Effect of Heat Treatment on the Structure, Wear and Corrosion of AISI L6 Tool Steel

This work is a contribution in analyzing structure, tribological behavior and corrosion of AISI L6 hardened tool steel. Structural characterization and tribological behavior of steel were investigated using Optical Microscopy (OM), Scanning electron microscopy (SEM), wear testing by friction on a pin-on-disc Tribometer and corrosion by potentiodynamic polarization. Comparing to the as-received steel, hardening has generated a fine martensitic microstructure causing a 1.5 times hardness increase. Hardening has contributed to improvement of wear resistance as the coefficient of friction has decreased from 0.86 to 0.67μ. An increase in corrosion resistance was observed after hardening treatment.

Experimental Study on The Effect of Cross Feed of Surface Grinding on the Vibration and the Surface Roughness of Hardened Tool Steel OCR12VM

The grinding process is a machining process to obtain qualified surface roughness levels and high dimensional accuracy. There are two types of processes in the grinding process, namely the roughening and finishing processes. The vibration effect of the roughing process can damage and shorten the life of the tool/machine, while in the finishing process, the effect of vibration will reduce the dimensional accuracy, shape, and surface smoothness of the workpiece. This study aims to determine the effect of crossfeed on the amplitude of vibration and surface roughness of the workpiece on the surface grinding process. The materials used are hardened tool steel OCR12VM with a variety of grinding stone types A46QV and A80LV made of aluminum oxide. The Variables of process parameters are crossfeed (mm / step) and depth of cut (mm). The measurement of vibrations uses an accelerometer, which is processed by the math CAD program in the form of amplitude and frequency. For surface roughness measurements, it is used the MT-301 surface test with 5 sample points and a sample length of 0.8 mm. The results show that the greater the cross-feed value, the bigger the amplitude of the vibration level and the surface roughness of the workpiece. The magnitude of the amplitude of the vibration on the acceleration that occurs in the grinding stone type A46QV starts from 6,7369 -18.7525 g.rms, while the grinding stone type A80LV starts from 5.0904 g.rms to 18.2821 g.rms. The surface roughness achieved in both grit 46 and grit 80 is from N3 to N5.

THE INFLUENCE OF CUTTING CONDITIONS ON THE SELECTED PARAMETERS OF THE SURFACE INTEGRITY

The article deals with an investigation of residual stress in machined surface under conditions of high-feed milling and determination of the influence of machining conditions on the size and types of stress resulting from cutting into the machined surface. As a testing material, the hardened tool steel W. Nr. 1.2343 (CSN 19552) was used. For the realization of the experimental activity, a high-feed milling head was used with exchangeable cutting inserts marked H600 WXCU 070515T. All surfaces were machined under different cutting conditions (200, 300, 350, 400 and 500mmin−1 cutting speed) in regard to the recommended parameters and machine tool options. The evaluated residual stress was measured in the depth of 8 μm under the surface with the device PROTO iXRD working on the principle of the X-Ray diffraction. Monitoring was carried out using an analysis of occurrence of tensile or compressive residual stress, and from these results, a possible dependence of the residual stress on the cutting conditions during milling process was determined.

Methodology for Reliable Tribological Investigations Applying a Micro Tribometer in Ball-on-Plate Configuration

Aim of this work is the development of a methodology for reliable tribological investigations when applying a micro tribometer. Experiments were conducted in ball-on-plate configuration with linear reciprocating motion. Two different sphere materials were applied: Al99.9 aluminum alloy and 1.4301 austenitic stainless steel. A textured surface from 1.2379 hardened tool steel machined by micro milling exhibiting an areal arithmetic mean height of Sa = 295 nm was used as counterpart. The experiments comprised of the investigation of the coefficient of friction and the evolution of the facet area on the spheres in contact with the textured surface depending on the normal load applied and the number of reciprocating cycles. For the early stage of the experiments an ongoing increase of the area of the facet on the spheres was found; occurring friction was manly governed by abrasion of the sphere’s material and three-body deformation. This was considered as unstable state of the tribological investigation process, not producing meaningful results. For the later stage equilibrium facet areas on the spheres were found and an ongoing conduction of the tribological experiments did not provoke any increase of their sizes. Here, occurring friction was mainly governed by adhesion. The final facet area on a sphere was directly dependent on the sphere’s materials and the applied normal loads. For all subsequent investigations applying a micro tribometer, only spheres exhibiting an equilibrium facet area should be used to gain robust results of tribological investigations, required for the development of e.g. dry deep drawing processes.