Posted April 20, 2016
By Tim Cabot
Partnering on Projects when Anodizing Aluminum
Recently, a customer asked about DCHN’s ability to fix minor defects on aluminum components of a common medical device after being returned from active field service. The customer has stringent quality standards for cosmetic defects on this instrument, and such defects result in the components being scrapped out before the device gets sent back to the end user. An understandable concern is that these components have a significant manufacturing cost, which translates to a high replacement cost.
That concern led to the following basic question: can the defects, whether caused by drops, scrapes, and other impacts on the surface of the part, be fixed, and the refurbished components used in place of new components? (In other circumstances, customers may be facing other cosmetic damage, such as fading, discoloration, or light corrosion caused by repeated cleaning and sterilization of Type II and Type III anodizing; more on a solution to this later in this article.)
When attempting to fix small defects, the customer had three concerns:
- Could DCHN match the color and finish of a new part?
- Could DCHN maintain the close tolerances of the component?
- Would the cost of refurbishing the component provide a savings vs. replacing a defective component with a new part?
While each customer has specifics relative to each product and aluminum anodizing project, there are answers that apply to many situations. The answers below generally apply to most projects where the goal is to refurbish parts to get them back to their original condition.
1. Repair of Defects: Generally, superficial defects, such as abrasion marks, marring, light corrosion, and light-wear areas can be fixed with a controlled stripping of the anodic coating, followed by a combination of a light chemical etch and/or mechanically finishing the part through bead blasting, tumbling, etc. Once the surface is restored, a new anodic coating can be put on the part and finished to the same color and texture as a new part.
More pronounced defects, where the aluminum part is damaged beyond the surface, such as punctures, deep scrapes, bent, or misshaped areas cannot be restored to the original condition, as one cannot economically replace missing aluminum, pop out a dent, or reshape the part.
Figure 1 is an example of defect that likely can be fixed. Figure 2 is an example of defect that cannot be fixed.
To be salvaged, the component part needs to be disassembled back to the original aluminum component (i.e., remove all other metal and non-metal parts in the assembly). If this cannot be done, the part may not be able to be fixed, as these other materials will interfere in the finishing process. (Look for an upcoming blog on how to prepare parts for refurbishment.)
2. Tolerance Control: Areas that have tight tolerances are usually better masked vs. stripping, fixing, and recoating. The masking stops those areas from being impacted by the fixing process. While such areas can be stripped and re-anodized, and where the small amount of material that is stripped can be replaced by a slightly thicker coating, this fix can change the color and translucency of the coating, making a visual match with virgin parts more challenging—and less reliable.
3. Cost Comparison: For highly machined aluminum components, it is always much cheaper to fix vs. replace the part—usually in the order of > 70% cheaper. This is in spite of the complex handling and finishing steps to fix the part, due to the amount of labor that is required.
Partnering on Projects
When assessing whether to replace or fix a slightly damaged part, the device manufacturer should partner with the metal finisher and adhere to two key steps. The device manufacturer will need to set specifications on:
- Defects—to define what sort of defects can be fixed and which will be scrapped
- Refinishing—to define acceptance criteria for refurbished parts if the criteria are different than new parts
The defect specification will identify fixable vs. not fixable defects to be sent out. Sorting the defects that can be fixed will be determined, in part, by the capability of your aluminum anodizer to meet your refinishing specification. A looser specification will always be easier to meet, but different metal finishers have different capabilities based on their processes and experience, so you shouldn’t accept a “loose” proposal. Generally, running a controlled project is the best approach to understand what can be done and to compare different suppliers.
Our recommendation is to avoid assuming that the parts can’t be fixed, and approach finding solutions from a development project orientation with your metal finisher, discovering if and how the components scrapped can be refurbished. Running a formal project can prevent a “hit or miss” situation that lands you in the “miss” column, and will almost always improve the ROI.
As always, if the part requires repeated cleaning and sterilization, we recommend moving to MICRALOX® coatings. These microcrystalline anodic coatings have 10X the chemical resistance compared to conventional anodic coating, and do not fade, discolor, and corrode like Type II and Type III coatings.
At DCHN, we know that many questions arise when considering aluminum anodizing, hardcoat, and other metal finishing jobs. Our white paper, “12 Proven Tips to Save Time & Money for Aluminum Anodizing, Hardcoat, and Other Metal Finishing Services," is a guide full of great tips to help you save time and money. Download it now.