Control Of The Welding Deformation For Aluminum Alloy Metro Beam

Aluminum alloy is a kind of silvery light metal, corrosion resistance with low den-sity, high specific strength, superb corrosion resistance, outstanding moldability andfine weldability. So it has been widely used to manufacture metro trains all over theworld. At present, the mainly used series of aluminum alloy including:5000(Al-Mg),6000(Al-Mg-Si) and7000(Al-Zn-Mg). However, the heat conductivity coefficient ofaluminum alloy is5times higher than that of carbon steel, which leads to a higherneed of welding input heat. Meanwhile, the thermal expansion coefficient of alu-minum alloy is2times as high as that of carbon steel, so it’s easy to cause weldingdeformation, which is hard to be straightened afterwards.For a metro train, Body bolster, which is a box structure, is the key position of thechassis. The mode of its welding joints includes V-groove butt weld(with backingplate),Unilateral V-groove T-joint, corner joint, plug welding joint, etc. The joints hererequire high welding quality, which is checked according to ISO10042-BC.The di-mensional precision is also highly required, which is generally checked according toISO13920-BF, while at some key position that is checked according toISO12768-mk.The dimensional tolerance in the width direction of the bolster shallbe±1mm. the traverse and longitudinal flatness shall be less than1.5mm.This dissertation performed qualitative analysis for the welding deformation reg-ularity of the body bolster structure. Meanwhile, the date of welding deformation ofthe bolster in a free state was acquired by process test. The results indicated that thetransverse shrinkage deformation(ΔB1+ΔB3) is4mm, the longitudinal shrinkage de-formation(ΔL1+ΔL2) is4.3mm, the longitudinal flexural deformation(ΔH1+ΔH2) is17mm, and the transverse flexural deformation and transverse angular distor-tion(Δh1+Δβ1) is3.5mm. These welding deformations have been far beyond the de-signed accuracy requirement, which made the bolster can’t be used normally.Body bolster welding by MIG welding, During the period of the bolster assemblywelding, the welding deformation was effectively controlled by using rigid fixed withwelding fixtures, reverse deformation and other methods for welding deformationcontrolling, which under the direction of welding deformation regularity and the date acquired by process test. The longitudinal flexural deformation of the bolster reducedfrom17mm to less than1.5mm. The transverse angular distortion reduced from3.5mm to less than1.5mm. The transverse shrinkage deformation reduced from4mmto less than1mm. The dimensional tolerance, traverse and longitudinal flatness of thebolster met the requirement of designed accuracy.