This paper aims to investigate the effects on material properties of layer-by-layer application of pressure during fabrication of polymeric parts by additive manufacturing (AM). Although AM, also known popularly as 3D printing, has set a new standard for ease of use and minimal restraint on geometric complexity, the mechanical part properties do not generally compare with conventional manufacturing processes. Contrary to other types of polymer processing, AM systems do not normally use (in-process) pressure during part consolidation.
Tensile specimens were produced in Somos 201 using conventional laser sintering (LS) and selective laser printing (SLP) – a process under development in the UK, which incorporates the use of pressure to assist layer consolidation.
Mechanical testing demonstrated the potential to additively manufacture parts with significantly improved microstructure and mechanical properties which match or exceed conventional processing. For example, the average elongation at break and ultimate tensile strength of a conventionally laser-sintered thermoplastic elastomer (Somos 201) increased from 136 ± 28 per cent and 4.9 ± 0.4 MPa, to 513 ± 35 per cent and 10.4 ± 0.4 MPa, respectively, when each layer was fused with in-process application of pressure (126 ± 9 kPa) by SLP.
These results are based on relatively small sample size, but despite this, the trends observed are of significant importance to the elimination of voids and porosity in polymeric parts.
Layerwise application of pressure should be investigated further for defect elimination in AM.
This is the first study on the effects of layerwise application of pressure in combination with area-wide fusing.
Support from the European Union Framework 6 Custom-fit project (No: 507437) is gratefully acknowledged. The authors also recognize and thank Susheel Anand Juvanapudi, Jonathan Watts and Denis Waldron of De Montfort University for their help in producing and testing samples. The development SLP rig was a collaborative effort between MTT Ltd (now Additive Manufacturing Products Division of Renishaw plc), CTG-PrintTEC GmbH and De Montfort University. ZEAC also provided support for material developments.
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