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Machining Ally (LM25)

I have been working on a beam engine that I had cast from patterns I made last year. The original castings used Cast Iron and I produced a working engine and was happy. Unfortunately it was so heavy two men couldn't lift it. So I had the parts recast in Ally and started again, no problems with the 23 inch long beam, good casting and just a few holes to drill, likewise most of the other bits, "A" frames etc. However the cylinder block has me demented. I was going to machine it and fit a liner, but the machining has been a disaster. It looks like a ploughed field. Not joking, ruts up to 20 or 30 thou deep with lots od chatter. I tried different tools/tips/angles/speeds/fluid, all to no avail. However a foundry man told me that that was normal for this grade of metal castings and it needed heat treated . "Bung it in your gas oven" he said. Is this true and has anyone a more technical version of his comments. like temp / times / method of cooling. I would be greatfull if you have. Cheers John

Reply to
jag341
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cylinder

greatfull

Google 'solution treatment' nothing to do with dipping in liquid, but all to do with modifying the grain structure of the alloy.

AWEM

Reply to
Andrew Mawson

Ummm, not much of a surprise if it hadn't been heat treated. You can't machine raw aluminium castings. I'm kind of surprised you got as far as selecting an alloy grade and a foundry to cast it and never realised this. Raw cast alloy is like toffee.

You could do with a copy of "The Properties and Characteristics of Aluminium Casting Alloys" by Alcan Enfield Alloys if it's still available anywhere. Try Alcan I guess.

Anyhoo, looking in my copy. For fully heat treated condition LM25-TF heat the casting for 4-12 hours at 525C to 545C, quench in hot water followed by

8-12 hours at 155C to 175C and cool in air. It will then cut as clean as a whistle. Or just give it to a heat treatment company and let them slap it in with another batch.

No harm is done by exceeding the stated times so aim for the upper limits above for a big casting like yours.

Reply to
Dave Baker

You can get a copy of the old AlFed book here:

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Not quite as specific as the one Dave mentioned, but useful info on your subject from P64.

-- Richard

Reply to
Richard Shute

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