Elastic-hereditary errors of fixation of non-rigid box blanks

Abstract

The literature review has shown that so far no studies have been carried out on the elastic deformations of open box blanks during installation and fixation in machine tools. In the analysis of the installation of non-rigid axisymmetric blanks, it is indicated that the existing shape error of the base surface elastically changes its shape during fastening, and the processed surface gets the correct shape, which, after removing the clamping force, is distorted, and the base surface is not restored to its original shape due to the removal of the allowance layer. Typical operations of preliminary shaping of an open box-shaped workpiece obtained from medium-alloy steel 30HGSA with increased strength are described. The workpiece has errors in the relative position of the elements up to ± 0.3 mm. In production conditions the elastic-hereditary errors of fixing non-rigid box blanks were determined when compensating for the initial position of the deformed wall of the blank, by monitoring with the built-in sensor of the machine. It has been determined that such compensation is insufficient. For theoretical justification of the new proposals, the calculation of the stress-strain state of the construction using finite element analysis was made, which showed the deviation values of the side walls of the blank. Errors that most affect the deviations of the side walls when processing blanks of reduced rigidity are noted. A method of fixing and processing of thin-walled body blanks is proposed, in which the base side of the blank is measured using an RMP40 sensor before clamping force and after it, followed by adding value difference compensations in the control program for processing on a CNC milling machine. A comparative analysis of the dimensional deviation under the action of clamping force and after release from the clamps was made. A trial batch of blanks was processed, confirming the results of theoretical studies.