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Porosity Detection in Aluminum castings

Porosity Detection in Aluminum castings

(OP)

Hello,

I was wondering if anyone had any experience in detecting porosity in aluminium die castings . We currently only detect the porosities after machining the surface away, but I would like to detect them before we waste money on the machining. I was thinking of maybe using NDI techniques like ultrasonic testing. Has anyone had any success with this or another technique?

The application is as follows, material thickness is roughly 10mm thick 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.


Regards

RE: Porosity Detection in Aluminum castings

RE: Porosity Detection in Aluminum castings

If porosity is important, could you have all the castings polymer sealed before machaning?

RE: Porosity Detection in Aluminum castings

2
On your thickness of material you use either X-rays or Gamma Rays.  We used X-rays on Aluminum .250" or less and Gamma or X-rays on anything thicker.  The choice depended on the complexity of the part and what we were trying to ascertain.

We had mixed results on 25,000 13# aluminum injected molded parts with Ultrasonics even with an automated immersion bath.  The area of interest was 3" dia with a 1/2" wall.
I would have to say that Ultrasonics have come a long way and you don't have to depend on bleary eyes to help interpret the results.  The end result was that we used Gamma radiography on half and X-ray on the other half.

I think CoryPad has put you on the right track of using X-rays with a digital imaging system with all types of automation if the quantity warrants.

I haven’t check out GE lately but at one time you could get a short term lease on the equipment form GE Leasing for evaluation.

RE: Porosity Detection in Aluminum castings

(OP)
Thanks a lot for the advice, it sounds like it's possible to achieve the inspection with either ultrasonics, x-ray or gamma ray testing.

Unclesyd

Did you have to send the parts outside for testing or was it some thing you did on site?

If on site how long did the inspection process take per part?

Is is a difficult process i.e. something that an operator could achieve after some training, or only something a qualified technician could do?

Cheers

RE: Porosity Detection in Aluminum castings

In general, defect inspection is difficult work so it requires trained personnel.  Much of the equipment from the suppliers I linked above is automatic (but very expensive), so it won't require much human interaction.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

RE: Porosity Detection in Aluminum castings


Did you have to send the parts outside for testing or was it some thing you did on site?

We accomplished all the inspection on site using ASNT Technicians

If on site how long did the inspection process take per part?

Gamma:
Initially our time per piece was 15-20 minutes for  batches of twenty parts.  This was mainly due to using large film sizes.  Once we located the focal point in the primary area of interest we were able to switch to smaller film size and do a lot with automating the development of same.  
We also did a tremendous amount of work in speeding up the whole process.  The end time per part was in the 5 minute range on a continuous basis.

X-Ray:
The process was somewhat slower than the Gamma but improved as time progress.  The X-Ray work required more attention to the equipment than the Gamma camera.  The saving grace was when we located a focal point and were able to use the smaller film we tripled the number of parts per shot.
We did use a fluoroscope toward the end but at the time it wasn’t very practical due to mechanical problems.  
We did go through several tube changes during the process of inspection.

Later work:
Some of these part have been inspected using current digital technology and these results were considered outstanding.  I only saw the digital images and wasn’t privy to the actual working of the process they used.   Their images were a lot prettier than our originals.

Is it a difficult process i.e. something that an operator could achieve after some training, or only something a qualified technician could do?

As stated the Gamma Radiography requires a license for the source and a certified technician to operate.   I am not up on the all the requirements on X-ray machines and operators, but I understand that all operators of portable machines have to be licensed by the state.  I certainly wouldn’t have unqualified people near an X-Ray machine.  We used several X-Ray sources in the labs and only had in house trained operators under supervision by a factory trained supervisor.  
I would want at least an ASNT Level II RT technician trained for a particular machine for any work with radiation, especially where it is not a routine job..   

I would get with each vendor and discuss with them your situation and requirements and get their recommendations.   A machine used in a production process would have to amenable to operation by an operator but under control of a trained technician.   
You might want to send sample out to local NDT testing companies and look at the results.

If you have any quantity of parts digital X-Ray is the way to go.  I understand that the degree of autmation is up to you.


I might add that primay reason for using our approch was that the part was used in everyday production with several thousand being in use at any one time on a 24/7/365 process.  

RE: Porosity Detection in Aluminum castings

Please let me explain my position about Your problem:

1. Yes, you can detect porosity wit X-ray equipment, but not with ultrasonic (ultrasonic is used for surface defects)
In Italy BOSELLO is very good supplier for X-Ray equipment with big experience for castings

2. You have to solve Your problem at the beginning of the process, means:

2A- discuss with Your foundry the porosity problem and ask them
* to make some modifications on the die (put in overflows, modify gate ...)
* to change some process parameters
in order to reduce porosity in the critical area
(PS: for high pressure die casting the presence of porosity is normal, the foundry and tool maker must build a die which reduces porosity in the critical area)

2B- reduce the machining stock - stock must be as less as possible, 0,5 mm is normally OK

Your foundry MUST have x-ray equipment in order to make statiscal checks of porosity
Check every part is really to expensive (or may be acceptable only if you make a very expensive machining).

If you need more details please contact

RE: Porosity Detection in Aluminum castings

This is a late response. There are several companies that offer industrial X-ray inspection, Some have been mentioned here before, but an industry leader has been omitted. BIR, Inc. provides computed tomography systems to several foundries in Germany, Asia, and the US.

www.birinc.com

The benefit that CT imaging provides is enormous.

RE: Porosity Detection in Aluminum castings

Cierpy,
"Yes, you can detect porosity wit X-ray equipment, but not with ultrasonic (ultrasonic is used for surface defects)"

This statement is not true.  UT can easily find porosity and it is a volumetric exam method.  Perhaps you were thinking of penetrant testing (PT).

But I do agree that radiography will find it easily.

RE: Porosity Detection in Aluminum castings

X-ray machine can help you.
 
We have used X-ray machines to check wheels for years.

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