The role of particle size on the laser sintering of iron powder
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INTRODUCTION
RECENTLY, rapid prototyping (RP) processes have been of considerable interest in industry as regards the technological impact on the lead time of product development.[1,2] In fact, RP offers a great opportunity for producers because it reduces the time it takes to develop technology and hence to get the product to market. Although RP has now reached a state of maturity, direct manufacturing of functional prototypes and tools is still in the early stages of development.[3,4] The main restrictions concern the inherent weakness of layer manufacturing processes such as surface quality and dimensional accuracy as well as material characteristics that do not fulfill the requirements of industrial applications. The former weaknesses have been addressed by the development of contouring and post contouring techniques, accompanied by the decrease of layer thickness.[5] A considerable amount of research work has been directed toward material development in order to overcome the latter.[6] A close look at the RP processes reveals that most successful processes for fabrication of functional parts are with powder materials. Some examples of these are three-dimensional (3-D) printing, selective laser sintering, laser-engineered net shaping, and direct metal laser sintering (DMLS). Among different available methods, DMLS has proven to be a suitable process for direct fabrication of functional prototypes without the need for mandatory postprocessing steps, e.g., debinding of polymeric materials and sintering.[7] However,
A. SIMCHI, Associate Professor, is with the Department of Materials Science and Engineering, Sharif University of Technology, Tehran, Iran. Contact e-mail: [email protected] Manuscript submitted August 12, 2003. METALLURGICAL AND MATERIALS TRANSACTIONS B
there are still some weaknesses in the existing DMLS technique, mainly due to the use of loosely laid powder beds. The most significant influences of using the loose powder bed in DMLS are (a) formation of coarse and laminated pores, (b) relatively rough surface quality, and (c) part shrinkage during laser sintering. Much research has been done to discover a solution to these problems; in particular, dealing with the materials investigation, for example, Klocke et al.[8] studied laser sintering of a mixture of copper and tin powder to create bronze parts, Prabhu and Bourell[9] investigated the supersolidus liquid phase laser sintering of prealloyed bronze powder for rapid prototyping, Greulich et al.[10] developed a blend that consists of a mixture of steel and bronze powders for direct laser sintering and Hauser et al.[11,12] studied the feasibility of direct laser sintering of stainless steel 314S powder in different argon/air atmospheric mixtures using a room-temperature powder bed. The DMLS of high-speed steel powders has been investigated by Niu and Chang.[13,14,15] Das et al.[16] reported laser sintering of a mixture of nickel superalloy and cermet powders to produce turbine blade tips. Laoui et al.[17] studied laser sintering of WC-Co hard met
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