Additive manufacturing or 3D printing is now the fastest growing sector of manufacturing globally. Professor Milan Brandt and Professor Murray L Scott assess its potential in the design and production of composite parts directly from CAD.
Companies such as Airbus, Audi, BMW, Boeing, Ford, General Electric, Hewlett-Packard and Nike, as well as many small and medium-sized enterprises globally, are using and exploring additive manufacturing (AM) technology for component and part production. Popular press, trade and technical journals are almost daily reporting on new and innovative printers; parts additively manufactured in both metal alloys and polymers; and component designs for AM that challenge the imagination.
The main driver has been globalisation, which is changing the nature and economics of manufacturing in high-wage countries such as Australia. On one hand, globalisation has led to new markets, but on the other, to new competitors, in particular from low-wage countries. Handling the challenge of product cost pressures, diversity and dynamics becomes the central focus for manufacturing companies in high-wage countries.
Advanced technology and research are seen as critical elements in addressing some of these challenges to deliver cost-competitive approaches to manufacturing for the companies in high-wage countries to remain profitable and in business. AM is seen as a solution to boost local manufacturing because of the many benefits it offers compared to traditional manufacturing. With additive technologies, parts can be built directly from computer models or from measurements of existing components to be re-engineered, and therefore bypass traditional manufacturing processes such as cutting, milling, casting and grinding. Benefits include:
- New designs not possible using conventional subtractive technology.
- Dramatic savings in time, materials, wastage, energy and other costs in producing new components.
- Significant reductions in environmental impact
- Faster time to market for products.
Ever since composite materials were first introduced, they have been pushing the boundaries of high-performance and lightweight designs in all branches of engineering. Composite manufacturing processes are in essence additive processes. In order to reduce the labour-intensive manual operations, and the need for a flexible automated composite process, organisations are investigating the feasibility of implementing AM techniques to aid the fabrication of composite parts.
There are several options for which AM can be implemented in the composite production process involving direct and indirect manufacture of composite parts. This article highlights the potential of AM in the design and manufacturing of composite parts directly from CAD in particular with fibre reinforced thermoplastics.
Growing applications
The use of composites in AM is definitely growing, as evidenced by the number of companies looking to take advantage of the material properties due to continuous filaments and the size of parts possible. The latter was demonstrated at the 2014 IMTS show in Chicago, USA, with the printing of the Strati carbon fibre reinforced plastic car using BAAM (Big Area Additive Manufacturing), by US collaborators Local Motors (Chandler, Arizona), Oak Ridge National Laboratory and Cincinnati Incorporated.
MarkForged has developed a process for fusing carbon fibre to other thermosetting materials and is offering a small desktop printer for this. The Mark One MarkForged printer allows users to embed electronics, sensors, ball bearings, hard mounting points and more into 3D printed parts made with carbon, glass and/or aramid fibres.
AM technologies relevant to composites have been around for a number of years, and some have been used for production, including the following: selective laser sintering (SLS); laminated object manufacturing (LOM); stereolithography (SL); fused deposition modelling (FDM); three dimensional printing (3DP); and ultrasonic consolidation.
AM techniques which have mainly been used with fibre composites, are SL, FDM and LOM. However, in a powder-based AM technique such as SLS, it is difficult to draw smooth layers of powder-fibre mixture. Long or continuous fibres, instead of short fibres, are difficult to incorporate into processing, therefore their use has been limited to LOM and SL techniques.
FDM, pioneered by Stratasys, is now one of the most widely adopted AM techniques. In the fused deposition process, a spooled filament of a thermoplastic polymer is fed into a liquefier, with the help of a pinch feed mechanism. The incoming solid filament acts as a plunger to extrude the material through a circular nozzle in the form of a molten bead of material. The extruded polymer is deposited according to a fill pattern established by software pre-processing onto the build platform or previous layer. After the layer is finished, the build platform is lowered and the cycle repeats.
The AM process using the filament-based extrusion technique of FDM requires the material to be processed into a filament form. This filament is extruded to a very high diametric tolerance. Parts obtained from the FDM process have mostly been used for model visualisation and form/fit verification. However, in recent years many new materials have been investigated to enable FDM to produce fully functional parts by incorporating a reinforcing material into the polymer matrix.
In conclusion, AM technologies are rising in importance globally because of the benefits that they offer compared to conventional techniques. In the composites area, direct manufacturing of parts is being driven by the research into improving their structural integrity through the addition of reinforcing filler materials and new deposition technologies. It has been shown that the extrusion-based additive manufacturing technique has a positive effect on the fibre alignment in the resulting parts. The main weakness of extrusion-based polymer AM parts is the interlayer bonding strength between adjacent layers. Further research is being conducted with short fibres and fibre fillers to investigate the bond formation of polymer filaments and their properties.
Professor Milan Brandt is the Technical Director of Advanced Manufacturing Precinct and Director of the Centre for Additive Manufacturing at RMIT University. Professor Murray Scott is Managing Director of Advanced Composite Structures Australia Pty Ltd and an Adjunct Professor at RMIT University. Article reprinted courtesy of Composites Australia.