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Common casting process

Common casting process

2019-09-25

Casting process

Techniques and methods for producing castings using casting theory and system knowledge. Including casting process, casting system, feed system, vent, cooling system, special casting process.

Casting process design includes: casting process drawing design, casting drawing design, casting assembly drawing design and process card production [1].

Historical evolution

Casting is an ancient manufacturing method that dates back 6,000 years in China. With the development of industrial technology, the quality of large casting directly affects the quality of products. Therefore, casting plays an important role in the machinery manufacturing industry. The development of casting technology is also very rapid, especially in the late 19th century and the first half of the 20th century, many new casting methods, such as low pressure casting, ceramic casting, continuous casting, etc., have been perfected and invested. In practice in the second half of the 20th century.

Operation method

Casting is the process of pouring molten metal into a mold and cooling it to obtain the desired shape and properties. Casting is a common manufacturing method with low manufacturing cost and high process flexibility. It can obtain complex shapes and large castings, and accounts for a large proportion of machinery manufacturing, such as machine tools for 60-80%, cars for 25%, tractors for 50% to 60%.

Due to the improvement of casting quality, casting accuracy, casting cost and casting automation, casting technology is developing towards precision, large-scale, high quality, automation and cleaning. For example, in China, precision casting technology and continuous casting technology, special casting technology, casting automation and casting molding simulation technology have developed rapidly.

The main varieties

The main casting processes include: metal melting, model making, casting solidification and stripping cleaning. The main materials used in casting are cast steel, cast iron, cast nonferrous alloys (copper, aluminum, zinc, lead, etc.).

Casting process can be divided into sand mold casting process and special casting process.

Special casting process

Special casting processes include centrifugal casting, low pressure casting, differential pressure casting, pressurized casting, gypsum casting, ceramic casting, etc. [2]

Die casting

Casting die casting is a process in which molten metal is injected into a mold under the action of the mold. Other external forces (excluding gravity). Generalized die casting includes die casting and vacuum casting machine, low pressure casting, centrifugal casting, etc. Narrow sense of pressure casting refers to die casting machine of metal mold, called die casting. These casting processes are currently the most commonly used and the cheapest in nonferrous metal casting.

Metal casting

Metal casting is the modern process of casting hollow mould made of metal (heat-resisting alloy steel, nodular cast iron, heat-resisting cast iron, etc.).

The metal type may be gravity casting or pressure casting. The metal mould can be reused. Once the molten metal is poured once, it can be cast once, with long life and high production efficiency. Metal castings not only have good dimensional accuracy, but also have a smooth surface, and the casting strength of the same molten metal is higher than that of sand casting, and are less likely to be damaged. Therefore, in the mass production of small and medium-sized non-ferrous metal casting, as long as the casting material melting point is not too high, usually preferred metal casting. However, metal casting also has some disadvantages: because heat-resistant alloy steel and the cavities used to process it are relatively expensive, metal molds are expensive, but the total cost is cheaper than die-casting molds. Too much. For small batch production, the cost of the molds assigned to each product is obviously too high, which is generally not acceptable. Moreover, because the metal mold is limited by the size of the mold material, the capacity of the mold cavity processing equipment and the casting equipment, it is not effective for extremely large castings. As a result, metal castings are rarely used in small batches and large parts. In addition, although the metal mold USES heat-resistant alloy steel, its heat resistance is still limited. It is commonly used in the casting of aluminum alloy, zinc alloy and magnesium alloy. It is less used in copper alloy casting and is used in ferrous metal casting. It's even less. But the overall cost is cheaper than the die casting mold. Too much. For small batch production, the cost of the molds assigned to each product is obviously too high, which is generally not acceptable. Moreover, because the metal mold is limited by the size of the mold material, the capacity of the mold cavity processing equipment and the casting equipment, it is not effective for extremely large castings. As a result, metal castings are rarely used in small batches and large parts. In addition, although the metal mold USES heat-resistant alloy steel, its heat resistance is still limited. It is commonly used in the casting of aluminum alloy, zinc alloy and magnesium alloy. It is less used in copper alloy casting and is used in ferrous metal casting. It's even less. But the overall cost is cheaper than the die casting mold. Too much. For small batch production, the cost of the molds assigned to each product is obviously too high, which is generally not acceptable. Moreover, because the metal mold is limited by the size of the mold material, the capacity of the mold cavity processing equipment and the casting equipment, it is not effective for extremely large castings. As a result, metal castings are rarely used in small batches and large parts. In addition, although the metal mold USES heat-resistant alloy steel, its heat resistance is still limited. It is commonly used in the casting of aluminum alloy, zinc alloy and magnesium alloy. It is less used in copper alloy casting and is used in ferrous metal casting. It's even less. For small batch production, the cost of the molds assigned to each product is obviously too high, which is generally not acceptable. Moreover, because the metal mold is limited by the size of the mold material, the capacity of the mold cavity processing equipment and the casting equipment, it is not effective for extremely large castings. As a result, metal castings are rarely used in small batches and large parts. In addition, although the metal mold USES heat-resistant alloy steel, its heat resistance is still limited. It is commonly used in the casting of aluminum alloy, zinc alloy and magnesium alloy. It is less used in copper alloy casting and is used in ferrous metal casting. It's even less. For small batch production, the cost of the molds assigned to each product is obviously too high, which is generally not acceptable. Moreover, because the metal mold is limited by the size of the mold material, the capacity of the mold cavity processing equipment and the casting equipment, it is not effective for extremely large castings. As a result, metal castings are rarely used in small batches and large parts. In addition, although the metal mold USES heat-resistant alloy steel, its heat resistance is still limited. It is commonly used in the casting of aluminum alloy, zinc alloy and magnesium alloy. It is less used in copper alloy casting and is used in ferrous metal casting. It's even less. Because metal molds are limited by the size of the mold material, the capacity of the cavity processing equipment, and the casting equipment, they are also ineffective for extremely large castings. As a result, metal castings are rarely used in small batches and large parts. In addition, although the metal mold USES heat-resistant alloy steel, its heat resistance is still limited. It is commonly used in the casting of aluminum alloy, zinc alloy and magnesium alloy. It is less used in copper alloy casting and is used in ferrous metal casting. It's even less. Because metal molds are limited by the size of the mold material, the capacity of the cavity processing equipment, and the casting equipment, they are also ineffective for extremely large castings. As a result, metal castings are rarely used in small batches and large parts. In addition, although the metal mold USES heat-resistant alloy steel, its heat resistance is still limited. It is commonly used in the casting of aluminum alloy, zinc alloy and magnesium alloy. It is less used in copper alloy casting and is used in ferrous metal casting. It's even less. Although the metal mould is made of heat-resistant alloy steel, its heat resistance is still limited. It is commonly used in the casting of aluminum alloy, zinc alloy and magnesium alloy. It is less used in copper alloy casting and is used in ferrous metal casting. It's even less. Although the metal mould is made of heat-resistant alloy steel, its heat resistance is still limited. It is commonly used in the casting of aluminum alloy, zinc alloy and magnesium alloy. It is less used in copper alloy casting and is used in ferrous metal casting. It's even less.

Die casting die casting

It is the metal mould die casting on the die casting machine.

There are two types of die-casting machines: hot-chamber die-casting machines and cold-chamber die-casting machines. Compared with cold chamber die casting machine, hot chamber die casting machine has the characteristics of high automation, low material loss and high production efficiency. However,, due to the heat resistance of the machine parts, it can only be used to produce castings of low-melting materials, such as zinc and magnesium alloys. Because of its high melting point, the widely used aluminum alloy die castings can only be produced on cold chamber die casting machines. The main characteristic of die casting is that the molten metal fills the cavity at high pressure and high speed and solidifies at high pressure. The disadvantages of die casting are as follows: as the molten metal in the process of filling the cavity at high pressure and high speed, the air inside the cavity is inevitably wrapped in the casting to form subcutaneous pores, so the aluminum alloy die casting is not suitable for heat treatment, and the zinc alloy die casting is not suitable for surface spraying (but can be painted). Otherwise, when heated as described above, the inner hole of the casting will expand with the heat, causing deformation or blistering of the casting. In addition, the mechanical cutting allowance of the die casting should be small, generally about 0.5mm, which can reduce the weight of the casting, reduce the cutting amount, reduce the cost and avoid the penetration of the dense layer. The surface, exposing the skin pores,

Investment casting

Lost wax casting, now known as investment casting, is a casting process with little or no cutting. It is an excellent technology in casting industry, and its application is very extensive. It is not only applicable to casting of various types and various alloys, but also produces castings with higher dimensional accuracy and surface quality than other casting methods, and even castings that are difficult to cast by other casting methods, which are difficult to cast and not easy to process. Can be cast through investment casting.

Investment casting is based on ancient wax casting. As an ancient civilization, China was one of the early countries to use this technology. For hundreds of years before British Columbia, the ancient Chinese laboring people created this lost wax casting technique, which was used to cast various exquisite designs and characters. Zhongding products and utensils, such as the spring and autumn period ceng hou yi tomb. The base of the tomb is a pair of intertwined dragons. They are end to end and staggered up and down to form a multi-layered cloud map in the middle. These patterns are difficult to make by ordinary casting techniques and by losing wax. The process can take advantage of the fact that paraffin wax has no strength and is easy to carve. Using ordinary tools, it can carve paraffin-like artifacts like the tomb of zeng houyi, and then add a gating system, paint, dewaxing and pouring. You can get the exquisite tomb of Zenghou Yi.

The practical application of modern investment casting method in industrial production was in the 1940s. At that time, the development of aviation jet engines required the manufacture of heat-resistant alloy parts, such as blades, blades, nozzles, etc., which were complex in shape, accurate in size, and smooth in surface. Because heat-resistant alloy materials are difficult to process, the shapes of the components are so complex that they cannot or cannot be made by other means. Therefore, it is necessary to find a new accurate molding process so that lost wax castings handed down from ancient times can pass through the material and process. With improvement, modern investment casting method has developed significantly on the basis of ancient technology. As a result,

In the 1950s and 1960s, China began to apply investment casting to industrial production. Since then, this advanced casting process has been greatly developed, and has been widely used in aviation, automotive, machine tools, ships, internal combustion engines, gas turbines, telecommunications equipment, weapons, medical equipment and cutting tools and other manufacturing industries. In the process. The making of art.

The so-called investment casting process, need to use the fusible materials such as wax or plastic) made of fusible model (hereinafter referred to as investment or model), coated with several layers of special refractory coating, drying and hardening of the monolithic forms after shell, melting model by steam or hot water from the shell, shell put in flask, and then around the filling dry sand molding, finally put the mould at high temperature baking furnace. Calcination (for example, when a high strength shell is used, the shell of the demoulding can be fired directly without modeling), and the mold or shell is fired and the molten metal is poured into it to obtain the casting.

The size accuracy of investment casting is high, generally up to ct4-6 (sand casting CT10~13, die casting CT5~7). Of course, due to the complex investment casting process, there are many factors that affect the precision of casting size, such as mold. The shrinkage of materials, the deformation of the melt, the change in the amount of shell during heating and cooling, the shrinkage of the alloy, and the deformation of the casting during solidification, etc., therefore, the size accuracy of the ordinary melt casting is higher, but the consistency still needs to be improved (the size uniformity of the casting using medium and high temperature wax is much higher).

When pressing the mold, the use of high-altitude cavity surface smoothness of the mold products, therefore, the investment mold surface smoothness is relatively high. In addition, the shell is made of a refractory coating, which is made of a special adhesive and a refractory material resistant to high temperature, and is applied to the investment mold, and the inner surface of the mold cavity is in direct contact with the molten metal with a high surface finish. Therefore, the surface finish of molten casting is higher than that of ordinary casting, generally reaching Ra.

The biggest advantage of investment casting is that, due to the high dimensional accuracy and surface finish of investment casting, it can reduce machining work, but only a small amount of machining allowance is needed on parts, and even some castings only have grinding and polishing allowance, and can be used without machining. It can be seen that the investment casting method can save a lot of machine tools and processing time, and greatly save metal raw materials.

Another advantage of investment casting is that it can cast complex castings of various alloys, especially high temperature alloy castings. The blades of a jet engine, for example, have a streamlined profile and cooling chamber that can hardly be machined. The production of investment casting can not only realize mass production, but also ensure the consistency of casting and avoid the stress concentration of residual cutting tools.

lost

Foam casting technology (EPC or LFC) is a solid mold made of foam plastic with the same structure and size as the parts. Impregnate, dry, then dry, shape, vibrate, and pour with fireproof adhesive paint. Molten metal causes the pattern to evaporate by heating, and a casting method is obtained for metal parts that conform to the pattern shape. Lost mold casting is a new technology with no edge and accurate molding. It does not require mold removal and the use of dry sand without adhesives to reduce contamination. It is considered the most likely process to achieve green casting in the 21st century. Technology.

Lost foam casting technology mainly includes the following:

1. Loss of pressure foam casting technique

Pressure lost mold casting is a new kind of casting technology which combines lost mold casting technology and pressure solidified crystallization technology. It is irrigated with sandbox pressure. After pouring molten metal to evaporate foam, quickly seal pressure irrigation. A casting method in which a gas is introduced at a certain pressure to solidify and crystallize a molten metal under pressure. The casting technique is characterized by significant reduction of casting defects such as shrinkage, shrinkage and porosity in the casting, increased casting density and improved casting mechanical properties.

2. Vacuum and low pressure lost mold casting technology

Vacuum low pressure lost mold casting is a new kind of casting technology which combines negative pressure lost mold casting with low pressure anti-gravity casting. The characteristics of vacuum and low pressure epc technology are as follows: combining the advantages of low pressure and vacuum epc technology, the filling process is completed under controlled pressure, which greatly improves the casting and filling capacity of the alloy; Compared with die casting, the equipment investment is small, the casting cost is low, and the casting can be heat treated and strengthened. Compared with sand mold casting, the casting has high precision, small surface roughness, high productivity and good performance. Under the action of anti-gravity, the gate becomes supplementary to shorten the passage and casting temperature. Low loss, liquid alloy under controlled pressure full solidification, alloy casting casting system simple and effective, high yield, compact structure; Vacuum low pressure epc has a lower casting temperature, suitable for all kinds of non-ferrous alloys.

3. Vibration lost mold casting technology

In the process of lost mold casting, vibration of certain frequency and amplitude is applied to solidify the casting under the action of vibration field. Solidification due to lost mold casting.

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