A smoothed particle hydrodynamics (SPH) numerical model is developed to simulate pulsed-laser ablation processes for micro-machining. Heat diffusion behaviour of a specimen under the action of nanosecond pulsed lasers can be described analytically by using complementary error function solutions of second-order differential equations. However, their application is limited to cases without loss of material at the surface. Compared to conventional mesh-based techniques, as a novel meshless simulation method, SPH is ideally suited to applications with highly nonlinear and explosive behaviour in laser ablation. However, little is known about the suitability of using SPH for the modelling of laser-material interactions with multiple phases at the micro scale. The present work investigates SPH modelling of pulsed-laser ablation of aluminium where the laser is applied directly to the free-surface boundary of the specimen. Having first assessed the performance of standard SPH surface treatments for functions commonly used to describe laser heating, the heat conduction behaviour of a new SPH methodology is then evaluated through a number of test cases for single-and multiple-pulse laser heating of aluminium showing excellent agreement when compared with an analytical solution. Simulation of real ablation processes, however, requires the model to capture the removal of material from the surface and its subsequent effects on the laser heating process. Hence, the SPH model for describing the transient behaviour of nanosecond laser ablation is validated with a number of experimental and reference results reported in the literature. The SPH model successfully predicts the material ablation depth profiles over a wide range of laser fluences 4-23 J/cm 2 and pulse durations 6-10 ns, and also predicts the transient behaviour of the ejected material during the laser ablation process. Unlike conventional mesh-based methods, the SPH model was not only able to provide the thermo-physical properties of the ejected particles, but also the effect of the interaction between them as well as the direction and the pattern of the ejection.2

U n d e rs ta n d in g th e E ffect of H e a t In p u t and S h e e t G ap on P o ro sity F o rm a tio n in F ille t Edge and F la n g e Couch L a s e r W e ld in g of A C -1 7 0 P X A lu m in u m A llo y fo r A u to m o tiv e C o m p o n en t M a n u fa c tu re An investigation is reported on the characteristics of porosity formation in high power disk laser welding o f AC-170PX (AA6014) alloy sheets (coated with titanium and zirconium) in two weld joint configurations: fillet edge and flange couch with AA4043 filler wire for potential automotive manufacturing applications. Porosity, macro-and microstructure characteristics, tensile strengths, microhardness, and joint geometry were investigated. It has been found that an increase in heat input and welding speed generates more porosity in both types of joints. The introduction of a 0.2 mm gap reduces porosity significantly in the fillet edge joints but it does not have noticeable effect on the flange couch joints. The mechanism of the porosity formation is discussed.