What is anodizing?

Anodizing is a key step in manufacturing aluminum CNC machined parts. An electrochemical process that involves coating a metal part with an oxide surface layer, anodizing gives the part additional sturdiness and a more attractive finish. While anodizing is most common with aluminum, other substrates can be Anodized, including magnesium and titanium. 

Anodizing ensures a part can resist corrosion and wear and tear from prolonged use, and that it retains its cosmetic appearance under any conditions. 

The most common types of anodizing are Type I (Chromic Acid Anodize), Type II (Sulfuric Acid Anodize) and Type III, also known as Hardcoat. Each type of anodizing is ideal for different materials and serves its own distinct manufacturing parameters. Despite each type’s specific advantages and drawbacks, they all work relatively the same way. 

How does anodizing work?

The simplest way to understand how anodizing works is in the name. To anodize a part, you connect it to a positive terminal of an electrical circuit, also called an anode. You then submerge the part in an acidic electrolyte bath solution. This solution contains chemical compounds, such as sodium phosphate, which fill the bath with positive and negative ions. 

Once the part is submerged and secured to a hanger so it doesn’t move around, you apply the negative end of the circuit, or cathode, to a metal electrode in the bath. When you send voltage through the circuit, the negative electrode attracts positive ions (cations) from the part, and the aluminum part attracts negative O2 ions (anions) from the solution. 

What should we know before Anodizing Parts?

While anodizing is integral to manufacturing high quality aluminum parts, there are a few things to keep in mind before going ahead with the process. Of course, not all materials can be anodized. You will likely only ever anodize aluminum, though titanium, zinc, tantalummay also need a swift anodizing round. 

To anodize a part, you have to fully submerge it into the solution. Usually, this requires you to mount the part on hangers, meaning that your part will include design features that do not make contact with the solution to be anodized. As a result, a part can never be fully anodized across 100% of its surface. 

Another factor to keep in mind is that the geometric dimensions and tolerances of your part may change with anodization. Anodizing builds up a layer on the part, so remember that when you’re in the design process. As well, anodizing will affect the surface roughness of your part.