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Staining on Aluminum 6061-T651


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This one has me stumped. We are running some semi conductor parts. And we get intermittent staining. One part will stain and the very next part doesn't. Our customer is very particular about this.

Specs,

Material - 6061-T651, all from the exact same heat lot of material. 

Coolant - Extreme Cut 250C  -  7%-9% / using RO water / PH 8.65

Here are two parts run consecutively.

598cdb15d9b27_Normalrunmach4431.thumb.JPG.3bf0e95e7063d91af6845389b63bd3d7.JPG

 

 

598cdb2fb6543_normalrunmach4430.thumb.JPG.90a75c4f25ab0afafa5beebb66dbbbb4.JPG

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@Jparis, I thought maybe the same thing. We may have to look into that

@DavidB, We only run this family of parts in the machine. Plus I've done countless tests on what stains this part and I can't get the coolant to stain. DI water will stain it, but we don't use DI. 

We do run thousands of .016 reamed holes in these part, and it creates a muddy mess in the coolant. I was thinking that maybe that is getting into the thru spindle and blasting the part. Like sand blasting it. But then I ask, why isn't it happening all the time? 

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47 minutes ago, jlw™ said:

I bet it depends on what CAM system you use.  I wonder if any one could tell me if Powerdesk stains parts.

That's an undocumented feature I'll bet. AND you have to pay your maintenance. :D:P 

 

:coffee:

 

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I see that you have some tapped holes.

Are you using tapping oil for tapping these?

Many tapping oils contain sulfurized fat (inactive) and/or chlorinated paraffin which will stain that material very easily & quickly.

You may want to take a look at a non-staining tapping fluid.

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Well, the part runs for about 12 hours. But other than that, the part NEVER sits in the machine with coolant on it. We have a strict cleaning process after each machining OPs. It's fluctuated over time, but right now we do a 50/50 - Alcohol / DI water bath, then blow dry to remove all excess coolant. I have experimented with 100% DI, and that will stain, see coupon below, but staining can be seen while the parts are running. before the bath. Plus I can't get the parts to stain with 50/50 DI and Alcohol. 

Also, no tapping fluid, just coolant. 

And yes we performed a PH test and it is similar to untouched coolant. 8.6 in the machine, and 9.0 untouched. We also did a TDS check and that reads 540ppm, whereas untouched=260ppm. 

 

598d9a6021898_Diwaterandcoolant.thumb.JPG.bea93c3d9da19211ea65a22aabe1d999.JPG

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You have some kind of chemical reaction going on or they are not even close on the material. I had some parts fail about 20 years ago and the Paper Mill had a clause in the PO that any failure due to your parts you were charged $30k an hour for the downtime. We had backup parts on the shelf and they failed also. We had to work a long weekend to make all new replacement parts and they worked like previous ones did before that batch of parts. I took the parts and had them tested and everyone of them failed the material spec they were called out tested to by the supplier. I passed that information on to the Paper mill and they went after the metal supplier. We were looking at that putting us out of business at the time.

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Thanks, everyone. 

I've been leaning towards a material issue as well. I can't explain it any other way. The coolant seems like a logical culprit, but Then there would be staining on every part. 

It's on a brand new (1 year old) Makino NX-51, So it doesn't noticeably leak oil. 

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10 minutes ago, Tim Johnson said:

598d9a6021898_Diwaterandcoolant.thumb.JPG.bea93c3d9da19211ea65a22aabe1d999.JPG

Is the non-stained area on this material where clamps were?

This was a coupon in a DI water test. The unstained areas are where the part was sitting on wooden blocks. But the DI staining was not a surprise. Just trying to create baselines to find some answers. We tested Coolant, DI, RO, Rust inhibitor, Alcohol, Way oil, Spindle oil, Alkaline wash, Coolant slurry,  and some combinations of. 

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