Material development at WZR

Development, use and monitoring of new materials: Our customers’ daily challenges are also ours. To this end, we would like to provide an insight into our thinking and approach today.

Since the Stone Age, the first step has been to select the right raw material. Ideally, this already brings the desired properties for the application. Thus, our ancestors set out for a nearby clay deposit to produce bowls for daily use.

Today, of course, this path is characterized by research for information on the best chemical composition, particle shape or particle size distribution for the desired application.
Once the right basic raw material – from a chemical point of view – has been selected, important physical parameters of the powder are determined in-house as part of the incoming inspection in order to validate the data sheet.

This is because grain size, shape and distribution are important influencing factors, especially in 3D printing. It is easy to imagine that grains with a diameter of 50 µm cause problems during binder jetting when the layer thickness should be 25 µm. It is even more unsightly if coarse grains clog the die of the 3D extruder. At the same time, however, grains that are too fine tend to agglomerate, which can cause an uneven print bed and a non-homogeneous distribution of chemical constituents in the raw material mixture – which only becomes apparent later during SEM/EDX examination.

Therefore, in addition to the particle size distribution, we determine the bulk & tap density by means of classical sieving or laser granulometry. This is done by weighing and compacting the powder (Fig. 1).

Figure 1: Determination of bulk density

In addition to validating the data sheet, we also get an idea of how the powder will behave as a printing paste or in the powder bed, which is often not yet ideal. Even more so, many high-performance materials such as technical ceramics are significantly more complex in their chemical composition than the clay our ancestors used for pottery. In an intermediate step, therefore, raw material mixtures must be produced and optimized by means of suitable combinations – always with a focus on the subsequent application of the material.

For example, the sintering temperature can be adjusted by suitable particle size combinations, while other mixtures reduce or increase the reactivity of individual chemical components. But processes such as the setting behavior or the interaction with our ink, which is developed in parallel, are also controlled here. In the case of the ink, which defines the components in the powder bed during binder jetting, other parameters such as viscosity, surface tension or the degree of filling with particles are in turn of enormous importance and influence the properties of the green bodies and sintered components.

Via different additives and binders, the properties are specifically modified, e.g. to increase green strength, surface activity, viscosity or the degree of ceramic or metallic particles. Later, initial blends are created for material extrusion or other additive manufacturing processes, or sintering trials are started to evaluate processability on the machines and proper sintering. Layer thicknesses, the saturation of the powder with ink, the selection of the right nozzle, but also the heating and cooling rates during sintering are decisive parameters here.

Once all the adjustments have been made, we first manufacture test specimens to evaluate the newly developed material analytically. Because even if the theory and the print image promise a perfect material, practice raises questions that can only be answered analytically: Is the interaction of ink and powder correct? Is the microstructure adequate for the purpose? How high is the strength?
Here, several cycles are usually run to make further adjustments in the printing or sintering process before the final component is manufactured.

Through regular (web) meetings, we involve you in the development (progress) steps and document our work to enable later transfer to series production or further developments.

You might also be interested in

Porous ceramics and how to use them right

Besides the determination of strength, the determination of open porosity and bulk density is the most common analysis we perform in-house – and also one of the simplest. Nevertheless, it is one of the most important test methods for characterising a sample (sometimes even non-destructively). This is because conclusions about other physical properties can be drawn directly from the open porosity.

New equipment at WZR

Anyone who visited us at the ” Keramik+” conference or at a later date will already have seen it: Our latest 3D printer. The CeraFab S65 from Lithoz uses the VPP process, in which a resin filled with particles is cured by light and which also enables the printing of very filigree structures. We have compiled more information on the VPP process here.

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