Die castings are solid metal parts and shapes that are formed in foundries through the process of die casting. Conducted in facilities called foundries, die casting works by applying high pressure and forcing molten metal into dies, also called molds or die molds, then letting the metal cool. Secondary finishing processes sometimes follow this process to bring die castings up to the quality their intended applications. Metals used in die casting are usually some type of non-ferrous metal casting, like bronze, lead, tin, aluminum, zinc, magnesium and copper. Alloys, especially steel alloys, may be used as well, but steel parts are usually forged instead.
Every die is cut from metal to create a certain shape, and most are made to create closed die castings. Closed die casting molds are made by cutting an original mold into two separate blocks, tooling them back together with their cavities aligned and spraying the new mold with a lubricant that helps regulate temperature and makes parts removal easier. Closed die casting molds can open and close, though, as their name suggests, they must be closed at the start of the casting process. Once closed, molten metal is poured into a shot sleeve and, under high pressure, injected into the die with a plunger.
When a cast has solidified, pressure drops, the die opens and ejector pins push out the solidified metal shape, which is called a “shot,” rather than a part, until it is tooled and deburred to remove any excess material. Excess material usually forms in leakage areas between the die mold cavities and in channels leading to the die mold, taking the the shape of flash, sprue, runners and gate. Flash is excess metal on a die cast part that extends past the die set’s parting line and blocks other metal from flowing past it and filling the mold. Sprue transfers molten metal to the runners, which are horizontal mechanisms connected to the sprue for the purpose of transferring molten metal to the mold.
Finally, gate refers to both the passage molten metal takes from the runners to the die cavity and the complete ejected content of a die. As noted above, sometimes, this excess material requires more than tooling and deburring, and undergoes more secondary processes, such as CNC machining, surface finishing and plating. Such processes may accomplish a variety of things, like the removal of blisters and blow holes, surface strengthening and the increase of conductivity or compatibility.
Despite a moderate decline in the usage of this forming method since the introduction of processes like injection molding and vacuum forming, the number of die cast products in our world is incalculable. Die castings make up the majority of products requiring the strength of a seamless die-cast metal part, like sink faucets, gas pump handles and gumball machines. Also, automobile engine blocks frequently feature die cast aluminum valve covers.
In the tech world, high tolerance magnesium die castings serve as housings and interior EMI enclosures of computer and electronic parts, while miniature zinc die cast parts service various electronic equipment applications. Zinc is also frequently die cast for use as cabinetry and door handles.
Why invest in die castings? For one, the process of die casting is affordable and versatile; it a offers high volume, low cost means of producing metal shapes, products and parts that have much closer tolerances and far more intricate designs than pieces produced by other methods. The intricacy of die castings does not slow down the process of fabricating them. Rather, die castings, especially zinc and aluminum ones, can be manufactured in large quantities at a low cost without facing compromise of quality.
Die castings are also produced with fewer secondary processes and less processing than those made through methods like metal stamping, hand tooling or forging. Their versatility continues with casting options; they may be made through hot chamber or cold chamber casting and they can be made into virtually any shape. Die castings are durable and strong, and highly popular worldwide. If your die molds are carefully designed, your materials thoughtfully selected and equipment properly installed and maintained, your investment will bear fruit.