Waterjet cutting process

Abstract

The invention relates to a method for processing a flat workpiece (2) on a waterjet cutting system with a worktable having a plurality of flat, upright support elements (3) arranged at intervals from one another. The invention is based on the objective of providing a simple and cost-effective method for processing a flat workpiece (2) on a waterjet cutting system, which reduces the risk of damage to the back side of the workpiece. To achieve the objective of the invention, the workpiece (2) is placed on a plurality of spacer elements (20) distributed over the surface of the workpiece (2) and having a lower slotted area into the slot of which a support element (3) is inserted, and a second unslotted area on the free end surface (21a) of which the workpiece (2) rests.

Description

The invention relates to a fastening device for fixing a workpiece to a flat, upright support element, having a main body to which two clamping jaws are movably fastened in relation to one another, which clamping jaws extend below the main body and are movable towards one another by means of a clamping means accessible from the upper side of the main body. The invention relates to a method for fixing a sheet workpiece on a water jet cutting installation with a worktable using the fastening device, which comprises a plurality of flat, upright support elements according to the above description, which are arranged at a distance from each other, wherein the workpiece is placed on a plurality of spacer elements, which are distributed over the surface of the workpiece.The fixing of workpieces during the processing of the workpieces ensures that the processing takes place precisely and precisely in position. The present development can be used in particular for workpiece fixing during mechanical processing and above all during cutting of the workpiece by means of a water jet. During water jet cutting, the workpieces rest on the narrow edges of flat support elements which are substantially in a vertical plane and are arranged in a basin which catches the water of the water jet. The support elements are replaceable because they are damaged by the water jet.From the publication CN 1 13 442 205 A a holding device for fixing a workpiece in a water jet cutting system is known. The holding device comprises a first guide rail, a second guide rail and a plurality of clamping devices. The first and the second guide rail are placed on the support elements of the water jet cutting system and fastened thereto by means of wing screws. At least one clamping device for fixing a workpiece to be machined is detachably fastened to each of the first and second guide rails. The clamping device comprises a compression spring and a cantilever pressed onto the workpiece by means of the compression spring. The fastening device is intended to enable rapid clamping and loosening of workpieces of different sizes and shapes in a water jet cutting installation.DE 10 2009 024 567 A1 describes a holding-down device for water jet cutting and a water jet cutting system having a Venturi nozzle, wherein a suction channel inlet of the Venturi nozzle opens into a support surface for a workpiece to be cut. DE 92 02 023 U relates to a support arrangement for the workpiece of a water jet cutting installation, in which the support has at least two upright carrier elements which are arranged parallel to the water jet and are fastened in exchangeable fashion in holding devices.The object of the invention is to provide a fastening device which can be handled more easily. Preferably, the fastening device should be designed in a simple and favorable manner, be able to be fastened securely, quickly and flexibly to a worktable and fix a workpiece securely and easily to the worktable. Furthermore, the risk of damage to the rear side of the workpiece is to be reduced.According to the invention, this object is achieved by a fastening device having the totality of the features of claim 1. A set for securing a sheet workpiece to a worktable having a plurality of flat, upright support members with such a securing device is given in claim 2. a method for securing a sheet workpiece to a waterjet cutting line with a worktable having a plurality of flat, upright support members spaced apart from each other using said set is given in claim 3.Advantageous embodiments are evident from the dependent claims.The fastening device described here for fixing a workpiece to a flat, upright support element comprises a main body to which two clamping jaws are movably fastened with respect to one another, which clamping jaws extend below the main body and are movable toward one another by means of a clamping means accessible from the upper side of the main body.The flat, upright support elements are generally vertically oriented metal sheets and are also referred to as wear plates. As mentioned above, the worktable of a water jet cutting plant comprises a basin for collecting the water, comprising a plurality of such support elements, which are substantially located in vertical planes and whose upper edge, remote from the support table, forms the support for a workpiece. Alternatively, the support element can also be a rod, a rib or a grid, wherein the rod, the rib or the grid has an edge pointing away from the worktable, on which the workpiece rests.The fastening device can be fastened to the support element by means of the clamping jaws in such a way that the main body is placed on the edge of the support element remote from the worktable and is fastened thereto by means of the clamping jaws. Often, a workpiece to be machined is plate-shaped and flat and is horizontally oriented for machining. For this purpose, the main body is placed against the edge of the support element which is at a distance from the worktable and the clamping jaws abut against two side surfaces of the support element which adjoin this edge and clamp the support element. The two jaws are movably attached to the main body relative to each other and project at least partially under the main body. The jaws are moved towards and away from each other by clamping means accessible from the top of the main body, respectively, to be moved from a clamping position with a small distance between the jaws to a release position with a large distance between the jaws. In the clamping position, the fastening device is clamped to the support element and in the release position is detachable therefrom. The upper side of the main body is the side of the main body facing away from the support element. The workpiece to be machined can be placed on the top side.The fastening device has a holding element which is arranged above the main body, that is to say on the side of the main body remote from the clamping jaws, and which is movable towards the main body by means of a clamping means. In other words, a holding member is proposed with which a workpiece to be machined and disposed on the upper surface of the main body can be pressed against the main body. The holding element is in particular flat and protrudes by less than 2.5 mm, preferably less than 2 mm, over the surface of the workpiece. The force with which the workpiece is pressed against the main body is produced by the clamping means. For this purpose, the clamping means presses or pulls the holding element in the direction of the main body. The clamping means is connected to the main body by a first section. This connection can be realized in a materially integral, positive-locking and / or non-positive-locking manner. The clamping means is connected to the holding element by a second section. This connection can likewise be realized in a materially integral, positive-locking and / or non-positive-locking manner. In this case, the clamping means can also be arranged and connected to the holding element in such a way that no region of the fastening device protrudes beyond the side of the workpiece facing away from the main body by more than 2.5 mm, preferably 2 mm.Overall, the fastening device is thus arranged substantially below the workpiece to be machined. A tool for machining the workpiece, in particular a nozzle of a water jet cutting installation, is frequently moved over the side of the workpiece facing away from the main body at a distance of a few millimeters. This distance is often less than 3 mm. Due to the design of the fastening device, which is arranged mainly below a workpiece to be machined and has only a flat holding element above the workpiece, it is possible to move the tool freely above the workpiece. The risk of the tool colliding with the fastening device and being damaged during the movement above the workpiece is thus reduced or eliminated.In practice, a gap can be formed between the clamping jaws in a first plane and a gap can be formed between the holding element and the upper side of the main body in a second plane, wherein the second plane is oriented at right angles to the first plane. By means of the two gaps oriented at right angles to one another, workpieces to be machined can be fixed with the fastening device in a horizontal orientation when the fastening device is fastened from above to a support element which projects vertically from a horizontal worktable. This is the case, for example, in water jet cutting installations in which the worktable has a trough or basin for collecting the water, in which the flat support elements extend vertically upward. The fastening device can also be used with flat support elements which do not extend exactly vertically. In this case, "bottom" means near the worktable and "top" means away from the worktable.In practice, the clamping means may be a clamping screw. The clamping screw has a connecting element, a threaded region and a driver. The connecting element, also called a rotary drive, serves for the form-fit connection with a tool for rotating the clamping screw, e.g. a screwdriver or wrench. The connecting element can be slot-shaped or cross-slot-shaped; it can be shaped as an internal hexagonal or six-arc tooth (TORX®). However, it can also be a square or hexagonal projection for a wrench. The clamping screw extends with the threaded region through a bore which extends through the main body and which has an internal thread. By means of the connecting element located on the upper side of the main body, the clamping screw can be rotated from the upper side and thus screwed into the bore and unscrewed therefrom. The driver is arranged at the end of the threaded region which is opposite the connecting element. With the driver, the clamping screw engages behind a respective recess made in the clamping jaws. The recesses in the clamping jaws are substantially geometrically complementary to the driver. The recesses can be provided on the sides of the clamping jaws facing each other, so that the clamping jaws abut with these sides against the clamping screw arranged in the main body. By screwing the clamping screw into the internal thread of the bore in the main body from the top side, a pressure is exerted on the clamping jaws via the driver, by means of which pressure the clamping jaws are pressed apart into the release position. By the screwing out of the clamping screw from the main body upwards, a tensile force is exerted on the clamping jaws via the driver, by means of which the clamping jaws are moved towards one another into the clamping position.The clamping jaws can in practice be pivotably attached to the main body. By pivoting the clamping jaws about pivot axes, it is possible to move the sides of the clamping jaws facing each other away from each other or to move them towards each other and to set the release position or the clamping position. For this purpose, both clamping jaws or only one of the two clamping jaws can be arranged pivotably. In particular, the clamping jaws can have separate pivot axes. The clamping means can then engage the clamping jaws in particular in a region lying between the pivot axes.In a practical embodiment, the main body may have a recess in which the clamping jaws are arranged. The recess is formed in a bottom surface of the main body, which is opposite to the top surface, and is formed at right angles to the top surface. In particular, the recess can be a slot, i.e. a narrow, elongated recess in a plane in which the clamping jaws are at least partially arranged. By inserting the pivotable jaws into a slot of the main body, the jaws are guided on the main body and the risk of a user of the device clamping the fingers is reduced. The main body may additionally include a second slot perpendicular to the first slot and perpendicular to the top surface. Between the clamping jaws, a gap is formed in a clamping plane, in which the flat support element can be clamped. The clamping plane can coincide with the plane of the second slot, so that the second slot guides the support element into its intended position between the clamping jaws. The main body can then be placed with the second slot on the upper edge of the support element and clamped to the support element with the clamping jaws arranged in the first slot.In practice, the clamping jaws can have a saw tooth profile on the sides facing each other. The fastening of the fastening device to the support element can be particularly secure by the saw tooth profile, because the saw teeth of the saw tooth profiles in the clamping position bear against the support element with high surface pressure.In practice, the holding element can be fastened to the upper side of the main body such that it can be displaced in a displacement direction which runs perpendicular to the upper side. The slidable attachment of the holding member allows workpieces of different thickness to be fixed between the top surface of the main body and the holding member.The implementation of the displaceable fastening of the holding element is particularly simple in practice if the holding element is fastened to the main body by means of an elastic tensioning means, for example a tension spring or bending spring, which pulls the holding element toward the upper side of the main body, wherein the main body has an oblique guide surface opposite the lower side of the holding element, which guide surface defines with the lower side of the holding element an insertion gap running obliquely to the displacement direction. A workpiece to be machined, for example a metal plate, wood plate or plastic plate, can be pushed obliquely into the insertion gap and, when the workpiece is pivoted down into a plane running at right angles to the displacement direction, lifts the holding element with respect to the main body and increases the gap. The elastic clamping means counteracts the lifting and thus fixes the workpiece to the fastening device.In a further practical embodiment, the clamping jaws can each have a projection on the sides facing away from each other. The projections serve as levers by means of which the clamping jaws can be pivoted from the clamping position into the release position. Manual actuation of the levers after releasing the clamping means moves the clamping jaws from the clamping position to the release position and allows removal of the main body from the support member.In practice, clamping jaws pivotably attached to the main body can be supported in slide bearings, in particular slide bearings with solid friction. The slide bearings ensure smooth pivoting between the release position and the clamping position. In addition, plain bearings are long-lived and easy to clean.Additionally or alternatively, in practice, the clamping jaws may be formed from a material with higher strength than the material of the main body. This reduces the wear of the mechanically stressed clamping jaws and increases the service life.A further aspect of the development described here relates to a method for fixing a planar workpiece on a water jet cutting installation having a worktable which has a plurality of flat, upright support elements according to the above description, which are arranged at a distance from one another, wherein the workpiece is placed on a plurality of spacer elements which are distributed over the surface of the workpiece. Each of the spacer elements comprises a lower slotted region, into the slot of which a bearing element is inserted, and a second unslotted region, on the free end face of which the workpiece rests.Furthermore, the proposal described here relates to the spacer element described above and to a set for fixing a workpiece to a worktable having a plurality of flat, upright support elements, comprising at least one fastening device according to the above description and a plurality of the spacer elements, i.e. two or more spacer elements. If the spacer element has a small, approximately punctiform upper end face for supporting the underside of the workpiece, at least three spacer elements should be used. Three points define an area. If the upper end face of at least one spacer element extends over a greater length, two spacer elements may suffice. With such long spacer elements, however, there is the risk that they are destroyed by the water jet, whereas punctiform spacer elements can be placed in such a way that only a few or no spacer elements are cut by the water jet.The spacer elements are used to achieve a distance between the underside of the workpiece and the support element. When cutting a workpiece with a water jet, the water, when the water jet is guided over a support element, impinges back from the upper edge of the support element and can strike against the underside of the workpiece. In the case of sensitive workpieces, for example decorative wood or acrylic glass, there is the risk that their underside is damaged by water which rebounds from the supporting elements. By placing the spacer elements on the support elements and the distance thereby created between the underside of the workpiece and the upper edges of the support elements, it is ensured that the kinetic energy of the water that rebounds when it impinges on the underside is sufficiently low to prevent damage to the underside. By fixing the workpiece with the fastening device, the workpiece is held securely and the workpiece is supported uniformly by the workpiece resting on the spacer elements. Due to the combination of the fastening device and the spacer elements, the workpiece maintains its predetermined position above the worktable during its machining, so that it can be precisely machined and damage to the underside due to water that rebounds is prevented.In practice, the length of the unslit areas of all spacer elements can be the same. As a result, a plane above the plane of the edges of the support elements is spanned by a plurality of spacer elements, on which plane a workpiece can be placed with a planar side. In particular, the length of the unslit areas of all spacer elements can also be identical to the distance between the upper side of the fastening device and the edge of the support element to which the fastening device is fastened.In practice, the spacer elements can be tubular. A slot can then be made in a lower end face of the tube at right angles to the end face. The end face opposite this end face is the free end face of the unslit area. The workpiece is placed on this free end face. Tubular spacer elements are compact and offer the advantage of being able to be placed locally on the wear plates in a particularly flexible manner. In the case of a known cutting pattern of a workpiece to be machined, it is thereby possible to position the spacer elements in such a way that a water jet machining the workpiece is guided past the spacer elements. Thus, the destruction of the spacer elements can be avoided.In this context, reference is also made to the possibility of visualizing the cut guide before the machining of a flat workpiece on a water jet cutting system by means of an optical representation of the machining pattern, in particular of a cut pattern to be produced. The machining pattern can be projected by means of a light beam, in particular by means of a laser beam, onto the worktable or onto the workpiece resting thereon. Due to the projected slice image, it is possible to predict which region is not cut by the water jet. The workpiece to be machined can then be aligned with the cut image, for example when a workpiece made of wood is machined and the course of the grain is to be matched to the cut guide. The fastening device and / or the spacer elements on which the workpiece rests can be arranged and positioned relative to the machining pattern in such a way that they do not lie on a cutting line and are not damaged by the water jet.As an alternative to a tubular configuration of the spacer elements, the spacer elements can be designed in the form of strips in practice, wherein the spacer elements designed as strips have a lower slotted region, with which a strip can be placed over a considerable part or the entire length of a straight support element (also referred to as wear plate). By using strip-shaped spacer elements, a workpiece can already be securely supported with two spacer elements. Few spacer elements have to be placed on the wear plates, as a result of which the method can be carried out particularly quickly.The spacer elements can in practice be formed from plastic. Plastic is particularly favorable and easy to process. At the same time, the strength of most plastics is sufficiently high to be able to bear the load of a workpiece. However, wood pipes, e.g. made of bamboo, can also be used.In practice, when machining the workpiece on a water jet cutting installation, the workpiece will be fixed with at least one fastening device according to the above description, wherein the fastening device is clamped onto a support element. As a result, the workpiece is securely mounted and can be precisely machined.Further practical embodiments and advantages of the development described here are described below in conjunction with the drawings. The following are shown: FIG. 1 shows a perspective view of a fastening device obliquely from below; FIG. 2 shows a perspective view of the fastening device from FIG. 1 obliquely from above; FIG. 3 shows a sectional side view of the fastening device from FIG. 1 ; FIG. 4 shows a sectional front view of the fastening device from FIG. 1 ; FIG. 5 is a perspective view of a spacer element that can cooperate with the fastening device from FIG. 1 in one set; FIG. 6 shows a perspective view of a further spacer element; FIG. 7 shows a perspective view of a further spacer element; FIG. 8 shows a perspective view of a further spacer element; FIG. 9 shows a perspective view of a further spacer element; FIG. 10 shows a perspective view of a further spacer element; FIG. 11 shows a first perspective view of a wear plate with spacer element according to FIG. 5 and fastening device according to FIG. 1 ; FIG. 12 shows a first perspective view of a wear plate with spacer element according to FIG. 5 and a further embodiment of a fastening device; FIG. 13 is an exposed perspective view of the fastening devices from FIG. 12 ; FIG. 14 shows a sectional illustration of the fastening devices and of the spacer element from FIG. 12 during the attachment of a workpiece; FIG. 15 is a view corresponding to FIG. 14 with the workpiece pivoted into the machining position; FIG. 16 shows a top view of a worktable for machining a workpiece with spacers and fastening devices; FIG. 17 is a perspective oblique top view of the arrangement from FIG. 16.FIGS. 1 to 4 show a first embodiment of the fastening device in different views. FIGS. 5 to 10 show spacer elements which are preferably used in combination with the fastening device from FIGS. 1 to 4. FIGS. 11 to 17 illustrate the interaction of the fastening devices and the spacer elements. In the drawings, identical elements or functionally identical elements are denoted by the same reference numerals.With the fastening device 1 shown in FIGS. 1 to 4, a workpiece 2 can be fixed to a flat, upright support element 3 of a worktable, as is illustrated, for example, in FIG. 11. The support element 3 is a flat sheet metal made of metal or plastic, which has a flat upper edge, on which the workpiece 2 is frequently placed directly in machining methods known from the prior art. Such support elements 3 are referred to as wear plates during water jet cutting. The wear blades 3 are usually located in a water basin or catch basin, which forms the worktable of a water jet cutting installation. As an alternative to a plurality of parallel wear plates 3, it is also known to use intersecting support elements which form a grid.The fastening device 1 has a main body 4 to which two clamping jaws 5 a, 5 bare fastened such that they can move relative to one another. The clamping jaws 5 a, 5 bare movably fastened by means of slide bearings 6 a, 6 bfixed to the main body 4, in which the clamping jaws 5 a, 5 bare each mounted such that it can be pivoted about a pivot axis. By pivoting the clamping jaws 5 a, 5 b, the clamping jaws 5 a, 5 bcan be moved towards each other into a clamping position and moved away from each other into a release position. Between the clamping jaws 5 a, 5 b, a gap 7 is formed in a first plane. When the mutually facing sides of the clamping jaws 5a, 5b are aligned substantially parallel to one another, the thickness of the gap 7 lying therebetween corresponds approximately to the thickness of the support element 3.The jaws 5a, 5b project partly below the main body 4 and thus extend at least partly below the main body 4. The recess is formed in the shape of a first slot 8. The first slot 8 defines the plane in which the clamping jaws 5 a, 5 bare pivotable. The width of the first slot 8 corresponds approximately to the thickness of the clamping jaws 5 a, 5 btransversely to their direction of movement. The clamping jaws 5 a, 5 band the slide bearings 6 a, 6 bin which the clamping jaws 5 a, 5 bare mounted are protected from soiling by the arrangement within the slot 8. In addition, the risk of a user clamping his fingers with the clamping jaws 5 a, 5 bis reduced.In FIG. 4, the clamping jaws 5a, 5b are shown divided along the middle plane of the gap 7, which is shown by a dot-dash line. The left jaw 5a is shown in the release position and the right jaw 5b in the clamping position. At right angles to the first slot 8, a second slot 9 is formed in the main body 4. The second slot 9 is located in the same plane as the gap 7 located between the clamping jaws 5 a, 5 b. The width of the second slot 9 is selected such that the support elements 3 can be pushed freely into the second slot 9.The clamping jaws 5 a, 5 bare moved by means of a clamping means which is accessible from the upper side 10 of the main body 4 and is designed as a clamping screw 11. The clamping screw 11 extends through a bore 12 with an internal thread in the main body 4 extending from the upper side 10 of the main body 4 as far as the first slot 8, the clamping screw 11 having a threaded region with an external thread, with which it can be screwed into the bore 12 or screwed out of it-in relation to the upper side 10. The upper end of the clamping screw 11 is designed as a grub screw and can be screwed completely into the bore 12 in the main body 4. The upper end of the clamping screw 11 has a connecting element 13 to which a screwing tool can be positively coupled. At the lower end, the clamping screw 11 has a driver 14. The driver 14 protrudes out of the bore 12 and into the first slot 8. The driver 14 engages behind a recess formed in the mutually facing sides of the clamping jaws 5 a, 5 band formed complementarily to the driver 14. By screwing the clamping screw 11 into the main body 4 from the upper side 10, a pressure is exerted on the clamping jaws 5 a, 5 bvia the driver 14 and the recess, by means of which pressure the clamping jaws 5 a, 5 bare pressed into the release position. As mentioned, the left half of Figure 4 shows the jaw 5a and the left half of the jaw 11 in this release position. The upward turning out of the clamping screw 11 has the effect that both clamping jaws 5 a, 5 bare pivoted towards each other into the clamping position. The right clamping jaw 5 band the right half of the clamping screw 11 are shown in this clamping position in FIG. 4.It should be noted that the clamping means can also be realized by any other elements. Instead of a clamping screw, for example, a so-called quick-action clamping device can be used, which is known from bicycle construction. A clamping lever with an eccentric is supported on the upper side 10 of the main body 4, wherein a shank with a driver is pulled upward by rotating the eccentric and the clamping jaws are moved into the clamping position.On the sides facing each other, the clamping jaws 5 a, 5 bhave a saw tooth profile 15 each. Due to the saw tooth profile 15, the clamping jaws 5 a, 5 bhave point-shaped contact areas with the surfaces of the support element 3 in the clamping position, whereby a particularly high surface pressure arises in the contact areas and secure fastening of the fastening device 1 to the support element 3 is ensured.In particular, when the clamping jaws 5 a, 5 bwith the saw tooth profiles 15 press into the material of the support element 3, a high force may be required to release the clamping jaws 5 a, 5 bfrom the support element 3 again. In order that the clamping screw 11 is not damaged, for example, when the clamping jaws 5 a, 5 bare released, the clamping jaws 5 a, 5 bmay have structures by means of which an additional force for opening the clamping jaws 5 a, 5 bmay be applied manually. These structures are formed as projections 16 a, 16 bon the mutually remote sides of the clamping jaws 5 a, 5 b. When the projections 16 a, 16 bare compressed (i.e. moved towards each other), the clamping jaws 5 a, 5 bare pivoted about their respective pivot axis into the release position. By simultaneously compressing the projections and screwing in the clamping screw 11, the clamping jaws 5 a, 5 bcan be easily released from the support element 3.For fixing the workpiece 2 to the fastening device 1 of FIGS. 1-4, a holding element 17 is arranged above the main body 4. In this embodiment, the holding element 17 is configured flat and has the shape of an annular disk. By means of a clamping means 18, which in the embodiment described here is formed as a clamping screw 18 screwed into a threaded hole 23 of the main body 4, the holding element 17 is fastened to the upper side 10 such that it can be displaced in a displacement direction running perpendicular to the upper side 10 of the main body 4. As a result, a second gap 19 is formed in a second plane extending at right angles to the first plane between the holding element 17 and the upper side 10 of the main body 4. The workpiece 2 can be clamped in the second plane between the upper side 10 and the holding element 17.As mentioned, FIG. 11 shows a fastening device 1 of FIGS. 1 to 4 clamped onto a wear plate 3 and fixing a workpiece 2. The wear plate 3 extends through the slot 9 and is clamped firmly with the clamping jaws. The workpiece 2 is a flat plate that is urged against the main body 4 of the fastening device 1 with the disk-shaped holding member 17.Furthermore, a spacer element 20 can be seen in FIG. 11, the free end face of which supports the plate-shaped workpiece 2. Embodiments of such spacer elements 20 will be explained in more detail with reference to FIGS. 5-10.FIG. 5 shows a spacer element 20 which is designed as a round tube piece with parallel end faces 21 a, 21 b. At right angles to the lower end face 21b, a diametrically extending slot 22 is made in the spacer element 20, the width of which slot is matched to the thickness of the support element 3. The spacer element 20 is pushed with the slot 22 onto the support element 3. Consequently, the width of the slot 22 should be slightly undersize with respect to the thickness of the support element 3 in order that the slot 22 expands elastically when it is pushed onto the support element and the spacer element 20 is seated firmly on the support element 3. The upper end face 21a forms the free end face of the spacer element 20 on which the workpiece 2 can rest. An unslit portion of the spacer 20 extends in the axial direction of the spacer 20 from the free end face 21 ato the slit 22, and as can be seen in FIG. 11, the length of the unslit portion of the spacer 20 is identical to the distance between the upper edge of the support member 3 and the upper surface 10 of the main body 4 of the fastening device 1 to which the fastening device 1 is fastened. The upper edges of the support elements 3 of a water jet cutting installation are generally located in one plane. Thus, a common plane can be defined by the upper side 10 of the fastening device 1 and the free end face 21 aof the spacer element 20, which plane forms the bearing plane for the planar lower side of the workpiece 2.In practice, a plurality of spacer elements 20 and / or fastening devices 1 can also span a common plane, as is shown in FIGS. 16 and 17. In this case, the length of the unslit areas of all spacer elements 20 is identical and corresponds to the distance between the upper side 10 of all fastening devices 1 and the lower side of the workpiece 2.The distance between adjacent spacer elements 20 is to be selected such that the workpiece 2 does not flex unacceptably between these spacer elements 20. The distribution of the spacers 20 over the surface of the workpiece may be irregular, as shown in FIG. 16. In FIGS. 16 and 17, a plate-shaped workpiece 2 having a square surface is fastened at all four corners by means of a fastening device 1, respectively. However, the number of fastening devices 1 can also be reduced or increased in order to fix the workpiece 2 securely. During machining with water jets impinging perpendicularly to the surface of the workpiece 2, hardly any transverse forces act on the workpiece 2 and the required holding force of the fastening devices 1 is quite low, so that fewer than four fastening devices 1 can suffice.The spacer elements 20 can also be distributed irregularly over the surface of the workpiece 2. It is possible to project the cut pattern which is to be produced by the water jet onto the worktable by means of a projection device, in particular using a laser. In the case of a workpiece made of natural material, for example a wood board or a stone board, grain and color patterns can be aligned with respect to the cut guide to be produced. It is also possible to distribute the spacer elements 20 at least in the majority over the surface of the workpiece 2 in such a way that they are not cut by the water jet. In this way, at least the majority of the spacer elements 20 can be used multiple times.The spacer elements 20 shown in FIGS. 5, 11, 12 and 14 have the shape of a tube with a circular cross section. The shapes of the spacer elements can, however, deviate from the circular shape. For example, rectangular tubes or other tube shapes can be used, the end surfaces of which extend at right angles to their axis of symmetry and which have a slot in a plane which preferably contains the axis of symmetry. Other shapes of the spacer elements, which are each mounted on a support element, are shown in FIGS. 6 to 10.FIGS. 6 to 10 show strip-shaped spacer elements. The spacer element 20 aof FIG. 6 has a cross section that resembles the gable side of a house. This cross section is composed in axial plan view of a rectangular basic shape and a roof section placed thereon with roof surfaces arranged symmetrically to the center line of the rectangle. In the middle of the lower base line of the rectangular basic shape, the slot 22 is arranged, which extends along the vertical axis of symmetry of the cross section upwards approximately as far as the middle of the height of the spacer element. The ridge line of the roof section of the strip-shaped spacer element 20a forms the free end face or end face 21a on which the workpiece rests.The spacer element 20 bof FIG. 7 has a circular cross section, wherein the slot 22 extends radially as far as the center of the cross section. The lateral surface of the strip-shaped spacer element 20a opposite the mouth of the slot 22 forms the free end surface 21a on which the workpiece rests. The same applies to the spacer element 20 cof FIG. 8, wherein the latter does not have a solid cross section, but rather a cylinder jacket with radial webs, which is manufactured as an extruded profile.FIG. 9 again shows a strip as spacer element 20 dhaving the same profile as the strip 20 ain FIG. 6, wherein cavities running in the longitudinal direction are provided, which save material and weight. The spacer element 20 dis manufactured as an extruded profile. The spacer element 20 eof FIG. 10 is also an extruded profile. The profile cross section corresponds substantially to that of the spacer element 20 dfrom FIG. 9, wherein the free end face 21 ais enlarged by a horizontally extending web.As mentioned above, FIG. 11 shows a combination of the fastening device from FIG. 1 with a spacer element 20 from FIG. 5.In an embodiment of the fastening device 1 shown in FIGS. 12 to 15, the main body 4, the clamping jaws 5 a, 5 band the clamping screw 11 are substantially designed as described above. Only the top 10 of the main body and the holding element 17 are designed differently. The upper side 10 of the main body 4 has a guide surface 24 which is beveled with respect to the horizontal underside of the holding element 17, and the holding element 17 is designed as a spring clamp. The spring clamp 17 urges the workpiece 2 in the direction of the top 10 when pivoted to the horizontal position as shown in FIG. 8. The spring clamp 17 thus simultaneously forms the clamping element. The screw 18 fixes the spring clip 17 to the main body 4 only in this embodiment.The top 10 of the main body 4 extends from its right edge of the main body 4 facing the observer towards the centre thereof. Adjoining the horizontal upper side 10 is the beveled guide surface 24. It is inclined in the direction of the underside of the fastening device 1, so that the workpiece 2 can be pushed laterally into the gap between the beveled guide surface 24 and the spring clamp 17, as shown in FIG. 8. When the workpiece 2 is pivoted down into the horizontal position, it presses the spring clamp 17 upwards from below. In this case, the spring clamp 17 deforms elastically. The workpiece 2 is thus held securely and can be used easily. The spring clamp 17, like the holding elements 17 of the above-described embodiment, has an opening 25 in order that a user of the fastening device 1 can engage a screw tool with the connecting element 13 of the clamping screw 11 under the spring clamp 17.It is pointed out that the shape of the holding element and of the clamping means can be varied and adapted to the respective machining operation and to the shape of the workpiece.The features of the invention disclosed in the present description, in the drawings and in the claims can be essential, both individually and in any combinations, for the realisation of the invention in its various embodiments. The invention is not limited to the described embodiments. It can be varied within the scope of the claims and taking into account the knowledge of the responsible person skilled in the art.List of reference characters1 Fastening device 2 Workpiece 3 Support element, wear lamella 4 Main body 5 a, 5 b Klemmbacken jaws 6 a, 6 b Gleitlager bearing 7 Gap in first plane 8 Recess, first slot 9 Second slot 10 Upper side 11 Clamping means, clamping screw 12 Bore 13 Connecting element 14 Driver 15 Saw tooth profile 16 Projections 17 Holding element 18 Clamping means, clamping screw 19 Second gap in second plane 20 Spacer element 21 a, 21 b Stirnflächen surfaces 22 Slot 23 Threaded hole 24 Guide surface

Claims

Fastening device (1) for fixing a workpiece (2) to a flat, upright support element (3), having a main body (4) to which two clamping jaws (5a, 5b) are movably fastened in relation to one another, which clamping jaws extend below the main body (4) and are movable towards one another by means of a clamping means (11) which is accessible from the upper side (10) of the main body (4), and having a holding element (17) which is arranged above the main body (4) and is movable towards the main body (4) by means of a clamping means (18).Set for fastening a flat workpiece (2) to a worktable having a plurality of flat, upright support elements (3), comprising: • a plurality of spacer elements (20, 20a-20e) having a slotted and an unslotted portion, and • at least one fastening device (1) according to claim 1.Set for fastening a flat workpiece (2) according to claim 2, characterised in that the spacer element (20, 20a-20e) has at least one of the following features: • it is tubular; • it is strip-shaped; • the unslotted section extends over a predetermined length; • it consists of plastic.Method for fixing a flat workpiece (2) on a worktable of a water jet cutting facility, which comprises a plurality of flat, upright support elements (3) which are arranged at a distance from one another, comprising a set for fastening a flat workpiece (2) according to claim 2 or 3, characterized in that the workpiece (2) is placed on a plurality of spacer elements (20, 20a-20e), which are distributed over the surface of the workpiece (2) and comprise a lower slotted region, into the slot (22) of which a support element (3) is inserted, and a second unslit region, on the free end surface (21a) of which the workpiece rests and is fixed to one of the flat, upright support elements (3) by means of the at least one fastening device (1).Method according to Claim 4, characterized in that the length of the unslit regions of all spacer elements (20, 20a-20e) is the same.Method according to Claim 4 or 5, characterized in that the workpiece (2) is fixed by means of at least one fastening device (1) which is clamped firmly on a bearing element (3).

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