Re: 3D Printed ATSF Tank Cars


Tom Madden
 

Dennis wrote:

So, why use Archer rivets? It would seem that the advantage of 3D printing is being able to add the fiddly bits at the computer, rather than having to tease them in place after paying big bucks to create the basic shell. I realize using Archer rivets is pretty easy, my question is really aimed at including surface detail other than rivets; sheathing bolts on side framing, fillet gussets on castings and the like.
Also, what is the layer thickness and pixel resolution in the "high fidelity slicing mode", and what did it do to build time?
Time for another of Madden's Infamous Treatises on 3D Printing That Aren't The Least Bit Interesting Now But Might Be Later....

Some background - I came into the rapid prototyping (RP) field with expertise in mold making and resin casting but none in the actual printing processes, so all I know about them comes from observation and a growing body of experience. Slicing is the data processing step by which a 3D CAD file is sliced into individual layers, with the resulting slices of data sent, one at a time, to the 3D printer. 3D Systems introduced high fidelity slicing in 2005 but our managers chose not to implement it. (It would only work on one of our six stereolithography [SLA] machines, the high resolution Viper, and it slows things down because slicing is done in real time and the machine would have to wait between layers for the data processing to catch up.) I wasn't even aware of it, nor were any of the shop supervisors. Basically, Hi-Fi slicing greatly reduces the jitter between layers so you get much smoother side walls - both vertical and contoured. It's an add-on to give better results with a machine's existing build modes, not a new build mode. By last fall our stable of SLA machines had grown to 14, eight of them Vipers. All of them have faster computers, so we upgraded the software and all the Vipers now run Hi-Fi slicing.

To be honest, Dennis, I was so blown away by the smooth surfaces that I when the SLA supervisor walked in with a flash drive and asked for one of my "miniature" designs for a demo run, I just went with those upper & lower tank shell files. The amazing thing is, those parts were built using the Viper's standard mode (.010" beam diameter, .004" layers) and not in high resolution mode (.003" beam diameter, .002" layers). Probably a good thing, because those tank bands are .006" thick and the SLA process won't build overhangs if the layer to layer offset is greater than about 75% of the beam diameter. (There has to be something underneath to build on. You can't create a .006" offset with a .003" beam.)

I don't know if a side wall with rivets etc. would build. I tried building the underframe that way, but it failed. For that, Shapeways and multi-jet modeling was the answer. There is no single RP process that does everything well, you still need lots of tools in your kit.

Care to give us a realistic cost number for someone who walks in off the street with usable STL files?
I'll check when I go in today.

Tom Madden

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