Research On Continuous Friction Welding Technology Of Hydraulic Cylinder Piston Rod Of Excavator

Hydraulic cylinder is one of the core components of construction machinery,and its performance directly determines the reliability and service life of engineering machinery products.At present,the earrings of the hydraulic cylinder piston rod and the rod body are mainly welded by gas protection.This welding method is not only inefficient,but also often has quality problems such as poor weld fusion,porosity,and inclusion.In order to ensure the welding quality of the piston rod,improve the qualification rate of the product and its service life,Xuzhou Xugong Hydraulic Co.,Ltd.introduced the friction welding technology of the hydraulic cylinder piston rod and conducted in-depth research.The friction welding technique is a welding method in which a joint base material is melted by frictional heat,and then an upset force is quickly applied to obtain a qualified weld bead.The state of the base metal,the welding parameters,the presence or absence of plating and the post-weld heat treatment method all have a certain influence on the weld bead performance.Therefore,this paper mainly studies the friction welding process of piston rod from three aspects: welding material preparation,parameter selection and post-weld heat treatment.In terms of welding parameters,the effects of frictional pressure,friction time,upset pressure and dwell time on the mechanical properties of welded joints are mainly studied.In the state of welding consumables,the effects of electroplating and end-face structure on the mechanical properties of joints are mainly studied.Finally,the heat treatment was carried out for the case where the impact strength of some weldments after welding was low.For piston rods with a diameter of 85 mm,when pre-plating welding is used,the friction pressure is 7.6 MPa,the friction time is 19 s,the upset pressure is 14.3 MPa,the upset time is 16 s,and 870°C is used for zero-time quenching after welding.Then,at 520°C for tempering and holding time of 140 min,the tensile strength of the piston rod welded joint can reach 800 MPa or more,the area shrinkage rate can reach 50% or more,and the joint qualified rate of 100% can be achieved.At the same time,the host did not have any welding quality problems during use,and achieved the expected research goals.It lays the foundation for theoretical research and engineering practice for the manufacture of engineering hydraulic cylinder piston rods and even the improvement of hydraulic equipment manufacturing technology and technological innovation.After quenching and tempering,through the tensile test of the weldment,the microscopic observation of the metallographic structure,the macroscopic and microscopic morphology analysis of the tensile fracture,it can be found that the “zero insulation” quenching heat treatment process can refine the grain and improve the weldment.Comprehensive mechanical properties.In other words,the strength and plastic toughness of the welded sample interface after the above quenching and tempering treatment are significantly improved compared with that before the heat treatment.Among the many factors affecting the tensile strength of friction welded joints,four factors,such as main friction pressure,main friction time,upset forging pressure and upset forging pressure,have a great influence on it.Among them,the different levels of forging pressure holding time have the greatest influence on it.The influence of upsetting pressure is second only to the holding time.The main friction pressure has little effect on the tensile strength of welded joints,and the main friction time has the least influence.In the quenching and tempering process,the influence on the tensile strength of the joint is,in descending order,the quenching holding time,the quenching temperature,the tempering temperature and the tempering holding time.In addition to the quenching and holding time,the influence of the other three factors on the joint strength is basically the same.Through the study of the state of the base metal before welding,it can be found that the welded joint with tensile strength higher than 800 MPa can be obtained whether it is pre-plating or post-plating.However,the tensile strength of the post-weld welded joint is lower than that of the pre-plated weld,and the welded joint before the plating is plastically fractured,and the welded joint is brittle fracture after plating.When producing a large diameter rod by friction welding,a welded structure with a convex center should be selected,which is generally an end surface with a convexity of 2°.This structure promotes the uniformity of the heating of the entire end face,ensuring that the entire welding surface can reach the required welding temperature.