Study On Push & Pull Feeding System And Process Exactly Control For CO₂ Short Circuit Welding

The development of modern manufacturing put forward higher requirements for final quality and processes of products, with the increasing requirement of high-quality sheet metal welding technology by the car, motorcycle, containers, household appliances and other light industry products Widely used. Because the sheet metal is sensitivity of the heat, and the heat input reducing and uniform energy distribution should be both ensure during welding process. For this feature, a short-circuit CO2 Welding transfer technics has porposed based on low-spatter, low-energy, precision control of the transfer process. The basic principle is: the droplet should be detached by the mechanical force using to pull the wire, according to control the current exactly to regulate the resistance heat between the wire and the base metal. First, this method can reduce the welding energy input and the spatter, second, it can make the transfer process become uniformity and orderliness. The energy distribution in the whole process can be precise control by adjusting welding parameters.Based on the above ideas, a digital welding power source has been designed as a platform, high-performance AC servo push-pull wire feeder is the core of the short-circuit transfer CO2 welding system, the low-spatter,low-energe and process precise controlled welding technics is achieved according to the software controlled method. Digital welding power source adopt digital signal processor (TMS320F2812)with high speed, high precision, and the CPLD (EPM7128STC100) with powerful logical-processing capability as the control of the core to reach the complex welding process control level based on software programme. In order to achieve the high frequency push-pull movement, Push-pull wire feeder part adopt the high-performance motion control card (PMAC2 PC-104) to control AC servo motor with low inertia and high response speed, at the same time, the buffer is used to harmonize the push-pull feeder and the steady rate feeder. This plan can reduce wire movement resistance , increase the feeder distance. According to the interface circuit, the welding power source and wire feeder system can be link together and work harmoniously.Consider the characteristics of the push-pull short-circuit CO2 welding technics, The feeder speed curve, welding voltage and current waveform Control program is pre-designed. During the short-circuit period, the current control program should be adopt. The voltage control program should be used to make the arc-length self-adjusting ability work. The selection principle of movement and welding parameter has proposed. According to adjust the current, voltage waveform and wire feeder, the push-pull short-circuit CO2 welding technics can work steadily and reliably. The characteristics of the droplet detachment during the welding process has been analysed, it supposed that the low feeder speed in the early of the short-circuit can ensure the wetting enough, and avoid spatter when instant short-circuit occurred; in the final of the short-circuit, the droplet detachment when the liquid bridge pulled break according to mechanical force with low current, so the spatter produced from liqiud bridge blast can be eliminate. The whole process accompany with wire push-pull movement can promote the droplet transfer softness and uniformity, achieve energe distribution precise control in welding process by adjusting the welding parameter.For the different characteristics of wire and base metal of welding process, the equivalent short-circuit current Ies and equivalent arc current Iea are defined to analyse the affect of welding energy distribution and reveal the mechanism of the low heat input of the push-pull short-circuit CO2 welding technics. When the wire feed speed is invariablenes, in order to lower the base metal heat input in welding process, the promoted function by the wire resistance heat should be adopt to lower the arc heat in arc period. The traditional short-circuit transfer method increase the resistance heat by increasing the wire extension, But the push-pull short-circuit CO2 welding technics increase the resistance heat by increasing equivalent short-circuit current, they can both achieve reduce the welding heat input in a certain extent. Comparative the energy of the two technics, because the additional mechanical force of the push-pull short-circuit CO2 welding technics get rid of the dependence in short-circuit period, So the energe of the push-pull short-circuit CO2 welding technics is less than the traditional short-circuit methods both in total energy and the arc energy, the energy distribution is good, and lay the foundation for achieving high-quality sheet metal welding technology.The effect of energe distribution rule when control parameter changed in push-pull short-ciucuit CO2 welding has been analysed. The result reveals that with the decreasing of final short-circuit current and the peak arc voltage, the energe can both be decreased for total welding energe and arc energe, so lower heat input welding method could be achieved. With the increasing of transfer frequency, the equivalent arc circuit current is incline to rise, and result in the more heat input for base metal. The analysis result shows that under the voltage control method during arc period, the equivalent short-circuit current Ies and the equivalent arc current Iea are the fundamental factors, the former is totally utilized to melt the wire by resistance heat, the latter determine the heat input for base metal.For the characteristics of the push-pull short-circuit CO2 welding system, the pull-ignite method is designed. This method can ignite reliably and ensure welding process steadily. The droplet of the push-pull short-circuit CO2 welding transfer in order, the energe distribute conformably, and the weld shape is good whatever welding in small or big current. Because the resistance heat reduce the heat input, weld shape is narrow and over-reinforcement, so the desire weld shape can be got by adjust IH and Up according to the welding requirements. In addition, the push-pull short-circuit CO2 welding can lower the transfer impact for welding pool, distribute energe uniformly, shape shallowly and uniformly, support widely perspective for surfacing process by the push-pull short-circuit CO2 welding technics.