Die casting
Quality
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 2
Zamak 2 zinc alloy usually used to produce some products which have high requirement of hardness and wear resistance but normal requirement of dimensions.
Zamak 3
Zamak 3 zinc alloy has good flow and mechanical properties. It usually is used to die casting products which doesn’t have high requirement of mechanical strength. For example, toys , lamps , decorations and some electrical device.
Zamak 5
Zamak 5 zinc alloy also has good flow and mechanical properties. It usually is used to some products which have normal requirement of mechanical strength. For example: Auto unit parts , electromechanical parts , mechanical parts and electrical components.
ADC12 alloy
ADC = Aluminum-alloy die casting = the Japanese aluminum alloy code , it is the die casting aluminum alloy (Al-Si-Cu alloy). It is suitable for producing cylinder head covers , sensor brackets , covers , cylinder blocks.. etc. this material is ruled by standard JIS H 5302-2000.
A380 alloy
A380 Aluminum alloy is a material which is usually used to produce aluminum die casting products. like ADC12, A380 also has good property of mechanical and thermal conductivity. But this material will cause the surface of product roughly because high silicon content. A380 aluminum usually is used to produce chassis for electrical equipment, engine mounts, gearboxes, furniture, generator parts and hand tool products.
Zinc, aluminum, and magnesium are main die casting materials. They are non-ferrous metals, and their mechanical properties are different. They are 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. Die casting alloy also has other features:
High corrosion resistance
High strength and high hardness
High thermal conductivity
Die-casting process
Die casting is a metal casting process. The meaning is to use a die casting machine to apply pressure to the mold. The mold is usually made by using high strength alloy(usually using stainless steel) , and the mold will be designed according to the requirement of products.
The material of die casting products is non-ferrous metal(ADC12 A380 ZAMAK2, 3,5).
Depending on the type of die casting , the manufacturer needs to choose to use hot chamber or cold chamber die casting machine.
Because the cost of die casting machine and molds is very expensive , die casting process is usually used to producing products which have high amount requirement.
Using die casting process to produce product could reduce the cost of production and easily to produce.
Die casting process is suitable for producing high amount medium (or small) size products, so die casting process is the most widely used of various casting process.
Compared with other casting techniques, die casting process could make product have flatter surface, higher dimensional consistency.
Some new die casting process are created in the fundamental of traditional die casting process. For example , Non-hole die casting process-reducing defect and porosity approach to 0%. Directly injecting die casting process – reducing waste and increase yield rate. There are also new die-casting processes such as precision high-speed die-casting technology and semi-solid die-casting invented by General Dynamics.
The traditional die casting process has four stages – Installing mold , injecting material , forming and ejecting products. This is the basis for various improved die casting processes. The mold installation includes the process of installation, preheating, spraying release agent…e.t.c. Release agents are used to help maintain mold temperature and help products can release from mold easily. When the mold
Is closed , the molten metal will be injected with high pressure. Then molten metal will be cooling down and the products will be ejected when the mold is opened.
the final stage is reducing the gate and overflow by using manual or punching mold.
The injecting speed is very fast during high pressure injecting molten metal process. It could make sure the molten metal is full in cavity before it transferred to solid state. It also could ensure no surface discontinuities occur even in products with thin-walled features that are difficult to fill.
However , rapid filling will cause gas remaining during die casting process. Although designing the overflow on the parting line could reduce this issue ,the issue of porosity couldn’t be avoided in die casting process.
Some products have the features which couldn’t or difficult to form during the die casting process. Supplier will produce these features by using secondary operation.
(Ex. drilling, tapping, and polishing.)
After the excess material is removed , quality management department will confirm the products have defects or not. The problems at this stage are and pock and short shot. These two defects are caused by insufficient mold and metal temperature , impurities in the molten metal , few vents or lubricant is too much. Other defects – shrinkage , porosity , flow mark and carbon particle remaining also have chance to be found.
There are two types of release agents: water-based release agents and solvent-based release agents. Generally, water-based release agents are more commonly used.
Oil-based release agent is used for products with deep holes, neutrons, sliders and molds with difficult-to-form features, which are convenient for mold release.
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