Vacuum Brazing Technology and Application

Vacuum brazing refers to a process method for brazing by using welding metal brazing filler metal without flux in a high vacuum environment.

Working principle:

The brazing filler metal is coated on the surface of the parts to be vacuum brazed and then put into the vacuum brazing furnace. The vacuum system starts to work and the air is pumped out. When the vacuum degree reaches 10-3Pa vacuum state, the heating starts and the heating reaches 10^-3Pa. At the brazing temperature required by the process, the brazing filler metal begins to melt, and the liquid brazing filler metal wets the base metal and fills the gap between the drill bits under capillary action. At the same time, the solder elements diffuse to the base metal, and the base metal dissolves in the liquid solder to form a high-quality brazing joint.

Advantage:

1. In the process of vacuum brazing, the workpieces to be brazed are under vacuum conditions, and there will be no oxidation, carbonization, decarburization, and pollution deterioration. The cleanliness of the welded joints is good and the strength is high.

2. When brazing, the brazing temperature is lower than the melting point of the base metal, which has little influence on the base material, the whole part is heated evenly, the thermal stress is small, and the deformation can be controlled to a minimum, which is especially suitable for the brazing of precision products.

3. The low pressure (vacuum) existing around the base metal and the brazing filler metal can remove the volatile gases and impurities released by the metal at the brazing temperature, which can improve the performance of the base metal.

4. It broadens the design path of the product, and the brazable parts are allowed to have narrow grooves, extremely small transition tables, blind holes, etc., especially suitable for parts with closed containers and complex shapes, and can also braze multiple adjacent brazing at one time. joints, or brazing multiple components in the same furnace, the brazing efficiency is high, and there is no need to consider the corrosion, cleaning, damage, and other problems caused by the flux.

5. The heat treatment process of the workpiece can be completed at the same time during the brazing process, the appropriate welding process parameters can be selected, and the brazing can be arranged as the final process to obtain a brazed joint whose performance meets the design requirements.

6. There are many kinds of metals that can be brazed, especially suitable for aluminum and aluminum alloys, titanium and titanium alloys, stainless steel, high-temperature alloys, etc.; also suitable for brazing connections of the same or dissimilar metals such as titanium, zirconium, niobium, molybdenum, tungsten, etc.; also Suitable for composite materials, ceramics, graphite, glass, diamond, and other materials.

Application

1. Vacuum brazing is widely used in honeycomb structures as sealing components of various types of aero engines. The brazing process of the honeycomb structure is to pre-set the brazing material in the honeycomb core, then assemble the honeycomb and the shell, and finally adopt the vacuum brazing method For brazing, the strength of the brazed joint is about 50% of the base material. The grouped stator blades of the aero-engine compressor are also manufactured by this brazing method. It consists of inner and outer rings and more than 10 blades connected by vacuum brazing. overall. In addition, vacuum brazing is also used in the manufacture of turbine guides, guide vanes, diffusers, flame tubes, oil filters, and other components in aero engines.

2. The AMB (active metal brazing) process is a further development of the DBC process technology. It uses a small number of active elements Ti and Zr contained in the brazing filler metal to react with the ceramic to form a reaction layer that can be wetted by the liquid brazing filler metal. A method of joining. It not only has higher thermal conductivity and better copper layer bonding but also has the advantages of smaller thermal resistance and higher reliability. It is more suitable for the preparation of ceramic copper-clad substrates for IGBT module packaging in electric vehicles and power locomotives. Especially in important fields such as wind energy, solar energy, heat pump, hydropower, biomass energy, green building, new energy equipment, electric vehicle, rail transit, etc., the rapid development of power electronics technology will form a huge impact on the key material of IGBT module packaging - ceramic copper clad laminate. need.

3. Brazed diamond tools are divided into two types: surface inlay and impregnation. The surface inlay tool is to directly braze the diamond on the surface of the substrate. The impregnated tool is to sinter diamond and other materials into a composite diamond composite. The sintering process is essentially diamond. Diffusion brazing process with the base material. The brazing of diamond tools is divided into three categories: single-layer diamond tool brazing, diamond bit brazing, and PDC composite brazing. It has been widely used in stone tools, woodworking tools, aerospace, and military industries.

4. Vacuum brazed plate-fin oil coolers are used in cars and boats. Plate-fin oil cooler has the characteristics of high heat transfer efficiency, compact structure, and lightweight. It is a replacement product for today's diesel engine coolers and has been widely used in automobiles, tractors, marine diesel engines, and other fields.

5. The use of vacuum brazing technology for the impeller in the air separation equipment greatly improves the manufacturing precision of the impeller with narrow flow channels, thus not only ensuring the design performance indicators but also reducing the manufacturing cost and shortening the production cycle.