Study On Vibration And Cutting Mechanism Of The End Face Of Retro-reflective Pyramid Sheet

With the development of the time and the change of society,the demand for special functional microstructures is increasing in the fields of road traffic,clothing,electronic manufacturing,etc.People place a high priority of the high efficiency,low-cost and high-quality manufacturing of microstructure functional surfaces.Retro-reflective pyramid is a kind of micro-structure functional surface with great potential because of its super-high retroreflection efficiency.However,its topology is complex and its manufacturing is extremely difficult,so the traditional overall processing method of die can no longer meet the processing requirements.Therefore,the processing method of processing prism structures on the end faces of multiple sheets and then splicing them to form a complete total reflection prism array mold is adopted.The retro-reflective pyramid array has high surface quality requirements,and most of them are machined by ultra-precision machining.At the same time,the retro-reflective pyramid has the characteristics of complex topological structure and poor rigidity of its thin sheet wall,and its machining process is poor,so it is easy to vibrate under the action of cutting force,which seriously affects machining surface quality.Therefore,cutting the end face of retro-reflective pyramid thin sheet has always been an internationally recognized manufacturing problem.In order to suppress the cutting vibration of thin sheets and improve the surface quality of thin sheets,this thesis establishes a dynamic model of cutting vibration of thin sheets based on the theory of string vibration,and explores the corresponding relationship between preload and natural frequency of thin sheets.By analyzing the cutting mechanism of thin sheet end face and improving the traditional processing method of thin sheet end face,a pre-tightening device for thin sheet die cutting is designed,and cutting experiments of thin sheet end face under different pre-tightening forces are carried out.The main contents are as follows:(1)Analysis of the dynamic characteristics of the thin sheet.Based on the theory of transverse vibration of string and torsional vibration of a rod,the differential equations of transverse and torsional vibration of sheet are derived.According to the vibration differential equation,the transverse and torsional vibration models of the cutting process are established pursuant to the pre-tightening condition.According to the vibration model,cutting force and pre-tightening force is the basic parameters to determine the amplitude and frequency of cutting vibration.With the increase of pre-tightening force at both ends of the sheet,the natural frequency of the sheet increases obviously,and the amplitude of vibration decreases obviously during the cutting process of the sheet.(2)The finite element simulation and test of the vibration characteristics(natural frequency and vibration mode)of the thin sheet are carried out.Firstly,the vibration characteristics of pre-tightening sheet are simulated by model.By changing the factors that affect the natural frequency of sheet(aspect ratio of sheet cross-section,pre-tightening force of sheet),the influence of aspect ratio of sheet cross-section on natural frequency of sheet is explored,and the relationship between pre-tightening force and natural frequency of sheet is established.Secondly,the modal hammering experiment is carried out under different pre-tightening forces by using the cutting pre-tightening device of sheet die,and the relationship between pre-tightening force and the natural frequency of the sheet is explored.Finally,the vibration model of the end face of the sheet is verified by finite element simulation and test results.The results are show that the vibration modes of the sheet are mainly transverse vibration and torsional vibration,and the natural frequency of the sheet increases continuously with the increase of preload.The results of simulation,experimental and theoretical calculation are consistent with the variation law of the pre-tightening force and the natural frequency,which prove the validity of the vibration dynamic model of the sheet.(3)Based on the vibration dynamic model of the thin sheet,the continuous and intermittent cutting process of the thin sheet is analyzed,and the cutting characteristics of the pre-tightening thin sheet end face(including the deflection characteristics of the thin sheet and the variable cutting angle characteristics of the cutter)are analyzed,and the geometric model of the cutting profile of the thin sheet end face is established.The results show that the machining deformation of the pre-tightening sheet in the cutting process is mainly affected by the torsional deformation of the sheet,and increasing the torsional stiffness of the sheet can effectively improve the surface machining quality.(4)Cutting experiment of retro-reflective pyramid sheet end face.Aiming at the problem that the end face of sheet can’t be pre-tightened during cutting,a pre-tightening device for sheet die cutting is designed.After completing a series of orthogonal experiments of cutting parameters to machine the end face structure of the sheet,and obtaining better cutting parameters in the orthogonal experiments,the cutting experiment with variable pre-tightening force shows that The machining surface quality is the best when the pretension force is 850 N.