When I popped into work on Monday to check on the Stratasys, here’s what was waiting for me:
A beautiful plate of Mendel parts!
Unfortunately, disaster struck when I was a bit rough with trying to remove the two large z-axis drive screw blocks. As you can see, the bottom layer remained attached to the support layer. I think this was due to two factors: 1) The back right corner of the build base was higher than any other part of the foam, and I think the ABS was extruded more forcefully into the mesh of the HIPS support layer. 2) I used a loose fill pattern on the entire build, so there wasn’t a great deal of tensile strength between the bottom layer and the interior – you can see the fairly large fill pattern inside the part on the left. The fact that I wasn’t as gentle as I could have been may have also contributed – now that I know that you can break parts when trying to remove them, I’ll be more careful in the future.
The other issue is one that the seller of the Stratasys had shown me, but I hadn’t yet seen it on one of my own parts. The photo shows how the bottom 4 layers or so of outline on one side did not get fused to the inner fill. This can be remedied post-production by dipping or spraying the part with Weld-On 3 or MEK. Note that the outline pass on the part is a lighter color than the fill – the ‘lobster red’ ABS filament loses its color as it sits in the extruder head and cooks – after sitting idle for a half hour or more, the first ABS out of the extruder is almost the color of the light gray support material. I don’t know if this is detrimental to the mechanical properties of the ABS, or if it is only cosmetic.
Sealing the parts is also a topic Frankie and I have discussed. I found that Fortus (the high-end division of Stratasys, with Dimension covering the low-end) has a number of interesting application notes available. The appnote on investment casting particularly caught my eye. While the documentation for my FDM 1600 notes that a special wax material (and accompanying support material) can be used to build wax masters, there seems to be little information available on this material and process – I’m guessing that ABS is a much more popular end-user material. Also, given that the head in my FDM 1600 is specifically marked ‘ABS’, I’m also guessing I’d need a separate head for ICW or investment casting wax prints. Given my previous contact with Stratasys, I’ll wager that my chances of acquiring such a head are slim-to-none. Anyhow, the application note indicates that ABS masters can be used for investment casting, given that the burnout process is done at a high enough temperature. I eagerly passed this information on to Frankie, but he was already ahead of me and showed me an aluminum pizza cutter grip that he had just cast from an ABS part from when he had borrowed a Stratasys demo unit last year. The fill texture of the FDM part was apparent, but not too bad. Ideally, filling in the mesh would be needed before creating the mold, but we have a few crazy ideas on how to accomplish this. Well, Frankie likely has ‘good’ ideas while I have the ‘crazy’ ideas.