# What is the simplest way to melt an area of plastic powder with light?

I want to melt a 10cm^2 area of nylon powder (melting thickness of 50 microns), and once melted it becomes a solid sheet of plastic. I can only use light radiation to melt this area, not conduction or convection.

What is the simplest way to make this happen?

One option is to use a powerful diode or co2 laser, and use a beam expander to enlarge the diameter of the focus spot so that it's 10cm^2. It will probably have to be homogenized because otherwise the distribution won't be uniform. Most likely in this scenario I will have to heat up the powder close to melting point, so that the laser only needs to provide enough energy to tip the nylon over it's melting point. Because if you didn't heat up the power, the laser would need to be 1000x more powerful.

The second option I've looked at is using an infrared radiation heater and just point is towards the layer. However I haven't been able to find a part that actually does this, because most infrared heaters are made to heat up outdoor spaces, and aren't hot enough to melt nylon powder.

Is there an easier way to make this happen that I'm not thinking about?

• a layer of powder is a volume, not an area Commented Dec 11, 2022 at 7:18
• Fair point. Melting a thickness of around 50 microns Commented Dec 11, 2022 at 15:34
• First step is figuring out how much power you need. What is the powder losing energy to? You may not be able to use conduction or convection, but are those working against you?
– Abel
Commented Jan 6 at 17:01

## 1 Answer

Selective Laser Sintering (SLS) is a 3D printing process in which a container of nylon powder is preheated by unfocused infrared tubes directed to the surface. The temperature generated does not melt the powder, but applies sufficient energy to the powder to allow a high power diode laser to "write" on the surface of the powder, providing surface melting of the powder. It is not a complete particle melting, hence the name sintering.

The SLS printer I have applies fifty micron layers with each pass of the depositor, obviously limiting the thickness. The laser spot diameter is also quite small, although I've forgotten the specifications, and is in the roughly one-hundred micron range, plus or minus twenty-five microns. It's not practical to de-focus the laser, as that reduces the effective power at the surface of the powder.

In the case of SLS printing, multiple passes of the laser create solid models. One is cautioned by the manufacturer to avoid large flat areas, as warping will result. If you require thickness of a level beyond micron dimensions, consider to create your sheet with a structural appearance of corrugated cardboard or similar truss-like shapes.

Another consideration if you use SLS printing is to have exit points for the un-sintered powder, unless cost (and other factors) is not a concern.

I would not consider SLS printing to represent "the simplest" option, however, but your constraints are severely limiting.

• The laser spot diameter is very small (around 0.1mm^2), which isn't what I'm looking for. Why do you say unfocusing the beam isn't an option? If you started with a laser that's 100 times more powerful, and unfocused the beam to 1mm^2, then it should be possible. Commented Dec 11, 2022 at 15:31
• I'm also really hoping there's a more simple way to generate light that doens't involve a laser, because the light being collimated isn't a requirement for me here. Commented Dec 11, 2022 at 15:33
• If you consider that a focused laser beam contains a specific amount of energy per unit area, when that area is increased, the energy per unit area is reduced. Thermal dissipation is going to be a factor. More energy in tiny spot means more likely to melt, less means less likely to melt. Regarding the no-laser option. The SLS unit I have uses only two 150 mm long IR heating tubes. More tubes = more energy, maybe enough to melt a single layer as you require. Commented Dec 11, 2022 at 21:26