STUDY FOR CONTROL OF DIMENSIONAL DISTORTION IN TEMPERED INDUSTRIAL PARTS

摘要

The presence of residual stress generated in the manufacturing process defines one of the biggest problems found in the mechanical metal industry. In the search of mechanical properties to a specific application, it is mandatory to impose the parts at very critical mechanical, chemical or thermal requests. The study analyzes all the steps that apply considerable stresses to the component during the manufacturing process and, therefore, discover which ones add more stresses to the yield limit of the material. It was also intended to contribute with relevant information regarding the surface integrity of the material, with bigger coverage in the residual stresses generated where, due to their nature and expressiveness, they can be beneficial or harmful to the component's useful life. Accordingly, the objective was to analyze the raw material of SAE 4140 steel through its microstructure and verification of its chemical and mechanical characterization. In order to reduce the occurrence of dimensional distortions in excess of tolerance, we sought to identify the most critical step and, therefore, act with viable possibilities and without relevant costs for the prevention of the problem encountered. In order to measure its stress and define the process in which the highest inclusion of residual tractive stresses is characterized, these being the deleterious ones for the process and for the product, we used the method of measuring residual stresses by ray diffraction in X. In your measurement, the stresses included on the surface of the specimens were measured at specific stages of the process. X-ray diffraction analysis analyzes the diffraction planes and their respective interplanar distances from a specific material, as well as the densities of atoms along the crystalline planes. Using mathematical models, it is possible to measure the residual stress existing in the investigated parts. In view of the analysis by X-ray diffraction, it was verified the existence of disordered variations and modifications of the crystalline phases on the material surface, at the end of the finish machining process. These crystalline phases which, together with a less aggressive fabrication, favor plastic deformation due to the presence of residual stresses which surpass those of the yield limit of the analyzed material. In this sense, it was possible to determine which the most critical operation related to the component request is the machining in which it is applied. Since the subsequent processes only aggravates this condition, resulting in an unusable component for the proposed application without adding a higher cost to the product, either through the use of some rework or scrap procedure.