Key Points of Electron Beam Welding Technology

Welding of Thin Plates

Electron beam welding can be used for parts with a plate thickness of 0.03~2.5mm, which are mostly used in instruments, pressure or vacuum sealed joints, membrane boxes, sealing structures, and other components.

Thin plates have poor heat conduction, and local heating is intense during electron beam welding. To prevent overheating, clamps can be used. Figure 1-18 shows a thin plate membrane box part and its assembly welding clamp, with the clamp material being pure copper. For ultra-thin workpieces, pulsed electron beam flow can be considered.

The high power density of the electron beam makes it easy to weld joints with a large difference in thickness. During welding, the thin plate should be closely attached to the thick plate, and the electron beam focal point should be properly adjusted to melt both sides of the joint evenly.

Figure 1-18 Membrane Box and Its Welding Clamp

1 – Tip
2 – Membrane Box
3 – Electron Beam
4 – Pure Copper Clamp

Welding of Thick Plates

Currently, electron beam welding can penetrate a 300mm thick steel plate in one pass. The depth-to-width ratio of the weld groove can reach 60:1. When the thickness of the welded steel plate is above 60mm, the electron gun should be placed horizontally for transverse welding to facilitate weld formation. The position of the electron beam focal point has a great impact on the melt depth.

Under a given electron beam power, adjusting the electron beam focal point to 50%~75% below the workpiece surface will give the electron beam the best penetration ability.

According to practical experience, adjusting the electron beam focal point to 1/3 of the plate thickness below the surface of the plate before welding can maximize the melting effect of the electron beam and ensure good weld formation.

Table 1-7 lists the effect of the vacuum degree of electron beam welding on the melt depth of steel plates. Good vacuum should be maintained during thick plate welding.

Filler Metal

From a practical operation perspective, electron beam welding should be performed without adding filler metal as much as possible.

However, in certain situations, such as when the assembly gap of the joint is too large to prevent weld sagging, when welding dissimilar metal joints to prevent the occurrence of cracks, when repairing weld defects or repairing worn-out parts, filler metal needs to be used.

Table 1-7 Impact of Vacuum Level on Melt Depth in Steel Plates during Electron Beam Welding

Welding ConditionsMelt Depth/mm
Vacuum Level/PaElectron Beam Working Distance/mmAcceleration Voltage/kVElectron Beam Current/mAWelding Speed/(cm/min)
<10-2500501509025
10-2200501509016
1051343175904

Filler metals can be made into wire, strip, granular, or powdered form according to needs. These can be sprayed or stacked at the joint or a reserved raised edge can be processed at the joint to serve as filler material. Currently, the most commonly used is wire with a diameter of 0.8~1.6mm.

Wire-shaped filler metal can be fed by a wire feeding mechanism or fixed by spot welding. The selection principle of wire feeding speed and wire diameter is to make the amount of filler metal 1.25 times the volume of the joint depression. During welding, electron beam scanning helps melt the wire and improve weld seam formation.

Welding of Complex Structures

Spot welding with an electron beam is an effective measure for assembling weldments, saving time and cost for fixing. In production, welding beam or weak beam is often used for spot welding. Lap joints can be positioned with penetration method or first positioned with weak beam, then completed with welding beam.

Because the electron beam is very thin, has a long working distance, and is easy to control, it can weld bottom joints with narrow gaps. This is not only useful for manufacturing new products, but also very effective when repairing scrapped parts. Complex and expensive castings are often repaired with electron beam welding.

For joints with poor accessibility, electron beam welding can only be performed if the following conditions are met:

1) The seam must be within the working distance allowed by the electron gun.

2) There must be a wide enough gap to allow the electron beam to pass through to avoid damaging the workpiece during welding.

3) There should be no interfering magnetic fields on the path of the electron beam.

Electron Beam Scanning and Deflection

Using electron beam scanning during welding can widen the weld seam, reduce the cooling speed of the molten pool, eliminate uneven penetration defects, and reduce the requirements for joint preparation.

Electron beam scanning is achieved by changing the excitation current of the deflection coil, causing changes in the transverse magnetic field. Common electron beam scanning patterns include sine, circular, rectangular, and sawtooth shapes. The usual electron beam scanning frequency is from 100 to 1000Hz, and the electron beam deflection angle is from 2° to 5°.

Electron beam scanning can also be used to detect the position of the weld seam and implement weld seam tracking. At this time, the scanning speed of the electron beam can be up to 50 to 100 m/s, and the scanning frequency can reach 20kHz.

Welding Defects and Control Measures

Like other fusion welding methods, electron beam welding joints can also have defects such as non-fusion, undercut, collapse, porosity, and cracking.

In addition, common defects in electron beam welding include uneven penetration, long voids, central cracks, and weld path deviation from the joint line caused by residual magnetism or interfering magnetic fields.

Uneven penetration occurs in non-penetrating weld seams, which is closely related to the formation of the molten pool and the flow of metal during electron beam welding. Increasing the small hole diameter can prevent this defect. Changing the position of the electron beam focus in the workpiece also affects the size and uniformity of the penetration.

Proper defocusing can widen the weld seam, which is beneficial to eliminate and reduce the uneven penetration defect. Long voids and central cracks are unique defects in deep penetration electron beam welding, reducing welding speed and improving material are beneficial to eliminate these defects.

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