Cox:SLS

Summary
This page gives a brief introduction the the concept of how the SLS fabrication system works, and the various steps in operating and maintaining the machine.

Mode of Operation
Selective Laser Sintering is an additive process that uses a laser to sinter fine powder into solid shapes. Various materials can be used in the system. Briefly, a typical SLS machine has two feed bins and one part bin. A roller deposits a thin layer of powder over the part bin. A laser then scans over the powder and sinters only areas which are determined by software in the controller PC. A more detailed description is available on Wikipedia

Setup

 * Verify cleanliness of build chamber (no buildup on the walls, limited powder on the edges)
 * Verify sufficient powder levels in feed bins
 * Check nitrogen connections and ensure that there is enough to last throughout the run.
 * Monitor coolant flowrate and pressure
 * Check that the laser lens is installed
 * Check that the bolts securing the roller to the arm are tightened
 * Extend heater deck and install heat shields
 * Put Blackbody in upright position

Starting Build

 * Load your .stl file into the desktop computer next to the process station
 * Open the build editor
 * Set up a new build, making sure the minimum extent of the part is at .104"
 * Include a heat shield in the build at a minimum extent of 0
 * Save and verify the build in the common mm_dd_yyyy file format
 * Run interference detection and preview to make sure there are no glaring errors in the build process.
 * Make sure sufficient powder is present in the machine, the program should warn you if there isn't enough, better to confirm independently.

Cleanup
Checklist for Cleaning SLS Machine (Mandatory after every build)


 * 1) PUT ON Protective Suit and latex gloves to prevent powder contamination.
 * 2) REMOVE laser window, keep a solid grip on the window as you transfer it to a cart for further cleaning.
 * 3) CAP laser aperture with red plastic cover.
 * 4) CREATE a clean work area on the cart for the actual laser window by stacking 2 or 3 large kimwipes on the cart.
 * 5) REMOVE the yellow retaining ring on the laser window assembly by unscrewing the machine screws with an allen wrench. Once the ring is removed, place one hand (did you remember to put on gloves?) on the window to prevent it from falling as you invert the assembly. Lightly tap on the window to make it pop out in the direction where the retaining ring was. Place the window with the side exposed to the build area face up on the mat of kimwipes and put the rest of the assembly to the side.
 * 6) APPLY a circular bead of EtOH directly on the top of the laser window. Use a small kimwipe folded in half and gently wipe in one direction, rotating the kimwipe as you progress along the window. Apply another circular bead and do the same wiping motion again with a new kimwipe, this time in the opposite direction.
 * 7) REPLACE the laser window into the assembly, making sure that the O-ring is sealed and that all allen wrenches are finger tight. Laser window cleaning is complete, but do not put the assembly back in the process station.
 * 8) REMOVE roller assembly. [[image:SLSclean2.JPG|thumb|200px|Removing roller assembly]]
 * 9) SCRAPE any powder that scattered away from the rolling zone into the overflow container (if on the side) or collect and throw in the BOS sifter.(if near the center)
 * 10) VACUUM any stray powder on the surface of the Process Station.
 * 11) WIPE DOWN all elevated interior surfaces (including drive belt) of the process station except for the center heater on the retracting platform. Use a rag moistened with EtOH. Some effort is required to remove gunk on upper surfaces. Keep at it until the waxy substance is gone.
 * 12) WIPE DOWN roller assembly with EtOH until all powder is removed.
 * 13) CLEAN Blackbody with Kimwipe to remove powder. Take care not to damage wires underneath the unit.
 * 14) SWAB the 3 IR sensors along the back rail, first with a swab soaked in EtOH, then followed by a dry swab.
 * 15) WIPE the upper surfaces of the Process Station using a rag sprayed with 3 spurts from the WD-40 Bottle
 * 16) CLEAN the window with a rag moistened with EtOH.
 * 17) REPLACE the laser window assembly and put the red cap back on the side of the machine.

Materials In Stock

 * EOS Polyamide
 * EOS Alumide (Aluminum/Polyamide mixture)

Lessons Learned

 * Prevent hair from getting into powder by wearing the bunny suit and elbow length gloves, cycling hat or bouffant whenever you are working inside the build chamber or breaking out parts. Individual hairs can sometimes pass through the sifter grid.
 * A single N2 gas cylinder will not get through a normal build. Use gas cylinders strictly as backups for a dewar.