Publications

Model based gap and melt rate control for VAR of Ti-6Al-4V

Beaman, J.J.; Williamson, Rodney L.; Melgaard, David K.; Shelmidine, G.J.; Hamel, J.C.

A new controller has been designed for vacuum arc remelting titanium alloys based on an accurate, low order, nonlinear, melting model. The controller adjusts melting current and electrode drive speed to match estimated gap and melt rate with operator supplied reference values. Estimates of gap and melt rate are obtained by optimally combining predictions from the model with measurements of voltage, current, and electrode position. Controller tests were carried out at Timet Corporation's Henderson Technical Laboratory in Henderson, Nevada. Previous test results were used to correlate measured gap to voltage and current. A controller test melt was performed wherein a 0.279 m diameter Ti-6Al-4V electrode was melted into 0.356 m diameter ingot. Commanded melt rate was varied from 20 to 90 g/s and commanded gap was held at 1.5 cm. Because no measure of electrode weight was available on the test furnace, electrode position data were analyzed and the results used to determine the actual melt rate. A gap-voltage-current factor space model was used to check estimated gap. The controller performed well, and both melt rate and electrode gap control were successfully demonstrated.