Papers by Keyword: Nitrided

Abstract: The surface of worn dies are often machined to remove the worn layer and then to re-form its shape. But, in machining operations for hardened materials, the high cutting force sometimes yields bending deflection of low stiffness tools, and results the decrease in productivity and accuracy.In this study, surface treatment by pulsed laser is applied for the high hardness materials to improve the machinability in the machining operation. Die steels are used as work material machined with ball endmills of carbide in the experiments where the cutting force and the actual depth of cut are measured to obtain the specific cutting energy and to evaluate the machinability. In endmilling operations of the nitrided die steels, the actual depth of cut is decreased by the bending deflection of endmill. However, the surface treatment with laser moderates the decreasing of the actual depth of cut. It is confirmed that the surface of workpiece pre-treated with laser has larger roughness than un-treated ones, and the specific cutting energy is decreased by laser surface pre-treatment.

Abstract: Effects of surface defect size and the method used to obtain the defect itself on bending fatigue behaviour of nitrided and shot peened steel was studied. Two different series of 15 sandglass specimens with a microhole in the minimum section generated after nitriding and shot peening treatments were considered. In one series the microholes were obtained by controlled electro-erosion. In the other series microholes were obtained by indentation, much more invasive that electro-erosion, simulating a damage due to a mechanical impact or scratch on the surface material, common on real components during the life span. In both cases the microholes act as a pre-existent crack. The results show that defects obtained by indentation lead to a minor fatigue limit with respect of larger defects obtained by electro-erosion. This was interpreted as the modification of the residual stress field due to the mechanical indentation. On the basis of the results some consideration is formulated about generating micro-holes with one of the discussed ways.