Sheet metal plates, section steels, pipe material, and other metal raw materials or sheet metal blanks are caused by uneven residual stress during the rolling, cold drawing, extrusion, and cutting processes, improper storage and transportation, and sheet metal components that suffer from processing such as stamping and welding. External forces may cause warping, bending, twisting, and other deformations. Elimination of these deformations is collectively referred to as the correction. Correction is a method of correcting the steel structure and raw materials whose geometric shape does not meet the requirements of the product to produce a certain degree of plastic deformation, to achieve the geometric shape required by the product. Various deformations must go through Correction treatment can be used for subsequent processing or assembly. Correction is an important auxiliary processing method in sheet metal processing. Generally speaking, correction work includes the following four aspects.
1. Correction of raw materials before blanking. For example, the rolling and bending of sheet metal must be uncoiled and leveled before it can be unloaded. For other plates and profiles, some of them may have "distortion" due to improper transportation and storage, and they must be leveled and straightened before cutting.
2. Correction of sheet metal blanks or intermediate process parts. For example, the leveling of plate parts and the straightening of section steel parts are generally carried out after blanking or forming.
3. Correction of welding deformation. It mainly includes the deformation of the shape and size of parts and products caused by welding, forming, etc.
4. Correction of deformed parts. The steel structure product is repaired after a period of use, and all deformed parts are corrected.
The essentials and methods of correction
Different residual stresses exist in the steel and components at different stages, and the residual stress causes plastic deformation of the steel or components. The deformation of steel or intermediate process parts will affect the normal operation of the number of parts, cutting, and other processing processes, and reduce the processing accuracy. If the deformation generated in the processing of parts is not corrected, it will affect the correct assembly of the entire structure, reduce the assembly quality, and even affect the strength and service life of the components. For this reason, based on clarifying the allowable deformation (the following table shows the allowable deviation value before blanking of general rolling materials), the workpiece should be analyzed to determine the correction method.
1. The essentials of correction
Before choosing a correction method and implementing a specific correction operation, you should master the essentials of correction according to the following steps.
The allowable deviation value before the general rolling material is blanked.
● Analyze the causes of deformation There are generally two reasons for the deformation of the workpiece: one is the deformation caused by an external force, and the other is the deformation caused by internal stress. For workpieces that are plastically deformed by external forces, corrective measures are generally taken for the deformed parts. For workpieces that are deformed due to internal stress, corrective measures are generally not taken for the deformed parts, but for the parts where the stress is generated, measures are taken to eliminate the internal stress or to balance the internal stress, and the workpiece can be straight.
● Analyze the internal connections of steel structures. Some steel structures are composed of many beams and columns. These beams and columns are interconnected and restricted to each other to form an organic whole. When correcting, we must not only see their superficial connections but also analyze the internal factors that restrict each other, so that a better correction effect can be obtained.
● Identify the location and direction of deformation. Steels of different specifications and components of different shapes, regardless of the cause of the deformation, must be carefully checked for the root cause of the deformation, and the center position and direction of the deformation must be found to facilitate the formulation of corresponding corrective measures. At the same time, it is convenient to use a ruler with a certain length for inspection after correction.
● Determine the correction method according to the implementation analysis, and the corresponding correction method can be adapted according to the actual situation.
Commonly used methods of sheet metal correction include mechanical correction, manual correction and flame correction. Mechanical correction is generally used for the straightening and leveling of metal raw materials and large sheet metal blanks (sheets, section steel, etc.); manual correction is mainly used to eliminate defects in the shape and size of sheet metal parts after forming or limited by production and processing equipment. Shape correction during correction; flame correction is mainly used for the straightening and leveling of large-scale sheet metal processing parts. Because it is not affected by the processing site and processing equipment, it is especially suitable for operations in the field and non-work sites.
The fundamental reason for the deformation of steel and components is that part of the fiber in the material is stretched under tensile stress but is compressed by the surrounding fibers; at the same time, another part of the fiber is shortened under compressive stress but is stretched by the surrounding fibers. Tensile stress and compressive stress always tend to be distributed in a balanced manner, which causes the deformation of the steel.
Although the various correction methods are different in operation, the basic principle is mostly the reverse deformation method, that is, the new direction and the opposite deformation are caused by various correction methods to offset the original deformation of the profile or component and make it reach the specified Shape and size requirements.
The purpose of correction is to shorten the elongated fiber and extend the shortened fiber by applying an external force, hammering, or local heating, and finally make the fiber length of each layer tend to be consistent, that is, the tensile stress and the compressive stress tend to balance, thereby eliminating deformation Or reduce the deformation to within the specified range.
Various deformation correction methods can sometimes be used in combination. For example, the external force can be applied to the workpiece for hammering while flame heating correction; partial heating of the workpiece during the mechanical correction, or manual correction after mechanical correction, can achieve better correction results.
At present, the correction of a large amount of steel is generally carried out by special equipment in the steel pretreatment stage. Small welded structures and various welded beams produced in batches are often corrected on large presses or support beds (straightening machines); large welded structures such as train carriages, automobiles, and passenger car bodies are mainly used for flame correction.
The correction of steel and workpieces takes a lot of man-hours, such as large and complex steel structures such as ships, trains, and trusses. From material preparation to the end of overall assembly and welding, more than 5 correction procedures are interspersed in each process stage. Therefore, in metal structure manufacturing engineering, various protective measures should be taken from the preparation of the steel material to the forming and assembly to avoid and reduce the occurrence of deformation as much as possible.