Die Castings are made by injecting or forcing melted metal into a harden metal mold, called a die. The advantage of die casting is that you can rapidly create thin wall complex shapes with high dimensional accuracy.  Once removed from the die, die castings normally require very little secondary operations, usually just the trimming of the flash, buffing, and plating. Die cast parts are generally between 1 and 20 Lbs, but can be as large as 50 Lbs. Good examples of die cast parts are door handles, hood ornaments, and lamp bases.

Zinc Die Castings

Just as die casting offers advantages over other manufacturing processes, zinc provides advantages over other die casting alloys. Die castings in zinc alloys are stronger, tougher, and more ductile than die castings, in aluminum or magnesium. Zinc alloys can be die cast larger, smaller, and with greater complexity. They can be cast smoother, easier, more accurately, and at lower cost. Zinc die castings can be readily painted and more easily plated than any aluminum or magnesium alloy. The melting point of zinc alloys is lower and prolonging die life.

The major advantages of zinc compared to aluminum and magnesium die casting alloys are:

• Lower cost in suitable applications
• Closer tolerances
• Faster production cycle times
• Thinner wall sections
• Higher tensile strength
• Higher impact strength
• More malleable
• Easier finishing

SAND CASTING PROCESS

In this casting process a pattern is made in the shape of the desired part. This pattern is made out wood, plastic or metal. Simple designs can be made in a single piece or solid pattern. More complex designs are made in two parts, called split patterns. A split pattern has a top or upper section, called a cope, and a bottom or lower section called a drag. Both solid and split patterns can have cores inserted to complete the final part shape. Where the cope and drag separates is called the parting line. When making a pattern it is best to tapper the edges so that the pattern can be removed without breaking the mold.

The patterns are then packed in sand with a binder, which helps to harden the sand into a semi-permanent shape. Once the Sand mold is cured, the pattern is removed leaving a hollow space in the sand in the shape of the desired part. The pattern is intentionally made larger than the cast part to allow for shrinkage during cooling. Sand cores can then be inserted in the mold to create holes and improve the casting's net shape. Simple patterns are normally open on top and melted metal poured into them. Two piece molds are clamped together and melted metal is then poured in to an opening, called a gate. If necessary, vent holes will be created to allow hot gases to to escape during the pour. The pouring temperature of the metal should be a few hundred degrees higher than the melting point to assure good fluidity, thereby avoiding prematurely cooling, which will cause voids and porosity. When the metal cools, the sand mold is removed and the metal part is ready for secondary operations, such as machining & plating. Sand casting is the least expensive of all of the casting processes.

INVESTMENT CASTING PROCESS

Investment Castings can be made in most steels and alloys, using the Lost Wax process (sometimes referred to as precision casting) to produce intricate and metallurgical accurate castings with very tight tolerances. This method is used to mass produce parts with near net dimensions and a high quality "as cast finish" thereby producing a visually attractive finish and reducing machining cost.
In this process an expendable pattern is made, normally by injecting wax or plastic into a metal mold. This pattern is then coated, by either pouring or dipping, with a refractory slurry (watery paste of silica and a binder) that will set at ambient temperature to produce a mold or shell. After hardening, the mold is turned upside down and the expendable pattern (wax or plastic) is melted out of the mold. To complete this refractory mold, ceramic cores may be inserted. Investment castings can be made in almost any pourable metal or alloy.

The investment casting process cost more than the other casting methods, but the more complex the parts the more economical it is to use because of the reduced need for secondary machining. In many cases investment castings will be used "as cast". This process is normally used for parts between 1 ounce to 10 Lbs, however, heavier parts are frequently made.

For more information and for other processes such as Shell Mould, Plaster Mould and Graphite Mould, please contact us.

Top