Recycling of metal chips by sintering and forging
Final Report Abstract
During conventional recycling, in which scrap is melted down, high material losses occur due to oxidation and burn-off, especially in the case of small elements such as chips. In addition to the high material losses, the energy and labour costs are significantly higher compared to alternative solid-state recycling (SSR). The chips are first consolidated into a green compact and then further processed in a subsequent heating and forming process. The aim of this project was to bring the resulting component properties as close as possible to those of a compact material through the multiaxial forming of cold-pressed samples made from wrought aluminium alloys. Cold pressing of the chips did not produce sufficient material bonding to run through the aforementioned processes without damage. Multiaxial forming (wrought) and the ECAP process were therefore utilised. Based on the results obtained, it was possible to prove that the interfacial bond prior to further forming has a decisive influence on the resulting material properties. Only in this way can tensile or shear stresses, which can occur in all available forming processes, be absorbed without causing renewed damage to the chip interfaces. Accordingly, the initial compaction is the decisive process step for the SSR of aluminium. Further investigations using an SPS/FAST process (Field Assisted Sintering Technique) have shown that this process is highly suitable for consolidating samples and removing interfaces by applying pure compressive stresses in order to subsequently process chips using forming technology.
