Fatigue life assessment of thermal cracked dies and moulds for remanufacturing

The conventional life cycle of dies and moulds is not eco-efficient, which shows great potential for the application of remanufacturing. It is of great importance to establish life evaluation technology for remanufacturers to predict the remaining service life of dies and moulds. The main contribution of this thesis is the development of key technologies for life evaluation of dies and moulds after remanufacturing through a thorough review of remanufacture related activities within the die and mould industry. It is proposed that evaluation of remaining service life of dies and moulds after remanufacturing is carried out using finite element modelling. It involves determination of residual stresses induced by repair welding, working conditions for the future operation and life model of die material. Specifically, the thesis is firstly focused on the design of representative die geometry. The geometry is optimized based on the effect of thermal loading and the effect of residual stress due to laser welding. Secondly, fatigue life model was established by conducting thermal fatigue tests and finite element modelling as well. Induction heating based test method was adopted for its capacity of achieving similar thermal shock effects. An energy based life model was derived by taking into account test period. The laser weld characteristics were studied using a sequential experimental design combining orthogonal method and uniform design. Radial Basis Function neutral networks were used to obtain regression models of weld performances for enabling process optimization. Heat source models were also calibrated by achieving sufficient agreement between numerical and experimental weld profiles. Lastly, the effect of residual stress on the fatigue life model was identified and the life model was updated. With close agreement between corresponding coefficients from two curve fittings, the corrected model is proved to be reliable for evaluating remaining useful life of remanufactured dies/moulds