| The connecting rod cracking technology is a new technology that cuts grooves in the inner hole of the big end of the connecting rod and applies a load to make the crack propagate to fracture rapidly,thereby realizing the rapid separation of the connecting rod cover end and the connecting rod body.It contains many advantages,such as fewer processing procedures,lower investment costs for equipment,energy saving and material saving,and better connecting rod quality.At present,cracking processing is the most important method of connecting rod production.The most important thing in cracking is the prefabricated cracking groove and the process of expanding and breaking,and the cracking groove is mainly obtained by broaching,wire EDM and laser processing.Because the cracking groove cut by laser is narrow and sharp,it is easy to crack,and has high cutting efficiency and high precision.There is no direct contact between the equipment and the connecting rod and there is no tool wear.Therefore,laser grooving technology has become the development trend of grooving at home and abroad.There are many tiny cracks at the bottom of the cracking tank processed by laser,and the expansion process of the connecting rod is to use the stress concentration of the microcracks at the bottom of the groove to make it break,which saves energy and improves efficiency in this way.However,the connecting rod expansion process occurs in an instant,and it is not easy to collect the crack initiation and propagation process,so it needs to be simulated with the help of finite element analysis software.In this paper,the influence of laser processing parameters on the geometric parameters of microcracks and cracking grooves and the crack propagation process are studied.The main research contents and the corresponding conclusions are as follows:(1)The theory of fracture mechanics is explained,the fracture process of the connecting rod is determined to be an I fracture mode,and the maximum principal stress criterion is set as the criterion for the initiation and propagation of the crack of the connecting rod expansion and fracture,which is the construction and simulation of the connecting rod model Provide a basis.(2)The experiment of laser processing connecting rod cracking tank was designed to explore the influence of laser processing parameters on the geometric parameters of the cracking tank and some conclusions were drawn: with the increase of peak power,pulse width and pulse frequency,the groove depth and width of the cracking tank increase accordingly.As the peak power increases,the radius of curvature and the opening angle first increase and then decrease.With the increase of pulse width and pulse frequency,the radius of curvature and opening angle gradually decrease.As the cutting speed increases,the groove depth,groove width,and opening angle of the cracking groove gradually decrease,and the radius of curvature first decreases and then increases.(3)The effect of microcracks on the cracking groove wall on the cracking of connecting rods was studied,and a single factor test was designed for the influence of laser processing parameters on the length density,area density and average width of the microcracks,and the conclusion was drawn: With the gradual increase of the peak power,the area density and length density of the micro-cracks first increase and then decrease within a certain range,while the average width of the micro-cracks gradually decreases,and it shows that the increase of the peak power will reduce the expansion in the width direction of the crack.With the gradual increase of pulse width,the area density and length density of microcracks generally show an increasing trend,while the average width of microcracks fluctuates up and down.With the increase of pulse frequency,the area density and length density of microcracks first increase,then decrease and then gradually increase,while the average width of microcracks fluctuates up and down.As the cutting speed increases,the area density of micro-cracks gradually decreases,the length density first decreases and then increases,while the average width generally shows a downward trend,indicating that the greater the cutting speed,the smaller and sparser the cracks.The number of crack statistics for each parameter shows that with the increase of the peak power,the cracks are firstly distributed densely and then sparsely.As the pulse width and pulse frequency increase,the crack distribution becomes denser.As the cutting speed increases,the crack distribution becomes sparser.(4)XFEM(expanded finite element)is used to simulate the crack propagation process of the connecting rod model,and the stress and strain distribution law during the initiation and propagation of the connecting rod model is analyzed.For crack initiation: the stress concentration in the cracking groove area of the connecting rod is obvious,and the stress distribution is butterfly-shaped.The larger part of the stress is located at the root of the cracking groove and is distributed at both ends of the preset crack.The plastic deformation of the connecting rod occurs at the root of the cut,and its maximum value is located near the predetermined crack,and no plastic deformation occurs in other parts.The minimum breaking force required for the expansion and breaking of the connecting rod cracking groove under different laser processing parameters and the law of influence on the breaking force and crack initiation time are obtained: as the peak power,pulse width and pulse frequency increase,the connecting rod initiation time is reduced,and the required breaking force for expansion and breaking is reduced accordingly.As the cutting speed increases,the connecting rod initiation time increases,and the required breaking force for expansion and breaking increases accordingly.Then,the reason for the error between the results of the breaking force of the expansion test and the results of the numerical simulation of the breaking force is analyzed. |
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