How to improve the bearing capacity of brazed joints?

In the design of brazed joints, the strength of the joint should be considered first, and then how to ensure the dimensional accuracy of the assembly, the assembly and positioning of the parts, the placement of solder, the gap of brazed joints and other technological issues should be considered.

So how to improve the bearing capacity of brazed joints? In brazed joints, one of the ways to increase the bearing capacity of the joint is to use lap joint in the joint design. Lap joint can make the joint have higher bearing capacity by increasing the lap area. Another way to increase the bearing capacity of the joint is to increase the lap length, but excessive increase of the lap length can not increase the bearing capacity of the joint proportionally. The practice shows that the lap length of the joint should be 3 ~ 4 times of the plate thickness.

Why is this? Butt joints have a uniform stress state, and save materials, reduce the weight of the structure, so it is called the basic joint form of fusion welding. In the brazing connection, because the strength of the solder is mostly lower than that of the base metal, the strength of the weld is also often lower than that of the base metal, which makes it difficult for the common butt joint to give full play to the bearing capacity of the base metal, and it is difficult for the butt joint to ensure the alignment of the connected parts and strictly control the size of the gap, especially when the thickness of the workpiece is small, it will make it more difficult. Therefore, butt joints are rarely used in brazed structures; T-joints and corner joints are similar to butt joints, and relatively few are used.

In addition, lap joint can increase the lap area to ensure that the joint has the same or even higher bearing capacity as the base metal when the joint strength is lower than the base metal, and the assembly requirements of lap joint are relatively simple, so lap joint becomes the most basic form of brazed connection.

Although lap joint has become the most basic form of brazed joint, there are some disadvantages of lap joint: increasing the amount of base metal and the weight of structure; sudden changes in the section of joint and resulting in stress concentration. Therefore, in the joint design, if it can meet the use requirements of the product without using the lapping method, the lapping joint shall not be used as much as possible. When lap joint is used as load-bearing connection, some measures should be taken to reduce the effect of stress concentration, such as making the section at the joint smooth transition.