Rack Marks on Anodized Aluminum Parts

What is Aluminum Anodizing?

In general, oxidation process can likely damage or weaken most metal parts. However, the oxidation process for aluminum alloy named aluminum anodizing can increase the ability of strength and anti-corrosion. The anodized parts have to be treated over four major processes. pre-clean, anodizing, dye and seal. You can also read our previous case study for more understanding about aluminum anodizing. Today, we are talking about rack marks showed on most of anodized aluminum part. What is rack marks? And, how it happened? You also must know how to make it invisible.


Why scratch-like marks on my aluminum part?

Have you ever seen the scratch-like marks inside the hole or on the thread of the CNC aluminum milling parts? We call the scratch-like mark a rack mark in the anodizing process. We use the customized jig for holding aluminum part as a conductor between electrode and CNC machined aluminum part for anodizing. Once anodizing process completed, the operator will remove the aluminum parts from the tightly holding jigs. Therefore, there will be small area without anodizing layer surrounded by the holding jigs, just same as the marks showed in below photo.


There will be rack marks on anodized aluminum part.
Rack Marks on Anodized Aluminum Part


How to minimize the rack marks on anodized machined parts?

Frankly speaking, there is no way to remove the rack marks. But, you have the choice to make it invisible or minimize the rack marks in anodizing process. For example, you can use threading rods or bolts into existing threaded holes for contact purpose. Or, you could ask the anodizing operator to squeeze the holding jigs onto the parts where will be invisible in future application. Actually, some of our important clients were asking us to squeeze the holding jigs onto the noted position of the CNC aluminum parts.


When you are designing an aluminum part which will be anodized,  to identify where the part can be racked will be grateful for the anodizer. If you have any project about CNC machining aluminum parts, you are welcome to send us RFQ for free project review.