Residual stress is a major problem for most metal based Laser Powder Bed Fusion (L-PBF) components. Residual stress can be reduced by appropriate build planning and post-process heat treatments; however, it is not always avoidable and can lead to build failures due to distortion and cracking. Accurate measurement of residual stress levels can be difficult due to high equipment set-up costs and long processing times. This paper introduces a simple but novel method of measuring residual stresses via a threepronged cantilever component, the three-prong method (TPM). The method allows for a quick and easy characterisation of residual stress for a wide range of machine parameters, build strategies and materials.Many different cantilever designs have been used to indicate residual stress within additive manufacturing techniques, such as the ones presented by (Zaeh and Branner, 2010;Yadroitsava et al., 2012Yadroitsava et al., , 2015. All of which share the same short-coming, that they indicate stress in one direction. If the principal component of stress is not aligned with the beam geometry it will underestimate peak stress values.A novel Three-Prong design is proposed which covers 2 dimensions by utilising 3 adjoined cantilever beams, a configuration which echoes that of hole-drilling where three measurements are used to calculate the stress field around a drilled hole. Each arm of the component resembles a curved bridge-like structure; one end of each bridge is cut away from the base plate leaving the centre intact. Deformation of the beams are then measured using a Co-ordinate Measurement Machine. Stress profiles are then estimated using finite element analysis by meshing the deflected structure and forcing it back to its original shape.In this paper, the new Three-Prong method is used to compare the residual stress levels of components built in Ti-6Al-4V with different hatch patterns, powers and exposure times.
Laser powder bed fusion (L-PBF) is a complex process involving a range of multi-scale and multi-physical phenomena. There has been much research involved in creating numerical models of this process using both high and low fidelity modelling approaches where various approximations are made. Generally, to model single lines within the process to predict melt pool geometry and mode, high fidelity computationally intensive models are used which, for industrial purposes, may not be suitable. The model proposed in this work uses a pragmatic continuum level methodology with an ablation limiting approach at the mesoscale coupled with measured thermophysical properties. This model is compared with single line experiments over a range of input parameters using a modulated yttrium fibre laser with varying power and line speeds for a fixed powder layer thickness. A good trend is found between the predicted and measured width and depth of the tracks for 316L stainless steel where the transition into keyhole mode welds was predicted within 13% of experiments. The work presented highlights that pragmatic reduced physics-based modelling can accurately capture weld geometry which could be applied to more practical based uses in the L-PBF process. Keywords Additive manufacturing • Laser powder bed fusion • Modelling • Keyhole-mode laser melting • 316L stainless steel Nomenclature ρ Density C p Specific heat capacity T Temperature κ Thermal conductivity α Thermal diffusivity t Timê n Unit normal to surface q v Volumetric energy input q Irradiated heat flux
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