Q: We are an automobile aluminum window manufacturer. We use aluminum extrusions for making windows, and these frames are black epoxy powder coated. In our three decades of business experience, it is a common phenomenon that many frames are rejected due to bad powder coating. As the users of these frames are some of the big automobile companies, slight mistakes are detected and the entire window is rejected.
Now the problem is no one in the powder coating industry does re-coating (i.e., removing the old coat and then re-coating again). Hence the entire window has to be scrapped. Is this because removing the powder coat from aluminum is not possible? Or practically not worth it?
We also did many experiments to remove the coat with various acids and alcohols, but it was not successful or practically viable.
A: This is a very common problem the world over. Powder-coated parts are assembled and sometimes even make it into the field when a serious visual defect is recognized. The challenge is to remedy the finish to the initial specification without having to scrap the part. This problem is multi-faceted, and I will attempt to address each issue.
The first problem has to do with the incidence of coating defects reaching the customer, in this case, big automotive companies. Obviously, your quality programs are not sufficient enough to eliminate the delivery of out-of-specification parts to your customer. Two measures need to be implemented: 1. An improvement in your process and quality control to eliminate the root cause of defects, and 2. A better inspection process to eliminate the shipment of bad parts.
Eliminating the root cause through better process control involves a multi-step troubleshooting program. You will be best served to use a brainstorming session with key production, engineering, sales, and quality personnel to:
- Define and characterize the defect(s)
- Examine possible causes (man, method, machine, material, Mother Nature)
- Qualify and rank possible causes
- Collect data to characterize defects
- Explore and recommend remediation actions to eliminate root cause(s)
- Implement remediation measures
- Continually monitor quality and adjust processes and procedures as necessary
Concurrent with your root cause analysis efforts, it will be wise to improve your inspection process to catch out-of-specification parts before they are packaged for shipment to your customer. Catching parts prior to packaging will allow you to reprocess them much more easily than after they have left your facility – or worse, after they have been assembled by your customer.
Your inspection process should employ highly trained individuals who can identify defects. It is very helpful to take photographs of typical defects and have the pictures prominently displayed in your inspection area. The operators should be aware of what constitutes a defect and what quality is acceptable. You should also keep daily records of defects and post the data on a board in the finishing/inspection area. Include definitive goals for quality.
As for fixing unacceptable parts once they have been assembled by your customer, this where I recommend a non-powder coating solution. You should work in conjunction with a liquid paint supplier to provide a touch-up paint to repair defects on assembled parts. It is requisite to work closely with the paint supplier to ensure acceptable adhesion of the touch-up paint to your powder coating. Likewise, it is important to collaborate on the specific process to repair the defects (i.e., identification of defect, sanding, cleaning, film thickness of touch-up, color requirements, etc.).
I do not recommend using a powder coating to repair an already assembled part, nor do I think it is wise to completely strip the powder coating if the defect can be ameliorated by sanding followed by cleaning and the application of a liquid touch-up paint.
The bottom line – focus on not producing defects and therefore eliminate the need for fixing bad parts that have left your facility.