... 5.Convenient and save labour YP-D21 20Khz Ultrasonic Metal Welding Machine By using the ultrasonic high frequeccy vibration principle, the ... temperature, which is mainly applicable to smelting of iron, steel, copper, aluminum, zinc as well as various precious metals;3.Heat ... tools, hardware parts and machine parts, hardware mold, etc.4.Welding/Brazing:It mainly aims to melt the solder by heating ...