硬质合金精密刀具高频感应钎焊工艺中几个问题的分析

Analysis of Several Problems on High Frequency Induction Brazing Technology of Cemented Carbide Precision Tools

本文对硬质合金精密刀具的高频感应钎焊技术进行了综述,介绍了高频感应原理,其基础是集肤效应和邻近效应;分析了硬质合金焊接的特点,由于钢和硬质合金之间线膨胀系数、热传导率等物理性能的差异,两者之间的钎焊在工艺上存在较多问题,如残余应力、裂纹、虚焊、夹渣、氧化、钎缝脆化等。本文重点探讨了硬质合金精密刀具高频感应钎焊的主要影响因素,包括焊接温度、加热速度、焊缝宽度、感应圈间隙及形状、工件表面质量、钎料钎剂性能等,得出结论：焊接温度应比钎料的液相线高20~50℃;过快或过慢的加热速度都会对钎焊质量造成不良影响;钎缝的最佳间隙大小应保持在0.01~0.1 mm之间;感应圈应有与焊件相适应的外形,尽量减少感应圈本身和焊件之间的无用间隙;增大工件表面的粗糙度,清除母材表面的氧化膜,去污除油,能够增大钎料在表面的附着力;宜选用润湿效果最好的银基钎料;氟硼酸钾是银基钎料的适宜钎剂。

The high frequency induction brazing technology for cemented carbide precision tools is summarized, and the high frequency induction principle is introduced, the foundation is skin effect and proximity effect. The characteristics of cemented carbide brazing are analyzed. Because the linear expansion coefficient and thermal conductivity between steel and cemented carbide are different, there exists more problems in the brazing process, such as residual stress, cracks, weak weld, slag, oxidation, emhrittlement brazing seam, and so on. This paper focuses on the main influencing factors of high frequency brazing welding of cemented carbide precision tools including brazing temperature, heating rate, weld width, induction coil gap, surface quality of workpiece, solder flux performance, etc. It is concluded that the brazing temperature should be 20- 50~C higher than liquids temperature of solder. Too fast or too slow heating rate will adversely affect the quality of brazing. The appropriate brazing gap should be 0.01~0.1 mm. The shape of induction coil should be similar to that of weldment. The useless gap between induction coil and weldment should be reduced as much as possible. In order to increase the surface adhesive of solder, the surface roughness of workpiece should be increased and the oxide film and oil fouling on base material surface should be cleaned. Silver-based solder with well wetting effect should be chosen. KBF4 is suitable flux forsilver-based solder.