MULTIREIN | Technical cleanliness in additive multi-material processing

Additive manufacturing – challenges for component cleaning

The advantage of additive manufacturing of being able to generate complex structures (e.g., filigree lattice structures, channels close to the contour, joints, etc.) also results in the disadvantage of the process-related accumulation of filmic and particulate impurities in fine and thus difficult-to-access gaps or channels in the component. Due to this, the cleaning concepts currently available on the market cannot be transferred directly. For example, some cleaning physics are not sufficient to guarantee process-reliable removal of contaminants in areas that are difficult to access. Particularly in the case of additively manufactured components, such as those generated at the MULTIMATERIAL Center Augsburg, the cleaning process must be adapted to geometries and the materials contaminants to be cleaned. Choosing the wrong technologies or parameters can cause damage to the components due to chemical, thermal or physical effects.

Bavarian Ministry of Economic Affairs, Regional Development and Energy
© StMWi

Video of the project »MULTIREIN«

Clean parts without residues

Concerning the upcoming post-processing, such as coating, bonding, or grinding, as well as the use of the components in the industrial environment, a component that has been cleaned of filmic contaminants following the requirements is necessary since even the smallest residues can lead to impairment of the function and durability. Since the starting material in laser beam melting also consists of a fine powder, it is difficult to delete this from the cavities to avoid damage to the system, such as clogging of cooling/lubrication channels or nozzles during operation. Agglomerates and sintered particles form in and on the components due to the thermal influence during laser melting (see Figure 1).

Agglomerates from powder materials (left) and sintering on the component (right)
© Fraunhofer IGCV
Figure 1: Agglomerates from powder materials (left) and sintering on the component (right)

Methods for the analysis of contaminations

Due to the increasing cleanliness requirements on the part of the industry, the MULTIREIN subproject is concerned with ensuring the technical cleanliness of additively manufactured multi-material components within the overall process chain. For this purpose, possible cleaning concepts are being researched to implement them in a prototypical process chain. In addition to the analysis and characterization of the impurities, these must be quantified using suitable measurement and detection methods. Since established methods for testing technical cleanliness can only be applied to additively manufactured components to a limited extent, they will be adapted on a case-by-case basis.

The timing of the analysis can play a decisive role here. Since, in most cases, the components are reworked, different types and quantities of contamination occur during the process chain. By analyzing the impurities at different points in the process chain, adapting the cleaning processes based on knowledge, and analyzing them repeatedly to check them, the cleaning process chain can be improved both economically and ecologically (see Figure 2).

Exemplary cleaning process chain
© Fraunhofer IGCV
Figure 2: Exemplary cleaning process chain

Adapted cleaning processes

To investigate the suitability of various cleaning and detection methods concerning the specific areas of application, selected use cases from the overall process chain of additive manufacturing are being investigated in MULTIREIN. In addition to different materials and geometries, these also include case-related impurities.

At Fraunhofer IGCV, a prototypical cleaning process chain is being implemented to remove the various impurities from de-powdering to fine cleaning for high-purity requirements. Fine cleaning is carried out by industrial processes such as ultrasound or cyclic nucleation. The advantage of the processes could be demonstrated by specially designed test artifacts. Figure 3 shows the residual particles on analysis membranes after cleaning at various points in the process chain.

Particle residues after different cleaning processes
© Fraunhofer IGCV
Figure 3: Particle residues after different cleaning processes

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