2.3 Jet transition mode Figure 3 Schematic diagram of jet transition state 3 Welding process selection basis and trend analysis 　 For the product structure of our company, due to the large welded components and thicker plates, pure CO2 gas and solid wire are currently used. In order to weld the welds, only the method of increasing the current can be adopted. Increasing the current brings about an increase in post-weld deformation of the structural components and an increase in material and energy consumption. In order to improve product quality and reduce production costs, it is necessary to start research from the welding process. Through the comparison of the above three types of droplet transfer modes, we believe that the choice of the third mode will bring the following benefits: (1) The appearance quality of the weld is obviously improved. At present, our company uses carbon dioxide gas shielded welding, the welding current is in the range of 280 ~ 300A, and the droplet transfer mode is the particle transition mode. Due to the large splash after welding, the appearance quality of the welded structural parts is affected, and to ensure the appearance quality, the post-weld cleaning work is very heavy and the cleaning cost is also increased. According to the actual production situation of our company, the corresponding cleaning workload of each structural member (50~60t) is about 1/3 of the welding workload. (2) The mechanical properties of the weld are improved. The following table compares the specific test data of mixed gas and carbon dioxide gas. From the data in the table, it can be found that the impact resistance value of the weld is significantly improved at low temperature. (3) The weld metal deposition rate increases and the amount of welding wire decreases. As shown in Fig. 4, as the current increases, the gas shielded welding rate will be lower than 90%, and the mixed gas deposition rate will increase by 10%, which will reduce the direct use cost of the wire. According to the current market price of 1.600 yuan / t, the welding wire with a diameter of 1.2mm saves 650 yuan per ton of welding consumables. Fig. 4 Comparison of deposition rate of CO 2 protective welding and mixed gas shielded welding of low alloy steel wire with carbon content of 0.45 (4) The welding speed is increased, and the unit production cost is reduced. The increase in welding speed depends on the choice of welding shielding gas, the heat transfer characteristics of the shielding gas, the oxidizing properties and the form of metal transition. A gas with high thermal conductivity enables the molten pool to maintain the highest heat and optimum fluidity. The gas with certain oxidizing property can effectively reduce the surface tension of the molten pool, improve the wettability of the weld metal on the surface of the base metal, and make the weld seam easy to form on the surface of the base material, and the arc is continuously formed. Under the premise of achieving jet transition, the welding speed is inevitably improved. Due to the increase in welding speed, labor costs and management costs per unit time must be reduced. Figure 5 5mg/g is the gas consumed per gram of deposited metal (mg) It can be seen from the above that the use of mixed gas and solid wire has become a welding process that can be selected and realized by various manufacturers. Previous page Paper Testing Equipment,Cobb Water Absorption Tester,Folding Endurance Testers,Digital Thickness Tester Dongguan Hengke Automation Equipment Co., Ltd. , https://www.hengkeinstrument.com
In the jet transition mode, the molten metal at the end of the wire passes through the arc along the arc axis in small particles to the weld pool. When the shielding gas is mixed with 80% argon, the form of the wire droplet transfer to any diameter will change from the particle transition state to the jet transition state as the current increases. In the jet transition state, the arc is in a compressed state, the droplet diameter is less than or equal to the wire diameter (Fig. 3), and the droplet transition rate can reach several hundred times per second. 
Gas type Mechanical behavior σ b
(N/mn 2 ) σ s
(N/mn 2 ) rate of reduction in area(%) Impact work J -40 ° C Normal temperature Mixed gas (Ar80%+20%CO 2 ) 410 253 26 62 106 CO 2 418 253 28 30 95 
(5) Due to the improvement of the metal deposition rate and the welding speed, the production time is necessarily shortened under the condition that the original production capacity is unchanged. Therefore, the amount of shielding gas used in the welding production process will drop significantly (Figure 5). This will reduce the amount of gas used and reduce the cost. 