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3D printing for investment casting article MEW 300

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Buffer09/01/2021 11:23:22
238 forum posts
102 photos

Neil

I thought this was a very interesting article and its something that I will definitely be trying. I had no idea that plaster of paris could be used for this.

Could you just explain a bit more about using a metal wire across the spout to hold back dross. Does it all just stick to the wire and the brass flows out under it?

Thanks

noel shelley09/01/2021 13:01:40
484 forum posts
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Very interesting idea Neil. To assist in the reduction of loss of zinc when melting brass, crushed charcoal (pea sized) works well. It also reduces the likelyhood of oxygen being absorbed, copper has an affinity for this element, this also applies to bronze. Any dross or the remains of the charcoal is skimmed off with a metal disc welded to a handle immediatly before pouring. Old plumbing fittings are ideal for melting. Preheat any metal before placing in the crucible to be ABSOLUTELY sure there is no moisture trapped in it ! For vastly improved success rates a dip pyrometer and display need to be used. These are available reasonably cheaply in the usual places. The probe is a K type inconel sheathed of .5m long, RS or other. For small or thin section items a temp of 1030*c and NEVER above 1050*c for brass and not more than 1150*c for bronze. For thick solid lumps 1000*c to 1020*c.brass, 1100*c bronze. Brass will start to melt at 900*c. Zinc boils at 927*c

Where the mold is nonporous, proper and complete burning out of the the pattern material is VITAL ! A failure to observe this point may well ruin both the mold and your day ! Noel.

Buffer09/01/2021 13:15:20
238 forum posts
102 photos

Noel. Would the result of pouring metal on pla be similar to water?

noel shelley09/01/2021 14:29:35
484 forum posts
14 photos

Hi Buffer, The molten metal, at a suitable pouring temp will pour like water, though less fluid. The PLA MUST be burnt out after the mold has been made. Look up" lost wax casting " This is a similar process though the the pattern making is different. An interesting process is that known as "polystyrene molding". Hope this helps, Noel.

Bo'sun09/01/2021 15:55:22
395 forum posts

Will 3D printing produce a decent surface finish for investment casting? I know some who have tried making patterns from a 3D printer for Petrobond (or green sand for that matter) casting, but the rough surface finish inhibits pattern withdrawal. I'm guessing that post print surface finishing isn't possible?

Buffer09/01/2021 16:57:33
238 forum posts
102 photos

Noel I don't think I made myself clear with my question to you. Are you saying that if the molten brass touches any left over PLA in the mold then there could be an explosion similar to molten metal on water?

JasonB09/01/2021 17:01:41
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You can improve the printed surface by fuming, sanding, painting etc or get a better quality printer.

If the metal toughes left over plastic the gasses from the burning plastic could make the metal bubble and spit it out the mould.

Edited By JasonB on 09/01/2021 17:03:27

Michael Gilligan09/01/2021 18:13:33
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Interesting to recall that we were discussing the possibilities in early 2014

**LINK**

https://www.model-engineer.co.uk/forums/postings.asp?th=92880&p=2

MichaelG.

noel shelley09/01/2021 19:42:17
484 forum posts
14 photos

Buffer, Not so much metal on water, as HANDGRENADE !

Jason, see above ! Lead or Die casting alloy is bad enough, brass or bronze - start running NOW !

A paster of paris type mold will absorb molten PLA which must be vapourised and driven off before ANY attempt is made to pour metal in ! The PLA Must first be melted out then BURNT out !

I have often been asked to cast from 3D printed patterns ! Only with a lot of remedial work are they normally any good. The problem is that unless the patterrn is PERFECTLY smooth will it release from the mold. The tiny ridges/layers will hold the sand and leave a poor surface or the mold will break up leaving ragged edges.

The idea seems on the face of it to be a pattern makers dream but at the level of hobby machines the finish is not good enough ! Sorry chaps ! Noel

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