Depending on the application, the Die Cast components will most often be formed using either Zinc, Magnesium or Aluminium. Each has its own characteristics when machining and may require associated processes such as drilling, tapping and reaming.
Aluminium is the probably the most widely used materials for die casting. One of the difficulties that comes with the machining of cast aluminium is that there is a wide range of hardness depending on the material grade. Hardness is a key factor in the machinability of any material, and in order to limit variation, careful process control is needed. Close control of the Alloy formation is needed and where possible, and a casting supplier should do its heat treatment in house. Aluminium does machine well and in order to get the best results, high speed steel tools are recommended. It’s important not to clamp the part too tightly as this can affect dimensional changes, and for reaming spiral-flute are preferable to straight-flute.
Manufacturers often specify Die Cast Zinc as very little is often needed in the way of proof machining. When compared to other die cast materials, Zinc allows for faster machining and less tool wear than aluminium alloys. One area of caution is in the use of coolant which can stain your part if not swiftly removed from the part. Although they may not need to be machined, quite often other processes such as tapping and reaming may need to be carried out. It is usually better to use fluteless thread forming taps for Die Cast Zinc as this will produce very little in the way of swarf. This is especially important for hydraulic and automotive applications.
Manufacturers are specifying Magnesium due to the lightweight nature of the metal. It has a fantastic strength to weight ratio and also offer protection from corrosion. Die Cast Magnesium has a low resistance to cutting and a relatively low heat capacity meaning it’s important to use tools with sharp cutting edges, large relief angles, small rake angles. In the past Magnesium was often cut without the use of coolant, but Bronte have found that this reduces the fire risk and eliminated material build up on the tool in turn extending tool life.
Many Die Cast Components will only need minimal proof machining in order to be produce finished components, but where you have large surfaces at play it is often better to get someone with extensive machining knowledge. Bronte Precision offer proof machining for large sized cast components, most often for the pump, oil and automotive industries.