Researchers from Columbia University in New York reported the latest research on reverse laser sintering of metal powders

Researchers from Columbia University in New York reported the latest research on reverse laser sintering of metal powders. The related achievements were published in Scientific Reports under the title "Invested laser sintering of metal powder".

The researchers demonstrated the ability of reverse laser sintering technology to manufacture metal powder parts. Researchers first deposit a layer of copper powder on a sapphire plate, then press the sapphire plate onto the component to be manufactured, and then use a 14W 445 nm laser to sinter the powder onto the component through glass irradiation, thus creating a 10 layer component. Then repeat this process multiple times, adding a new layer to the component being printed each time until it is complete. The researchers discussed the potential applications and impacts of this process, including the ability to directly manufacture multi material metal components without using a powder bed.

Figure 1: (a) Coating release agent on glass, (b) Depositing material powder onto release agent, (c) Removing powder not captured by release agent, (d) Pressing substrate onto upper surface of powder layer, (e) Passing laser through glass in a pre programmed mode, (f) Lifting substrate with molten material powder, (g) Removing unmelted powder from glass, (h) Repeat the process until printing is completed, and remove the printed piece from the substrate.

Figure 2: (a) Test setup, glass bracket/substrate installed on the XY gantry above the laser, orange acrylic shielding cover used to block any unstable laser. (b) Tin substrate connected to rubber insulation board installed on the upper platform. (c) Image of uncoated sapphire glass in the bracket installed above the laser.

The researchers created a printed sample composed of copper powder (Figure 3a). The researchers successfully completed this task without causing any visible damage to the glass. The printed sample consists of 10 layers. Due to the manual lifting of the platform during the printing process, the alignment between layers is not perfect. This can be seen from the printed piece (Figure 3b), where the first few layers can be seen on the surface of the "final" layer.

Figure 3: 10 layer copper washer printed using the proposed process. (a) A magnified image of the upper printed surface of the multi-layer copper printed sample (b) shows the layer boundary on the left side of the image, with one marked with a black oval (c, d). SEM observation of the necking behavior in different areas of the copper powder treated printed layer.

Due to these experiments being conducted in an open-air environment, the processed metal is highly likely to undergo oxidation, as can be clearly seen from some darkened areas of the printed material. This oxidation will reduce the strength of printed samples, so any practical application of this printing process needs to be carried out in a deoxygenated environment.

In addition to 10 layers of printing, researchers also made single-layer samples to observe the behavior within the layers. For analysis, researchers used Zeiss Sigma VP scanning electron microscopy to analyze the powder bonding behavior. Although some areas with higher oxidation levels seem to have undergone more melting, particles generally exhibit early stage necking behavior (Figure 3c, d). The bonding degree of the powder is extremely low, which means that some form of post-treatment is needed to better fuse the particles, which can be achieved through bulk sintering or secondary laser.

Researchers have demonstrated that using reverse laser sintering devices to manufacture copper parts is feasible. Currently, due to the relatively low laser power, particle bonding is relatively rare. Post processing methods can be used to improve adhesion, such as bulk sintering.

In addition, in previous experiments, researchers have demonstrated the ability of this process to print polymer materials. The addition of copper has opened the door to printing containing metals and plastics.

Due to the extremely low degree of sintering, in this article, researchers do not need to compensate for the layer thickness changes caused by heating. However, if future project iterations attempt to cause greater sintering/melting during the laser phase, it is necessary to consider changes in layer thickness.

Future work will include developing methods for generating support structures to achieve more complex printing.

Source: Sohu