The vacuum furnace welding method is a relatively new welding technique that does not use flux under vacuum conditions. Since welding occurs in a vacuum environment, it effectively eliminates the harmful effects of air on the workpiece, allowing for successful welding without the need for flux. It is primarily used for welding metals like copper and difficult-to-weld alloys such as aluminum, titanium, high-temperature alloys, remeltable alloys, and ceramics. The weld joints are bright and dense, with good technical performance and corrosion resistance. Vacuum welding equipment is generally not used for brazing of carbon steel and low-alloy steel. The welding equipment in a vacuum furnace consists mainly of a vacuum brazing furnace and a vacuum system. There are roughly two types of vacuum brazing furnaces: hot-wall furnaces and cold-wall furnaces. Both types of furnaces can be heated using natural gas for heating or electrically, and can be designed as side-mounted, bottom-mounted, or top-mounted (type D) structures, with the vacuum system being applicable.
The vacuum system primarily includes vacuum equipment, vacuum pipelines, and vacuum valves. The vacuum equipment typically consists of scroll-type mechanical pumps and oil diffusion pumps. Only mechanical pumps can achieve a vacuum level below 1.35×10^-1 Pa. To achieve high vacuum levels, it is necessary to use an oil diffusion pump simultaneously, which can reach a vacuum level of 1.35×10^-4 Pa. The air pressure in the system is measured using a vacuum gauge. Vacuum furnace brazing involves removing air from a vacuum furnace or brazing chamber for brazing. It is particularly suitable for large-area continuous brazing joints and also for the connection of special metals such as titanium, zirconium, niobium, molybdenum, and tantalum. However, vacuum brazing has the following drawbacks:
Metals are volatile under vacuum conditions, thus vacuum brazing is not advisable for base materials and solders containing volatile elements. If vacuum brazing is necessary, corresponding complex process measures should be adopted.
Vacuum brazing is highly sensitive to the surface roughness, assembly quality, and fitting tolerances of brazed parts, and it demands a high level of theoretical proficiency from both the working environment and the operator.
The vacuum equipment is complex, requiring a significant one-time investment and high maintenance costs.
