Prediction and Optimisation of Weld Bead Geometry of Plasma Transferred Arc Hardfaced Valve Seat Rings

Abstract

Automatic weld hardfacing is being employed increasingly in process and power industries. Plasma transferred arc welding (PTAW) has become a natural choice for automatic hardfacing due to its reliability, better process control, ease of use, low dilution and high volume production. Increasing the use of PTAW in its automatic mode, will increase dependence on the use of equations to predict the dimensions of the weld bead. The development of such mathematical equations using a five factor, five level factorial technique to predict the geometry of the weld in the deposition of Stellite 6 (Co-Cr-A) alloy onto carbon steel valve seat rings (ASTM A105) is presented. The developed models have been checked for their adequacy and significance by the F test and t test respectively. Main and interaction effects of the control factors on dilution and bead geometry are presented in a graphical form that aids rapid selection of the process parameters to achieve the desired quality of overlay. The results obtained from the mathematical models have been optimised and also tested using conformity test runs. Optimising the process parameters reduced the amount of metal deposited and enhanced the mechanical and metallurgical properties of the hardfaced layers.