Prevention of Workpice Form Deviations in CNC Turning Based on Tolerance Specifications.

The simultaneous action of cutting forces and gradients of temperature due to different effects in turning, end result in deflections of the machine-workpiece-tool system and in a structural thermal drift. In turn, these factors lead to a deviation of the tool-point away from the theoretical path and consequently, to final dimensional and form errors on the workpiece manufactured. Traditionally, these non-desired deviations have been compensated by on-line corrections of the tool position, even although they were not strictly necessary according to the tolerance specifications on the workpiece drawings. These type of compensations require the use of machine-tools equipped with multiple sensors, already available in modern and precise machine-tools but not always in common ones, which are more reasonable from an economic point of view. On the other hand, on-line compensations modify the predicted working conditions and in turn, chatter or other undesirable effects can appear such as moving away from optimal cutting conditions. Taking this into account, a new approach is proposed in this work for prediction and compensation of deviations in turning by considering them at the planning stages prior to machining operations, mainly focused on development of CAPP systems for CNC turning. Tolerance specifications are considered as limiting values for the admissible workpiece deviations which are predicted by using a developed model based on the strain energy theory.