Casting Design Optimization Using Numerical Simulation of Precision Forging Die for Large Titanium Alloy Integral Bulkhead

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In this paper, the competing requirements of material strength, casting formation and residual stress are considered in the design of a large bulkhead integral isothermal forging die using a design approach that incorporates an outer ring plus a die body. Thermal stress assembly was conducted to resolve the various manufacturing issues encountered in the production of this large-scale casting. This paper also proposes a design method for an expansion joint and material-saving holes to homogenize the cross-sectional thickness of the casting die by solving problems associated with defects and hot cracking during the casting process. The finite element method was used based on the equivalent liquid level descending method, the Niyama criterion, etc., to analyze the pouring of the sand model with different risers to choose the casting process. To resolve the occurrence of hot cracks during production, the design was optimized and the process was improved in combining with the simulation analysis result, after which carrying out another finite element analysis and by re-verifying the production process again. The results show that the simulated porosity, shrinkage and stress distribution are in accord with the practical production status. Based on the mechanical properties and a microstructure analysis, the tension strength of the K3 casting die at 950 °C is approximately 635 MPa, and the microstructures are typical dendrites. However, through the simulation, practical production, and analysis of the mechanical properties and microstructure, the die design method proposed in this paper offers benefits in solving casting forming problems and hot cracking of an integral oversized titanium bulkhead casting die, and a K3 superalloy die with a weight of 7.8 tons was successfully cast.