Design And Analysis Of Pre-stress Grinding Fixture And Loading System

Pre-stress Grinding Hardening(PSGH)is a technique of integrating pre-stress grinding with grinding hardening.Pre-stress cutting is a technique which could reduce residual tensile stress effectively.Furthermore,the technique could even transfer the stress state of surface from tensility to compresion.Grinding hardening is a technique that could utilize a large amount of heat produced by grinding to quench the surface of workpiece.The PSGH process have both advantages of two techniques we discussed above,it can reduce using coolant and cost of production.Therefore the PSGH can be environment-friendly and be benefit to sustainable development and green manufacture.Based on previous researches which investigate pre-stress cutting and grinding hardening separately,this thesis explores the possibility of integrating them together.Due to the complex process of formation of residual stress on surface,which involve temperature change,rapid cooling speed and transformation of metallographic structure(from austenite to martensite),etc,there is no equation for relation between pre-stress and residual stress.To determine the equation,this thesis designs a pre-stress fixture which can provide accurate pre-stress.Focusing on pre-stress fixture,this thesis presents following contributions:1.For providing axial force for workpiece with fixture,a screwdriven device which converse torque to axial force is invented.The numerical relation between pre-stress of workpiece and torque of screw is calculated based on geometry and physical theory.To raise the range of pre-stress,a new power supply device with step servo motor(DC)and planetary reducer is used to replace former scheme and the new one rasie 60%of pre-stress range.A control system with feedback is designed to increase the accuracy of pre-stress.Finally,the fixture could provide about up to 4.4 ton axial force and down to 4.4 degree per second.2.Analyzing the structure of fixture with finite element method is to check stability and reliability of fixture.Meanwhile,to determine the parameters of grinding process(involving grinding depth,rotating speed of grinding wheel and etc.),analysis of modal of the whole fixture has been done.Natural frequency and its correspond mode of vibration is presented in the thesis.Based on harmonic response analysis,the amplitude of surface on workpiece is controled within 1.27e-5?1.75e-3mm.3.To determine to real strain change on the surface,a series of experiments using strain gauge were designed.The equations of relation between torque and pre-stress and the relation between strains on workpiece and on a part of fixture are established by analyzing the experimental data eventually.Data fitting by least square method and BP neural net method are used to establish the equations.Error analysis of both methods are presented in the thesis.The results of experiment suggest that the new control system can increase 12%to accuracy of pre-stress.