HK1034485B - An apparatus for clamping a work piece - Google Patents

Description

Device for clamping workpiece

Technical Field

The present invention relates to a device for clamping a workpiece in a precise position in the working area of a machine tool, comprising a chuck member adapted to be secured in the working area of the machine tool, a workpiece support adapted to be secured to and clamped on the chuck member, and a clamping mechanism for clamping the workpiece support to the chuck member.

Background

Such devices known from the prior art are used primarily for clamping workpieces to be machined with high precision in the working area of machine tools. It is particularly important that the repetition accuracy is also maintained. In other words, the workpiece received on the workpiece holder must be clamped on the chuck members of the workpiece holder several times in succession, whereby, in such a case, for example, the workpiece holder carrying the workpiece to be machined must be clamped on different machine tools which carry out different machining operations in succession and which are each equipped with the same chuck member, or the workpiece holder is clamped on a measuring and detection station which is equipped with the same chuck member, the workpiece should always have an exact positioning in the X direction, the Y direction and in the angular direction around the Z direction.

Such a device is disclosed, for example, in european patent nr.0,255,042. The apparatus includes two pairs of positioning belts that are elevated above the surface of the chuck member and have contact surfaces for orienting the workpiece support in the X and Y directions. In addition, four pins are provided which are higher than the surface of the chuck member. The pins are used to define the Z-position of the work support. The cooperating workpiece supports include a flat surface adapted to bear against the pins provided on the chuck member. In addition, the workpiece support surface has two pairs of slots positioned in correspondence with one of said positioning strips. The groove has a flexible lip which tends to rest against the contact surface of the chuck member band. Finally, the work piece carrier has a central bore which receives a draw bolt member by means of which the clamping force required to maintain a defined position between the work piece carrier and the chuck member is transmitted. Thus, the chuck member includes a centrally located ball lock mechanism that cooperates with the draw bolt member.

It can be seen as a disadvantage of the known device that it is relatively unstable, especially when large and heavy workpieces are to be machined. Therefore, it cannot overcome a high tilting phenomenon or a torsion force, which is basically generated in the case of a large cutting work or a work to be worked. Because of the limited space available, it is in many cases undesirable to increase the size of the device to increase stability.

Disclosure of Invention

It is therefore an object of the present invention to provide a device for clamping a workpiece in a precise position in the working area of a machine tool, wherein a workpiece holder is clamped to a chuck member, whereby the workpiece to be machined has an increased resistance to tilting phenomena and to torsion forces, while avoiding the risk of displacement of the workpiece holder and the workpiece relative to the chuck member, all in connection with maintaining the required small dimensions and a high degree of precision, positioning the workpiece holder relative to the chuck member, in particular in the case of repeated clamping, as explained above.

To achieve these and other objects, the present invention provides a device for clamping a workpiece in a precise position in the working area of a machine tool, comprising a chuck member adapted to be fixed to the working area of the machine tool, a workpiece support adapted to be fixed to and clamped on said chuck member, clamping means for clamping said workpiece support to said chuck member and adapted to be transferred from a release condition to a clamping condition and vice versa.

The chuck member includes a first positioning member and the work support includes a second positioning member. The first and second positioning members are adapted to cooperate with each other to define the position of the work piece carrier relative to the chuck member along three coordinate axes extending perpendicular to each other, namely, an X-axis, a Y-axis and a Z-axis, and with respect to an angular direction about the Z-axis.

A clamping mechanism secures said work piece carrier to the chuck member once said work piece carrier is transitioned to said clamped state to maintain the defined position.

The first locating member is formed by a tapered concentric pin and the second locating member is formed by a double step slotted recess. The double step groove has two shoulder portions, the edges of which protrude into the interior of the double step groove. The edges are at a distance from each other that is slightly less than the width of the tapered concentric pin, measured between those locations where the workpiece holder contacts the edges when clamped to the chuck member.

In order to further increase the resistance to accidental position changes caused by tilting and twisting phenomena under heavy loads, in a preferred embodiment concentric pins are provided which are evenly distributed along the top surface edge of the chuck workpiece, whereby at least circumferentially opposite sides of the concentric pins are tilted with respect to the device Z-axis. In addition, the first positioning member includes raised surface portions that are located on the top surface of the chuck member and extend to the edge thereof.

A further increased resistance against high torsional forces is obtained if the recess is machined with a shoulder portion, which is arranged in the upper part of the work piece holder, whereby the shoulder portion protrudes inside the hollow cylindrical work piece holder, the position of the recess corresponding to the position of the concentric pin provided on the chuck member.

Drawings

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

FIG. 1 shows a perspective view of a chuck member;

FIG. 2 shows a top view of the chuck member of FIG. 1;

FIG. 3 shows a perspective view of a workpiece holder component;

FIG. 4 shows a bottom view of the workpiece holder component of FIG. 3;

FIG. 5 shows a cross-sectional view of the workpiece support member of FIG. 4 taken along line V-V of FIG. 4;

FIG. 6 shows an enlarged partial schematic cross-sectional view of a concentric bore and a concentric pin.

FIG. 7 shows a cross-sectional view of the chuck member of FIG. 1 taken along line VII-VII of FIG. 2; and

FIG. 8 shows a cross-sectional view of the chuck member of FIG. 1 taken along line VIII-VIII of FIG. 2;

fig. 9 shows a cross-sectional view of the chuck member of fig. 1 taken along line IX-IX of fig. 2.

Detailed Description

As shown in the embodiments of the drawings, the means for clamping the workpiece in the correct position within the working area of the machine tool comprises the chuck member 1 shown in fig. 1, 2 and 7-9 and the workpiece support member 25 shown in fig. 3-5. The chuck work piece is adapted to be secured within the working area of a machine tool (not shown in the drawings) while the work piece support member 25 is adapted to receive and hold a work piece to be machined. It is emphasized that the term "workpiece" is to be understood in a general sense, in particular the workpiece may also be a tool to be machined, for example an electrode of an electroerosion machining apparatus.

As seen in particular in fig. 7-9, the chuck member 1 basically comprises three parts, namely a bottom or base member 2, an intermediate part 3 and a head part 4. In the embodiment shown in the figures, the base member 2 has the shape of a circular disc with a central hole 5, the function of which will be further explained below. The intermediate part 3 is provided with a central hole 6 having the same diameter as the hole 5 and being in the shape of a cylindrical or sleeve-shaped member. The middle part is connected to the bottom member 2 by screws 7. Finally, the head 4 also has a central hole 8 and is also of the same diameter as the central holes 5 and 6. The head has a generally cylindrical or hat shape with an inner diameter greater than the outer diameter of the intermediate section 3. On the one hand, the head is connected to the base member 2 by a screw 9; on the other hand, the head is connected to the intermediate part 3 by a screw 10. Finally, the head 4 is provided with an outer circumferential shoulder 20. A sealing member 21 is inserted into the top surface of the shoulder 20.

By means of the above-described design, a chuck housing can be realized which is extremely inflexible and flexurally rigid and which, in addition, can be easily disassembled, for example for maintenance.

The top face 24 of the head 4 has four projecting concentric pins 22, which are substantially prismatic and uniformly distributed along the edge zone of the top face 24 of the head 4. Two of the opposed concentric pins 22 define an extension of the X-axis, while the remaining two of the opposed concentric pins 22 define an extension of the Y-axis that extends perpendicular to the X-axis. The intersection of the X and Y axes defines a Z axis (FIGS. 7-9) extending perpendicular to the X and Y axes. At least two opposing sides of the concentric pin 22 are slightly angled with respect to the Z-axis, as further explained below.

In addition, the top surface 24 of the head 4 has four flat portions 23, each of which extends radially between two adjacent concentric pins 22 in this embodiment. The flat portion 23 is slightly higher than the top surface 24 of the head 4. These flat portions 23 serve as Z-references, as further described below.

Fig. 3-5 show the design of the workpiece holder member 25. As seen in fig. 3 and 5, the one-piece workpiece support 25 includes a circumferential portion 26 having a generally cylindrical or barrel shape and an annular top portion 27. The inner diameter of the circumferential portion generally corresponds to the outer diameter of the head portion 4 of the chuck member 1, although there is a gap so that the workpiece holder 25 can be placed on the chuck member 1.

The inner wall of the circumferential portion 26 of the work holder 25 has a ring groove 28, and the two side walls of the ring groove 28 are tapered away from each other as viewed in a direction toward the inside of the circumferential portion 26. In other words, the ring groove 28 has a generally V-shaped cross-section. The purpose and function of the ring groove 28 will be further explained below.

The top 27 of the work support 25 has an annular shoulder 29 which projects inwardly of the circumferential portion 26. The average diameter of this shoulder 29 thus corresponds substantially to the diameter of a circle along which the four concentric pins 22 provided on the head 4 of the chuck member 1 are located. The front faces of these shoulders 29 project inside the circumferential portion 26 of the workpiece holder 25, they are smooth flat base faces and serve as Z-reference for the workpiece holder 25. Which is adapted to cooperate with a flat portion 23 provided on an upper surface 24 provided on the head portion 4 of the chuck member 1 as described above. In addition, the front face has four recesses 30 which are evenly distributed along the circumference of the front face. The exact design of these grooves is further explained below. The four recesses 30 are adapted to cooperate with the four concentric pins 22 provided on the top surface 24 of the head portion 4 of the chuck member 1 as described above.

Although four concentric pins 22 and four grooves 30 are illustrated and shown as interfitting in the present embodiment, it will be appreciated that three, six, eight or a greater number may be provided which is a mathematical subset of the concentric pins 22 and grooves 30 hass (Hirth) engagement to ensure positioning of the component holder 25 relative to the chuck component 1 in the X and Y directions and with respect to the angular direction.

FIG. 6 shows an enlargement of concentric groove 30 and concentric pin 22, a schematic partial cross-sectional view. The recess 30 is designed as a double step groove comprising two shoulders 31a and 31 b. As noted above, the concentric pin 22 is slightly tapered because at least two circumferentially opposite sides of the concentric pin 22 are slightly inclined relative to the Z-axis. In practice, the angle of inclination may be in the range 3 to 9. The edges 32a and 32b of the shoulders 31a and 31b protruding inside the recess 30 are a reliable basis for defining the position of the workpiece holder 25 relative to the chuck member 1 in the X-direction and the Y-direction as well as with respect to the angular direction. The distance between the edges 32a and 32b is therefore slightly smaller than the width of the conical concentric pin cooperating with the groove 30, which width is measured between the contact points or lines of contact of the two opposite sides of the pin 22 when the workpiece holder 25 is clamped firmly on the chuck member 1.

The mutual dimensions of the workpiece holder 25 and the chuck member 1 are chosen such that the following results are obtained:

if the work piece holder 25 is loosely seated on the chuck member 1, the concentric pins 22 are fitted into the corresponding concentric grooves 30, whereby the side faces 22a of the concentric pins 22 are in linear contact with the corresponding edges 32a and 32b of the shoulders 31a and 31b, respectively. In this condition, the flat basal end surface of the shoulder portion 29 of the work support 25, which serves as the Z-reference of the chuck member 1, has not yet abutted against the flat surface portion 23 provided on the head portion 4 of the chuck member 1, and the flat surface portion 23 is slightly higher than the head top surface and serves as the Z-reference of the chuck member 1. In this case, on the contrary, there is a gap of about 1/100 mm width between the end face of the shoulder 29 and the surface of the planar portion 23. On the other hand, it must be emphasized that the position of the workpiece holder 25 in the X-direction and the Y-direction and with respect to the angular direction with respect to the chuck member 1 is finally determined.

Once the workpiece holder 25 is loosely seated on the chuck member 1 and finally positioned with respect to the X-direction and the Y-direction and with respect to the angular direction, the clamping mechanism described below works in such a way that, in practice, the workpiece holder 25 is pulled towards the chuck member 1 with a force in the range of 2000 and 3000 newtons. Under the influence of this clamping force acting in the Z direction, the shoulders 31a and 31b are elastically deformed in the region of the edges 32a and 32b, respectively, in particular to such an extent that the end face of the shoulder 29 of the workpiece holder 25 abuts against the slightly raised flat portion 23 of the head 4 of the chuck member 1. The result is that the workpiece holder 25 is also accurately positioned in the Z-direction relative to the chuck member 1.

The clamping force required to clamp the workpiece holder 25 against the chuck member 1 is generated in this embodiment as follows:

due to the fact that the inner diameter of the head part 4 is larger than the outer diameter of the intermediate part 3, an annular cavity 11 is formed between the two parts 3 and 4. The annular chamber 11 is sealed by suitable seals shown in the figures (e.g. figures 7-9) but not shown in detail. In this way, an annular piston 12 is accommodated inside the annular chamber 11, which is movable along the central axis Z of the chuck member 1. The annular piston 12 is provided with a plurality of blind holes 13 evenly distributed circumferentially and adapted to receive tensioning or clamping springs 14, respectively. The spring 14 bears against the underside of the head 4 and biases the annular piston 12 to move downwardly. In addition, the annular piston 12 is provided with an outer circumferential groove 15. The lower side wall of the slot 15 slopes downwardly and outwardly. The grooves are adapted to partially receive a plurality of clamping ball members 18.

Below the annular piston 12, an empty annular chamber 16 is provided, which communicates with a connecting bore 17 provided in the bottom element 2. Through the connecting bore 17, pressurized air is introduced into the annular chamber 16, which acts on the annular piston 12 and moves it upwards against the pressure of the spring 14.

The head 4 is provided with a plurality of radially extending bores having a diameter substantially corresponding to the diameter of the clamping ball members 18 and for receiving these clamping ball members 18. The height of these holes and the height of the above-mentioned peripheral groove 15 are in such a relation that the clamping ball members 18 of the insertion holes can enter the peripheral groove 15 when the annular piston 12 is moved to its uppermost position against the pressure of the spring 14 by the pressure air in the annular chamber 16. Thereby, the clamping ball 18 can enter the peripheral groove 15 to such an extent that the clamping ball 18 is no longer higher than the outer circumference of the head 4. Finally, the head 4 is provided with an outer circumferential shoulder 20. A sealing member 21 is inserted into the top surface of the shoulder 20.

The axial position of the annular groove 28, i.e. the height in relation to the Z-axis, is defined such that the clamping ball 18, schematically shown in fig. 5, can enter the annular groove 28 when the component holder 25 is loosely seated on the chuck member 1. In this case, the clamping ball 18 is slightly offset axially downwards relative to the axially extending symmetry plane S-S of the ring groove 28. In other words, the above-mentioned plane of symmetry S-S of the annular groove 28 is positioned slightly above the centre of the clamping ball 18 inserted into the hole of the intermediate portion 3 of the chuck member 1 when the work piece holder 25 is loosely seated on the chuck member 1. The top 27 of the work support 25 has an annular shoulder 29 which projects inwardly of the circumferential portion 26. The average diameter of this shoulder 29 thus corresponds substantially to the diameter of a circle along which the four concentric pins 22 provided on the head 4 of the chuck member 1 are located. The front faces of the shoulders 29 project inside the circumferential portion 26 of the workpiece holder 25, they are smooth flat base faces and serve as Z-reference for the workpiece holder 25. Which is adapted to cooperate with a flat portion 23 provided on an upper surface 24 provided on the head portion 4 of the chuck member 1 as described above. In addition, the front face has four recesses 30 which are evenly distributed along the circumference of the front face. The exact design of these grooves is further explained below. The four recesses 30 are adapted to cooperate with the four concentric pins 22 provided on the top surface 24 of the head portion 4 of the chuck member 1 as described above.

The axial position of the annular groove 28 on the work piece carrier 25 is positioned in such a way that the clamping balls 18 of the chuck member 1 can enter the groove 28 when the work piece carrier 25 is loosely seated on the chuck member; thereby, the plane of symmetry S-S of the ring groove 28 is located slightly above the centre of the clamping ball 18, while the clamping ball 18 is inserted into a radially extending hole of the intermediate portion 3 of the chuck member 1. On the other hand, in order for the workpiece holder 25 to be loosely seated on the chuck member 1, the clamping balls 18 of the chuck member 1 must be in their retracted position. This can be achieved by supplying air under pressure into the annular chamber 16 below the annular piston 12 (see figures 7-9), as a result of which the annular piston 12 is forced upwards against the pressure of the spring 14. Therefore, the outer circumferential groove 15 provided on the annular piston 12 is moved to a position aligned with the clamping ball 18, and the outer circumferential groove 15 is not higher than the surface of the intermediate portion 3 of the chuck member 1.

After the workpiece holder 25 has been loosely seated on the chuck member 1 and positioned with respect to the X-direction and the Y-direction and with respect to the angular direction, the overpressure in the annular chamber 16 is removed, as a result of which the annular piston 12 is moved downwards under the influence of the force exerted by the spring 14. The clamping ball 18 is thus pressed into the annular groove 28 of the workpiece holder 25. Due to the above-mentioned slightly asymmetrical rest position between the clamping ball 18 and the ring groove 28 and the V-shaped design of the ring groove 28 (as seen in cross-section), the work piece carrier 25 is pulled against the chuck member 1 in such a way that the end face of the shoulder 29 abuts against the slightly raised flat portion 23 of the head 4 of the chuck member 1. The result is that the workpiece holder 25 is also accurately positioned in the Z direction relative to the chuck member 1 and the clamping operation is completed.

From these explanations, it is clear that, in particular in the present embodiment, at twelve positions evenly distributed along the circumference of the intermediate portion 3 of the chuck member 1, clamping forces acting parallel to the Z direction are transmitted by the clamping balls 18 to the workpiece holder 25, thereby clamping the latter to the chuck member 1. In other words, the entire clamping force acting on the workpiece holder 25 is composed of twelve individual clamping force components, each of which is transmitted by twelve clamping balls 18. Therefore, the line of action of these clamping force components lies on the cylindrical surface MF (see fig. 2-5 and 7-9); depending on the chosen dimensions of the chuck member 1 and the workpiece holder 25 and the location of the end faces of the concentric pin 22, the groove 30 and the shoulder 29, the cylindrical surface extends through, i.e. intersects, or extends against, the members 22, 30 and 29, preferably slightly outwardly. It is thus ensured that the clamping forces act exactly at these really required positions, as a result of which the bending stresses present in the prior art workpiece supports are greatly reduced or completely avoided. In addition, compared with the prior art work support using the center clamping device, the inclination phenomenon generated during the work processing is well endured.

It will be appreciated that the annular piston 12 may also be hydraulically operated to replace pressurized air.

The final shaping of the recess 30 of the workpiece holder 25 is accomplished by plastic deformation, for example by stamping. Therefore, a very high accuracy can be obtained even in batch production. The concentric pin 22 with slightly inclined sides in cooperation with the groove 30 ensures that very high torques are transmitted.

The stability and rigidity of the chuck member/workpiece support system in the clamped state also contributes to the workpiece support, including its concentric members in the X, Y, Z and angular directions, being a one-piece construction. Due to the generally cylindrical or hat-shaped shape of the workpiece holder 25, the basic parts and components of the chuck member 1 are closed during operation of the system, and therefore the concentric members 22, 23 and 30 are well protected against contamination. Such protection may be improved by providing a seal 21, the seal 21 being located at the top side of the shoulder 20, against which the lower surface of the circumferential portion 26 of the work support 25 rests.

Central holes 5, 6 and 8 are provided in the base member 2, the intermediate part 3 and the head part 4, respectively, which are associated with the generally annular design of the workpiece holder 25 and which also enable clamping and machining of elongated workpieces. For example, the bore may receive therein a turbine blade of a turbine rotor for machining a so-called "fir tree" of the turbine blade.

If this device does not function with the central aperture of the clamping system of the present invention as described above, an additional central clamping mechanism may be provided to further increase the clamping force applied to the workpiece support, or an additional independent clamping system known in the art, for example to clamp smaller workpieces.

Claims (14)

1. Apparatus for clamping a workpiece in a precise position in the working area of a machine tool, comprising a chuck means adapted to be secured to the working area of the machine tool, a workpiece support means adapted to be secured to and clamped on said chuck means, clamping means for clamping said workpiece support means to said chuck means and adapted to be transferred from a release condition to a clamping condition and vice versa, said chuck means comprising first locating means, said workpiece support means comprising second locating means, said first and second locating means being adapted to cooperate with each other to define the position of said workpiece support means relative to said chuck means along three coordinate axes extending perpendicular to each other and with respect to an angular direction, and said clamping means securing said workpiece support means to said chuck means once said workpiece support means is transferred to said clamping condition to maintain said defined position, characterized in that said first positioning means comprise conical concentric pin means, said second positioning means comprise groove means in the form of a double stepped groove means having two shoulders, the edges of said shoulders protruding inside said double stepped groove means at a distance from each other slightly smaller than the width of said conical concentric pin means, said width being measured between those positions where said edges are in contact when said workpiece holder means is clamped to said chuck means.

2. The apparatus of claim 1 wherein said concentric pin means are uniformly distributed along the periphery of the top surface of said chuck means so that at least circumferentially opposite sides of said concentric pin means are inclined with respect to the Z axis of the apparatus.

3. The apparatus of claim 2 wherein said concentric pin means is inclined at a side angle in the range of 3 ° to 9 °.

4. The apparatus of claim 1 wherein said first positioning means further comprises a raised surface portion located on the top surface of said chuck means and extending to the edge thereof.

5. The apparatus of claim 1 wherein said chuck means is generally cylindrical and said workpiece support means is generally hollow cylindrical covered at one end by a generally annular plate member, whereby said workpiece support means encloses said chuck means when the apparatus is in the clamped condition.

6. The apparatus of claim 1 wherein said groove means is formed as a shoulder portion disposed at an upper portion of said workpiece holder means, said shoulder portion projecting from said hollow cylindrical workpiece holder means, whereby the position of said groove corresponds to the position of concentric pin means disposed on said chuck means.

7. The apparatus of claim 1 wherein said second positioning means further comprises a machined flat surface portion of a shoulder portion provided on said workpiece support means, said flat surface portion being adapted to rest against said raised surface portion provided on the top surface of said chuck means.

8. The apparatus of claim 1 wherein said chuck means and said workpiece support means have central apertures for receiving elongated workpieces.

9. The apparatus of claim 1 wherein said clamping means comprises circumferentially acting clamping means having a plurality of clamping balls uniformly distributed about the circumference of said chuck means, said workpiece support means including an annular groove in the inner cylindrical surface thereof, said clamping balls being adapted to engage said annular groove.

10. The apparatus of claim 9 wherein said chuck means includes an annular chamber, said clamping means includes annular piston means biased by spring means and axially movably mounted in said annular chamber, said clamping balls bearing against said annular piston means, whereby upon axial movement of said annular piston means, said annular piston means is adapted to press said clamping balls into annular grooves provided in said workpiece support means.

11. The apparatus of claim 9 wherein said clamping balls are received in radially extending bores disposed in said chuck means and evenly distributed along the circumference thereof.

12. The apparatus of claim 9 wherein said holding means comprises twelve gripping balls.

13. The apparatus of claim 9 wherein said ring groove provided in said workpiece support means is generally V-shaped in cross-section.

14. The apparatus of claim 9 wherein the axial position of said annular groove provided in said workpiece support means is defined such that when said tool support means is loosely seated on said chuck means, said clamping ball enters said annular groove provided in said workpiece support means whereby the plane of symmetry of said annular groove provided in said workpiece support means is located slightly above the center of the clamping ball inserted into the radially extending bore.