Vacuum brazing technology for carbide cutting tools
Whether the vacuum brazing process of cemented carbide tool is correct or not plays an important role in welding quality. The heating speed has obvious effect on welding quality. Rapid heating will lead to cracks and uneven temperature of cemented carbide sheet, but too slow heating will lead to surface oxidation and reduce joint strength.
Uniform heating of cutters and carbide plates is one of the basic conditions to ensure welding quality in vacuum welding of cemented carbide cutters. If the heat temperature of the carbide plate is higher than that of the tool rod, and if the melted filler metal wets the carbide plate instead of the tool rod, the strength of the joint will be reduced. When the alloy sheet shears along the welding layer, the solder will not be damaged, but will be separated from the alloy sheet. Milling marks on the support surface of the tool rod can also be seen on the welding layer. If the heating speed is too fast and the temperature of the tool rod is higher than the temperature of the alloy sheet, the opposite will happen.
Vacuum brazing flux, placement order and mutual position of filler metal and cemented carbide directly affect brazing quality. The correct way to place the filler metal is to place the filler metal on the slot, sprinkle the filler metal on the slot, then put the hard alloy, and spread a layer of filler metal on the top of the hard alloy along the side welding. Thus, during brazing, it is easy to control the brazing temperature and reduce the excess solder attached to the outside of the soldering. The vacuum brazing temperature of the workpiece should be controlled correctly in the process of vacuum brazing.
High vacuum brazing temperature will lead to welding oxidation and zinc evaporation in zinc-containing solder. Low vacuum brazing temperature will lead to poor fluidity of the weld, and there are a lot of pores and slag in the weld, which is the main reason of de-welding. Vacuum brazing temperature should be higher than the melting point of filler metal 30-50 ℃. At this point, the filler metal has good fluidity and permeability, and is easy to penetrate the entire weld.
In vacuum brazing, the vacuum degree is maintained at 5 10-2pa. The heating rate of vacuum brazing is an important parameter in the process of vacuum brazing. The rate of overheating leads to a sharp decrease in vacuum, and the cemented carbide and filler metals are easy to oxidize. In production, vacuum brazing process is as follows: from room temperature to 800 ℃, the rate of 10 / min, 30 minutes; Then set the temperature at a speed of 9 / min and hold it for 10 minutes. Then cool it in the oven.
In the 800 ℃ heat preservation is uniform in order to make the base metal heating; When the temperature at a rate of about 9 ℃ / min to set temperature, vacuum degree would not be significantly reduced; Short-term insulation at a set temperature allows the filler metal to fully melt and prevents excessive evaporation of magnesium particles at high vacuum. Although the cooling rate of cemented carbide brazing is required during cooling, no cracking due to excessive stress is found during furnace cooling. According to the melting point of filler metal, vacuum brazing temperature for 1105-1120 ℃, a total of six brazing temperature.