The Study On Micro-plasma Arc Welding Process And Welds Forming Of Ultrafine Mesh

Ultrafine stainless steel wire mesh was widely used as a tool to separate and filter water, gas, oil and other medium in the field of aviation, petroleum, chemical, mechanical and electrical, electronics, textile, printing, etc, because it has the characteristics of permeability, a larger tensile strength, high temperature resistance and excellent corrosion resistance properties. But the expansive application is limited because the difficulty of welding process was added caused by the special structure of stratification and cycle distribution of the ultrafine wire mesh and the critic demand of welding heat input. Therefore, it is vital to choose the suitable welding method. The micro-plasma arc welding(MPAW) is one of the ideal welding method used in ultrafine wire mesh, because its arc is compressive and stable arc, its energy is high concentrated, and it has the characteristics of high efficiency and high yield. Because of the close relationship between the weld formation and the welding quality of the ultrafine wire mesh, the welding process and weld formation of ultrafine wire mesh in MPAW were studied, which offered the theoretical basis for the nationalization of precise wire mesh welding and had important academic theory and practical significance.In this paper, The different fringes length of mesh joint and assembly methods of butt joint were introduced firstly, then the six different assembly methods of butt joint welded by MPAW and the morphology of welds were studied to analyze the welds forming conditions and influential factors of the morphology of “Spherical”, “Ellipsoid” and “Spindle” welds. The results show that: when other variables unchanged, with the distance of left and right weft heat radiating increases, the radius of the spherical joints increase,with an average heat input increase the radius of the spherical joints increases and then stabilized. With the distance of left and right weft heat radiating increases,, the long axis length of ellipsoid joints increases and finally tends to a constant value. with the distance of left weft heat radiating increases, the short axis length of ellipsoid joints first increased and then reduced. On this basis, Six kinds of assembly method of lap joint welded by MPAW were introduced and the morphology of the welds were studied to analyze the welds forming conditions and influential factors of the morphology of “ Vermicular”, “Continuous”, “Square” and “Triangle” welds. Based on the experimental data, the concrete effects of overlap size, the position of welding, the average heat input and the heat dissipation distance of the two sides of the joint on the shaping morphology of the kinds of welds’ morphology were analyzed. The results show that: when other variables unchanged, the volume of worm-like joints increases as the length of the upper screen edges increases, along with the lower screen length increase the overall volume of the joints increased. With the length of the upper screen increases continuous joints volume increases, and achieved maximum volume 0.412mm3 when the upper screen length is 1 mm. With the upper screen length increases square joints volume increased substantially.To meet the heat input requirement in the welding process of the ultrafine stainless steel wire mesh, the pulse MPAW was studied because pulse current parameters can be adjusted to precise control heat input. The characteristics of pulse current and its parameter variation of pulsed arc were introduced, the influence of base current, peak current, frequency and duty ratio on the formation of weld of the butt joint between the long fringes was analyzed, and further discuss the formation mechanism of pulse parameters on welds. The results showed that The energy of the arc was affected by the base value and peak value of pulse current, and the peak current was mainly used for melting base material of joint, the base current was used to make the weld pool have the cooling time and preheat base material. The frequency of pulse current was changed mainly by changing the actual peak current, base current and the distribution of rising edge and falling edge. The rising edge and the falling edge of the pulse signal increased along with the increasing of pulse frequency. When the welding frequency was too large, the real pulse current could not reach the setting current value, which made the influence of pulse reduction. The duty cycle was mainly influenced by the distribution of the base value current and the peak current, which affected the distribution of the arc energy and affect the formation of the welds.