I have a medical component that goes into a laparoscopic instrument. We have the component coated with a DLC (Diamond-Like Carbon) coating. We're having an issue with the surface finish of the part after coating. The coating we're using seems to be a little rougher than we'd like, so we're investigating polishing the steel before coating. Right now, we are using 440A and 17-4 Stainless Steel. We're looking to get the Ra value to ~.10 by incorporating a polihing/buffing process on our parts. The parts are very small (2" in length, .250" in width, and two .040" arms that extend from one end of the part to the other)(Envision a V-Shape when you think of the part geometry). Anyway, does anyone know of the proper process to polish these parts to the Ra value that we're looking to achieve? Our current Ra value is ~.65. If anyone knows of a particular vendor that I should get in contact with, I'd really appreciate any information I can get. Thanks so much!!!
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Polishing SS Parts
- Thread starter Vig16
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What method is the manufacture using for the DLC coating? What about Electroless Nickle?
Heckler![[americanflag]](/data/assets/smilies/americanflag.gif "[americanflag] [americanflag]")
Sr. Mechanical Engineer
SWx 2007 SP 4.0 & Pro/E 2001
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This post contains no political overtones or undertones for that matter and in no way represents the poster's political agenda.
Heckler
Sr. Mechanical Engineer
SWx 2007 SP 4.0 & Pro/E 2001
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_`\(,_
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This post contains no political overtones or undertones for that matter and in no way represents the poster's political agenda.
17-4 laproscopic instruments? Made via metal injection molding potentially? Not quite sure about the 440A, but we do MIM some 17-4 parts. Are you trying to hit all of the surfaces? If it is a MIM part, you're going to likely have to take a few thousandths off of the surfaces to get past the "grainy" texture.
If it is a powdered metal component, the steps you take may be a bit different from that of a machined component.
If it is a powdered metal component, the steps you take may be a bit different from that of a machined component.
- Thread starter
- #6
The process that the vendor uses is PVD. We're looking into new coatings that we can use, so the Electroless Nickel might be an option. Is Nickel a problem in the medical industry with allergic reactions to the element though?
The metals are first EDM prepared to get the outside profile of the component, then there are machined features in the part. None of the parts are MIM prepared.
Also, we are looking to hit all the parts of the components, which is the issue we're having. The coating gets into the easily visible surfaces, but the surfaces that are on the sides of the arms are lacking coating from time to time. This is why we're looking for a polishing process with small media to get all areas of the parts.
Thanks for your input guys, I really do appreciate it!
The metals are first EDM prepared to get the outside profile of the component, then there are machined features in the part. None of the parts are MIM prepared.
Also, we are looking to hit all the parts of the components, which is the issue we're having. The coating gets into the easily visible surfaces, but the surfaces that are on the sides of the arms are lacking coating from time to time. This is why we're looking for a polishing process with small media to get all areas of the parts.
Thanks for your input guys, I really do appreciate it!
What is the intent of the coating? Hardness? Matte Finish? Keeping sharp edges?
Without knowing any of this... I would say consider AlTiN (Aluminum Titanium Nitride)... If you use a certain ratio of Aluminum to Titanium it will give a dark gray/black finish, it will keep a sharp, and you can electropolish beforehand for a better surface finish after coating. In any case, the surface roughness after the coating will reflect the surface roughness before coating.
If you can, stick to 17-4 PH when using a heated coating. You can bring it to a higher temperature than you can with 400 Series, and it creates a better reaction and a tougher coating.
Good Luck.
V
Mechanical Engineer
"When I am working on a problem, I do not think of beauty, but when I've finished, if the solution is not beautiful, I know it is wrong."
- R. Buckminster Fuller
Without knowing any of this... I would say consider AlTiN (Aluminum Titanium Nitride)... If you use a certain ratio of Aluminum to Titanium it will give a dark gray/black finish, it will keep a sharp, and you can electropolish beforehand for a better surface finish after coating. In any case, the surface roughness after the coating will reflect the surface roughness before coating.
If you can, stick to 17-4 PH when using a heated coating. You can bring it to a higher temperature than you can with 400 Series, and it creates a better reaction and a tougher coating.
Good Luck.
V
Mechanical Engineer
"When I am working on a problem, I do not think of beauty, but when I've finished, if the solution is not beautiful, I know it is wrong."
- R. Buckminster Fuller
- Thread starter
- #8
We're coating mostly to assist with friction between mating parts, but also a little for hardness to prolong the life of the steel. We've experimented with AlTiN, but the coating itself was little rougher than the current DLC coating that we're using. What I mean by this is that the mating part which runs along our other part ends up getting hung-up in the coating during use, thus causing a delay in the instrument. The vendor for the AlTiN suggested a polishing process on our virgin parts (pre-coating) to bring the surface roughess down to an Ra of 0.1. We electropolish the parts before coating, so that's obviously not polishing our parts enough. This is why I believe we need a polishing process with media to get into the smaller areas of the part...
Hmm, sounds tricky. Maybe a note to ask your PVD supplier. Everything that I've been told is that PVD is a line of sight coating method. If you don't have a direct line of sight to the sides of the arms, you're bound to have thinner coating in those areas.
For polishing...check Extrude Hone's website. They have something called orbital flow machining or surface flow machining. The right slurry and motion might polish your parts in the manner in which you need. I've never used it, so I can't speak for its effectiveness.
Can you change coating types? PVD is nice when you have a limited temperature window, but there are CVD coatings out there that might do the trick and provide better depth/penetration. Depends on your applicable window I guess, and whether the parts are likely to distort/warp. With the CVD, your surface finish should be less of an issue.
For polishing...check Extrude Hone's website. They have something called orbital flow machining or surface flow machining. The right slurry and motion might polish your parts in the manner in which you need. I've never used it, so I can't speak for its effectiveness.
Can you change coating types? PVD is nice when you have a limited temperature window, but there are CVD coatings out there that might do the trick and provide better depth/penetration. Depends on your applicable window I guess, and whether the parts are likely to distort/warp. With the CVD, your surface finish should be less of an issue.
You may also wish to check into ultra high purity surface finishing processes if you are trying to get a good Ra.
Matt
CAD Engineer/ECN Analyst
Silicon Valley, CA
sw.fcsuper.com
Co-moderator of Solidworks Yahoo! Group
Matt
CAD Engineer/ECN Analyst
Silicon Valley, CA
sw.fcsuper.com
Co-moderator of Solidworks Yahoo! Group
You might want to look at:
They have a variety of very good finishing processes that might get you what you need.
They have a variety of very good finishing processes that might get you what you need.
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