Distortion prediction and minimisation in additive manufacturing

An additive manufacturing apparatus for fabricating a workpiece, comprising:

• a heat source, a wire feeder, a work table for supporting a substrate on which material is deposited, a movement mechanism for providing relative movement of the heat source, wire feeder and work table, and an evacuated chamber enclosing the heat source, wire feeder, work table and movement mechanism;
• a control device for controlling operation of the heat source, wire feeder, work table and movement mechanism, wherein the control device is configured to minimize heat loss from the substrate and the deposited material during fabrication by preventing an average temperature of the workpiece from falling by more than 10% between deposition of successive layers of the material;
• and
• a computer system including:
• a main memory for storing computer readable code for a finite element analysis application module;
• and
• at least one processor coupled to the main memory, said at least one processor executing the computer readable code in the main memory to cause the application module to carry out finite element analysis on a finite element thermo-mechanical model of the workpiece prior to and during fabrication to predict shape distortion and/or residual stress development in the workpiece.