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Classification of welding

2021-07-07 Page view : 201 views

Classification of welding:
Welding is generally divided into three categories: fusion welding, pressure welding, and brazing.

Most of the welded parts are welded by steel plates or section steels. Aluminum and aluminum alloys, copper and copper alloys, titanium and titanium alloys, cast iron, plastics and other materials can also be welded.

The weldability of the material is a prerequisite for determining whether the structure can be welded, and the designer must consider the weldability of the material.

Attention should be paid to the design of welded joints and welds in the design. Try to make the street form simple and continuous structure to reduce the turning of the force flow line. It is not appropriate to choose too large weld foot size and reduce weld cross-sectional size. Haiying considers the feasibility and convenience of structure manufacturing.

Welding will produce welding residual stress and deformation in the welded structure, and certain defects will also appear. The structural design should minimize the number of welds, choose reasonable weld size and shape, and reasonably choose the structure and position of welds.

Process measures to reduce deformation: anti-deformation method, rigid fixation method, select reasonable welding methods and specifications, heat treatment during or after welding to eliminate or reduce stress measures, improve the heat treatment of welds and heat-affected zone structure, select reasonable Assembly welding sequence, etc.

Structural design process principle:
1. Minimize the number of welds

Note: Appropriate use of section steel and stamping parts to minimize the number of welds; the use of profiled structure instead of rib structure can effectively reduce the deformation of the thin plate.

2. Reasonably arrange the position of the weld:

Note: The weld is as symmetric as possible to the central axis of the section, or the weld is close to the central axis to reduce deformation;

3. The weld seam should avoid too dense or crossing:

4. The welding seam should try to avoid the place of maximum stress or stress concentration:

Note: The welding seam should be located as far as possible at the place where the bending moment, the stress is small, and the place where the geometry and size of the structure are unchanged.

5. The welding seam should avoid the machined surface as much as possible:

Note: For workpieces that need to be processed after welding, the welding seam should avoid the processed surface

6. Pay attention to smooth transition when welding workpieces of different thicknesses

Note: Smooth transition can reduce stress concentration

7. The joint form should be selected correctly:

Note: The street style should be selected correctly when brazing. The strength of the butt joint is worse than that of the base material, and it is only used for unimportant or low-load parts: the strength of the lap joint can reach the strength of the base material, and the lap length is generally 2 to 5 times the thickness of the plate. Copper and its alloys have high thermal conductivity, and the welded joints should be designed to be symmetrical to the heat source. Make both sides of the joint have the same heat dissipation conditions, and obtain uniformly formed welds. Commonly used butt joints, try to avoid lap joints, T-shaped and inner corner joints.

8. Three-axis crossing welds should be avoided:

Note: The cross weld is easy to cause two-way tensile stress, thereby reducing the recovery of the joint. Cutting off the inner corner of the top of the rib can improve the stress state.

9. The joint form with less rigidity is adopted:

Note: The use of flanging connection instead of embedded pipe connection can make the welding seam more free to shrink.

10. Avoid stress concentration:

Note: Avoid geometric discontinuities in the area of ​​residual tensile stress. When there is geometric discontinuity in the area of ​​residual tensile stress, it will cause further increase of internal stress.
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11. The angle of the welding end should be as gentle as possible:

Note: Where there is an acute angle at the welding end, the angle should be made as slow as possible, and the acute angle at the end of the stiffener should be cut off.

12. Do not place the unwelded side of the bent weld in the tensile stress area:

Note: The bent weld should be designed on the side under tension, not on the unwelded side under pressure to avoid premature failure.

13. The operating space of the electrode should be considered when manual arc welding:

Note: The designed welding seam position should consider the welding rod operation space, which should be convenient for welding and inspection. The welding rod is at a 45-degree angle to the welding surface, and the vertical distance between the welding rod and the highest point of the blocking edge must be greater than 15mm.

14. When submerged arc automatic welding should consider the convenience of storing flux at the joint:

15. Electric welding or seam welding should consider the convenience of electrode extension:

Note: For the convenience of operation, the angle is better than 75 degrees.

16. Design of tensile welds for mechanical joints:

Note: The design of tensile welds should consider the strength of the welds, as well as the structural strength of the supporting welds. If the web is stiffened between the web and the wing, the deformation of the web is small. When the load is large, it should be reinforced on both sides of the web.

17. Use reasonable welding technology to avoid welding cracks:

18. Change the joint form to reduce the joint stress:

Note: Turn the weld of the workpiece into a contact weld to reduce the joint stress. The unilateral V-shaped groove is changed to a V-shaped groove to avoid large Z-direction stress in the thickness direction of the steel plate.

19. Change the structure to avoid excessive concentration of welds

20. Use reasonable welding joints to avoid stress concentration as much as possible:

After reading these design principles, can you cite the corresponding design taboo structures and their improvement methods for the corresponding design principles!

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