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Among the several techniques for additive manufacturing (AM), fused deposition modelling (FDM) is widely used. Fused deposition modelling process uses a thermoplastic material, which is melted and then extruded layer by layer through a nozzle, in order to create a three‐dimensional object. As a result of the default setting of process parameters provided by the manufacturers, produced parts normally have a poor surface finish, low mechanical properties, low dimensional accuracy, and increased residual stresses compared to the parts produced using conventional manufacturing processes like molding (casting). Qualities of fused deposition modelled (FDMed) parts are generally affected by process parameters including the layer thickness, extrusion temperature, build orientation, printing speed, raster angle, infill density, raster width, nozzle diameter, and air gap. Increasing infill density, printing temperature, and decreasing print speed and layer thickness lead to increase mechanical strength and improve the surface finish of the printed parts. The optimal process parameters are preferred to achieve superior properties of the parts. This paper reviews the optimal fused deposition modelling process parameters on part qualities for making the stability of used deposition modelled parts for use. Various process parameters are identified in order to obtain desirable qualities in the manufactured parts. Areas for future research are proposed.

Recycled polypropylene filaments for fused filament fabrication were investigated with and without 14 wt% short fibre carbon reinforcements. The microstructure and mechanical properties of the filaments and 3D printed specimens were characterized using scanning electron microscopy and standard tensile testing. It was observed that recycled polypropylene filaments with 14 wt% short carbon fibre reinforcement contained pores that were dispersed throughout the microstructure of the filament. A two-stage filament extrusion process was observed to improve the spatial distribution of carbon fibre reinforcement but did not reduce the pores. Recycled polypropylene filaments without reinforcement extruded at high screw speeds above 20 rpm contained a centreline cavity but no spatially distributed pores. However, this cavity is eliminated when extrusion is carried out at screw speeds below 20 rpm. For 3D printed specimens, interlayer cavities were observed larger for specimens printed from 14 wt% carbon fibre reinforced recycled polypropylene than those printed from unreinforced filaments. The values of tensile strength for the filaments were 21.82 MPa and 24.22 MPa, which reduced to 19.72 MPa and 22.70 MPa, respectively, for 3D printed samples using the filaments. Likewise, the young's modulus of the filaments was 1208.6 MPa and 1412.7 MPa, which reduced to 961.5 MPa and 1352.3 MPa, respectively, for the 3D printed samples. The percentage elongation at failure for the recycled polypropylene filament was 9.83% but reduced to 3.84% for the samples printed with 14 wt% carbon fiber reinforced polypropylene filaments whose elongation to failure was 6.58%. The SEM observations on the fractured tensile test samples showed interlayer gaps between the printed and the adjacent raster layers. These gaps accounted for the reduction in the mechanical prop-How to cite this paper:

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Residual stresses induced during the layer-by-layer fabrication process affect mechanical properties and dimensional accuracy of additively manufactured components. Some of these effects cannot be corrected by post processing like heat treatment. This work aims at optimizing fused deposition modelling process parameters for the least residual stresses during 3D printing of carbon fiber reinforced nylon 12 hip implant. Taguchi design of experiment was used to study the effect of printing temperature, layer thickness and print speed on the residual stresses using the Digimat-additive manufacturing software. The results show that the optimal factor setting levels for minimizing part residual stresses were printing temperature of 255 °C, layer thickness of 0.3 mm, and a print speed of 50 mm/s. Printing temperature has the most significant influence on the residual stresses. The combination of the optimum parameter levels yielded the least simulation residual stresses of (41.75�6.53) MPa while the experimental residual stress results were (40.7�7.7) MPa. The simulated and experimental results agreed with minimal percentage difference of (2.51�0.04) %. Tensile and compressive properties of 3D printed carbon fiber nylon 12 composite hip implant matched those of cortical bone. The fracture surface of failed tensile specimens revealed that failure occurred through fiber pull-out and matrix fracture Keywords: Carbon fiber nylon 12 composite / fused deposition modelling (FDM) / hip joint implant / mechanical properties / residual stresses Schlüsselwörter: Kohlefaser-Nylon 12-Verbundwerkstoff / Schmelzschichtung (FDM) / Hüftimplantat / mechanische Eigenschaften / Eigenspannungen