Views: 191 Author: Site Editor Publish Time: 2020-10-20 Origin: Site
Casting Introduction
The liquid metal is dumping into a mold cavity suitable for the shape and size of the part, and it is cooled and solidified to obtain the production method of the blank or mechanical components, which is usually called liquid metal forming or casting.
liquid metal → filling → solidification shrinkage → casting
It can produce parts with arbitrarily complex shapes, especially casting parts with complex inner cavity shapes.
Strong adaptability, unlimited alloy types, and various casting size.
Wide sources of materials, castings can be remelted, and low equipment investment.
High scrap rate, low surface quality, and poor working conditions.
Sand casting
Investment casting
Die casting
Low-pressure casting
Centrifugal casting
Gravity die casting
Vacuum die casting
Squeeze casting
Lost foam casting
Continual casting
Sand mold casting is a widely used casting form. As the name suggests, the mold is made of sand. Sand mold casting requires putting a finished part model or a wooden model (pattern) in the sand and then filling the pattern with sand. After the pattern is taken out of the box, the sand forms a mold. Steel, iron, and most non-ferrous alloy castings can be cast by sand casting.
It is suitable for making blanks with complex shapes, especially with complex inner cavities.
The casting has wide adaptability and low cost.
For materials with poor plasticities, such as cast iron, sand casting is the best choice for manufacturing its parts.
automobile engine cylinder block, cylinder head, crankshaft, and other castings.
Precision investment casting, also known as lost wax casting, includes processes such as pressing wax, repairing wax, assembling trees, dipping slurry, melting wax, casting molten metal, and post-processing. Lost wax casting is to use wax to make a wax mold of the part to be cast, and then coat the wax mold with mud. This is a mud mold. After the clay mold is dried, put it in hot water to melt the internal wax mold. Take out the clay mold from the melted wax mold and fire it into a pottery mold. Generally, a pouring port is left when making a mud mold, and then molten metal is poured from the pouring port. After cooling, the required parts are made.
High dimensional accuracy and geometric accuracy.
High surface roughness.
It can cast complex castings, and the cast alloy is not limited.
complicated procedures and high cost.
It is suitable for the production of small parts with complex shapes and high precision requirements, such as the blades of turbine engines.
Custom die casting is a metal casting process, which is characterized by applying high pressure to the molten metal using the cavity of the mold. Molds are usually made of higher-strength alloys. This process is somewhat similar to injection molding. Most die castings are iron-free, such as zinc, copper, aluminum, magnesium, lead, tin, and lead-tin alloys. Depending on the type of die casting, a cold chamber die casting machine or a hot chamber die casting machine is required.
The metal liquid is subjected to high pressure and fast flow rate during die casting.
Good product quality, stable size, and good interchangeability.
The production efficiency is high, and the die-casting mold is used frequently.
It is suitable for mass production with good economic benefits.
Castings are prone to small pores and shrinkage porosity.
Die-casting parts have low plasticity and are not suitable to work under impact load and vibration.
When a high melting point alloy is die-casting, the mold life is low, which affects the expansion of die-casting production.
Die castings were first used in the automobile industry and instrument industry, and then gradually expanded to various industries, such as agricultural machinery, machine tool industry, electronics industry, defense industry, computers, medical equipment, watches, cameras, and daily hardware.
Low pressure die casting refers to a casting method in which the mold is generally placed above a sealed crucible, and compressed air is introduced into the crucible to cause low pressure (0.06～0.15MPa) on the surface of the molten metal so that the molten metal rises from the riser pipe to fill the mold and control solidification. This casting method has good feeding and compact structure, easy to cast large thin-walled complex castings, no risers, and a metal recovery rate of 95%. The advantage is that it is pollution-free and easy to realize automation. However, the equipment cost is high and the production efficiency is low. Generally used for casting non-ferrous alloys.
The pressure and speed during pouring can be adjusted, so it can be applied to various casting molds (such as metal molds, sand molds, etc.), casting various alloys and castings of various sizes.
Bottom injection type filling is adopted, the filling of molten metal is stable, and there is no splash phenomenon, which can avoid the entrapment of gas and the erosion of the wall and core, which improves the qualification rate of castings.
The casting crystallizes under pressure, the structure of the casting is dense, the outline is clear, the surface is smooth, and the mechanical properties are high, which is particularly advantageous for the casting of large and thin-walled parts.
The feeder riser is omitted, and the metal utilization rate is increased to 90-98%.
Low labor intensity, good working conditions, simple equipment, easy to realize mechanization and automation.
Mainly traditional products (cylinder head, wheel hub, cylinder frame, etc.).
Centrifugal casting is the technology and method of injecting liquid metal into a high-speed rotating mold so that the liquid metal is filled with the mold and formed into a casting by centrifugal movement. Due to the centrifugal movement, the liquid metal can fill the mold well in the radial direction and form the free surface of the casting. A cylindrical inner hole can be obtained without a core. It helps to eliminate the gas and inclusions in the liquid metal, affects the crystallization process of the metal, and improves the mechanical and physical properties of the casting.
There is almost no metal consumption in the gating system and the riser system, which improves the process yield.
The core can not be used when producing hollow castings, so the metal filling ability can be greatly improved when producing long tubular castings.
The casting has high density, few defects such as pores and slag inclusion, and high mechanical properties.
It is convenient to manufacture barrel and sleeve composite metal castings.
There are certain limitations when used in the production of special-shaped castings.
The diameter of the inner hole of the casting is not accurate, the surface of the inner hole is rough, the quality is poor, and the machining allowance is large.
Castings are prone to segregation of specific gravity.
The centrifugal casting was first used to produce cast pipes. At home and abroad, the centrifugal casting was used in metallurgy, mining, transportation, irrigation and drainage machinery, aerospace, defense, automobile, and other industries to produce steel, iron, and non-ferrous carbon alloy castings. Among them, the production of centrifugal cast iron pipes, internal combustion engine cylinder liners, and shaft sleeves is the most common.
Gravity casting refers to the process of injecting molten metal into a mold under the action of the earth's gravity, also known as gravity casting. The generalized gravity casting includes sand casting, metal casting, investment casting, lost foam casting, mud casting, etc. The narrow gravity casting mainly refers to metal casting.
Gravity die casting has large thermal conductivity and heat capacity, fast cooling speed, compact structure of the casting, and about 15% higher mechanical properties than sand castings.
Castings with higher dimensional accuracy and lower surface roughness values can be obtained, and the quality stability is good.
Since sand cores are not used and rarely used, it can improve the environment, reduce dust and harmful gases, and reduce labor intensity.
Gravity die casting has no air permeability, and certain measures must be taken to derive the air in the cavity and the gas produced by the sand core.
Gravity die casting is prone to cracks during solidification.
Gravity die casting has a longer period and higher cost. Therefore, good economic results can only be shown in mass production.
Gravity die casting is not only suitable for mass production of non-ferrous alloy castings such as aluminum alloys and magnesium alloys with complex shapes but also suitable for the production of iron and steel metal castings and ingots.
An advanced die-casting process that eliminates or significantly reduces the pores and dissolved gases in the die-casting parts by removing the gas in the die-casting mold cavity during the die-casting process, thereby improving the mechanical properties and surface quality of the die-casting parts.
Eliminate or reduce the pores inside the die casting, improve the mechanical properties and surface quality of the die casting, and improve the plating performance.
To reduce the backpressure of the cavity, lower specific pressure and alloys with poor casting properties can be used, and it is possible to die-cast larger castings with small machines.
The filling conditions are improved and thinner castings can be die-casted.
The mold sealing structure is complicated, and it is difficult to manufacture and install, so the cost is high.
If the vacuum die-casting method is improperly controlled, the effect is not very significant.
Squeezing die casting is a method in which liquid or semi-solid metal is solidified and flow-shaped under high pressure to directly obtain parts or blanks. It has the advantages of a high utilization rate of liquid metal, simplified process, and stable quality. It is an energy-saving metal forming technology with potential application prospects.
Direct squeeze casting: spray paint, cast alloy, close mold, pressurize, hold pressure, release pressure, split mold, demold blank, reset.
Indirect squeeze casting: spray coating, mold clamping, feeding, filling, pressurization, pressure retention, pressure relief, mold separation, blank demolding, resetting.
It can eliminate internal defects such as pores, shrinkage, and porosity.
Low surface roughness and high dimensional accuracy.
It can prevent casting cracks.
It is easy to realize mechanization and automation.
Lost foam casting (also known as solid casting): It is to combine paraffin wax or foam models similar in size and shape to the castings to form clusters. After brushing and drying refractory coatings, they are buried in dry quartz sand for vibration modeling. It is a new type of casting method in which the mold is vaporized by pouring under pressure, and the liquid metal occupies the position of the mold.
pre-foaming→foaming→dipping coating→drying→modeling→pouring→falling out→cleaning
The casting has high precision and no sand core, which reduces the processing time.
No parting surface, flexible design, and a high degree of freedom.
Clean production, no pollution.
Reduce investment and production costs.
It is suitable for the production of precision castings of various sizes with complex structures, unlimited alloy types, and unlimited production batches. Such as gray cast iron engine box, high manganese steel elbow, etc.
Continuous casting is an advanced casting method whose principle is to continuously pour molten metal into a special metal mold called a crystallizer. The solidified (crusted) casting is continuously pulled out from the other end of the mold, and it can obtain castings of any length or a specific length
Since the metal is rapidly cooled, the crystal is dense, the structure is uniform, and the mechanical properties are better.
Save metal and increase yield.
It simplifies the process, eliminates modeling and other processes, thus reducing labor intensity.
Continuous casting production is easy to realize mechanization and automation and improve production efficiency.
