Aluminum Die Casting – A Thorough Description On The Heavy Duty Processes Used With Die Casting Parts.

Die casting is really a metal casting process 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 healthy and work similarly to aluminum die casting parts during the process. Most die castings are produced from non-ferrous metals, specifically zinc, copper, aluminium, magnesium, lead, pewter and tin-based alloys. Dependant upon 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 also this is likely to limit the procedure to high-volume production. Manufacture of parts using die casting is pretty simple, involving only four main steps, which will keep the incremental cost per item low. It is actually especially suited for a sizable number of small- to medium-sized castings, which is why die casting produces more castings than almost every other casting process. Die castings are characterized by a good surface finish (by casting standards) and dimensional consistency.

Two variants are pore-free die casting, which is used to get rid of gas porosity defects; and direct injection die casting, which is often used with zinc castings to minimize scrap and increase yield.

History

Die casting equipment was invented in 1838 with regards to 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 became the prominent form of equipment in the publishing industry. The Soss die-casting machine, created in Brooklyn, NY, was the initial machine being sold in the open market in North America. Other applications grew rapidly, with die casting facilitating the expansion of consumer goods and appliances through making affordable the creation of intricate parts in high volumes. In 1966, General Motors released the Acurad process.

The primary 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 main 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 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; employed for special kinds of corrosion resistance. Such alloys usually are not used 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 enter 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 on the market and added further automation, with sometimes a large number of casting machines at one newspaper office.

There are a variety of geometric features to be considered when creating a parametric type of a die casting:

Draft is the quantity of slope or taper provided to cores or other aspects of the die cavity allowing for convenient ejection of your casting through the die. All die cast surfaces that are parallel for the opening direction in the die require draft to the proper ejection of the casting through the die. Die castings which feature proper draft are easier to remove from the die and result in 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 may be included in a die casting to get rid of undesirable edges and corners.

Parting line represents the point at which two different sides of your mold come together. The location of the parting line defines which side from the die will be the cover and the ejector.

Bosses are put into die castings to provide as stand-offs and mounting points for parts that will have to be mounted. For max integrity and strength in the die casting, bosses must have universal wall thickness.

Ribs are added to a die casting to provide 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 those features will grip for the die steel during solidification. To counteract this affect, generous draft needs to be put into hole and window features.

Equipment

The two main basic forms of die casting machines: hot-chamber machines and cold-chamber machines. These are typically rated by 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 your hot-chamber machine

Hot-chamber die casting, also called gooseneck machines, depend on a pool of molten metal to give the die. At the beginning of the cycle the piston from the machine is retracted, allowing the molten metal to fill the “gooseneck”. The pneumatic- or hydraulic-powered piston then forces this metal from the Zinc die casting to the die. The main advantages of this product include fast cycle times (approximately 15 cycles a minute) and the ease of melting the metal in the casting machine. The disadvantages on this system are that it is restricted to use with low-melting point metals and therefore aluminium cannot 21dexupky used since it picks up a few of the iron whilst in the molten pool. Therefore, hot-chamber machines are primarily used in combination with zinc-, tin-, and lead-based alloys.

These are used as soon as the casting alloy should not be employed in hot-chamber machines; such as aluminium, zinc alloys using a large composition of aluminium, magnesium and copper. The procedure for such machines start with melting the metal inside a separate furnace. A precise volume of molten metal is transported towards the cold-chamber machine where it is fed into an unheated shot chamber (or injection cylinder). This shot is going to be driven to the die by way of a hydraulic or mechanical piston. The largest downside of this method will be the slower cycle time due to should transfer the molten metal from your furnace towards the cold-chamber machine.