Abstract
Ultra High Molecular Weight Polyethylene (UHMWPE) is a semi-crystalline polymer that has remarkable properties of high mechanical properties, excellent wear resistance, low friction and chemical resistance, and it is found in many applications such sporting goods, medical artificial joints, bullet proof jackets and armours, ropes and fishing lines [1]. UHMWPE parts cannot be produced easily by many conventional processes because of its very high melt viscosity resulting from its very long chains [2]. Additive Manufacturing (AM) is moving from being an industrial rapid prototyping process to becoming a mainstream manufacturing process in a wide range of applications. Laser sintering of polymers is one of the AM techniques that is most promising process owing to its ability to produce parts with complex geometries, accurate dimensions, and good mechanical strength [3]. This paper reports attempts to laser-sinter UHMWPE and assesses the effects of laser energy density on the flexural properties of the sintered parts. The properties of the UHMWPE sintered parts were evaluated by performing flexural three point bending tests and were compared in terms of flexural strength, flexural modulus and ductility (deflection). Part dimensions and relative density were evaluated in order to optimise the laser sintering parameters. Thermal analysis of samples was made by differential scanning calorimetry (DSC) for the virgin powder. Results show that flexural strength, modulus and ductility are influenced by laser energy density and flexural strength and modulus of 1.37MPa and 32.12MPa respectively are still achievable at a lower laser energy density of 0.016J/mm2 (Laser power of 6W). Part dimensions and bulk density are also influenced by laser energy density.
Highlights
Results from other work indicated that the microstructure, physical, mechanical properties and quality of the laser sintered parts are fundamentally affected by laser power, laser speed and scan spacing which are directly related to the amount of energy applied on the powder surface in the part bed
LS parts have achieved bulk density in range of around 0.34–0.38 g/cm3 which is higher than the bulk density of 0.20–0.25 g/cm3 reported by the manufacturer (Celanese GUR® 2122 Ultra High Molecular Weight Polyethylene (UHMWPE) datasheet)
The average flexural strength of the sintered parts increased with increase in laser energy density up to 0.027 J/mm2 with a maximum value of the flexural strength of 2.12 ± 0.05 MPa
Summary
Additive Manufacturing (AM), or 3D printing as it is more commonly referred to, is defined by the ISO Technical Committee 261 on Additive Manufacturing, in cooperation with ASTM Committee F42 on Additive Manufacturing Technologies, as “a process of joining materials to make parts from 3D model data, usually layer upon layer, as opposed to subtractive manufacturing and formative manufacturing methodologies” [4]. After the laser has finished tracing one cross section of the model, a new load of powder is applied on top by roller or blade mechanism. LS build parameters include laser power, laser speed, scan spacing, powder layer thickness, number of scans, part bed temperature, feed bed temperature, build size, roller speed, time between layers, and heating-cooling rates [3]
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