How do weldments relieve stress? What can be achieved?

How to relieve stress after welding? Welding stress and removal method.

Hello, 1. The cause of welding stress: the uneven temperature field of the welding process.

2. The main methods to reduce deformation are: (1) selecting a reasonable welding sequence; (2) Use symmetrical welds (such as I-sections) as much as possible; (3) Adopt the anti-deformation method.

3. The main measures to control deformation in the welding process: (1) Adopt anti-deformation; (2) Use a small hammer to hammer the middle weld bead; (3) Adopt a reasonable welding sequence; (4) Rigid fixation by using work fixtures; (5) Analyze the rebound constant.

4. Welding stress elimination method.

1) The failure method of stress relief is vibration aging (eliminating 30%-50% of stress); (2) Thermal aging (eliminate 40%-70% of stress); (3) Haoke can PT aging (eliminate 80%-100% of stress).

Reason: Weldment deformation refers to the thermal strain near the melted metal and the base metal due to the local heating and cooling of the weldment during the welding process, which will produce shrinkage stress when the weldment bead is cooled, thus causing the weldment to bend, twist or twist and other phenomena, which is called deformation. From the above, it can be seen that the deformation is caused by the result of thermal expansion and cold contraction during the welding construction process, so it can also be said that temperature is the main factor causing deformation.

The method of elimination is to pre-heat the area of 100 200mm to the left and right of the weld before welding, and then slowly cool it along with the weld after welding.

Metal and plastic cannot be welded directly, but ultrasonic riveting can be used to connect metal and plastic parts together. Generally, the metal parts of electronic appliances and auto parts are connected with plastic parts by ultrasonic riveting technology, the metal parts are punched with holes, and the plastic parts have small cylinders through the holes of the metal parts, and the plastic cylinders are welded into mushroom heads by ultrasonic welding machines to achieve the effect of connection.

Generation and prevention of welding stress.

In general, tensile stress is the "harmful stress" that causes fatigue of metal parts. Tensile stress can gradually cause hidden dangers such as metal warping, surface cracking and even disconnection. We often talk about the elimination of residual stress, mainly aimed at tensile stress.

Whereas, compressive stress is often beneficial. Compressive stress increases the deformation capacity of raw materials. The metal raw material is in a state of strong three-way compressive stress in the extrusion deformation zone, which can give full play to its plasticity and obtain a large deformation.

Improve the deformability of raw materials. Compressive stress can increase the closing force of microcracks and hinder crack propagation. It can resist the partial tensile stress caused by the external load in the service state, so as to prolong the fatigue life.

Tensile stress and compressive stress in welding residual stress

The fatigue strength of the welded structure is closely related to the residual stress, due to the large residual tensile stress in the welded part, resulting in fatigue cracking in the welded part, and the speed and length of crack propagation are proportional to the size of the tensile stress. Welding stress may cause hidden dangers in the welding part of the workpiece, and long-term use will cause tensile deformation and even cracking, causing unpredictable troubles and losses. Therefore, for metal weldments, it is very necessary to eliminate the residual stress of welding.

1. For the whole, vibration aging equipment is used to eliminate the residual stress of welding.

The variable load stress of the component reaches a certain value, and the residual stress in the structure gradually decreases after multiple cyclic loading, that is, the residual stress of part of the welding can be eliminated by the method of vibration. A device for relieving stress using vibration aging for large weldments. The advantages of the vibration method are that the equipment is simple, the cost is low, the time is relatively short, and there is no oxidation problem during high temperature tempering, and it has been applied to a certain extent in production.

2. For the welding part, the Hauk can welding stress relief equipment is adopted.

For the weld toe, welding stress relief equipment is used for targeted local stress relief. By using high-frequency shock vibration, the undercut and pit at the weld are treated into a smooth transition, and the defective structure such as cracks on the microscopic metal surface can be changed, which can greatly improve the welding life and prevent welding cracking.

Local welding strain relief equipment.

The vibration aging equipment corresponds to the entire mechanical workpiece, so it is actually the residual stress of the entire component that is eliminated. For weldments, more targeted treatment is required.

Hawker welding strain relief equipment is a device specially designed to eliminate residual stress in welding. The high-frequency ultrasonic impact can be carried out back and forth on the welding toe part of the weld by hand, and this high-frequency vibration is more targeted and more effective to remove the residual stress of welding, smooth the weld, and greatly improve the firmness of the weldment.

The heat treatment effect of overall stress relief is generally better than that of local heat treatment. Welding residual stresses can also be eliminated or adjusted by mechanical tensile method (preload method).

Welding is a commonly used joining method, but the welding stress generated after welding will affect the stability and service life of the workpiece. Here are six ways to relieve welding stress:1

Annealing treatment: By heating the welded part to a high enough temperature, and then slowly cooling the key to relieve stress. 2.

Vibration treatment: The stress generated during the welding process can be relieved by mechanical vibration or ultrasonic vibration during welding. 3.

Machining: Through cutting, grinding and other machining methods, the surface layer of the welded part is removed to relieve stress. 4.

Heat treatment: By controlling the temperature and cooling rate of the welding part, the stress generated during the welding process is relieved. 5.

Thermal compression: Pressure is applied under the condition of heating to cause plastic deformation of the welded part to relieve stress. 6.

Use welding deformation to offset stress: During welding, the stress is offset by adjusting the welding deformation, and the purpose of stress relief is achieved by rolling trembling.

In order to eliminate and reduce the residual stress of welding, a reasonable welding sequence should be adopted, and the weld with a large amount of shrinkage should be welded first. When welding, the stiffness of the weldment is appropriately reduced, and the appropriate part of the weldment is heated locally, so that the weld can shrink relatively freely to reduce the residual stress. Heat treatment (high temperature tempering) is a common method to eliminate residual stress in welding.

The heat treatment effect of overall stress relief is generally better than that of local heat treatment. The residual stress of welding can also be eliminated or adjusted by mechanical tensile method (preload method), for example, the hydraulic test can be used for pressure vessels, or it can be locally heated to 200 on both sides of the weld to create a temperature field, so that the weld area can be stretched to reduce the residual stress.

If it can be eliminated as a whole, vibration aging equipment can be used.

If it is local, such as a weld, ultrasonic impact or Hawkeron welding stress relief equipment can be used to eliminate the weld toe of the weld.

During the welding process of the weldment, the thermal stress, phase transformation stress, processing stress, etc. exceed the yield strength, so that the stress left in the weldment after cooling cannot be eliminated.

In this way, the macroscopic stress that remains in the weldment after the weld has cooled is called the residual weld stress. The uneven temperature field of the welding process and the local plastic deformation and the different specific volume of the structure caused by it are the root causes of welding stress and deformation.

Welding Residual Stress Relief Method:

The hammer weld area is used to control the welding residual stress, and the weld and its adjacent areas are tapped with a small hammer after welding, so that the metal can effectively reduce the welding residual stress.

The preheating method is used to control the residual stress of welding. The larger the temperature difference on the component body, the greater the residual stress of welding. Preheating the components before welding can reduce the temperature difference and slow down the cooling rate, both of which can reduce the residual stress of welding.

The "Heating Reduction Zone Method" is used to control the residual stress of welding. When welding, heating the parts that hinder the free expansion and contraction of the welding area, so that it expands and contracts at the same time as the welding area, can reduce the welding stress, this method is called the "heating subtraction area method", and the heated part is called the "subtraction area".

High-temperature tempering is utilized to eliminate welding residual stresses. Since the maximum value of the residual stress of the component usually reaches the yield point of the material, the yield point of the metal will decrease at high temperatures. Therefore, when the temperature of the component is increased to a certain value, the maximum value of stress should also be reduced to the yield point value at that temperature.

If the residual stresses in the structure are to be completely eliminated, the member must be heated to a temperature where its yield point is equal to zero, so the tempering temperature is generally taken close to this temperature.

Overall high temperature tempering.

The entire component is heated to a certain temperature in a furnace, and then kept warm for a period of time before cooling. 80% and 90% of the residual stress in the component can be eliminated through the overall high-temperature tempering, which is the most widely used and most effective method to eliminate the residual stress in production.

The tempering time depends on the thickness of the component, and the steel is calculated according to the wall thickness of l 2min per millimeter, but it should not be less than 30min, and it does not have to be higher than 3h, because the elimination effect of residual stress decreases rapidly with time, so the excessive processing time is unnecessary.