Selection and assembly positioning of fixtures for brazing

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When selecting a fixture, the brazing method, brazing temperature, shielding gas, and base metal material properties should be considered simultaneously. Different brazing methods have different requirements. Specific examples are as follows:

1) During SIMUWU vacuum brazing process, the only limitation of the fixture material is that it must be stable at the brazing temperature, and it is with expansion properties that match the brazing workpiece, by which contains no vaporized substances and substances that may pollute the brazing atmosphere.

2) It is usually required to place the fixture near the inductor during induction brazing. If this situation exists, the clamp material is limited to materials that are not affected by the induction field.

3) In salt bath brazing, the fixture used should be moisture-free and always have a clamping effect, and the buoyancy effect of molten salt must be considered. And the fixture material must not react with molten salt.

4) Due to the large thermal expansion coefficients of aluminum and magnesium, the fixture for brazing these materials must be equipped with springs or some other forms of adjustment devices. Generally, nickel-based heat-resistant alloys and stainless steel can be used as spring materials.

When brazing, the components connected by brazing parts must be fixed in position for assembly. The relative position is always fixed throughout the brazing process to ensure that the welding gap meets the design requirements, and the gap is uniform, and the assembly gap and position are uniform. The method must use brazing fixtures and positioning fixtures.

Assembly and positioning of brazed parts
The assembly and positioning of brazed parts depends on the brazing technology used, the brazed material and the joint form of the brazed component. The assembly and positioning methods used for brazing parts of different structures are different. Specific examples are as follows:
1. For sheet metal components, spot welding is often used to locate the position, such as resistance intermittent spot welding, capacitor energy storage spot welding, argon arc spot welding and riveting methods for assembly.

2. Cylindrical parts, pipes and solid parts can be brazed and assembled in a variety of ways. If possible, the assembly method used should ensure that the joint gap is uniform throughout the brazing process. The methods used for assembling cylindrical parts are: pile shoulder, flared mouth, bell mouth, curling, upsetting, knurling and embossing, etc.

3. For the assembly positioning of more complex structures, such as in the aviation industry, it often requires precise assembly methods for positioning. The conditions are as follows:
Ø The brazed structural parts must maintain a qualified joint gap at the brazing temperature and conform to the characteristics of the brazing filler metal, base metal and the brazing method used;
Ø In many cases, during brazing assembly, air passages, cooling holes, etc. must be considered. After the brazing material is completed, there should be no brazing material on the fixture;
Ø In the design of the joint, the “self-clamping” assembly structure is used for self-positioning to ensure the assembly gap and the uniformity of the gap.