What principles should be paid attention to in the process design of welded structure?

Date：2021-10-12 13:03:54Views：1545

Most of the weldments are welded by steel plate or section steel. Aluminum and aluminum alloy, copper and copper alloy, titanium and titanium alloy, cast iron, plastic and other materials can also be welded. The weldability of materials is a prerequisite to determine whether the structure can be welded. Designers must consider the weldability of materials. Attention shall be paid to the design of welded joints and welds in the design. Try to make the street form simple and the structure continuous, reduce the turning of the force flow line, do not choose too large weld leg size, reduce the weld section size, and consider the feasibility and convenience of structural manufacturing.

Welding will cause welding residual stress, deformation and some defects in the welded structure. The structural design shall minimize the number of welds, select reasonable weld size and shape, reasonably select structural form and arrange weld position, etc. Process measures to reduce deformation: anti deformation method and rigid fixation method, selection of reasonable welding methods and specifications, measures to eliminate or reduce stress during or after welding heat treatment, improvement of heat treatment of weld and heat affected zone, selection of reasonable assembly and welding sequence, etc.

Generally, there are many requirements for the technological design of welded structures, which can be summarized as follows:

Design of weld arrangement:

1. It shall be arranged in a position convenient for welding as far as possible;

2. It shall be arranged at the flat welding position as far as possible;

3. The weld arrangement shall be conducive to reducing welding stress and deformation;

Welding method selection:

Select the appropriate welding method according to the size and shape of the workpiece, the welding capacity, welding quality requirements, efficiency and process feasibility of the factory;

Design of welded joints:

1. Design basis of welded joint: design requirements, welding difficulty, welding cost and construction conditions;

2. Design of breach form: there are four general forms: I \ V \ x \ U. the basis for selection is: plate thickness, groove processing method, welding processability, welding method, welding position, deformation control, penetration requirements and economy;

Selection of welding materials:

Welding materials with good weldability shall be preferred, otherwise corresponding measures shall be taken.

What principles should be paid attention to in the process design of welded structure? The arrangement is as follows:

1. Minimize the number of welds

Note: profile steel and stamping parts shall be properly used to minimize the number of welds; Using profiled structure instead of ribbed plate structure can effectively reduce the deformation of thin plate.

2. Reasonable arrangement of weld position

Note: the weld shall be symmetrical to the central axis of the section as much as possible, or the weld shall be close to the central axis to reduce the deformation;

3. Welds shall be avoided from being too dense or crossed

4. The weld shall avoid the maximum stress or stress concentration as far as possible

Note: the weld shall be located where the bending moment and stress are small, and where the geometry and size of the structure remain unchanged.

5. The weld shall avoid the machined surface as far as possible

Note: for the workpiece to be processed after welding, the weld shall avoid the processing surface

6. Pay attention to smooth transition when welding workpieces with different thickness

Note: smooth transition can reduce stress concentration

7. The joint form shall be selected correctly

Note: the brazing form shall be selected correctly. The strength of butt joint is worse than that of base metal, and it is only used for unimportant or low load parts: the strength of lap joint can reach the strength of base metal, and the lap length is generally 2 ~ 5 times of plate thickness. Copper and its alloys have high thermal conductivity, and the welded joint shall be designed to be symmetrical to the heat source. Make both sides of the joint have the same heat dissipation conditions to obtain a uniform weld. Butt joints are commonly used, and lap, T-shaped and internal corner joints shall not be used as much as possible.

8. Welds with triaxial intersection shall be avoided

Note: the cross weld is easy to cause two-way tensile stress, which reduces the recovery of the joint. Cutting the inner corner from the top of the rib plate can improve the stress state.

9. The joint form with less rigidity shall be adopted

Note: using flanging connection instead of embedded pipe connection can make the weld have more free shrinkage space.

10. Avoid stress concentration

Note: avoid geometric discontinuities in the area of residual tensile stress. When there is geometric discontinuity in the region of residual tensile stress, the internal stress will be further increased.

11. The angle of welding end shall be as gentle as possible

Note: where there is an acute angle at the welded end, the angle shall be slowed down as far as possible, and the acute angle at the end of the stiffener shall be cut off.

12. The unwelded side of the bent weld shall not be placed in the tensile stress area

Note: the weld subjected to bending shall be designed on the tensile side, not on the pressure unwelded side, so as to avoid premature failure.

13. The operating space of welding rod shall be considered during manual arc welding

Note: the designed weld position shall consider the operation space of welding rod, which shall be convenient for welding and inspection. The electrode forms a 45 degree angle with the welding surface, and the vertical distance between the straight line of the electrode and the highest point of the barrier edge shall be greater than 15mm.

14. During automatic submerged arc welding, the convenience of storing flux at the joint shall be considered

15. Convenient electrode insertion shall be considered for electric welding or seam welding

Note: for the convenience of operation, the angle should be greater than 75 degrees.

16. Design of tensile weld of mechanical strand

Note: the strength of the weld and the structural strength of the supporting weld shall be considered in the design of tensile weld. If the stiffened plate is added between the web and flange plate, the deformation of the web will be small. When the load is large, reinforcement shall be added on both sides of the web.

17. Adopt reasonable welding process to avoid welding cracks

18. Changing joint form to reduce joint stress

Note: change the workpiece weld into contact weld to reduce the joint stress. Change the unilateral V-shaped groove into V-shaped groove to avoid large Z-direction stress in the thickness direction of the steel plate.

19. Change the structural form to avoid excessive concentration of welds

20. Reasonable welded joints shall be adopted to avoid stress concentration as far as possible

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