What is die casting? Process, type of process, metal, advantage, application

What is die casting? Process, type of process, metal, advantage, application

Ⅰ Introduction to die casting

Die casting is a manufacturing process in which molten metal is pressed into a mold under high pressure to produce metal parts, including mold making, metal melting, and the injection of molten metal into the mold. Die casting can produce precision and complex shape parts, is an efficient, precision manufacturing process, is a rapid development of modern times an efficient, less cutting metal forming process method. This process method has been widely used in aerospace, automotive, electronics, consumer goods, construction and other industries.

Ⅱ Die casting history

Die casting technology originated in the middle of the 19th century, the initial development purpose is to manufacture movable type printing for the printing industry, in 1838, in order to manufacture movable type printing mold, people invented die casting equipment, the first die casting related patent issued in 1849, it is a small, used to produce printing press type manual machine. In 1885, Otto Mergenthaler invented the Linotype, a machine that could die-cast an entire line of text into a single type, which brought unprecedented innovation to the printing world. After the printing industry entered large-scale industrialization, the traditional hand pressure type has been replaced by die casting, with the continuous growth of consumer products, Otto's invention has been more and more applications, people can use die casting to manufacture parts and components in large quantities, and its potential has rapidly expanded to other fields such as automotive, aerospace and electronics.

Ⅲ Die casting process

1.Mold preparation

After the mold is manufactured, it is cleaned to remove contaminants that may affect the quality of the part, in addition, it is preheated to prevent thermal defects such as cracks, which need to spray lubricant into the mold cavity, lubricant can help the casting release in addition to helping to control the temperature of the mold, cracks occur when there is a significant temperature difference between the mold and the liquid metal.

2.Select mold type according to production:

• Single cavity die is the simplest type of die, with one cavity, capable of producing one part per cycle.

• Multi-cavity dies have more complex designs characterized by the same cavity in a single die. It can produce multiple but identical parts per cycle, so it can be used for mass production of individual parts.

• Combination molds have different design cavities within the mold. As a result, they are more flexible and can create different types of parts in each cycle.

• A unit die is a special die suitable for manufacturing parts with complex geometry without loss of accuracy, such as die casting products with castings or thin walls.

3.Injection filling

Injection depends on whether it is a hot chamber system or a cold chamber system, for the cold chamber system, the melting takes place outside the casting machine, and the hot chamber system melting takes place inside the hot chamber casting machine. The high-pressure injection results in a very fast filling of the mold, allowing the molten metal to fill the mold before any part sets. In this way, even thin wall parts that are difficult to fill can avoid surface discontinuities. However, this can also cause air retention, because it is difficult for air to escape when filling the mold quickly. This problem can be reduced by placing exhaust ports on the parting line, but even very sophisticated processes can leave lower pores in the center of the casting. Most die casting can be completed by secondary processing to complete some structures that cannot be completed by casting, such as drilling and polishing.

4.Cooling and removal

The molten metal is allowed to cool and solidify to form the final part, and cooling occurs while the mold is still clamped. In addition, depending on the change in die casting, cooling may be performed while maintaining or increasing pressure. After the casting solidifies, loosen the mold and remove the parts.

5.prune

The process of trimming requires the separation of residue, including molding, runner, gate and flash edge. This process is usually done by a special finishing mold extrusion casting to remove raw edges and other defects that leave excess material on the part. Other methods include sawing and grinding. In addition, die castings can undergo other surface treatments to improve mechanical properties, function and aesthetics.

Ⅳ Die casting type

1.Hot chamber die casting

Hot chamber die casting, sometimes called gooseneck die casting, consists of a molten pool of liquid and semi-liquid metals that are pressed to fill the mold. At the beginning of the cycle, the piston of the machine is in a contracted state, and the molten metal can fill the neck of the goose. A pneumatic or hydraulic piston squeezes the metal and fills it into the mold.

The advantages of this system include fast cycle speed (about 15 cycles per minute), easy automation, and the process of melting the metal. Disadvantages include the inability to die cast metals with higher melting points, as well as aluminum, which will carry the iron out of the melting pool. Therefore, hot chamber die casting machines are generally used for zinc, tin and lead alloys. Moreover, hot chamber die casting is difficult to use for die casting large castings, usually this process is die casting small castings.

2.Cold chamber die casting

Cold chamber die casting is an important process for metals with high melting temperatures, and can be used when die casting cannot be used for metals 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 off in a separate crucible. A certain amount of molten metal is then transferred to an unheated injection chamber or injector. The metal is injected into the mold by hydraulic or mechanical pressure. Due to the need to transfer molten metal into the cold chamber, the biggest drawback of this process is the long cycle time. Cold chamber die casting machines are also divided into vertical and horizontal, vertical die casting machines are usually small machines, and horizontal die casting machines have various models.

Comparison of hot chamber die casting and cold chamber die casting

Ⅴ Changes in die casting process

1.Gravity die casting

Gravity casting differs from traditional die casting in that the mold is filled using gravity. The advantages of the process include reduced energy consumption, waste generation, air retention and high dimensional accuracy. Suitable for the automotive industry, for the manufacture of engine block, cylinder head, pump housing and transmission housing and other structural parts.

2.Pressure die casting

Pressure casting is divided into two types: low pressure casting (LPDC) and high pressure die casting (HPDC). Each has its advantages, depending on the filling mechanism. The filling of HPDC is carried out at high pressure (1000 psi to 25,000 psi), making it fast and suitable for the production of thin-walled parts. In LPDC, filling is performed at low pressure (0.08MPa to 0.1MPa). This prevents air retention and makes it suitable for manufacturing parts with precise dimensions and no holes. Pressure casting is suitable for high-precision machining, for example, the aerospace and automotive industries use it to manufacture structural parts, engine blocks and cylinder heads.

3.Vacuum die casting

Vacuum casting differs in the use of vacuum to prevent air retention, which improves surface finish and dimensional accuracy. It is suitable for the automotive, medical and aerospace industries, and common parts include transmission cases, brackets and aluminum implants.

4.Extrusion die casting

Extruded castings have the advantages of improved mechanical properties, reduced porosity and higher dimensional accuracy. It is commonly used to make components such as car suspensions, steering knuckles and transmissions.

5.Semi-solid die casting

Semi-solid die casting, also known as thixotropic or rheological casting, produces parts with strict tolerances and dimensional accuracy. It is suitable for manufacturing parts with complex geometry, such as transmissions and engine mounts.

Ⅵ Common die casting metal

The main metals used for die casting include zinc, copper, aluminum, magnesium, lead, tin, and lead-tin alloys, although die casting iron is rare, but also feasible. Special die-cast metals include ZAMAK, aluminum-zinc alloys, and American Aluminum Association standards: AA380, AA384, AA386, AA390, and AZ91D magnesium. The characteristics of various metals are as follows:

Zinc

The easiest metal to die cast, the manufacture of small parts is very economical, easy to coating, compressive strength, high plasticity, long casting life.

Aluminum

Light weight, high dimensional stability in the manufacture of complex and thin-wall castings, strong corrosion resistance, good mechanical properties, high thermal and electrical conductivity, and high strength at high temperatures.

Magnesium

Easy to machine, high strength-to-weight ratio, the lightest of commonly used die-cast metals.

Copper

high hardness, strong corrosion resistance, commonly used die-casting metal mechanical properties of the best, wear resistance, strength close to steel.

Lead and tin

 High density, high dimensional accuracy, can be used as special anti-corrosion components. Due to public health concerns, this alloy cannot be used as food processing and storage equipment. Alloys of lead, tin and antimony (sometimes containing a little copper) can be used to make hand-type letterpress and gold stamping.

Tin-base alloy

Tin-based alloys are soft and malleable metals with a low melting point (232 ° C). In addition, it also has good corrosion resistance and fluidity, suitable for metal die casting. Tin is often used in combination with other metals such as copper and antimony for better mechanical properties.

Ⅶ Advantages and disadvantages of die casting

1.advantage

Excellent accuracy

The accuracy depends on the type, variation and pre-designed die casting mold, which produces parts with high dimensional accuracy.

Manufacture complex parts

Manufacturing Parts with complex geometry can be manufactured, including cast inserts, thin walls, etc.

High production efficiency

Die casting is a high-volume production process with a low cost per unit of part, and the speed depends on casting changes and mold design.

Excellent surface finish

Cast metal parts have a smooth surface finish, especially when using technologies such as low pressure casting, gravity casting and semi-solid casting. The pressure ensures the correct filling of the die, improves dimensional accuracy and reduces air retention, thus ensuring minimum porosity. Subsequent surface treatment is also possible.

Long die life

Molds are usually made of high-quality steel that is strong enough to withstand the high pressures and temperatures associated with the die casting process.

2.Disadvantage

High mold cost

Casting equipment and molds and mould-related components are very expensive compared to other casting methods, and the impact of mold costs on production costs can be reduced for high-volume parts manufacturing.

Suitable for non-ferrous metals

Suitable for non-ferrous metals with medium optimum melting points, such as aluminium, zinc and magnesium. Ferrous metals such as steel and iron have higher melting points and require special equipment to cast them.

Suitable for metals with high fluidity

In normal die casting, the last batch of castings will always have pores. Therefore, no heat treatment or welding can be carried out, because the gas in the gap will expand under the action of heat, resulting in internal micro-defects and surface stripping.

Ⅷ Application

Ⅸ Ending

Die casting of metal parts is an efficient, precision metal manufacturing process that is widely used in the production of parts in a variety of industries, including automotive, aerospace, electronics, and many other industries.

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