| Rapid development of made in China.The increasing demand for sheet metal in terms of production and quality needs to improve the processing level of sheet metal technology and promote the large-scale development of sheet metal processing.In this paper,the die-changing device,as a major part of sheet metal bending processing,is taken as the research object and have been deeply studied about the scheme and structure design,the optimization of key mechanism and the reliability of motion accuracy.This paper mainly completes the following research work:On the basis of analyzing and discussing the overall scheme of the die changing device for sheet metal bending dies,the innovative design scheme of the die loading and unloading mechanism is researched: The 2-DOF eleven-bar mechanism composed of a spatial four-bar mechanism and 2-DOF seven-bar mechanism in series and parallel combination,combined with the planar four-bar mechanism,completes the process of die-loading and die-unloading;all 2-DOF eleven-bar kinematic chain type are analyzed and screened,and the kinematic chain type of the die-loading and die-unloading mechanism is determined;by adopting the innovative design method of metamorphic mechanism,the position limit is used to reduce the degree of freedom;thus,a new design scheme of the loading and unloading mechanism of sheet metal dies is obtained.For the sheet metal die-loading and die-unloading mechanism,disassembles the multi-bar mechanism and synthesizes the scale of the slider-crank mechanism by the method of rigid body guidance;by using the Pythagorean theorem,the dimensional equations of the mechanism are established and the parameters of the mechanism are solved;the dimensions of four rods in space are calculated by using the coordinate numerical analytic method;the three-dimensional model of the die-changing device is established,and the kinematic simulation analysis of the die-loading and die-unloading mechanism is carried out,and the kinematic characteristics of the device are obtained,it provides a basis for optimizing some characteristic parameters which affect the stability of the whole motion.By using graphical method and mathematical analysis method,the die-taking mechanism of the die-loading and die-unloading mechanism is optimized from the aspects of structure optimization and CAM follower movement track,which solves the problem of sudden speed change and avoids the impact of the mechanism;the motion law of the servo motor is improved,also the precision,stability and service life,but the motion impact of the slider is reduced;based on the Sensitivity analysis,an optimization mathematical model is established,which aims at the acceleration of the down-sliding block.The optimization results show that the peak acceleration of the down-sliding block is reduced by about 30% at the key stage,the pressure angle is in the best range of-45 ° ～ 45 °.For the sheet metal die-loading and die-unloading mechanism,a motion mathematical model is established which aims at the forward movement and the direction of taking die.The error of the die-loading and die-unloading mechanism is analyzed under different combinations of three conditions: dimensional error,clearance error and part wear and the reliability model of its motion accuracy was constructed.The calculation results verified that the device can meet the design requirements under the circumstances of each error,and can complete all the actions accurately and stably. |
