A complete collection of metal forming methods, what else is there besides machining?
Material forming method is an important part of part design and a key factor in the processing process. In addition to machining, metal injection molding, plastic forming and 3D printing that have emerged in recent years are all main technologies. Let’s take a closer look at these metal forming methods The characteristics of the craft.
casting
Liquid metal is poured into the mold cavity that is suitable for the shape and size of the part, and is cooled and solidified to obtain blanks or parts. It is usually called liquid metal forming or casting.
Process flow: liquid metal → filling → solidification shrinkage → casting
Process features:
1. It can produce parts with arbitrary complex shapes, especially those with complex inner cavity shapes.
2. Strong adaptability, unlimited types of alloys, almost unlimited size of castings.
3. The source of materials is wide, the waste products can be remelted, and the equipment investment is low.
4. High scrap rate, low surface quality and poor working conditions.
Casting classification:
(1) Sand casting (sand casting)
Casting method for producing castings in sand molds. Steel, iron and most non-ferrous alloy castings can be obtained by sand casting.
Process flow:
Technical Features:
1. It is suitable for making blanks with complex shapes, especially with complex inner cavities;
2. Wide adaptability and low cost;
3. For some materials with poor plasticity, such as cast iron, sand casting is the only forming process for manufacturing its parts or blanks.
Application: Engine cylinder block, cylinder head, crankshaft and other castings of automobiles
(2) Investment casting (investment casting)
Usually, it refers to making a pattern from a fusible material, covering the surface of the pattern with several layers of refractory material to make a shell, and then melting the pattern and discharging the shell, so as to obtain a mold without a parting surface, which can be filled after high-temperature roasting. Casting solutions for sand pouring. Often referred to as "lost wax casting".
Process flow:
advantage:
1. High dimensional accuracy and geometric accuracy;
2. High surface roughness;
3. It can cast castings with complex shapes, and the casting alloys are not limited.
Disadvantages: complicated process and high cost
Application: It is suitable for the production of small parts with complex shapes, high precision requirements, or difficult other processing, such as blades of turbine engines, etc.
(3) Die casting
Using high pressure to press molten metal into a precision metal mold cavity at high speed, the molten metal is cooled and solidified under pressure to form a casting.
Process flow:
advantage:
1. During die-casting, the metal liquid bears high pressure and the flow rate is fast
2. Good product quality, stable size and good interchangeability;
3. The production efficiency is high, and the die-casting mold can be used frequently;
4. It is suitable for mass production and has good economic benefits.
shortcoming:
1. Castings are prone to tiny pores and shrinkage.
2. Die castings have low plasticity, so it is not suitable to work under impact load and vibration;
3. When die-casting high-melting point alloys, the life of the mold is low, which affects the expansion of die-casting production.
Application: Die castings were first used in the automobile industry and the instrument industry, and then gradually expanded to various industries, such as agricultural machinery, machine tool industry, electronics industry, defense industry, computer, medical equipment, clocks, cameras and daily hardware and other industries .
(4) Low pressure casting (low pressure casting)
Refers to the method of filling the mold with liquid metal under a lower pressure (0.02-0.06MPa) and crystallizing under pressure to form a casting.
Process flow:
Technical Features:
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 various sizes;
2. Bottom injection type filling is adopted, the molten metal filling is stable without splashing, which can avoid the gas involved and the erosion of the mold wall and core, and improve the qualified rate of castings;
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 feeding riser is omitted, and the metal utilization rate is increased to 90-98%;
5. Low labor intensity, good working conditions, simple equipment, easy to realize mechanization and automation.
Application: mainly traditional products (cylinder head, wheel hub, cylinder frame, etc.).
(5) centrifugal casting (centrifugal casting)
A casting method in which molten metal is poured into a rotating mold, and the mold is filled and solidified under the action of centrifugal force.
Process flow:
advantage:
1. There is almost no metal consumption in the pouring system and riser system, which improves the process yield;
2. There is no need for a core when producing hollow castings, so the metal filling ability can be greatly improved when producing long tubular castings;
3. The casting has high density, fewer defects such as pores and slag inclusions, and high mechanical properties;
4. It is convenient to manufacture composite metal castings such as barrels and sleeves.
shortcoming:
1. There are certain limitations when used to produce special-shaped castings;
2. The diameter of the inner hole of the casting is not accurate, the surface of the inner hole is relatively rough, the quality is poor, and the machining allowance is large;
3. Castings are prone to specific gravity segregation
application:
Centrifugal casting was first used to produce cast pipes. At home and abroad, centrifugal casting technology 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, the production of castings such as centrifugal cast iron pipes, internal combustion engine cylinder liners and shaft sleeves is the most common.
(6) Metal mold casting (gravity die casting)
A molding 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:
advantage:
1. The thermal conductivity and heat capacity of the metal mold are large, the cooling speed is fast, the structure of the casting is dense, and the mechanical properties are about 15% higher than that of the sand casting.
2. Castings with high dimensional accuracy and low surface roughness 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.
shortcoming:
1. The metal mold itself has no air permeability, and certain measures must be taken to export the air in the cavity and the gas generated by the sand core;
2. The metal type has no concession, and the casting is prone to cracks when it solidifies;
3. The metal mold manufacturing cycle is longer and the cost is higher. Therefore, good economic effects can only be shown when mass-produced in large quantities.
application:
Metal mold 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 for the production of iron and steel metal castings and ingots.
(7) Vacuum die casting (vacuumdie casting)
It is an advanced die-casting process that improves the mechanical properties and surface quality of die-casting parts by eliminating or significantly reducing the pores and dissolved gases in the die-casting parts by extracting the gas in the die-casting mold cavity during the die-casting process.
Process flow:
advantage:
1. Eliminate or reduce the pores inside the die casting, improve the mechanical properties and surface quality of the die casting, and improve the coating performance;
2. To reduce the back pressure of the cavity, alloys with lower specific pressure and poor casting performance can be used, and it is possible to die-cast larger castings with small machines;
3. The filling conditions are improved, and thinner castings can be die-cast;
shortcoming:
1. The mold sealing structure is complicated, and it is difficult to manufacture and install, so the cost is high;
2. If the vacuum die-casting method is not properly controlled, the effect will not be very significant.
(8) Squeeze casting (squeezing die casting)
The method of solidifying liquid or semi-solid metal under high pressure, flow forming, and directly obtaining workpieces 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 extrusion casting: spray paint, cast alloy, mold clamping, pressurization, pressure maintaining, pressure relief, mold splitting, blank demoulding, reset;
Indirect extrusion casting: coating, mold clamping, feeding, filling, pressurization, pressure holding, pressure relief, mold parting, blank demoulding, reset.
Technical Features:
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 generation of casting cracks;
4. It is easy to realize mechanization and automation.
Application: It can be used to produce various types of alloys, such as aluminum alloy, zinc alloy, copper alloy, ductile iron, etc.
(9) Lost foam casting
The paraffin or foam models similar in size and shape to the castings are bonded and combined into model clusters. After brushing refractory paint and drying, they are buried in dry quartz sand for vibration molding, and poured under negative pressure to vaporize the model, and the liquid metal occupies Model position, a new casting method that forms a casting after solidification and cooling.
Process flow: pre-foaming→foaming molding→dipping paint→drying→modeling→pouring→shaking→cleaning
Technical Features:
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 precision castings of various sizes with complex structures. The types of alloys are not limited, and the production batches are not limited. Such as gray cast iron engine case, high manganese steel elbow, etc.
(10) Continuous casting (continual casting)
An advanced casting method, the principle is to continuously pour molten metal into a special metal mold called a crystallizer, and the solidified (crusted) casting is continuously pulled out from the other end of the crystallizer, It can obtain castings of any length or specific lengths.
Technical Features:
1. Due to the rapid cooling of the metal, the crystallization is dense, the structure is uniform, and the mechanical properties are good;
2. Save metal and increase yield;
3. The process is simplified, and the modeling and other processes are exempted, thus reducing the labor intensity; the required production area is also greatly reduced;
4. Continuous casting production is easy to realize mechanization and automation, and improves production efficiency.
application:
The continuous casting method can cast steel, iron, copper alloy, aluminum alloy, magnesium alloy and other long castings with constant cross-sectional shapes, such as ingots, slabs, billets, pipes, etc.
plastic forming
Using the plasticity of the material, the process method of processing the workpiece with less cutting or no cutting under the external force of the tool and the mold. There are many types of it, mainly including forging, rolling, extrusion, drawing, stamping and so on.
(1) forging
It is a processing method that uses forging machinery to apply pressure to metal blanks to cause plastic deformation to obtain forgings with certain mechanical properties, certain shapes and sizes.
According to the forming mechanism, forging can be divided into free forging, die forging, ring rolling and special forging.
Free forging: generally on a hammer forging or hydraulic press, using simple tools to hammer metal ingots or blocks into required shapes and sizes.
Die forging: It is formed by using a die on a die forging hammer or a hot die forging press.
Ring rolling: refers to the production of ring parts with different diameters through special equipment ring rolling machines, and is also used to produce wheel-shaped parts such as automobile hubs and train wheels.
Special forging: including roll forging, cross wedge rolling, radial forging, liquid die forging and other forging methods, which are more suitable for the production of parts with special shapes.
Technological process: forging billet heating→roll forging billet preparation→die forging forming→edge trimming→punching→straightening→intermediate inspection→heat treatment of forgings→cleaning→straightening→inspection
Technical Features:
1. The quality of forgings is higher than that of castings and can withstand large impact force. The plasticity, toughness and other mechanical properties are also higher than castings or even higher than rolling parts.
2. Save raw materials and shorten processing hours.
3. High production efficiency.
4. Free forging is suitable for single piece and small batch production, and has great flexibility.
application:
Rolls and herringbone gears of large rolling mills, rotors, impellers, and retaining rings of turbogenerators, working cylinders and columns of huge hydraulic presses, axles of locomotives, crankshafts and connecting rods of automobiles and tractors, etc.
(2) rolling
A pressure processing method in which the metal blank passes through the gap between a pair of rotating rolls (various shapes), and the cross-section of the material is reduced and the length is increased due to the compression forming and rolling of the rolls.
Rolling classification:
According to the movement of the rolled piece, there are: longitudinal rolling, horizontal rolling, and skew rolling. Longitudinal rolling is a process in which metal passes between two rolls with opposite rotation directions and produces plastic deformation between them; the direction of movement of the rolled piece after deformation is consistent with the direction of the axis of the roll; Roll axis non-special angle.
application:
It is mainly used in metal profiles, plates, pipes, etc., as well as some non-metallic materials such as plastic products and glass products.
(3) extrusion
Under the action of three-way uneven compressive stress, the billet is extruded from the orifice or gap of the mold to reduce the cross-sectional area and increase the length, and the processing method to become the desired product is called extrusion. This processing of the billet is called extrusion molding. .
Process flow:
Preparation before extrusion → casting rod heating → extrusion → stretching, twisting and straightening → sawing (cutting to length) → sampling inspection → artificial aging → packaging and storage
advantage:
1. Wide range of production, product specifications and varieties;
2. Large production flexibility, suitable for small batch production;
3. The product has high dimensional accuracy and good surface quality;
4. Less equipment investment, small workshop area, easy to realize automatic production.
shortcoming:
1. Large loss of geometric waste;
2. Uneven metal flow;
3. Low extrusion speed and long auxiliary time;
4. Tool wear is large and the cost is high.
Scope of production application: mainly used to manufacture long rods, deep holes, thin-walled parts, and special-shaped cross-section parts.
(4) Pulling
A plastic processing method in which an external force acts on the front end of the drawn metal to pull the metal blank out of a die hole smaller than the section of the blank to obtain a product of corresponding shape and size.
advantage:
1. Precise size and smooth surface;
2. The tools and equipment are simple;
3. Continuous high-speed production of long products with small cross-sections.
shortcoming:
1. The amount of deformation per pass and the total deformation between two annealings are limited;
2. Length is limited.
