Characteristics and applications of induction brazing and vacuum brazing

(1) Characteristics of induction brazing

Induction brazing is a welding method that uses high frequency, intermediate frequency or power frequency induction current as a heat source. Specifically, the conductive workpiece is placed in a changing electromagnetic field, and the induction heating power supply provides a single-turn or multi-turn induction coil with a changing current, thereby generating a magnetic field. When the workpiece is placed between the induction coils and enters the magnetic field, Eddy currents enter the interior of the workpiece, producing precisely controlled, localized heating.

During induction heating brazing, the brazed part of the part is placed in an alternating magnetic field, and the heating of this part of the base metal is achieved by the resistance heating of the induced current it generates in the alternating magnetic field. The intensity of the induced current in the conductor is proportional to the frequency of the alternating current. As the frequency of the alternating current used increases, the induced current increases and the heating speed of the weldment becomes faster.

When alternating current passes through a conductor, the current density at the surface of the conductor is larger and the current density inside the conductor is smaller. When the high-frequency current passes through the conductor, the current density difference on the conductor cross-section increases, and the current mainly concentrates on the conductor surface, which is the so-called skin effect. Since induction heating brazing is heated from the inside out, unlike laser heating brazing, its effect is not affected by changes in brazing position or joints. Induction heating brazing can provide faster, uniform heating than soldering iron. Soldering iron tips wear out and need to be replaced frequently, while induction coils are virtually wear-free because they are non-contact. Brazing with induction heating instead of a gas flame has many advantages. It conducts more heat per unit area of material, and the brazing temperature is usually reached in seconds, resulting in shorter heating cycles and increased throughput.

(2) The rapid development and application of vacuum brazing technology is mainly because it has a series of advantages compared with other brazing methods:

①In 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 During brazing, the brazing temperature is lower than the melting point of the base metal, which has little effect on the base material, the whole part is heated evenly, and 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 around the base metal and the brazing filler metal can eliminate the volatile gases and impurities released by the metal at the brazing temperature, and can improve the performance of the base metal.

④Because no flux is used, there will be no defects such as pores and impurities, which improves the corrosion resistance of the base metal, avoids pollution, saves the process of cleaning residual flux after brazing, saves time, improves working conditions, and is environmentally friendly. No pollution.

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 It can braze multiple adjacent brazing seams at one time, or braze multiple components in the same furnace, and the brazing efficiency is high.

⑦ There are many kinds of metals that can be brazed, especially suitable for brazing aluminum and aluminum alloys, titanium and titanium alloys, stainless steel, high temperature alloys, etc. Also suitable for brazing joints of the same or dissimilar metals as titanium, zirconium, niobium, molybdenum, tungsten, etc. Vacuum brazing is also suitable for composite materials, ceramics, graphite, glass, diamond and other materials.

⑧It has broadened the design approach of products, and can braze parts with narrow grooves, extremely small over-tables, blind holes, closed containers, and parts with complex shapes, without considering the corrosion, cleaning and damage caused by flux, etc. And other issues.

(3) Disadvantages of vacuum welding

① Metals are volatile under vacuum conditions, so it is not easy to apply vacuum brazing to metals and brazing materials containing volatile elements. If it is really necessary, special technological measures should be adopted.

②Vacuum brazing is sensitive to the influence of the surface roughness, assembly quality, fit tolerance, etc. of the parts before brazing, and has high requirements on the working environment.

③The one-time investment of vacuum brazing equipment is large, and the maintenance cost is high.