Poonjolai Erasenthiran

Investigating mechanical anisotropy and end-of-vector effect in laser-sintered nylon parts

Abstract A study investigating the effects of part-build orientation in the laser sintering process is presented. The investigation uses tensile, flexural, and compression testing methods to assess the changes in the mechanical properties of laser-sintered nylon-12 parts. The test parts were built in the x, y, and z orientations with the x axis parallel to the direction of the laser scanning, the y axis perpendicular to the direction laser of scanning, and the z axis in the direction of powder layers. The results from the tests show that the build orientation of the parts has an effect on the mechanical properties produced. The tensile tests show a maximum difference of 16 per cent and 11.2 per cent in strength and modulus respectively for parts built in the x, y, and z axes. The flexural tests show a 9.4 per cent and 7 per cent maximum difference in strength and modulus respectively for the parts produced in the x, y, and z axes. For the compressive tests, there is a 3.4 per cent and 13.4 per cent maximum difference in strength and modulus respectively for the parts produced in the x, y, and z axes. A statistical analysis of the results obtained highlights the presence of anisotropy in tensile and compression parts owing to their build orientation in the laser sintering machine. The test parts built in the x axis orientation showed the highest strength and modulus values while the parts built in the z axis orientation showed poor strength and modulus values. However, this is not the case for the flexural test parts, which show the highest strength and modulus values are from those built in the y axis orientation. Analysis has shown that this is due to the end-of-vector effect, which is most prominent in the y axis orientation. This effect should always be considered during laser sintering, when mechanical integrity is vital.

Evaluating the use of functionally graded materials inserts produced by selective laser melting on the injection moulding of plastics parts

Abstract The demand for productivity and shape complexity on the injection moulding industry necessitates new research to improve tool design, material, and manufacturing. A research field is the development of functionally graded materials (FGMs) to build injection moulds. For example, moulds built with the FGMs technique can have distinctive regions with higher heat conduction. Higher rates of heat transfers from thicker regions of the injected part can be useful to produce better and cheaper injection moulded polymer parts. It is possible to obtain moulds with differential conductivity by adding locally, during the fabrication of the mould, copper to the mould base material such as tool steel. In this work, an investigation into the effect of FGM copper (Cu)-tool steel mould insert over polymer injected parts is presented. The work is divided in two parts: a numerical thermal analysis comparison between Cu-tool steel graded and tool steel inserts and an injection moulding experiment with comparisons between mould surface temperature and degree of crystallinity of polypropylene parts. The numerical model was used to compare different behaviour of the mould heat transfer according to the mould insert material. Thereafter, a bolster was built to hold FGMs and tool steel inserts obtained by a selective laser fusion process. Polypropylene was injected over the inserts to compare with the numeric results. To observe the effect of the cooling rate in the polypropylene parts using the graded inserts, the degree of crystallinity of the parts was measured by differential scanning calorimetry (DSC) test. The temperature of the mould was also evaluated during the injection cycles. The results showed that the graded Cu-tool steel inserts tested had lower capacity to store heat energy. As Cu was added to the tool steel, the mixture proved to transfer heat more efficiently but it had less capacity to absorb heat.

Investigation of fully dense laser sintering of tool steel powder using a pulsed Nd: Yag (neodymium-doped yttrium aluminium garnet) laser

Abstract A 550W neodymium-doped yttrium aluminium garnet (Nd:YAG) pulsed laser was used in the solid freeform fabrication (SFF) process to form fully dense sintered parts. Tool steel powder was chosen due to its wide acceptance in the tool-making industry. Unlike many processes applying either thermoplastic binder or metals of low melting points in the powder mixture, this process enables a direct fusion of material to solid parts without a further post-processing step. This paper presents a methodology and the results of high-power laser sintering of tool steel powder. The investigation includes the effects of various process parameters on the fully dense laser sintering results on a single bead and single layer and the related scan strategy to build up solid cubes. This process could eventually produce pre-forms with complex material structures rather than finished tools or parts.

Scanning strategies and spacing effect on laser fusion of H13 tool steel powder using high power Nd:YAG pulsed laser

Layered manufacturing technologies have been used to produce complex parts of diversified materials through different physical/chemical manufacturing principles. Nevertheless only a few materials are commercially available to build parts suitable for engineering applications. In this paper, the powder fusion of H13 tool steel is investigated. A high power Nd:YAG pulsed laser source on a CNC machine was used to fuse the powder, layer by layer, building solid cubes for further analysis. Four different laser vector scanning strategies were evaluated by comparing the results of porosity and layer distortion. The complexity of the laser/powder interaction shows that a complex strategy must be used to avoid porosity and distortion.