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The Traditional Die-casting Process Consists Of Four Steps

Wuxi Hoohi Engineering Co.,Ltd | Updated: Oct 19, 2017

The traditional die-casting process consists of four steps, or high-pressure die-casting. These four steps include mold preparation, filling, injection and sand removal, which are also the basis for a variety of improved version of the die casting process. In the preparation process need to spray the mold cavity on the lubricant, in addition to the lubricant can help control the temperature of the mold can also help cast off the mold. The mold can then be closed and the molten metal is injected into the mold with high pressure, which is in the range of about 10 to 175 MPa. When the molten metal is filled, the pressure will remain until the casting solidifies. And then put the push rod will launch all the castings, due to a mold may have multiple mold cavity, so each casting process may produce multiple castings. The process of the doffing process requires separation of the residue, including the mold port, the runner, the gate, and the flash. This process is usually done by squeezing the casting with a special dressing die. Other doffing methods include sawing and grinding. If the gate is relatively fragile, you can directly hit the cast, so you can save manpower. The extra mold port can be reused after melting. The usual yield is about 67%.

High-pressure injection results in a very fast filling of the mold so that the molten metal can fill the entire mold before any part of the solidification. In this way, even the thin-walled parts that are difficult to fill can also avoid surface discontinuities. But this will also lead to air retention, because the rapid filling of the mold when the air is difficult to escape. This problem can be reduced by placing the exhaust port on the parting line, but even a very sophisticated process will leave the pores in the center of the casting. Most die-casts can be done by secondary processing to complete structures that can not be completed by casting, such as drilling and polishing.

an examination

See also: Casting defects

After the completion of the drape can check the defects, the most common defects include stagnation (pouring dissatisfaction) and cold scar. These defects may be caused by the temperature of the mold or molten metal, the metal mixed with impurities, too little ventilation, too many lubricants and other reasons. Other defects include stomata, shrinkage, hot cracking, and flow marks. Flow marks are traces of gate defects, sharp corners, or excess lubricant left on the surface of the casting.

Lubricants

Water-based lubricants are known as emulsions and are the most commonly used lubricant types, due to health, environmental and safety considerations. Unlike solvent-based lubricants, if the minerals in the water are removed by the appropriate process, it is not left in the casting by-product. If the process of treating water is not a matter of course, the minerals in the water can cause casting surface defects and discontinuities. There are four main water-based lubricants: water-doped, oil-blended, semi-synthetic and synthetic. Water-impregnated lubricants are preferred because water is used to cool the surface of the mold by evaporating the oil while the lubricant is being used, which helps to release the mold. Typically, the proportion of such lubricants is 30 parts of water mixed with 1 part oil. In extreme cases, this ratio can reach 100: 1.

Oil that can be used for lubricants includes heavy oil, animal fats, vegetable fats, and synthetic oils. Heavy residue has a higher viscosity at room temperature, and it becomes a film at high temperatures in the die casting process. Lubricant by adding other substances can control the emulsion viscosity and thermal properties. These substances include graphite, aluminum and mica. Other chemical additives can avoid dust and oxidation. Water-based lubricants can be added emulsifiers, so that oil-based lubricants can add water, including soap, alcohol and ethylene oxide.

For a long time, solvent-based lubricants commonly used include diesel and gasoline. They are favorable for the casting to be removed, but a small explosion occurs during each die-casting process, which results in the accumulation of carbon elements in the cavity. Compared to water-based lubricants, solvent-based lubricants are more homogeneous.


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