What are the processes of die casting?

The high-pressure die casting process (or conventional die casting) consists of four main steps. These four steps include mold preparation, filling, injection, and sand drop, and they are the basis for various modified versions of the die casting process. Let's introduce these four steps in detail.

Here is the content:

• Preparation

• Filling and injection

• After sanding

Preparation

The preparation process involves spraying the mold cavity with lubricant, which helps control the temperature of the mold in addition to helping to release the die casting. Water-based lubricants, called emulsions, are the most commonly used type of lubricant for health, environmental, and safety reasons. Unlike solvent-based lubricants, it does not leave by-products in the die casting if the minerals in the water are removed using the proper process. Minerals in the water can cause surface defects and discontinuities in the casting if the water is not treated properly. There are four main types of water-based lubricants: water-in-oil, oil-in-water, semi-synthetic and synthetic. Water-in-oil lubricants are the best because when the lubricant is used the water cools the surface of the mold by evaporation while depositing oil, which can aid in release.

Filling and injection

The mold can then be closed and the molten metal is injected into the mold with high pressure, which ranges from about 10 to 175 MPa. Once the molten metal is filled, the pressure is maintained until the die casting has solidified. The pusher then pushes out all the die castings, and since there may be more than one cavity in a mold, more than one casting may be produced per die casting process. The sand drop process then requires the separation of residues, including mold builders, runners, gates, and flying edges. Other methods of sanding include sawing and grinding. If the sprue is more fragile, the casting can be dropped directly, which saves labor. Excess mold-making sprues can be reused after melting. The typical yield is about 67%.

High-pressure injection results in filling the mold very quickly so that the molten metal fills the entire mold before any part solidifies. In this way, surface discontinuities can be avoided even in thin-walled sections that are difficult to fill. However, this can also lead to air trapping, as it is difficult for air to escape when filling the mold quickly. This problem can be reduced by placing air vents in the parting line, but even very precise processes can leave air holes in the center of the casting. Most die casting can be done by secondary processes to complete some structures that cannot be done by die castings, such as drilling and polishing.

After sanding

The most common defects include stagnation (under-pouring) and cold scars. These defects can be caused by insufficient mold or molten metal temperature, metal mixed with impurities, too little venting, too much lubricant, etc. Flow marks are traces left on the die casting surface by gate defects, sharp corners, or excessive lubricant.

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