Fukuhisa Matsuda

On the Optimum Welding Conditions of Thicker Plate in Electron-Beam Welding

With utilization of the theoretical epuation which shows the penetration depth in electron-beam welding, the theoretical equation for the general estimation of optimum weld heat input is induced for the specimens of which thickness and material are known, when there are welded by I-shape butt type and single pass method. Moreover the experimental equation for the estimation of ptimum weld heat input is made by rearranging a number of the actual optimum weld heat input which have been obtained in Sciaky Co. Ltd., U. S. A. and in N. R. I. M., Japan.After the theoretical and experimental equations are compared and discussed, the equation for the general estimation of optimum weld heat input is decided respectably.Therefore, when the thickness and material of specimens are known before welding, with utili-zation of the above equation, the accurate estimation for optimum weld heat input which gives the fully penetrated bead by single pass for I-shape butt type joint is become possible hereafter.

Calculation by Thermal Conduction Theory and Its Discussion for the Penetration Depth in Electron-Beam Weld Bead

With utilization of penetration mechanism in electron-beam welding, an equaption which estimates the penetration depth in bead by calculation is induced from thermal conduction theory in this report.Moreover, to examine the valiuity of the equation, each penetration depth which is estimated by the equation is compared and discussed with the actual depth in numerous beads under the same welding conditions.As a result of this discussion, it becomes apparent that the induced equation for calculation of the penetration depth gives successfully the penetration depth in actual bead.Therefore, if the welding condition and physical constants for the used material are known, the penetration depth in actual bead can be easily estimated by simple calculation using the above equation.

Characteristics of Electron-Beam for Welding

The electron-beam diameter and intensity distribution of the NRIM 1.5 kW electron-beam welder, home-made, were measured by interrupting the beam with a water-cooled copper plate. The effects of filament current, anode voltage, welding beam current and focusing voltage on beam focusing were studied experimentally.The following conclusions were obtained:1) The intensity distribution of electron-beam current on the specimen surface showed approximately a normal distribution.2) The electron-beam was of a cone shape with a vertex angle of 7 degrees.3) The minimum diameter of electron-beam on the specimen is affected severely by filament current, anode voltage, welding current and focusing voltage. Greater values of filament current and anode voltage and smaller welding current contributed to making the diameter of electron-beam smaller.4) In electron-beam welding, the beam diameter on the specimen should always be noted besides welding current, anode voltage and welding speed.

Effect of Electron-Beam Welding Parameters on Characteristics of Bead Section

The effects of anode voltage, welding current, beam diameter, welding speed and thickness of specimen on the characteristics of bead section (such as, penetration, width and penetration-to-width ratio) were studied with the 1.5 kW NRIM electron-beam welding equipment for type 304 stainless steel, low carbon steel, aluminium, brass, zirconium and titanium.The following conclusions were obtained:(1) An increase of anode voltage or welding current increased the penetration greatly and the width slightly. An increase of beam diameter greatly reduced the penetration but increased the width. An increase of welding speed coordinately reduced both the penetration and width.(2) New parameters were introduced to correlate satisfactorily the effects of anode voltage (V), welding current (I), welding speed (ν) and beam diameter (φ) on penetration (ρ) and width (ω) in bead welding; that is:ρ=κa×E1.7×Ι1/ν0.4×1/φ0.8ω=κb×E0.1×Ι0.2/ν0.5×φ0.6 (φ<8mm)ρ/ω=κc×E1.6×Ι0.8×ν0.1×1/φ1.4where, ka, kb, and kc arc constants which depend on the material.(3) An electron-beam was shown to cause a deep and wedge-shaped penetration in various materials, provided a sufficient weld heat input which exceeds a critical value is used for a given beam diameter.(4) The effect of plate thickness on bead characteristics for a given welding condition is slight only for metals of poorer heat conductivity and comparatively high welding speeds.

Welding Forces and Bead Formation Mechanism in Electron-Beam Welding

Fundamental researches and considerations for welding forces and bead formation in electronbeam welding were done to make use of the measured results of actual vertical force in welding.The conclusions were as follows :(1) Vertical force in electron-beam welding is generally increased with an increasing of welding current at constant anode voltage and welding speed.The vertical force in carbon steel plate is about 2 to 3 times greater than that in aluminium at the same weld heat input.(2) The vertical force is caused by the repulsion of metal vapour in evaporation because the repulsive force by calculation agrees with the measured force. However, forces of collision of electron-beam and repulsion by magnetic phenomenon are negligibly small compared with the repulsive force of evaporation(3) It seems that maximum temperature in molten metal of carbon steel, aluminium, titanium or zirconium is about 200 to 400°C higher than the melting temperature of each metal.(4) Forces which push up the molten metal backward in the back of electron-beam consist of the repulsive force of evaporation, capillary action in wedge-shape hole and surface tension in the solidus line of crater.It seems that drilling action by electron-beam is stopped and held at the constant depth in molten metal when the push-up forces reach the counter-balance to the forces, such as weight of molten metal and repulsive force in crater, which pull down the molten metal to the bottom of the wedge-shape hole.