Investigation of the influence of the method of fixing the cut-off tool inserts on its stress state

Abstract

Cut-off tools equipped with carbide inserts are commonly used in turning operations. Due to the very heavy conditions in which such blades work, they fail, as a rule, not as a result of their operation, but due to the breakage of carbide inserts. This study investigates the causes of such failures and methods to prevent such phenomena. A thorough analysis of the current state and research methods of stress state in cutting tools, including turning cutters, was carried out. Methods of stress reduction in carbide inserts were also analysed. This paper focuses on the study of the stress state in cut-off tools with brazed carbide inserts. The stress state in the carbide inserts and the influence of different fixation methods of carbide insert to the holder were considered. The main approach to stress studies was the photoelasticity method, which allows quickly and clearly obtaining and evaluating the results. Models of carbide inserts were made of optically sensitive material. It as a part of a complex model of a cut-off tool with a carbide insert with three different methods of fixation were loaded with a force by means of a specially designed stand simulating the cutting force. The study was carried out on a PPU-7 polarisation-projection unit. Isochromatic and isocline patterns were obtained. The estimation of the principal stresses was performed by the difference of shearing stresses for three cross sections of the insert: at the surface, in the middle and at the base. It was found that the best result is given by the method in which the insert on the side far from the cutting edge has a bevel made at an angle of 10°