Transient Melt Pool Response in Additive Manufacturing of Ti-6Al-4V

Additive manufacturing (AM) processes are candidates for manufacturing and repair in the aerospace industry. For process stability, control of melt pool dimensions is imperative. This can be achieved via feedback and/or feedforward control approaches; however, the time needed for a change in process variables (beam power and travel velocity) to translate into changes in melt pool dimensions is a critical concern. Prior works have determined the relationship between process variables and melt pool geometry, which can be monitored in situ for feedback control. In the current work, Ti-6Al-4V is studied as it is commonly used in aerospace applications due to its desirable properties. Melt pool depth response is determined in terms of response distance rather than response time in order to develop a relationship that is not dependent on the position or path taken in the Power-Velocity (P-V) Process Map, but instead on the initial and final melt pool geometry. Research is performed through finite element simulations run in the ABAQUS™ software package and validated by experiments performed at the NASA Langley Research Center on their Electron Beam Free Form Fabrication system and at Carnegie Mellon University on their Arcam system. The work presented investigates the transient melt pool response due to changes in process variables in steady state build geometries, as well as extending relationships to transient build geometries and other AM systems yielding a comprehensive understanding of melt pool response across all direct metal AM processes. These relationships will allow for the development of effective feedback and feedforward control systems.