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 DIE CASTING BASICS:


This page has been designed as a brief description of the basic process of die casting. The description is in the most basic form in layman's terms, so it can be understood even by those not familiar with die casting.

INTRODUCTION TO DIE CASTING:
In the die casting process a mold (called the die) is required.  The mold is constructed from very high quality steel specially made for molds (dies).  The molds (dies) are reusable and are made of two halves. During the process of die casting, molten metal is injected into the closed die under very high pressure through a relatively small hole in one half of the die. When the molten metal has solidified sufficiently, the two parts of the die are opened to expose the actual casting inside.  The casting is then removed from the die, cooled further and then trimmed.  The trimming separates the gates and runners from the casting. The gates and runners are incorporated into the mold design as a way to distribute molten metal to the various parts of the mold.  The trimmed gates and runners are then usually re-melted with new metal also being added. After trimming, further operations can be performed such as drilling and tapping, powder coating and assembly of finished components, etc.

APPLICATION:
Die casting is used to make various cast alloy parts in different sizes for a wide variety of applications. The die casting process is very efficient and can produce large volumes of castings in a short period of time and has extremely precise repeatability. The flexibility of product types, casting sizes, a virtually infinite possibility of shapes makes die casting the preferred process for a wide variety of industries. While die casting molds (dies) are more expensive than molds for other forms of casting, such as sand casting and permanent mold casting or gravity casting, die cast parts offer many advantages such as very high tolerances, precise repeatability, less porosity, sharply defined parts and a possibility of textured or smooth surfaces.

LIMITATIONS:
With the development of CAD programs and the development of sophisticated shot monitoring and shot control systems of die casting machines, most limitations have been overcome.  There are basically only two limitations left.  The first is size and weight of the casting.  The size of the physical dimensions of the casting will determine the size of the machine that is required. However, obviously there is a size limit to this. The item being cast must fit into the mold (die) with sufficient clearance all around the casting and then mold (die) itself then must fit into the die casting machine. The mold (die) clearance determining factor is the "distance between tie bars" on the die casting machine. The mold (die) must be able to fit between these dimensions with reasonable clearance.  So for example, a 600 ton die casting machine usually will have a distance between tie bars of 737 mm H x 737 mm W (29"H x 29"W).  If the mold (die) is bigger than that you will have to move up to the next size of machine.  The largest size of machine ever produced has been a 4000 ton machine with a "distance between tie bars" of 1780 mm H x 1780 mm W (70" H x 70" W) and a max shot weight of 65kg (143 lbs). 

The other limitation is the weight of the casting. For example, a 600 ton die casting machine usually has a maximum shot weight of about 7 kg (15 lbs). The shot weight is defined as the total weight of the metal that is injected.  The shot weight therefore includes the actual casting plus any runners, gates and the biscuit. The reason for the weight limitation is that the die casting machine must have sufficient power and velocity to inject molten metal through the shot sleeve into the die and to fill the die cavity completely with the metal before the metal starts to solidify. The whole process must be done within milliseconds and at tremendous pressure otherwise the extreme ends of the mold (die) will not get filled or will be partially filled. The result will be a scrap casting and wasted effort. While the calculation of "weight to velocity to time" is extremely complicated, die casting machine manufactures have already done most of the work for you by "standardizing" this ratio.  As such, each machine manufacturer builds a relatively standardize range of machines with relatively standardized shot weight ranges and relatively standardized distances between tie bars. For a comparison chart please see our Machine Buy's Guide.


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