Study On The Optical Fiber Laser Processing Technology Of The Initial Cracking Groove Of The Engine Connecting-rod

Connecting-rod cracking technology is one processing theory,which apply the load in the big hole of connecting-rod fully leading to fracture splitting and control the splitting orientation,eventually,making the connecting-rod breaking into two parts.For now,the key factors to ensure the quality of connecting-rod fracture splitting is the processing quality of cracking groove.Nowadays,the major domestic cracking groove processing theory are mechanical broaching and wire cutting,when the mechanical broaching tool is worn,the curvature radius of cracking groove will increase while the groove depth decrease which result in cracking instability,the machining accuracy and productivity of the wire cutting is lower.Then the advantages of laser grooving is obvious,using laser processing connecting-rod groove have many obvious advantages,not only the laser machining efficiency is high,but have no tool wear and gain the groove with a high quality and high location precision.The laser grooving has gradually become the important processing method of connecting-rod fracture splitting.Our research team put forward by using optical fiber laser processing groove,joined research and development of the first domestic laser processing connecting-rod cracking groove equipment cooperated with Guangdong Shihui ShiLi Connecting-Rod Co.,Ltd.Because of the complexity in the procession of laser grooving,a certain parameter selection is difficult in laser grooving technology,so the process of laser grooving in connecting-rod fracture splitting experiment and research is particularly important.Based on the principle of optical fiber laser and laser grooving technology,the article aims to study on the laser processing parameters on the effect of connecting-rod cracking groove and to gain a proper optimization scheme for the actual cracking groove processing.Besides,a preliminary study of micro-cracks on the surface of the cracking groove is obtained in proper laser processing parameters.The main contents and corresponding conclusions are as follows:(1)Using COMSOL simulative software for the study on the formation of cracking groove,it has been set different pulse energy to study in the influence on temperature field distribution of the materials.With the increase of pulse energy,the thermal effect of the materials is more obvious,the depth and width of the cracking groove increase.Controlling the size of pulse energy could guide the formation of the connecting-rod cracking groove to obtain a proper cracking groove in specified requirements;(2)Laser processing parameters include the laser parameters and mechanical controlling parameters.With the increase of laser parameters(peak power pulse,pulse width and pulse frequency),the depth and width of the cracking groove increases,so as the field angle and the curvature radius.;For the mechanical controlling parameters,with the increase of grooving speed,the depth and width of cracking groove decreases,but influence of field angle and curvature radius is not obvious.As for choosing the assistant gas and its pressure for removing the waste and quenching the surface of cracking groove.As for the off-focus value,it has been studied that the negative focal position can reach the biggest depth for cracking groove;(3)As for the micro-cracks on surface of cracking groove and its growth under the influence of process parameters,it has been studied that with the decrease of peak power and the increase of grooving speed,the length of micro-crack decreases and it has a scattered arrangement on the surface of cracking groove.The higher the peak power,the longer the micro-crack length,so the crack density increases,which is mainly affected by cementite.With the increase of peak power,the average width of micro-cracks decreases first and then increase,which is mainly affected by oxide;(4)To obtain a process parameters optimization for actual connecting-rod production,the significance of influencing factor between peak power,pulse width and pulse frequency affecting to quality parameters of cracking groove has been studied.It also study the interaction between peak power and pulse width resulting in the change of the depth and width of cracking groove,which provide a basis for parameter selection in connecting-rod production.In the end,using the result of orthogonal experiment,the predictive parameters of JL4T18 connecting-rod have been obtained.Then it gets a relevant result,successfully used in practical production.