Die casting is a metal casting procedure that is observed as forcing molten metal under high pressure in a mold cavity. The mold cavity is made using two hardened tool steel dies which have been machined fit and work similarly to CNC precision machining along the way. Most die castings are produced from non-ferrous metals, specifically zinc, copper, aluminium, magnesium, lead, pewter and tin-based alloys. Based on the form of metal being cast, a hot- or cold-chamber machine can be used.
The casting equipment along with the metal dies represent large capital costs which has a tendency to limit the procedure to high-volume production. Creation of parts using die casting is fairly simple, involving only four main steps, which ensures you keep the incremental cost per item low. It really is especially suited for a large quantity of small- to medium-sized castings, which is why die casting produces more castings than almost every other casting process. Die castings are seen as a a very good surface finish (by casting standards) and dimensional consistency.
Two variants are pore-free die casting, that is utilized to eliminate 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 just for producing movable type to the printing industry. The very first die casting-related patent was granted in 1849 for any small hand-operated machine just for mechanized printing type production. In 1885 Otto Mergenthaler invented the linotype machine, a computerized type-casting device which took over as the prominent type of equipment in the publishing industry. The Soss die-casting machine, manufactured in Brooklyn, NY, was the initial 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 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 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 an overview of the 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 relating to steel parts.
Silicon tombac: high-strength alloy created from 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 sorts of corrosion resistance. Such alloys will not be 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 type in letterpress printing and hot foil blocking. Traditionally cast at your fingertips jerk moulds now predominantly die cast following the industrialisation of your type foundries. Around 1900 the slug casting machines came on the market and added further automation, with sometimes lots of casting machines at one newspaper office.
There are many of geometric features that need considering when creating a parametric type of a die casting:
Draft is the volume of slope or taper given to cores or any other parts of the die cavity to enable for easy ejection of the casting through the die. All die cast surfaces which can be parallel for the opening direction of your die require draft for your proper ejection in the casting from your die. Die castings that feature proper draft are easier to remove from the die and cause high-quality surfaces plus more precise finished product.
Fillet will be the curved juncture of two surfaces that could have otherwise met at a sharp corner or edge. Simply, fillets could be included with a die casting to take out undesirable edges and corners.
Parting line represents the idea at which two different sides of your mold get together. The location of the parting line defines which side of the die is definitely the cover and which is the ejector.
Bosses are included in die castings to provide as stand-offs and mounting points for parts that will need to be mounted. For max integrity and strength in the die casting, bosses need to have universal wall thickness.
Ribs are put into a die casting to provide 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 the features will grip to the die steel during solidification. To counteract this affect, generous draft must be included with hole and window features.
There are 2 basic varieties 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, also 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, that enables the molten metal to fill the “gooseneck”. The pneumatic- or hydraulic-powered piston then forces this metal out of your Zinc die casting into the die. The advantages of this technique include fast cycle times (approximately 15 cycles one minute) as well as the ease of melting the metal inside the casting machine. The disadvantages of this system are that it is limited by use with low-melting point metals and that aluminium cannot 21dexupky used because it picks up a number 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 when the casting alloy should not be used in hot-chamber machines; some examples are aluminium, zinc alloys having a large composition of aluminium, magnesium and copper. This process for these machines get started with melting the metal in the separate furnace. Then a precise volume of molten metal is transported towards the cold-chamber machine where it can be 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 drawback to this product is the slower cycle time due to have to transfer the molten metal from the furnace to the cold-chamber machine.