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The result of the scan of the weld surface along the radial depth direction b along the outer circumferential circumference of the shaft joint area C can only show defects in the weld bead in the coincident region where the electron beam is introduced and taken out. The defect in the coincidence zone is the tip defect inside the weld, which is a common defect of electron beam welding with large thickness section [1], which can be improved by measures such as reasonable attenuation of welding current and electron beam scanning, but it is difficult to completely complete the ring weld. eliminate.
The middle convex light-colored area corresponds to the electron beam nail tip defect of a, and the continuous light-colored area of ​​both ends shows that the weld root has an unfused defect, and the ultrasonic reflection measurement has an unfused depth of about 4 mm.
The sample (b) is taken from the maximum weld deviation of the weld circumference, and the cross-sectional shape of the weld is observed. It is shown that the weld fusion line formed by the unfused seam distance is about 0.2 to 0.6 mm.
The first part of the process simulation part weld cross-section shape analysis and discussion The first part of the process simulation piece anatomical analysis results show that the weld root from the weld toe 4mm began to appear unfused defects. The ELA-30 vacuum electron beam welder is a gun-type, medium-pressure (60kV), 30kW electron gun. The optimum working distance for electron beam welding is about 150mm.
The large-scale propulsion gear welding method involved in this paper is the electron gun fixed, the parts rotate, and the radial accuracy of the parts assembly is ±0.04mm. The electron beam alignment uses the secondary electronic imaging and tracking system, and the alignment accuracy is relatively high.
The reason for the analysis of weld weld bias to produce unfused defects is as follows: First, the physical deviation of the electron beam movement trajectory caused by electron gun physical support (hanging frame) or electron beam generation and bunching; second, large section 18CrNi4A low alloy carburizing steel The effect of remanence of the gear assembly; third, the thermoelectric (magnetic) effect generated during the electron beam welding of the shaft and gear leads to the deflection of the electron beam [2].
To this end, the design test verifies the vertical deviation of the electron beam action. The test plan determines two pairs of 18CrNi4A low alloy steel flat specimens and 60mm thickness titanium alloy test panels prepared in the same state as the parts, respectively verifying the offset of the electron beam along the X and Y directions in the coordinate plane. X, Y coordinates). The 18CrNi4A low alloy steel test plate was demagnetized before welding, and the surface magnetic flux density was below 3 Gauss (3×10-4T).
The welding 1 process parameters and auxiliary measures used in the verification test are identical to the part welding. And the cross-sectional shape of the weld of the low-alloy steel and titanium alloy of 18CrNi4A along the X and Y coordinate directions obtained under the same welding process conditions.
a welding along the X direction b along the Y direction welding verification test obtained 18CrNi4A low alloy steel weld cross-sectional shape a welding along the X direction b in the Y direction welding verification test obtained titanium alloy weld cross-sectional shape 18CrNi4A low alloy steel welding The seam and the root are obviously deviated from the center of the joint, and the partial width is about 2mm, which eliminates the misalignment factor; while the cross-section shape of the medium-titanium alloy weld shows that the formed weld is more accurately centered on the joint.
The cross-section morphology of the weld obtained from the first process simulation part and the process test plate is comprehensively analyzed. The lower end of the weld is curved or parabolic, and has obvious characteristics that the electron beam is affected by the electromagnetic field. Inquire about the processing steps of the parts. Before the welding, the surface grinding crack is detected by the magnetic powder method for the front grinding process. The magnetic detection produces a strong DC electromagnetic field, and then the DC square wave alternating attenuation is used to demagnetize to the surface flux density of the part. Military requirements.