How to Finish an Aluminium CNC Machined Part

Aluminium alloys are often a great option when it comes to choosing the right material for you CNC machined parts and prototypes. In addition to the wide range of physical and mechanical properties that they offer depending on the chosen alloy, aluminium parts can be finished in a variety of ways. These are some of the most common ones.

As machined

Being the simplest option, choosing to leave the parts as they come out of the CNC machining centre can be a viable option for prototypes and/or parts that do not have particular aesthetic or scratch/abrasion resistance requirements. Nevertheless, by paying special attention to the optimal choice of alloy, tools and cutting parameters, “as machined” parts can still look great without any additional finishing steps. Have a look at our Parts Gallery to see a few examples of our “as machined” work. 

Glass bead and sand blasting

Bead blasting is a finishing process where the machined part is blasted with tiny glass beads using a highly pressurised air gun. The impacted surfaces of the part are free of smears, contaminants, and media embedments; high points are blended and pores sealed. A wide range of finishes from matte to satin are achievable. The peening action of the media further acts to impart a layer of compressive stresses on the surface of the part. This increases fatigue life, decreases susceptibility of the part to stress corrosion, and enhances surface strength. However, it is advisable to use this process only when the dimensional tolerances of a part or a specific feature are not critical.

In a similar fashion, sandblasting is a process that uses a high-pressure stream of sand to remove material. It is therefore more aggressive than glass bead blasting.

Electroplating

Electroplating is a common metal finishing technique that improves corrosion protection, provides greater wear resistance or enhances the appearance of a product. This process involves immersing the aluminum workpiece into an electrolytic solution and introducing an electric current to deposit dissolved ions of another metal onto the surface. Common plating metals are tin, nickel, silver and gold.

Anodising

Anodising is an electrochemical process that provides additional protection aside from the oxide film that develops naturally on aluminium and its alloys. With this process, a durable, porous anodic oxide layer is formed on the surface of the aluminium which can also be dyed to provide a wear resistant colour to your parts.

Powder coating

Powder coating is a finishing process that involves coating a part with a coloured polymer powder using an electrostatic spray gun. The coating is then cured in an oven at a temperature of about 200°C. Powder coating improves the strength and wear characteristics of a part, as well as its corrosion and impact resistance.

A glass bead blasted and anodised part in EN AW-6082-T651 aluminium alloy

At CNC Proto we specialise in the machining of non-ferrous metals, mostly 6000 and 7000 series aluminium alloys, and engineering plastics. You can see a list of the standard finishes we offer in our Services page. If your parts require a specific finish other than the ones listed, feel free to let us know on our Quote Request form!

For more articles on CNC machining, materials and design of machined parts, be sure to check our Resource Library.

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Fernando Duarte Ramos

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With an MSc. in Mechanical Engineering, Fernando has worked 8 years at CERN designing and building the next generation of particle detectors alongside top European engineers and physicists. Being passionate about CNC machining, he started CNC Proto, an online CNC machining service in Europe dedicated to providing fast turnaround, high quality parts at a competitive cost. Learn more About Us

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