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How to fix porosity in an aluminum mold for roto-molding

Hi everyone,

Just looking for some insight into how I might fix/fill some porosity holes in a sand cast aluminum mold I am currently using for rotomolding plastic parts.

It seems after a few attempts at sand casting our mold we still can't escape the porosity from showing up after we've finished polishing the mold and it's leaving a pretty undesirable finish on our rotomolded parts.

Is there a good (preferably cost effective) solution to filling in all the showing porosity holes, and/or putting some sort of smooth coating on the aluminum mold to finish it?

Thanks!
- Anthony

Anthony Yap
Boat manufacturer - Kuala Lumpur, Malaysia
October 18, 2010

WE have thermally sprayed Aluminium onto cavities, holes of cast moulds. thermal input less than 80° C.

S.Guna
- Shah Alam, Malaysia
October 27, 2010

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December 11, 2010

Depending on geometry of surface, wall thickness, number and depth of pores and other relevant parameters additional options to the ones already mentioned may include:
A) Same metal than mold:
1- Micro TIG welding with aluminum rod
2- ESD welding with Al rod

B) Different metal than mold:
3- Brush plating with special Ni+alkaline Cu+acid Cu+Ni
4- Conventional electroplating (cyanide+acid Cu+Ni)
5- Alkaline EN+acid EN+acid Cu+EN.

Intermediate and final dressing of surface will most surely be required.
G. Marrufo

Guillermo Marrufo
Monterrey, NL, Mexico

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Thanks for the responses guys, lots to think about.

Thanks again guys.

Anthony Yap
- Kuala Lumpur, Malaysia
December 12, 2010

Just to add another possibility you could consider vacuum impregnation to fill the porosity before plating to give your final finish.

Brian Terry
Aerospace - Yeovil, Somerset, UK
December 14, 2010