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Study of Mechanism Using Two-Direction Pre-Stress to Control Welding Distortion and Hot Cracking

Author: LiuPeiZhi
Tutor: LiuXueSong
School: Harbin Institute of Technology
Course: Materials Processing Engineering
Keywords: two-direction pre-stress residual stress welding distortion plastic region
CLC: TG404
Type: Master's thesis
Year: 2008
Downloads: 58
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To avoid the problem of residual stress, welding distortion and hot cracking of the hard aluminum thin plate after welding, the two-direction pre-stress method is used in mechanical way. The method is to use pre-tensile stress at the longitudinal direction and pre-compress at the transverse direction before welding, it can reach the effect that the welding distortion is controlled, residual stress is deduced and hot cracking is avoided.The transverse compress can also work on reducing welding longitudinal distortion in simulation. The experiment equipments are designed, including the pressing heat, platen, flatform, new fixfure and the experimental bench. The transverse compress works alone experiments confirm that the simulation results are right. The longitudinal pre-tensile stress experiment conforms that the pre-tensile stress can reduce the value of maximal longitudinal residual stress deeply, and the distribution trends of longitudinal residual stress along the longitudinal direction of different lengths of specimen are mainly the same, the steady region of stress of longer specimen is longer. Tensile experiment gives us the conclusion that the tensile strengths of specimen after welding at two-direction pre-stress method and that after traditional welding are mainly the same. Metallic phase experiment conforms that the long strip grains of the specimen from the fusion area to weld joint of pre-stress action are more than that of traditional welding, and the grains arrange more ordinal.The mechanisms of pre-tensile stress controlling welding distortion and pre-compress prevent hot cracking are researched in simulation, it gives us the conclusion that the pre-tensile stress can reduce the value of longitudinal compress plastic strain, the pre-tensile stressσand the maximum value of longitudinal compress plastic strainε′max have a relation closed to that of linearity, the pre-compress can increase the value of transverse plastic strain, the value of pre-compressσand the maximum value of transverse plastic strainεmax have a relation closed to that of second order. In order to reach the similar controlling of residual stress effect, the pre-tensile stress is near to the double value of the pre-compress, there is a coefficient of correction to correct the relation of the two stresses. The two-direction pre-stress method can make the plastic region shorter than that of traditional welding.In order to get the best action effect of a certain width of transverse compress working, the center of compress working width is at the back of the heat source when the width of compress working is not more than 20mm, the distance is 20mm; and the distance is 10mm when the width of compress working is more than 20mm;the value of compress has no effect on best working position; as the width of compress working and the value of compress increase, the effect of controlling becomes better. The tensile stress can also work after welding, it can reduce the residual stress and welding deformation, as the pre-stress is larger, the controlling effect is better, the stress work before welding has the better controlling effect than that working after welding.The conclusions gained in this article by simulating and experiments can not only enrich the theory research of welding stress and distortion, but also provide guidance to practical use of the research conclusions.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Welding, metal cutting and metal bonding > Welding general issues > Stress and deformation of welded structures
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