Die casting is really a metal casting method that is characterized by forcing molten metal under high pressure into a mold cavity. The mold cavity is generated using two hardened tool steel dies which were machined into shape and work similarly to CNC precision machining during the process. Most die castings are produced from non-ferrous metals, specifically zinc, copper, aluminium, magnesium, lead, pewter and tin-based alloys. Based on the sort of metal being cast, a hot- or cold-chamber machine is used.
The casting equipment along with the metal dies represent large capital costs which will limit the process to high-volume production. Production of parts using die casting is comparatively simple, involving only four main steps, which will keep the incremental cost per item low. It can be especially suited for a huge volume of small- to medium-sized castings, which is why die casting produces more castings than every 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, which is used with zinc castings to lower scrap and increase yield.
Die casting equipment was invented in 1838 when it comes to producing movable type for your printing industry. The very first die casting-related patent was granted in 1849 for a small hand-operated machine for the purpose of mechanized printing type production. In 1885 Otto Mergenthaler invented the linotype machine, an automated type-casting device which became the prominent kind of equipment within the publishing industry. The Soss die-casting machine, created in Brooklyn, NY, was the very first machine to get available in the open market in America. Other applications grew rapidly, with die casting facilitating the development 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 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; aluminum die casting to, e.g. The Aluminum Association (AA) standards: AA 380, AA 384, AA 386, AA 390; and AZ91D magnesium.F This 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 easiest 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 from steel parts.
Silicon tombac: high-strength alloy created from copper, zinc and silicon. Often used as a replacement for investment casted steel parts.
Lead and tin: high density; extremely close dimensional accuracy; used for special forms of corrosion resistance. Such alloys are certainly not used in foodservice applications for public health reasons. Type metal, an alloy of lead, tin and antimony (with sometimes traces of copper) can be used for casting hand-set type in letterpress printing and hot foil blocking. Traditionally cast in hand jerk moulds now predominantly die cast once the industrialisation of the type foundries. Around 1900 the slug casting machines came onto the market and added further automation, with sometimes dozens of casting machines at one newspaper office.
There are a variety of geometric features that need considering when making a parametric model of a die casting:
Draft is the amount of slope or taper provided to cores or any other elements of the die cavity to allow for quick ejection in the casting through the die. All die cast surfaces that are parallel for the opening direction of your die require draft for the proper ejection in the casting through the die. Die castings that feature proper draft are simpler to remove in the die and lead to high-quality surfaces and more precise finished product.
Fillet is the curved juncture of two surfaces that might have otherwise met in a sharp corner or edge. Simply, fillets can be included in a die casting to get rid of undesirable edges and corners.
Parting line represents the purpose from which two different sides of your mold come together. The position of the parting line defines which side of your die is definitely the cover and the ejector.
Bosses are put into die castings to serve as stand-offs and mounting points for parts that should be mounted. For optimum integrity and strength of your die casting, bosses should have universal wall thickness.
Ribs are included with a die casting to offer added support for designs that require maximum strength without increased wall thickness.
Holes and windows require special consideration when die casting because the perimeters of these features will grip on the die steel during solidification. To counteract this affect, generous draft should be included in hole and window features.
The two main basic kinds of die casting machines: hot-chamber machines and cold-chamber machines. These are typically rated by simply 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, depend on a pool of molten metal to feed the die. At the outset of the cycle the piston from the machine is retracted, that enables the molten metal to fill the “gooseneck”. The pneumatic- or hydraulic-powered piston then forces this metal out of 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 on this system are that it must be limited to use with low-melting point metals and that aluminium cannot 21dexupky used because it picks up some of the iron while in the molten pool. Therefore, hot-chamber machines are primarily used with zinc-, tin-, and lead-based alloys.
They are used as soon as the casting alloy can not be employed in hot-chamber machines; such as aluminium, zinc alloys using a large composition of aluminium, magnesium and copper. The process of these machines get started with melting the metal in a separate furnace. Then a precise volume of molten metal is transported for the cold-chamber machine where it really is fed into an unheated shot chamber (or injection cylinder). This shot will then be driven in the die by way of a hydraulic or mechanical piston. The greatest downside of this system is definitely the slower cycle time because of the have to transfer the molten metal from the furnace towards the cold-chamber machine.