Quite often cast components will require a level of proof machining in order to produce a finished item. There are different processes in order to create a casting, and each of these will influence the way a part needs to be machined or finished.
As its name suggests in order to create sand castings, a specialised sand is used to form the part cavity and influence the way in which the metal will flow. The sand is placed into a three dimensional pattern to give it the right shape and most often a mould will be created in two halves and then put together. Sand Castings often need proof machining as the metal may pick up the texture of the coarse sand, and also to create a smooth surface on the two halves of the parting line to ensure they fit together smoothly. Sand casting is a relatively inexpensive technique and so this machining cost can easily be incorporated into the finished product.
The fastest of the casting processes, die cast parts are formed when molten metal is forced at high pressure into the mould. This technique allows for a fast turnaround and is often used on higher volume production. The main materials that are Die Cast are Zinc, Magnesium and Aluminium. Zinc often does not require a lot of proof machining. Magnesium has a low resistance to cutting and low heat capacity meaning when machining you need sharper cutting edges and large relief angles in order to get the best performance. When Machining Cast Aluminium, it is better to work at high speeds.
This process is also known Lost Wax Process. A mould is taken of the component, usually in silicone and wax is poured into this. This wax ‘copy’ is attached to an assembly alongside other copies and then coated in a ceramic slurry which dries to create a shell. The wax copies are then melted out of the shell, forming a mould for metal to be poured into. These produce castings with excellent surface finish which often don’t require machining but may require other processes such as drilling, tapping and reaming.
Bronte Precision are able to provide proof machining as well as associated services such as boring, drilling, tapping and reaming of cast parts. We specialise in larger sized components and work extensively with engineering castings most often used in Oil, Pump and Automotive applications. We are ISO certified and used to working alongside a wide range of different cast materials.