Abstract
The fatigue life of the die-casting dies depends on the heat checks, which are characterized by fine shallow cracks on the surface due to cyclic thermal stress. According to the recent study, laser-processing is effective to repair cracks and extend the life of dies. The purpose of this study is to develop a reliability evaluation method for laser repaired die to validate the effect of repair technique. The proposed method was applied for simple die model. First, the effect of laser-melting process on hot work tool steel (SKD6) has been evaluated by rotating bending fatigue test. As a result, the fatigue strength of the laser-processed specimen decreases remarkably in compared with that of base metal. However, it can be recovered by heat treatment at 773 K. This could be due to a high yield strength resulted in a secondary-hardening effect. At the same time, cyclic thermal stress applied to the die was evaluated by finite element methods and failure probabilities for required number of cycles were calculated. As a result, the failure probability for laser-processed die increased remarkably in compared with that of non-processed ones. However, it can recover 773 K tempered die.
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