Diecast Quality - ASTM e505 Spec

<...IP67...> represents immersion in water up to 1m, which is around 0.1bar. If it fails a vacuum test then sooner or later "the submarine will sink" and water will get in, making <...IP67...> an overstatement of the enclosure's capabilities.

<...would it be possible to meet IP 67 requirement with this ASTM grade casting?...> Of course it is possible. Experience, including that described in the original posting, simply indicates how likely it is.

Currently the failure is less likely, but we worry that this could get worse because the tool is aging.

We have had no issues in the past with alu diecast projects. Hence, we over looked the spec and did not mention that in the drawing during kickoff.

To get the supplier attention I have no other statement other than the ASTM level 2 what our supplier has promised.

I went through the standard and did a search in the internet to correlate leak tightness and ASTM spec. However, no luck.

Therefore, i seek your expertise to understand correlation between ASTM e505 and leak tightness.

Based on your experience could you please share How probable is to get this sort of failure with Alu diecast parts!

Are there any statements to connect ASTM 505 and leak issue?

Thank you

Which is harder: Refining your casting process or filling the pores with an epoxy coating or similar process?

Supplier claimed/claims that they have best in class process and we pay for it.

We do not want to pay for their inability to meet the spec.

Impregnation is still an option but has its own limitation due to construction.

Regarding process, supplier claims that they perform degasification!

I understand your concerns. We do have occasion to have some rather complex parts cast. There are some notes below, but I'm guessing your cost targets are a lot lower than ours.

1. MATERIAL: ALUMINUM ALLOY CASTING IAW FIND NO. 28, MECHANICAL CLASS 10, INSPECTION CLASS 3, FOR H01 ONLY: INSPECTION GRADE C. ALL CASTINGS SHALL BE RADIOGRAPHED, LIQUID PENETRANT INSPECTED AND TENSILE TESTED. THE SYMBOL DESIGNATES THE SOURCE AND DIRECTION OF TENSILE TEST PULL OF THE INTEGRALLY CAST BARS. UNLESS SPECIFIED BY THE PROCURING AGENCY, DESTRUCTIVE FIRST ARTICLE TESTING SHALL BE WAIVED. SURFACES THAT HAVE BEEN GROUND, GRIT-BLASTED OR OTHERWISE SUBJECTED TO PROCESSES THAT PROMOTE SMEARING OF THE MATERIAL SHALL BE ACID ETCHED PRIOR TO LIQUID PENETRANT INSPECTION.

5. AFTER IMPREGNATION, TREAT WITH CHEMICAL FILM IAW FIND NO. 22.

6. AFTER CHEMICAL CONVERSION COAT, MASK ALL HOLES AND SURFACES MARKED . THEN HARD ANODIZE IAW FIND NO. 23 AND SEAL FOR MAXIMUM CORROSION PROTECTION. COMPLETE COVERAGE OF INSIDE SURFACES NOT REQUIRED.

11. AFTER ALL MACHINING, IMPREGNATE CASTING IAW FIND NO. 25 USING FIND NO. 16.

22. AFTER HARD ANODIZE, PRESSURE TEST EXTERNALLY FOR ONE CYCLE TO 160 +/-10 PSIG IN WATER AT AMBIENT TEMPERATURE FOR 15 MINUTES. PRESSURIZATION AND DEPRESSURIZATION RATE NOT TO EXCEED 500 PSI/MINUTE. STRUCTURAL FAILURE OR LEAK IS SUFFICIENT CAUSE FOR REJECTION OF PART. TEST SHOULD BE COMPLETED PRIOR TO PAINT.

Hello Sir Robin.

Thanks a lot for your hints! For sure, the next project will have all necessary note in a more exaggerated way!

Unfortunately, it is too late to define them in the drawing for this project!

Hence, I am looking at logical reason or a statement from spec to link the leak issue.

Thank you

...then this is a supply chain quality issue that needs to be addressed with the supplier.

While IP67 deals with water resistance, ASTM E505 deals with porosity and structural integrity, so you're comparing apples and oranges...Certainly it could be argued that these two qualities are related, but at the same time not mutually inclusive....It's possible your problem could be solved by increasing the thickness of the casting, or as somebody mentioned, a coating process, or it might be solved by tweaking the casting material or the process even further...But guaranteeing one standard does not automatically qualify for the other...

...."Against liquids, an IP67 rated gadget's protection is limited to about 30 minutes of immersion in up to a meter or three feet of freshwater. This means it is water-resistant but not water-proof. "...

https://www.komando.com/tips/375296/what-does-ip67-mean-for-your-gadgets/all

https://www.dynacast.com/porosity

...also you haven't said what caused the failure....Was it porousness, cracks, shrinkage, mold irregularity, slag intrusion, you need to do a forensic analysis and determine the cause....

https://www.haworthcastings.co.uk/news/casting-defects-and-how-to-prevent-them-part-1

Hello Solar Eagel,

X-Ray test did not reveal the defects, but the Liquid penetrant test does!

Our supplier informed us that connected porosity is the reason!

How probable it is to get this sort of issue with Alu diecast?

General wall thickness 2,5mm

Thank you.

Well it's a money decision....what's the cheapest route? going to a 3.0 mm thickness, or secondary impregnation...?

According to what I've read the minimum thickness for this standard is 3.2 mm...

I understand IP67 does not mean leak proof enclosure!

Even we do not check the parts for leak proof characteristics, our leak test has defined leak rate, when the leak rate goes beyond permissible value then we declare the parts as defective!

Get the supplier to do the <... leak test has defined leak rate...> and only receive parts that are not defective, especially as <...do not want to pay for their inability to meet the spec...>; the problem goes away, and becomes the supplier's to solve on the basis of reducing the defect rate to zero with the incentive of the supplier improving its business.

The process requires a commercial input.

• The customer requested 10,000 parts from a Japanese equipment supplier with a defect rate of less than 0.03%, i.e. 3 in 10,000. The infuriated Japanese supplier shipped two packages, one with 9,997 parts in it and the other with just 3. When the customer telephoned for an explanation, the supplier responded that the smaller package "contains the defective ones you asked for".

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There are numerous reasons for castings having leak issues. Have you determined if the porosity in the casting are from gas, inclusions or shrink? Aluminum shrinks when solidifying, so unless there are non-critical areas to “feed” the area solidifying, there will be porosity.

Is this a high-pressure aluminum die casting? If so, these inherently are prone to porosity issues because of air entrapment when the aluminum is pushed into the die at high pressure. To reduce the potential of having porosity, variations of the high pressure die casting process reduce the air entrapment by using lower pressure to fill the mold (medium or low pressure), or in some processes, the mold is filled by using vacuum and pulling the metal into the die. Or, combinations of vacuum and pressure.

The casting design is critical to produce structurally sound castings. No matter if this is a high pressure or lower pressure process, the solidification rate of the casting will drive the design. It is key to have the wall thicknesses are uniform as possible, tapering from the wall portion farthest from the gate (where the metal comes into the die) or if there is a riser (a thicker section of aluminum that is the last to solidify and allows feeding the areas of the casting with liquid metal that are solidifying first (shrinking). Interestingly, with high pressure die casting, the thinner the walls, the better. The key for sound castings with good mechanical properties is the solidification rate of the aluminum. Hence, sand casting typically have lower mechanical properties than metal dies due to the faster solidification rate with the metal die (sand acts as a insulator). There are tricks to improve the sand casting process, but that’s for another time.

You mention that there are holes drilled in the casting. If there are bolt bosses cast into the part, these normally are thick areas of the casting as act as risers and will feed areas of the casting solidifying around the bosses. When you drill through the bosses, this can open porosity deep in the casting.

I apologize for the long answer, but eliminating porosity in castings, high pressure or not, starts at the design stage, through the die design and using proper aluminum melting techniques. If no changes are possible to the design, or die, then vacuum impregnation can be used. Good luck!

Firstly, die casting is NOT my background but did spend some time with injection moulding plastic.

You have confirmed that linked porosity is the observed defect from the suppliers analysis. If the part doesn't meet the spec, then it doesn't meet the spec, that's simple.

Porosity usually comes from either

• air entrapment (hopefully the die caster has this sorted with their pressure profile.
• contaminants (Hopefully not)
• Shrinkage during cooling.
• Turbulence around tool coring.

Shrinkage can come from too high melt temperature of the raw material (Often used by suppliers to reduce cycle time with lower viscosity melt), so having the supplier lower the melt temp would reduce shrinkage during cooing and thus reduce voids. Note that your end product might also be dimensionally larger.

Shrinkage can also come from faster cooling (Often used by suppliers to reduce cycle time using a cooler tool) and not allowing the material to migrate from the runner/sprue system into the cavities formed.

If it is due to tool core turbulence, then revision of the gating location might provide solution to this.

Have you had "mouldflow" analysis done on the part and the tool to determine optimum situation???? That will provide you with optimum fill speed, temperature profile, cooling profile and gate location.

your casting supplier may be casting too hot.