Study On The Surface Ultrasonic Rolling Strengthening And Fatigue Behavior Of The Cam-Tappet Contact Pair Material Of Engine Valve Train

The cam-tappet mechanism of the valve train system is one of the key parts to ensure the reliability and service life of the engine.The function of this mechanism is that controlling the opening and closing of valve to take in fresh air and discharge gas.In normal working condition,the cam and tappet are in contact under high-load cyclic alternating stress indicating that the working condition is significantly harsh.In this case,the contact surface is prone to fatigue failure and sliding wear,which impacts the working of valve train system and even the entire engine.Therefore,it is extremly significant that to study the strengthening processing of the contact fatigue and sliding wear performance of cam and tappet materials.In this dissertation,the surface ultrasonic rolling processing(SURP)is applied to strengthen the cam material C53 and the tappet material GCr15.The authors studied the surface properties,contact fatigue and sliding wear performance of the two materials at different SURP parameters.The main research results are as follows:(1)The surface properties of cam material C53 and tappet material GCr15 at different SURP parameters were studied.The study found that when the SURP 3 passes,C53 material can obtain the best comprehensive surface properties at the static pressure of 600 N.And at SURP 3 passes,GCr15 material obtains the best surface morphology at 1000 N,and the highest microhardness and residual compressive stress at 1200 N.Under the specified static pressure,C53 material gain the best comprehensive surface properties at SURP 3 passes.And 3 passes SURP can help GCr15 material gain the best surface morphology and the highest residual compressive stress,but 5 passes SURP to obtain the highest microhardness.(2)In the study of the effect of SURP parameters on the contact fatigue performances of cam material C53 and tappet material GCr15,it was found that the changes of fatigue resistance of the cam and tappet materials show the same trend of rising first and then falling as the increase of static pressure at SURP 3 passes.And at the static pressure of 600 N and 1000 N,the cam material and the tappet material showed the best contact fatigue performance respectively.At the specified static pressure(the static pressure of the cam material is 600 N,and the tappet material is 1000 N),the contact fatigue performances of the two materials have the same tend that go up first and then fall down with the increase of SURP passes(1/3/5 passes respectively).The two materials both reached the best contact fatigue performances at SURP 3 passes.(3)The sliding wear performances of cam material C53 and tappet material GCr15 at different SURP parameters were studied.The research result shows that at SURP 3 passes,as the rising of static pressure,the sliding wear performance of the two materials have the same tend which increase first and then decrease.And cam and tappet materials gain the best sliding wear performance at the static pressure of 600 N and 1000 N respectively.At the specified rolling static pressure,the sliding wear performances of the two materials increase first and then decrease simlarly as the increase of SURP passes,and the best performance is obtained when processing passes is 3 respectively.