Analysis of the influence of welding deformation on the fatigue life of roller chain

Analysis of the influence of welding deformation on the fatigue life of roller chain

Introduction
As an important basic component widely used in various mechanical transmission and conveying systems, the performance and life of roller chain have a vital impact on the reliability and operating efficiency of the entire equipment. Among the many factors that affect the fatigue life of roller chain, welding deformation is an important aspect that cannot be ignored. This article will deeply explore the influence mechanism, degree of influence and corresponding control measures of welding deformation on the fatigue life of roller chain, aiming to help practitioners in related industries better understand this problem, so as to take effective measures to improve the quality and reliability of roller chain, extend its service life, and ensure the stable operation of mechanical system.

1. Structure and working principle of roller chain
Roller chain is usually composed of basic components such as inner chain plate, outer chain plate, pin shaft, sleeve and roller. Its working principle is to transmit power and motion through the meshing of roller and sprocket teeth. During the transmission process, the various components of the roller chain are subjected to complex stress, including tensile stress, bending stress, contact stress and impact load. The repeated action of these stresses will cause fatigue damage to the roller chain, and ultimately affect its fatigue life.

2. Causes of welding deformation
In the manufacturing process of roller chain, welding is a key process used to connect the outer chain plate with the pin shaft and other components. However, welding deformation is inevitable in the welding process. The main reasons include:
Welding heat input: During welding, the high temperature generated by the arc will cause the weldment to heat up locally and rapidly, causing the material to expand. During the cooling process after welding, the weldment will shrink. Due to the inconsistent heating and cooling speeds of the welding area and the surrounding materials, welding stress and deformation are generated.
Weldment rigidity constraint: If the weldment is not rigidly constrained during the welding process, it is more likely to deform under the action of welding stress. For example, when welding some slender outer chain plates, if there is no proper clamp to fix them, the chain plate may bend or twist after welding.
Unreasonable welding sequence: An unreasonable welding sequence will lead to uneven distribution of welding stress, which will in turn aggravate the degree of welding deformation. For example, in multi-pass welding, if the welding is not performed in the correct order, some parts of the weldment may be subjected to excessive welding stress and deform.
Improper welding parameters: Improper settings of parameters such as welding current, voltage, and welding speed can also cause welding deformation. For example, if the welding current is too large, the weldment will be overheated, increasing the heat input, resulting in greater welding deformation; if the welding speed is too slow, the welding area will stay too long, which will also increase the heat input and cause deformation.

3. The mechanism of the influence of welding deformation on the fatigue life of roller chain

Stress concentration effect: Welding deformation will cause local stress concentration in components such as the outer chain plate of the roller chain. The stress level in the stress concentration area is much higher than that in other parts. Under the action of alternating stress, these areas are more likely to produce fatigue cracks. Once the fatigue crack initiates, it will continue to expand under the action of stress, eventually causing the outer chain plate to break, thereby causing the roller chain to fail and reducing its fatigue life. For example, welding defects such as pits and undercuts on the outer chain plate after welding will form a stress concentration source, accelerating the formation and expansion of fatigue cracks.

Geometric shape deviation and matching problems: Welding deformation may cause deviations in the geometry of the roller chain, causing it to be inconsistent with other components such as sprockets. For example, the bending deformation of the outer link plate may affect the overall pitch accuracy of the roller chain, causing poor meshing between the roller and the sprocket teeth. During the transmission process, this poor meshing will generate additional impact loads and bending stresses, aggravating the fatigue damage of the various components of the roller chain, thereby reducing the fatigue life.
Changes in material properties: The high temperature during welding and the subsequent cooling process will cause changes in the material properties of the welding area. On the one hand, the material in the heat-affected zone of welding may experience grain coarsening, hardening, etc., resulting in reduced toughness and plasticity of the material, and more prone to brittle fracture under fatigue load. On the other hand, the residual stress generated by welding deformation will be superimposed on the working stress, further aggravating the stress state of the material, accelerating the accumulation of fatigue damage, and thus affecting the fatigue life of the roller chain.

4. Analysis of the influence of welding deformation on the fatigue life of roller chains
Experimental research: Through a large number of experimental studies, the influence of welding deformation on the fatigue life of roller chains can be quantitatively analyzed. For example, researchers conducted fatigue life tests on roller chains with different degrees of welding deformation and found that when the welding deformation of the outer link plate exceeds a certain limit, the fatigue life of the roller chain will be significantly reduced. The experimental results show that factors such as stress concentration and material property changes caused by welding deformation will shorten the fatigue life of the roller chain by 20% – 50%. The specific degree of influence depends on the severity of welding deformation and the working conditions of the roller chain.
Numerical simulation analysis: With the help of numerical simulation methods such as finite element analysis, the influence of welding deformation on the fatigue life of the roller chain can be studied in more depth. By establishing a finite element model of the roller chain, considering factors such as geometric shape changes, residual stress distribution and material property changes caused by welding deformation, the stress distribution and fatigue crack propagation of the roller chain under fatigue load are simulated and analyzed. The numerical simulation results are mutually verified with the experimental research, further clarifying the mechanism and degree of influence of welding deformation on the fatigue life of the roller chain, and providing a theoretical basis for optimizing the welding process and structural design of the roller chain.

5. Measures to control welding deformation and improve the fatigue life of the roller chain
Optimize welding process:
Choose a suitable welding method: Different welding methods have different heat input and heat influence characteristics. For example, compared with arc welding, gas shielded welding has the advantages of low heat input, high welding speed and small welding deformation. Therefore, advanced welding methods such as gas shielded welding should be preferred in the welding of roller chains to reduce welding deformation.
Reasonable adjustment of welding parameters: According to the material, size and other factors of the roller chain, the welding current, voltage, welding speed and other parameters are accurately controlled to avoid welding deformation caused by excessive or too small welding parameters. For example, under the premise of ensuring the quality of the weld, the welding current and voltage can be appropriately reduced to reduce the welding heat input and thus reduce the welding deformation.
Use a suitable welding sequence: For roller chain structures with multiple passes of welding, the welding sequence should be reasonably arranged so that the welding stress can be evenly distributed and the local stress concentration can be reduced. For example, the welding sequence of symmetrical welding and segmented back welding can effectively control the welding deformation.
Application of fixtures: Designing and using suitable fixtures is crucial to controlling the welding deformation of roller chains. Before welding, the weldment is firmly fixed in the correct position by fixtures to limit its movement and deformation during welding. For example, by using the rigid fixation method and applying appropriate clamping force at both ends of the outer chain plate, bending deformation during welding can be effectively prevented. At the same time, after welding, the fixture can also be used to correct the weldment to further reduce welding deformation.
Post-weld heat treatment and correction: Post-weld heat treatment can eliminate welding residual stress and improve the material properties of the welding area. For example, proper annealing of the roller chain can refine the material grain in the welding area, reduce the hardness and residual stress of the material, and improve its toughness and fatigue resistance. In addition, for roller chains that have already produced welding deformation, mechanical correction or flame correction can be used to restore them to a shape close to the design and reduce the impact of geometric shape deviation on fatigue life.

6. Conclusion
Welding deformation has a significant impact on the fatigue life of roller chains. The stress concentration, geometric shape deviation and matching problems, and material property changes generated by it will accelerate the fatigue damage of roller chains and reduce their service life. Therefore, in the manufacturing process of roller chains, effective measures must be taken to control welding deformation, such as optimizing welding technology, using fixtures, performing post-weld heat treatment and correction, etc. Through the implementation of these measures, the quality and reliability of roller chains can be significantly improved, and their fatigue life can be extended, thereby ensuring the stable operation of mechanical transmission and conveying systems, and providing strong support for the production and development of related industries.