Letter 30001

Passivating Laser Marked 15-5 PH Stainless Steel Parts [Connecticut] 

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We are manufacturing components made from 15-5 PH Stainless steel for use in some of our aerospace assemblies. They require laser marking and passivating. These parts cannot be submerged in a liquid solution thus require passivating with a cotton or foam swab over the markings. A company has created a liquid solution for us made from water, potassium dichromate, and phosphoric acid. Not sure if this is a viable solution or if there is a more effective process.

Does anyone have any information on passivating 15-5 PH in terms of surface preparation and passivating the laser marked area?

Thanks,

Gary

Gary P [last name deleted for privacy due to age of posting]
Manufacturing Engineer (Aerospace engineering) - Wallingford, CT, USA

I would look at two other approaches. Check with Stellar Solutions, who advertises here, possibly their citric based gel would be a more practical solution to the problem. Another approach would be to talk to the brush plating companies. At least one has a brush electropolish which looks like it would be a good way.

James Watts
- FL

Thanks for your input James, I will look them up.

Gary
- Wallingford

Thanks a lot for the information.

Gary
- Wallingford

Gary, why the heck would these require passivation? The way to do assemblies, as you know, is to passivate the piece parts before you assemble. Unless there's machining on these parts, through which stray iron particles can get onto the surface of the 15-5, then the original passivation is still good.

When we have to machine assemblies, we use carbide tooling or grinding wheels dedicated to stainless steels, or some other such controls to make sure we don't need to passivate again. Mere laser marking will NOT affect the surface such that it'll require passivation again.

Does your company have evidence that laser marking WILL affect 15-5 corrosion resistance? I've never seen such, and we've been laser marking for decades...

Lee Gearhart
- East Aurora, NY

Lee, thank you for your information. Before I started working here, these laser marked parts were sent out for corrosion testing. I'm told the laser marking did corrode, (without passivation over the marking). I think I will run some tests myself. Anyway, the parts are passivated after all machining, except for laser marking due to lot control. I need to rub a passivating solution over the laser marking. Your saying the laser marking has no effect on the original passivated surface, and does not require re-passivating? Does it matter how deep the laser marking is?

Thank you

Gary P [last name deleted for privacy dsue to age of posting]
- CT

Depending on the type and power of the laser you will normally destroy the properties of the steel due to the high heat of the laser etch. This is a major problem in the surgical and orthopedic industries which has been resolved with the products mentioned above. Many of these assemblies must be laser etched AFTER assembly, and then the laser mark will rust in autoclaving or other disinfecting processes, or in corrosive atmospheres. The weakest part of the device for corrosion will be the laser etch. This is why they use a paste on the laser etch area after assembly, but it must be a product that passivates the etch without totally removing the desired black color. Let us know if we can help.

Lee Kremer Stellar Solutions, Inc. Algonquin, IL, USA

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