The hydraulic actuator is a component of a certain type of engine in our country, which is composed of cover, liner, piston, rubber seal ring and other parts. The cover and the liner are assembled by vacuum electron beam welding. Its structural characteristics determine the following special requirements for the welding process:

　　1) The component temperature rise should be small

　　 It can be seen from Figure (1) that rubber seals are used in many places in the hydraulic actuator. According to the design requirements, the maximum temperature during the welding process should not exceed 100 ℃ at a distance of 20 mm from the center of the weld seam. If the temperature rises too high, it will burn or even burn the sealing ring, making the sealing ring ineffective.

　　2) No splashes in the cavity

Once the spatter or weld bead falls off on the back of the weld and flows into the inner cavity of the hydraulic actuator cylinder, it will cause the inner surface of the cylinder to be strained or the seal ring will be damaged during the movement of the piston, which will not be able to seal, resulting in the entire hydraulic actuator cylinder. scrapped.

　　3) Welding distortion should be small

　　The wall thickness of the hydraulic actuator cylinder is only 2mm, and it is easy to deform during the welding process, causing the piston of the hydraulic actuator cylinder to not move normally, so the design requires that its ellipticity should not exceed 0.02mm.

Based on the above, on the one hand, the component has strict requirements on welding deformation. In addition, due to the assembly of rubber seals near the inner cavity weld during combined welding, there are strict restrictions on the temperature of the component during the welding process, which brings special difficulties to the welding process. . Spatter and deformation can be controlled by reasonably selecting the joint form and controlling the welding process parameters. However, the strict control technology of the component temperature rise lacks accumulation and experience. Therefore, the strict control of the component temperature during the welding process becomes the key to the successful assembly of the component , Need to focus on experimentation and exploration.

　　1 Optimum method for measuring temperature of workpiece in vacuum chamber

　　1.1 Optimal temperature measurement method

　　 From 200 to 100 BC, ancient Greek Philon and Hiron each manufactured a thermometer based on the principle of air expansion. Since then, the development of temperature measurement technology has varied and varied. The classification and characteristics of commonly used temperature measurement methods are shown in Table (2). It can be seen from the comparison of the above table that the expansion method, pressure method, resistance method, and thermal radiation method have their limitations due to the need to measure temperature in a vacuum state. The use of K-type thermocouples for temperature measurement has the advantages of good linearity, fast response, high accuracy, wide temperature measurement range, suitable recording and control, and moderate price. It is especially easy to implement on site and has strong operability. Therefore, We use K-type electric coupler to measure the temperature of the workpiece in the electron beam welding process.

　　 (2) Classification and characteristics of commonly used temperature measurement methods

　　1.2 Implementation of temperature measurement method

　　Because of the need to measure the temperature of the workpiece in the vacuum chamber, it is first necessary to solve the connection problem of the thermocouple and the workpiece. In actual processing, we use capacitor energy storage welding to weld the thermocouple to the designated temperature measurement location, and use capacitor energy storage welding to fix the thermocouple's compensation wire with a narrow strip of metal foil.

　　 The compensation wire is connected to the reserved terminal of the vacuum electron beam welding machine. Corresponding terminals outside the vacuum chamber are connected to the DR020R digital temperature circuit detector through compensation wires. The recorder can be used to automatically measure, display, monitor and record the temperature of the workpiece during the welding process. It can also read and print the temperature of the workpiece measured by the thermocouple in the welding process.

In the actual welding, it should be noted that the compensation wire of the thermocouple inside the vacuum chamber should be looped around the workpiece twice, with a proper margin, and then connected to the reserved terminal of the vacuum electron beam welding machine to prevent the workpiece from rotating during the welding process , The thermocouple is broken, which will affect the normal operation of temperature measurement and welding.

　　2 Control of workpiece temperature during vacuum electron beam welding

　　 In practice, the temperature rise of the workpiece is controlled by using heat dissipation tooling and optimizing welding parameters. A pair of semi-cylindrical copper heat sinks with a thickness of about 30mm are used, which are closely attached to the outer surface of the hydraulic cylinder to assist in heat dissipation.

　　 First of all, the process test is carried out through simulation parts, and the preferred welding parameters are as follows:

　　Accelerating voltage: 150KV

　　 Welding current: 7.5mA

　　 Focusing current: 2088mA

　　 Welding speed: 20㎜/s

　　 Perform visual, X-ray, and fluorescent inspection on the simulated parts after welding, and there are no defects such as incomplete penetration, cracks, and pores. At the same time, the metallographic examination was performed, and the reverse side was well formed without spatter.

　　The actual measurement result is: the temperature rise in the near seam area 20mm away from the center of the weld seam is 62℃, and the workpiece temperature rise control effectively meets the design requirements.

　　Based on the test, we welded the actual components. A total of nearly 100 components were welded without any waste, and the ellipticity of the cylinder after welding was less than 0.005 mm, and the geometric dimensions met the requirements of the design drawings.

　　3 Conclusion

　　The temperature measurement method is economical and practical when assembling the hydraulic actuator by electron beam welding, and the temperature control process of the workpiece is simple and effective. The ellipticity of the processed parts increased by no more than 0.005mm after the actual measurement, and the temperature during the welding process at a distance of 20mm from the weld seam was about 62℃. The temperature rise control of the workpiece effectively met the design requirements and has been put into mass production. This method is also suitable for welding other parts that have special requirements for the temperature of the components during the welding process.