Laser Marking - slag residue fouling carbide forming tools
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  1. #1
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    Default Laser Marking - slag residue fouling carbide forming tools

    We are developing a forming tool that takes polished stainless strip and creates cylinders with it. We mark the strip with a part number and feed it through a forming section (forcing the strip into a flat angled piece of carbide) which causes it to curl into a cylinder and then we part it off.

    The problem is that we are using a laser marking system and as the mark is forced into the carbide to form the radius bend, the laser mark scrapes along the carbide and the dark “slag?” powder that makes up the mark begins to build up on the carbide and eventually creates a hard lump on the surface of the carbide and begins to make scratches in the part.

    We haven’t tried to lubricate the strip yet, but will try that next. However any lube we add will likely need to be washed off so we would like to avoid that if possible.

    Anyone dealt with blunt forming of stainless steel strip that has been laser marked before forming? We don’t want to have to deal with laser marking after forming.

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    Laser marking in air ?

    I just worked on a laser welding machine, they used an argon shield.

    Don't forget the backside if the SS get's discolored on the back.

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    Diamond like carbon (DLC) coating on the carbide bending block? It's supposed to be slicker than Teflon. It's dry, so no cleanup. I'm not sure about its service life though.

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    We built a CNC laser welding machine last year and used shielding gas with good results. It didn’t occur to me to use a shielding gas when laser marking. The machine works great until we fire up the laser then within 50 cylinders everything goes to crap.

    We are going to attempt a stepwise effort today to see if we can reduce the production of abrasive particles by . . .

    1.) pre cleaning strip with isopropyl alcohol before marking
    2.) post cleaning after marking (duct tape an electric toothbrush and air blast?) to the line.
    3.) add shielding gas to the laser area

    We didn’t anticipate that laser marking would introduce such a significant barrier to finishing this machine and getting it approved for production.

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    Duct tape an electric toothbrush, very funny..! Yes, I think that post laser cleaning station is key. I doubt surface contamination is the problem, more likely it’s the actual metal constituents oxidizing that are the problem, unless your stock is really filthy. I don’t know how easily you can add an argon envelope to that station, if it’s an easy add on it might take care of the problem, but I bet it’s also going to reduce the legibility of the marking also. (As will post cleaning) might need to up the laser power.

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    I"ve heard of (but never used) oils used in stamping industry called "vanishing oils" - which as one would expect are meant to provide just barely enough lube for a metal forming operation and then evaporate. (I heard about them in the context of stamping - but the project went a different way.)

    Why wouldn't iso alcohol work as a post-marking step?

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    Quote Originally Posted by motion guru View Post
    We didn’t anticipate that laser marking would introduce such a significant barrier to finishing this machine and getting it approved for production.
    This is a good example of why new product development is not a totally predictable, waterfall-planning-process, one-and-done, "put an MBA on it" sort of thing.

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    Quote Originally Posted by sfriedberg View Post
    This is a good example of why new product development is not a totally predictable, waterfall-planning-process, one-and-done, "put an MBA on it" sort of thing.
    We call these red team jobs. Bleeding edge development that we invariably wind up losing money on. The problem is that when you don’t plan enough contingency, you lose way more money than you dreamed possible. The long view is that you have future sales that allow you to recover those losses with a reasonably standardized product.

    2019 has had too many red team jobs and not enough repeat work . . . certainly a year we won’t forget soon.

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    Likely impractical for some reason, but emboss a shallow cleaning knurl or transverse (or maybe better oblique) rib pattern on every 20th part. Those parts discarded after scrubbing off residue from carbide.

    Denis

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    I assume this is a fiber laser for direct metal marking without spray. What type of mark are you doing? Are you actually etching, or just doing carbon development (some laser companies confusingly call it annealing)?

    With the little laser marking I've had done, the former leaves a rough surface with the black stuff you're talking about. If you can get the carbon development cycle down right, it leaves a dead smooth surface.

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    Quote Originally Posted by DanielG View Post
    I assume this is a fiber laser for direct metal marking without spray. What type of mark are you doing? Are you actually etching, or just doing carbon development (some laser companies confusingly call it annealing)?

    With the little laser marking I've had done, the former leaves a rough surface with the black stuff you're talking about. If you can get the carbon development cycle down right, it leaves a dead smooth surface.
    Mark includes a part number and manufacture’s logo, it is dead smooth.

    The laser marker is a Keyence unit. We’re going to focus today on using a hollow font and logo to cut down on heat generation and see how that goes. The mark is fine on large radius parts, but when forming small radius parts, the stresses are high and the laser mark seems to scrub on the carbide more creating a fine powder that builds up and starts scratching subsequent parts.

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    What happens if the mark isn't continuous in the direction of rolling, and is instead made up of dots or transverse lines. My guess is that regular stainless is more ductile than the marked stainless. The gaps in the mark could allow localized yielding. No idea if this would work, or if the mark would be acceptable to your customer, but it would be an inexpensive fix and it wouldn't add moving parts or residue.

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    Have the standard TiCN or TIN PVD coatings been tried?
    If a large piece of carbide tell your coater where the work is being done and that none elsewhere matters to keep the price down.

    A carbide grade with additives to provide a resistance to build up? (C-5,C-6,C-7)
    How good is the surface finish on the top side so that things won't stick?
    A rake change on the top surface to provide more sliding in the cut to remove any buildup?

    That leftover on the surface by the laser is simply rock hard but it also makes the mark more readable.
    If you are doing box codes removing or cleaning this may create problems for the end customer's readers.

    Bob (very wild ass guesses here, have never done this slitting let alone the laser problem)

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    Hi Bob,

    You will likely be contacted by this customer after the first of the year as they get very little help and poor service from their existing carbide supplier and we passed your contact information to them yesterday.

    Today we had some success by adding lubrication. Prior to lube we could make 100 parts (with no laser mark) and all parts were perfect. Turn on the laser mark and things went south within 5-10 parts.

    We then dressed the carbide forming tool with a diamond debur tool and then restarted with lube on the stainless. We used a non-soap based grease applied in a very thin film. 80 parts later and not a scratch. In fact the forming forces go down quite a bit with the lube. Now we have to figure out a way to apply the lube sparingly as it only takes a very little to solve the problem.

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    Pulse sprayer just before the carbide elements? How much room do you have to play with, can you mount a lube reservoir where it can be accessed and refiled safely?

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    No room anywhere near the carbide tooling - but a foot away on the material infeed (after the laser) grants a few inches of space . . . looking at Nordson Liquidyn P-Jet valve now. I want to be able to control volume to 0.02 - 0.05 ml . . . I can add a stainless doctor blade after the dot dispense location to spread the lube over the laser mark to 0.001" thick which should be plenty.

    Liquidyn P-Jet CT Valve Dispensing Berulub Grease - Dispense Test Videos - Nordson EFD Video Gallery

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    Quote Originally Posted by motion guru View Post
    Mark includes a part number and manufacture’s logo, it is dead smooth.

    The laser marker is a Keyence unit. We’re going to focus today on using a hollow font and logo to cut down on heat generation and see how that goes. The mark is fine on large radius parts, but when forming small radius parts, the stresses are high and the laser mark seems to scrub on the carbide more creating a fine powder that builds up and starts scratching subsequent parts.
    Any more detail available on the laser source?

    If it's a nanosecond fiber laser (which I suspect it is), you should be able to get a clear, indelible mark with zero height. If the process isn't dialed in then you can get what you describe (carbon and alloy oxide residue on the surface).

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