TIWARI Scientific Instruments (TSI) is an equipment-oriented German start-up company that focuses on material thermal measurement and testing systems and metal and ceramic additive manufacturing technologies, and provides services for the European Space Agency (ESA). The fuse FFF 3D printing process developed by it can add metal or ceramic particles to the wire, and finally obtain metal or ceramic parts, thereby providing manufacturing capabilities for space applications.
The stainless steel, titanium, aluminum oxide and silicon carbide parts manufactured using this process have undergone comprehensive non-destructive and destructive tests in the ESA materials and electrical components laboratory to evaluate their added value and space usability. Surprisingly, these 3D printed parts have higher mechanical properties than traditionally manufactured similar products. Among them, stainless steel can be extended to 100% that was previously impossible without breaking.
As an incubator of ESA, TSI focuses on the thermal and mechanical properties of materials. Based on high thermal conductivity, 3D printing of pure copper has always attracted attention, and TSI hopes to launch a low-cost 3D printing solution. Recently, the company successfully adopted FFF technology to achieve high-density, complex structure, and oxygen-free pure copper radiator printing.
Processing pure copper into powder or filament is extremely challenging. Although there are many 3D printing processes for pure copper, most of them are isolated cases, and there are very few companies engaged in each process. The use of green laser printing is an important development of the current powder bed technology, but there are very few green lasers suitable for 3D printing, and the products launched by TRUMPF are not currently sold separately. For demanding applications, parts printed with SLM may still require additional machining and post-processing, which may affect the composition and performance of the parts.
Using FFF technology, the layer thickness of the part printing is set to 50μm, and the roughness due to the layer thickness will be reduced due to shrinkage during the sintering process. Parts can be manually polished or machined under green conditions, thereby reducing the cost of further post-processing, and then debinding and sintering. Using TSI technology, the density of metal and ceramic parts can exceed 99%.
Using extrusion technology to 3D print metal parts, currently well-known foreign companies include Desktop Metal and Markforged, and domestic companies include Shenghua 3D, Shanghai Fuzhi and Longitudinal Cube. DM's equipment has been launched for many years, but it seems that there is not much news in terms of upgrades and applications. The technologies of domestic manufacturers are mostly similar. In terms of materials, most foreign companies can produce materials independently, while domestic companies mostly use third-party materials.
Generally, the binder content of the metal wire is relatively high, and the volume ratio is about 40%. During the TCT 3D printing exhibition, Shanghai Fuzhi demonstrated its company’s extrusion-based metal 3D printer. The degreasing furnace placed next to the printer is very conspicuous; Shenghua 3D also displayed its degreasing furnace on its official website; and Exone and other companies’ sticky The binder spray technology is to complete debinding and sintering in one step, and there is no separate debinding process.
Markforged metal 3D printed parts
Foreign researchers have used Exone equipment to conduct research on pure copper materials, but the prepared materials are not high in density and other properties, and require hot isostatic pressing to achieve densification (and only the sintered density exceeds 90% It is necessary); at the same time, it is also found that the particle size distribution of the powder and the ink composition are the key factors that affect the performance of the part. In February of this year, Digital Metal announced the launch of pure copper 3D printing materials, becoming the first equipment manufacturer to provide officially certified pure copper materials and processes for the binder jet 3D printing system. According to the data released by the company, the density of pure copper formed by the binder injection technology is 96.6%, and the copper purity is 99.9%. However, it is not known whether the company's post-treatment process also includes hot isostatic pressing.
In terms of DLP pure copper 3D printing process, foreign Holo company uses a high-resolution optical imager to 3D print the slurry of pure copper powder and photosensitive resin, which is also combined with the already mature metal injection molding (MIM). End process, debinding and sintering the printed green body, and finally produce high-performance parts. Holo has also optimized the composition of the resin matrix, which is different from the wax-based materials used in metal injection molding, where certain chemicals can affect the mechanical or chemical properties of the sintered parts. Holo Company claims that its slurry has excellent dispersibility, can form a uniform layer thickness during the printing process, and the printer can solidify a new layer in less than 10 seconds. At present, the density of pure copper formed by Holo through the DLP+ degreasing sintering process is 96-98% on average, which is enough to achieve the thermal conductivity and conductivity of 95% of bulk copper. In addition, this process may also reduce the problem of cracks caused by laser printing.
For the development of pure copper 3D printing process, the main focus is on thermal conductivity and electrical conductivity. The conductivity of copper is directly related to its purity. Any contaminants, especially iron, will affect the final performance. In fact, in addition to laser and electron beams that can directly melt and form pure copper, processes such as DLP, FFF, and 3DP cannot get rid of the degreasing and sintering process. As a new type of metal 3D printing that has become popular in recent years, people should pay more attention to the links after 3D printing.