| Summary: | 碩士 === 國立成功大學 === 機械工程學系 === 87 === Abstract
Traditional ways for measuring residual stresses are hole-drilling method accompanying with strain gages. The most usual way is High Speed Hole-Drilling Method and there is a standard (ASTM E837) for this method. But the method is suitable for soft metal only; it can’t deal with material with high hardness and high wear and of course, with hard surface coating. Therefore, this study focused on the possibility of measuring surface residual stresses of hard surface coating on tool steel with TiN coating by EDM Hole-Drilling Method.
This study investigated the effect of parameters of EDM with surface roughness, white layers and cracks through full factorial design. Furthermore, choosing the major parameters and evaluating their effect on measuring residual stresses by EDM Hole-Drilling Method.
The results of this study indicated that the surface roughness after EDM does not depend on material, but affected by the discharge current and pulse-on duration. The thickness of white layer affected strongly by pulse-on duration. The density of surface cracks increased by longer pulse-on duration and lower discharge current. After the investigation of EDM characteristics, the “cracks” was chose as major factors of EDM parameters to measure residual stresses.
Firstly, S45C was applied to evaluate the suitability of EDM parameters, then apply them on TiN coating on SKD61. The results of measuring residual stresses indicated that as the thickness of TiN increased, the value of residual stresses measured is increased also. Although the “parameters with cracks formed” induced larger stresses by itself, but because the influence cracks, the residual stresses measured is lower then “parameters with no cracks”.
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