MULTISURV | Methods of process monitoring in multi-material processing

At Fraunhofer IGCV, a developed process step made it possible to produce 3-D multi-material components from copper-chromium-zirconium and tool steel 1.2709. Thus, powder bed monitoring systems must be able to detect the coating defects that already occur during mono-material processing, such as grooves, waves, or insufficient powder supply, and to distinguish materials from one another. Thermography has great potential for this inspection task, as it can distinguish optically similar materials based on their different emission behavior. In the course of the project, a flash lamp for excitation of the powder bed and a thermographic camera were therefore integrated into an AconityOne, to be able to investigate the potential of this technology for this inspection task (see Figure 1). In addition to the detection of classic process deviations, the investigation objects were material differentiation and the detection of layer thickness differences. These are shown as examples in Figure 2.

The quality control of additively manufactured (metallic) components still represents a hurdle to faucet into highly regulated industries such as aerospace. Process-related imperfections such as pores, cracks, delaminations, or lack of fusion defects, which can occur even with minor deviations in the process parameters or process conditions, must be reliably detected. Process monitoring technologies used so far usually record the melt bath emissions. However, these only allow limited conclusions to be drawn about the actual component quality. Therefore, this project investigates the extent to which the process laser can serve as an excitation source to detect bonding defects in already solidified layers using active thermography. Figure 3 shows an example of the reaction of artificial discontinuities introduced into test cubes made of 1.4404 to laser excitation. In the further course of the project, it is now necessary to investigate which discontinuity sizes can be detected with this test approach and how this process can be automated.

In addition to those already mentioned, the monitoring of the material composition in the components' transition areas also represents a new requirement for the process monitoring of MM processing. To assert this, a spectrometer is being integrated into the process to investigate any emissions that occur. Specifically, the aim is to determine whether the material composition in these transition areas can be used to conclude the functionality of these structures (e.g., insulation effect) and whether material impurities can be detected.