Aluminum Surface Finish cost comparison

[MikeSBSI]

I am looking for a general cost comparison for the finishing operations for aluminum alloy. The specific question I am trying to determine the answer to is: Is there a cost effective (cheaper) alternative to Anodizing aluminum alloy for which we can retain the Emissivity and thermal conductance and not have to mask off (high labor charges) grounding area's for a PCB?

1. Conversion Coatings (Iridite)
2. Anodize
3. Electroless Nickel
4. Alumniplate
5. Iridite w/ high emissivity paint

Could someone help me put these finishes (and any other I have missed) in order from least to most expensive?

Notes:
-(1,3,&4) don't have the emmisivity close to (2&5).
-5 still requires the labor to masking for holes and interior surfaces.
- I am designing a small electronic enclosure which needs to disipate about 8-10W. We are looking at ways to optimize the enclosures ability to expel heat.

Thanks in advance!

Mike

 

[Compositepro]

Why do you need any finish at all? That is the first question. You've asked the second question which depends on the answer to the first.

 

[MikeSBSI]

We have already asked the first question and determined, yes we need a finish for corrosion resistance and at 70 degC surface temp we need to radiate as much heat as possible. It just so happens Anodizing gives us a great surface finish and a high but doesn't have great electrical conductivity and PCB contact area's need to be masked off.

Thanks for the response. Can you help me with the cost comparison?

 

[KENAT]

There may be more than one way of looking at this, as you your self say it's not just the process cost that needs to be considered but also any other labor for masking or other secondary ops.

PCB contact areas don't need to be masked off. They need to be free of anodize. I've had parts where it was more economical to anodize the whole thing and then effectively spot face areas that needed to be free of anodize rather than use masking.

Color will probably play a factor in radiation, with black being best as I recall. This factor may go against any treatments that aren't available as black since a secondary op will be required.

Also do you want direct cost or do factors like being able to do it in-house V sending it to a vendor etc come in to play?

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

http://eng-tips.com/market.cfm?

What is Engineering anyway: faq1088-1484

 

[MikeSBSI]

KENAT,

I agree at the multiple ways to approach anodizing (i.e. masking vs spotface).

In general I am asking in terms of farming the part out and having it ready for assembly when it comes in. I am more interested in direct cost.

Realistically we have an internal shop that initially machines the housing components, then they are sent out for finishing. We could have the finisher or in house machine spot face. This adds additional engineering/drawing time. But the low production number of units, say <100 over the life of the product. This project is driving the search for alternative finishes/coatings but I believe what I learn can be applied to future products.

 

[KENAT]

So depending on your parts shape, where annodize is required etc, one idea might be:

Machine the external shape.

Anodize.

Machine the internal shape.

Chem Conversion as required (iridite/chromate conversion/alodine/alochrome whatever you call it)

You don't necessarily need extra drawing time - the drawing just states that certain surfaces have annodize and others don't.

The extra time will be in the routing/work instruction.

However, for what your question really seems to be take a look at:

http://www.prime-plating.com/services.html

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

http://eng-tips.com/market.cfm?

What is Engineering anyway: faq1088-1484

 

[drawoh]

MikeSBSI,

Conversion coatings are electrically conductive, so there is no need for masking. They do not look nearly as good as anodize, but they are good paint substrates.

I would estimate that chemical conversion coating costs approximately the same as anodizing. If it has to look good, you need to anodize and mask, or you need to paint, all at extra cost.

JHG

 

[Eng5100]

I might suggest tapping into the AL or using PEMs. Al isn't great for grounding, but if it this is related to ESD issues at all then I would consider taptite screws into the Al or machince screws into PEMs. Order for your options may be 2, 3, 4, 5, 1 least to most expensive. Most depend on the going rate of the material at the time. Anodizing is cheap.