5 Ways of Removing the Internal Stress in Metal When Welding
- Introduction to welding
- Internal stresses in welding and their effects
- Importance of removing internal stress when welding
- Five ways of removing the internal stress when welding
Introduction to welding
Welding is a process for joining two or more metal or thermoplastic parts together. In the welding process, the material of the parts to be joined is melted or softened by heating and applying pressure or adding filler material to form a permanent joint. However, an inevitable and non-negligible problem in the welding process is the occurrence of internal stresses.
Internal stresses in welding and their effects
During the welding process, heating from the source makes the temperature of the welded area rise, while a temperature gradient is generated around the welded area. Due to the thermal expansion and contraction of the metal during heating and cooling, the thermal stresses generated during the welding process can cause internal stresses to develop. These internal stresses may lead to deformation, cracking, brittleness or cause stress corrosion of the welded joint, which seriously affects the quality and service life of the welded joint. Therefore, the elimination of internal stresses in welding is an important issue in the welding process. Reasonable control and management of internal stress is required, and appropriate pre-heating, pre-stressing, and post-heat treatment measures need to be taken to reduce the generation of internal stress and improve the quality and reliability of welded joints. It is also necessary to detect and solve the possible internal stress problems in welded joints in time through inspection and analysis.
Importance of removing internal stress when welding
First, improved strength and toughness of welded joints. The internal stresses present in welded joints can lead to joint deformation and cracking, thus reducing the load-bearing capacity and fatigue life of the joint. Once internal stresses are eliminated, it can avoid the deformation and cracking of welded joints, improving the strength and toughness of welded joints.
Second, increased corrosion resistance of welded joints. Internal stresses can cause loose and unstable grain boundaries in welded joints, which can lead to problems such as oxidation and corrosion. If the welding residual stress is too large, it will aggravate the corrosion deformation of the material structure, thus affecting the corrosion resistance of the material.
Finally, extended service life of welded joints. The internal stresses present in a welded joint can cause gradual failure and fatigue of the joint during use. By eliminating these internal stresses, the life and service life of the welded joint can be extended and the reliability of the welded joint can be improved.
In summary, the elimination of internal stresses in welding is an important issue in the welding process, which is of great significance for improving the quality, reliability and life of welded joints.
Five ways of removing the internal stress when welding
I. Preheating to remove the stress
Preheating is one of the methods to remove internal stresses in welding. Its function is to reduce the accumulation of internal stresses by heating the welded area to a certain temperature, putting the welded joint into a relatively stable condition. The principle of preheating is that during the welding process, the welded material is subjected to heating and cooling for a short period of time, resulting in stresses within the weld area. Preheating allows for a uniform temperature in the welded area, thereby reducing the deformation of the welded material and the generation of internal stresses.
Preheating operates by heating the weld area to a certain temperature before welding, usually by flame heating, electric heating or induction heating. The temperature and time of preheating depends on the type and thickness of the welded material, the welding method and other factors. When performing preheating, consideration should be taken into the following points: 1. The preheating temperature & time. Preheating temperature and time should be determined on a case-by-case basis and generally need to be adjusted according to the type and thickness of the weld material and the welding method, among other factors. 2. Uniform heating. Preheating should be evenly heated to avoid overheating or localized low temperatures. 3. Avoid overheating. Overheating can cause distortion and cracks in the weld area, so the preheating temperature needs to be controlled to avoid overheating. 4. Keep the welding area dry. Impurities such as moisture or oil should not be present in the weld area; otherwise it will negatively affect the weld quality.
II. Post-heating to remove residual stress
Post-heating is a post-weld heat treatment technique whose main function is to eliminate residual stresses, improve structure and enhance performance by heating the welded parts. During the welding process, residual stresses are generated inside the welded parts due to thermal stresses, resulting in deformation and cracking of the welded joints. The post-heat treatment can improve the organization of the welded parts by heating to eliminate residual stresses, thus improving the strength and toughness of the welded joints.
The specific methods of post-heating treatment include the selection of appropriate heating process parameters, heating time and heating temperature, and should be adjusted according to the characteristics and requirements of the specific weld material. When post-heat treatment is carried out, attention should also be paid to prevent secondary deformation and thermal cracking generated during the heating process. Besides, the welded joint should be properly cleaned and surface treated before heating to ensure the effect of post-heat treatment.
III. Cooling to control the stress
During the metal welding process, the cooling rate of the welded part has an important influence on its organization and properties. Rapid cooling rate may lead to problems such as cracks and deformation of the welded parts and reduce the weld quality. With proper cooling control, the cooling rate can be adjusted to achieve the proper organization and properties of the welded parts at different temperatures and improve the weld quality and service life.
To operate cooling includes the selection of a suitable cooling medium and control of the cooling rate, etc., which should be adjusted according to the characteristics and requirements of the welded material. Attention should also be paid to prevent welding defects such as cold cracks and deformation. Before cooling control, the welded parts should be cleaned and surface treatment to ensure the effect of cooling control.
IV. Vibration Process to offset stress
Vibration processing is a process that changes the surface form of a workpiece by means of mechanical vibration. In metal welding, vibration processing can be used to reduce residual stresses and eliminate internal defects and improve the quality of welded joints. The principle of vibration processing is to reduce the residual stresses and eliminate defects by applying vibration forces to the surface of the welded part and generating corresponding strains and stresses, thus causing a redistribution of stresses within the welded part.
This operation method generally includes the selection and position installation of the vibrator, the setting and control of vibration frequency, vibration amplitude and other parameters. When vibration processing is carried out, attention needs to be paid to the control of vibration frequency and amplitude to avoid excessive vibration causing deformation or damage to the welded parts. In addition, the timing of vibration processing is also important, which is usually carried out after or in the middle of welding to prevent interference on the welding process.
V. Water Jet Cooling to reduce the stress
Heat from welding can cause thermal expansion and residual stresses of metal. By harnessing the cooling effect of water, Water Jet Cooling offers a reliable solution to mitigate such issues by rapidly reducing temperature on workpiece surfaces; thus preventing undesired deformation or stress.
Water jet cooling mainly includes the selection of the water jet, the adjustment of the water flow and jet angle, and control of the cooling time. When carrying out water jet cooling, attention needs to be paid to the size of the water flow rate and the selection of the injection angle, which should be adjusted according to different welding materials and welding thickness. At the same time, the time needs to be controlled to avoid deformation or cracking of the workpiece caused by excessive cooling.
Furthermore, it is crucial to address these aspects in water jet cooling to enhance efficiency and safety: Maintain cleanliness and functionality of water jets to uphold optimal performance of welded joints. Regulate both the duration and coverage of water jet cooling to circumvent unintended consequences on surrounding zones. Prioritize safety measures while employing water spray cooling methods to mitigate the risk of injury from water splash or other factors.
The above methods are commonly used to eliminate internal stresses in welding. Preheating and post heat treatment can reduce the stresses by heating and holding the material at a uniform temperature. Cooling can control the cooling rate of the welded parts to decrease the residual stresses. Vibration processing can reduce internal stresses by changing the stress field through external force. Water jet cooling can decrease thermal stresses by reducing the temperature of the weld area.
The choice of these methods needs to be determined on a case-by-case basis. When using these methods, attention also needs to be paid to the method of operation and precautions to avoid adverse effects on the quality of the welding. It is also important to consider the material, shape, size and other elements of the welded part. The selection of a suitable method for the elimination of internal stresses in the weld can improve the quality and life of the welded part and reduce maintenance costs, and therefore has an important role in the welding process.
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