Aluminum Tooling Wear

[Brad1979]

I have a part that's been in production for a few years. Its made out of a 35% glass filled Zytel. The mold tooling is aluminum. The last shipment of parts we got in were fine and now there is one feature on our part that is out of tolerance (by about 0.003" on a .750" diameter bore) on the parts they are making for us right now. Our supplier says there is material wear on the aluminum tool. Does anybody know if it is pretty common for a tool to just all of a sudden show signs of wear? I was kind of expecting the tool to wear down more gradually than that. Is this typical?

 

[MikeHalloran]

My favorite molder, now unavailable for comment, made many aluminum molds for me, and produced many thousands of parts from them, in that exact same material, and similarly abrasive stuff.

He was never able to predict, or willing to guarantee, how many parts a given mold would produce before needing work; he said sometimes a few hundred, sometimes thousands, and then something would wear.

His way of dealing with the problem was what you might call lamellar molds. E.g. instead of sinking a blind cavity into a monolithic block, he would bolt and dowel together a plate with a through hole, and a plain plate, and so forth. So he could remove and replace single features of the mold. Each mold had many components, all of relatively simple geometry, all machined to precise tolerances, and all replaceable.

My hypothesis is that machining aluminum work-hardens the surface, ever so slightly, to a very shallow depth, just as an artifact of the cutting process, and not overtly controlled. When that 'skin' wears away, it exposes the softer aluminum underneath, which wears at a much higher rate and becomes noticeable in short order.

You could disprove my hypothesis if you can find parts from prior lots that exhibit gradual wear of the feature in question. I don't think you will.




Mike Halloran
Pembroke Pines, FL, USA

 

[dgallup]

Aluminum tooling for injection molding glass filled nylon is usually considered prototype or very short run tooling. I'd say you did very well to get a few years of production out of it. Usually the wear out will be confined to a few places where the flow velocity is high or it has to make sharp bends. Usually nobody notices until the parts stop working.

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[MacGyverS2000]

My hypothesis is that machining aluminum work-hardens the surface, ever so slightly, to a very shallow depth, just as an artifact of the cutting process, and not overtly controlled. When that 'skin' wears away, it exposes the softer aluminum underneath, which wears at a much higher rate and becomes noticeable in short order.

I take very soft copper sheets and form them to a relief pattern underneath. Once formed, I hit it with a fast-rotating ball (think Dremel, though it's really my CNC router) that finalizes the creases and heats up the spot as it passes over. This hardens the surface and I don't have to worry about minor scratches. Aluminum should do the same, so you're likely on the right track in your thinking...

Dan - Owner

http://www.Hi-TecDesigns.com

 

[Paulkuklych]

Injection moulds made from aluminium are difficult to maintain. They require a lot more attention and care compared to steel moulds. Clamping force must be as low as possible and the mould must be cleaned everyday so that plastic residue does not build up and damage the shut off faces. Having the wrong processing parameters can also damage the mould and consequently the part dimensions too. I am not surprised you are having problems after a few years of production. That's a good life span.

Paul Kuklych