Brazing is to use a metal material with a lower melting point than the parent material as the brazing material, heating the weldment (parent material) and the solder to a temperature higher than the melting point of the solder, but lower than the melting point of the parent material, and using the liquid solder to soak the parent material , A method for filling the joint gap, and mutually diffusing with the parent material to realize the connection of welding pieces.
Brazing is a traditional and widely used cemented carbide welding method. Its process is mature and reliable. Induction heating brazing is also one of the widely used methods now.
The advantages of induction heating brazing are rapid heating, short solder liquefaction process, and can be performed in various atmospheres (air, shielding gas, vacuum), which can reduce the overheating and oxidation of the cemented carbide, which is beneficial to improving the welding quality; the method The disadvantage is that the equipment is more complicated, the one-time investment is large, and the skin effect of induced current is second. When brazing large and thick workpieces, the heating temperature is uneven, it is difficult to ensure the quality of brazing, and the efficiency is low, so it is generally only applicable It is used for small size welding parts with simple structure (preferably shaft type).
The process parameters of induction heating brazing generally include factors such as the gap between the seam, the heating speed, the cooling speed, the shape and size of the induction ring, and the manner of adding the solder flux. These factors must have a suitable combination range, and the fluctuation of the factors will adversely affect the quality of the weld, especially the large welding stress in the cemented carbide.
Weld gap value is an important parameter to ensure the quality of brazing. It is generally believed that the smaller the brazing joint, the greater the welding stress, and vice versa. If the gap of the solder joint is too small, 'crowding' and 'imperviousness' will occur, which will reduce the strength of the joint and increase the welding stress; while if the gap is too large, the capillary action will weaken, which will also lead to 'imperviousness' and reduce the joint strength . Therefore, the moderate gap of the weld seam has a great effect on reducing welding stress and enhancing weld fastness.
Heating and cooling rates have a significant effect on the quality of the solder joints. If the heating speed is too fast, a large stress will be generated in the alloy; if the heating is too slow, the high-temperature residence time will be long. Although this can improve the wetting and diffusion of the liquid solder, it will cause the oxidation burnout of the alloy. Generally, it is suitable that the heating does not exceed 100 ° C / s. If the cooling rate is too fast, a large shrinkage stress will be generated in the alloy. If the cooling rate is too slow, although it can reduce the welding stress, it is not good for the quenching of the steel material, so it is generally suitable to be 60 ° C / s.
The induction coil is an important element of induction heating equipment. The energy of the AC power is transmitted to the welding piece to heat it. Therefore, whether the structure of the induction coil is reasonable has a great impact on the quality of soldering and production efficiency. The principles for the correct design and selection of induction coils are: the induction coil should have a shape suitable for the weldment, minimize the useless gap between the induction coil itself and the weldment, and the gap is preferably not greater than 2 to 3 mm in order to improve heating efficiency . In order to make the welding piece heating smoothly and uniformly and prevent local overheating at the sharp corners of the welding piece, parameters such as the number of turns of the induction coil and the alternating frequency of the induced current should be selected reasonably.