The Different Characteristics of Vacuum Brazing and Fusion Welding in Brazing

The significant difference between vacuum brazing furnace brazing and fusion welding methods is that during vacuum brazing furnace brazing, the work is often heated as a whole (such as brazing in the furnace) or uniformly heated around the brazing seam in a large area. Therefore, the relative deformation of the workpiece and the residual stress of the joint are much smaller than fusion welding, making it easier to ensure the precise size of the workpiece. And the selection range of brazing materials is relatively wide. In order to prevent changes in the parent structure and properties, brazing materials with relatively low liquidus temperature can be selected for vacuum brazing. During the vacuum brazing furnace brazing process, the brazing process should be selected appropriately to ensure that the brazed joint does not require machining. In addition, as long as the brazing conditions are appropriately changed, it is also beneficial for multiple brazing seams or large batches of workpieces to be brazed together or continuously. Especially beneficial for the transition between dissimilar metals, which cannot be achieved by metal and non-metallic methods.

Due to different heating methods, brazing in high-temperature vacuum brazing furnaces can be divided into flame brazing, furnace brazing, vacuum brazing, induction brazing, etc.

Vacuum brazing furnace brazing uses a metal material with a lower melting point than the base material as the brazing material, heating both the weldment and the brazing material to a temperature higher than the melting point of the brazing material and lower than the melting point of the base material, making the brazing material ellipsoid into a liquid. The wetting of the base metal by brazing fluid is achieved by filling the gaps between the joints of the base metal and generating mutual diffusion with the base metal under the action of fine flow. The dissolution and diffusion between the base metal and the brazing filler metal have changed the composition of the brazing seam and the interface base metal, making the composition, structure and performance of the brazing joint greatly different from that of the brazing filler metal and the base metal. solid solution, compound and eutectic may be generated, thus forming a solid joint.

The main drawback of vacuum brazing furnace brazing is that the composition and properties of the rod material and the base metal are not possible: they are often close, and sometimes have significant mutual benefits. For example, heavy metal brazing aluminum can inevitably lead to varying degrees of electrochemical corrosion between the joint and the base metal. In addition, most materials cannot achieve equal strength between the brazing joint and the base metal during brazing, and can only be improved by increasing the overlap area.

In the design of welding structures and vacuum brazing furnace brazing structures, it is hoped that the joint and the connected part have the same ability to withstand external forces. Although the load-bearing capacity of vacuum brazing furnace brazing joints is related to the strength of the brazing material, the size of the brazing seam gap, the bonding force between the brazing material and the base metal, and the brazing rate, the joint form also plays a significant role.

The design principles of vacuum brazing furnace brazing joints are as follows.

Brazed joints generally do not use traditional forms of butt joints, T-joints, or corner joints due to poor load-bearing capacity. Brazed joints are usually in the form of overlap to improve load-bearing capacity“

Prevent stress concentration. For this reason, avoid arranging the joint at the corners or sudden changes in the cross-section of the welded part, or at positions with excessive stiffness. Materials with different thicknesses can increase the thickness of thin parts to reduce stress concentration.

The joint design is conducive to the reasonable placement of solder. Vacuum brazing furnace vacuum brazing is pre placed, and the filling position of the brazing material should be considered when designing the joint. If it is necessary to open a preset solder groove, it should be opened on the base metal with a thicker cross-section.

When designing joints without affecting the structural performance of kitchen components, necessary protrusions, grooves, and process steps should be provided to ensure positioning and assembly. The geometric shape of the workpiece is different, and the shapes of various joints are also different.