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1、大型客车车身结构及焊接工艺分析(二)（Analysis of body structure and welding technology of large bus）Analysis of body structure and welding technology of large busThe non-bearing chassis structure is simpler, which is the flat plate structure of various rectangular steel pipes and sections. The reverse clamping fixtur
2、e or horizontal fixture welding can be used. It is convenient and economical to roll the clamping fixture, and the welding deformation is small, but the fabrication cost of the fixture is high.The whole bearing body frame is the grille type space structure, the clamping device adopts fixed type. To
3、ensure the assembly accuracy of the left/right skeleton, the assembly size of the large number of the base after welding is required. In the production, two methods are used to guarantee: one is to improve the precision of the size of the material and the welding jig, and then the small amount of ma
4、nual grinding to achieve the assembly precision. Another is to use a walking automatic cutter to complete the process. The latter method produces high efficiency, but the equipment investment is bigger.The six large frame welding body welding is the key process in the car body welding. The process n
5、ot only determines the precision of the assembly dimension of the bus body hexahedron, but also the throat procedure that restricts the productivity of the welding line. In order to improve the assembly accuracy and production efficiency, the domestic and foreign advanced passenger car factory adopt
6、s the special assembly equipment to complete the positioning of the body hexahedron. The equipment is composed of the body bottom positioning mechanism, the left/right skeleton clamping mechanism, the front/rear positioning mechanism, the top lifting gear and the power system. The equipment can be d
7、ivided into two types: pass and non-pass, depending on whether the transport mechanism of the vehicle body is passed between the fitting equipment.The structure of the fitting equipment is relatively complex, and its base positioning mechanism is composed of the whole process vehicle and the lifting
8、 unit. The integrated process vehicle is a very high precision base clamping positioning and transportation mechanism. The positioning device can be adjusted to meet the positioning requirements of different sizes. After the whole process vehicle is loaded with the initial positioning of the equipme
9、nt, the lifting machine lifts the craft car to the second position. After finishing the welding of the body hexahedron, the closing device comes back and the lifting machine comes back down.If the structure of the base frame is different, such as non-carrying, semi-carrying, full-bearing and all-bea
10、ring body hybrid production, different process vehicles can be used. Therefore, the fitting equipment can meet the needs of all kinds of bus body welding. The drawback is that the equipment invests heavily.Not by type and loading equipment chassis positioning mechanism is fixed in the middle of the
11、combined loading equipment platform structure, the chassis and body contact area is large, body force balanced chassis, and therefore particularly suitable for chassis stiffness difference of body frame compound, such as the monocoque body compound. The structure of non - pass - fitting equipment is
12、 simple and therefore low cost. The disadvantage is that the model has relatively poor adaptability, such as: not suitable for semi-bearing body welding; When the height of the chassis is very different, the assembly line (Z / 0) of the height direction of the body is inconvenienced.The body frame a
13、ssembly equipment has certain production flexibility. By designing the clamping mechanism of several types of vehicles at the same time in the fitting equipment (in order to avoid interaction with each other, some can be designed to be oscillating),It can be used for the production of hybrid line of
14、 different models. In addition, close the left/right side of the chuck device installed in a horizontal chute, can be adjusted, the horizontal chute can be adjusted up and down along the longitudinal chute, through, adjust collet chuck position or replacement parts, can produce more variety of model
15、s, but the adjustment workload is very big, can only by instalments production, not suitable for mixed flow production.2, left/right skin and front/rear enclosure3. Left/right skinBuses left/right side skin generally adopt prestressed envelope process, by the side of the skin plate tensioned to sche
16、dule length after welding on the side of the skeleton, keeping the interior of the steel plate in a certain number of residual tensile stress. The prestressed skin can make the skin smooth and beautiful, and it can improve the rigidity and strength of the body frame. According to the mechanism of residual stress in steel plate, the prestressed skin is divided into two kinds: thermal stress skin and tensile stress.Heat stress skinThe thermal s
