Die casting


Mold design
Die casting process
Secondary Operation
Inspection and Assembly

Selection of die casting materials:

The alloys used in casting are usually aluminum, magnesium, and zinc. Fuchia industry usually uses the following alloys as the main raw materials of products:

Zamak alloy

The alloy elements often added to zinc alloy zamak are aluminum, copper, magnesium and other alloys. Zinc alloys have low melting point, high fluidity, easy welding and plastic processing, corrosion resistance in the atmosphere, and the material has a high recovery rate. It is a die-casting part. The common raw materials.

Zamak 2

Used for mechanical parts with special requirements for mechanical properties, high hardness requirements, good wear resistance, and general dimensional accuracy requirements.

Zamak 3

Good fluidity and mechanical properties. Used in castings that do not require high mechanical strength, such as toys, lamps, ornaments, and some electrical devices.

Zamak 5

Good fluidity and good mechanical properties. Used in castings that have certain requirements for mechanical strength, such as auto parts, electromechanical parts, mechanical parts, and electrical components.

ADC12 alloy

ADC= Aluminum-Alloy Die Castings Japan's aluminum alloy grade, also known as No. 12 aluminum, Al-Si-Cu series alloy, is a die-cast aluminum alloy, suitable for cylinder head covers, sensor brackets, covers, cylinder blocks, etc. The executive standard is: JIS H 5302 -2000 "Aluminum Alloy Die Casting".

Magnesium alloy AZ91D

AZ91D belongs to the category of cast magnesium alloy, which is mainly processed by die casting assisted later processing, and the appearance can be changed by surface methods such as electrophoresis. It is characterized by high specific strength and greatly improved corrosion resistance compared to pure magnesium. It is mainly used for the shells of electrical products, small-sized thin or special-shaped brackets, etc. A represents metal aluminum Al, Z represents metal zinc Zn, 9 represents 9% aluminum content, 1 represents 1% zinc content, and the last D is the identification code. (National standard GB/T5153-2003).

Zinc, aluminum, and magnesium are the three main die casting alloys. They are usually non-ferrous metals, and their mechanical properties vary greatly, making them suitable for almost all types required by manufacturers. The die-casting alloy is not only resistant to high working temperature, but also can be completely recycled and reused. Die casting alloy also has:

Good corrosion resistance
High strength and high hardness
High thermal conductivity
High conductivity
Excellent electromagnetic interference/radio frequency interference (EMI/RFI) shielding
Easy to finish

Die-casting process

Die casting is a metal casting process that is characterized by forcing molten metal under high pressure into a mold cavity. The mold cavity is created using two hardened tool steel dies which have been machined into shape and work similarly to an injection mold during the process. Most die castings are made from non-ferrous metals, specifically zinc, copper, aluminum, magnesium, lead, pewter, and tin-based alloys. Depending on the type of metal being cast, a hot- or cold-chamber machine is used.

The casting equipment and the metal dies represent large capital costs and this tends to limit the process to high-volume production. Manufacture of parts using die casting is relatively simple, involving only four main steps, which keeps the incremental cost per item low. It is especially suited for a large quantity of small- to medium-sized castings, which is why die casting produces more castings than any other casting process. Die castings are characterized by a very good surface finish (by casting standards) and dimensional consistency.

The following are the four steps in traditional die casting, also known as high-pressure die casting,these are also the basis for any of the die casting variations: die preparation, filling, ejection, and shakeout. The dies are prepared by spraying the mould cavity with lubricant. The lubricant both helps control the temperature of the die and it also assists in the removal of the casting. The dies are then closed and molten metal is injected into the dies under high pressure; between 10 and 175 megapascals (1,500 and 25,400 psi). Once the mould cavity is filled, the pressure is maintained until the casting solidifies. The dies are then opened and the shot (shots are different from castings because there can be multiple cavities in a die, yielding multiple castings per shot) is ejected by the ejector pins. Finally, the shakeout involves separating the scrap, which includes the gate, runners, sprues and flash, from the shot. This is often done using a special trim die in a power press or hydraulic press. Other methods of shaking out include sawing and grinding. A less labor-intensive method is to tumble shots if gates are thin and easily broken; separation of gates from finished parts must follow. This scrap is recycled by remelting it.The yield is approximately 67%.
The high-pressure injection leads to a quick fill of the die, which is required so the entire cavity fills before any part of the casting solidifies. In this way, discontinuities are avoided, even if the shape requires difficult-to-fill thin sections. This creates the problem of air entrapment, because when the mould is filled quickly there is little time for the air to escape. This problem is minimized by including vents along the parting lines, however, even in a highly refined process there will still be some porosity in the center of the casting.
Most die casters perform other secondary operations to produce features not readily castable, such as tapping a hole, polishing, plating, buffing, or painting.

After the shakeout of the casting it is inspected for defects. The most common defects are misruns and cold shuts. These defects can be caused by cold dies, low metal temperature, dirty metal, lack of venting, or too much lubricant. Other possible defects are gas porosity, shrinkage porosity, hot tears, and flow marks. Flow marks are marks left on the surface of the casting due to poor gating, sharp corners, or excessive lubricant

Water-based lubricants are the most used type of lubricant, because of health, environmental, and safety reasons. Unlike solvent-based lubricants, if water is properly treated to remove all minerals from it, it will not leave any by-product in the dies. If the water is not properly treated, then the minerals can cause surface defects and discontinuities.

Die casting is mainly divided into two types – hot chamber and cold chamber die casting:

Hot chamber die casting:

The metal pool of hot chamber die-casting contains molten liquid and semi-liquid metal, which fills the mold under pressure. The advantages of this system include fast cycle speed (approximately 15 cycles per minute), easy automatic operation, and convenient metal melting process. Disadvantages include the inability to die-cast metals with higher melting points, as well as the inability to die-cast aluminum, because aluminum will bring iron out of the melting pool. Therefore, hot chamber die casting machines are generally used for alloys of zinc, tin and lead. Moreover, hot chamber die casting is difficult to die-cast large castings, usually this process is die-casting small castings.

Cold chamber die casting:

Cold-chamber die-casting can be used when die-casting metals that cannot be used in the hot-chamber die-casting process, including aluminum, magnesium, copper, and zinc alloys with high aluminum content. In this process, the metal needs to be melted first in a separate crucible. Then a certain amount of molten metal is transferred to an unheated injection chamber or nozzle. By hydraulic or mechanical pressure, these metals are injected into the mold. Due to the need to transfer the molten metal into the cold room, the biggest disadvantage of this process is the long cycle time. Cold chamber die casting machines are divided into vertical and horizontal types. Vertical die casting machines are usually small machines, while horizontal die casting machines have various models.

The biggest advantage of the die-casting process is that it can be mass-produced and has a high degree of consistency between products. Not only is a single component, customers can also design complex shapes, including external threads and a very small draft angle, so that the opportunity for secondary processing To minimize, multiple parts can also be integrated into a single part, eliminating assembly operations and labor costs, while simplifying inventory control.

Other advantages include:

1. The thickness of the casting wall can be changed to meet the target demand as much as possible
2.Lower tolerance
3.Optimize the process to shorten the time required for the process steps
4.Reduce unnecessary raw material loss
5.Extend mold life