WO2000045982A1 - Compensating clamping device - Google Patents

Abstract

The clamping device having a clamping chuck and clamping jaws is designed for clamping a workpiece with an almost rotational symmetry but having irregularities in shape or differences in relation to an exact symmetry in a machine tool and for compensating for the resulting unbalance. The clamping jaws (1) are fitted with sliding compensation elements (4). The outer ends of the surfaces of the compensation elements facing the workpiece (34) are supported on the workpiece in radial direction and their free ends are supported on free moving retainer ring (3).

Description

Compensating jig

The invention relates to a clamping device with a chuck, which is provided with clamping jaws, for clamping an approximately rotationally symmetrical workpiece, however, which is subject to shape inaccuracies or deviations from the exact symmetry in a processing machine. This enables a precisely defined, aligned clamping between centers for parts that have inaccurate shapes or are asymmetrical.

Such inaccuracies in shape can arise, for example, during thermal treatment (delay in hardness), with cast or forged parts (process-related tolerances) or with deliberately asymmetrical parts.

If rotationally symmetrical, shaft-like parts, which have geometric inaccuracies due to a previous machining or treatment, have to be machined on the inside and outside of a turning, milling or grinding machine, methods are already available: For example, an additional machining operation can provide a precise basis be created. But this means an additional effort.

Alternatively, special chucks with two, three or more jaws with an integrated compensation mechanism can be used. However, this compensation mechanism has a large mass and a large internal friction. When unsymmetrical parts are clamped, the entire compensation mechanism is moved out of the axis of rotation, resulting in a large imbalance, which grows square with increasing speed. These compensating chucks are therefore only suitable for use at low speeds. Due to the internal friction, the compensation is only possible with a certain inaccuracy of approx. 0.1 mm. The invention has for its object to provide a clamping device in which the disadvantages of the prior art are avoided.

This is achieved according to the invention by means of a clamping device in which the clamping jaws are provided with slidingly mounted compensating pieces, the surfaces of which face the workpiece rest on the workpiece with the outer end in the radial direction and with the inner end on a freely movable compensating ring.

Exemplary embodiments of the invention are described below with reference to the accompanying drawings. Show it:

Figure 1 is a sectional view of a clamping device with a fixed centering.

Figure 2 is a sectional view of a clamping device with sprung centering.

3 shows a sectional illustration of a clamping device with opened clamping jaws;

Fig. 4 is a sectional view of the clamping device according to FIG. 1 with a warped workpiece and

5 shows a sectional view of the tensioning device according to FIG. 1 without counter-centering.

The clamping devices shown in the figures have an essentially commercially available chuck 8 with exchangeable clamping jaws 1. A centering device 11 built in the chuck in the form of a centering tip is used in connection with a counter-centering device 21, which is normally installed in an existing machine part or is used, the precise alignment of the workpiece 34 to be clamped between the centers 31 and 32nd

The clamping jaws are provided on their inner side with circular grooves 46 which are trapped in a T-shape and in which circular segment-shaped compensating pieces 4 are slidably mounted such that they can perform an oscillating movement.

A compensating ring 3 is arranged between the clamping jaws 1 and the chuck 8 and can move freely in a region limited by corresponding recesses in the clamping jaws relative to the axis of the clamping device. The compensating pieces 4 rest with their inner ends on the compensating ring 3.

The compensating pieces 4, which are movable in the interchangeable jaws 1, i.e. are mounted in an oscillating manner, for compensating clamping of the workpiece on the asymmetrical part 33 of the workpiece 34. In the clamped state, the front ends 44 of the compensating pieces 4 lie on the asymmetrical part 33 of the workpiece 34 in an adapted position, while the opposite sides 45 of the compensating pieces 4 rest on the freely oscillating compensation ring 3, the compensation ring 3 being displaced by the compensation pieces 4 in the opposite direction of the asymmetrical part 33 of the workpiece 34 and thus counteracting the existing imbalance of the workpiece 34.

The centering device 11 can, as shown in FIG. 1, be built into the chuck 8 in a fixed manner or spring-loaded in accordance with FIG. 2.

During the clamping process, the jaws 1 move radially and synchronously inwards. The clamping stroke can be 1 mm to 10 mm depending on the type and make of the chuck. As soon as a compensating piece 4 touches the asymmetrical part 33 of the workpiece 34, this swings in the direction of the compensating ring 3 until all the compensating pieces 4 with the front end 44 and the opposite side 45 rest on the asymmetrical part 33 of the workpiece 34, or on the oscillating compensating ring 3. In this process, the compensating pieces can be moved easily (oscillating), since no pressure has yet built up in the contact surfaces (bearing) 46 to the clamping jaws 1.

After the tensioning process, as shown in FIG. 5, the counter-centering device 21 can be removed. The workpiece is now held in the aligned position by the centering device 11 and the compensating pieces 4. The now built-up clamping pressure of the jaws 1 prevents the same due to the large friction in the contact surfaces 46 to the compensating pieces 4. The free part of the workpiece can now be machined both inside and outside.

The advantage of the invention is that commercially available, inexpensive chucks can be used. Due to the low friction of the compensating pieces during the clamping process, the work pieces can be clamped very precisely in their position between the centering devices 11, 21. Due to the low mass of the compensating pieces and the compensation of the unbalance of the workpiece by the compensating ring, high speeds are possible, which allows a rational processing of the workpieces. A slight imbalance is gentle on the storage of the machine; the result is lower maintenance costs and a longer service life.

Claims

claims 1. Clamping device with a chuck, which is provided with clamping jaws, for clamping an approximately rotationally symmetrical, but with shape inaccuracies or Deviations from the exact symmetry Workpiece in a processing machine, characterized in that the clamping jaws (1) with sliding bearings to compensate for an existing imbalance Compensating pieces (4) are provided, the workpiece (34) facing surfaces with the outer end in radial Place the direction on the workpiece and with the inner end on a freely moving compensating ring (3). 2. Clamping device according to claim 1, characterized in that the compensating pieces (4) in the form of a segment of a circle and are slidably mounted in circular grooves (46) in such a way that they can carry out an oscillating movement.