Finishing Water Jet Parts
- Micah Black
Why Finish Parts
When parts get waterjet, there seem to be a ‘film’ of some sort left on the surface, it might just be dust from the abrasive in the water that gets on the parts when removing. We have tested and can spot-weld just fine through the 'film', but it would be great to have a cleaner surface.
This, as well as the inherent burrs on waterjet parts, made me interested to figure out any existing waterjet finishing processes.
Finishes Used in Industry
This link explains a few of the finishes in use at Big Blue Saw: https://www.bigbluesaw.com/saw/faqs/parts/what-types-of-finishing-are-offered-with-waterjet-cutting.html
The ‘Pad Prep’ finish seems to be what we want to remove the surface ‘film’ and knock down some of the burrs:
This page seems to be previously posted on the Big Blue Saw site, and has the details of the “Basic Finish” mentioned in the image above:
https://planiverse.wordpress.com/2014/04/28/finishing-waterjet-cut-parts/
Required Parts
So it seems we need a non-woven abrasive pad to perform the finishing and hopefully remove the ‘film’ on the surface (or the ‘frosting’ as the article above mentioned - here’s a few waterjet pages that mention frosting - https://wardjet.com/news/waterjet-water-level-control, https://www.omax.com/news/blog/5-tank-tips-better-abrasive-waterjet-cutting).
But what is a non-woven abrasive pad?
https://www.nortonabrasives.com/en-us/resources/expertise/how-choose-and-use-non-woven-abrasives
Seems like they are just the regular type of coarse kitchen sponge or scouring pad. So we’ll do some testing with one of those and see how well it works.
Testing
I used a regular kitchen sponge/scouring pad (one of the yellow and green ones) and used the scouring pad side (green) on this part to see if I could clean up the surface. On the left is the part that I used the scouring pad on, and on the right is as-received. The material cleans up really well, and seems to take on a bit of a 'brushed' look - which is expected, and it seems to roughen the surface a little. On the right, you can see a dull finish with lots of grime on it (no, this is not just from my fingerprints) - they just make it look a little worse. One thing to note, the scouring pad was catching on a bunch of the burrs, and being pretty much ripped apart by them. This used up a small corner of the pad, maybe a 4x2cm area, worn down by about 3mm is I had to guess. Hopefully the drill mounted versions that are meant for this type of work will stay together a bit better, but this looks very promising. It does not look like the scouring went through the nickel coating, but this should be something to watch out for (and maybe even go through the nickel and stainless steel on the bolted connections? - just an idea, maybe will evaluate further later).
We should get one with a bit of a finer pattern if possible (so the ‘brushed’ look on the surface has smaller grooves to get better contact for spot welding and the bolted series connections have a flatter surface to apply the pressure).
A couple local options to get the finishing pads:
This one is likely the best option: https://www.canadiantire.ca/en/pdp/mastercraft-surface-prep-discs-kit-2-in-0547501p.html#srp
https://www.canadiantire.ca/en/pdp/maximum-strip-it-abrasive-flex-disc-4-1-2-in-0541823p.html#srp
Final Results
I purchased the sanding pads from Canadian Tire and ran them over the pieces with my cordless drill.
The Blue pads worked great for removing the burrs on bottom side and the grey fine pad worked really well to remove all the contamination from the surface of the other side. The pads seem pretty tough, so I think they should be good to do all of the pieces, but are pretty cheap so if they start degrading, purchasing another set is no problem.
Just be careful to keep the pieces flat while sanding and be careful around the edges to make sure you don’t catch an edge with the sanding pads and bend it up. Putting it on a flat surface and doing the sanding from the top should work pretty good for this. Keep in mind that we don’t want to expose any of the steel underneath the nickel, so make sure to not sand too much.
Next step - sand all the pieces!