Analysis of Selective Laser Sintering print parameter modelling methodologies for energy input minimisation : a thesis presented in partial fulfilment of the requirements for the degree of Master of Engineering in Mechatronics at Massey University, Albany, New Zealand
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Date
2017
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Massey University
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Abstract
Additive Manufacturing (AM) is the name given to a series of processes used to create solids, layer
upon layer, from 3 Dimensional (3D) models. As AM experiences rapid growth there exists an
opportunity for Selective Laser Sintering (SLS) to expand into markets it has not previously
accommodated. One of the ways SLS can accomplish this is by expanding the range of materials that
can be processed into useful products, as currently only a small number of materials are available when
compared to other AM technologies. One of the biggest barriers to the adoption of materials is the
danger inherent to high-energy processes such as SLS. The aim of this research was to identify
opportunities to improve current methods for modelling the relationship between material
specifications, and printing parameters. This was achieved by identifying existing models used to
determine printing parameters for a new material, identifying weaknesses in current modelling
processes, conducting experimentation to explore the validity of these weaknesses, and exploring
opportunities to improve the model to address these weaknesses. The current models to determine
printer parameters to achieve successful sintering include both the Sintering Window (SW) and the
Energy Melt Ratio (EMR). These two models are complementary, and both are required to establish all
common print parameters. They include both thermal and physical powder properties, but do not include
any optical properties. This is significant because the nature of the SLS printing process relies on
concentrated delivery of laser energy to achieve successful sintering. Analysis of two similar polyamide
powders, one black and one white, identified that the two powders were similar thermally and
physically, which meant the models predicted that they should both sinter successfully utilizing the
same set of print parameters. Results of the experimental trials showed that no trials involving the white
powder sintered successfully, and trials involving the black powder suffered from issues with either
insufficient energy to successfully remove parts without damage, or excessive energy causing excess
powder to bond to the part. Further experimentation was carried out to investigate the differences in
optical properties using Fourier Transform Infrared Spectroscopy (FTIR) and Spectrofluorophotometry.
FTIR revealed that there was a difference in absorption as a material property, indicating that
differences in laser energy absorption could explain the results seen in the trials.
Spectrofluorophotometry revealed minimal differences in fluorescence of the powders, suggesting it an
unlikely source of energy loss. Future work is recommended to research a standardised form of testing
setup that can be used to categorize the reflectance of a material, as current work relies on proprietary
experimental setups. Finding methods of classifying the laser absorption that is easily available to
operators would enable refinement of the EMR equation to reflect the energy losses during printing,
and remove another barrier for adoption of new materials.
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Keywords
Three-dimensional printing, Additive Manufacturing