Detecting porosity in Aluminium Castings

[genericmech03]

Hello,

I thinking of using ultrasonic or x ray porosity detectors to pick up porosity in aluminum die castings. The porosities are located under the surface of a raw casting so we currently only find them after we machine them. We would like to detect porous parts before wasting money on machining. The material thickness of the aluminium casting ranges from 25mm to 3mm and the porosities we want to detect range roughly from 0.4mm to 2.0mm in diameter. The surface of the casting would have a degree of roughness (a maximum being Ra=8) and is also curved, smallest radius being 3mm.

Has anyone had any experience, success or otherwise regarding this

Ideally I'm looking for a quick check performed by hand on the suspect areas of the casting, for each part.


Thanks

 

[monkeydog]

Can the part be helium leak checked?
It will not tell you the degree of porosity, but some trial and error will tell you an acceptable range.

 

[limct]

Have you considered any improvement on the part, tooling and casting parameter or machine tonnage to reduce the porosity problem? A 2mm pore should not exist if all these are taken care of. Spend some time on this would be better of for you to do in-process checking.

Best regards,
ct

 

[metengr]

The two methods you proposed RT (radiographic testing) and ultrasonic testing (UT) are suitable to detect sub-surface porosity. There is no "quick check" method for either process. The question comes down to cost and time.

How much do you really want to spend on RT or UT? Both methods have there advantages and disadvantages regarding time and possible surface preparation (for UT). I would suggest calling several non-destructive testing companies and have them provide you with an estimate on cost for each process.

You did not mention the size of the component, but in most cases RT (x-ray) is probably the preferred method. You will most likely have to send the pieces out to the lab.

 

[israelkk]

You should purchase your castings according to some known specifications. In the aeospace bussiness it is customaty to use specs like MIL-A-21180D ALUMINUM-ALLOY CASTINGS, HIGH STRENGTH which can be found at

http://assist.daps.dla.mil/eAccess/index.cfm?ident_number=14588

Such specification will assure that your castings is up to standard and the supplier is responsible for its quality and testings.

 

[BillPSU]

Are you making the castings or machining only. Call your casting supplier and talk to him about your problem. Is the problem shrink, metal not degassed, poor risering, turbulence in the metal when cast. There could be many process parameters affecting the soundness of the casting and if the supplier is not aware of the problem he will do anything about it. Talk to him first before you spend any more time and effort on inspecting the quality in.

Bill

 

[swall]

Are these really die castings? By that I mean high pressure die casting. 25mm wall thickness strikes me as excessive for a die casting. With die castings, you will get porosity in the center of the wall and good outer skin layers. That is the nature of the beast, and when you machine through the outer skin, you are removing the best metal.

 

[genericmech03]

The casting part's thickness varies form 25mm to 3mm. The ideal route to take would be to solve the problem at the supplier's end, however despite lengthy efforts they just don't seem able to consistantly achieve as required by the porosity spec. So in the mean time we are wasting money and worse, risking porous product being send to the customer. I'm currently waiting to see what the NDT guys have to say.

 

[etch]

You could always go down the cost of Real-time xray. We used to use it to check high value parts at $800-$1000 per casting, for aerospace.

We had the similar problem of wasitn alot of time and possible money machining casting that would subsequently fail at later stages.

Turn around times for these were 4 to 5 mins per casting. We then found out it was good for process checking and you could go and take a few castings off a production line and blast them through the x-ray in a few minutes and you get a result.

Initially the outlay is expensive but you could justify a costing on it based on saving maching costs, tooling and time

As we all know castings are cheap but its the inherent cost in machining and testing that adds the value so catching defects at an early stage is preferable.

id would say that the cost of x-ray (wet film) versus relatime x-ray is a no-brainer. With traditional x-ray you have chemicals, film, disposal and more importantly time loss waitying for result.