Theoretical And Experimental Investigations On Ultrasonic Vibration Assisted Turning Of Difficult-to-Cut Materials

Taking the processing quality,metal removal amount,productivity and capacity utilization into consideration,the turning process is a widely used and economical machining approach.However,along with the extensive use of various precision instruments and components,there is an increasing demand for the machining precision and processing quality.At the same time,various difficult-to-cut materials have gained widespread application and the quantity of turning processing has been increased in the mechanical manufacturing,which enable the difficulty of turning processing to be unceasingly enhanced.For the conventional turning technique,as it is generallyaccompanied by the problems containing big cutting force,chip removal di:fficulties,and serious tool wear in cutting process,these can lead to worse machining quality,lower machining efficiency and higher cost of machining.The conventional turning includes significant limitations,nevertheless,the ultrasonic vibration assisted turning,which is a new type of special processing method,has provided a novel approach for high quality and efficiency processing of difficult-to-cut materials.The special machines for ultrasonic vibration assisted machining have beenmanufactured in the domestic and overseas;however,this kind of special machine has the disadvantages of small application range,high fabricating cost and inferior universality,so the special machines are not conducive to popularization.In view of the above reasons,the ultrasonic vibration system is installed on the general machine tool in this research to meet the requirement of the ultrasonic vibration cutting in actual production.Additionally,three widely used and typical difficult-to-cut materials are applied to the experimental research,and the machining effect of ultrasonic vibration assisted turning is analyzed particularly from the aspects of machined surface quality,cutting force,tool wear and chip morphology.The investigation will provide theoretical support and experimental basis for the progress and application of the ultrasonic vibration assisted turning of difficult-to-cut materials.The main research contents of this paper are as follows.(1)This research analyzes the principle of ultrasonic vibration assisted turning and the composition of machining system.For the challenge that machining difficulties of difficult-to-cut materials and higher demands for the machining quality and efficiency represent,starting with cutting principle and processing technology,the ultrasonic vibration method is employed to scheme out a ultrasonic vibration system and special fixture,which are installed into the CA6140 type general-purpose lathe.Consequently,the machining system of ultrasonic vibration assisted turning,of which vibrational frequency is 20 kHz and the ultrasonic amplitude is adjustable,is established.Furthermore,the designed machining system can realize a turning with and without ultrasonic vibration.(2)The machined surface formation mechanism of ultrasonic vibration assisted turning is researched,and the machined surface quality evaluation method is introduced in the thesis.The experiments for turning the workpiece of 304 austenitic stainless steel are performed with and without ultrasonic vibration using the designed machining system of ultrasonic vibration assisted turning.And the machined surface topography of ultrasonic vibration assisted turning is analyzed in comparison to that of conventional turning.Moreover,this paper studies and analyzes the influence rule of the ultrasonic amplitude,cutting speed,depth of cut and feed rate on the 3D surface roughness Sa and Sq,3D surface topography and surface microtopography.(3)The generation mechanism of cutting force in ultrasonic vibration assisted turning,with the composition and decomposition of cutting force is discussed in the dissertation,and the cutting force model is established.The cutting force test system is designed on the basis of the established machining system of ultrasonic vibration assisted turning.The contrast experiments for turning the workpiece of 304 austenitic stainless steel are conducted systematacially with and without ultrasonic vibration under the condition of diverse process parameters.In addition,the influence rule of process parameters on cutting force is researched.And the relational model between process parameters and cutting force is obtained by analysis of regression.Thereby,the mutual relation among these process parameters is effectively controlled,and the high-quality and high-efficient processing is ultimately achieved.(4)The tool wear mechanism of ultrasonic vibration assisted turning is revealed through analyzing the main form,cause and influence factors of tool wear.The model of the friction between flank face of cutting tool and workpiece in ultrasonic vibration assisted turning is applied to analyze inhibiting effect of ultrasonic vibration on the tool wear.And the experiments for turning the workpiece of 304 austenitic stainless steel with ultrasonic vibration are performed to verify the inhibiting effect of tool wear.Additionally,this paper studies the effect of ultrasonic vibration parameters and cutting parameters on the tool flank wear land width and the tool wear conditions of rake face and flank face.These studies can facilitate to promote tool life.(5)The type and change of the chip are presented,and the chip formation mechanism of ultrasonic vibration assisted turning is analyzed in the paper.The chips,obtained by turning the workpiece of 304 austenitic stainless steel under the condition of diverse process parameters,are collected,and the distinction between the chip morphology of ultrasonic vibration assisted turning and that of conventional turning is contrastively analyzed from the perspective of the macro morphology and micro morphology of chip.Meanwhile,the change of chip morphology and related causes are studied when cutting speed,depth of cut and feed rate are increased respectively,thus obtaining the relation between chip morphology and machined surface quality,cutting force and tool wear.(6)In order to further verify that ultrasonic vibration assisted turning has advantages of superior machining effect,which is harder to achieve by conventional turning,and suit to turning not only the 304 austenitic stainless steel but also other difficult-to-cut materials,so the experiments for turning the workpieces of GH4169 Ni-based superalloy and 5A06 Al-Mg alloy are performed with and without ultrasonic vibration.Besides,the surface roughness,surface topography of machined workpiece and chip morphology conditions are analyzed.Simultaneously,the experimental results,obtained by turning the three difficult-to-cut materials,are contrastively analyzed.Ultimately,the influence rules of ultrasonic vibration assisted turning on machining diverse materials are obtained.