Gryniuk A. Plasma-arc welding of aluminum alloys with multipolar asymmetrical current.

The thesis is devoted to research features of processes of plasma - arc welding by multipolar asymmetrical current (PAW) of aluminum alloys. It is established that in addition to the basic parameters that are typical for DC welding, such as welding current, welding speed and plasma gas flow, in plasma-arc welding with multipolar current, additional means of increasing the penetration depth are the frequency of multipolar current and arc balance (flow duration of direct polarity). Increasing of the frequency of multipolar current from 50 to 200 Hz allows to increase the penetration depth of the welds in 2 -2.5 times. Welds of aluminum-lithium alloys obtained by plasma arc welding with multipolar current have 30% higher strength and toughness in eccentric tensile compared to the welds obtained by conventional tungsten inert gas welding. Measures to eliminate gas porosity in the welding of aluminum-lithium alloys were developed by changing the pressure on the liquid metal due to modulation of the welding current or pulsing supply of plasma gas have been developed. It was found that pulse supply (with a frequency of 4-6 Hz) of plasma gas with a ratio of maximum flow to minimum 10: 1 at a level of minimum flow of the order of 0.1 l / min is more efficient than current modulation. In this case, with the increase of welding speed up to 200 cm / min, there is no deterioration in the formation of the weld surface, which is inherent in welds with current modulation. The influence of welding speed on the strength of welded joints of aluminum alloys with different chemical composition is determined. The effect of "peak" welding speed is revealed, consist in the increasing of strength indexes with increasing welding speed to a certain value. After reaching the "peak" speed, there is a decrease in strength. For heatstrengthened alloys with a thickness of 2.0 mm, this value is in the range from 120 to 200 cm / min. The decrease in the amount of copper in the main metal increases the value of the "peak" welding speed. The combined usage of plasma arc welding and gas metal arc welding for joining aluminum alloys up to 16 mm of thickness at one pass with the treatment of edges is proposed. The industrial implementation of the results of work in the manufacture of plasma arc welding of elements of electrical fittings at PJSC "Motor- Sich" (Ukraine), as well as in serial production in LLC "RPS "PLAZER" (Ukraine) equipment for manual, automatic (robotic) plasma arc welding, including two complexes which are currently operated by enterprises and organizations of the PRC.