envelops both of the conveyors 92 and 94 is connected with a vacuum pump 112 to evacuate the portion of the layup which is in the region of the fluid jet A. The conveyor belts 100 and 106 are preferably air permeable to draw air from the layup over a substantial zone of the layup at each side of the cutting station defined by the bridge 90 and Y-carriage supporting the nozzle 24. The chamber 110 also collects the fluid from the jet and the vacuum pump 112 evacuates the fluid along with the air.  
  A pair of travelling belt systems 130 and 132 are mounted to the bridge 90 at opposite sides of the fluid nozzle 24 and rest upon the layer L to generate further compressive forces for hardening of the sheet material as it passes under the cutting jet A. The belt system is comprised ofa pair of parallel rollers 134 and 136 extending over the layup in the Y-direction and an endless belt 138 mounted on the rollers and having one belt portion resting on the sheet material. The belt system 132 is constructed in a similar manner and includes a pair of parallel rollers 140 and 142 and an endless belt 144 mounted on the rollers.  
  The rollers 134, 136, 140 and 142 may be either powerdriven rollers or freely rotated rollers which turn as the conveyors 92 and 94 move the layup under the nozzle 24. If the rollers 134, 136, 140 and 142 are power-driven, the drive motors for the rollers are coordinated with the servo-motors driving the conveyors 92 and 94 to prevent slippage between the layup and the endless belts 138 and 144.  
  The weight of the rollers 134, 136, 140 and 142 is supported entirely by the layup L and hence applies compressive forces to the portions of the layup lying at each side of the cuttingjet under the belts 138 and 144. Since the belt systems 130 and 132 produce holddown forces independently of the vacuum chamber 110, they may be used either by themselves or to augment the compressing forces produced by the vacuum chamber. Conversely, the vacuum chamber 110 may be used alone or in combination with the belts.  
  It will be observed that the belt systems 130 and 132 may complement the vacuum system is the belts 138 and 144 are manufactured from an air-impermeable material. Such material seals the layups in the vicinity of the jet A if the material comprising the layup is airpermeable and, therefore, prevents leakage of air through the layup into the vacuum chamber even after the layup has been cut by the jet A. The belts 138 and 144 then serve as a non-consumable, impermeable overlay and, accordingly, the impermeable overlay 22 may be omitted.  
  FIG. 5 is a longitudinal cross-sectional view of still another cutting apparatus utilizing a water jet cutting tool in combination with a vacuum table 14. (Elements previously described in connection with FIGS. 1-3 bear the same reference numerals in FIG. 5). The bed 16 of the table 14is rendered porous by bristled mats such as illustrated in FIG. 2, a metallic honeycomb such as shown in FIG. 3 or any other suitably porous material permitting vacuum to be generated at the support surface of the bed to compress the layup resting thereon. The table may also be divided into a series of laterally extending vacuum zones which are sequentially actuated as the X-carriage 28 traverses the table in the X direction.  
  A non-consumable sealing device at one side of the cutting jet nozzle 24 extends between the X- carriage 28 and the adjacent end of the vacuum table 14. The sealing device 150 is comprised of a roller 154 mounted on the X-carriage 28 and an impermeable overlay 156 which rests upon the upper tier of the sheet material forming the layup L. The roller 154 has its axial ends mounted in vertically oriented slots in the X- carriage 28 so that the roller is free to shift vertically relative to the carriage 28 and so that the weight of the roller rests upon the layup immediately adjacent the cutting jet A. The overlay 156 is a strip of airimpermeable material such as the polyethylene film which forms the overlay 22 in FIG. 1. The overlay 156 is attached to the one end of the vacuum table 14 during a cutting operation by an anchoring clamp 158 and the opposite end is wound upon the roller 154 in substantially the same manner as a window shade is wound on its supporting roller. A driving torque is constantly applied to the roller 154 during a cutting operation (either by a torque motor or a torsion spring not shown) to keep the overlay 156 under tension and to permit the overlay to be reeled onto or off the roller 154 in synchronism with the motion of X-carriage 28 over the layup. Accordingly, the overlay 156 is laid down upon or retrieved from the layup L as the X-carriage moves longitudinally back and forth along the table 14 and the entire expanse of the layup between the cutting jet nozzle 24 and the anchoring clamp 158 remains covered and sealed during the cutting operation. Vacuum or the reduced pressure generated at the support surface of the porous bed 16 cooperates with the overlay 156 to compress the layup into a hardened mass, and to thereby aid the cutting process as described above in connection with FIGS. 13.  
  A corresponding sealing device 160 extends between the X-carriage 28 and the end of the vacuum table 14 opposite the anchoring clamp 158 to seal that expanse of the layup at the side of the cutting nozzle 24 opposite the sealing device 150. The device 160 has the same construction as the device 150 and includes a rotationally torqued roller 164 supported on the X-carriage 28 and an air-impermeable overlay 166 wound upon the roller 164 and anchored at the opposite end of the table.  
  It will be understood that the sealing devices 150 and 160 at opposite sides of the cutting jet A, replace the overlay 22 shown in FIGS. 1-3 and operate in substantially the same manner. Several points are noteworthy, however. The overlays 156 and 166 are not consumed or cut during the cutting operation. Also, sealing of the longitudinal edges of the layup with the overlays 156 and 166 is accomplished more efficiently by positioning blocks of sealing material, for example, a closedcell, foamed plastic, adjacent the longitudinal edges of the layup and spreading the overlays 156 and 166 over the top of the layup and the sealing blocks. A more complete description of the windowshade type sealing devices 150 and 160 may be had by reference to U.S. Pat. No. 3,742,802 issued July 3, 1973 to the Assignee of the present invention.  
  While the present invention has been described in several preferred embodiments, it will be understood that still further modifications and substitutions can be had without departing from the spirit of the invention. For example, in addition to the bristle bed or honeycomb beds described above, other liquid permeable materials, such as open-celled plastic foam, may be employed. Although such foam may also be cut by the fluid jet A, it can be treated as an expendible material and may be replaced from time to time after extended use. The pressure chamber 70 may take other forms such as illustrated in U.S. Pat. No. 3,750,507 referenced above. Free rolling spherical weights within a cage suspended from either the X- or Y-carriages as shown and described in US patent application Ser. No. 282,544, filed Aug. 21, 1972 by the Assignee of the present invention may be used to compress the sheet material in the layup. A conveyor-type bed different from that illustrated in FIG. 4 may be formed by mounting segments of honeycomb on interconnected slats so that an endless belt is formed. The endless sealing belts 138 and 144 shown in FIG. 4 may be attached to the X-carriage in the embodiment of FIG. 1 for their sealing function. The rollers 136 and 140 can operate without the associated belts as described in U.S. Pat. No. 3,693,489 referenced above to compress the sheet material. It will also be understood that the fluid nozzle 24 can be held by a rigid frame over the layup and the layup can be moved relative to the nozzle in both the X- and Y-directions. Accordingly, the present invention has been described in several embodiments by way of illustration rather than limitations.  
 I claim:  
 1. Apparatus for cutting sheet material comprising:  
 supporting means defining a fluid permeable support surface on which the sheet material may rest and a&#39;fluid collection chamber below the surface and communicating with the surface for the transfer of fluid from the surface to. the chamber;  
 a cutting tool mounted above the support surface and including a fluid jet nozzle directed toward the fluid permeable support surface to impinge a high velocity fluid cutting jet upon the sheet material;  
 controlled drive means for moving the cutting tool and the sheet material relative to one another in directions parallel to the support surface to move the fluid cutting jet from the nozzle along a desired line of a cut on the material; and  
 means for compressing the sheet material on the support surface at least in the region of the material being cut by the jet including vacuum generating means cooperating with the fluid collection chamber and the fluid permeable surface for drawing a vacuum or reduced pressure in the region of the sheet material being cut.  
 2. Apparatus for cutting as defined in claim 1 wherein:  
 the supporting means comprises a porous, fluid permeable bed defining the support surface; and  
 the vacuum generating means is connected to the porous bed and communicates with the sheet material on the support surface through the porous bed.  
 3. Apparatus as defined in claim 2 wherein:  
 the porous, fluid permeable bed comprises a bed of bristles having free ends substantially in a common plane to thus define the support surface.  
 4. Apparatus as defined in claim 2 wherein:  
 the porous, fluid permeable bed comprises a honeycomb structure having cells opening at the support surface.  
 5. Apparatus for cutting as defined in claim 1 wherein:  
 the means for compressing further comprises an airimpervious overlay spread upon the sheet material to be cut.  
 6. Apparatus for cutting as defined in claim 1 wherein:  
 the supporting means comprises a conveyor having a movable conveyor surface defining a portion of the support surface.  
 7. Apparatus for cutting as in claim 1 wherein:  
 the supporting means comprises a pair of conveyors placed end-to-end with an intervening gap between the conveyors; and the fluid jet nozzle is directed toward the intervening gap.  
 8. Apparatus for cutting sheet material as in claim 1 wherein:  
 the compressing means further comprises a roller positioned adjacent the cutting tool and on the sheet material; and the controlled drive means also moves the roller and the sheet material relative to one another in one coordinate direction 9. Apparatus for cutting sheet material as in claim 1 wherein:  
  the compressing means further comprises a pair of parallel rollers positioned adjacent the cutting tool on the sheet material and an endless belt mounted on the rollers and having one belt portion resting against the sheet material. 10. Apparatus for cutting sheet material as defined in claim 1 wherein:  
  the compressing means further comprises a pressure chamber positioned adjacent the cutting tool above the support surface and having one side confronting the sheet material on the support surface and having at least one aperture exposing the sheet material to pressure within the chamber. 11. Apparatus for cutting sheet material as in claim wherein:  
 the pressure chamber and the cutting tool are struc&#39; turally connected together; and the drive means moves the cutting tool together with the pressure chamber relative to the sheet material. 12. Apparatus for cutting sheet material as defined in claim 1 wherein:  
  the means for compressing further comprises a pair of parallel rollers positioned adjacent the cutting tool above the support means and the sheet material resting upon the support surface, and an endless belt formed by an air-impervious material and mounted on the rollers whereby the one portion of the belt between the rollers and the sheet material resting upon the support surface may rest in sealing relationship upon the sheet material. 13. Apparatus for cutting sheet material as defined in claim 1 wherein:  
 the compressing means further comprises means for sealing the sheet material spread upon the supporting means including a roller supported with the cut ting tool for movement by the controlled drive means and a strip of air-impermeable material wound upon the roller whereby the strip may be anchored to the supporting means and the roller may move with the cutting tool while the strip of air-impermeable material is reeled onto or off of the roller in accordance with the controlled movement of the cutting tool relative to the sheet material on the support surface. 14. Apparatus for cutting as defined in claim 13 wherein:  
 the sealing means includes a pair of rollers mounted 15. A method of cutting pattern pieces from limp sheet material comprising the steps of:  
 applying a compressive force to the spread sheet material in a direction generally normal to the plane of the material and the support surface on which the material is spread by drawing a vacuum from a chamber below the fluid permeable support surface through the support surface;  
 generating a fluid cutting jet;  
 directing the fluid cutting jet onto the compressed sheet material at a cutting point to cut through the material in the direction normal to the material and the support surface;  
 collecting the spent fluid from the jet in the chamber below the permeable support surface; and  
 controllably moving the spread sheet material and the fluid cutting jet relative one another in directions generally parallel to the plane of the sheet material to move the cutting point of the jet along a desired line of cut defined by the periphery of a pattern piece.  
 16. The method of claim 15 wherein:  
 the step of applying further comprises generating a region of increased air pressure over the limp sheet material in the spread condition.  
 17. The method of claim 15 wherein:  
 the step of applying comprises applying an additional compressive force to the exposed surface of the sheet material in a localized region of the spread material adjacent the cutting point of the fluid jet; and  
 an additional step comprises controllably moving the additional compressive force and the sheet material relative to one another during the step of directing to maintain the cutting point of the fluid jet and the localized region subjected to the compressive force in adjacent relationship.  
 18. A method of cutting sheet material as defined in claim 17 wherein:  
 the step of applying an additional compressive force comprises generating a positive holddown pressure over the spread sheet material adjacent the fluid cutting jet.  
 19. A method of cutting as in claim 18 wherein:  
 the step of generating a positive holddown pressure comprises generating a region of increased air pressure over the spread sheet material.  
 20. A method of cutting as in claim 18 wherein:  
 the step of generating a positive holddown pressure comprises placing a roller on the spread sheet material adjacent the cutting jet.  
 21. A method of cutting as in claim 18 wherein:  
 the step of generating a positive holddown pressure comprises placing a pair of parallel rollers and an endless belt extending around the rollers on top of the spread sheet material.