The invention relates to a clamping system for crankshafts and similar parts, on crankshaft working machines.
In clamping-up crankshafts and similar workpieces in machines for working them, especially when they have been forged or cast and have not yet been machined, the problem consists particularly in mounting them firmly in such a definite and reproducible manner that, in spite of the relatively small cross section of a crankshaft in comparison to its total length, no flexing or twisting of the crankshaft will occur in spite of the cutting forces and temperatures involved in the machining.
The manufacturing process most frequently employed at the present time is to work the crankshaft casting, before it is actually machined on a crankshaft cutting machine, at one or more cheek surfaces precisely defined with reference to the crankshaft axis of rotation, using a special machine for the purpose. In the subsequent process on the crankshaft cutting machine, the crankshaft is then clamped at the previously worked cheek surfaces by means of levers and faceplates, so that any inaccuracy of these surfaces with respect to the axis of rotation of the crankshaft results in a distortion of the crankshaft when it is clamped in the crankshaft working machine. This, together with the deformation of the crankshaft due to the cutting forces, expresses itself in an off-center position of the machined journal areas with reference to the crankshaft axis after it is unclamped. The disadvantage of this manner of proceeding consists mainly in the fact that the working of a crankshaft in this manner is very complicated and time-consuming, since on the one hand a special machine is needed for the production of the pre-cut clamping surfaces. Furthermore, it is found to be disadvantageous that, in the case of another necessary clamping-up for another series of operations, such as a finishing operation or clearance cutting operation, the crankshaft is put under tension because the crankshaft is deformed or distorted as a result of the preceding roughing operation, and thus the pre-cut clamping surfaces are no longer in the originally defined position with respect to the axis of rotation of the crankshaft. This error then has a negative effect accordingly on the subsequent machining accuracy. This necessitates greater machining allowances and hence increased cost in the next manufacturing operation, such as the grinding operation for example. Furthermore, the tension control that is essential in a clamping device of this kind, is not available.
The invention is therefore addressed to the task of creating a clamping device by which crankshafts which have not yet been machined on the journals and cheeks, can be clamped up in crankshaft processing machines in a defined position repeatably and without flexing the crankshaft, even in the case of slightly differing crankshaft forgings and varying clamping forces.