Additive manufacturing is digital manufacturing in its purest form. As such it is advancing at rates that are comparable to those established by Moore’s Law for processing power, doubling in size and speed every year and a half or so. However, unlike computer processors, additive manufacturing involves mechanical process and – more importantly – it involves real matter. As such, the most determining factor in the evolution of AM is the advancement of material science. Composite materials are the segment where the benefits of AM in terms of automation may have the biggest impact.
In the latest 3D-Printed Composites Materials Markets – 2017: An Opportunity Analysis and Ten-Year Forecast SmarTech Publishing built the most in-depth and accurate assessment to date on the use of composite materials in additive manufacturing, analyzing the technologies that can enable automated production of parts and components based on chopped, continuous and even nano-size fiber composites in both thermoset and thermopolymer matrices. With overall global revenues estimated at more than $500 million by 2026 we forecast this to become a major segment in additive manufacturing and a major opportunity for manufacturing as a whole over the next ten years.
AM is viewed in the industry as a way to streamline and automate manufacturing processes, without sacrificing the benefits offered by fiber-based composites in terms of weight optimization and strength. For the polymer 3D printing industry, the ability to 3D print composite materials parts represents a more direct path toward industrial end-use part production, including very large and geometrically complex parts for lightweight aircraft and cars.
Today there are two main 3D printing technologies that are exploring the use of composites: one is material extrusion (also known as FDM, fused deposition modeling) and the other is powder bed fusion (PBF), which mainly consists of SLS (selective laser sintering).
Composites in material extrusion
The material extrusion approach to composite manufacturing can be split up into a few different main areas of application, some of which are still mainly in a research phase. The most practical application of FDM for composite manufacturing is for manufacturing of custom lay-up and sacrificial tooling. This means that you can rapidly 3D print tools to apply standard composite prepregs in order to make complex composite parts. The sacrificial tooling takes this to a new level, enabling manufacturing of highly complex composite structures without assembly, by removing the 3D printed tool simply dissolving it in water. The unique ST 130 material exclusively produced by FDM 3D printer market leader Stratasys is strong enough to hold its shape during autoclave treatment. This is today the only system that enables exploitation of both continuous fiber composites in terms of mechanical performance and 3D printing in terms of advanced geometry.
The future is in full automation of composite manufacturing. MarkForged, a US based 3D printer manufacturer, developed a material extrusion technology capable of placing continuous fiber (carbon, glass or Kevlar) between the layers of a material extrusion 3D printed thermopolymer part (mainly nylon). This technology is also able to rotate the fiber in order to obtain both unidirectional and roving patterns and it is today the only commercially available method to 3D print using continuous fiber composites.
Other manufacturers and research institutions – including primarily the Più Lab at Milano Politecnico University – are developing technologies which use a 6-axes robotic arms to extrude both continuous fiber composites within a thermoset or UV curable resin matrix. These approaches are still in the development stage at this time.
That’s why many 3D printer manufacturers are now exploring the possibilities deriving from the 3D printing of long (up to 3 mm) chopped fiber composites, mainly in a thermopolymer matrix made of ABS or nylon. The most practical application of this approach was developed by US-based Cincinnati Incorporated, with its BAAM (Big Area Additive Manufacturing) platform. Using composite ABS-carbon fiber pellets, BAAM was used by the Lawrence Livermore National Laboratory and by a US start-up called Local Motors to 3D print the entire body of a family of electric cars, in just one print. The carbon fiber gave the thermopolymer materials better mechanical properties but also reduced warping due to temperature differences throughout the thermal extrusion process.
Using nylon-carbon fiber composite pellets, Stratasys went one step further and developed an 8-axis robotic arm capable of building large complex structures by extruding material and precisely placing it within a three-dimensional space. This platform is currently in a beta testing phase at Stratasys manufacturing partners such as Ford and Boeing. Several other low-cost material extrusion manufacturers and filament manufacturers are developing and using long chopped fiber thermoplastic filaments, with nylon-carbon fiber (with up to 20-30% CF) being the most popular today.
Composites in powder bed fusion
Powder bed fusion (PBF) is the other area where short (a few hundred microns) chopped fiber composite materials are likely to continue to experience significant adoption. The market landscape for PBF technology is very different, with entry level SLS systems priced at €200,000 and above. While the market was dominated by two players for close to two decades (EOS and 3D Systems), in recent years new companies have approached the market including Prodways, Ricoh. HP also entered the market developing its own PBF technology called MJF (MultiJet Fusion), which is up to ten times faster than standard SLS.
The presence of more companies drove large chemical groups to develop new materials, focusing primarily on glass fiber (or glass bead) and carbon fiber nylon composites. While giants such as Arkema and BASF are now active in this segment, the technological leadership in terms of composite powders for AM belongs to the Italian CRP Group and its Windform family of materials for PBF. These materials have found applications mainly in automotive and aerospace prototyping however they are also starting to implemented in end-use part production as well.
One other technology that would enable 3D printing of continuous fiber composites in a thermopolymer prepreg matrix is also currently in development and should be mentioned here. The SLCOM 1 system, developed by EnvisionTEC, uses a lamination technology and rolls of prepregs to produce 3D parts. A tungsten blade cuts out the layers of a part and a high-temperature process fuses the thermopolymer matrix to set it in place. This process does not offer the same performance on the Z axis as it does on the X and Y axes, however, it can use high-performance thermopolymers such as PEEK which alone is able to guarantee significant strength to the part.