The surface quality of machined aluminium
Compared to other metal materials, aluminium is easy to machine. But the surface quality of machined aluminium is different for the wide range of alloys available and depend of their machinability.
Machinability of aluminium
The term machinability includes all those properties which are relevant for the machining and cutting process [1]:
- the wear of tools
- the necessary cutting force
- the resulting form of the chips
- the surface quality of the machined aluminium parts
Machined aluminium surface quality
The behaviour of the aluminium alloy
In general, the machined surface roughness, adheres to the same rules that apply to the form of chips. The following rule applies for wrought alloys at least:
- the higher the strength and hardness of the wrought alloy to be machined, the smoother is the surface produced.
The effect of cutting speed
The cutting speed is an important machining parameter which influences the surface quality. In general, the roughness is inversely proportional to the cutting speed. At low cutting speeds the roughness of the surface produced increases dramatically, due to the increased edge build-up. The region of low cutting speeds must, as a rule, be avoided when aluminium is to be machined. Edge build-up is a phenomenon which is typical for aluminium and is caused by the periodical sticking and removal of aluminium particles deposited on the cutting tool (Figure 3101.03.01).
The effect of tools
The influence of the tool construction on the quality of the surface produced can be ascertained from the previously mentioned process: It is important that the chips can glide smoothly over the cutting tool surface. This means that a sufficiently large rake angle, good lubrication and a smooth cutting tool surface are essential. A clean smooth surface cannot be obtained using worn cutting tools.
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