Wednesday, October 16, 2013

A Win, a Failure, and another Win?

Warning: This is going to be a pic-heavy post.

The success

So, as many of you know, I've been working hard on my software -"Creation Workshop", preparing for the next Beta 12 release. I've finally found some time to re-build my UV DLP machine to produce some proper prints. Last night, I made a few successful test prints on my newly re-designed machine.

Shown here is the newly- redesigned machine.
My previous setup had issues with the stability of the Z-Axis. It had too much wobble and play in the z-axis, and this was causing issues with separating the model from the vat, as well as creating z-artifacts. As you can see, the Z-axis has been completely rebuilt with 1010 T-Slot aluminum extrusions. 
I folded the geometry of the machine. The projector is now laying horizontally, and I use a FSM (Front Surface Mirror) to project the image onto the surface of the vat. The new Z-Axis is rock solid. Also featured on this machine is a tilt mechanism which helps separate the model from the PDMS coated vat every layer.

A top-down view of the Vat tilting mechanism.

I took the time to install a limit switch for the Z-Axis, so I know when the build plate is exactly touching the bottom of the vat. I used the X-Axis to control the tilting mechanism, and placed a limit switch for the X-axis to trigger when the vat was perfectly level.

Now, I can use homing for the X&Z axis's to move the machine into the initial position.

After a bit of fiddling, a code change, and a ton of calibration and dry runs, I decided it was time to make a test print. I chose the 'Tardis' model.

My first 'Successful' print.

I had a mechanical failure at the last few layers, but overall, it was a good print. I'm still going to need to fine-tune my layer times and Z/X axis movements.

The Failure

I'm always a believer that a failure can teach far more than a success. My machine definitely failed in an un-expected way. I (re)built  most of my Z-Axis using 1010 T-Slot extrusions, however; there were a few choice FDM-printed parts in the build.

Some history
One thing I noticed a few months ago was that the 3d UV Resin I was using was EXTREMELY corrosive to ABS plastic. I had spilled a few drops of it on the tilt mechanism, and the plastic all but dissolved right before my eyes.

I had a similar failure last night. Here's a pic of the destruction:
The UV Resin dissolved the ABS

This L-Bracket as well as the printed green 3x2 plate were dissolved by the UV Resin. Catastrophic failure occurred approximately 1 hour into the print.

The bottom half that attaches to the build plate.

The issue is that the UV resin came over the side of the top of the build plate in the vat. It then traveled by capillary action up the ABS fibers of the green plate and the grey L-brackets. Both FDM ABS prints were dissolved and failed.

The Win?

  My initial guess is that something in the un-exposed UV resin acts as a solvent for ABS plastic. Interestingly enough, my last iteration of my z-axis had this same problem that I was able to avoid. My last Z-Axis also used a 3d-printed ABS interface plate. How did it avoid destruction?
A plate used to connect the aluminum build plate to the Z-Axis on my last machine
As I recall, last time I encountered this, I saw the UV resin was soaking into my printed plate, and I quickly used my UV Laser to cure the resin embedded in the ABS plastic. This worked out well and made the interface plate solid as a rock.

Composite materials
After the failure with the brackets and the plate last night, I re-examined the saturated - cured interface plate from my previous Z-Axis. The resin had completely become embedded and hardened within the material. After a few un-scientific 'hardness' tests with a hammer, I believe that this composite material is much harder and tougher than either ABS or the UV would be on it's own.
I may have to do some more testing with saturating FDM printed ABS plastic with UV Resin and curing the material to test durability of parts in the future.

Next Steps

My machine should be simple enough to fix. I'm going to replace the printed L-brackets with aluminum brackets. I'll probably take the time to add in a screw-adjustment for leveling and quick removal of the build plate.

I'm very happy with the results of my first printings, I think now I have a working machine to test with, adding new functionality to my 'Creation Workshop' shouldn't be too difficult.

1 comment:

  1. Great blog post!

    I learned a lot here. I'm always on the lookout for what dissolves what WITHOUT effecting other materials. That's interesting too about how you found that the dissolving action is deactivated upon solidification. This has to got have some important application later on down the road! :D

    As for the composite, perhaps space for capillary action could be designed into the structure purposefully and then a catalyst curing resin could be used to harden all internal parts of the structure.

    Love the print! I cannot even see the layering on that!