A verified model of transient and residual stresses in laser direct metal deposition

Abstract

Laser Direct Metal Deposition (LDMD) has proved a versatile technique, but a recognized problem that has still not been overcome is the transient and residual stresses that are generated during the process. These can lead to cracking or to a reduction in final properties and expected lifetime of any product produced by the method.In order to understand and work towards ways to reduce the stresses, this paper presents a versatile model to predict them. The model couples computational fluid dynamics methods with finite elements methods so that all necessary physical effects including the gas-powder flow, the laser-powder interaction and melt pool dynamics are covered. Inputs to the model are the known LDMD process parameters such as powder mass feed rate and laser power. The model is explained and verified against 316L stainless steel parts built with a coaxial laser deposition system. Modeled and measured residual stresses distributions agree well.Laser Direct Metal Deposition (LDMD) has proved a versatile technique, but a recognized problem that has still not been overcome is the transient and residual stresses that are generated during the process. These can lead to cracking or to a reduction in final properties and expected lifetime of any product produced by the method.In order to understand and work towards ways to reduce the stresses, this paper presents a versatile model to predict them. The model couples computational fluid dynamics methods with finite elements methods so that all necessary physical effects including the gas-powder flow, the laser-powder interaction and melt pool dynamics are covered. Inputs to the model are the known LDMD process parameters such as powder mass feed rate and laser power. The model is explained and verified against 316L stainless steel parts built with a coaxial laser deposition system. Modeled and measured residual stresses distributions agree well.