Welding Turning Tool-Notices for Turning Tool Welding

When welding the tool, the height HC of the tool body should be greater than the height HT3 times of the blade.

Hard bonding has poor weldability. Because of its high carbon content, the surface layer which has not been cleaned after sintering often contains more free carbon, which hinders the wetting of solder. By carefully cleaning the welded surface, when spraying on the welding tool, the tool body height HC should be greater than the blade height HT3 times.

Because of its high carbon content, the uncleaned surface layer after sintering often contains more free carbon, which hinders the wettability of solder. The wettability of cemented carbide can be improved by carefully cleaning, spraying, grinding and polishing the welded surface.

The hardness and brittleness of cemented carbide are high. If the welding process is slightly neglected, the blade will be scrapped because of cracks. Therefore, how to avoid welding cracks has become an important problem to be solved in the process of tool welding.

1) The influence of heating on the crack formation of cemented carbide. The thermal expansion coefficient of cemented carbide blade and steel (tool rod) is quite different, and the thermal conductivity of the alloy is also worse than that of the tool body material. If the tool is heated rapidly during welding, it will produce a large internal stress, which will cause the blade to crack at the welding layer, so the welding temperature control is adopted. The melting point of the solder selected at about 30-50 C is lower than 60 C of the tool rod. When welding, the flame should be heated uniformly from the bottom to the top and slowly preheated for welding. Therefore, it is necessary to form a uniform local overheating between the groove and the welding surface of the blade, which will make the temperature difference between the blade itself or the blade and the tool rod larger and thicker blades more stringent. Thermal stress will make the blade edge crack, so it is necessary to preheat the tool bar before warming up. If the blade and the tool bar are heated together, the flame should be moved back and forth to warm up, so that the local overheating caused by the heat concentration can be avoided.

2) The influence of tool groove shape on crack formation is inconsistent with or quite different from the welding surface of the tool rod, forming a closed or semi-closed groove shape, which can easily lead to too many welding surfaces and too large welding layer. Because of the inconsistent shrinkage rate after thermal expansion, it is also easy to cause too much stress at the welding site of the tool blade, resulting in cracking in satisfactory use. The area of brazing surface should be reduced as much as possible under the requirement of required weld strength.

3) The influence of cooling on the crack formation of cemented carbide During or after welding, depressed atmosphere or rapid cooling or poor flux dehydration will cause the blade to burst and crack penetration. Therefore, good dehydration welding of solder should not be placed in water to rapidly cool, but in lime, asbestos powder, sand and so on. However, it is cooled with the furnace after holding for more than 6 hours at about 300 C.

4) Defects on the bottom of the groove affect the formation of cracks. The contact surface between the blade and the groove is uneven. If there are black pits and local unequal reasons, the welding can not form a plane bond, resulting in uneven distribution of solder. This not only affects the strength of the weld, but also causes stress concentration, leading to blade fracture. Therefore, the blade should be grinded. Contact surface, the welding surface of the blade groove should be cleaned. In the process of matching the milling blade groove with the blade, it is required that the supporting part of the tool rod extend not more than 0.5mm. If the supporting part of the tool rod extend too large or the supporting part of the tool rod is weak, the tool will bear tension and fracture during welding.

5) The influence of secondary heating on the formation of cracks. After brazing, copper brazing filler metal does not completely fill the cracks, and virtual welding occurs in some cases. In some cases, the blade falls off the tool pole during the process of discharging. Therefore, secondary heating is needed. As a result, the binder Co is seriously burned and the WC grain grows, which may directly lead to the blade. Crackle.