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    Default Mould reconditioning help required.

    Hi guys

    I work for a small rubber moulding company and regularly have to repair or replace moulds that have been damaged or just wore out. Quite often the mould could be repaired if the the damage was fixed seamlessly.

    The moulds are usually made from bright mild steel and have a working temp of 175c. They are under lots of pressure and are cleaned by glass bead blasting. I have means to MIG, MMA and silver solder in the workshop. The crux is that many of the moulds have sharp edges/corners that either round of or have pockets when soldered/welded.

    The ideal solution is a softer than mild steel filler that I can bond to the mould preferably without melting the base metal. That way I can build up the repair and machine smooth. These repairs are sometimes just to get one rushed job done then a new tool is ordered. Mig spatter is also a problem.

    At the moment I'm looking for aluminium/steel rods for the stick welder to try out. I'm thinking if they exist and are softer than mild steel they might enable me to sculpt the mould details as required.

    Sorry for the long winded post. I'd be grateful for any suggestions/tricks of the trade you can give me. These repairs could be as little as 0.005" to 0.020" thick so things can be quite tricky at times.

    Cheers

    Tallen

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    The first questions are is the mold carbon steel or stainless, are they hard chrome plated or nitrited? Most of the mold work I have seen done was with TIG. MIG and stick are for laying down a lot of metal, not what you want to do.

    Tom

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    Hi Tom

    The moulds are just mild steel (low-medium carbon), none are stainless or chromed. EN24 is our usual steel grade and our volume production moulds are nitrided. We are growing enough to justify chromed/tougher moulds in the near future.

    The query is geared more toward repairing one of our custom moulds. I have thought about tig but I don't currently have one. Ideally I'm looking for a rod I can use with the equipment I have to complete a current job quickly (today or the next couple of days).

    I can purchase a tig of it's the right way to go but I'm time limeted on this job.

    Cheers

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    You have mentioned that you can silver-solder: if you have ox-acetylene torch, you should consider brazing with a bronze rod, which flows much less than silver and is better for build-up. Plenty of choices in the alloys, but I don't feel I have the expertise to guide you to one in particular and, if time is a factor, you're probably better off with a good-enough rod available locally/quickly.

    Perhaps, asking a local welding shop what is their favorite bronze rod for filling (and, maybe, buy some from them) could be a good starting point.

    Paolo

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    Have a look at the Eutalloy Ultra Jet metal deposition system potentially very precise

    YouTube
    Last edited by Tray; 10-31-2019 at 08:48 AM. Reason: typos always typos

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    Quote Originally Posted by Tray View Post
    Have a look at the Eutalloy Ultra Jet metal deposition system potentially very precise

    YouTube
    If the Op can't get the company to buy a TIG unit, how would they justify this ?

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    I would definitely suggest that you invest in and learn to run a tig welder. The newer machines can use a very low starting amperage and will allow you to build up very sharp corners without too much dmage. If you are welding on nitrided surfaces, make sure that you do not get the arc on the parent material, only on the bead from the rod.

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    Thanks for the replies guys! Lots of good ideas.

    Before posting I had looked a lot at different technologies to overcome this problem, many were unsuitable due to current time frame. In fact I had to bite the bullet and start the repairs today. In the end I chose to run with the mig.

    To start I cut/shaped some 0.010" shim to protect adjcent faces from spatter. These faces were also sprayed with anti spatter and the shim too. Once the shim was in place I ran a low temp bead around the part right on the sharp corners. I made sure the bead sat proud on both faces to enable milling later. Once the entire perimeter was surrounded I began to padweld, building up the internal area. It's a thick part so I wasnt too worried about distortion. The built up area is a two inch strip covering half of a five inch diameter. Sadly it cant be put in a lathe.

    Once the welding was complete the shim was removed and once cooled the part was set up for milling. I used a 10mm carbide slotdrill to mill the weld down and was reasonably happy with the results. There were a few pockets left which I can spot weld an buff down. The mould will be bead blasted so there is a little forgivness on finish.

    I still need to mill 3 edges but the diameter is complete. The mould is for an outer seal (looks like a pair of headphones).

    I'm planning to buy a tig and get my hands on some silicone bronze. It's basically a brazing process so I can repair without melting the base metal. The metal deposition looks awesome but the tig has much more utility vs price.

    Big thanks for all the replies guys, I may have gone with the mig on this one but you have given me a good idea how I should prepare for the future.

    Cheers

    Tallen

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    Hi Tallen:
    I have to say I'm super impressed.
    I do quite a lot of mold repair (for plastic injection molds) and I would be soiling my panties before I tried to MIG weld them.
    Give yourself a lot of credit for ingenuity and for "Can-Do" attitude and big brass balls too.

    I concur with those who recommend a nice little inverter TIG like a Miller Dynasty... they are apparently great for mold welding although I've never had the pleasure of using one.
    For the kind of repairs you describe TIG brazing with silicon bronze rod is also a good way forward as others have commented.
    It will take some playing around but if you can do a respectable job with a MIG, you'll be tickled to death with what you can achieve with a nice TIG.

    In my shop I use a laser welder; way overkill for what you're describing and totally unsuitable for anything larger than a repair that's about the size of a small coin.
    Attached are a few pictures of mold welds from my shop.
    These are too small to even try to TIG weld, unless you're a real master with torch control, but with a laser welder, they're not all that hard.
    Kind of shows you the limits of what's possible though and if you get good with micro-TIG, you can get pretty darn close.
    You can also cover large damaged areas which I cannot do with the laser.


    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining
    Attached Thumbnails Attached Thumbnails dscn3221.jpg   dscn1058.jpg   dscn2905.jpg  

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    Quote Originally Posted by Tallen View Post
    Thanks for the replies guys! Lots of good ideas.

    Before posting I had looked a lot at different technologies to overcome this problem, many were unsuitable due to current time frame. In fact I had to bite the bullet and start the repairs today. In the end I chose to run with the mig.

    To start I cut/shaped some 0.010" shim to protect adjcent faces from spatter. These faces were also sprayed with anti spatter and the shim too. Once the shim was in place I ran a low temp bead around the part right on the sharp corners. I made sure the bead sat proud on both faces to enable milling later. Once the entire perimeter was surrounded I began to padweld, building up the internal area. It's a thick part so I wasnt too worried about distortion. The built up area is a two inch strip covering half of a five inch diameter. Sadly it cant be put in a lathe.

    Once the welding was complete the shim was removed and once cooled the part was set up for milling. I used a 10mm carbide slotdrill to mill the weld down and was reasonably happy with the results. There were a few pockets left which I can spot weld an buff down. The mould will be bead blasted so there is a little forgivness on finish.

    I still need to mill 3 edges but the diameter is complete. The mould is for an outer seal (looks like a pair of headphones).

    I'm planning to buy a tig and get my hands on some silicone bronze. It's basically a brazing process so I can repair without melting the base metal. The metal deposition looks awesome but the tig has much more utility vs price.

    Big thanks for all the replies guys, I may have gone with the mig on this one but you have given me a good idea how I should prepare for the future.

    Cheers

    Tallen
    Very nicely done sir.

    What wire dia ?
    s-6 solid wire ?
    What gas ?

    I was doing fine work with a 120 vac "lunchbox" Lincoln MIG with .023 wire, I hold the end of the gun (the nozzle) like a TIG, use other hand to actuate trigger.

    I was going to remove the trigger, and extend the wires to a small remote switch
    for easier usage. An aftermarket MIG gun manuf will sell me a straight small MIG gun with a remote trigger (hold it like a pencil)

    Maybe you could modify yours until you get the proper TIG.

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    Hi Marcus

    Shocked at the size of those beads! That's tiny detail. I'm going to check out a few videos on lazer welding after this!

    I have to admit I was not relishing the thought of repairing this one but all in all it went better than I expected. We use compression moulds so cheaper, sometimes crude and probably simpler than your plastic injection moulds so a little less risk if I mess it up hehe.

    Cheers

    Tallen

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    Hi Doug

    We are pretty bare bones at the moment so I'm using what I have to hand.

    1mm wire with argoshield co2/argon mix

    It's not very pretty but it gets the job done. I intend to tool up better in the near future. The welder is also one of my most hated pieces of equipment as it seems to compensate slightly on every setting. It's as if it adjusts its wire feed depending on the current I choose. This makes fine tuning of the power/wire a pain. I honestly don't know if it's how the welder is designed to dump things down or a fault. I much prefer full control over the wire feed as it yields better results.

    Your suggestion about small mig gun sounds interesting. Some of the moulds are pretty thick, would that cause many problems with such fine wire?

    Thanks

    Tallen

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    Hi Tallen:
    The things to remember specifically about mold welding is that you have a couple of very different considerations than regular fabrication or structural welding.
    One is obvious...you need to place a bead exactly where you intend and you can't have divots at the ends of the weld bead (places where you've burned the corners away for example, or craters in the weld bead from starting and stopping)

    The second, and far less obvious is that the strength of the weld typically doesn't matter nearly as much as it does in a structural weld that's expected to carry loads.
    You are only adding material that is missing, and so long as it sticks good enough to survive molding forces it is good enough.
    This is your saving grace because it means you can get away with some severely frowned-upon practices in order to avoid burning away the corners, and one of those is running beads that are technically way too cold.

    Two things matter in this regard:
    First is the total energy you put into the weld and it manifests as heat.
    Second is the energy density you put in the weld pool as you are making the weld.

    The laser puts in very little total energy but it has immense energy density.
    That means it can take a huge lump of steel and melt only a tiny corner of it without heating up the whole block.

    Contrast that with any other welding strategy:
    TIG, MIG and stick is next down on the list and they are a long way down compared to the laser.
    Oxy acetylene is even further down the list...you need to heat the whole damned block almost to red heat to weld successfully because you can't get the heat in fast enough to melt the area you care about.

    Of those other processes, TIG is the most controllable in terms of where you put a bead, and how small the smallest you can place is because it still has usable energy density, just not as intense as the laser.

    The trade off, as the energy density and the total energy you put in gets smaller, is that the weld gets crappier because the block is sucking the heat back out too fast to form a decent puddle:
    It's more grainy
    It has lower adhesion to the parent metal.
    It has more structural defects like voids and cracks.
    The transition from parent metal to filler is more abrupt.
    The parent metal will chill it, effectively hardening the weld but in an uncontrolled way.

    So even with TIG, the accepted protocol is to preheat the entire mold insert, then weld it and then slow cool it, but with a laser you can typically ignore all that and still get usable repair welds...you just can't rely on them to be decently strong welds.
    It's less of an issue with low carbon steels than with tool steels, but the principle remains.

    So for all of what you are doing, TIG gives the best compromise, but the comment you made about fine wire and thick molds is certainly relevant.
    Fortunately you don't need to care all that much about the strength of your welds so long as you are always aware of what they are going to be asked to do.
    Filling a defect...no sweat.
    Holding bits together against compression forces...not so much.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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    That sounds good, as far as the small MIG gun, IIRC they are limited to about 120 amps, and it sounds like your running much lower than that.

    One thing I wanted to try (but never got round tuit) is adding a large amount
    of electrolytic capacitors to the welding machine output.

    Ther used to be a system that, (I think) did this (the patent is very mis leading)
    called the "rapid arc" and it was used for overlay applications.

    It claimed less dilution with the parent metal.

    As we are running short arc, the claim was that all that capacitance would allow
    much greater short circuit current flow, the wire melting and not the base metal
    as much.

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    A trick I have see to get rid of undercut is to hammer the weld bead
    This will lower the weld but raises the base metal a bit

    Peter

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    Quote Originally Posted by Peter from Holland View Post
    A trick I have see to get rid of undercut is to hammer the weld bead
    This will lower the weld but raises the base metal a bit

    Peter
    Problem with that is that if there isn't a good bond, you risk knocking the weld off.

    Tom

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    Quote Originally Posted by TDegenhart View Post
    Problem with that is that if there isn't a good bond, you risk knocking the weld off.

    Tom

    You could also see that as a advantige A test for at least some bond

    Peter

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    Quote Originally Posted by implmex View Post
    Hi Tallen:
    I have to say I'm super impressed.
    I do quite a lot of mold repair (for plastic injection molds) and I would be soiling my panties before I tried to MIG weld them.
    Give yourself a lot of credit for ingenuity and for "Can-Do" attitude and big brass balls too.

    I concur with those who recommend a nice little inverter TIG like a Miller Dynasty... they are apparently great for mold welding although I've never had the pleasure of using one.
    For the kind of repairs you describe TIG brazing with silicon bronze rod is also a good way forward as others have commented.
    It will take some playing around but if you can do a respectable job with a MIG, you'll be tickled to death with what you can achieve with a nice TIG.

    In my shop I use a laser welder; way overkill for what you're describing and totally unsuitable for anything larger than a repair that's about the size of a small coin.
    Attached are a few pictures of mold welds from my shop.
    These are too small to even try to TIG weld, unless you're a real master with torch control, but with a laser welder, they're not all that hard.
    Kind of shows you the limits of what's possible though and if you get good with micro-TIG, you can get pretty darn close.
    You can also cover large damaged areas which I cannot do with the laser.


    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

    Off topic but is there much money in welding molds or is most of it done in house? I ask because I could easily do that by hand with TIG.

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    Quote Originally Posted by Hardplates View Post
    Off topic but is there much money in welding molds or is most of it done in house? I ask because I could easily do that by hand with TIG.
    Google Maps

    Market is kinda saturated here.....

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    Quote Originally Posted by digger doug View Post
    Google Maps

    Market is kinda saturated here.....

    I'm a few hours east but copy that. Was just wondering as I used to weld mostly exotic materials which is easy money at a elevated hourly rate if you know what your doing (which most people don't when welding with exotics).....the hard part is finding the work.... Was just curious

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