What is Anodizing?
Anodizing (a.k.a. anodising) is process using electrolytic passivization that provides an outside skin or layer of protection on aluminum (and certain other) metals. Anodizing increases wear resistance and is done with dye to color the parts! Anodizing is not an added layer (e.g. like a paint or coating) but rather chemically changes the outer layer of the base material. However, as discussed below, anodizing does add some thickness to the part dimension. Luckily the anodizing thickness is predictable and controllable!
- Type II Anodizing is the most common. Everything from consumer electronics to an aluminum rifle scope mount – this stuff is generally Type II.
- Type III (Hardcoat) is, in layman’s terms, a thicker anodizing. Any anodizing process only works for so long, as the anodizing surface becomes non-conductive and thus self-limits how long a part can be anodized. Type III Hardcoat Anodizing is done with higher voltage at a lower acid bath temperate to help achieve “more” anodizing before the process has reached its limit.
- Type II and Type III anodizing refer to the style (e.g. voltage and temperate) of the anodizing process. They do NOT specify color or dye!
- Dye: this is how anodizing changes the parts color, look and aesthetic! In layman’s terms: the anodizing process exposes pores of the material. These pores must be sealed as a final step to anodizing (even for clearcoat anodizing) or else the part would corrode. During this sealing process, the anodizer can add a dye to color the part. Colors like black, tan, red and OD green are common in our experience. Custom colors may be available but may entail longer lead times, higher cost or higher minimum quantity.
How to Outsource Anodizing:
We have had thousands of parts anodized over the years. Here are the tips and tricks we’ve learned:
- Good anodizers are difficult to find. Some anodizing companies may run three shifts (to keep the tanks working…) and process over 100,000 parts per week. That means hiring labor and processing quality control to handle 600 parts per hour! This is a huge contrast to a small machine shop with low volume (possibly only a few parts per day) and highly skilled labor. You may have spent 20 hours machining a part; to the anodizer, that part is just one of *thousands* they may handle that week.
- In contrast with the prior bullet point, there are also small “job shop” anodizing shops who deal in smaller quantities and/or quicker turn-around times.
- Thickness: Generally, anodizing thickness is half in the material, half additive. See section below on Thickness for additional information.
- Most Anodizing Companies do not want non-aluminum material mixed in (e.g. no steel helicoils, no brass threaded inserts, etc)
- Packaging is KEY! Parts need to be individually wrapped or they need to be compartmentalized boxes. A cheap option for small parts is Egg Crates.
- Anodizing companies will likely mix your parts with others. Their goal will be to fill each tank with parts.
- Do parts or holes need masked? Masking holes is relatively expensive as it requires time consuming labor, a consumable plug, and increases the risk of a ‘bad’ part if the plug malfunctions.
- Break sharp edges! Sharp edges or any chamfer under 0.005″ (0.12mm) can lead to the anodizing cracking.
- Clean your parts! Some can do this for you. Surface oils may come off in the first anodizing stage, but they also may not. Do this yourself- or confirm they can do it for you.
How much does Anodizing cost?
- It is common to see a minimum charges ranging from $65 to $125. This is for Type II and only for colors that your anodizer is already running (e.g. clear, black, etc).
- Anodizing is inexpensive when done in bulk. When we sent in camera adapters and small firearms mounts, we paid $2 per part for quantities of 200 or more.
- Type III hardcoat anodizing is more expensive and it takes longer for an anodizer to run (e.g. the cycle time). For example, the Saunders Machine Work Tormach fixture plates are Type III hardcoat anodized.
How to Request an Anodizing Quote and Long Term Relationships and Terms
- Type of Anodizing
- Dye color. If you need a certain color, you need to speak with the anodizing company about their ability to match an existing part, Pantone color, etc.
- Give them the surface area of the part. Click here for video tutorial on how to find the Surface Area of your Part in Autodesk Fusion 360!
- Explain how the parts should be racked or held (e.g. have you provided a threaded hole for racking, or is there a specific area you want the part to be hooked or held)
- List a completion date, but be reasonable. If uncertain, call first to ask their availability or if they offer rush pricing.
- They ARE going to either damage, cosmetically blemish or lose some parts. Again, anodizing is a high volume business. Plan for that – and address upfront how to handle it. When we were outsourcing thousands of GoPro camera mounts, we had an agreement for a per-piece-lost-credit. These were small parts which could fall off the christmas tree style racks. They usually lost about 10 per 1,000 pcs. With our Tormach fixture plates, they won’t lose them, but we have had cosmetic blemishes. Negotiate this with your anodizer up front but remember: mistakes will happen. If you’re looking for an anodizer who will do you parts for a competitive price and *never* make a single mistake, well – in our experience that doesn’t exist!
- Continuing on anodizing mistakes: ask your anodizer how they handle mistakes. If an operator sees an error or goof, if he or she supposed to fix it themselves? Do they start a repair/problem ticket? Do they reach out to the customer to evaluate how to handle?
- Ask about certifications – whether ASTM, MIL-SPEC or other certifications – a certification process can help ensure quality, consistency and a papertrail to help build a long term recipe for success.
- Click here for sample Anodizing Purchase Order form!
- Anodizing Companies may offer in-house trucking or courier service – e.g. they will pick up and deliver your parts (possibly for a fee, possibly baked into price). Ask!
- Give your anodizer racking instructions! Provide them with a hook point or thread they can use. Call this out on a drawing. Large parts should have multiple contact points; this provides for more stable racking and helps more evenly distribute the electrical current throughout the part, yielded more consistent dye and thickness anodizing results.
- Be clear in your PO or RFQ re: type of anodizing, dye, thickness. Spec if parts must be free of scratches. Include Go/no-go gauges for critical bores.
- Anodizing thickness is, in our experience, half “in” the material, half “added” to the material thickness.
- Example: 0.001″ Anodizing would add 0.0005″ to the parts outside dimension on all anodized faces
- Example: a 2″ cube anodized with an anodizing specification of 0.001″ would measure 2.001″ on all faces because 0.0005″ has been added to each face of the cube.
- Example: a 1.5″ bore anodized with an anodizing specification of 0.001″ would measure 1.499″ after being anodized (0.0005″ of material has been added to the radius)
- Thickness is not necessarily consistent across the part, particularly for large parts. The further from the anode, the less anodizing has occured.
- It *is* possible to “pull” a part mid-anodize and check for thickness and then, if needed, put the parts back in to add more (assuming the anodizing has not reached its “self limit” of thickness)
- Threaded holes: We run H8 taps for parts that will be hardcoat anodized. This ‘H’ value of a tap increases the pitch diameter; in other words, it is a slightly oversized tap.