Research On Metal Transfer Behavior Of MAG Welding With Preheated Wire

The MAG welding with preheated wire is a new high-efficient welding method. By preheating the wire, this process changes the melting heat distribution of the wire, which can increase the frequency of droplet transfer, reduce the droplet size, increase deposition rates and reduce base metal heat input and so on. In this article, with theΦ3.2mm wire, we have a systematic analysis on the preheating temperature of the wire, arc shape, metal transfer, deposition rates and base metal heat input on the MAG welding with preheated wire .In the paper, we establish the test system, welding system, measurement system of the wire temperature, high speed camera system of arc shape and metal transfer, electric signal acquisition systems. The key of the entire testing process is the design of welding torch,including a MAG welding torch and a TIG welding torch, and the former torch located in the upper of the conductive nozzle to ensure the stability of preheating wire and the effect.The heat for the wire melting mainly come from the hot of TIG arc, the resistance heat of the contact tip to workpiece distance and the main MAG arc heat. We measure the wire temperature by infrared thermometer and divide this task into two steps. Firstly, the speed of the wire is a constant with no arc and the wire temperature is higher.Secondly, the speed of the wire is changed while the arc is on and the wire temperature is lower with a large fluctuation.During the experiment, we obtain the arc shape and droplet transfer behavior by the high speed camera and the laser for the backlight. Then ,we use data acquisition card , the current and voltage sensors in the MAG welding with the preheated wire to obtain electric signal. The test results show that the metal transfer frequency, droplet size, the form of metal transfer and the droplet temperature in the conventional MAG welding can be changed by preheating the welding wire.The resurfacing welding process shows that with the preheating of the wire in the method, when the current passing through the base metal is a constant, the greater the preheating current increases , the faster the wire melts, therefore the deposition rates significantly increases. In addition, if the total of preheating current and currents flowing through the base metal keeps a constant, the wire melting rate will not vary with the increase of the preheating current. The larger the preheating welding current is, the smaller the current flow through the base metal and the shallower weld penetration will be obtained. It is very important to the high strength steel which is sensitive to heat input .