The welding production process can be summarized as the process of manufacturing welding structures using materials (including basic metal materials and various auxiliary and filling materials, purchased blanks and parts, etc.) processed into products through equipment (material preparation equipment, assembly welding equipment, etc.). The main body of this process is the staff participating in production, including direct (basic production workers, auxiliary workers, engineering technicians) and indirect (management personnel, service personnel) production personnel and inspection personnel. Of course, it also requires the energy source (i.e. power) to operate the machine and a certain production space (i.e. workshop space) to carry out this production process. So welding production is composed of materials, equipment, site, power, and personnel, which are the components of welding production.

1. Material processing technology

The material processing of welding production, including steel pre-treatment, refers to the preparation and processing before assembly and welding, which refers to a series of processing of the basic materials of the vast majority of welding structures - metal rolled materials, such as steel pre-treatment including correction (straightening), cleaning, surface protection treatment, pre cutting, etc; Marking (marking), cutting (cutting), edge processing, forming (including bending), and groove preparation before welding. It accounts for approximately 25% to 60% of the total processing workload. If the processing technology of the material is poor, such as poor quality of the blank, large size error, lack of interchangeability, improper groove processing, or irregular or deformed parts, it will make assembly difficult, reduce welding quality, and sometimes cannot be assembled at all, requiring repair, greatly reducing production efficiency. The adoption of mechanized and automated assembly and welding technology requires more stringent requirements, otherwise welding defect will occur. Therefore, it is important to develop reasonable material processing technology in order to obtain a stable welding production process and ensure excellent product quality. The following are several main material processing techniques:

(1) Pretreatment of steel

1) Correction: Due to transportation, storage, rolling, cooling, and other processes, the rolled steel undergoes unexpected deformations such as waves, overall bending, local protrusions, and edge bending. Some rolled materials, such as 5mm or less thick steel, are supplied in rolls and must be flattened and corrected before being put into welding production. Otherwise, it will affect the accuracy of processes such as marking, marking, and cutting. The deformation generated during material processing (such as thermal cutting) also needs to be corrected, and this correction is called the second correction. According to statistics, 10% to 100% of steel plates and flat steels (varying depending on thickness), and 10% to 20% of profiles need to be corrected. Correction is usually carried out in a cold state. Excessive cold straightening (bending) will make materials brittle, so in order to limit excessive plastic deformation, cold straightening and cold bending are limited. Table 5-15 shows the provisions of the national standard "Code for Acceptance of Construction Quality of Steel structural engineering" (GB 50205-2001), and the relative deformation corrected according to this provision is not more than 1%. To prevent brittle fracture of cold corrected (and cold bent) steel at low temperatures, the specification stipulates that carbon structural steel shall not be cold corrected or bent at ambient temperatures below -16 ℃ and low alloy structural steel below -12 ℃. Correction and bending beyond the specified range in Table 5-15 require heating, which generally should not exceed 900 ℃. During secondary straightening of processed or welded blanks, the weld reinforcement should be limited or removed to prevent excessive plastic deformation in the joint area. In modern welding production, machine tools are often used for correction, and manual correction is rarely used. The use of a steel plate straightening machine can correct the thickness of steel by 0 It uses the principle of repeated rolling with multiple rollers to achieve calibration purposes, ranging from 5 to 50mm. Small and medium cross-section profiles can also be corrected using a multi roll profile straightening machine, but I-beams, channel steels, and large cross-section profiles need to be corrected using a profile straightening press. In some cases, especially for the secondary correction of steel or the correction of welded parts, flame correction is often used. Its principle is to use welding or cutting torque of gas welding or gas cutting, or a specialized flame correction heating gun to heat the deformed parts of the corrected steel or welded parts, such as the elongation and deformation of fibers, to produce compressive plastic deformation. Then, it is quickly cooled, and the elongation fibers are shortened, thereby eliminating deformation.

The corrected steel surface should not have obvious concave or damaged surfaces, and the scratch depth should not exceed 0 5 mm, and should not exceed 1/2 of the negative allowable deviation of the steel thickness. The allowable deviation after steel correction refers to the allowable deformation value of the steel before transferring to the next process.

2) Surface cleaning and surface protection treatment: Removing rust, oil stains, and oxides from the surface of steel and parts is often overlooked in welding production. The result of doing so may disrupt normal production, such as hindering the continuous operation of CNC cutting; It is difficult or even impossible to use efficient welding methods, such as submerged arc welding, narrow gap welding, resistance spot welding, and seam welding. There are two main types of cleaning methods: mechanical method and chemical method. The former includes sandblasting or shot peening, manual wind (electric) grinding wheel or wire brush or abrasive cloth polishing, scraping or polishing, etc. The latter uses solvents for cleaning, which has high efficiency, uniform and stable quality, but high cost, and may cause environmental pollution (such as substandard treatment of waste liquid and air). The commonly used method is to soak in a dilute sulfuric acid (2% -4% mass fraction) tank, then neutralize in a limestone (1% -2% mass fraction) tank, and then dry.

If the surface is not cleaned and put into production in a timely manner, it will continue to rust. Surface protection treatment is the process of spraying primer (conductive) and drying on the surface of steel after correction and cleaning. China has built over 20 steel pretreatment production lines composed of specialized equipment in industries such as shipbuilding, heavy machinery, boilers, and construction machinery, including processes such as leveling, shot blasting and rust removal, 40 ℃ preheating, acid pickling and phosphating, primer spraying, and drying (60 ℃).

(2) The process of setting out, marking, and marking is used to check the correctness of the design drawings, determine the blank cutting size of the parts, and make sample plates. Drawing the design structure at a 1:1 scale (enlarged sample) is called lofting. Setting out is a precise, meticulous, and highly skilled work that has a significant impact on future processing. Generally, lofting is carried out in the lofting room. In order to improve lofting efficiency and quality, optical lofting and computer lofting are used in modern welding production.

Marking the parts or blanks to be machined on metal materials for cutting or assembly is called marking, while marking with a template is called marking. The marking and marking are carried out on a dedicated platform, which should be within the range of crane activity. When using profiling templates or CNC cutting machines for cutting, it is not necessary to pre mark and mark the material.

(3) Cutting and welding production is called metal tailoring, so the cutting and cutting of various metal materials is an important step. The introduction has already introduced significant advancements in the cutting process in welding production, mainly referring to mechanized and automated thermal cutting processes. Coupled with the advancement of thermal cutting itself, the original concept of low production efficiency and poor cut quality in thermal cutting has fundamentally changed. Some factories use mechanized and automated (CNC) thermal cutting processes to cut all or most of the steel with a thickness of 6mm or more, eliminating the steps of marking and marking, greatly improving the cutting quality. Many product edges are products of mechanized thermal cutting, with smooth cuts and correct part sizes, greatly improving product quality.

Another type of cutting is shear cutting, which is called mechanical cutting compared to a large amount of manual thermal cutting. It is usually cut at room temperature, commonly used equipment such as shear machines (gantry shear machines), disc shears, punching machines, and combined punching and shearing machines. Its action is similar to that of household scissors. At the incision between the upper and lower knives, the metal undergoes compression, bending, and shearing, resulting in separation. This incision undergoes cold work hardening, and the cut metal undergoes overall twisted plastic deformation. Most cutting equipment can only cut straight lines, and very few cutting machines can cut grooves. The maximum cutting thickness is not greater than 40mm for gantry shear machines, while for disc shear machines with non linear cuts, the maximum thickness that can be cut is 20-25 mm. For profiles, in addition to using a combined punching and shearing machine for cutting, there are also processes using a circular toothless saw, a tool steel band saw machine, or a contact arc spark saw. Using the above cutting and sawing methods for material cutting, as the equipment is mostly fixed, it is often equipped with separate lifting and transportation equipment and roller tracks, which are within the scope of the lifting equipment in the workshop. Even so, the labor intensity of workers is still relatively high.

(4) Bending and forming work account for a significant proportion in the manufacturing of bent and formed welded structures, with some structural metal materials requiring 80% to 90% bending and forming processing. For example, long-distance pipeline structures, boilers, pressure vessels, spherical vessels, and other chemical and petroleum equipment all belong to this category of structures. The vast majority of bending and partial forming processes are carried out in the cold state, with the aim of preventing excessive deformation from causing cold work hardening and a decrease in material mechanical properties. Therefore, the specifications specify the minimum curvature radius and maximum bending vector height for cold bending, as shown in Table 5-15. Beyond this range, hot forming and bending (coiling) heated to 900~1000 ℃ can be used. Before the temperature drops to 7000 ℃ (carbon steel) and 800 ℃ (low alloy structural steel), this processing shall be completed and the workpiece shall be Free cooling. Similar to orthopedics, the minimum temperature for winter processing is specified. At present, roller bending machines, also known as rolling machines or roller beds, are still used for bending processing. Bending machines are commonly used in the form of three rollers, and there are also four roller bending machines. Modern bending machines (such as PSIO) can cold roll steel plates with a maximum thickness of 190mm, hot roll plates with a thickness of up to 380mm, and plates up to 3 6m is a three roll bending machine with horizontal movement of the lower roll, which is mainly used to roll thick wall pressure vessels of nuclear reactors. The thickness of cold rolled steel plates in domestic manufacturing and use of rolling machines is also above 60mm, and the length is divided into 1 5~2m, 2. Various series including 5-3m, 8-13m, etc. When the three roll bending machine rolls a circle, there is a length of α The straight edge, as shown in Figures 5-21b, is called the remaining straight edge. The improvement method is shown in Figure 5-21c, using a mold made of thick plates for pre bending (pre bending can also be pressed using a mold on a press); It can also be bent using a four roll bending machine, as shown in Figure 5-21d and e; You can also bend it into a strip first α After welding the longitudinal weld seam (not fully welded) of the straight edge cylinder blank, it is then inserted into the roller bed for correction. Figure 5-21f shows the situation of a three roll plate rolling machine with two lower rollers that can move horizontally (or the upper roller moves horizontally relative to the two lower rollers) to eliminate the remaining straight edges during the rounding process. Thin plates with a thickness of less than 6mm can also be rolled without any remaining straight edges using a two roll bending machine with a polyurethane elastic outer sleeve on the lower roll.

In fact, various pre bending methods still have some straight edges, which are allowed as long as they are within the range of roundness error, such as plate thickness δ

To prevent twisting during rolling, the workpiece must be aligned at the beginning of the rolling process, so that the busbar of the workpiece is parallel to the axis of the roller. The three roller plate rolling machine is equipped with a baffle to ensure the alignment of the workpiece, or an inclined feeding method can be used to make one lower roller act as a baffle for alignment; When rolling plates with four rollers, one side of the roller can be raised as a baffle.

The rolling process is divided into one feed and multiple feeds. Depending on the process and equipment limitations, that is, during cold rolling, the maximum allowable deformation rate must not be exceeded, and there should be no slipping between the plate and roller. The allowable stress of the roller and the maximum power of the equipment must not be exceeded. If one feed cannot meet the requirements, multiple feeds can be used to complete the rolling process. The minimum bending radius given in the equipment manual of the rolling machine refers to the minimum bending radius when feeding the nominal specification plate specified by the rolling machine in one feed, and the minimum bending radius can be close to the upper roll radius when feeding multiple times. The fewer feed times for rolling, the higher the efficiency, while the roundness error is relatively larger. When rolling a circle, it is always completed with the least or one feed within the allowable range of process, equipment conditions, and roundness errors, in order to achieve the highest productivity.

Considering the rebound of steel during cold rolling, a certain amount of over coiling must be applied during the rolling process, even if the diameter of the workpiece after rebound is the diameter required by the machining drawing. Therefore, when rolling, the diameter of the workpiece before rebound is used to determine various process parameters. The radius R 'of the cylinder before rebound is based on the radius R of the workpiece (half of the pitch diameter), the cross-sectional shape coefficient K1, the relative strengthening coefficient k0 of the steel, and the thickness of the plate δ、 Yield limit of steel σ Calculate s and elastic modulus E using the following formula.

In the formula, m - depends on R, δ The constant of,.

Other symbols as mentioned earlier; K1- For rectangular sections that are often rolled, it can be taken as 1.5; The relative strengthening coefficient k} of steel can be taken as 11 for Q235-A 6； 14 can be taken for Q345 (16Mn); 18MnMoNiR can be taken as 17.6 grade; And the yield limit σ s。 Can be taken as 240MPa, 350MPa, 520MPa, etc. respectively, while E is taken as 2 1 x 105MPa。 You can use the formula above to determine the inner diameter D and plate thickness of the rolled cylinder according to the drawing requirements δ Calculate the inner diameter d of the cylinder before rebound:

Given the radius R 'of the cylinder before rebound, the geometric parameters for symmetric and asymmetric three roll and four roll rolling can be obtained using geometric relationships. For example, when symmetrically rolling plates with three or four rollers, the appropriate distance between the centers of the upper and lower rollers during rolling can be determined by knowing the distance between the centers of the lower rollers, the wall thickness of the cylinder, the radius of the upper and lower rollers, and the radius of the cylinder before the spring is R '. When asymmetric three roller plate rolling, the left position angle of the upper roller and the relative position angle of the upper roller during rolling can be determined. The upper roller deviates from the center distance between the two lower rollers, and the distance the upper roller presses down from the highest position can be determined, as shown in Figure 5-21f α、β、 Roll parameters such as x and y.

If the maximum distance between the upper and lower rollers of the asymmetric three roller plate rolling machine is set to H (which can be obtained from the equipment parameters), and the diameters of the upper and lower rollers are Da and Db respectively, the downward displacement y1 of the workpiece compressed by the upper roller can be calculated:

Due to asymmetric rolling, the upper roller will lean to one side (as shown in the middle figure of 5-21f). The angle a between the force line of the upper roller and the line connecting the center of the cylinder and the deviation from the center of the lower roller on the side is called the left position angle, and the vertical centerline of the cylinder, also known as the center line of the two lower rollers and the line connecting the center of the cylinder and the center of the lower roller on the other side, is called the relative position angle

In the formula, B - the remaining straight edge (i.e. set as α）， Under the condition of asymmetric rolling with three rollers, B is greatly reduced, with B=k δ， here

K is the residual straight edge coefficient, with a minimum value of 1.5, δ Is the thickness of the plate;

L - is the center distance between the two lower rollers (see Figure 5-21f), and other symbols are the same as before.

If H 'is used to represent the distance between the center of the cylinder and the center of the two lower rollers before rolling back, then:

Compared to this center, in asymmetric rolling, the vertical and horizontal positions y and x of the upper roller can be calculated by the following equation:

When the calculation result y is positive, it indicates that the center of the cylinder is upward before being rolled back; Two is positive, indicating that the center of the cylinder is to the right before being rolled back. With these parameters, three-roll asymmetric rolling can be carried out. If programmed, it can be used for CNC three roller plate rolling machine to perform CNC automatic plate rolling.

When hot rolling is required, correctly control the temperature of the rolling process as mentioned earlier. The heating furnace should be arranged near the rolling machine, with a distance of about 6-10m, depending on the size of the processed workpiece and equipment. The hot coil does not rebound, so there is no need to overwind. For thin plates that do not allow cold rolling, if hot rolling is used due to poor rigidity and difficulty in lifting, warm rolling can be used. The so-called warm rolling refers to the heating temperature below the metal recrystallization temperature and above the blue brittleness temperature.

Curved parts are inspected using curved templates. When the chord length of the part is less than or equal to 1500mm, the chord length of the template should not be less than 2/3 of the chord length of the part; When the chord length is greater than 1500mm, the chord length of the sample should not be less than 1500mm. The gap between the formed part and the sample plate shall not exceed 2 Unless otherwise specified in the technical requirements, the tolerance for the size of the curling cylinder can be referred to as 0mm