In the development of ELP, two technologies are combined into one whole: obtaining a high-quality raster image in secondary and reflected electrons (SEM) and a balanced three-electrode scheme of electron beam welding, which is common to both devices and consists of a cathode-anode block and a control electrode. The crossover calculation was carried out and optimized taking into account the features of beam formation for both optoelectronic systems.
Due to the properly balanced configuration of these elements and the focusing system, it is possible to achieve a beam diameter at the welding point of 15 µm.
For stable operation of the gun, it uses differential dry pumping by a separate turbomolecular pump and a vacuum control sensor in the cathode-anode block. ELP is equipped with electromagnetic raster centering, stigmatizing and focusing systems, a reflected electron detector with coaxial placement.
A secondary electron detector with a tilt angle of 45 degrees is installed in the chamber, as well as a coaxial video surveillance system for the workpiece in the same direction as the electron beam, which ensures observation of the welding process at low welding currents.
The ELP provides for operation with two types of cathodes: V-shaped (tungsten) or LaB6 (lanthanum hexaboride). The design of the gun allows you to quickly change the cathode units within 2-3 minutes due to the preliminary alignment of the cathode in the block using special technological devices.
Source optical system |
three electrode |
cathode type |
straight filament, tungsten or LaB6 |
accelerating voltage |
60 sq. |
Power |
2 kw |
Raster system |
electromagnetic |
Deflection angle |
+/- 15 degrees |
Focusing system |
electromagnetic |
Minimum beam size |
15 µm |
Minimum welding current |
0.02 mA |
|
1-7 kHz |
dimensions |
540 mm x 150 mm |
Weight |
70 kg |
The installation is equipped with systems that allow to work in the mode of a scanning electron microscope (SEM) to obtain in real time the surface of the welded products with a high resolution of up to 15 microns. This allows for positioning and welding with very high precision.
To obtain an SEM image, the setup is equipped with two detectors of secondary and reflected electrons. One detector (reflected electrons) is installed at the end of the gun, the second - on the wall of the vacuum chamber (see Fig. 11). This arrangement allows you to optimize the contrast of the part image. High image quality (Fig. 12,13,14,15) is provided by a two-lens focusing system and a low-noise amplification path used in SEM.
The SEM mode has a fast sweep mode of 250 x 250 points for real-time operation and a high resolution mode of up to 2000 x 2000 points. The operator uses these modes according to the situation. Fast - for preliminary positioning of the product and high resolution - for detailed viewing of the surface of products with high resolution. The high resolution mode can be used for welding quality control and defect detection.
Permission |
up to 15 µm (depending on system setup) |
Image size at fast scan |
256 x 256 dots |
Slow scan image size (software) |
up to 2000 x 2000 dots |
Electronic - optical zoom range |
up to 1000 times |
Brightness and contrast adjustment |
|
Number and type of detectors |
Reflected electron detector - 1 pc. |
Displaying an image on a monitor |
With the possibility of documentation |
The vacuum system consists of two independent systems controlled by one system for controlling the operation of actuators. One system ensures the production of vacuum and its control in the vacuum chamber, the second - in the cathode-anode block of the gun.
The pumping systems consist of a dry fore pump and a turbomolecular pump of appropriate capacity.
Vacuum fittings (gate, valve, actuator) are built on pneumatic actuators. The system includes a compressed air compressor that provides automatic control of the pressure in the pneumatic system. There is a vacuum shutter between the chamber and the gun, which allows for independent air inlet into the gun or chamber. Vacuum sensors are installed at control points to control the vacuum level.
Turbomolecular pump (TMP) pumping chamber |
2000 l/s |
Turbomolecular pump (TMP) pumping gun |
80 l/s |
Foreline pump for pumping out TMP chamber and foreline chamber |
not less than 100 m3/h. |
Fore vacuum pump for pumping TMP ELP and cathode-anode part of ELP for fore vacuum |
5 cu. m/h |
Type of valve and gate drives |
pneumatic |
Working pressure in the pneumatic system |
6 bar |
Working pressure in the chamber |
1.3 x 10 to the minus fifth power mbar |
Operating pressure in the cathode-anode part of ELP |
1.3 x 10 to the minus fifth power mbar |
Time to reach working vacuum |
no more than 5 min. |
Noise level of pumps |
no higher than 75 dB |
TMP cooling |
stationary cooling system |
