Die casting is actually a metal casting process that is characterized by forcing molten metal under high-pressure in a mold cavity. The mold cavity is produced using two hardened tool steel dies that have been machined into condition and work similarly to CNC precision machining along the way. Most die castings are made from non-ferrous metals, specifically zinc, copper, aluminium, magnesium, lead, pewter and tin-based alloys. According to the form of metal being cast, a hot- or cold-chamber machine is commonly used.
The casting equipment and the metal dies represent large capital costs and also this is likely to limit the method to high-volume production. Production of parts using die casting is fairly simple, involving only four main steps, which keeps the incremental cost per item low. It is actually especially designed for a huge quantity of small- to medium-sized castings, which is why die casting produces more castings than some other casting process. Die castings are seen as a a good surface finish (by casting standards) and dimensional consistency.
Two variants are pore-free die casting, that is utilized to get rid of gas porosity defects; and direct injection die casting, that is utilized with zinc castings to lessen scrap and increase yield.
Die casting equipment was invented in 1838 just for producing movable type for that printing industry. The first die casting-related patent was granted in 1849 to get a small hand-operated machine when it comes to mechanized printing type production. In 1885 Otto Mergenthaler invented the linotype machine, a computerized type-casting device which became the prominent sort of equipment from the publishing industry. The Soss die-casting machine, made in Brooklyn, NY, was the very first machine to get sold in the open market in North America. Other applications grew rapidly, with die casting facilitating the growth of consumer goods and appliances by making affordable the production of intricate parts in high volumes. In 1966, General Motors released the Acurad process.
The principle die casting alloys are: zinc, aluminium, magnesium, copper, lead, and tin; although uncommon, ferrous die casting is also possible. Specific die casting alloys include: Zamak; zinc aluminium; water proof aluminum enclosure to, e.g. The Aluminum Association (AA) standards: AA 380, AA 384, AA 386, AA 390; and AZ91D magnesium.F This is a summary of the advantages of each alloy:
Zinc: the most convenient metal to cast; high ductility; high impact strength; easily plated; economical for small parts; promotes long die life.
Aluminium: lightweight; high dimensional stability for complex shapes and thin walls; good corrosion resistance; good mechanical properties; high thermal and electrical conductivity; retains strength at high temperatures.
Magnesium: the best metal to machine; excellent strength-to-weight ratio; lightest alloy commonly die cast.
Copper: high hardness; high corrosion resistance; highest mechanical properties of alloys die cast; excellent wear resistance; excellent dimensional stability; strength approaching that relating to steel parts.
Silicon tombac: high-strength alloy made of copper, zinc and silicon. Often used as a substitute for investment casted steel parts.
Lead and tin: high density; extremely close dimensional accuracy; useful for special types of corrosion resistance. Such alloys are certainly not found in foodservice applications for public health reasons. Type metal, an alloy of lead, tin and antimony (with sometimes traces of copper) is used for casting hand-set enter letterpress printing and hot foil blocking. Traditionally cast in hand jerk moulds now predominantly die cast after the industrialisation from the type foundries. Around 1900 the slug casting machines came onto the market and added further automation, with sometimes many casting machines at one newspaper office.
There are a number of geometric features to be considered when designing a parametric style of a die casting:
Draft is the amount of slope or taper provided to cores or another parts of the die cavity to permit for convenient ejection from the casting from the die. All die cast surfaces which can be parallel for the opening direction of the die require draft to the proper ejection of the casting through the die. Die castings that come with proper draft are simpler to remove through the die and lead to high-quality surfaces and much more precise finished product.
Fillet is the curved juncture of two surfaces that could have otherwise met at a sharp corner or edge. Simply, fillets could be included in a die casting to get rid of undesirable edges and corners.
Parting line represents the purpose in which two different sides of the mold get together. The positioning of the parting line defines which side of the die may be the cover and which is the ejector.
Bosses are included with die castings to serve as stand-offs and mounting points for parts that should be mounted. For optimum integrity and strength from the die casting, bosses need to have universal wall thickness.
Ribs are put into a die casting to deliver added support for designs which need maximum strength without increased wall thickness.
Holes and windows require special consideration when die casting because the perimeters of these features will grip for the die steel during solidification. To counteract this affect, generous draft should be included in hole and window features.
There are two basic varieties of die casting machines: hot-chamber machines and cold-chamber machines. These are rated by exactly how much clamping force they could apply. Typical ratings are between 400 and 4,000 st (2,500 and 25,400 kg).
Hot-chamber die casting
Schematic of a hot-chamber machine
Hot-chamber die casting, often known as gooseneck machines, rely upon a pool of molten metal to feed the die. At the start of the cycle the piston of your machine is retracted, which allows the molten metal to fill the “gooseneck”. The pneumatic- or hydraulic-powered piston then forces this metal out from the Zinc die casting into the die. Some great benefits of this product include fast cycle times (approximately 15 cycles one minute) along with the comfort of melting the metal within the casting machine. The disadvantages of the system are that it must be confined to use with low-melting point metals which aluminium cannot 21dexupky used as it picks up several of the iron whilst in the molten pool. Therefore, hot-chamber machines are primarily used with zinc-, tin-, and lead-based alloys.
These are used when the casting alloy should not be found in hot-chamber machines; these include aluminium, zinc alloys with a large composition of aluminium, magnesium and copper. The process for these machines start with melting the metal in a separate furnace. Then this precise quantity of molten metal is transported for the cold-chamber machine where it is actually fed into an unheated shot chamber (or injection cylinder). This shot will be driven in to the die by way of a hydraulic or mechanical piston. The greatest disadvantage of this technique is definitely the slower cycle time due to should transfer the molten metal through the furnace for the cold-chamber machine.