Thermal and Residual Stress Modelling of the Selective Laser Sintering Process

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Thermal and Residual Stress Modelling of the Selective Laser Sintering Process Ameer K. Ibraheem, Brian Derby and Phillip J. Withers Manchester Materials Science Centre, University of Manchester and UMIST, Grosvenor Street, Manchester M1 7HS, UK. ABSTRACT The production of functional tool steel components by selective laser sintering requires an understanding of the effects of the laser processing parameters on the microstructure evolution during the fabrication process. This would allow the production of tools that have predictable and reproducible microstructure, good mechanical properties and low residual stresses. In this paper, finite element modelling has been carried out to investigate the temperature distribution and residual stresses during laser sintering of hot-work tool steel powders. The effects of the laser power and scanning rate on the selective laser sintering process have been investigated. Thermal residual stresses accumulated during the process have been predicted and compared with strain measurements made using neutron diffraction. INTRODUCTION A suite of materials processing technologies has emerged capable of producing mechanical components directly from computer-aided design models, without the need for partspecific tooling. These technologies represent new processing capabilities known as rapid prototyping (RP). The basic feature of this fabrication approach is the repetitive deposition of material layers. In this process, the laser beam is focused onto a powder bed. A single layer of the part to be manufactured is melted, then the platform is lowered, powder is delivered on top of the previously processed layer, and the laser is scanned again to melt the second layer of the part on top of the first layer, and so on. This method offers the possibility of direct fabrication of metallic parts in a single step process. It’s also, capable of producing functionally complex components on a reduced lead-time, and therefore, a significant reduction in production cost can be anticipated. This manufacturing style matches very well with the economically sensitive markets of today. This has been the main driver for investigating and developing these processes. However reliable manufacture can only be achieved if the process is developed to the degree that reproducible tools having satisfactory properties can be built. A better understanding of the effects of all parameters that influence the laser sintering process, such as laser power, scanning rate, scanning spacing, scanning pattern is needed. Only then can a tool that has a maximum strength and minimum residual stress be fabricated. Finite element modelling is useful in this respect for selecting operating parameters to minimize residual stresses in the manufactured components. Other investigators have used finite element modelling for 1D, 2D and 3D thermal analysis to simulate the selective laser sintering process using a single material [1-2], or multiple materials [3]. These simulations have provided valuable insight into how thermal gra