Keywords

3D printing, rapid prototyping, large area sintering, projection sintering, Polyamide 12 (PA12), polymer sintering

Abstract

Purpose – Projection sintering, a system for selectively sintering large areas of polymer powder simultaneously with a high power projector is introduced. The paper evaluates the suitability of laser sintering process parameters for projection sintering as it uses substantially lower intensities, longer exposure times, and larger areas than conventional laser sintering (LS).

Design/methodology/approach – The tradeoffs in sintering outcomes are evaluated by creating single layer components with varied exposure times and optical intensities. Some of these components were cross-sectioned and evaluated for degree of densification while the single layer thickness and the maximum tensile force was measured for the rest.

Findings – Shorter exposure times and higher intensities can create thicker and therefore stronger parts than when equal energy is applied over longer exposures. This is different from laser sintering in which energy input (Andrew’s Number) is accepted as a reliable process variable. This difference is likely because significant thermal energy is lost from the sintering region during the exposure time—resulting in reduced peak temperatures. These thermal losses can be offset by imparting additional energy through increased exposure time or light intensity.

Practical implications – Most methods for evaluating LS process parameters, such as the energy melt ratio and Andrew’s Number, estimate energy input from basic process parameters. These methods don’t account for thermal losses and assumes the powder absorbs all incident light. These methods become increasingly inaccurate for projection sintering with visible light where exposure times are much higher (>1s) and a larger portion of the light is reflected from the power’s surface. Understanding the appropriate sintering criteria is critical for the development of long-exposure sintering.

Originality/value – A new method of selectively sintering large areas is introduced that could sinter a wider variety of materials by enabling longer sintering times and may increase productivity relative to LS. This work shows that new processing parameters are required for projection sintering as traditional LS process parameters are inadequate.

Original Publication Citation

Justin Nussbaum and N. B. Crane, “Evaluation of Processing Variables in Polymer Projection Sintering”, Rapid Prototyping Journal, https://doi.org/10.1108/RPJ-04-2017-0070, V 24, n 5, p880-885, 2018.