Thermal spraying brings strong synergy effects at Rybak + Hofmann

Plastic 3D printing and thermal spraying - a synergetic combination

Thermal spray processes represent a major challenge in plastic coating, but when combined they offer enormous functional advantages (Images: rhv-Technik)

A new coating system makes it possible to thermally coat 3D-printed plastic components. This allows metal alloys such as stainless steel and molybdenum as well as hard metals such as tungsten carbide-cobalt or oxide ceramics such as zirconium oxide to be applied to plastics.

Plastics generally exhibit low temperature resistance and high thermal expansion compared to metals and ceramics. Thermoplastics in particular are susceptible to high temperatures. The two most common 3D printing technologies - SLS process and FDM process - use such plastics. This makes thermal coating a challenge, as hot spray particles collide against the component surface in the process.

Two opposing material properties, i.e. temperature-sensitive and temperature-requiring, must therefore be combined in the design. Otherwise, the wrong spray parameters will result in excessive temperature stress and the plastic will burn on the surface - making adhesion of the thermal spray coating impossible.

 

rhv-Technik is very active in process development and has its own design department for special tasks.
rhv-Technik has won the first prize at the 3D printing challenge of Neu-Ulm University with its plastic coating system.

At rhv-Technik, arc spraying processes, flame spraying processes, but also high-speed spraying processes are available, which, in addition to the material, enables a variety of different layer properties Furthermore, the components can be processed after the process, for example by grinding. When designing the plastic component, care must be taken to design it for injection molding from the outset. This includes in particular avoiding sharp edges. Plastics with an oxygen index higher than 21 percent and good wettability should also be used wherever possible.

However, PLA and PA12 are the most commonly used plastics in the FDM and SLS processes. SLS process can be coated. It is also interesting to print components from water-soluble plastics and coat them thermally. The subsequent dissolution of the plastic and a so-called layer transplantation allow the production of thin-walled hollow structures, which are difficult to produce using other manufacturing processes.

Generically produced components on the rise

Up to now, the majority of components coated by thermal spray processes have been produced by machining or casting. However, these proportions could change in the near future, as 3D printing is gaining ground in all industries. Even if many conventional production methods of machining metallic components will not be easily replaced even in the medium term for larger quantities, the manufacture of 3D-printed components represents an attractive alternative, especially for geometrically complex components - or if the weight factor plays a major role.

In the above-mentioned application cases, the issue was always the basic coatability, i.e. the optimum adhesion of the thermal spray coating on a plastic-printed 3D component. Another possible application is the production of 3D-printed components on which nothing should adhere, but which must still have heat resistance properties. Applications would be, for example, covers of metallic customer components for thermal spraying, which are to be used several times for environmental and sustainability reasons and replace the previously used cover tape.

Reusable, 3D-printed masking elements for a wave-like component help save resources and costs in the coating process.

As always, design issues involve, on the one hand, the correct selection of suitable 3D printing materials, spray additives, substrate preparations and spray parameters, in order to either realize the most adhesive functional layer possible or to select specifically non-adhesive plastics. On the other hand, it is also a matter of designing the masking, i.e. capturing the geometry of the customer component to be covered, which is not always available as a CAD drawing.

Scanning robots and different surface detection systems were tested by rhv-Technik together with Aalen University and the DBU - Deutsche Bundesstiftung Umwelt - and the results were evaluated.

Overall, it is clear that the demand for resistant and temperature-resistant 3D-printed components is increasing and that there is also an increased rethinking of resource conservation

rhv-Technik would like to combine these trends to develop a 3D-printed masking for the coating of components which, with the help of a thermal spray coating, is both erosive and abrasive as well as more thermally resistant than a plastic component. In the future, the results of the project could also be used for coating additively manufactured components in lightweight construction, tooling, complex cooling applications or heat-resistant applications.

By the way, in 2022, rhv-Technik participated in the 3D printing challenge organized by the Neu-Ulm University of Applied Sciences with the coating process for plastics and not only made it to the finals with its project, but was also able to convince the jury - consisting of representatives from research and teaching - and take home the first prize. No wonder, because the team from rhv-Technik succeeded in combining several opposing factors within the partly DBU-funded research project with 3D printing and thermal spraying.

The potential of the combination of 3D printing and thermal coating was confirmed by winning the German 3D Printing Challenge 2022. Winning this Challenge impressively demonstrates the interest of companies in the coating system.

With the possibility of functionalizing generically produced plastic components with thermal spray coatings, rhv-Technik has in any case brought an interesting process with a broad application potential onto the market.

Rybak + Hofmann rhv-Technik www.rhv-technik.de