Q345 steel containing certain alloy elements and carbon equivalent value is 0.39%, has certain hardening tendency, in the big plate and the cooling speed too fast under the condition of welding, prone to cold crack. When, in addition, the major technical parameters of welding heat input is too big, easy to cause the hot cracking formation of weld or thermal strain in heat affected zone embrittlement. In terms of the structure of weldment, rectangular tube length and cross section is large, thin rod type, complex welding deformation and deformation easily in the process. Therefore, the welding deformation control become a difficult problem.
1. The scheme of rectangle tube compound
To meet the requirements of strength, the rectangular tube cross section size is 300 mm * 200 mm, thickness of 3 mm, design requirements for the distortion and parallelism deviation 1.2 mm or less, production technology is difficult. Therefore, through the investigation and study, sheet Yun eventually determine the use of symmetric two half bent into a trough and shell, and then USES the manufacturing technology of CO2 gas shielded welding welding.
2. The welding process
(1) open V groove symmetrical trough two and a half to help large bending machine press forming, according to the technological requirements processing butt welding groove, the reserved clearance. The design of the welded joint is a weak link in the welding engineering. To control the internal quality of weld and welding groove form structure manufacturing quality has a very important role. Groove design must consider the fusion than parent metal, welding space, welding position and comprehensive economic benefits. Should press type calculation of transverse shrinkage value Δ B.
Δ B = 5.1 A omega/delta + 1.27 d
Type in A omega - weld cross-sectional area, mm; The delta - thickness, mm; D - weld root gap, mm.
Find Δ B and A relationship between omega can list according to the relationship between analysis, data processing, optimization design, after the Yun rectangular pipe butt weld groove form
(2) to control the welding deformation of the rectangular tube because of its shape as part of the thin rod, thus the welding deformation is very difficult to control. The welding deformation of the main deflection (bending), lateral bending, angular distortion and distortion, etc. For the rectangular tube, is the main deformation of the lateral contraction, the rectangular section size affected, each side should be indented reserved clearance around 90%; After weld transverse contraction, inward bending on both ends of the vertical plate, make component form waist drum shape; More heat input, due to the weld section, inevitably cause larger longitudinal contraction, the component in the length direction deflection; For welding distortion caused by the unreasonable correction is very difficult and sometimes have to cut open welding or whole scrap.
From the welding deformation theory, the main factors influencing the size of the welding deformation is: the weld dimension, the greater the deposited metal, the more the greater the deformation; Weld size is equal, weld heat input, the greater the deformation caused by the greater; Large weld, the welding section than through welding deformation is smaller; Weld layout asymmetric or symmetric but not welding, weld position deviation, the greater the deformation; Artifacts rigidity is smaller, the greater the deformation.
Welding specification through process test and analysis, to determine the rectangular pipe butt weld using double CO2 gas shielded welding. Welding material with H08Mn2SiA, 1.2 mm wire; Protection for pure CO2 gas. The first layer seam welding current of 200 ~ 250 a, the second is 240 ~ 320 a. The arc voltage is 24 ~ 26 v. Must process requirement is: the first layer of weld penetration, guarantee on the back of the forming good; Welding current, arc voltage, welding speed and wire feed speed can be adjusted according to equipment model.
Welding sequence in order to reduce the deformation, rectangular butt welding welding sequence should be in accordance with the following principles: take from middle to both sides layered piecewise symmetric skip welding, the welding deformation is smaller than direct welding, is advantageous to the stress dispersion and release, avoid complex stress in the weldment. Through swing welding, welding formed by the start of a narrow plastic deformation zone only once, and due to the continuous swing welding, large amount of heat input, large heating area, by the compression plasticity deformation area is big, so after welding contraction deformation is very large. Hierarchical block skip welding, cross section of each layer are small and the required quantity of heat is small, and each layer is divided into several segments skip welding, every welding a largely re-established on the cold plate temperature field at a time, every time a narrow plastic deformation zone, and the plastic deformation area average width (i.e., the size of the transverse shrinkage) is smaller than corresponding layered through welding, longitudinal contraction is small, compared with the direct continuous fill a swing welding deformation is smaller.
Based on the above analysis, the first jump from middle to both ends segmented weld 1 (see figure 1), the first layer flip jump from middle to both ends segmented weld 2 layer, the first weld 2 should be larger than the weld 1 welding specification, to produce a larger reverse force, make the original deformation correction. Then again in the same way the welding seam 1 second and weld 2 tier 2.
Hope you could understand more about Q345B hollow section.
没有评论:
发表评论