Keywords: forging, trimming, finite element, tetrahedron, NURBS.

The accuracy and mechanical quality are vitally important for net-shape forging production. This is especially true for the forging of high temperature alloys into complex shapes such as aeroengine aerofoil blades. In the actual forging process, the forged blades are trimmed immediately after unloading of the top die at high temperature. In current 3D finite element (FE) simulation for the blade forging, the cooling stage is carried out after unloading without trimming of the flash area. This procedure does not take into account either the thermal effect during flash trimming or the redistribution of residual stresses due to the trimming operation. To overcome this problem, a simple method is developed to directly modify the FE model, in which elements in the flash area are eliminated, a new boundary is reconfigured according to the trimline defined by a B-spline curve and state variables in the old mesh are mapped into the new mesh. Two transformation methods are employed, i.e. the inter/extrapolation method for data at the nodal positions and the inverse distance weight method for the values on the integration points. By utilising the remesh functionality of DEFORM 3D, the distorted elements along the trim line are remeshed to achieve a better mesh quality. By using the new model, the effect of the trimming operation on hot forged blades can be simulated without running time-consuming simulations of the trimming operation with a complex shape.

In this paper, forging, trimming and remesh operations of current methods are briefly reviewed followed by a description of the element removal and state variable mapping. A C++ program was developed to implement the procedure of elements removal, geometry reconfiguration, data mapping and automatic run of FE simulations using DEFORM 3D. Using this program, FE simulations in hot forging a 3D blade shape were carried out with and without the trimming operation. This enables an evaluation of the effect of the trimming operation on the cooling process and the dimensional and shape accuracy of the forged blades. It offers a basis for further appraisal of this technique for an enhanced predictability of the material behaviour and distortion of general precision forging processes.

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