SLM Update

Work resumes with this project. In truth, I've been passively working away on getting this printer back up and running since the LMWD video. The effort has been largely scattered across rebuilding the piston assembly to prevent any movement of the substrate and better tolerate heat soak, and integrating the new laser and power supply.

The build piston is still of a very 'DIY' nature. It makes use of a 54mm hole saw loaded with substrates to help increase thermal mass and to provide elevation for the substrate that will serve as the base of the print. The cantered blades of the hole saw also work well to prevent any rotation as they bite into the edge of the substrate but will flex enough to allow the substrate to be swapped. However, I imagine with repeated heat cycling that this won't be consistent and may require some 'adjusting'. I have mentioned in the past that I wanted to get this part of the printer machined, and still intend to do so, but as of this moment I am not sure whether I should working toward cooling the substrate or preheating it. If the substrate is cooled it will yield all of the issues that conventional metal printers face (stress/warping due to rapid fluctuations in heat) as well as require more input from the laser. If the substrate is preheated then it will most likely be a scratch build as nothing will be able to be made from plastic.

As for the laser, I ended up using 6 high flow copper heatsinks (3 top, 3 bottom) to create a cradle to keep the unit cool. I've yet to put the unit through its paces but if there's a chance the laser can operate without a refrigerated chiller I would think this is it. For comparisons sake, the NUBM31 I used in my early videos displaced a similar amount of heat (~190W) over a much smaller area, although could tolerate 70C versus 55C. This lower temperature threshold is one of the reasons I have avoided fiber coupled diode lasers until now. 55C isn't too bad but fiber coupled units often have lower thresholds, as low as 30C.

The power supply is now integrated into the build. I had bought this unit under the pretense that it has rise time control. It does and it doesn't. What it actually has is a series of presets which are bound to a time scale where the trigger time for each preset can be adjusted, allowing the PSU to transition between settings over the specified interval. However this feature does not work with remote triggering which is very disappointing. I have found that despite this, the constant current response is very good and doesn't allow for overshoot meaning I can simply enable/disable the supply without being conscious of rise time. Unfortunately these diode lasers are very sensitive to transients/ESD as it only takes around 2V/25uA of reverse biased voltage/current to kill the laser hence the need for a good quality PSU.

There's quite a bit more to discuss but I'm going to leave that for the next video. Here's a short video of me testing the laser at 1A, measuring the loss of the gas enclosure window. The display is blown out but it reads 15.5W uncovered and 13.5W covered.