Home  > INFO CENTER  > NEWS  > 

Common foundry process documents

Common foundry process documents

2019-09-23

Foundry Technology

Technology and method of casting production using casting theory and system knowledge. Including casting technology, casting system, feed system, ventilation, cooling system, special casting technology, etc.

Foundry process design includes: design of foundry process drawing, design of foundry drawing, design of foundry assembly drawing and production of process card [1].

Historical evolution

Casting is an ancient manufacturing method, which can be traced back to 6000 years ago in China. With the development of industrial technology, the quality of large castings directly affects the quality of products. Therefore, foundry plays an important role in the mechanical 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 and so on, have been improved and invested. It was actually used in the second half of the 20th century.

Operation method

Casting is the process of pouring molten metal liquid into the die and cooling and solidifying 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, which account for a large proportion in mechanical manufacturing, such as machine tools accounting for 60-80%, automobiles 25%, tractors 50-60%.

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

Main varieties

The main casting processes include: metal melting, mold making, casting solidification and mold cleaning. The main materials used for casting are cast steel, cast iron, cast non-ferrous alloy (copper, aluminium, zinc, lead, etc.).

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

Special Casting Technology

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 refers to the process in which molten metal is injected into the die under the action of the die. Other external forces (excluding gravity). Broad sense die casting includes die casting and vacuum casting die casting machine, low pressure casting, centrifugal casting and so on; narrow sense die casting refers to the metal die casting of die casting machine, known as die casting. These foundry processes are currently the most commonly used and cheapest in non-ferrous metal casting.

Metal casting

Metal casting is a modern process for casting hollow dies (heat-resistant alloy steel, nodular cast iron, heat-resistant cast iron, etc.) made of metal.

Metal types can be gravity casting or pressure casting. Metal die can be reused. Once molten metal is poured once, one casting can be obtained, which has long service life and high production efficiency. Metal castings not only have good dimensional accuracy, but also have smooth surface. When casting the same molten metal, the casting strength is higher than that of sand casting, and it is unlikely to be damaged. Therefore, in the case of large-scale production of small and medium-sized castings of non-ferrous metals, as long as the melting point of casting materials is not too high, metal casting is usually preferred. However, metal casting also has some shortcomings: because heat-resistant alloy steel and its cavity are relatively expensive, metal molds are expensive, but the total cost is cheaper than die casting molds. That's too much. For small batch production, the cost of the mould allocated to each product is obviously too high, which is usually not easy to accept. Moreover, due to the size of the die material, the ability of the cavity processing equipment and the casting equipment, the metal die is also ineffective for very large castings. Therefore, metal castings are seldom used in small batches and large parts. In addition, although heat-resistant alloy steel is used in metal dies, its heat resistance is still limited. It is usually used in the casting of aluminium 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 total cost is cheaper than that of die casting die. That's too much. For small batch production, the cost of the mould allocated to each product is obviously too high, which is usually not easy to accept. Moreover, due to the size of the die material, the ability of the cavity processing equipment and the casting equipment, the metal die is also ineffective for very large castings. Therefore, metal castings are seldom used in small batches and large parts. In addition, although heat-resistant alloy steel is used in metal dies, its heat resistance is still limited. It is usually used in the casting of aluminium 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 total cost is cheaper than that of die casting die. That's too much. For small batch production, the cost of the mould allocated to each product is obviously too high, which is usually not easy to accept. Moreover, due to the size of the die material, the ability of the cavity processing equipment and the casting equipment, the metal die is also ineffective for very large castings. Therefore, metal castings are seldom used in small batches and large parts. In addition, although heat-resistant alloy steel is used in metal dies, its heat resistance is still limited. It is usually used in the casting of aluminium 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 mould allocated to each product is obviously too high, which is usually not easy to accept. Moreover, due to the size of the die material, the ability of the cavity processing equipment and the casting equipment, the metal die is also ineffective for very large castings. As a result, there are few metal castings.


Die casting die casting

It is the metal die casting on the die casting machine, and is the most productive casting technology at present.

Die-casting machine is divided into two types: hot chamber die-casting machine and cold chamber die-casting machine. 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 machine parts, it can only be used to produce castings of low melting point materials, such as zinc alloys and magnesium alloys. Because of its high melting point, the widely used aluminium alloy die castings can only be produced on the cold chamber die casting machine. The main feature of die casting is that molten metal fills the cavity at high pressure and high speed, and solidifies at high pressure. The disadvantage of die casting is that in the process of filling the cavity with molten metal at high pressure and high speed, the air in the cavity is inevitably wrapped in the inner part of the casting to form subcutaneous voids, so the aluminium 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 heat, resulting in deformation or foaming of the casting. In addition, the mechanical cutting allowance of die castings should be small, generally about 0.5 mm, which can reduce the weight of castings, reduce the amount of cutting, reduce costs and avoid the infiltration of dense layer. The surface reveals the subcutaneous pore.

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 foundry industry, and its application is very extensive. It is not only suitable for casting of various types and alloys, but also has higher dimensional accuracy and surface quality than other casting methods. It is even difficult to cast by other casting methods. These foundries are difficult to cast and handle. Casting can be done by investment.

Investment casting is based on ancient wax casting. As an ancient civilization, China was one of the early countries to use this technology. In the centuries before British Columbia, the ancient Chinese labourers created this wax-loss casting technology for casting various exquisite patterns and characters. Zhong Ding's products and utensils, such as the tombs of Zeng Houyi in the Spring and Autumn Period. The base of Zengguyi Tomb is a pair of interwoven dragons. They are connected from end to end, interlaced up and down to form a multi-layer cloud map in the middle. These patterns are difficult to make by ordinary casting technology and by wax loss method. This process can take advantage of the fact that paraffin wax has no strength and is easy to carve. Using common tools, it can carve paraffin-like handicraft like the tomb of Zeng Houyi, then add pouring system, paint, dewaxing and pouring. You can get a beautiful Zenghou Yi tomb.

The practical application of modern investment casting method in industrial production was in the 1940s. At that time, the development of aero-jet engines required the manufacture of heat-resistant alloy components, such as blades, impellers, nozzles, etc. They were complex in shape, precise in size and smooth in surface. Because heat-resistant alloy materials are difficult to process, the shape of components is so complex that they cannot or cannot be manufactured by other methods. Therefore, it is necessary to find a new precise forming process so that wax-loss castings passed down from ancient times can pass through materials and processes. The modern investment casting method has been greatly developed on the basis of the old technology. Therefore,

In the 1950s and 1960s, investment casting was applied to industrial production in China. Since then, this advanced casting technology 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 manufacturing industries. In the process. The manufacture of works of art.

The so-called investment casting process only needs to use fusible materials (such as wax or plastics) to make fusible models (investment or models for short), coated with several layers of special refractory coatings, dried and hardened to form an integral shell. The model melts from the shell by steam or hot water, and then places the shell in a flask and fills it with dry materials around it. Sand forming, and finally the mold is placed in a high temperature calciner. Calcination (for example, when using a high strength shell, the demoulding shell can be fired directly without forming), and the die or shell is fired and molten metal is poured into it to obtain the casting.

Investment casting has high dimensional accuracy, generally up to CT4-6 (sand casting CT10-13, die casting CT5-7). Of course, due to the complexity of investment casting process, there are many factors affecting the dimensional accuracy of castings, such as molds. The shrinkage of materials, the deformation of investment mold, the change of shell quantity during heating and cooling, the shrinkage of alloys, and the deformation of castings during solidification, etc. are the main reasons why the dimensional accuracy of ordinary investment casting is high, but the consistency still needs to be improved (the size uniformity of castings with medium and high temperature wax is much higher).

When pressing the die, the die products with high surface finish of the cavity are used, so the surface finish of the investment die is relatively high. In addition, the shell is made of refractory coatings, which are made of special binders and high temperature refractory materials, and are coated on investment moulds, and the inner surface of the cavity is in direct contact with the molten metal with high surface finish. Therefore, the surface finish of investment castings is higher than that of ordinary castings, generally reaching Ra.6.6-3.2 um.

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

Another advantage of investment casting technology is that it can cast complex castings of various alloys, especially superalloy castings. For example, the streamlined profile and cooling chamber of jet engine blades can hardly be machined. The production of investment casting process can not only realize batch production, but also ensure the consistency of castings and avoid the stress concentration of residual cutting tools after processing.

Lost foam casting

Foam casting technology (EPC or LFC) is a solid mold made of foam plastic, and its structure and size are the same as parts. Impregnate with refractory adhesive paint, dry, then dry, shape, vibrate, and pour in. The molten metal evaporates the pattern by heating, and the casting method of the metal parts conforming to the pattern shape is obtained. EPC is a new technology with no edge and precise forming. It does not need to take molds and use dry sand without adhesives to reduce pollution. It is considered to be the most possible process to realize green casting in the 21st century. Technology.

There are mainly the following kinds of EPC technology:

1. Pressure loss foam casting technology

Pressure lost foam casting (EPC) is a new casting technology which combines EPC technology and pressure solidification crystallization technology. It is irrigated with sand box pressure. After pouring the molten metal to evaporate the foam, the pressure irrigation is quickly sealed. A casting method in which a certain pressure gas is introduced to solidify and crystallize molten metal under pressure. The casting technology is characterized by significant reduction of casting defects, such as shrinkage, shrinkage and porosity in castings, increased density of castings and improved mechanical properties of castings.

2. Vacuum Low Pressure EPC Technology

Vacuum low pressure EPC is a new casting technology developed by combining negative pressure EPC and low pressure counter gravity casting. The characteristics of vacuum low pressure EPC technology are: combining the technical advantages of low pressure casting and vacuum EPC, the filling process is completed under controlled pressure, which greatly improves the filling capacity of alloy casting; compared with die casting, the investment of equipment is small, the cost of casting is low, and the castings can be heat treated and strengthened. Compared with sand casting, the casting has high precision, small surface roughness, high productivity and good performance, and the gate becomes a supplement to shorten the channel and pouring temperature under the action of anti-gravity. Low loss, full solidification of liquid alloy under controllable pressure, simple and effective casting system of alloy castings, high output, compact structure, low pouring temperature of vacuum low pressure EPC, suitable for all kinds of non-ferrous alloys.

3. Vibration EPC Technology

Vibration EPC technology imposes certain frequency and amplitude vibration in the process of EPC, which solidifies the castings under the action of vibration field. Because the solidification process of EPC is applied to metal solution for a period of time, the relative movement between liquid phase and solid phase results in dendritic cracking, and the nucleus increases in liquid phase, which refines the final solidification structure, improves feed and improves mechanical properties of the castings. The technology utilizes the existing compact shaking table for lost foam casting. The mechanical vibration generated by the vibration motor makes the molten metal nucleate under dynamic excitation. It achieves the purpose of refining the structure. It has the advantages of simple operation, low cost and no environment. Pollution methods.

4. Semi-solid EPC Technology

Semi-solid EPC technology is a new casting technology which combines EPC technology with semi-solid technology. Because the process is characterized by controlling the relative proportion of liquid and solid phases, it is also called transformation control semi-solid forming. This technology can improve the density of castings, reduce segregation, improve dimensional accuracy and casting performance.

5. Casting Technology for Lost Shell

Shell loss casting technology is a new casting method combining investment casting technology and lost foam casting. The method is to apply multilayer refractories to the surface of foam moulded products, which are made of foam mold and have the same shape as that part, and after being hardened and dried, the pattern of the foamed plastic is burned and disappeared. Form a shell and get fired. Then casting, in order to obtain a new precision casting method of higher size precision castings. It has the characteristics of large volume and high precision in EPC, and has the advantages of casting precision and investment casting strength. Compared with conventional investment casting, foam plastics has the advantages of low cost, convenient pattern bonding and easy vaporization, which overcomes the melt deformation problem caused by easy softening of investment casting mould and can be produced. Large-Size Alloy Composite Castings

6. foam foam casting technology.

EPC suspension casting is a new practical casting technology, which combines EPC with suspension casting. The technical method is to evaporate the pattern of foam plastics after molten metal is injected into the mould, and mix the suspension agent in the riser model (or place the suspension agent in the specific position of the pattern, or suspend the reagent to foam with EPS). Physicochemical reactions occur with molten metals to improve the overall (or partial) structural properties of castings.

Because of its low cost, high precision, flexible design, clean and environmental protection, it is suitable for complex castings. EPC technology conforms to the general trend of the development of casting technology in the new century and has broad prospects for development.

Fine grain casting

The principle of FGCP is to strengthen the nucleation mechanism of alloys by controlling the co-investment casting process, to form a large number of nuclei during the casting process, and to prevent grain growth, so as to obtain the average grain size. Uniform, fine and isotropic equiaxed crystal castings with size less than 1.6 mm. The grain size of typical fine grained castings is ASTM 0~2. Fine grain casting reduces the size of primary carbide and enhances the gamma'phase in superalloy, and improves the grain size of castings. Therefore, the outstanding advantage of fine grain casting is that it greatly improves the low cycle fatigue life of castings at medium and low temperature (< 760 C), and significantly reduces the dispersion of mechanical properties of castings, thereby improving the design tolerance of castings. At the same time, the technology also improves the tensile and durability of the castings to a certain extent, and the castings have good heat treatment properties.

Fine grain casting technology can also improve the machinability of superalloy castings and reduce the possibility of processing screw holes and sharp edge cracks. Therefore, this technology can extend the application of investment casting to forgings, thick machined parts and forging components. In precision casting of aeroengine parts, fine grained castings are usually used instead of some forgings or fine grained ingots.

Process Brief

"Short-flow" casting process uses hot metal from blast furnace directly into electric furnace for heating and adjusting composition. After modification treatment, casting eliminates the process of melting molten iron back into molten iron, which is energy-saving and effective. The casting production method of reducing cost is one of the optimization techniques promoted by foundry association.

The "short process" process has been well applied in Shandong and other provinces. Among the 72 pilot enterprises of high quality foundry pig iron base recently announced, the number of enterprises adopting "short process" in Shandong enterprises has reached 12. It has played an important role in promoting the construction of foundry pig iron base and optimizing its development. Foundry industry cluster, which will promote the development of foundry industry to a higher level.

Sand Mould Casting Technology

Sand casting is a traditional casting process, in which sand is used as the main forming material to make moulds.

Gravity casting technology is mainly used in sand casting.

Gravity casting refers to the process of injecting molten metal into the mould under the action of the earth's gravity, also known as casting. Generality

Foundry craft book

Gravity casting includes sand casting, metal casting, investment casting, slurry casting, etc. Narrow gravity casting refers to metal casting.

Sand moulds are usually cast by gravity. When there are special requirements, they can also be used in low pressure casting and centrifugal casting. Sand casting has a wide range of adaptability. It can use small parts, large parts, simple parts, complex parts, single parts and large batches. Moulds used for sand casting were formerly made of wood, commonly known as wood moulds. The disadvantage of wood mould is that it is easy to deform and damage, besides sand casting produced by single piece, it can also use aluminum alloy mould or resin mould with high dimensional accuracy and long service life. Although prices have risen, they are still much cheaper than metal casting moulds, and the price advantage is particularly prominent in small batches and large quantities of parts. In addition, sand moulds have higher refractoriness than metal moulds, so materials with higher melting points, such as copper alloys or ferrous metals, are also used in this process. However, there are also some shortcomings in sand casting: because each sand casting can only be poured once, the castings are damaged after casting and must be reconstructed, so the production efficiency of sand casting is low; and because the overall nature of sand is soft and porous, the sand casting has low dimensional accuracy and rough surface. Castings damaged after casting must be re-shaped, so the production efficiency of sand casting is low, and because the overall nature of sand is soft and porous, sand casting has low dimensional accuracy and rough surface. Castings damaged after casting must be re-shaped, so the production efficiency of sand casting is low, and because the overall nature of sand is soft and porous, sand casting has low dimensional accuracy and rough surface.

Chat Online 编辑模式下无法使用
Chat Online inputting...