TECHNOLOGY | 3D PRINTING
Right: Tooling cores produced using Accura AMX Durable materials on 3D Systems SLA equipment
study with Local Motors (the since-defunct US startup that aimed to build low-volume additive manufactured specialist vehicles) to validate the feasibility of recycling scrap thermoplastic parts and shavings from the 3D printing process. The study aimed to explore more sustainable
alternatives to landfilling for large, printed LFAM parts in anticipation of wider adoption. It included analysing the printability and mechanical proper- ties of SABIC’s LNP Thermocomp AM reinforced compound after being printed, reclaimed, ground and reprocessed into pellet form. The study determined that material from post-production parts and scrap could potentially be reused in LFAM or other processes, such as injection moulding or extrusion, at amounts up to 100%. “As adoption of large format additive manufac- turing accelerates, it is essential to find sustainable alternatives to landfilling large, printed parts,” says Walter Thompson, Senior Applications Develop- ment Engineer at SABIC. “Our study showed great potential for reusing these materials and marks a first step in supporting reuse within the value chain.” There are challenges to reusing large, printed
Right: 3D Systems pioneered 3D printing; the SLA 750 Dual is one of its latest production systems
parts. No established value chain exists for reclaim- ing post-production LFAM parts and scrap. This complex sequence of steps includes managing the logistics of locating, collecting and transporting large parts to a facility capable of cleaning, cutting, regrinding and repurposing the material. Another challenge is the potential degradation from multiple heat cycles (grinding, re-pelletising, re-compounding). Each adds to the cumulative heat history. The SABIC/Local Motors study included evaluations for print- ability, throughput and mechani- cal properties. Six material samples of LNP Thermocomp AM compound were prepared containing levels of repro- cessed content at 0, 15, 25, 50, 75 and 100%, respectively. The samples were monitored for changes in throughput and melt flow rate on SABIC’s Big Area Additive Manufacturing (BAAM) machine. Supplied by Cincinnati Incorporated — the pioneer, along with Oak Ridge National Laboratory in the US of LFAM — the BAAM machine is located in SABIC’s Polymer Processing
64 COMPOUNDING WORLD | May 2022
IMAGE: 3D SYSTEMS
Development Center in Pittsfield, Massachusetts. Each sample was used to print a single-wall
hexagon, which is Sabic’s typical test part geometry for processing and material characterisation. All printed well, with a smooth, shiny surface and straight, even layers that demonstrated no issues with material flow. For the mechanical property evaluation, speci- mens were cut from each hexagonal printed part. These were tested for tensile properties using Test Method D638 and for flexural modulus using a three-point bend test following a modified ASTM D-790 test method. Results showed very good tensile properties in the part samples containing smaller percentages of regrind and only incremen- tal declines in the samples that included larger percentages of regrind. The 100% regrind sample experienced just a 20% reduction in tensile properties in the X-axis and a 15% reduction in the Z-axis. For flexural properties, the same gradual trend occurred, with flexural modulus declining by just 14% in the X-axis and 12% in the Z-axis for the sample containing 100% regrind. As expected by the study’s
participants, tensile and flexural testing showed decreasing mechani- cal strength as the percentage of regrind increased. This is typical of regrind used in other process- es such as injection moulding and extrusion.
Back to the future 3D printing is considered a new technology by many but it is now 36 years since the invention of the first 3D printing process – stereolithography – and the process inventor 3D Systems has introduced new machinery and new resins with the aim of lowering the cost of stereo- lithographic printing and post- processing.
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IMAGE: 3D SYSTEMS
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