Automobile axle car chassis as moving lines important component of the force complex, it is not only load-bearing and power transmission, but also under enormous dynamic load and static load formed by the bending moment and torque, this requires adequate rear axle strength, stiffness and toughness. Among the weld. The quality of Types Of Welding Electrodes axle housing is directly related to the car's driving safety and the safety of passengers and drivers. Therefore, to ensure the welding quality of the rear axle is very important.
An analysis of welding

1.1 Welding of Materials

The materials used in the current multi-axle vehicle for low carbon steel, 20 steel-based, its chemical composition (mass fraction,%) for: 0.17.o. 23C. 0.17 ~ 0.37Si, 0.35 ~ 0.65Mn, Cr

In the smelting process of the S content has conducted a serious control, which ensures a higher Mn / S values. Reduce the formation of low melting point eutectic material risk of hot cracking good inhibition. Therefore, this material is relatively good weldability. Welding cold cracking, hot tearing tendency smaller. Conventional welding methods can be applied to the welding of this material. However, considering the production efficiency. Now the basic welding axle vehicles to use more CO: gas shielded arc welding.

1.2 Feasibility process

The role of CO2 gas shielded arc welding method of welding an efficient production of the next process is widely used. C02 gas shielded arc welding penetration. Higher productivity than the welding arc l ~ 3-fold; CO2 gas shielded arc welding using short circuit transfer technology for a full range of welding, welding thin-walled structures for high quality welding deformation and welding speed; CO2 gas prices cheap, and before welding treatment can be a simple weldments. The cost of welding electrode arc welding and submerged arc welding only the 40% ~ 50%; CO2 gas shielded arc welding is easy to achieve mechanization and automation in the automotive welding can reduce the equipment, facilities, fixtures reduce the cost of multiple inputs improve production efficiency; rust resistant and low hydrogen weld. Into one, the structure shown in Figure l. As the car axle in the vehicle, not only to support the body, but also to transfer the load, so the force of their situation is more complicated, in order to clearly reflect the role of axle load conditions of the situation, the whole bridge was stress-strain finite element analysis , the results showed that the central three-junction connecting the stress concentration phenomenon more apparent. This is because there is a big gap junction (used for welding and groove). The emergence of welded joints in itself undermine the structural integrity of the stress is easy to produce mutations. The welding process is a thermal shock process, the weld metal solidification process of non-equilibrium crystallization of large amounts of residual stress can not be promptly released, but remain within the structure caused by stress concentration.

Results from the strength point of view. As the loading and structural reasons, the structure of localized stress concentration exists (maximum stress calculation results show that there is a dynamic load factor increased when the stress concentration. Maximum stress values ??have increased, while reducing the fatigue life, so for the vehicle axle welding research is necessary.

3 welding process optimization

From the above analysis can be found, the materials used in vehicle axle a low carbon steel, welding is better, but because of its unique structure. The existence of large residual stress will cause welding defects. The fatigue life of the material can not meet the appropriate standards, so the traditional welding process to optimize the transformation is particularly important. PLC control technology as a new control technology, as with fast response, high precision, small size and has the advantages of industrial production is widely used. To this end the PLC control technology into CO2 gas shielded arc welding process, precise control of the small arts through the PLC in the process of arc, arc stability, arc rates, and equipment associated with it precisely guide fixture, thereby ensuring the quality of welding controllability and reproducibility. After the appropriate pre-commissioning tests, the welding process parameters for the corresponding optimal design, the optimum range of process parameters in Table l, welding current location) problems in the manufacturing process to ensure that the process should be strengthened; take into account material ER49. 1.
4 Performance analysis of welded joints

In order to verify the PLC control C02 gas shielded arc welding process parameters on the feasibility and optimality, which parameters of welded joints and make the appropriate mechanical properties and microstructure analysis.

4.1 Hardness Analysis
As the special structure of the vehicle axle. In the process, the detection process is difficult to be processed into tensile specimens, tensile test, and the traditional hot-rolled steel of tensile strength and hardness of the relationship between a certain proportion, that the tensile strength equal to the hardness value of 3.5 times, so the hardness of welded joints and make the appropriate tests. This approximate evaluation of its tensile strength. Figure 2 shows the hardness distribution of weld joints. Shows that the hardness of the maximum in the region of welded joints, base metal and weld hardness were lower than the HAZ. The base metal and weld compared, slightly higher than the hardness of the weld base material. Hardness distribution through the data can be found in the weld hardness was more evenly distributed. Hardness, tensile strength by folding up into the appropriate technical requirements, which illustrate the application of PLC-controlled automatic welding machine in a given Welding Consumables process parameters within the range of Si can effectively control the welding defects. And a good problem to solve the lack of penetration. The mechanical properties of welded joints corresponding technical requirements.
4.2 Metallographic analysis of welded joints
In order to more clearly reveal the mechanical properties of welded joints of the underlying causes. Of welded joints to the corresponding microstructure analysis, metallographic image shown in Figure 3. Can be seen, both the base metal, weld or its organizational form are P + F, are just two forms of organization differ. Of P in the parent material was arranged in a certain direction. Scattered in the grain boundary a certain amount of F, which is typical of the rolling Organization: The rules in the weld metal in its organization has been unable to find rolling. Instead, a large number of dendrites and equiaxed; to Ai in the region because of the location between the base metal and weld between, so in between their organizations, but the organization has been thick. This morphology and the hardness of the above data the basic agreement, which fully shows that PLC-controlled CO2 gas shielded arc welding process is basically feasible, but also the quality of clearance.
5 Conclusion
(1) C02 gas shielded arc welding process can be successfully applied to the vehicle axle welding.
(2) PLC under the control of C02 gas shielded arc welding process, the use of precise control technology, to further improve the performance of welded joints, to meet actual production needs.

  A continuous seam welding, roll disk continuous rotation, the current constantly through the workpiece. This method is easy to make the overheating of the surface electrode wear is serious, and therefore rarely used. High-speed seam welding (4-15m/min) 50Hz AC every half weeks to form a solder joint, AC zero crossing equivalent to the off time, which is similar to the following intermittent seam welding, and thus the system cylinder Barrel industry.
2 intermittent seam welding, roll disk continuous rotation, composed of discontinuous current through the workpiece to form a weld nugget each other to take Diego. Because the current is interrupted by rest time, the roll plate and the workpiece to be cooled, thus can improve the life of the rolling disk, reducing the width of the heat-affected zone and deformation of the workpiece, the better the quality of welding. This approach has been widely used in seam welding of a variety of less than 1.5mm steel, high temperature alloys and titanium alloys. Intermittent seam welding roller tray to leave the welding zone, the nugget crystallization under reduced pressure, so it is prone to overheating surface shrinkage and cracks (such as in the welding of high temperature alloys). Ride in the solder joints stacked more than 50% of the length of the nugget, the latter point of the molten metal can be filled before the shrinkage, but the last point of the shrinkage is difficult to avoid. However, the domestic development of computer control box, able to weld finishing part of the point by point to reduce the welding current, in order to solve this problem.
Step seam welding, roll disk intermittent rotation, the current through the workpiece when the workpiece is not moving, melting and crystallization of the metal in the roll plate fixed to improve the heat and pressure of the solid condition, and thus can more effectively to improve the Types Of Welding Electrodes quality and prolong the life of the rolling disk. This method more than aluminum, seam welding of magnesium alloy. For seam welding of high temperature alloys, and also can effectively improve the quality of welding, but the domestic exchange of this type of welder, and thus has not been applied. When welding the hard aluminum. And a thickness of 4 +4 mm above metal must be a Tungsten Welding Electrode, in order to form each solder joint can spot imposed by forging force, or while using warm cold pulse. In the latter case is rarely used.