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RODUCTION

ADDITIVE Manufacturing (AM) has seen a surge of interest in the recent years.[1] It possesses certain characteristics which gives it an edge over conventional manufacturing methods. For instance, AM is able to cut down on material wastages when only the required amount of raw materials are used. Another advantage of AM is design freedom. Instead of manufacturing multiple components and assembling them, AM allows the user to print the part as a single-body unit.[2] Furthermore, it is difficult to produce part with complex geometries using conventional manufacturing. However, with AM, intricate design can be produced with relative ease.[3] An example is the use of lattice structures for weight reduction without compromising on the structural integrity of the part.[4]

J.L. TAN is with the Singapore Centre for 3D Printing, School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, 639798, Singapore and also with SLM Solutions Singapore Pte. Ltd., 25 International Business Park, #02-15/17 German Centre, Singapore, 609916, Singapore. C. TANG and C.H. WONG are with the Singapore Centre for 3D Printing, School of Mechanical and Aerospace Engineering, Nanyang Technological University. Contact e-mail: [email protected] Manuscript submitted January 30, 2018.

METALLURGICAL AND MATERIALS TRANSACTIONS A

In selective laser melting (SLM), several process parameters affect the quality of the printed parts. The energy density E, which is the applied energy per volume of material, is given by[5–7] E¼

P ; vhL

½1

where P is the laser power, v is the laser scanning speed, h is the hatch spacing, and L is the layer thickness. Based on Eq. [1], it can be deduced that the energy density is a function of these four parameters. However, apart from these parameters, there are other factors which can affect the quality of the fabricated parts. For instance, the powder size distributions will affect the packing density of the powder bed layer, whereas the laser spot size will affect the intensity of the laser.[8,9] Using a wider distribution of powder sizes has shown to give a denser part compared to that obtained when using a narrower powder size distribution.[10] Increasing the laser spot size will lead to a decrease in energy intensity since the laser power will cover a bigger area of the powder bed and this may result in incomplete melting of the powders. As such, the quality of the part is dependent on a variety of parameter combinations. Read et al. conducted a series of experiments using four parameters with five different values each.[11] Therefore, a total of 625 runs were conducted to test every possible combination without any additional samples to test for repeatability. This shows that relying solely on experiments to determine

the optimal process parameters is not only time consuming but also expensive. The use of simulation and modeling is a viable approach in tackling this obstacle. There are a variety of modeling techniques used to simulate the SLM process. Fu and