Questions for the Ages

Preventing material waste is a mutual goal for finishers and their customers. Effective communication is critical in this respect. Here are some common questions that anodizers should be prepared to address when working with both new and existing customers…


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One of the mutual goals of a customer and a finisher is first pass yield. There are several steps to attain a successful run of material. Achieving this first requires a good working relationship and strong communication between the customer and the finisher —one within which questions and answers flow back and forth. Here are some examples of critical customer questions demonstrating how this dialog can contribute to first pass yield:

How can I manage consistency in aluminum?

The easiest way to ensure consistency in your aluminum parts is do business with a single extruder on a given job. Should a metal-related issue arise there is only one source to question.

What if I mix alloys?

Mixed alloys or tempers will not produce uniform results. For best results use 6063 alloys for extrusions and 5005 for sheet stock.

Can I bend machine anodized aluminum?

Anodic films are very hard. In fact on a gemological scale of 1–10, where a diamond is a 10, an anodic film is rated a 9, similar to that of a sapphire. As a result, most post-production bending, or “torquing,” of the aluminum will lead to the film “crazing,” which will give the appearance of a spider web. Specifically, the film produces a series of small cracks—just like glass.

Where should I store my aluminum?

Store aluminum in a dry and controlled environment. Do not allow moisture to build up between the pieces, as this will cause severe corrosion known as white rust that cannot be removed in the finishing process.

Why should I avoid tape or adhesives on material?

Often information about a specific job is taped to the aluminum material. When the tape is removed it can leave an adhesive residue that may not be removed in the pre-treatment process.

What results am I looking for?

There are many specifications finishers anodize to, and the most popular are: AAMA 611-98 and MIL-A-8625. When specific parameters are needed, it is important to provide the finisher with the desired requirements as early as possible to ensure the job is finished correctly the first time.

Should I be concerned with welding on aluminum?

The heat developed from the welding process can disturb the metallurgy on nearby metal and cause a localized discoloration after anodizing. To avoid this, use the proper alloy welding wire (5356 alloy) and the lowest heat consistent with good practice.

Why do I need proper drainage holes?

Holes are essential for drainage of solution and they allow entrapped gas to escape. Even the tightest of welded joints will still cause anodize chemicals to weep out.

How should I rack my parts?

At the racking points, the aluminum carries the current needed for the anodize process. Some finishers actually weld customer material to spline bars; others use a screw down bolt system. In either case, contact marks are visible on the aluminum. It is important to define what is acceptable in regards to exposed surfaces and rack marks. One particularly problematic alloy when welding is 4043. When this alloy is welded, it typically turns a smutty black.

What can I do to get the product where it needs to be in the best condition?

Both the fabricator and finisher need to follow good shipping practices to ensure the highest quality material arrives at the desired location. The fabricator should package metal carefully prior to shipment to the finisher to ensure the metal arrives dry and free of scratches and dents.

What else can I do to get a higher quality finish?

The anodize process is in many ways like a computer process—garbage in, garbage out. Avoid sending your finisher metal with deep scratches, dings, heavy die lines, die pick-up, etc. These metal quality defects will show through the anodize process. On a positive note, the anodize process can mask some other common metal defects. For instance, the etch process will moderately decrease, or even remove small scratches, nicks and light die lines. As a rule, if you run your fingernail across the defect and can noticeably feel the defect, it will not be removed in the anodize process.

This questions and answers process between customer and finisher will help to reduce material waste and contribute to accomplishing first pass yield. It is important all specifications, terms and conditions, and other concerns are clearly understood by the customer and the finisher. It is through this continual communication that first pass yield can be a reality.

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