Abstract
KEYWORDS
manufacturing trends, electron beams welding, transmission gear.
ABSTRACT
Electron beams (EB) material processing is a non-conventional technique used in aeronautics, nuclear technologies, microelectronics, automobile industries, heavy construction, etc. Electron beam have many special properties which make them particularly well suited for use in materials handling through melting, welding, surface treatment, etc., taking into account that this manufacturing is performed in vacuum. High energy EB is fundamentally a unique way of delivering large amounts of concentrated thermal energy to materials. The mean theoretical and experimental researches regarding at electrons beam action is achieve in specific power range of (105 – 107) W/cm2, (transient process and depth melting), this is the most interesting from point of view of the physics of process. In this range, the electrons beam action is characterised through “cutter” melting phenomena or depth fusion. The temperature repartition on channel height is not uniform, having a maximum (about 5000 K) on the bottom of the channel and a minimum (about 2500-3000 K) on the top of the channel. At electrons beam processing, in brake zone of electrons, depending on accelerating voltage, current intensity, beam diameter, etc., is possible to obtain the following process: heating, melting formation, vaporization, etc. Welding conditions is mainly controlled by beam output power, welding speed and focal position. The EB focus point is kept constant because the bias voltage is controlled.Nowadays, the EB equipments are very used for the precision welding in automobile industry: transmission gear, pistons, pulleys, compressors for car air-conditioners, turbo-chargers. The automobile manufacturers are currently using the EB machines, mainly for transmission gear parts. Status of development of materials processing with electron beam and some welding applications for transmission gears, are presented in this paper, based on experiments made on a high power electron beam processing system. It was studied the influence of accelerating voltage on the depth of penetration and the depth – width ratio. It was welded the transmission gears of different dimensions and studied the influence of focussing point on material surface at different values for focus current. Also, it was welded two gears at the intermediate axis from speed box at ARO automobile. The welding parameters was calculated based on simplified relation, started with imposed depth penetration h=(2…2,5) mm. From accelerating voltage of 40 kV and based on material properties (20MnCr12), the EB power for welding is (1…1,5) kW and speed of (0,18…0,2) m/min. For a very good quality of welding is need a preheating process of joint at 0,5 kW and overfocussed EB. In this case the diameter of EB is (1…2) mm, on the material surface. The EB, welding in a vacuum, guaranties stable welding quality and this is easily achieved with a long beam focusing depth and prevention oxidation. Causing the EB to oscillate is reducing welding defects: cracks, blow hole, etc. The experimental results of this paper was supported by an EB material processing equipment developed by "Petru Maior" University of Tg. Mureş and Electrical Research Institute ICPE Bucharest.