# Metal sintering layer-by-layer with DLP

As of current technological advancements, there exists Metal 3D printers that make use of Digital Light Processing (DLP) projector to 3D print metal objects. These printers use a mixture of metal powder and binder. The mixture is placed on the build platform and a laser light beam (or UV light beam, I'm not sure) projection of the layer to be printed is projected on top of the mixture. The light causes the binder to bind the metal powders to each other creating the desired layer. Similar process is repeated for subsequent layers until the object is fully printed. Once fully printed the object is de-binded and sintered in an oven to form the final object.
Now, my question is, like in SLS 3D printing, why cant we directly shoot high-power laser beams with the help of DLP projector onto the powder (without the binder) and cause the metal powder to sinter there itself?

• Why using a DLP to position the powder, we already have printers at work (SLM) that use lasers to melt the laid down powder without the need to bind it first. What you suggest seems like an unnecessary extra step. Our latest machine does not require to lay down the powder first, the laser and the powder directly meet at the object, this eliminates another step in the printing process.
– 0scar
Mar 31 '20 at 9:11

## 1 Answer

SLS uses a high powered laser to smelt the binder of a ceramic or the metal itself. We are talking about at least a 40 W laser which focuses its power on a circle of about 50 µm. How much power are we talking about with that lowest viable laser for plastic SLS?

$$\frac{40\ \text{W}}{\pi \ 62.5\times 10^-9\ \text{m}^2}=640\times 10^6 \frac{\text{W}}{\text{m}²}$$

A typical SLA/DLP machine like the Sparkmaker runs on 48 W in total. Assuming that's 40 W for their $$55\text{ mm}\times98\text{ mm}=0,00539\text{ m}^2$$, so the total projector power of the Sparkmaker is

$$\frac{40\ \text{W}}{\pi \ 0,00539\ \text{m}^2}=7.421\times 10^3 \frac{\text{W}}{\text{m}²}$$

That's about 5 orders of magnitude too little to smelt a layer in the same time. To get a DLP-like projector doing SLS work, you'd need a light source that runs at about a similar power per square meter - wich would just melt the moment it turns on.

• i.e. that laser would have to be impractically powerful, and your equipment might very well just vaporize into a ball of plasma the second you turned the machine on. Mar 31 '20 at 18:12