Laser sintering is an approachable problem after it’s been broken down a bit. One of the parts of the problem that I am excited about working on is modeling the heating and heat transfer in the heat-affected zone of the powder bed, which is something I think will be important moving forward, especially when it comes to selecting and processing print materials. One of the basic questions is how exactly does laser radiation at 10.6 microns heat matter? How does any EM radiation lead to heating? And how does wavelength affect that heating? Then come the mechanisms by which heat is transmitted within the material: contact heat transfer, convective heat transfer, and secondary (transmitted) laser heating. And then there are losses too: conductive, convective, and radiative. So there’s a clear framework for building the analysis, but I will need to dust of some textbooks to get the details right.
Tonight I was able to use a RAMBo board running slightly modified (will push to github ASAP) Marlin firmware to drive the X axis on the laser cutter. I mapped the step and direction pins for the X axis to the motor extension pins on the RAMBo board and then hooked the step and direction lines up to the driver module (a Leadshine M860). With a little help from Steve Kelly, the board was able to smoothly move the laser head in the X and Y directions. Some calibration is definitely needed, but I have control over the motion system now. Next comes the laser.
I spent a couple afternoons modeling the first prototype. These screenshots show the prototype under development— I still need to finish modeling the powder distributor hardware and tie up a few loose ends. I am not satisfied yet with the motor mount, but think that it will serve its function. The body will be laser cut from 1/4” acrylic will mainly be secured with acrylic glue. Other features include:
- Removable front panel to allow easy access to the interior of the pistons.
- “Dropped” z-motors to isolate motors from powder.
- Guided z-motion system to reduce wobble and tilting of the piston heads.
- Low profile powder distributor that tucks out of the print plane during layer sintering.
- 100mm x 100mm x 100mm build chamber.
This prototype is more of a proof of concept that won’t involve heating the powder reservoir (which is very important, but a little tricky to implement). I will use what I learn through experimentation on this platform to inform the design of the second prototype.
Planning is must for hardware development. This chart covers the basic flow of research and design tasks necessary to implement successful SLS printing. I’ve been focusing on hardware development and process modeling this past week and will attempt to drive the laser cutter motion system with a RAMBo board later this week.
I’d like to introduce the 80 Watt laser cutter that is making this project possible. SeeMeCNC provided two discounted laser cutters, both of which are going to enable a lot of exciting research. Above is a tour of the machine including the laser head, the Zinc Selenide meniscus focusing lens, the 80 Watt CO2 tube, and a very hackable stepper motor driver (Y-axis).
The RepRap Family Tree is an interesting and informative structure that details patterns and bursts of development. Critical RepRap designs, such as the Prusa Mendel, Sells Mendel, and DeltaBot, emerged as platforms for development and advancement of 3D printing technology.
Fused-extrusion technologies have grown more sophisticated over the past six years, and the community has recently been doing tremendous work in the new (to RepRap) technologies of Delta position systems and photopolymerized resin printing.
This project aims to shed light on the fundamental processes and hardware design challenges that compose this technology by systematically quantifying processes and problems to make this technology accessible to further experimentation. By leveraging the resources, both practical and intellectual, found at the Advanced Manufacturing Research Institute (AMRI) at Rice University I hope to open this powerful and exciting technology for further exploration by the RepRap community. Perhaps this technology could even begin a new limb on the RepRap family tree.