I recently took a trip to New York where I spent a lot of time discussing 3D printing with CAD professionals, sculptors, and hackers. It was an incredible experience to be in an environment where everybody else was as excited about 3D printing and its far-reaching implications as I was. The discussions I had during this visit helped organize my ideas about future prototypes of my SLS printer and I have laid out a new research agenda for further exploration.
Problem One: Sintering the Wax
Current solution: IR laser
- High-power LEDs and focusing optics
- Thermal print heads
- Plasma spark gap print head
- NiChrome-based heater system
Currently, the high-power infrared limits the accessibility of the system by creating a difficult safety issue. While lasers are extremely useful for targeted energy delivery, I think that there are other (safer and more accessible) options for the sintering process. Essentially, the problem is one of precise heat/energy injection. The laser injects energy into a small area of print powder, heating the carbon component of the powder and melting the wax. So far, this has worked, but there may be better approaches.
My visit to New York and NYC Resistor left me excited about exploring the ideas that I passed up for the laser system. These included using high power LEDs and focusing optics, the print heads of thermal receipt printers (an idea originally proposed by Seth Foster, a fellow engineering student, during a brainstorming session before I had built my prototype). We also discussed various other methods of heat injection such as NiChrome wire and plasma print heads. I think that some of these ideas merit further investigation.
High-power LEDs can output a significant quantity of dispersant light for much lower costs than laser diodes. Laser light, being coherent, is much easier to handle, so the challenge in using LEDs is an optical one. The goal is to produce a crisp, focused spot of light of comparable energy density to that of the 1.5-Watt laser that I used in the first prototype. Though it was difficult to measure the spot size of the laser, it is safe to assume that the power density lay somewhere between 1.9 and 7.6 Watts per mm^2 (based on 0.5mm and 1.0mm spot diameters, respectively). Sparkfun carries high power LEDs and accessories. I’ve begun looking at datasheets for some of the LED options to get an idea of what output powers (mW or lumens) are available.
In addition to the power-density requirement, the output of an LED-driven print head would have to have a spatial power distribution similar to that of the laser spot.
Thermal print heads already reach the temperatures necessary to melt wax. According to this paper, they Additionally, they are relatively cheap, have the bonus of being a salvaged material, and already have resolutions of 200dpi and up, making it a great candidate for high resolution prints. I have found some good technical information about thermal print heads. This document provides some information about the direct thermal printing process and its sister process, thermal transfer printing. Direct thermal printing involves contact (great heat transfer) between the thermal print head and the print substrate. Making contact with the print powder using such a print head and actually translating the head would be difficult, but perhaps not impossible. The thermal transfer process strikes me as an interesting and full of potential for 3D printing. If the thermal “ink” on one side of the transfer ribbon was in fact a thin film of thermoplastic, maybe the transfer process could be used to successively lay down the layers of a 3D print. Another project for another day.
Plasma spark-gaps pose an interesting approach to exposing the powder to high temperatures. Again, the issue of controlling the spatial power distribution comes into play, but I suspect that a well-placed ceramic shroud could help greatly in focusing the intense heat produced. Does anybody have suggestions for measuring the radiant spectrum of a plasma arc? I’d like to measure the power density of some portion of the arc’s spectrum.
NiChrome wire can generate temperatures well above those necessary to melt waxes and many thermoplastics. I’m going to perform a couple of quick experiments with NiChrome wire to see if it’s possible to use close proximity sections fo wire to melt the wax print powder accurately.@1 year ago with 2 notes
#3D printing #SLS #SLS 3D printing #open source #laser sintering #lost wax casting