Effect of Print Density on the Properties of High Speed Sintered Elastomers
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NTRODUCTION
ADDITIVE manufacturing (AM) was introduced in the late 1980s and is now defined by the American Society for Testing of Materials (ASTM) as ‘the process of joining materials to make objects from 3D model data, usually layer upon layer, as opposed to subtractive manufacturing technologies’.[1] Originally AM was used as a visualization tool for final products, this was known as Rapid Prototyping. The potential of AM for functional components was recognized and this led to direct manufacture of end products, ushering in the term AM. Materials typically used in AM are metals, polymers, and ceramics although other materials such as chocolate and paper have been used.[2] There are three primary categories which the processes are placed into; powderbased systems such as Laser Sintering (LS), solid-based systems which include Fused Deposition Modeling, and liquid-based systems such as Stereolithography. High Speed Sintering (HSS) is an evolution of the LS process, manufacturing products layer upon layer from a polymer powder. The feature which differentiates the two technologies is the means by which energy is delivered to each powder layer to initiate sintering and consolidation of powder. In LS, this task is completed by the use of a scanning laser. To create the desired geometry in HSS, an inkjet print head deposits a Radiation Absorbing Material (RAM) directly on to the powder surface. An IR lamp then passes over the surface and exposes the entire build area to infra-red. The RAM absorbs a high level of the incident IR energy causing nearby powder particles to sinter and consolidate, while areas of powder that have not received RAM do not become hot enough to sinter and remain as ADAM ELLIS, Post-Doctoral Research Associate, LIAM HARTLEY, Undergraduate, NEIL HOPKINSON, Professor of Manufacturing Engineering, are with the Department of Mechanical Engineering, The University of Sheffield, Sheffield, U.K. Contact e-mail: adam.ellis@sheffield.ac.uk Manuscript submitted October 2, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS A
discrete powder particles acting as a support for the next layer.[3,4] HSS is currently used to manufacture polymer-based products and these include polyamides such as Nylon 12 and Nylon 11, elastomers, and other thermoplastics.[5] To date HSS has been used to manufacture parts for the aerospace, automotive, construction, and footwear industries, however, other areas are being researched in order to expand its potential.[6]
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PROBLEM DEFINITION
Previous work has shown that print density/grayscale has a significant effect on the mechanical properties of Nylon 12 parts. This is because the amount of energy absorbed by the powder corresponds to the amount of RAM deposited on the surface (print density). Results for Nylon 12 showed that mechanical properties improved as the amount of RAM deposited increased up until a certain point, after which mechanical performance decreased.[7] However, no research has yet been performed to investigate how print density influences the mechanical properties of ela
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