Die casting is actually a metal casting method that is characterized by forcing molten metal under high pressure in a mold cavity. The mold cavity is created using two hardened tool steel dies which has been machined healthy and work similarly to CNC precision machining during the process. Most die castings are made of non-ferrous metals, specifically zinc, copper, aluminium, magnesium, lead, pewter and tin-based alloys. Depending on the type of metal being cast, a hot- or cold-chamber machine is commonly used.
The casting equipment as well as the metal dies represent large capital costs and this will limit the process to high-volume production. Production of parts using die casting is relatively simple, involving only four main steps, which keeps the incremental cost per item low. It is actually especially suited for a big number of small- to medium-sized castings, this is why die casting produces more castings than every other casting process. Die castings are observed as a good surface finish (by casting standards) and dimensional consistency.
Two variants are pore-free die casting, which is often used to get rid of gas porosity defects; and direct injection die casting, which is used with zinc castings to lessen scrap and increase yield.
Die casting equipment was invented in 1838 for the purpose of producing movable type for the printing industry. The initial die casting-related patent was granted in 1849 for a small hand-operated machine with regards to mechanized printing type production. In 1885 Otto Mergenthaler invented the linotype machine, an automated type-casting device which took over as the prominent kind of equipment from the publishing industry. The Soss die-casting machine, manufactured in Brooklyn, NY, was the initial machine to get available in the open market in Canada And America. Other applications grew rapidly, with die casting facilitating the expansion of consumer goods and appliances simply by making affordable the creation of intricate parts in high volumes. In 1966, General Motors released the Acurad process.
The key die casting alloys are: zinc, aluminium, magnesium, copper, lead, and tin; although uncommon, ferrous die casting can also be 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 The following is an overview of some great benefits of each alloy:
Zinc: the easiest 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 simplest 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 of steel parts.
Silicon tombac: high-strength alloy manufactured from copper, zinc and silicon. Often used as a replacement for investment casted steel parts.
Lead and tin: high density; extremely close dimensional accuracy; utilized for special kinds of corrosion resistance. Such alloys usually are not utilized in foodservice applications for public health reasons. Type metal, an alloy of lead, tin and antimony (with sometimes traces of copper) is commonly used for casting hand-set enter letterpress printing and hot foil blocking. Traditionally cast at hand jerk moulds now predominantly die cast after the industrialisation from the type foundries. Around 1900 the slug casting machines came to the market and added further automation, with sometimes lots of casting machines at one newspaper office.
There are a number of geometric features to be considered when producing a parametric kind of a die casting:
Draft is the level of slope or taper presented to cores or some other areas of the die cavity to allow for quick ejection in the casting through the die. All die cast surfaces which are parallel for the opening direction in the die require draft to the proper ejection of your casting in the die. Die castings which include proper draft are simpler to remove from your die and result in high-quality surfaces and more precise finished product.
Fillet will be the curved juncture of two surfaces that might have otherwise met at a sharp corner or edge. Simply, fillets can be added to a die casting to get rid of undesirable edges and corners.
Parting line represents the purpose where two different sides of any mold combine. The position of the parting line defines which side in the die may be the cover and which is the ejector.
Bosses are added to die castings to serve as stand-offs and mounting points for parts that will have to be mounted. For optimum integrity and strength of your die casting, bosses need to have universal wall thickness.
Ribs are included in a die casting to offer added support for designs which require maximum strength without increased wall thickness.
Holes and windows require special consideration when die casting as the perimeters of those features will grip towards the die steel during solidification. To counteract this affect, generous draft should be added to hole and window features.
The two main basic kinds of die casting machines: hot-chamber machines and cold-chamber machines. These are rated by just how much clamping force they can apply. Typical ratings are between 400 and 4,000 st (2,500 and 25,400 kg).
Hot-chamber die casting
Schematic of the hot-chamber machine
Hot-chamber die casting, also called gooseneck machines, rely upon a swimming pool of molten metal to feed the die. At the start of the cycle the piston of the machine is retracted, which allows the molten metal to fill the “gooseneck”. The pneumatic- or hydraulic-powered piston then forces this metal out of the Zinc die casting in the die. The advantages of this system include fast cycle times (approximately 15 cycles one minute) and the ease of melting the metal within the casting machine. The disadvantages on this system are that it is limited by use with low-melting point metals which aluminium cannot 21dexupky used mainly because it picks up a number of the iron in the molten pool. Therefore, hot-chamber machines are primarily used with zinc-, tin-, and lead-based alloys.
These are typically used as soon as the casting alloy can not be used in hot-chamber machines; these include aluminium, zinc alloys having a large composition of aluminium, magnesium and copper. The process for such machines start with melting the metal inside a separate furnace. Then a precise quantity of molten metal is transported to the cold-chamber machine where it really is fed into an unheated shot chamber (or injection cylinder). This shot will be driven into the die by a hydraulic or mechanical piston. The largest disadvantage of this product will be the slower cycle time as a result of have to transfer the molten metal through the furnace on the cold-chamber machine.