Abstract. In order to improve the stiffness characteristics of orthopedic devices implants that mimic the mechanical behavior of bone need to be considered. With the capability of Additive layer manufacturing processes to produce orthopedic implants with tailored mechanical properties are needed. This paper discusses finite element (FE) analysis and mechanical characterization of porous medical grade cobalt chromium (CoCr) alloy in cubical structures with volume based porosity ranging between 60% to 80% produced using direct metal laser sintering (DMLS) process. ANSYS 14.0 FE modelling software was used to predict the effective elastic modulus of the samples and comparisons were made with the experimental data. The effective mechanical properties of porous samples that were determined by uniaxial compression testing show exponential decreasing trend with the increase in porosity. Finite element model shows good agreement with experimentally obtained stress-strain curve in the elastic regions. The models prove that numerical analysis of actual prosthesis implant can be computed particularly in load bearing condition IntroductionThe major challenge in developing medical implant devices is to produce biocompatible alloys which possess good tensile and fatigue properties. The technique used to manufacture these alloy can markedly affect the mechanical and metallurgical properties of the resulting components [1]. Additive manufacturing (AM) was proposed as a novel candidate for the fabrication of customized biomedical implants with the cobalt alloys. Among them, is direct metal laser sintering (DMLS) which has been a high demand since it offers a lower time-to-market, a near-net-shape production, a higher material utilization rate, along with its ability to produce functional metallic parts with mechanical properties comparable to those in bulk materials [2]. From the previous studies, SLM has the potential of controlling porosities according to the capacity of providing different energy inputs by its processing parameters while in DMLS process all the parameters were constant. A study on cobalt chromium molybdenum (CoCrMo) powder using DMLS shown that minor porosity produced by the highest layer thickness, which provided a better particle packing. Thus thermal conductivity among the particles was enhanced and subsequently permitted successful densification, and finally removed or shrunk pores.Cobalt (Co) in CoCrMo alloys exhibits high corrosion resistance and has excellent wear resistance which makes Co, often employed as artificial joints and body implants. Co also shows stability of allotropic transformation at room and elevated temperatures. In biomedical applications, CoCrMo

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Metallic orthopedic implants to replace or generate lost bones caused by traumatic road traffic injuries often failed prematurely after surgery. Bone resorption caused by stress shielding of metallic implants became a main concern as it can potentially lead to bone implant failure. Metallic scaffold designed in porous structures fabricated using additive manufacturing (AM) are widely used as bone implant, since the elastic modulus of the scaffolds can easily tailored according to the bone properties, and the large surfaces are beneficial to cell in-growth. The microarchitecture of scaffold can control their mechanical and biological properties, but it is found that there is lack of systematic approach to select a cell topology with full perspective requirements of bone implant. This paper presents a systematic approach of design space mapping for two CoCrMo unit cell shapes namely square and diamond to understand the relationship between geometrical parameters with additive manufacturing limitation, mechanical and bone ingrowth requirements. The compressive response of the components was simulated by finite element analysis and the influence of design parameters on the scaffold behaviour was compared theoretically with Gibson and Ashby model. The FEA give prediction for effective elastic modulus of 3 GPa to 4.8 GPa for diamond type and range of 6 GPa to 29 GPa for square type. Experimental results showed accurate prediction of compression elastic modulus with average error of 13% for diamond type and 35% for square type respectively. The significance of the methodology and the results showed that different design parameters of the structures can play a major role in the mechanical behaviour of the metallic scaffold.

In recent years, additive manufacturing with highly design customization has gained an important technique for fabrication in aerospace and medical fields. Despite the ability of the process to produce complex components with highly controlled architecture geometrical features, maintaining the part's accuracy, ability to fabricate fully functional high density components and inferior surfaces quality are the major obstacles in producing final parts using additive manufacturing for any selected application. This study aims to evaluate the physical properties of cobalt chrome molybdenum (Co-Cr-Mo) alloys parts fabricated by different additive manufacturing techniques. The full dense Co-Cr-Mo parts were produced by Selective Laser Melting (SLM) and Direct Metal Laser Sintering (DMLS) with default process parameters. The density and relative density of samples were calculated using Archimedes' principle while the surface roughness on the top and side surface was measured using surface profiler. The roughness average (Ra) for top surface for SLM produced parts is 3.4 µm while 2.83 µm for DMLS produced parts. The Ra for side surfaces for SLM produced parts is 4.57 µm while 9.0 µm for DMLS produced parts. The higher Ra values on side surfaces compared to the top faces for both manufacturing techniques was due to the balling effect phenomenon. The yield relative density for both Co-Cr-Mo parts produced by SLM and DMLS are 99.3%. Higher energy density has influence the higher density of produced samples by SLM and DMLS processes. The findings of this work demonstrated that SLM and DMLS process with default process parameters have effectively produced full dense parts of Co-Cr-Mo with high density, good agreement of geometrical accuracy and better surface finish. Despite of both manufacturing process yield that produced components with higher density, the current finding shows that SLM technique could produce components with smoother surface quality compared to DMLS process with default parameters.