HK1110034B - Clamping apparatus for positioning and fixing work pieces - Google Patents

Description

Clamp for positioning and fixing workpiece

Technical Field

The present invention relates to a jig for positioning and fixing a workpiece to be machined on a table of a machine tool. The invention is particularly useful for wire etching processing equipment. In particular, the invention relates to a clamp comprising at least one clamping rail member adapted to be attached to a machine tool table, and at least one work piece holder adapted to be clamped on the clamping rail member in a precisely positioned position.

Background

If a tool or a workpiece to be machined must be clamped to the table of the machine tool, the tool and workpiece are typically secured independently to the pallet in a first step and the pallet is clamped to the chuck member in a second step. In most cases, the chuck member is rigidly connected to the machine tool. The driving of the clamping elements of the chuck member is typically performed manually, electromechanically, pneumatically or hydraulically.

Document EP-B-0202452 discloses a fixing and reference system for a wire spark-etching machine. The fixing and reference system comprises a flat reference element, a plate-type strip made of hardened steel, which is suitable for being attached to the table of a wire electroerosion machine. The cross-section of these reference elements is substantially wedge-shaped, whereby the top surface has a larger width than the bottom surface. The reference element includes a side surface adjacent to the top surface and extending at an angle to the top and bottom surfaces to form a Y-direction frame of reference. Furthermore, the reference element comprises several continuous bores for receiving bolts, with which the reference element can be mounted in threaded bores on the machine table. The X-direction reference frame consists of a block-shaped part with a stop surface mounted on the front surface of the reference element. The workpiece clamped on the worktable is positioned against the side surface adjacent to the top surface of the reference element and clamped by the clamping member. Such a fixture and reference system may be useful for light weight workpieces. In addition, the manufacture of the reference element is laborious and expensive.

Document US-A-5,019,129 discloses A holding system for workpieces having A clamping frame provided with A fixed and A movable clamping jaw. A clamp provided on the machine tool includes a dovetail projection connected to a fastening plate having a corresponding groove. The fastening plate is adjustable and can be held in place with a clamping mechanism. An adapter is connected to the fastening plate, and a dovetail groove is additionally provided and to which the clip holder can be connected. The clamping mechanism for holding the fastening plate in place includes a spring biased pin and a locking screw.

Document EP- ｃA-1402985 discloses ｃA clamp comprising ｃA frame member and connected to ｃA machine table. The frame member has two side legs and a distance element interposed therebetween. In addition, the frame member comprises two guide elements running between the two side legs. The lockable sliding member is guided in a displaceable manner by two guide elements. The slide member is adapted to receive and grip a workpiece.

Disclosure of Invention

The object of the present invention is to improve a clamp for positioning and fixing a workpiece to be machined on the table of a machine tool, in particular a wire etching machining apparatus, so that it is simple in design and can be manufactured at low cost, is rigid and particularly suitable for clamping workpieces of different shapes, and is capable of clamping and releasing workpieces quickly and easily, respectively.

To this end, the invention provides a clamp for positioning and fixing a workpiece to be machined on a table of a machine tool, in particular a wire etching machining apparatus. The fixture includes at least one clamping rail member adapted to be attached to a table of a machine tool, and at least one work piece holder adapted to be clamped on the clamping rail member at a precisely positioned location. The clamping rail member is provided with an elongated raised portion defining an elongated recess between its bottom surface and the table surface and including a clamping element extending into said elongated recess. Each work piece holder comprises at least one raised gripping portion adapted to be inserted into the elongated recess and clamped in place by the clamping element.

Drawings

Embodiments of the invention are further described below with reference to the accompanying drawings, in which:

FIG. 1 shows a perspective view of a clamp;

FIG. 2 shows a top view of the clamp;

FIG. 3 shows a cross-sectional view A-A of the clamp of FIG. 2;

FIG. 4 shows a cross-sectional view B-B of the clamp of FIG. 2;

FIG. 5 shows a cross-sectional view C-C of the clamp of FIG. 2;

fig. 6 shows a perspective view of a workpiece clamped in the fixture.

Detailed Description

FIG. 1 shows a perspective view of a clip according to one embodiment of the present invention. In particular, the clamp is adapted to hold a workpiece in a precisely positioned position on the table 1 of a machine tool (not shown). In certain embodiments, the machine tool may be a wire etching processing apparatus. In the present embodiment, the table 1 of the machine tool is composed of three thick flat plate members 1a, 1b, and 1c, each of which is rectangular and arranged in a U-shaped manner. Between these slabs 1a, 1b and 1c, the working or machining area is continuous, in which the machining tools of the machining device can move freely in X, Y and Z directions. Of course the table 1 shown in fig. 1 is only one of many embodiments and other different arrangements are possible.

In this embodiment the clamp comprises three clamping rails 2, 3 and 4, which are of substantially identical design, and three differently formed work piece holders 5, 6 and 7. Within the scope of the invention, the clamping device of course comprises at least one clamping rail 2, 3 and 4 and at least one work piece holder 5, 6 and 7. Each clamping rail 2, 3 and 4 has a bottom surface facing the table 1, flat and constituting a Z-reference surface. Each of the three clamping rails 2, 3 and 4 is rigidly connected to one of the three slab members 1a, 1b and 1c of the machine table 1 by means of a fastener, for example a screw, not shown in the drawings.

In the following, the overall design of the clamping rail is explained further by describing the central clamping rail 3 in detail. The other two clamping rails 2 and 4 are of course of the same design as the rail 3. In particular, the front end face of the clamping rail 3, i.e. the face facing the aforementioned working area, has an elongated raised portion 9. The raised portion 9 defines a recess 10 between itself and the table 1, in particular the designated slab member 1 b. The groove 10 is generally rectangular in cross-section. The clamping rail 3 is thus substantially L-shaped in cross-section. The male part 9 has a plurality of threaded holes 11 adapted to receive clamping elements in the form of screws 13. Two of these screws 13 are shown in fig. 1 as an example. The front end face 12 of the elongate raised portion 9 is flat and forms a bearing surface for the assigned work piece holder 5, 6, 7, as will be explained in more detail later. The bottom surface of the clamp rail 3 is also flat, and is supported on the top surface of a prescribed slab member 1b of the table 1 that rigidly connects the clamp rail 3 to the table 1 and the slab member 1b, respectively.

In order to be able to position the work piece holders 5, 6, 7 relative to the clamping rails 2, 3, 4, i.e. in the X or Y direction, reference pins are provided which can be inserted into the threaded holes 11 of the assigned clamping rail 3, thus forming a lateral stop member for the particular work piece holder 5, 6, 7. Instead of a reference pin, a stop member may be provided which is positionally fixed to a particular position by means of a screw 13. The stop member is of particular advantage if the workpiece has to be positioned relative to only one of the clamping rails and/or if only a very small workpiece has to be clamped with one clamping rail. Likewise, the stop member proves to be advantageous if the same workpiece element (for example the workpiece holder and the workpiece together) has to be positioned relative to the clamping rail. Finally, it is worth mentioning that no stop members are necessary at all if the workpiece has to be fixed to two clamping rails arranged at 90 degrees to each other.

The work piece holder 5 has a raised clamping portion 15 for clamping the work piece holder 5 on the clamping rail 3. On the side where the clamping portion 15 is located, the work piece holder 5 has a reference surface 17. The top surface of the raised clamping portion 15 has an inclined clamping surface 16 which is adapted to be connected by means of the clamping screw 13 of the clamping rail 3 in such a way that the work piece holder 5 is pushed into the recess 10 when clamping the work piece holder 5 onto the clamping rail 3. Thus, the reference surface 17 of the work piece holder 5 abuts against the front end surface 12 of the clamping rail 3 and is thereby positioned in the X or Y direction. The bottom surface 18 of the work piece holder 5 has a flat Z-reference surface supported on the table 1 which clamps the work piece holder 5 on the clamping rail 3; the workpiece holder is thus positioned in the Z direction. The side of the work piece holder 5 facing the clamping portion 15 has a shoulder 19 projecting downwardly from the flat bottom surface 18 and at its end a raised portion 20, the top surface of the raised portion 20 serving as a bearing surface 21. The bearing surface 21 extends in the same plane as the flat bottom surface 18 of the workpiece holder 5 as a support in the Z-direction of the workpiece. Once the work piece holder 5 is clamped to the clamping rail 3, the bearing surface 21 of the raised portion 20 extends in the plane of the surface of the table 1 and thus in the Z-plane defined by the machine tool.

Furthermore, the work piece holder 5 comprises several threaded holes 22 adapted to receive clamping members by means of which a work piece can be fixed to the work piece holder 5, as will be explained in more detail later. The work piece holder 5 serves primarily as a Z-direction support member for large work pieces, wherein such large work pieces are preferably fixed to at least two work piece holders.

Of course, a flat-bottom work piece holder may be used, whereby the above-mentioned downwardly projecting shoulder 19 may be omitted so that its front end is not lower than the machine table surface, i.e. the Z-reference surface. This is of particular importance if the clamp of the invention is used on a machine tool having a continuous flat table, with a working area not lower than the table of the machine tool. Instead of using work piece holders with a continuous flat bottom surface, it is possible to use some sort of distance element, the thickness of which corresponds at least to the Z-direction distance of the downwardly projecting shoulders 19 of the work piece holder 5. In practice, such a distance element will be inserted below the work piece holder 5 so that the downwardly projecting shoulder 19 is no longer below the surface of the table 1 of the machine tool in the Z-direction.

The workpiece holder 6 is designed in a 90-degree angle shape; the front faces of the two cathetuses are each provided in a corresponding manner with raised portions 24, 25 offset by 90 ° from one another, the top edges of which constitute the Z-axis bearing faces for the workpiece. The work piece holder 6 also includes several threaded bores 32 adapted to receive screws for attaching the clamping members. Along the two inner surfaces, the work piece holder is provided with two recesses 29, 30 in each case, which extend along the total height of the work piece holder 6 and subdivide the raised portions 24, 25 into separate portions. These grooves enable the etching wire to move between the work piece attached to the work piece holder 6 and the work piece holder itself, as will be explained in more detail later with reference to fig. 2.

The rear side of the work piece holder 6 has two clamping sections 26, 27 offset by 90 ° from one another, by means of which clamping sections 26, 27 the work piece holder can be connected to the clamping rail. A further clamping portion 28 is provided between the two clamping portions 26, 27 and offset by 45 ° with respect to each of the clamping portions 26, 27. The result is that the work piece holder 6 can be connected to the clamping rail in three different positions. Such a workpiece holder 6 is particularly suitable for holding rectangular and circular workpieces. In addition, a large workpiece can be held by the two workpiece holders 6. Likewise, if desired, the workpiece can be held in a position that is offset by 180 ° from the initial position for machining.

The work piece holder 7 is designed in the shape of a rectangular clamping frame. The workpiece holder 7 has four frame sides 43, 44, 45, 46 defining an opening 42 for receiving a workpiece to be clamped and machined. One of the frame sides, namely frame side 43, has a clamping portion 34; however, of course, instead of a single clamping portion, there may be two or three. The top surface of the clamping portion 34 has a flat clamping surface parallel to the bottom surface 37 of the work piece holder 7. The bottom surface of the work piece holder 7 is a continuous flat surface. The inner sides of the two frame sides 43, 44 of the work piece holder 7 are provided with holes 37, 38 adapted to receive stop pin members 39. The stop pin members 39 inserted into the holes 37, 38 project slightly from the inner side edges of the particular frame sides 43, 44, thus forming stop members for clamping the work piece in the work piece holder 7. With such a stop pin member 39, the work piece holder can be manufactured at low cost. For example, as a base material of the work holder 7, a general steel is used instead of the quenched and tempered steel or the annealed steel. In addition, the inner side edge of the work holder 7 does not require high machining accuracy because the X-direction and Y-direction reference surfaces are established by the stopper pin members 39. Of course, the holes 37, 38 can also be used for the etching wires to extend through them if the work piece is attached to the work piece holder 7.

The other two sides 45, 46 of the frame have horizontally extending threaded holes 40, 41 adapted to receive clamping elements (not shown) for clamping a workpiece in the opening 42.

In contrast to the work piece holders 5, 6 described previously herein, the frame-shaped work piece holder 7 does not have a clamping portion whose top face constitutes a Z reference for a work piece clamped in the work piece holder. In order to reliably fix the Z-direction position of the work pieces clamped in the openings 42 of the work piece holders 7, the work piece holders 7 are placed on top of a flat plate member, such as a strictly flat ground granite plate. After that, the work piece to be received in the work piece holder 7 is placed in its opening 42, said opening 42 being clamped to the work piece holder by means of screws inserted in the threaded holes 40, 41.

Fig. 2 shows the inventive clamping apparatus in a plan view, wherein each work piece holder 5, 6, 7 is clamped to a clamping rail 2, 3, 4. Specifically, the work piece holder 5 is clamped to the center clamp rail 3, while the angular work piece holder 6 is clamped to the left clamp rail 2 and the clamp frame-shaped work piece holder 7 is clamped to the right clamp rail 4. Each work piece holder 5, 6, 7 is secured by means of a clamping screw 13a, 13 b; 13c, 13 d; 13e, 13f are clamped to the designated clamping rails 2, 3, 4.

In this view, the angular workpiece holder 6 can be clearly seen to have the above-mentioned third clamping portion 28, which extends between the two clamping portions 26, 27 (fig. 1) angled at 90 °. Additionally, an exemplary workpiece 31 is shown attached to the angular workpiece holder 6. By providing the above-mentioned recesses 29, 30 on the inside edges of the legs of the angled work piece holder 6 and preferably machined on their surfaces, it is very well possible to insert etching wires between the work piece 31 clamped onto the work piece holder 6 and the legs of the work piece holder 6. In this way, the workpiece 31 clamped on the workpiece holder 6 can also be machined from its rear side by wire etching, or the actual position of the workpiece 31 can be determined simply and automatically by touching the etched wire from all four sides until the wire touches the workpiece 31.

Fig. 3 shows a cross-sectional view in the direction a-a of the clamp according to the invention in fig. 2. It can be seen that the clamping screw 13b exerts a pressure on the clamping portion 15 of the work piece holder 5, thus rigidly connecting the latter to the clamping rail 3. The clamping screw 13b has a convex front end face which engages with the inclined top face 16 of the clamping portion 15 of the work piece holder 5 in such a way that the work piece holder 5 is pressed with its flat bottom face down on the slab member 1b on the one hand and with its rear reference face on the flat front end face 12 of the clamping rail 3 on the other hand. Moreover, it can be seen that the bearing surface 21 of the convex portion 20 adapted to support the workpiece is located at the same height level as the top surface 8 of the slab member 1b of the table 1. The result is that the work piece supported on the surface 21 of the raised portion 20 of the work piece holder 5 is accurately aligned relative to the surface 8 of the slab member 1b of the table 1. As can be seen from fig. 3, the bottom surface 23 of the clamping rail 3, which forms the Z-direction bearing surface, extends perpendicularly to its front end surface 12, which forms the stop surface. In order to ensure that the rear reference surface 17 of the workpiece holder 5 is reliably supported on the flat front end face 12 of the clamping rail 3, the clamping portion 15 is slightly shorter in the horizontal direction than the depth of the recess 10 (fig. 1) of the clamping rail 3. Once the work piece holder 5 is clamped on the clamping rail 3, a gap S occurs between the front end face of the clamping portion 15 of the work piece holder 5 and the rear wall of the recess 10. The gap S simultaneously forms an area which can accommodate dirt particles without any negative effect on the clamping accuracy of the work piece holder clamped on the clamping rail. Moreover, the surface responsible for the correct positioning of the work piece holder, i.e. the flat front end surface 12 of the clamping rail 3, is easy to clean.

Figure 4 shows a cross-sectional view of the clamp B-B of figure 2 according to the invention. Also in this case, the convex front end face of the clamping screw 13c exerts a pressure on the clamping section 26 of the work piece holder 6 in such a way that the work piece holder 6 is pressed down with its flat bottom face 33, which forms the Z-direction reference face, on the one hand against the surface 8 of the slab member 1a and with its rear reference face against the flat front end face of the clamping rail 2 on the other hand. Further, the convex portions 24, 25 are located on the same height level as the surface 8 of the slab member 1a of the table 1.

Once the clamping portion 26 is inserted into the groove 10 of the clamping rail 2, the work piece holder 6 is held in place by the clamping rail 2 even if the clamping screw 13c has not been fully tightened. The essential advantage is that the work piece holder 6 can be released after rough positioning relative to the guide rail 2 without the risk of slipping out of the groove 10.

Figure 5 shows a cross-sectional view of the clamp C-C of figure 2 according to the invention. In this case, since the top surface of the clamping portion 34 of the work piece holder 7 is flat and extends parallel to the bottom surface 36 of the work piece holder 7, the work piece holder 7 having a clamping frame shape is pressed vertically only against the surface 8 of the slab member 1c by the clamping screw 13 e. When clamping is approached, the workpiece holder 7 is pressed by hand against the clamping rail 4. Once the work piece holder 7 is clamped, its flat bottom surface 36 is located at the same level as the surface 8 of the slab member 1c of the work table 1. In this example, furthermore, one of the horizontally extending threaded holes 41 adapted to receive a clamping screw (not shown) for clampingly connecting a workpiece to the workpiece holder 7 is visible.

Fig. 6 shows a perspective view of the work piece holder 6 clamped on the clamping rail 3 and the work piece 47 attached to the work piece holder 6. In order to position the workpiece holder 6 correctly relative to the clamping rail 3, a stop member (not shown in fig. 6) can be provided. By means of two clamping members 48, 49, a workpiece 47, for example of cuboid shape, is clamped on the angular workpiece holder 6. The work piece 47 is positioned relative to the two side walls of the work piece holder 6 and the raised portions 24, 25, so that there is a defined X, Y, Z position. The work 47 clamped on the angular work holder 6 can freely reach a wide range so that it is easy to machine by a machine tool such as a wire etching machine.

The clamp according to the invention is of modular design: on the one hand, one or several clamping rails can be used, and on the other hand differently designed workpiece holders can be assigned to clamp different types of workpieces. Due to the differently designed workpiece holders, it is possible in practice to clamp each arbitrary workpiece accurately and quickly with one or several clamping rails. Without the work piece holder described above, it is possible within the scope of the invention to provide other work piece holders having a design differing from the work piece holder illustrated and described above. For example, a work piece holder in the form of a so-called tilting head or floating tool holder may be used.

An additional advantage can be found in the fact that the clamp is not sensitive to contamination and that it is so rigid that large, relatively heavy workpieces can be clamped with the clamp of the invention. The clamp of the invention shows further advantages, in particular for use with large and heavy workpieces, by virtue of the workpiece holders 5, 6, 7 having their clamping portions 15, 26, 27, 34 matched to the recesses 10 of the assigned clamping rails 2, 3, 4. In practice, a large workpiece and its attached workpiece holder may initially be brought into an approximated position and then released manually by an operator with both hands. Subsequently, it is gripped by the gripping portions 15, 26, 27, 34 of each work piece holder 5, 6, 7 inserted into the grooves 10 of the gripping rails 2, 3, 4, even if the work piece holders 5, 6, 7 are slightly inclined downwards. Finally, the work piece holders 5, 6, 7 can be clamped on the assigned clamping rail by tightening the special clamping screws. A similar situation can be observed during release of the workpiece once it has been machined. The significant advantage of the invention compared to the known clamping devices is that, in the known clamping device, the workpiece holder has to be supported by hand, while simultaneously tightening and releasing the clamping elements, respectively, with the other hand.

Claims (14)

1. A clamp for positioning a workpiece to be machined on a machine tool table, comprising at least one clamping rail member adapted to be attached to said table of said machine tool, and at least one work piece holder adapted to be clamped in a precise position to said clamping rail member, wherein each of said at least one clamping rail members has an elongated raised portion, an elongated recess is defined between a bottom surface of the elongated raised portion and a surface of the table and includes a clamping element extending into the elongated recess, and each of said at least one work piece holder comprises at least one raised clamping portion adapted to be inserted into said elongated recess and clamped in place by a clamping element, and the clamping element is configured to press against the correspondingly raised clamping portion of the at least one workpiece holder towards the work table.

2. A clamp as claimed in claim 1, wherein at least one clamp rail member has a flat base surface adapted to be supported on the table of the machine tool and to define a Z-direction reference, the elongate raised portion of the clamp rail member including a front end surface extending perpendicular to the flat base surface.

3. The clamp of claim 2, wherein said at least one work piece holder has a reference surface on a side of said holder where said clamping portion is located, said reference surface adapted to rest against a front face of said at least one clamping rail member.

4. The clamp of claim 3, wherein said clamping portion of said at least one work piece holder has an inclined clamping surface at a top surface of said clamping portion, said clamping element provided on said elongated raised portion of said at least one clamping rail member engaging said inclined clamping surface such that when said work piece holder is clamped in said clamping rail member, said work piece holder is urged toward said clamping rail member to rest with its reference surface against a front end surface of the clamping rail member.

5. A clamp as claimed in claim 1, wherein said at least one clamp rail member has a flat bottom surface adapted to bear on said table of said machine tool.

6. The fixture of claim 5, wherein said at least one work piece holder includes a downwardly extending shoulder located on a side of said work piece holder remote from said clamping portion, a distal portion of said shoulder having a surface extending in the same plane as a planar bottom surface of said work piece holder.

7. The jig of claim 1 wherein the work piece holder is configured as an angular element having two legs, and including two raised portions offset from each other by 90 °, the top surfaces of the legs forming bearing surfaces for attaching a work piece to the work piece holder.

8. The clamp of claim 7, wherein said workpiece holder configured as an angular element comprises first and second clamping portions offset 90 ° from each other.

9. The clamp of claim 8, wherein said workpiece holder configured as an angular element comprises an additional clamping section between said first and second clamping sections offset from each other by 90 °, said additional clamping section extending in a direction enclosing an angle of 45 ° with the extension of both said first and second clamping sections.

10. The clamp of claim 8, wherein at least one of said two legs of said work piece holder is provided with a vertically continuous groove at an inner edge, said vertically continuous groove subdividing said clamping section into a plurality of separate sections.

11. The clamp of claim 1, wherein the work piece holder is configured as a clamping frame member having at least one opening adapted to receive a work piece, wherein at least one side of the frame of the work piece holder has a horizontal continuous threaded bore adapted to receive a clamping screw for clamping the work piece to the clamping frame member.

12. The fixture of claim 11, wherein at least one side of the frame of the work piece holder has a vertically continuous bore located at an inner side of the frame facing the opening and adapted to receive the retaining pin member.

13. The fixture of claim 11, wherein the workpiece holder has a continuous flat bottom surface.

14. The fixture of claim 1, comprising at least two clamping rail members and at least two differently configured work piece holders.