Product Code: ICAL09_1907

Application of Holographic Beam Shaping in Selective Laser Melting for the Fabrication of Functional Polymer Components
Authors:
Darrel Bunyan, Loughborough University; Loughborough Great Britain
Richard Heath, Loughborough University; Loughborough Great Britain
John Tyrer, Loughborough University; Loughbrough Great Britain
Matthew Gibson, Loughborough University; Loughborough Great Britain
Presented at ICALEO 2009

The applications of selectively laser sintered polymer components have been greatly limited by their poor mechanical properties as a result of high levels of residual porosity. This paper looks at the effects of using holographic beam shaping to modify the shape and power distribution of a Gaussian laser beam and the effects this has on the laser melting of polymers. A Holographic Optical Element (HOE) was used to produce a rectangular beam geometry with an even power distribution, to give an even energy input to the powder surface. The ability of the HOE to provide a beam that allows time-temperature control in the material was utilised. This is particularly important with the melting of polymers as there is little thermal conductivity and a short range from melting to boiling, leading to only partial melting of the powder (sintering), or degradation of the material. This configuration was used to fuse together conventional SLS Nylon 12 powder and another Nylon-based powder that was able to produce clear depositions. The beam shape used allowed the whole width of the beam to induce an even temperature in the polymer, leading to complete melting without degradation. Fused specimens were examined by microtome and optical microscopy. It was observed that the levels of porosity present in the conventional SLS Nylon could be greatly reduced, yielding a material with a continuous and homogenous structure as a result of complete melting and fusion of the powder. The second, Nylon-based material yielded further improvements in porosity reduction. In this case the polymer exhibited a lower melt viscosity allowing the flow to be controlled through the shape of the HOE, providing depositions with smooth flat surfaces. This powder has been used to produce solid polymer of near full density and is optically clear up to 1.5mm wall thickness.