Vacuum forming replaces pre-preg lay-up

Tom Shelley reports on how to greatly speed up the manufacture of complex, curved sheet composite parts for aerospace applications

It has been brought to our attention that an unnamed US defence contractor has been able to substitute vacuum forming onto rapid manufactured tools for a conventional manufacturing process involving carbon fibre lay-up and heat curing. The company is said to use FDM (Fused Deposition Modelling) Titan machines from Stratasys and a Formech vacuum forming system to greatly reduce cost and labour requirements for parts that include air ducts, engine cowlings and antennae covers. Using the Titan to make a tool, vacuum forming begins in as little as one day after a design has been completed. Since the forming process itself takes only minutes, the parts can be made in less time than it takes to fabricate a conventional fibre lay-up tool. Because of the low pressure and temperature of forming operations, forming tools can be made from materials such as ABS, polycarbonate (PC) and polyphenolsulphone (PPSF/PPSU), all of which can be made on FDM machines. Although tool life will not equal that from an aluminium tool, FDM tools can have lives of from 100 to 1,000 parts, depending on the FDM material and the thermoplastic used in the part. PC and PPSF/PPSU have glass transition temperatures of 160 deg C and 229 deg C respectively, higher than that of ABS. As well as speed of manufacture from STL files derived from CAD systems, FDM tools can be made porous, which is particularly advantageous when vacuum forming, avoiding the need to drill holes in tools made by more conventional methods. Stratasys machines are available in the UK from Laser Lines based in Banbury. Laser Lines