磁研法在模具曲面中的抛光机理与技术研究

针对目前模具自由曲面抛光过程的难加工问题.按照模具曲面抛光要求,结合电磁场理论,提出采取磁性的磨料,通过磁场中磁力的作用实现对模具自由曲面型腔抛光加工的新工艺.从磁力研磨的加工特点着手,对抛光工艺过程的主要参数进行分析,并对磁力研磨运动轨迹的规划和生成进行探讨,提出自由曲面磁力研磨时获取均匀表面去除的方法.     

基于UG软件的芯盒内表面抛光路径生成方法

近些年,随着数控技术和CAD／CAM技术在模具工业中的广泛应用,数字化和机器人等抛光方法对复杂模具曲面进行抛光处理的应用得到了较快的发展,并成为模具曲面加工中行之有效的方法。本文针对芯盒内表面抛光过程中的不同抛光曲面,分析了UG模具曲面加工运动中各种路径的生成方法;     

基于MasterCAM的模具曲面抛光路径生成方法研究

为提高模具曲面抛光的表面质量和效率,采用数字化自动抛光不失为一种好的方法,MasterCAM是常用的CAD/CAM加工软件之一,根据目前MasterCAM软件的曲面加工路径设定方法,着重对模具曲面抛光路径生成方法进行探讨.并针对模具表面的不同曲面采取了相应的抛光路径生成方法,以获取较理想的抛光效果.     

应用于模具自由曲面的新型气囊抛光技术

为提高模具自由曲面抛光的效率和品质,提出一种基于柔性抛光理念的新型气囊抛光技术。建立相应的机器人抛光系统,研究旋转型膨胀气囊抛光工具及抛光过程中各因素对抛光表面粗糙度的影响。对气囊抛光工具的位置和姿态控制问题以及抛光工具,以一定下陷深度和倾斜角度与被抛工件接触时的接触区域的相关特性进行分析。在机器人抛光系统上进行抛光正交试验和试验数据分析,获取表面粗糙度的不同影响因数的最优参数组合,试验中被抛光曲面平均表面粗糙度达到了0.007 μm。研究结果表明,气囊抛光技术可实现抛光工具与被抛光工件的大面积柔性接触,通过气囊内部气压的调节和机器人抛光系统对抛光工具的运动轨迹和姿态的精确控制,可有效地提升自由曲面抛光的品质和效率。     

曲面磁力抛光刀具路径规划与驻留时间算法研究

复杂曲面的自动抛光加工方法与效率一直是困扰模具曲面加工的难题,将磁力抛光与数字化测量、控制技术相结合,可以较好地解决曲面抛光加工的效率与自动化问题。参考数控加工理论,对自由曲面加工的刀具轨迹以及轨迹生成算法进行了分析,重点探讨了抛光刀具的驻留时间控制算法。     

面向精密抛光的复杂模具曲面三维重构方法

针对机器人辅助模具精密抛光系统发展的要求,提出了一种复杂模具曲面三维重构方法。分析了模具抛光件型线三维重构方法的原理和实现过程,并详细讨论了面向精密抛光的复杂模具曲面三维造型方法的关键技术,包括节点的选取、端点切矢的选取等;给出了在精密抛光系统中,复杂模具自动抛光曲面的编程控制策略和实现方案。应用所提的面向精密抛光的复杂模具曲面三维重构方法能使精密抛光系统在加工的不同阶段始终蕴涵不等的模具曲面加工信息,从而提高了抛光效率和产品质量,并降低了工人劳动强度。     

基于接触特性优化的模具曲面气囊抛光实验研究

为提高模具自由曲面上的气囊抛光加工效果,在六自由度气囊抛光实验平台上对不同曲率半径的二维曲面模具进行了气囊抛光实验研究。首先,研究了模具自由曲面上不同曲率表面对于气囊抛光过程中接触区域的接触面积、接触宽度,接触力和抛光效果的影响规律;在此基础上,提出了在气囊抛光过程中通过调节气囊抛光头的下压量和内部充气压力来改变接触面积、接触宽度和接触力值的方法,使抛光时不同曲率表面接触区域内的平均接触压力相同,且沿运动方向的接触宽度也相同,从而使不同曲率表面在抛光后的抛光质量接近,使整个模具自由曲面的抛光效果达到最佳;最后,运用上述方法对二维曲面模具进行了抛光实验。实验研究结果表明,经过接触特性优化,不同模具曲率表面气囊抛光后接触区域内的抛光质量接近,抛光效果得到提高。     

机器人模具抛光自由曲面刀具轨迹的生成研究

以HNC-IR教学机器人为对象,对机器人模具抛光中自由曲面的抛光刀具轨迹的生成和干涉处理进行了研究,提出了适合于机器人抛光的面自由曲面刀具轨迹生成算法,此算法生成的抛光刀具轨迹具有形式简单、在曲面表面分布均匀等优点,适合于机器人抛光。     

模具曲面抛光工艺知识的获取

针对模具曲面抛光工艺规划专家系统开发中的抛光工艺知识的获取问题进行了研究,在分析了模具曲面抛光工艺过程的基础上,探讨了抛光工艺知识的特征,给出了抛光工艺知识的获取方法,为模具抛光工艺过程的智能化奠定了基础。     

工业机器人模具抛光方法研究及仿真

提出了一种针对复杂型腔模具使用工业机器人进行抛光的方法,该方法可以实现稳定的力控制和精确的位置控制,且此抛光方法很易在线实现。为了保证模具不同法矢量曲面材料去除率的一致,提出根据曲面法矢量实时地调整电主轴转速的方法。系统刚度不同的机器人抛光需要采用不同的PI参数,该自适应PI控制算法可以进行抛光系统刚度的评估和PI参数的调整。仿真结果表明该方法可以很好地实现模具的抛光。     

Research on unbounded abrasive polishing process with assisted ultrasonic vibration of workpiece

Ultrasonic-assisted machining was an effective method to improve the material removal quality especially to difficult-to-cut metal materials. The ultrasonic vibration was usually superimposed on the machining tool but seldom on the workpiece, although the ultrasonic vibration of workpiece could improve the processability of material more effectively. In this paper, a rectangle hexahedron ultrasonic sonotrode with optimized slots was developed as a platform to realize the assisted ultrasonic vibration of workpiece and the ultrasonic-assisted polishing process of austenitic stainless steel was also studied. The unbounded abrasive was selected as polishing medium, and the path compensation strategy of soft polishing tool was carried out for getting uniform polishing force. The orthogonal experiments were designed to study the optimization of ultrasonic polishing parameters and the relation between different types of ultrasonic polishing path and polishing quality. The results appear that the horizontal ultrasonic vibration of workpiece can reduce polishing force and improve polished surface roughness, which can also reinforce the proportion of plastic shear effect in the material removal process. The ultrasonic polishing path keeping consistent with workpiece vibration direction can get more uniform polishing force and better surface roughness. And the 45° oblique crossing ultrasonic path can get the maximum average polishing force reduction by 75.2 %.     

Theoretical and experimental investigation of surface generation in swing precess bonnet polishing of complex three-dimensional structured surfaces

Three-dimensional structured surfaces (3D-structured surfaces) possessing specially designed functional textures are widely used in the development of advanced products. This paper presents a novel swing precess bonnet polishing (SPBP) method for generating complex 3D-structured surfaces which is accomplished by the combination of specific polishing tool orientation and tool path. The SPBP method is a sub-aperture finishing process in which the polishing spindle is swung around the normal direction of the target surface within the scope of swing angle while moving around the center of the bonnet. This is quite different from the ‘single precess’ and ‘continuous precessing’ polishing regime, in which the precess angle is constant. The technological merits of the SPBP were realized through a series of polishing experiments. The results show that the generation of complex 3D-structured surfaces is affected by many factors which include point spacing, track spacing, swing speed, swing angle, head speed, tool pressure, tool radius, feed rate, polishing depth, polishing cloth, polishing strategies, polishing slurry, etc. To better understand and determine the surface generation of complex 3D-structured surfaces by the SPBP method, a multi-scale material removal model and hence a surface generation model have been built for characterizing the tool influence function and predicting the 3D-structured surface generation in SPBP based on the study of contact mechanics, kinematics theory, abrasive wear mechanism, and the convolution of the tool influence function and dwell time map along the swing precess polishing tool path. The predicted results agree reasonably well with the experimental results.     

Modelling of the Polished Profile in Computer-Controlled Polishing by a Sub-Aperture Pad

High-quality part surfaces with high surface finish and form accuracy are increasingly in demand in the mold/die and optics industries. The computer-controlled polishing (CCP) is commonly used as the final procedure to improve the surface quality. This paper presents a theoretical and experimental study on the polished profile of CCP with sub-aperture pad. A material removal model is proposed based on the evaluation of the amount of material removed from the surface along a direction orthogonal to the tool path. The model assumes that the material removal rate follows the Peterson equation. The distribution of the sliding velocity at the contact region is presented. On the basis above, the approaches to calculate the polished profiles are developed for the sub-aperture pad polishing along a straight path and a curved path. The model is validated by a series of designed polishing experiments, which reveals that polishing normal force, angular spindle velocity, feed rate and polishing path all have effects on the polished profile. The result of experiments demonstrates the capability of the model-based simulation in predicting the polished profile.     

Numerical analysis of hydrodynamic process of circular-translational-moving polishing (CTMP)

By keeping a pad moving relative to a wafer along a circular path without rotation, we developed a polishing technique called circular-translational-moving polishing (CTMP), which permits multidirectional polishing of the work piece and thus bears the advantage of isotropic polishing and a potential increase of material removal rate (MRR) on the wafer. To illuminate the mechanisms of CTMP and determine the optimum process variables in a CTMP process, a three-dimensional hydrodynamic lubrication model for CTMP with a smooth and rigid pad under a quasi-stable state is established in a polar coordinate system. The model equations are further calculated numerically by the finite difference method. The instantaneous distribution of fluid pressure is obtained, which shows that a negative pressure exists. The reason for negative pressure in CTMP and its effect on polishing is discussed. Moreover, the nominal clearance of the fluid film, roll, and pitch angles under different working conditions are obtained in terms of the applied load, moments, and polishing velocity. The obtained numerical analysis can be used as guidance for choosing operation parameters in a practical CTMP application.     

Numerical analysis of hydrodynamic process of circular-translational-moving polishing (CTMP)

By keeping a pad moving relative to a wafer along a circular path without rotation, we developed a polishing technique called circular-translational-moving polishing (CTMP), which permits multidirectional polishing of the work piece and thus bears the advantage of isotropic polishing and a potential increase of material removal rate (MRR) on the wafer. To illuminate the mechanisms of CTMP and determine the optimum process variables in a CTMP process, a three-dimensional hydrodynamic lubrication model for CTMP with a smooth and rigid pad under a quasi-stable state is established in a polar coordinate system. The model equations are further calculated numerically by the finite difference method. The instantaneous distribution of fluid pressure is obtained, which shows that a negative pressure exists. The reason for negative pressure in CTMP and its effect on polishing is discussed. Moreover, the nominal clearance of the fluid film, roll, and pitch angles under different working conditions are obtained in terms of the applied load, moments, and polishing velocity. The obtained numerical analysis can be used as guidance for choosing operation parameters in a practical CTMP application.     

Development and Polishing Process of a Mobile Robot Finishing Large Mold Surface

□ A novel self-determination polishing robot finishing large mold free-form surface is developed, and the finishing process method is researched. Contrary to traditional approaches, our premise is that a large mold surface can be polished by using a small robot. This robot system is mainly composed of a polishing robot part, a computer system and a visual positioning system. A type of robot with four uniform distribution wheels was designed, which has two driving wheels and two driven wheels. Active compliant control of the polishing tool was provided by a pneumatic servo system, and a new special compliant abrasive tool was proposed on the basis of robot characteristics. The process planning steps consisted of subdividing the free-form surface, choosing an abrasive tool, planning the polishing path and optimizing machining parameters. Based on the orthogonal experiment and the grey relational analysis method, the optimal parameter combination was obtained for polishing force, tool speed and feed rate. Aiming to polishing times, the surface roughness method and polishing efficiency method were studied in detail. The polishing experiments were carried out in the robot using process parameters obtained by the efficiency method. These research results provided significant theory foundation and experimental data for a mobile robot planning polishing to realize intelligible process parameter selection.     

Magnetic polishing of three dimensional die and mold surfaces

A new magnetic polishing technology applicable to die and mold manufacturing has been studied using the magnetic polishing tool. The key idea is that magnetic force is used to produce the polishing pressure so that polishing of curved surfaces can be possible without exact control of tool path. This makes the polishing automation of dimensional dies and molds very easy. In this study, experiments have been executed using the magnetic polishing tool and mini CNC milling machine without tool path control. Some mirror-like surfaces have been acquired by two stages of polishing: firstly, wheel type magnetic polishing and, secondly, magnetic abrasive polishing.     

不锈钢电水壶曲面机械抛光方法研究

为解决不锈钢电热水壶在手工抛光方式中存在的污染严重、抛光效率低和质量不稳定等问题,成功自主研发了一套电水壶曲面自动化机械抛光系统,该系统采用了多磨具多工位的抛光方法,可夹持三个水壶同时进行抛光,提高了抛光效率。为确保水壶表面抛光质量,规划了螺旋式刀具路径,同时提出了基于示教法的抛光刀位数据生成方法,并利用NURBS曲线拟合的方法对刀具轨迹进行优化。实验结果证明,与手工抛光方式相比较,该方法大大提高了抛光质量和效率。     

Trajectory planning of optical polishing based on optimized implementation of dwell time

This paper presents a study on the trajectory planning of optical polishing based on an optimized implementation of dwell time to improve the polishing quality and efficiency of optical surfaces. The large-scale, sparse, and ill-posed linear equation solution is transformed into a quadratic programming problem with boundary constraint, and the monotone projection gradient method is adopted to obtain an optimal dwell time solution by considering its fluctuation characteristic. Then, parametric polishing paths are constructed using cubic B-spline curves to guarantee one-to-one correspondence between each curve segment and dwell time of a removal spot. Finally, an interpolation process of polishing trajectory is proposed on the basis of the equal–proportional feed rate adjustment strategy to improve the implementation accuracy of dwell time. Simulation and experimental results show that the proposed dwell time algorithm and spline interpolation method can considerably improve the solution accuracy of dwell time and the convergence rate of the form error during polishing. These results provide important scientific basis and technical support for the high-efficiency and high-precision polishing of large-aperture aspheric optical surfaces.