Feature first published in the January/February 2023 issue, with Sylvia Monsheimer (Evonik) and Ralf Anderhofstadt (Daimler Trucks & Buses). Roles, statements and projects reflect that period.
Polymers play an important role in additive manufacturing. Automotive, aerospace and medical applications can require materials that retain their properties under demanding conditions. Progress towards series production depends on the material, process and requirements of each part.
Let’s be clear: plenty of examples have already demonstrated that high-performance polymers processed via AM, have enabled the fabrication of tooling or end-use applications. The fact is, for those materials to be considered as a replacement of metals, for them to deliver high-value parts in low-quantity production runs, there are a number of requirements they should meet.
This feature examines the challenges of adopting high-performance polymers for series production and their opportunities in tooling and end-use parts.
While various contributions have been considered, Sylvia Monsheimer, Head of Industrial 3D Printing & New 3D Technologies at Evonik, has been invited to share key insights alongside Ralf Anderhofstadt, Head of Center of Competence Additive Manufacturing, Printing Shop & Media at Daimler Trucks & Buses.
Evonik develops 3D printing materials under its INFINAM® brand. Its polymer formulation experience provides the material supplier’s perspective.
Daimler Trucks & Buses provides the industrial user’s perspective, notably on spare parts. In its October 2022 announcement, Daimler said it had examined almost 40,000 part types for 3D printing suitability. This did not mean all were already available through AM. The number of part types assessed must also be distinguished from the number of units actually produced and installed.
Anderhofstadt told us they currently work with numerous partners and service providers, which is why they test all known production processes in AM and test them for series suitability. At the moment, their focus is on SLS, MJF and, of course, FDM, depending on the application.
Understanding the concept of “high-performance” polymers
A polymer is a macromolecular structure. A plastic is a material formulated from polymers and, where applicable, additives or fillers. The terms overlap in the industrial applications discussed here but are not strict synonyms.
Technically speaking, high-performance polymers (HPPs) are a group of materials that can retain their desirable mechanical, thermal, and chemical properties when subjected to harsh environments such as high temperature, high pressure, and corrosive chemicals.
The polymer pyramid generally places high-performance materials above engineering and commodity polymers. It is a classification guide, not a certification of every material property or suitability for an application.
These formulations can demand more complex production and processing, at higher cost. Synthesis complexity or price does not, however, guarantee better performance in every situation. Selection requires comparison of the properties relevant to the intended function.
Low mass, suitable chemical resistance or insulating properties can make some polymers attractive compared with metal solutions. These benefits depend on formulation, fillers and service conditions. Radar absorption and freedom from finishing are not universal polymer properties.
“A significant advantage lies in the high-temperature resistance, which is why this is also very interesting for the automotive sector. This is of course underlined by the properties such as high tensile strength and high chemical resistance. As a result, high-performance polymers are increasingly becoming an interesting alternative to metals”, Daimler’s expert points out.
Surprisingly, the properties that make high-performance polymers helpful are often the ones that make them difficult or impossible to produce using common AM machines without high heat processes.
“If we’re talking about series production – parts that are produced for an end-use application – we will meet the following challenges then: We do not only have to replace the step of building a part but also adjustments of production process steps before and after building a part have to be considered and proven. In other words, we have to work on the integration into process chain which mainly is application driven. And turnkey solutions as a whole are not available. However, this point always is underestimated”, Monsheimer states from the outset.
Anderhofstadt agrees with her as he emphasizes the need for technical and qualitative release processes: “for series parts, it is of course essential to achieve 100% of the properties of the part in the overall context in order to achieve the quality standards. This is also the basis for reproducibility, which is absolutely necessary for series production.”
Added to that the “costs consideration”, and you make the conversation encompass the entire manufacturing chain:
“Another challenge for sure are costs of the overall 3D printing solution. The competition with injection molding is unbeatable for a large number of simple parts. Additive Manufacturing technologies in general offer advantages if freedom of design can be used or assemblies made in one part can be done. In doing so, [it is necessary to redesign the part(s) with AM in mind]. Eventually, special materials for special applications are still missing. Here we step in by continuously extending our product portfolio of application-driven 3D printing materials”, Evonik’s representative adds.
So, what challenges are we talking about?
Manufacturing challenges involve material availability, thermal behaviour and part validation.
The first thing we will keep from Monsheimer’s latest comment is the limited number of high-performance polymers. Interestingly, the process is not as simple as creating forms of traditional polymers used in injection molding for AM.
Interlayer bonding deserves particular attention with PEEK. Delamination is the separation of layers; anisotropy means properties vary with direction and can exist without visible separation. Orion presents its Thermal Radiation Heating system as a way to improve bonding by controlling heat input during deposition. Its cited CubeSat work illustrates the approach but does not by itself establish complete isotropy or automatic qualification for flight.
Thermal gradients, residual stresses and stable processing temperatures influence the resulting quality. Controlling them requires considering material, machine and process parameters together. Monsheimer therefore emphasizes collaboration between material and technology suppliers:
“A good material is the key! This means, having a safely processable material fulfilling all needs 3D printing processes or the respective application require – at the best price. If this setup of material properties vs. costs ratio is given, we can start working on other challenges.”
Geometry, stiffness, creep and service temperature limit possible substitutions; no polymer suits every structure. Boltenstern’s jewellery using Evonik PA12 illustrates a polyamide application, not the performance of a polymer such as PEEK. In automotive, Anderhofstadt described the following work during the interview:
“We are currently in some final testing of high-performance polymers for series applications. The first information on this will also be officially announced soon, as this range is also very interesting for us in the truck and bus sector.
We have already installed more than 50,000 3D-printed series parts in our vehicles. The focus is currently still on the polymer sector, but we have already implemented several series applications made of various metals. In addition to brackets, various covers and handle inserts in the metal area, typical parts are also carriers or various components on the exhaust system”, Anderhofstadt enthuses.
Moving forward, and with regard to the automotive industry, Anderhofstadt points out the need for high-performance polymers to meet other requirements:
“I am thinking strongly about properties such as fire protection and thus the flame retardancy of the materials. And of course, this must also be in line with the sustainability goals. And to supplement this even further: for series production, it is essential that these materials can be used for economical production”, he completes.
Monsheimer also emphasizes environmental considerations. Recyclability depends on material, mixtures, collection and available processing routes for polymers as well as metals. Comparison should consider the part’s life cycle rather than oppose all metals to all plastics.
“After prototyping, applications are the next challenge for materials because now materials have to be optimized for particular applications”, Monsheimer concludes.
This article first appeared in the January/February 2023 issue of 3D ADEPT Mag.
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