b. Effect of brazing temperature on the strength of brazed joints
As shown in Fig. 5, seven temperature points were selected for the brazing test on the high frequency induction welder. After welding, the tool is sandblasted to remove the scale generated during the welding process, and then the cutter is placed on a shear failure test device to measure the shear strength, and the relationship between the brazing temperature and the shear strength is obtained. 5). As the soldering temperature increases, the shear strength increases. The shear strength changes greatly around 670-680 °C; the shear strength is relatively stable near 690 °C.
Figure 5 Relationship between brazing temperature and shear strength
c. Effect of constant temperature holding time on the strength of brazed joints
When brazing a PCD composite sheet, the effect of the constant temperature holding time on the shear strength of the joint is also important. Figure 6 shows the shear strength change curve at different constant temperature holding times when the brazing temperature in air is 690 °C. As can be seen from the figure, the joint shear strength increases as the constant temperature holding time increases. When the constant temperature holding time is less than 16s, the shear strength rises faster; after the constant temperature holding time is longer than 16s, the shear strength does not change much. If the temperature is kept too long, the PCD layer is seriously damaged, which affects the performance of the tool after welding.
Figure 6 Relationship between brazing constant temperature holding time and shear strength
d. Effect of brazing metal surface roughness on joint strength
The surface roughness of the PCD composite sheet carbide substrate and the 45 steel shank brazing has an important influence on the shear strength of the brazed joint. Figure 7 shows the relationship between the surface roughness of the brazing metal and the shear strength at a brazing temperature of 690 ° C and a constant temperature holding time of 20 s. Fig. 7a is a graph showing the relationship between surface roughness and shear strength of a 45 steel shank; Fig. 7b is a graph showing the relationship between surface roughness and shear strength of a cemented carbide substrate of a PCD composite sheet. As mentioned above, the brazing material has a stronger wetting effect on 45 steel and a weaker wetting effect on the cemented carbide. The surface roughness of the composite sheet cemented carbide substrate mainly affects the wettability of the solder to itself during the brazing process. As the surface roughness increases, the capillary action of the rough surface of the cemented carbide surface enhances the wettability, and the contact area with the liquid solder increases, thereby accelerating the 45 steel to the liquid solder. Melt, enhance the strength of the brazing seam. At the same time, as the surface roughness increases, the brazing defects also increase, which seriously affects the welding quality of the PCD composite sheet. The test shows that when the welding surface roughness of the 45 steel arbor is Ra712?m and the surface roughness of the cemented carbide substrate is Ra0.180~0.250?m, the quality of the brazing seam obtained by the high frequency induction brazing PCD composite is the best. .
(a)
(b)
Figure 7 Relationship between surface roughness and shear strength of brazing metal
4 Conclusion
Through the experimental study on high frequency induction brazing of PCD composite sheet and 45 steel shank, the following conclusions can be drawn:
(1) When the high-frequency induction brazing PCD composite sheet, the brazing temperature has the greatest influence on the shear strength. In order to obtain a joint with a high brazing strength, the highest possible brazing temperature (the brazing temperature of this test is 690 ° C) should be used.
(2) Brazing constant temperature holding time is another important process parameter that affects the brazing strength. The brazing strength increases as the brazing constant temperature holding time increases. According to the test results, when the high-frequency induction brazing PCD composite sheet is used, the constant temperature holding time can be selected from 16 to 20 s.
(3) The brazing strength increases with the increase of the surface roughness of the PCD composite sheet cemented carbide substrate and the 45 steel shank brazing surface. Under normal circumstances, the surface roughness of the 45 steel arbor welding can be Ra7 ~ 12? m, the surface roughness of the welding surface of the cemented carbide substrate can be Ra 0.180 ~ 0.250? m.
(4) The use of partial unequal gap brazed joint design can effectively reduce brazing defects and welding stress such as pores and slag inclusions, and improve brazing quality.
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