Abstract
This research work focusses on the implementation of a viscoplastic creep model in the thermomechanical simulation of the wire arc additive manufacturing (WAAM) process for Ti-6Al-4 V structures. Due to the characteristic layer by layer manufacturing within the WAAM process, viscoplastic material effects occur, which can be covered by implementing a creep model in the thermomechanical simulation. Experimental creep tests with a wide temperature, load and time range were carried out to examine short-term creep behaviour in particular. A Norton-Bailey creep law is used to accurately fit the experimental data and describe the base material’s creep behaviour. Subsequently, the fitted Norton-Bailey creep law was implemented in the thermomechanical simulation of the WAAM process. Finally, to determine the effect of creep on global distortion and local residual stress state in the substrate, simulations of a simplified linear, three-layer WAAM structure, with and without applying the implemented creep law, were carried out and compared to experimental data. The thermomechanical simulation with implemented creep model reveals a significant improvement in the numerical estimation of distortion and residual stress state in the substrate. The maximum distortion is reduced by about 13% and respectively the mean absolute percentage error between simulation and experiment decreases by about 34%. Additionally, the estimation accuracy with respect to the local residual stress state in the substrate improved by about 10%.
Highlights
Additive manufacturing (AM) represents an innovative technology for a time- and cost-efficient production of geometrically complex components and structures
One AM technology used for large, medium complex structures is wire arc additive manufacturing, in which the wire is fed as base material, melted by means of an electrical arc and additively added layer by layer on a substrate
Implementation of a Norton-Bailey creep model [26, 27] for the thermomechanical simulation of the wire arc additive manufacturing (WAAM) process based on the experimental creep test results for material out of a substrate
Summary
Additive manufacturing (AM) represents an innovative technology for a time- and cost-efficient production of geometrically complex components and structures. Studies focusing on validation and calibration of thermomechanical process simulation with experimental data of additive manufacturing processes reveal an overestimation regarding simulated distortion and residual stress [18, 19]. Presentation of a methodology for the development, implementation and validation of a creep model in the simulation of the WAAM process, by focussing on the characterization of the base material and validation with the substrate. Implementation of a Norton-Bailey creep model [26, 27] for the thermomechanical simulation of the WAAM process based on the experimental creep test results for material out of a substrate. Comparison of simulated distortion and residual stress state in the substrate with measured data for a three-layer WAAM structure to assess the impact of implementing the viscoplastic creep material behaviour
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