Hipping Aluminum Castings

[swall]

Does anyone know/have experience using HIP to repair surface porosity on machined surfaces of alumimum castings? I would envision TIG welding the porosity first, to give the HIP pressure something to push against in order to close up the pores. I don't have a specific need; it is more of a hypothetical question.

 

[Carburize]

Check the Bodycote web site

http://www.bodycote.com/?OB=60&POB=1&ID=329

They are world leaders in this technology and may have information posted.

 

[arunmrao]

I am not sure if porosity revealed on the surface can be closed by HIPPING. A cheaper means might be to use vacuum impregnation to cover the pores after machining.

 

[yates]

If it's important to get rid of the surface porosity at all costs (this would appear to be so if you're considering hipping) why not try IVD aluminum deposition followed by glass-bead peening. I can see no advantage in weld plus HIP over conventional repair i.e. dig it out and reload with weld.

 

[pavancp]

HIPing though removes most of the porosity, it changes the shape of the final product to some extent(pores have to be fed from somewhere!). So HIPping after machining probably is not a proper path.

 

[tripleZ]

Generally you're going to HIP your parts PRIOR to machining. As Pavancp stated, it will close up the porosity inherent in the part and will modify the size as a result. It also depends on the surface porosity that you're trying to remove. I press and vacuum sinter T15 blades to near net density, then send them out to be HIPed to close up any remaining porosity that exists internally. But the blades still have surface porosity (as it IS metal powder). They have to have about 0.005" taken off per side to get all of the rough cast removed. If this is what you're trying to achieve, I'd design your mold a little larger, HIP, then final machine. Impregnation will be difficult if you have no interconnected porosity. Things like resin will also be detrimental if the part is going to see any real source of heat. Bodycote is an excellent source for HIPing, and if you're looking at impregnation, try Casting Impregnators in Waukesha, WI. We've used them for some items before. They might be able to give you some additional info as well.

 

[swall]

Thanks for all of the responses. Pretty much what I expected.