CNC milling and turning of aluminum is done in countless factories around the world. Reason for Landes to do it better than the gray matter. Few places can mill such complex shapes of aluminum as we do, to an accuracy of a few micrometers. So we call this level of CNC milling and turning “high-end machining.”
Accurate CNC milling and turning
Aluminum is a highly machinable material, both for milling and turning. But it also deforms easily, especially when it gets hot, e.g. during machining. The malleability of aluminum requires a special approach when working with close tolerances. After all, we want to prevent the aluminum from vibrating or deforming. This risk exists particularly with thin walls.
During CNC milling and turning, we monitor the stability of the component at each stage. We do this by choosing the right sequence of operations and the right intermediate forms.
To check the dimensions, we have an air-conditioned measuring room, where we prevent measurement deviations due to expansion or shrinkage.
Use the right tools
For machining, it is important to apply the right machining conditions. This starts with the geometry of the cutting tool. Aluminum requires a relatively large chip angle and clearance angle. The special cutting tool for aluminum is equipped with this.
Also, aluminum tends to adhere to the cutting surface, especially in unfavorable cutting conditions, causing a false cutting edge to build up. To prevent this buildup on the tool, the tool for aluminum is made as smooth as possible. By polished cutting edges or special coatings, for example, friction is reduced and buildup prevented.
The machine for machining aluminum will need to be extra stable. Aluminum can be machined well at high speeds because aluminum conducts heat particularly well. An increase in temperature and unfavourable machining conditions are thus prevented. Machine stability at high speeds is therefore very important for aluminum. Internal vibrations lead to rejection of products or possibly even damage to the machine.
The (high speed) machining centers or machines must have sufficient power. Machining aluminum at high speeds with sufficient feed rate makes these demands on the power of the machine. For milling steel values of approx. 6 m/s apply, for aluminum 30 m/s and higher.
Many aluminum alloys can be machined well without coolants and lubricants. If coolants and lubricants are used anyway, for example for alloys with a high silicon content, more than 10%, then there are four aspects to consider. First, preferably use an evaporating machining fluid to extract additional heat. Even on the hobby lathe in the shed, you can hear and see immediate improvement when you apply such a fluid.
Second, watch out for bacterial growth in the machining fluid. This can result in a very low pH value causing you to corrode/etch the aluminum. This gives an undesirable corrosion appearance.
Third, dry aluminum parts. When products are left wet, coolants and lubricants leave markings on the aluminum, thus leading to damage to the appearance of aluminum products.
Fourth, the classic use of machining fluids (full beam on the cutter) causes large thermal shocks, which can cause cracks in the cutting edges. This can shorten the tool life and makes it unpredictable. It is recommended to dry mill first, or use a metered amount of cutting oil/fluid directed at the cutting area rather than the cutter.
Avoiding sharp transitions
In CAD, it is easy to engineer sharp edges while this can result in very detrimental impact to the product when loaded. Adding radii of ~ 0.5 mm in the design provides a huge improvement for the application of the product. This radius must be incorporated into the tool.
A sharp transition leads to notch effects which can cause a product, especially when using a low-strength alloy, to crack prematurely resulting in breakage.
Because the CAD file is increasingly being read directly into the machine tool, this step, previously often done by the machine tool technicians, is now (inadvertently) omitted.