Die casting is a manufacturing process in which molten metal is injected into a mold cavity under high pressure and then cooled to form a part. It is often used for producing parts with complex shapes, intricate details, and thin walls. Die cast parts are usually made from metals such as aluminum, zinc, copper alloys, magnesium, lead or tin-based alloys.
History
Die casting originated from movable type printing molds in 1838. In 1849, J. J. Sturgiss obtained the patent of the first manual piston hot chamber die casting machine in history in the United States, which was used to continuously produce printing machine type.
In 1885, the German-American inventor Ottmar Mergenthaler invented the Linotype typesetting machine. He molded the entire row of independent type into a long type, which greatly changed the traditional printing technology of manual typesetting, and the production efficiency increased rapidly.
In the 1900s, the printing industry has widely used die casting machines to produce the required lead types. Cast typesetting has become a pioneer in automation.
The modern cold-chamber die casting machine was invented by Czech engineer Jesef Pfolak. He separated the crucible furnace for molten alloy and the injection system, overcame the problem that the molten soup of the hot-chamber die casting machine would corrode the injection system, and significantly improved the pressure. The shooting power is also more suitable for industrial mass production needs.
Definition
Die casting is one of the production methods of metal material melting and casting. It is quite similar to the plastic injection that most people are familiar with, except that the molten material is metal. In response to the high temperature, high pressure and short curing time of the molten soup, the die casting mold used materials, runner design, melting equipment and injection system are very different from plastics.
Features
Compared with traditional casting methods, such as: low pressure casting, sand casting (commonly known as: foundry), gravity casting (or permanent mold casting), generally "die casting" refers to "high pressure die casting (HPDC)", which is a relatively precise casting method that can be mass-produced quickly.
During die casting, the dimensional tolerance of die casting parts can be controlled within a small range. The Near Net Shape after die casting is almost equal to the finished product, and the surface is flat and smooth. When the mold design is accurate, most of the die casting parts do not need additional polishing or milling can be used, even parts with external threads can be directly die casted.
Applications
The application of die casting parts, from common hardware parts in life, such as: brooches, belt heads, decorations, zipper pullers, key lock cylinders, chassis switches, building or car door handles, truck rearview mirrors, wheel axle covers, etc. etc., higher precision digital camera parts, audio and video connectors, computer connector housings, optical communication transceiver housings, 5G base stations or notebook computer housings, various heat sinks, etc., so that automobile steering wheels, steering linkage parts, automobile hoods, carburetor casings, motorcycle brake handles, etc., even the complex parts of aerospace vehicles such as aircrafts with the highest quality requirements are mostly made by die casting, and the application range is really wide .
Advantages
- High dimensional accuracy
Depending on product characteristics, area size and structural complexity, the dimensional tolerance of die castings can usually be controlled within +/-0.05mm.
- The casting surface is smooth
The surface smoothness of the die casting part depends on the smoothness of the die casting mold surface. Usually, the surface accuracy is about 12s~25s(W), which can achieve a fairly good surface smoothness. Unless the die casting conditions are not ideal, the surface of the die casting part is easily affected. influences.
- The strength and structure of the casting are good
Because die castings solidify rapidly under high pressure and high temperature, encountering relatively low temperature in the external environment of the mold cavity, the crystal grain size is very small, only about 0.013mm, so the strength of die castings is also better than castings made by other casting methods. In addition, the thickness of high-pressure die castings can be made thinner than sand molds or low-pressure metal mold castings, and the weight is reduced, and the cost is relatively reduced.
- It can be produced in large quantities and save costs
Because the die casting molds are made of special heat-resistant steel, the mold life is relatively long. At the same time, because of the fast cooling speed, the time required for each casting cycle (cycle time, one injection cycle of the die casting machine) is saved, and because the processing margin of the die casting parts is small, the material and processing costs are saved, so the die casting method is still by far the most economical casting method.
- It can keep the production environment clean and tidy
Since die casting production adopts automatic production and molds can be reused, the die casting production environment can be kept clean and tidy. For die casting parts, it can be regarded as a clean and waste-free production mode, and for die casting workers, it is even more relatively safe and clean working environment.
Disadvantages
- High upfront capital expenditure
The equipment required for die casting production, such as: die casting machines, melting furnaces, holding furnaces and die casting molds, etc., are still much more expensive than low-pressure casting, sand casting or gravity casting.
- Alloys used in die casting are limited
At present, there are only six non-ferrous metals suitable for die casting, including zinc, tin, lead, copper, magnesium, and aluminum. Among them, copper alloy has the highest melting point and tin the lowest. Use and purpose of the alloy, but its basic elements are still these six metals.
- Poor air tightness of castings
Because the alloy melt is filled into the die casting cavity by high speed and high pressure in a non-vacuum environment, the air in the cavity will be compressed and driven away, and because some structures of the mold will cause turbulent flow, the air that has nowhere to go pores or shrinkage holes will be formed locally in the mold cavity, which will affect the airtightness of the casting. In severe cases, it will affect the appearance or even the mechanical strength of the casting, so that general die castings are not suitable for welding or heat treatment, so as to avoid internal air expansion caused by high temperature, further damage the casting structure or strength. Therefore, the quality of the mold runner design will be the first factor affecting the quality of die castings.
- The thicker the thickness, the more difficult it is to produce
Usually, the understanding of the strength of general mechanical parts is that the thicker the thickness, the stronger the strength, but for die casting parts, the thicker the thickness, the easier it is to generate higher porosity inside the die casting part, and the easier its shrinkage occurs. In response to this problem, although the automobile and motorcycle industry has developed the method of high vacuum die casting, there will still be a very small amount of air (standard value is less than 5cc/100g Al), depending on the environment and application of castings. Whether the conditions are acceptable, and because the die casting machine needs to be equipped with vacuum valves and controllers, the mold must also be designed with a vacuum circuit to match the airtightness of the vacuum, and the cost will naturally increase.
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