Detailed explanation of ten foundry techniques
What is casting?
Liquid metal is poured into the mold cavity which is suitable for the shape and size of the part, and then cooled and solidified to obtain the blank or part, which is usually called liquid metal forming or casting.
Process flow: liquid metal → mold filling → solidification shrinkage → casting
- 1. It can produce any complex shape parts, especially those with complex cavity shape.
- 2. Strong adaptability, unlimited alloy types and almost unlimited casting size.
- 3. Wide sources of materials, waste products can be remelted, and equipment investment is low.
- 4. High waste rate, low surface quality and poor working conditions.
|Sand casting||Investment casting||Pessure casting||Low pressure casting||Centrifugal casting||Metal mold casting||Vacuum casting||Squeeze casting||Lost Foam Casting||Continuous casting|
Sand casting: casting method for producing castings in sand mold. Steel, iron and most non-ferrous alloy castings can be obtained by sand casting.
Technological process of sand casting
- 1. It is suitable for making blank with complex shape, especially with complex cavity;
- 2. Wide adaptability and low cost;
- 3. For some materials with poor plasticity, such as cast iron, sand casting is the only forming process to make parts or blanks.
- Application: automobile engine cylinder block, cylinder head, crankshaft and other castings.
Investment casting: it usually refers to the casting scheme that the pattern is made of fusible material, the shell is made of several layers of refractory material coated on the surface of the pattern, and then the pattern is melted out of the shell, so as to obtain the mold without parting surface, which can be filled with sand after high temperature roasting. It is often called “lost wax casting”.
- 1. High dimensional and geometric accuracy;
- 2. The surface roughness is high;
- 3. It can cast castings with complex shape, and the cast alloy is not limited.
Disadvantages: complex process, high cost.
Application: it is suitable for the production of small parts with complex shape, high precision requirements, or difficult to carry out other processing, such as turbine engine blades, etc.
Die casting: high pressure is used to press liquid metal into a precision metal mold cavity at high speed, and the liquid metal is cooled and solidified under pressure to form a casting.
- 1. During die casting, the metal liquid bears high pressure and fast flow rate;
- 2. Good quality, stable size and good interchangeability;
- 3. The production efficiency is high and the die casting die is used many times;
- 4. It is suitable for mass production with good economic benefit.
- 1. The casting is easy to produce small pores and shrinkage porosity;
- 2. Because of the low plasticity of die casting, it is not suitable to work under impact load and vibration;
- 3. When high melting point alloy is die cast, the service life of mould is low, which affects the expansion of die casting production.
Application: die casting was first used in automobile industry and instrument industry, and then gradually expanded to various industries, such as agricultural machinery, machine tool industry, electronic industry, national defense industry, computer, medical equipment, clock, camera and daily hardware.
Low pressure casting
Low pressure casting: it refers to the method of making liquid metal fill the mold under low pressure (0.02-0.06mpa) and crystallize under pressure to form a casting.
- 1. The pressure and speed can be adjusted during casting, so it can be used for various casting types (such as metal mold, sand mold, etc.), casting various alloys and castings of various sizes;
- 2. The bottom injection filling is adopted, the metal liquid filling is stable and free of splash, which can avoid the gas and the scour of the mold wall and core, and improve the qualified rate of the casting;
- 3. The casting crystallizes under pressure, the structure of the casting is compact, the outline is clear, the surface is clean and the mechanical properties are high, which is particularly advantageous for the casting of large thin-walled parts;
- 4. The metal utilization rate was increased to 90-98% by eliminating the shrinkage riser;
- 5. Low labor intensity, good working conditions, simple equipment, easy to realize mechanization and automation.
Application: mainly used in traditional products (cylinder head, hub, cylinder frame, etc.).
Centrifugal casting: it is a casting method of pouring molten metal into the rotating mold, filling the mold and solidifying under the action of centrifugal force.
- 1. There is almost no metal consumption of gating system and riser system to improve the process yield;
- 2. In the production of hollow castings, the core is not needed, so the metal filling capacity can be greatly improved in the production of long tubular castings;
- 3. The casting has high density, less porosity and slag inclusion, and high mechanical properties;
- 4. It is easy to manufacture composite metal castings of cylinder and sleeve.
- 1. There are some limitations in the production of special-shaped castings;
- 2. The inner hole diameter of casting is not accurate, the surface of inner hole is rough, the quality is poor, and the machining allowance is large;
- 3. The casting is easy to produce specific gravity segregation.
Centrifugal casting was first used in the production of cast pipes. At home and abroad, centrifugal casting process is used in metallurgy, mining, transportation, drainage and irrigation machinery, aviation, national defense, automobile and other industries to produce steel, iron and non-ferrous carbon alloy castings. Among them, centrifugal cast iron pipe, cylinder liner and shaft sleeve are the most popular.
Gravity die casting
Metal mold casting: it is a kind of forming method that liquid metal fills metal mold under the action of gravity and cools and solidifies in mold to obtain casting.
- 1. The results show that the thermal conductivity and heat capacity of the metal mold are large, the cooling rate is fast, the microstructure of the casting is compact, and the mechanical properties of the metal mold are about 15% higher than those of the sand mold.
- 2. The casting with higher dimensional accuracy and lower surface roughness can be obtained, and the quality stability is good.
- 3. Because the sand core is not used or seldom used, the environment is improved, the dust and harmful gas are reduced, and the labor intensity is reduced.
- 1. Since the metal mold itself has no air permeability, certain measures must be taken to derive the air in the cavity and the gas produced by the sand core;
- 2. The metal mold has no concession, and the casting is easy to crack during solidification;
- 3. The manufacturing cycle of metal mold is long and the cost is high. Therefore, only in mass production, can it show good economic effect.
Application: metal mold casting is not only suitable for mass production of non-ferrous alloy castings such as aluminum alloy and magnesium alloy with complex shape, but also suitable for production of iron and steel metal castings and ingots.
Vacuum casting: advanced die casting technology which can eliminate or significantly reduce the porosity and dissolved gas in the die casting by removing the gas in the die casting cavity during the die casting process, thus improving the mechanical properties and surface quality of the die casting parts.
- 1. Eliminate or reduce the porosity in the die casting, improve the mechanical properties and surface quality of the die casting parts, and improve the coating performance;
- 2. The alloy with lower specific pressure and poor casting performance can be used to reduce the back pressure of the cavity, and it is possible to use small machine to die larger castings;
- 3. The filling condition is improved, and the thin casting can be cast.
- 1. The sealing structure of die is complex, and it is difficult to manufacture and install, so the cost is high;
- 2. If the vacuum die casting method is not controlled properly, the effect is not very significant.
Squeezing die casting
Squeeze casting: is to make liquid or semi-solid metal under high pressure solidification, flow forming, directly obtain parts or blank method. It has the advantages of high utilization rate of liquid metal, simplified process and stable quality. It is an energy-saving metal forming technology with potential application prospect.
Direct squeeze casting: spray coating, pouring alloy, mold closing, pressurization, pressure holding, pressure relief, parting, blank demoulding, reset;
Indirect squeeze casting: spray coating, mold closing, feeding, mold filling, pressurization, pressure holding, pressure relief, parting, blank demoulding, reset.
- 1. It can eliminate the internal defects such as porosity, shrinkage and porosity;
- 2. Low surface roughness and high dimensional accuracy;
- 3. It can prevent casting crack;
- 4. It is easy to realize mechanization and automation.
Application: it can be used to produce all kinds of alloys, such as aluminum alloy, zinc alloy, copper alloy, ductile iron, etc
Lost foam casting
Lost foam casting, also known as real mold casting, is a new type of casting method that combines the wax or foam model bonded to the size and shape of the casting into a model cluster. After coating the refractory coating and drying it, it is embedded in dry quartz sand in the vibration modeling, pouring under negative pressure, making the model gasified, the liquid metal occupies the mold position, and solidified and cooled to form a new casting method.
Process flow: pre foaming → foaming molding → dipping coating → drying → molding → pouring → sand falling → cleaning
- 1. The casting has high precision and no sand core, which reduces the processing time;
- 2. No parting surface, flexible design and high degree of freedom;
- 3. Clean production, no pollution;
- 4. Reduce investment and production costs.
Application: it is suitable for the production of all kinds of large and small precision castings with complex structure, unlimited alloy types and batch production. Such as gray cast iron engine box, high manganese steel elbow, etc.
Continuous casting: it is an advanced casting method. Its principle is to continuously pour molten metal into a special metal mold called mould, solidify (crust) the casting, and continuously pull it out from the other end of the mould. It can obtain casting of any length or specific length.
- 1. Because the metal is cooled rapidly, the crystal is dense, the structure is uniform and the mechanical properties are good;
- 2. Save metal and improve yield;
- 3. The working procedure is simplified, and the molding and other working procedures are avoided, so the labor intensity is reduced; The required production area is also greatly reduced;
- 4. Continuous casting production is easy to realize mechanization and automation, improve production efficiency.
Application: continuous casting can be used to cast long castings such as steel, iron, copper alloy, aluminum alloy and magnesium alloy with constant cross-section shape, such as ingot, slab, bar blank, tube, etc.
Source: China Flanges Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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