Processing technology analysis of special sheet metal-Sheet metal process analysis
Processing technology analysis of special sheet metal-Sheet metal process analysis
In recent years, with the increasingly complex domestic and international situation, customers' demand for protective vehicles is gradually increasing, and the interior and exterior surfaces of protective vehicles are mostly special steel plates. The early special car body structure is generally welded joint structure of special steel plate, but the welding seam is the weak link of protection, so the design of reducing welding seam by bending integration gradually replaces the original welding splicing structure. The tensile strength of general special series steel plate is 3-5 times (1500-2100 MPa) of conventional steel plate. The material performance is special, easy to crack, and has large rebound and hardness. The structure and strength of ordinary processing technology and cutting tools can not meet the requirements of special steel plate processing
Bending process of special sheet metal products
The special steel plate is extremely hard and has toughness. By optimizing the alloy composition and combining with the special direct quenching process, the high hardness and high toughness are obtained. The elongation is only about 7%, and the hardness is generally up to 550hbw. The structure, hardness and bending parameters of the ordinary bending die can not meet the processing requirements. It has large springback, easy cracking and easy indentation on the outer surface. Generally, V-shaped and U-shaped bending dies are used by manufacturing enterprises. The R-angle of the lower die is a fixed structure. The width of the V-shaped hole is generally 4-6 times of the material thickness, and the R-angle of the upper die is usually 1-1.5 times of the material thickness
For special sheet metal products, we mainly discuss free bending. Our company has redeveloped the special bending die for special sheet metal, as shown in Figure 4. The R-angle of the lower die adopts the removable and rolling LD material roller structure. The R-angle, v-mouth width and angle of the upper die and the lower die are redesigned. Here, the larger springback factors of special sheet metal products must be considered. For example, the R angle of the upper die can be 3-6 times of the material thickness, the R angle of the lower die can be 4-8 times of the material thickness, and the width of the V-port can be 6-12 times of the material thickness Marks all work well. In addition, the following problems need to be noted during bending: (1) attention should be paid to bending at right angles to the rolling direction, all defects should be removed by grinding before bending, and the shear edge should also be polished flat. (2) Bending force and springback will increase with the increase of special sheet metal strength. The higher the hardness of sheet metal, the greater the bending force and springback.
Based on the consideration of cost and maintenance, R angle of upper die, R angle of lower die and upper and lower mold body can adopt removable structure, which is convenient for maintenance and can reduce cost. The special sheet metal bending process has the advantages of flexible production, which is convenient for product upgrading and adjustment, and can effectively meet the welding accuracy requirements. Small initial investment, short investment cycle, relatively low requirements for equipment and personnel, which is conducive to reducing enterprise costs.
Cutting technology of special sheet metal products
For special sheet metal products cutting process, there are the following several ways.
(1) Water jet. This process can be used for blanking of all special sheet metal products and is the preferred method because there is no heat affected zone and the risk of cracking can be eliminated completely.
(2) Laser cutting. For the blanking of thick special sheet metal products, this process can be used for cutting. The incision produced by this process is narrow, and the heat affected zone is also narrow, generally less than 3mm.
(3) Plasma cutting. Special sheet metal products can also be cut by this process. The width of the incision produced by this process is generally 3-4 mm, and the width of the heat affected zone is not more than 5 mm. And plasma cutting can be carried out underwater, which can reduce deformation and produce a narrower heat affected zone.
(4) Gas cutting. This process can be used for special steel plate with thickness up to 60mm. This process will produce a 2-5mm wide notch, and the heat affected zone is generally 4-10mm wide. It is worth mentioning that uncontrolled gas cutting may lead to hydrogen induced cracking (also known as cold cracking) for special steel plates with high hardness, which may also occur when the plate thickness exceeds 20-30mm. The thicker the plate, the higher the sensitivity to cracking. In order to avoid cracks in the process of cutting or after cutting, the most effective method is to preheat the steel plate, and then carry out high temperature insulation on the cutting parts. Preheating consists of heating the entire steel plate or an area at least 100 mm wide on both sides of the target notch to the specified minimum temperature before cutting, which can be achieved by using constant temperature heating furnace, heating blanket, etc., and in some cases, gas heating furnace can be used to maintain the temperature throughout the whole process (the same equipment can be used for high temperature insulation of cutting parts). Only when the cutting part is wide enough to consume too much heat, can low speed cutting be used.
(5) Grinding wheel. This process is generally used for cutting pipe and round steel, and also can be used for straight-line cutting of special sheet metal products. The notch width is equal to the grinding wheel thickness, and there is almost no heat affected zone.
In recent years, with the increasingly complex domestic and international situation, customers' demand for protective vehicles is gradually increasing, and the interior and exterior surfaces of protective vehicles are mostly special steel plates. The early special car body structure is generally welded joint structure of special steel plate, but the welding seam is the weak link of protection, so the design of reducing welding seam by bending integration gradually replaces the original welding splicing structure. The tensile strength of general special series steel plate is 3-5 times (1500-2100 MPa) of conventional steel plate. The material performance is special, easy to crack, and has large rebound and hardness. The structure and strength of ordinary processing technology and cutting tools can not meet the requirements of special steel plate processing
Bending process of special sheet metal products
The special steel plate is extremely hard and has toughness. By optimizing the alloy composition and combining with the special direct quenching process, the high hardness and high toughness are obtained. The elongation is only about 7%, and the hardness is generally up to 550hbw. The structure, hardness and bending parameters of the ordinary bending die can not meet the processing requirements. It has large springback, easy cracking and easy indentation on the outer surface. Generally, V-shaped and U-shaped bending dies are used by manufacturing enterprises. The R-angle of the lower die is a fixed structure. The width of the V-shaped hole is generally 4-6 times of the material thickness, and the R-angle of the upper die is usually 1-1.5 times of the material thickness
For special sheet metal products, we mainly discuss free bending. Our company has redeveloped the special bending die for special sheet metal, as shown in Figure 4. The R-angle of the lower die adopts the removable and rolling LD material roller structure. The R-angle, v-mouth width and angle of the upper die and the lower die are redesigned. Here, the larger springback factors of special sheet metal products must be considered. For example, the R angle of the upper die can be 3-6 times of the material thickness, the R angle of the lower die can be 4-8 times of the material thickness, and the width of the V-port can be 6-12 times of the material thickness Marks all work well. In addition, the following problems need to be noted during bending: (1) attention should be paid to bending at right angles to the rolling direction, all defects should be removed by grinding before bending, and the shear edge should also be polished flat. (2) Bending force and springback will increase with the increase of special sheet metal strength. The higher the hardness of sheet metal, the greater the bending force and springback.
Based on the consideration of cost and maintenance, R angle of upper die, R angle of lower die and upper and lower mold body can adopt removable structure, which is convenient for maintenance and can reduce cost. The special sheet metal bending process has the advantages of flexible production, which is convenient for product upgrading and adjustment, and can effectively meet the welding accuracy requirements. Small initial investment, short investment cycle, relatively low requirements for equipment and personnel, which is conducive to reducing enterprise costs.
Cutting technology of special sheet metal products
For special sheet metal products cutting process, there are the following several ways.
(1) Water jet. This process can be used for blanking of all special sheet metal products and is the preferred method because there is no heat affected zone and the risk of cracking can be eliminated completely.
(2) Laser cutting. For the blanking of thick special sheet metal products, this process can be used for cutting. The incision produced by this process is narrow, and the heat affected zone is also narrow, generally less than 3mm.
(3) Plasma cutting. Special sheet metal products can also be cut by this process. The width of the incision produced by this process is generally 3-4 mm, and the width of the heat affected zone is not more than 5 mm. And plasma cutting can be carried out underwater, which can reduce deformation and produce a narrower heat affected zone.
(4) Gas cutting. This process can be used for special steel plate with thickness up to 60mm. This process will produce a 2-5mm wide notch, and the heat affected zone is generally 4-10mm wide. It is worth mentioning that uncontrolled gas cutting may lead to hydrogen induced cracking (also known as cold cracking) for special steel plates with high hardness, which may also occur when the plate thickness exceeds 20-30mm. The thicker the plate, the higher the sensitivity to cracking. In order to avoid cracks in the process of cutting or after cutting, the most effective method is to preheat the steel plate, and then carry out high temperature insulation on the cutting parts. Preheating consists of heating the entire steel plate or an area at least 100 mm wide on both sides of the target notch to the specified minimum temperature before cutting, which can be achieved by using constant temperature heating furnace, heating blanket, etc., and in some cases, gas heating furnace can be used to maintain the temperature throughout the whole process (the same equipment can be used for high temperature insulation of cutting parts). Only when the cutting part is wide enough to consume too much heat, can low speed cutting be used.
(5) Grinding wheel. This process is generally used for cutting pipe and round steel, and also can be used for straight-line cutting of special sheet metal products. The notch width is equal to the grinding wheel thickness, and there is almost no heat affected zone.
