Finishing - SLA Printed Models - Glassy Finish to Make Model Transparent

Problem statement 

I was struggling to get the finish on a transparent model to be fully transparent.  The model (IPhone protective cover with “I Am Canadian” logo and text on inside surface) was printed using clear resin (Anycubic clear tough v2.0 resin) for transparency on a Anycubic Photon Mon 5MS Pro SLA printer.  After curing process all surfaces had a matte finish so the painted embossed logo and text were very blurry when viewed from the exterior facing surface.  

Resolution Approach

To get the embossed logo and text so show up clearly the model needed to be fully transparent and have a glassy surface.  A search of the internet provided a number of potential solutions (sand/polish or dip in resin and then cure). 

• Dip and Cure - for this model the process to dip in clear resin would add an additional thin layer of plastic to the model and that would cause the tightly measure specs to no longer be viable for holding the IPhone.  I abandoned this option quickly.

• Sand and Polish - this seemed the only other viable option, so I proceeded with this one.

Solution  

• Post Processing steps (more about this in another article that I am working on) - Once the print had completed printing and removed from the printer post resin drip I did an initial clean using IPA for a few minutes (to remove excess uncured resin) and then a wash using water to remove any IPA.  The model then dried for 24 hours and then underwent UV curing process for 10min to set the model.

• Sanding and Polishing - Initially for the first trial I did all the sanding by hand but in subsequent trials I used two dremel tools to save time.   

  • Exterior surface - Depending on the condition of the surface I either started with a 60 grit (area that had intense number of supports connections) or 400 grit (fairly smooth surfaces).  I then for each of those areas worked my way up through to up to 10,000 grit (almost glassy surface) for the exterior surface after which I did a buff and polish to get that really glassy look.  

  • Interior Surface - This surface had no supports and was fairly smooth to begin with so I started with a 800 grit and worked through to 1000 grit and then prepped the area for painting the emboss logo.

    • Painting (more about this in another article that I am working on) - At this point I taped (reduce chance for paint to end up on areas not to be painted) and then painted the embossed logo area and let it dry and then repeated the pain process to ensure adequate coverage. 

    • Final sanding -  I progressed with re-sanding with the 1000 (removed any excess paint from outside the embossed area and then progressed up to 10,000 grit in areas not painted.

Learnings

• After trying out the solution a number of times there were some learnings that I can share below

• While sanding by hand works well it takes a lot of time and is tough on the fingers so I used a Dremel with the respective sanding grit heads to speed up the process 

• Sanding wet works better than sanding dry

• Before moving to the next grit level wash and inspect the model to ensure any scratches for lower grit sandpaper have been removed before moving to the next level of sandpaper.

Safety

• Safety glasses are a must and if there are significant fumes (SLA printing/post processing) a mask is also required.  I wear Nitril gloves for handling SLA related processes and materials.

Tools Used

• Dremel Multimax MM30

• Dremel Tool (4300)

• Sanding disks for Dremel tool

• Sandpaper for manual use