Die casting is a metal casting method that is characterized by forcing molten metal under high-pressure right into a mold cavity. The mold cavity is created 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 made from non-ferrous metals, specifically zinc, copper, aluminium, magnesium, lead, pewter and tin-based alloys. According to the sort of metal being cast, a hot- or cold-chamber machine is utilized.
The casting equipment along with the metal dies represent large capital costs which has a tendency to limit the process to high-volume production. Creation of parts using die casting is relatively simple, involving only four main steps, which ensures you keep the incremental cost per item low. It is especially suitable for a large volume of small- to medium-sized castings, which explains 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 used to remove 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 for a small hand-operated machine just for mechanized printing type production. In 1885 Otto Mergenthaler invented the linotype machine, a computerized type-casting device which became the prominent type of equipment in the publishing industry. The Soss die-casting machine, manufactured in Brooklyn, NY, was the 1st machine to get sold in the open market in North America. Other applications grew rapidly, with die casting facilitating the increase of consumer goods and appliances simply by making affordable producing intricate parts in high volumes. In 1966, General Motors released the Acurad process.
The main 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 a summary of the advantages of each alloy:
Zinc: the simplest 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 of steel parts.
Silicon tombac: high-strength alloy made from copper, zinc and silicon. Often used as a replacement for investment casted steel parts.
Lead and tin: high density; extremely close dimensional accuracy; useful 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 utilized for casting hand-set key in letterpress printing and hot foil blocking. Traditionally cast at hand jerk moulds now predominantly die cast once the industrialisation from the type foundries. Around 1900 the slug casting machines came into 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 creating a parametric kind of a die casting:
Draft is the level of slope or taper provided to cores or another areas of the die cavity allowing for easy ejection from the casting through the die. All die cast surfaces that are parallel for the opening direction of the die require draft for your proper ejection of the casting from the die. Die castings which feature proper draft are easier to remove from the die and lead to high-quality surfaces and much more precise finished product.
Fillet will be the curved juncture of two surfaces that could have otherwise met at the 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 idea from which two different sides of any mold combine. The positioning of the parting line defines which side in the die will be the cover and which is the ejector.
Bosses are included in die castings to offer as stand-offs and mounting points for parts that will need to be mounted. For max integrity and strength from the die casting, bosses need to have universal wall thickness.
Ribs are included with 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 since the perimeters of these features will grip to the die steel during solidification. To counteract this affect, generous draft should be added to hole and window features.
There are two basic kinds of die casting machines: hot-chamber machines and cold-chamber machines. These are generally rated by exactly 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 any hot-chamber machine
Hot-chamber die casting, often known as gooseneck machines, depend on a swimming pool of molten metal to give the die. At the outset of the cycle the piston in the machine is retracted, that allows the molten metal to fill the “gooseneck”. The pneumatic- or hydraulic-powered piston then forces this metal out from the CNC precision machining in to the die. Some great benefits of this method include fast cycle times (approximately 15 cycles one minute) along with the simplicity of melting the metal inside the casting machine. The disadvantages of this system are that it must be restricted to use with low-melting point metals and therefore aluminium cannot 21dexupky used as it picks up several of the iron while in the molten pool. Therefore, hot-chamber machines are primarily used in combination with zinc-, tin-, and lead-based alloys.
These are typically used when the casting alloy can not be used in hot-chamber machines; some examples are aluminium, zinc alloys using a large composition of aluminium, magnesium and copper. The procedure for such machines begin with melting the metal inside a separate furnace. Then a precise amount of molten metal is transported to the cold-chamber machine where it can be fed into an unheated shot chamber (or injection cylinder). This shot will then be driven to the die by a hydraulic or mechanical piston. The greatest drawback to this product is the slower cycle time due to the must transfer the molten metal from your furnace on the cold-chamber machine.