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Vacuum Heat Treatment of TV Satellite Antennas

“Live Star” is the abbreviation of broadcast and TV live satellite. Direct broadcast satellite broadcasts video, graphic and sound programs point-to-point through satellite, and directly for the majority of users to receive. The most important component of live satellite TV is the signal transceiver composed of the flat panel antenna.

A flat panel antenna refers to an antenna that only propagates in one specific direction. Flat panel antennas are generally used in point-to-point situations. They are called “patch antennas”. There are several types of flat panel antennas, such as vibrator type and slot type. They are characterized by small size, light weight, small wind resistance, and easy installation and use; the built-in tuner integrates the antenna and the tuner, and the adjustment is convenient; the efficiency of the flat panel antenna Higher, especially suitable for the reception of live satellite TV.

With the development of space-borne flat panel antennas towards high integration, light weight and high performance, the requirements for the mechanical properties of antenna materials are getting higher and higher. At present, the vacuum brazing material of spaceborne antenna is usually 3A21 aluminum alloy, which has the characteristics of easy processing and high precision. strength requirements.

6061 and 6063 aluminum alloys belong to the six series medium-strength alloys, which have good cutting performance and excellent welding performance. Although the tensile strength and yield strength will be greatly reduced after vacuum brazing, the tensile strength can be increased to the required range through heat treatment strengthening, so that the entire material can meet the design requirements.

The flat panel antenna is a large-scale thin-walled multi-layer hollow complex structural component, and is an important component of the live broadcast satellite. The six-series aluminum alloy material is used, which puts forward higher requirements on the mechanical strength and flatness of the antenna. The heat treatment strengthening process to ensure these requirements is One of the key processes in antenna manufacturing technology.

The basic structure of the satellite-borne flat-panel antenna is shown in the figure. The overall size is 666mm×495mm×30mm. It is made of 6063 aluminum alloy. The antenna is vacuum brazed with four-layer parts. The thinnest part is 0.8mm. It is a large-scale high-precision thin-walled antenna Layer hollow complex structural components. There are nearly 1,000 circularly polarized bosses of 0.8mm×2.6mm on the antenna radiation surface, and there are many stand-alone units installed on the antenna installation surface, which has high requirements on the mechanical strength and flatness of the antenna. The manufacturing process of this antenna is shown below.

1.Heat treatment strengthening tooling design:

Influencing factors of antenna deformation

In order to ensure the flatness of the antenna, it is necessary to design a special tool to control the deformation of the antenna. It is required to reduce the thickness and simplify the fixture as much as possible while meeting the rigidity, so as to minimize the influence on the quenching and cooling rate. The factors that affect the flatness of the antenna are:

1) The overall gas quenching cooling rate of the antenna;

2) The cooling rate of the upper, lower and surrounding areas of the antenna;

3) The clearance margin between the tool and the antenna needs to consider the different thermal expansion coefficients between the tool and the antenna;

4) During heating and cooling during the heat treatment strengthening process, the antenna and the tooling should be free to expand and contract to prevent local deformation caused by adhesion at high temperature.

Considering the above factors, a special conformal tooling for heat treatment strengthening process is designed. As shown in the figure, the antenna is located in the middle of the tooling.

The design includes the following points:

1) The tooling should keep away from the circularly polarized boss of the antenna radiating surface to provide a reference plane for the radiating surface and the mounting surface, which has sufficient rigidity at the solution temperature (540°C).

2) Under the condition of ensuring thermal rigidity, the fixture should be thinned and simplified as much as possible to minimize the influence on the quenching cooling rate. The tooling is in a frame structure, so that the gas can be blown to the parts from up and down and around during gas quenching.

3) The gap design considers the expansion coefficient α of the antenna and the tooling. The expansion of the antenna from 20 °C to the solution temperature of 540 °C is calculated as 0.31mm, and the expansion of the stainless steel tooling is calculated as 0.12mm. Taking into account the flatness of the antenna itself and the flatness of the tooling, to prevent the local gap from being too small during installation and causing extrusion deformation during installation or after expansion, the gap between the antenna and the tooling surface after installation is designed to be 0.55mm.

4) To prevent adhesion at high temperature, set a layer of graphite paper on the radiating surface of the antenna and the bonding surface of the tooling.

5) Fixing holes for temperature measuring thermocouples are designed on the fixture.

2.Quenching process parameters:

Quenching and strengthening of aluminum alloys is also known as solution aging treatment. Therefore, the solution temperature was selected as 540 °C, and in order to make the elements in the aluminum alloy evenly distributed into the matrix, the solution time was taken as 2.6 h.

In order to ensure the flatness and strength of the antenna, an appropriate cooling rate should be used. When the vacuum air quenching pressure is 0.08MPa, the cooling rate is close to 24°C/min, which is greater than the critical cooling rate of 7.2°C/min, which can not only ensure the antenna strength requirements, but also reduce the antenna quenching deformation. Therefore, the quenching pressure of vacuum air is taken as 0.08 MPa, and the cooling rate of the antenna is controlled by adjusting the wind blowing distance of the upper, lower and surrounding areas by blowing strong cold nitrogen gas at the same time.

The specific quenching process is as follows:

By analyzing the influencing factors of the gas quenching deformation of the antenna, the gas quenching strengthening process of the aluminum alloy after vacuum brazing was studied, and a special tooling was designed. Finally, during the heat treatment strengthening process, the strength of the matrix material and the weld seam were improved, and the fabrication was successfully completed.

Selection of vacuum heat treatment equipment: In addition to good process design, the selection of vacuum heat treatment equipment is also an important factor in completing the process. The RVGQ vacuum air quenching furnace produced by SIMUWU is an excellent choice for completing this type of process. Its process performance can fully meet the needs of such hot processing, with good temperature control accuracy, temperature uniformity and gas quenching uniformity. The whole process is controlled by PLC, and the production is convenient and fast. High process repeatability, stable production, quality output can be guaranteed.