Distortion control in a wire-fed electron-beam thin-walled Ti-6Al-4V freeform

The solid-state phase change (SSPC) temperature is important in the accurate thermal-mechanical simulation of a wire-fed electron-beam freeform. The SSPC temperature of the Ti-6Al-4V material was determined to be 850 degrees C by variable temperature XRD measurements. The forming process of a typical thin-walled TC4 piece was modeled, and the most accurate predictions were achieved with the determined SSPC temperature. The thin-walled piece could be formed if the electron beam operated at a scan current between 100 and 150 mA and a speed below 100 mm/s. The distributions of the residual stress were consistent in the reciprocating and unidirectional scan modes; however, the former produced less distortion. In the reciprocating mode, shrinkage distortion dominated and increased with the scan current. The maximum distortion along the x-axis increased from 0.18 to 0.32 mm when the current increased from 100 to 150 mA. A dynamic current scheme reduced the maximum distortion along the x-axis to 0.12 mm, and a constant temperature constraint at the bottom of the substrate reduced the distortions along the x- and z-axes to approximately zero.