Stronger 3D printed composites

Plastic 3D printing start-up AIM3D reports on the effectiveness of a composite extrusion modeling (CEM) process using PA6GF30 polyamide.

The composite extrusion modeling (CEM) 3D process shows great potential in terms of cost-effectiveness compared to alternative 3D printing processes. In cooperation with the University of Rostock, Germany, AIM3D has conducted a series of tests with PA6GF30 (BASF Ultramid B3WG6) material. Test specimens were printed on the AIM3D ExAM 255 and ExAM 510 machines and the tensile strength of the specimens was compared with alternative processes such as injection molding and conventional 3D printing. Evaluations of the material tests were surprising: printed PA6GF30 is clearly superior to other 3D printing processes and almost achieves the tensile strength of classic injection molding.

High tensile strength

PA6GF30 is an indispensable material in industrial series production applications, combining high mechanical properties with temperature and media resistance. PA6GF30 is thus a fully established material for applications in automotive, special-purpose machine construction or in equipment technology. PA6GF30 components are highly suitable for replacement applications for metal or aluminum parts wherever operating temperatures allow (PA6GF30: 130°C in continuous use, 150°C for short periods). With regard to mechanical properties, such as tensile strength, very high values were obtained by 3D printing on the AIM3D ExAM 255 and ExAM 510 systems. Compared to powder bed processes or 3D printing processes that use filament materials, the CEM process systems achieve tensile strengths that come close to classic thermoplastic injection molded processes.

Material tests

First, tensile bars were printed on an ExAM 255 machine with PA6GF30 and on the larger ExAM 510. The orientation of the 3D printed webs was also varied. 0° for a lay-up in line with the tensile direction (the orientation of the fibers was also in the tensile direction) and +/- 45° for a pattern with an alternating direction of +/- 45° to the tensile direction. AIM3D compared this both with data sheet values for injection molding with the original material and with filament use for comparable PA6GF30 filaments. In addition, a comparison was made with a PA12 material used for 3D powder bed printing, as this material is often used as a reference in 3D printing. Figure 1 shows that CEM technology is very close to injection molding but has a significant advantage over filaments. This phenomenon is due, among other things, to the fact that the original granules used from BASF's injection molding technology actually contain up to 3mm long glass fibers which can withstand the tensile forces for a longer period.

In comparison, the fiber length in the filaments is significantly shorter for technological reasons. Generally, a distinction is made between fiber-reinforced and fiber-filled (if only short fibers are used). If other characteristics from the data sheet of BASF’s Ultramid B3WG6 material used in the test are also considered, the combination of high strength when 3D printing and the high continuous operating temperature of 130°C to 150°C means that this is a universally applicable material. Paired with excellent printability on the CEM systems, versatile applications such as grippers or handling tools can be printed in the future.

Today, these components are usually milled from aluminum, which is material intensive. In contrast to this, 3D printing shows great potential in terms of material costs, conserving resources, component weight, speedy component production and ultimately greater energy efficiency. A general approach when printing these components should not be forgotten: the application of bionic design approaches can increase performance of 3D printed components with regard to their mechanical properties. In summary, there are numerous positive aspects in terms of costs (unit costs) as well as the enhanced performance parameters of a 3D printed component. The results of the investigations at the University of Rostock will be part of a scientific publication.

Cost advantages

Compared to conventionally manufactured components, the particular appeal of 3D printing lies in the functional integration available through 3D printing-compatible design approaches. Functional integration means that assemblies can be manufactured in one printing process, just one of the strategic advantages of 3D printing. AIM3D has produced a motor mount-equipped extruder housing made of PA6GF30 as a demonstration of the process. The motor mount, two air ducts routed in the walls, a ventilation outlet and a mounting for sensors were all integrated into the housing as a single component. In the case of a conventional production strategy with milled aluminum parts, three or four parts would have had to be milled from one block, resulting in a waste of raw materials. In addition, time would be required during the design phase to devise a workaround to avoid the use of special tools such as slot drills and to implement a suitable form-fitting connection of the components. The time spent writing CAM milling programs is also eliminated, especially for small batch production. Manual assembly work is significantly reduced, which also has a positive effect on the cost calculation of the parts.

The CEM process

PA6GF30 can be difficult to use for 3D printing. It is rather difficult to obtain and, where it is available, at 20 to 30 times the price of other materials currently. When processing with filaments, additives must also be used, which can have an unfavorable influence on both price and certification. Original granulates, as used in classic injection molding applications, form the reference for costs at around €5-6/kg. The CEM process is unique in enabling the use of commercially available granules without filaments where the material procurement costs are the same as for injection molding yet without the tooling costs. However, as a 3D printing process, it is more likely to be found in the small and medium-sized series production segment. In addition, there are the freedoms of 3D printing in terms of geometric freedom (such as undercuts), bionic designs or selective densities (different strengths, material savings, selective elasticity, etc).

“Pricing that is comparable to injection molding for raw materials which do not contain filaments is a tremendous advantage for our CEM 3D printing systems technology,” said Dr Vincent Morrison, CEO of AIM3D. “Using PA6GF30, our ExAM 255 machine is able to produce both complex, delicate parts with fine print resolution, as well as large structural components with greater layer thicknesses, resulting in maximum cost-effectiveness with state-of-the-art 3D printing.”

Aluminum substitution

Of course, a 3D printing process cannot match the cost savings of injection molding for medium-sized or large series production runs. Its advantages lie more in the production of smaller batches and bionic design approaches. However, 3D printing has the upper hand in the case of small to medium-sized production runs and rapid prototyping, since here tooling costs form a disproportionate part of price calculations. Above all, using the CEM process instead of milled aluminum production has potential, according to Dr Morrison. “Aluminum as a material is comparatively expensive because of its energy-intensive production,” he explained. “Aluminum parts are often milled from a solid block. This puts great pressure on pricing. Added to this are the current shortages of raw materials. PA6GF30 material printed with our CEM technology as an alternative production solution creates completely new dimensions in terms of cost efficiencies. This applies all the more when bionic design approaches come into play to increase component performance.”

Additive manufacturing

The CEM process combines the metal injection molding (MIM) process, which is already established worldwide, with process technologies from additive manufacturing. This is based on both the fused deposition modeling (FDM) process and the selective laser melting (SLM) process, thus creating an optimal blend of conventional production methods and innovative additive manufacturing.
The result is a very simple process, based on inexpensive and widely available injection molding pellets while offering the freedom of additive manufacturing without the need for molds. The CEM process not only significantly lowers material costs, but also drastically cuts machine costs. Common problems in metal manufacturing, such as residual stresses, are significantly reduced with the CEM process.

Fused granulate modeling

Fused granulate modeling (FGM) is an additive manufacturing process and is based on the widely-used thermoplastic melt layer process (FDM/FFF).

The print head processes pellets into a thin melt thread and applies it to the build area. Thanks to the automatic generation of support material, more complex shapes can also be realised, enabling custom-made production or prototype production with injection molding technology. In contrast to the common melt-layer processes, such as fused filament fabrication (FFF), FGM does not use an elaborately produced filament, but conventional series-production thermoplastic injection molding pellets.