As an added benefit, Thermwood believes it will soon produce moulds and tooling that function properly under vacuum in a heated, pressurised autoclave without the use of any type of coating to seal the printed tools.
Working toward this goal, Thermwood engineers have printed 50% carbon fibre filled PPS panels on its LSAM additive manufacturing machine that held vacuum to an industry acceptable level in independent testing. The test was conducted by the Fleet Readiness Center, FRC-East, located at MCAS Cherry Point, NC under a previously announced cooperative research and development agreement (CRADA) partnership, and the results met FRC-East acceptance criterion that the bag must not lose more than 2 in Hg over 5 minutes.
Previously, other unaffiliated companies have tested actual tools printed by Thermwood from 20% carbon fibre filled ABS and have also found that those tools held vacuum to an acceptable level without the use of any sealer or coating. However, the ABS material is not suitable for high temperature applications.
Despite that, several parts have been made from those tools under vacuum at room temperature and at slightly elevated temperatures. Thermwood has also already printed a 50% carbon fibre filled three dimensional PPS mould which has not yet been tested. Thermwood’s goal is to produce moulds that will be used in a production autoclave, molding finished parts suitable for actual end use.
Thermwood’s additive printing process differs fundamentally from conventional fused deposition modeling (FDM) printing. Most FDM processes print parts by melting and extruding a relatively small bead of thermoplastic material onto a heated build plate that is contained within a heated chamber. The heated chamber keeps the extruded material from cooling too much before the next layer is added.
Thermwood machines print a large bead at such a high rate that a heated environment is not needed. It is basically an exercise in controlled cooling. Print speed is adjusted so that each layer cools to the proper temperature just as the next layer starts to print resulting in a continuous printing process that produces high quality parts. Thermwood believes this fundamentally different approach produces superior parts.