Research on welding technology of aluminum alloy c

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Research on the welding process of aluminum alloy car body of rail vehicles

in order to realize the high-speed operation of rail vehicles, the car body of rail vehicles adopts lightweight design and aluminum alloy structure, so as to reduce axle weight, save energy and reduce wheel rail impact. However, in the manufacturing process of aluminum alloy car body, MIG welding process is usually used for the welding of aluminum alloy profiles and plates. The linear expansion coefficient of aluminum alloy is about twice that of steel, and the volume shrinkage during solidification is 6.5% - 6.6%, so welding deformation is easy to occur. For the welding of thin-walled aluminum alloy profiles (the thinnest part is 2.3mm), the welding deformation is large, and welding defects such as pores and cracks are often produced. The welding is difficult, and many problems will be encountered in the production process. Therefore, when welding the aluminum alloy car body, it is necessary to master the welding process of the aluminum alloy car body, so as to reduce the weld defects and welding deformation, improve the welding quality, and ensure that the geometric size and strength of the car body meet the design requirements

1 requirements for welding process of aluminum alloy car body

aluminum alloy car body of railway vehicles mainly uses three kinds of aluminum alloys: 5000 series, 6000 series and 7000 series. Among them, 5000 series are aluminum magnesium alloys with good weldability; 6000 series is aluminum magnesium silicon alloy, with good weldability and high welding strength; 7000 series is an aluminum zinc alloy. Due to the addition of zinc, the weldability is deteriorated and the welding strength is also reduced. Due to the low melting point and large thermal conductivity and thermal expansion coefficient of aluminum alloy, cracks, poor fusion, pores and other defects are easy to occur during welding. MIG/TIG welding process is generally used for the welding of aluminum alloy car body of railway vehicles. During welding, attention should be paid to the environment, welding wire and welding method, so as to ensure the quality of welding

1.1 environmental requirements

because the thermal conductivity of aluminum and aluminum alloy is relatively large, under the same welding process conditions, the cooling rate of aluminum alloy is (4 ~ 7) times that of steel. During the rapid cooling process of aluminum alloy, the solubility of hydrogen decreases and a large amount of gas is released, which cannot be eliminated under the condition of rapid cooling and forms a large number of pores

2 welding process of aluminum alloy car body

according to the experience summary of aluminum alloy welding technology and the welding deformation law of aluminum alloy car body, the welding process flow is formulated for the general assembly and welding of car body: size adjustment before pre assembly and welding, cleaning before welding, automatic welding and grinding after welding

from the above welding process flow, we can see that the welding quality and overall geometric dimension of the aluminum alloy car body should be controlled to meet the technical requirements and reduce the amount of base note of the car body: we must strengthen the process control, and reduce the welding deformation of the car body and improve the welding quality by pre deformation control of the geometric dimension of the aluminum alloy car body in the process of pre assembly and pre welding size adjustment

2.1 geometric dimension control of car body welding

during the welding process of aluminum alloy car body, the neutral axis (the axis passing through the center of gravity) cut by the center line of the weld and the structure is not heavy, and the power battery industry is in trouble: overcapacity subsidies reduce the rise or asymmetry of raw material prices, resulting in bending and deformation of the rear wall after car body welding. This kind of deformation is mainly manifested in the changes in the straightness, width, height and diagonal of the rear wall of the car body welding, which can not meet the technical requirements: through practice, the corresponding process measures are formulated from the aspects of welding sequence and pre deformation control. The main measures are as follows:

(1) in the aspect of car body welding sequence, in order to minimize the deformation caused by welding misalignment, it is formulated during welding, The welding direction is the same, welding from one end to the other end: welding should be symmetrical, and one and two sides should be welded at the same time

(2) in the pre deformation control party, mainly before welding, measure the straightness of the side wall of the mountain car body, the width and height of the car body and the broken diagonal line through special process equipment and measuring equipment. According to the analysis of the recorded data, the car body is prefabricated and deformed through chain block, process ejector rod and other tools

(3) now select five measuring points evenly from the length direction of the car body. The following table shows the changes of the dimensions of the five measuring points of the car body in each process flow

3 defects easily produced in the welding of aluminum alloy materials and Prevention Countermeasures

due to the low melting point of aluminum alloy and the large thermal conductivity and thermal expansion coefficient, cracks, poor fusion, pores and other defects are easy to occur during welding

3.1 cracks

there are mainly two kinds of cracks produced during aluminum alloy welding: solidification cracks and liquefying cracks in the product boundary. Parts where welding cracks are easy to occur: the beginning and end of the weld

3.2 blowholes

hydrogen is the main cause of Blowholes in aluminum alloy welding. Among the sources of hydrogen intrusion (protective gas accounts for about 12%, electrode wire adhesion accounts for about 24%, base metal adhesion accounts for about 7%, from Ning impact testing machine, which is used to measure the impact resistance of metal materials under dynamic load, the proportion of hydrogen intrusion in Ning gas is about 57%), The countermeasures to prevent pores are as follows: (1) the oil and water on the surface of base metal and welding wire should be removed. (2) After unpacking, the welding wire should be used up as soon as possible. If the welding wire is not used up that day, it should be removed and sent to the incubator for storage

3.3 welding deformation

aluminum alloy welding is another provincial scientific and technological innovation platform established by Yishan vertical to shrinkage deformation, bending and warping, wave deformation, angular deformation and other welding deformation and welding residual stress. Measures to prevent welding deformation: (1) reasonable welding sequence, and formulate welding sequence scheme if necessary. (2) Mechanical fixation, according to the product structure, design and make appropriate tooling, woven bag stretching fixture

4 summary

the rail vehicle body is made of aluminum alloy by welding. The requirements in the technical conditions of car body manufacturing are extremely strict. The aluminum alloy has the characteristics of low melting point, high thermal conductivity and thermal expansion coefficient, and the need for high current and rapid welding in the welding process, which increases the difficulty: through continuous exploration and improvement in the production and manufacturing process of car body, gradually improve the manufacturing technology of aluminum alloy car body: reduce the existing defects in welding, So as to improve the welding quality and work efficiency

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