CNC Knowledge: The most comprehensive and detailed explanation of the casting process! Did you get it back?

A production method in which liquid metal is poured into a mold cavity matched to the shape and size of the part, then cooled and solidified to obtain a blank or part, generally called liquid metal forming or casting.

Process flow: liquid metal → mold filling → solidification shrinkage → casting

Process characteristics:

1. It can produce parts of any complex shape, especially parts with complex internal cavity shapes.

2. Strong adaptability, no restrictions on alloy types and almost no restrictions on the size of castings.

3. The material sources are wide, the waste can be remelted, and the equipment investment is small.

4. High scrap rate, poor surface quality and poor working conditions.

Cast ranking:

(1) Sand casting

Sand casting: A casting method that produces castings in a sand mold. Castings of steel, iron and most non-ferrous alloys can be obtained by sand casting methods.

Process flow:

Sand Casting Process

Technical characteristics:

1. Suitable for manufacturing blanks of complex shapes, especially those with complex internal cavities;

2. Wide adaptability and low cost;

3. For some materials with low plasticity, such as cast iron, sand casting is the only forming process to make parts or blanks.

Application: automobile engine cylinder blocks, cylinder heads, crankshafts and other castings

(2) Investment casting

Investment casting: generally refers to making a model from a fusible material, covering the surface of the model with several layers of refractory materials to form a mold shell, then melting the model and extruding the mold shell, thus obtaining a mold without separation surfaces. , which is then grilled at high temperature. Then the casting plane can be filled with sand. Often called “lost wax casting”.

Process flow:

Investment casting process

Process characteristics

advantage:

1. High dimensional accuracy and geometric accuracy;

2. High surface roughness;

3. It can cast castings of complex shapes, and the casting alloys are not limited.

Disadvantages: complicated process and high cost

Application: Suitable for producing small parts with complex shapes, high precision requirements or other difficult-to-process parts, such as turbomachinery blades, etc.

(3) Die casting

Die Casting: It uses high pressure to press molten metal into a precision metal mold cavity at high speed. The molten metal cools and solidifies under pressure to form a casting.

Process flow:

Process characteristics

advantage:

1. When die casting, the metal liquid bears high pressure and has rapid flow.

2. The product has good quality, stable dimensions and good interchangeability;

3. High production efficiency and frequent use of die casting molds;

4. Suitable for mass production and has good economic advantages.

default:

1. Castings are prone to small pores and shrinkage.

2. Die casting parts have low plasticity and are not suitable for working under impact loads and vibration;

3. When die casting high melting point alloys, the mold life is low, which affects the expansion of die casting production.

Application: 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, the national defense industry, computers, medical equipment, clocks, cameras and everyday life. material. .

(4) Low pressure casting

Low pressure casting: refers to a method in which liquid metal fills the mold under relatively low pressure (0.02 ~ 0.06 MPa) and crystallizes under the pressure to form a casting.

Process flow:

Technical characteristics:

1. 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 different sizes;

2. Through bottom injection mold filling, the molten metal is filled smoothly without splashing, which can avoid gas involvement and erosion of the mold wall and core, and improve the mold rate. qualification of molded parts;

3. The casting crystallizes under pressure. The casting structure is dense, the outline is clear, the surface is smooth, and the mechanical properties are high, which is especially beneficial for the casting of large and thin-walled parts;

4. The feed riser is omitted and the metal utilization rate is increased to 90-98%;

5. Low labor intensity, good working conditions, simple equipment and easy to achieve mechanization and automation.

Application: Mainly traditional products (cylinder heads, wheel hubs, cylinder frames, etc.).

(5) Centrifugal casting

Centrifugal casting: It is a casting method that pours molten metal into a rotating mold, fills the mold under the action of centrifugal force, and solidifies.

Process flow:

Process characteristics

advantage:

1. There is almost no metal consumption in the door system and riser system, thereby improving the process efficiency;

2. No core is needed when producing hollow castings, so the metal filling capacity can be greatly improved when producing long tubular castings;

3. The casting has high density, few defects such as pores and slag inclusions, and high mechanical properties;

4. It is convenient to manufacture composite metal castings such as cylinders and sleeves.

default:

1. There are some limitations when used to produce special-shaped castings;

2. The inner hole diameter of the casting part is inaccurate, the inner hole surface is rough, the quality is poor, and the machining allowance is large;

3. Castings are subject to gravity segregation.

application:

Centrifugal casting was first used to produce cast iron pipes. Centrifugal casting technology is used in metallurgy, mining, transportation, drainage and irrigation, aviation, national defense, automobile and other industries domestically and abroad to produce steel, iron and non-ferrous carbon. alloy castings. Among them, the production of castings such as centrifugal cast iron pipes, cylinder liners and internal combustion engine rings is the most common.

(6) gravity die casting

Metal Mold Casting: Refers to a casting method in which liquid metal fills a metal mold under the action of gravity and cools and solidifies in the mold to obtain a casting.

Process flow:

Process characteristics

advantage:

1. The metal mold has high thermal conductivity and heat capacity, rapid cooling rate, dense casting structure and mechanical properties which are about 15% higher than those of sand castings.

2. Castings with higher dimensional accuracy and lower surface roughness values ​​can be obtained, and the quality stability is good.

3. Because sand cores are not used or rarely used, the environment is improved, dust and harmful gases are reduced, and labor intensity is reduced.

default:

1. The metal mold itself is not breathable, and certain measures must be taken to exhaust the air from the mold cavity and the gas generated by the sand core;

2. The metal mold has no concessions, and cracks are likely to occur when the casting solidifies;

3. The manufacturing cycle of metal types is long and the cost is high. Therefore, good economic effects can only be demonstrated when mass production is carried out in batches.

Application: Metal mold casting is not only suitable for the mass production of complex-shaped aluminum alloy, magnesium alloy and other non-ferrous alloy castings, but also suitable for the production of iron castings and steel, ingots, etc.

(7) Vacuum casting

Vacuum Casting: An advanced die casting process that eliminates or significantly reduces pores and dissolved gases in die casting parts by removing gas from the die casting mold cavity during the die casting process, improving thus the mechanical properties and the surface. quality of die casting parts.

Process flow:

Process characteristics

advantage:

1. Eliminate or reduce pores inside die casting parts, improve the mechanical properties and surface quality of die casting parts, and improve plating performance;

2. To reduce the back pressure of the mold cavity, alloys with lower specific pressure and poor casting performance can be used, and it is possible to pressure cast larger castings with small machines;

3. The filling conditions are improved and thinner castings can be die-cast;

default:

1. The mold sealing structure is complex and difficult to manufacture and install, so the cost is high;

2. If the vacuum casting method is not properly controlled, the effect will not be very significant.

(8) Pressing die casting

Compression casting: It is a method of solidifying and creeping liquid or semi-solid metal under high pressure to directly obtain parts or blanks. 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 prospects.

Process flow:

Direct compression casting: spray coating, alloy casting, mold closing, pressurization, pressure holding, decompression, mold splitting, blank demolding, reset;

Indirect compression casting: spray coating, mold clamping, feeding, mold filling, pressurization, pressure holding, decompression, mold splitting, blank demolding and resetting.

Technical characteristics:

1. It can eliminate internal defects such as pores, shrinkage cavities and shrinkage porosity;

2. Low surface roughness and high dimensional accuracy;

3. It can prevent the occurrence of casting cracks;

4. It is easy to realize mechanization and automation.

Application: Can be used to produce various types of alloys, such as aluminum alloys, zinc alloys, copper alloys, ductile iron, etc.

(9) Lost Foam Casting

Lost foam casting (also known as true mold casting): Paraffin or foam models similar in size and shape to the casting are linked and combined into model clusters. After being painted with refractory paint and dried, they are buried in dry quartz sand and vibrated. shape. This is a new casting method that vaporizes the model by pressing it down, and the liquid metal occupies the position of the model, then solidifies and cools to form a casting.

Process flow: pre-foaming → foam molding → coating → drying → shaping → casting → sand falling → cleaning

Technical characteristics:

1. The casting has high precision and does not contain sand core, reducing 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: Suitable for producing precision casting parts of various sizes with complex structures. There is no limit on alloy type and production batch. Such as gray cast iron motor housing, high manganese steel elbow, etc.

(10) Continuous casting

Continuous Casting: This is an advanced casting method. Its principle is to continuously pour molten metal into a special metal mold called a crystallizer. The solidified (crusted) castings are poured continuously to the other side of the crystallizer. it can get castings of any length or a specific length.

Process flow:

Technical characteristics:

1. Because the metal is cooled quickly, the crystallization is dense, the structure is uniform, and the mechanical properties are good;

2. Save metal and increase efficiency;

3. The process is simplified and modeling and other processes are eliminated, thereby reducing labor intensity; the required production area is also significantly reduced;

4. Continuous casting production is easy to implement, mechanized and automated, and improves production efficiency.

Application: Continuous casting method can be used to cast steel, iron, copper alloys, aluminum alloys, magnesium alloys and other long castings with constant section shape, such such as ingots, slabs, bar blanks, pipes, etc.