Die casting

"Hot Chamber" Die Casting Diagram

Die casting is an efficient method of creating a broad range of shapes, die castings are one of the most mass produced components today and are found in many items in and around the home. Many toy cars use die casting in their production, as do real vehicles. Die casting offers high accuracy in its products with a good quality surface finish which is suitable for many products without the need for extra polishing or machining.

The Process
Die casting first requires the creation of a steel mould (called a ‘die’) of the part to be cast, these moulds once created are fitted to the die casting machine and injected under pressure with the desired molten metal or alloy of choice. There are two methods of injection, these being hot chamber and cold chamber.

Hot Chamber method
Hot chamber casting machines use an oil or gas powered piston to drive the molten metal heated within the machine into the die. The piston pulls back allowing the molten metal to fill what is called the “goose neck” once the liquid metal has filled the goose neck the piston can then force the liquid metal into the die. The clamping force used to inject the metals can range from 400-4000 tons. This method has fast cycle times which can be as low as seconds when producing small parts.

Cold Chamber Method
Cold chamber casting machines do not heat the metal, the molten metal must be ladled into the cold chamber manually or by an automatic ladle system, the molten metal is then forced into the die by a hydraulic piston at high pressure.

Die Casting Advantages

• High dimensional accuracy is achievable



• Fast Production



• Thinner walls are achievable when compared to investment casting (0.6mm -0.8mm)



• Wide range of possible shapes



• Simplified assembly (external threads can be cast, or holes cored to internal tap drill size)



• Good finish (1 μm - 2.5 μm) (depending on purpose not all parts will require extra finishing)

Die Casting Disadvantages

• Castings must be smaller than 600mm and the thickest wall section should be kept below 13mm



• High initial cost (Cost of moulds and machine set up)



• A large production volume is required to make the process cost effective



• Some porosity is common with die casting



• Die casting is limited to high fluidity metals (Zinc, Aluminium, Magnesium, Copper, Lead and Tin)