Statistical Control of the Technological Process Stability to Manufacturing Cylindrical Parts into High Series

Abstract

This paper presents a calculation algorithm for verifying on-line of the manufacturing process stability in large and mass series of some cylindrical parts from axes type. Through experimental investigations, we conducted a statistical control on a sample parts batch to determine the machining accuracy of some checking turret lathes. In the first phase, we performed a statistical analysis of the technological process preceding the manufacture of cylindrical parts in large and mass series. For checking the normality assumption of the deviations for parts machined, we established the main statistical parameters as being arithmetic mean and standard deviation. With these parameters, I could calculate the fraction of probable defective parts. In the second phase, we determined the control limits for the arithmetic mean and standard deviation. With these parameters I could pursue in chronological order the actual achievement of the workpiece size. In this way, I could check the technological process stability on-line for well-defined period's time, between two successive adjustments of the machine-tools. Introduction. Following the actual technological manufacturing process of the cylindrical parts from the axes type, these will have deviations from the dimensional accuracy and geometric shape [2 and 7]. The main factors contributing to the processing deviations emergence are [1, 6, 8 and 9]: the geometrical inaccuracy of machine-tools; the imprecision of the measuring instruments used; the fastener imprecision of workpiece and of the cutting tools; the wear of cutting tools; the variation and modification during the cutting process the thermal parameters for machine tools, fastener devices, workpiece and cutting tools; the elastic deformation of the technological system; the unevenness of cutting depth; the variation of internal stresses into the processing material.