Study On Key Technology And Equipment Of Machining 36MnVS4 Splitting Connecting Rod With Pulse Fiber Laser

Compared with the traditional method of machining connecting rod,the way of processing splitting connecting rod realizes the rapid and brittle splitting of connecting rod by taking advantage of stress concentration in the process of prefabricating splitting crack.It is not necessary to process the joint surface and the bolt holes,and the three-dimensional structure naturally formed on the crack surface can be used to precisely match the connecting rod body and cover.It has become the most important way for manufacturing connecting rods at home and abroad because of its good processing quality,low cost,high efficiency,fewer procedures,material-saving and so on.The process of machining cracking groove is the key procedure for the new technology of splitting connecting rod.Therefore,a set of equipment of precision,efficiency and stability is the basis for the application of splitting connecting rod technology.In the process of splitting grooves,laser machining has a narrower and sharper profile of cracking grooves compared to mechanical broaching and wire-cut electric discharge machining,becoming the trend of machining splitting connecting rods at home and abroad with its high efficiency,high precision and good stability.At present,the application and equipment development of the technology of laser machining connecting rod cracking groove is still at the preliminary stage at home.Except for the Nd: YAG laser processing equipment for machining connecting rod groove developed by Jilin University and Han's Laser,high-end laser processing equipment can only be got by import.With automotive engine connecting rods developed to be more high-quality,lightweight,and low-cost,the new alloy steel 36 Mn VS4 is a representative material for machining connecting rods.With its high fatigue strength,good cutting performance and substantial reduction in weight,it has been widely used by many European automotive manufacturers,and it has broad application prospects in the future.Though some achievements have been made in the development of 36 Mn VS4 materials in domestic,its application is still in its infancy and only a few manufacturers use this new type of connecting rod material.At present,the research on machining the 36MnVS4 connecting rod with pulse fiber laser in China has not been reported.Therefore,it is greatly important to develop a new type of fiber laser equipment,to explore the processing mechanism,to optimize the laser processing parameters,to improve the yield of the splitting connecting rod,to reduce the manufacturing cost of the automobile and to study the key technology and equipment of fiber laser processing 36MnVS4 connecting rod groove.This thesis mainly focused on the research of equipment and process of the 36 Mn VS4 connecting rod cracking groove manufactured by pulse fiber laser,including the following contents:(1)Designing and developing fiber laser equipment used for the automobile engine connecting rod cracking groove,mainly including the selection of lasers,laser heads and laser light guide systems,and the optimal selection of laser incident angles and laser processing paths,and the design of connecting rod positioning fixtures and mechanical motion structures.(2)The microstructure and mechanical properties of 36 Mn VS4 were investigated,including energy spectrum analysis to find out its mass percentage,metallographic structure to observe the metallographic composition,uniaxial tensile test to measure the yield strength,tensile strength,fracture stress and other mechanical parameters of the material,and SEM is to observe fracture morphology to certify that its fracture criteria fitted the maximum principal stress criterion.It was found that there were pores,micro-cracks and “serrated” pits at the bottom and side of the cracking groove.The thickness of the heat-affected zone was less than 100 um.The best cracker depth was 600 ?m with machining allowance taken into account.(3)The ABAQUS software was used to perform finite element analysis on the process of splitting connecting rod.The main stress distribution in the vicinity of the cracking zone was analyzed.The starting point of splitting in the process of machining the connecting rod was thought to be the point that was the sharpest in the middle face of the big hole according to the principle of the point with maximum stress concentration.The influence of different groove depths,opening angle and stress angle radius had on the stress concentration of the root of the cracking groove were analyzed.The results showed that the stress concentration at the root of the cracking groove increased with the increase of the groove depth and decreased with the increase of the opening angle and the radius of curvature.The depth of the groove had the most significant effect on the stress concentration,and the geometric parameters of the cracking groove were optimized through the results analysis.(4)Experimental study on fiber laser processing of 36 Mn VS4 splitting connecting rod.It was figured out that the laser in negative defocusing was more conducive to the processing of the cracking groove.Through the single factor tests,the depth,width,opening angle,radius of curvature of the cracking groove changing with the pulse peak power,pulse width,pulse frequency and cutting speed were studied.And optimal parameters were obtained by conducting the orthogonal experiments.Based on the depth of the cracking groove,the factors affecting the depth of the cracking groove were ranked by pulse width>peak power>cutting speed >pulse frequency by range analysis.Cracks cutting through parameter optimization were of better quality,and the optimal parameters were when pulse width was 40?s,peak power was 800 W,pulse frequency was 900 Hz and cutting speed was 1.4m/min.The cracking groove could obtain a better quality after optimization.