通过恰当选择无心磨削循环时间来提高工件圆度

在无心磨削中可获得的工件圆度直接与磨削过程中所选择的循环时间长短有关。本文提出了一种能通过恰当选择循环时间来达到降低工件圆度误差这一目的的系统方法。本文首先研究了成圆过程中的瞬间特征，且当初始圆度误差被有效排除而棱圆形还未能在工件表面完全展开之时，就能获得上面所提到的工件圆度的最小误差值。然后介绍的是这种应用于切入式无心磨削及通磨无心磨削过程中的计算机模拟方法，它是通过选择最佳的磨削循环时间来达到将工件圆度误差值减至最小值这个目的的。最后介绍的是通磨无心磨削过程中能评估棱圆稳定性的平均增长率概念。     

提高薄壁缸套在无心磨机床上磨削合格率的改进措施

针对批量生产中薄壁缸套在无心磨机床上磨削的合格率只有90％左右的问题,找出薄壁缸套磨削后产生“棱圆度”、“棱边形”、“锥度”等主要误差项目的成因；通过改进缸套中心位置、托板与磨轮的位置、导板的位置,以及调整冷却方式、确定合理的磨削用量、磨削条件等措施,将产品合格率提高到99％以上,取得了显著的经济效益.这种改进措施对于其他薄壁套筒类零件的精加工外圆表面磨削具有一定的参考价值.     

高精度无心磨削圆度保证和成圆过程解析

为了对无心磨削的圆度误差进行研究,讨论了影响高精度无心磨削过程的关键因素,包括稳定性、磨削参数、砂轮和导轮,给出了改进圆度误差的措施。在时域内对无心磨削成圆过程进行了解析。在解析研究中考虑了成圆过程的非线性环节,通过工件的轮廓和工件与砂轮、托板和导轮之间的作用研究工件的成圆过程。实验结果和理论结果的对比显示,解析模型可以对成圆过程进行准确预测。     

无心磨床中心高对硬质合金微钻圆度的影响研究

无心磨中心高对硬质合金微型钻头柄部圆度有显著影响,中心高过低将导致柄部圆度呈三边形或五边形。这篇文章探讨无心磨中心高对硬质合金微钻柄部圆度影响的原理和计算公式,运用无心磨削的成圆理论,根据工件尺寸和托板斜面角度获得最佳切削角范围,根据不同中心高算出砂轮、导轮磨损后的尺寸相应切削角,通过比较切削角所处范围选择最佳中心高,并通过试验来验证。试验结果证明,当无锡MG1020无心磨床中心高由3 mm调高到4 mm后,硬质合金微钻柄部半精磨和精磨圆度都有显著改善,不但圆度数值减小,而且圆度图形无三边形或五边形。试验结果与理论分析一致,说明适当增加无心磨中心高能改善圆度,特别是能有效消除低次奇数边形。但中心高过高会导致加工不稳定,须理论计算结合试验确定最合适的高度。     

新型无心磨削技术研究及其在微细工件加工中的应用

提出一种用于微细工件加工的新型无心磨削技术。该技术采用超声椭圆振动板取代传统无心磨床中导轮,在加工中超声椭圆振动板和托板共同支撑和控制工件的运动。通过FEM优化设计超声振动板的结构;利用测试系统对其性能进行测试,确保超声振动板端面振动轨迹可以通过施加在PZT上的输入参数来控制;通过工件转速评价装置证实振动板端面超声椭圆振动能精确控制工件旋转速度。在改进后的无心磨床上对工件进行磨削实验,结果表明:硬质合金材料工件磨削后其直径为0.06 mm,长度为15 mm,长径比达到250,证实了该技术对微细工件加工的有效性。     

新型无心磨削技术研究及其在微细工件加工中的应用

提出一种用于微细工件加工的新型无心磨削技术。该技术采用超声椭圆振动板取代传统无心磨床中导轮,在加工中超声椭圆振动板和托板共同支撑和控制工件的运动。通过FEM优化设计超声振动板的结构;利用测试系统对其性能进行测试,确保超声振动板端面振动轨迹可以通过施加在PZT上的输入参数来控制;通过工件转速评价装置证实振动板端面超声椭圆振动能精确控制工件旋转速度。在改进后的无心磨床上对工件进行磨削实验,结果表明：硬质合金材料工件磨削后其直径为0.06 mm,长度为15 mm,长径比达到250,证实了该技术对微细工件加工的有效性。     

圆锥轴承套圈基准端面的不平面度对滚道形状精度的影响

无心磨削圆锥轴承的内套圈是按其外表面(在两个固定托板上)及按其基准端面(在回转磁盘上)定位的.这时达到的滚道形状精度,大多取决于套圈工件基准端面的不平面度,从而引起套圈轴线相对主轴轴线回转.     

不规则零件的无心磨削

介绍了无心磨床磨削不规则零件时的特点,阐明了无心磨削不平衡零件及局部有缺口零件的加工精度（圆度）差的主要原因是由工件的跳动引起的,通过对各种不同重量、不同形状、不平衡量及不同缺口的各类零件的无心磨削的加工精度进行分析后,归纳出无心磨削不规则零件的磨削特点,所得到的解决此类零件的磨削方法以及磨削不规则零件的最佳磨削参数,可供技术人员参考。     

圆柱零件无心磨削时导轮廓形研究

通过对砂轮、导轮、工件、托板坐标系相互位置的分析，建立了导轮廓形的数学模型，得到圆柱零件无心磨削时导轮廓形的表面特征。经过实验得出了导轮廓形面与工件半径的关系曲线。理论分析和计算表明：位移量h存在时，导轮表面是准双曲面的一部分。导轮廓形的曲率随着工件半径r的增大而减少。提出了用金刚石笔修整导轮廓形时的机床调整参数。通过数值模拟，建立了目标函数。应用参数化法获得最优参数值，提高了无心磨削圆柱零件的加工精度。     

圆度误差测量的探讨

我们在使用圆度仪测量圆度误差时 ,经常遇到调整精度达到何种程度就能够满足测量要求的问题。如果做到测量前心中有数 ,就不用去花费过多的时间进行调整 ,从而快速而准确地测量出圆度误差。下面就讨论一下影响圆度误差的测量问题。被测工件的轮廓形状总是由宏观的形状、波度和微观形状 (粗糙度 )等构成。我们一般在测量圆度误差时 ,选择滤波 1～ 5 0档 ,这样既反映了工件的有效轮廓 ,又排除了零件表面粗糙度及高中频波度的影响。在测量条件设定后 ,影响圆度测量误差的主要原因是被测工件定位的偏心和倾斜。下面分别讨论 :1)被测工件中心对圆…     

Simulation investigation of through-feed centerless grinding process performed on a surface grinder

This paper proposes a simulation method for investigating the through-feed centerless grinding process performed on a surface grinder, where a compact centerless grinding unit, composed of a guide plate, an ultrasonic elliptic-vibration shoe, a blade, and their respective holders, is installed onto the worktable of a surface grinder, and the through-feed centerless grinding operation is performed as the workpiece located on the guide plate is fed into the space between the grinding wheel and ultrasonic shoe. The geometrical arrangement of the grinding apparatus including the contact lines on the grinding wheel, ultrasonic shoe, and blade are analyzed firstly for building a 3-D simulation model. Then, the workpiece forming process and the effects of major process parameters such as the workpiece eccentric angle, the stock removal, the ultrasonic shoe tilt angle and the applied voltage amplitude on the machining accuracy (i.e. workpiece cylindricity and roundness) are clarified by simulation and experiments. The obtained results indicate that higher machining accuracy can be achieved under the conditions of larger workpiece stock removal, smaller ultrasonic shoe tilt angle and higher applied voltage amplitude, while the workpiece eccentric angle is at 6°.     

A new in-feed centerless grinding technique using a surface grinder

This paper deals with the development of an alternative centerless grinding technique, i.e., in-feed centerless grinding based on a surface grinder. In this new method, a compact centerless grinding unit, composed of an ultrasonic elliptic-vibration shoe, a blade and their respective holders, is installed onto the worktable of a surface grinder, and the in-feed centerless grinding operation is performed as a rotating grinding wheel is fed in downward to the cylindrical workpiece held on the shoe and the blade. During grinding, the rotational speed of the workpiece is controlled by the ultrasonic elliptic-vibration of the shoe that is produced by bonding a piezoelectric ceramic device (PZT) on a metal elastic body (stainless steel, SUS304). A simulation method is proposed for clarifying the workpiece rounding process and predicting the workpiece roundness in this new centerless grinding, and the effects of process parameters such as the eccentric angle, the wheel feed rate, the stock removal and the workpiece rotational speed on the workpiece roundness were investigated by simulation followed by experimental confirmation. The obtained results indicate that: (1) the optimum eccentric angle is around 6°; (2) higher machining accuracy can be obtained under a lower grinding wheel feed rate, larger stock removal and faster workpiece rotational speed; (3) the workpiece roundness was improved from an initial value of 19.90 μm to a final one of 0.90 μm after grinding under the optimal grinding conditions.     

A new through-feed centerless grinding technique using a surface grinder

This paper proposes an alternative centerless grinding technique, i.e., through-feed centerless grinding using a surface grinder. In the new method, a compact centerless grinding unit, composed of a guide plate, an ultrasonic shoe, a blade, and their respective holders, is installed onto the worktable of a surface grinder, and the through-feed centerless grinding operation is performed as the workpiece located on the guide plate is fed into the space between the grinding wheel and ultrasonic shoe. The ultrasonic shoe, produced by bonding a piezoelectric ceramic device onto a metal elastic body, is tilted at a small angle so as to provide sufficient force to control the workpiece rotational motion and to feed the workpiece along its axis by the ultrasonic elliptic-vibration. In this paper, the workpiece motion control tests were carried out firstly to make sure that the workpiece rotational speed and through-feed rate can be exactly controlled by the ultrasonic shoe which is essential for performing high-precision grinding operations. Then, the effects of major process parameters such as the workpiece eccentric angle, the stock removal, the ultrasonic shoe tilt angle and the applied voltage amplitude on the machining accuracy (i.e. workpiece cylindricity and workpiece roundness) were clarified experimentally. The obtained results indicate that: (1) the workpiece rotational speed can be adjusted by changing the applied voltage amplitude, whereas its through-feed rate can be adjusted by changing both the applied voltage amplitude and the ultrasonic shoe tilt angle; (2) the optimum eccentric angle is 6°, and a larger stock removal, a smaller tilt angle, or a higher applied voltage is better for higher machining accuracy; (3) the workpiece cylindricity and roundness were improved from the initial value of 16.63 μm and 14.86 μm to the final ones of 1.49 μm and 0.74 μm under the optimal grinding conditions.     

Effects of process parameters on workpiece roundness in tangential-feed centerless grinding using a surface grinder

The present authors proposed a new centerless grinding method using a surface grinder in their previous study [Wu, Y., Kondo, T., Kato, M., 2005. A new centerless grinding technique using a surface grinder. J. Mater. Process. Technol. 162–163, 709–717]. In this method, a compact centerless grinding unit composed mainly of an ultrasonic elliptic-vibration shoe is installed onto the worktable of a multipurpose surface grinder to perform tangential-feed centerless grinding operations. However, for the complete establishment of the new method it is crucial to clarify the workpiece rounding process and the effects of process parameters such as the worktable feed rate, the stock removal and the workpiece rotational speed on the machining accuracy, i.e., workpiece roundness, so that the optimum grinding conditions can be determined. In this paper, the effects of the process parameters on workpiece roundness are investigated by simulation and experiments. For the simulation analysis, a grinding model taking into account the elastic deformation of the machine is created. Then, a practical way to determine the machining-elasticity parameter is developed. Further, simulation analysis is carried out to predict the variation of workpiece roundness during grinding and to discover how the process parameters affect the roundness. Finally, actual grinding operations are performed by installing the previously constructed unit onto a CNC surface grinder to confirm the simulation results. The obtained results indicate that: (1) a slower worktable feed rate and higher workpiece rotational speed give better roundness; (2) better roundness can be also obtained when the stock removal is set at a larger value; (3) the workpiece roundness was improved from an initial value of 23.9 μm to a final value of 0.84 μm after grinding.     

Basics for In-Process Roundness Error Improvement by a Functional Workrest Blade

A centerless plunge feed grinding process can be conducted “below center” in order to increase process productivity. This statement results from the fact that the workpiece, in such a set up of the grinding gap, is fixed between grinding wheel, control wheel and workpiece rest blade, thus allowing higher feed rates of the grinding wheel support. But when grinding “below center”, the advantage of a higher productivity is accompanied by a negative effect, the arise of a polygonal workpiece form. Regarding only the geometrical rounding effect as one reason for this process characteristic phenomenon, different workpiece center displacements are examined and analytically described. The knowledge of relevant workpiece center movements within a centerless grinding application allows a quantified analysis of the influence of these displacements on the geometrical rounding effect. Deriving from such an analysis, a functional workrest blade is discussed, which influences the stability of the geometrical rounding effect.     

Simulation of plunge centerless grinding processes

Workpiece out-of-roundness is one of the most important problems in centerless grinding. Besides geometrical and kinematical effects, the dynamical behavior of the machine structure, the grinding and regulating wheel together with the support blade fundamentally influence the process stability and the workpiece accuracy. The paper presents a method for a numerical simulation of plunge centerless grinding processes in time domain. Under consideration of the geometrical conditions of the grinding gap and the dynamical compliance behavior of the grinding system the developed algorithm enables a quantitative determination of the workpiece out-of-roundness, the progression of grinding and reaction forces as well as the calculation of dynamical displacements.     

Determination of waviness decrease rate by measuring the frequency characteristics of the grinding force in centerless grinding

In centerless grinding, it is difficult to optimize the grinding conditions for minimizing the workpiece roundness error because of the high number of process parameters such as center height angle, blade angle, and stock removal rate. We had previously proposed a function for evaluating grinding conditions, i.e., the waviness decrease rate, in order to automatically select the optimum process parameters. In order to build a closed-loop control system for the process parameters, however, it is necessary to find a practical way to determine the waviness decrease rate. In this paper, the relationship between the waviness decrease rate and the dynamic components of the grinding force was investigated analytically. It was found that the frequency characteristics of the waviness decrease rate show a similar tendency to those of the grinding force. A grinding force measurement system was built and experiments for measuring the frequency characteristics of the grinding force were carried out. As a result, it was confirmed that the waviness decrease rate can be determined by measuring the frequency characteristics of the grinding force.     

SiCp/Al复合材料超声振动研磨工艺研究

针对SiCp/Al材料传统研磨方法加工困难,研磨工具磨损快,加工后难以获得高质量表面等问题,采用超声振动研磨加工方法可以显著改善其加工效果。通过对单磨粒的超声振动轨迹进行分析,得出其运动轨迹为空间椭圆形,可实现磨粒与工件间歇性的接触加工;采用树脂结合剂金刚石磨头对SiC体积分数为40%的SiCp/Al材料进行超声振动研磨加工试验,在不同的主轴转速n、进给速度v和研磨深度a_p以及磨料粒度d下,利用单因素试验法对工件进行研磨,检测加工后工件表面粗糙度,得出各工艺参数对工件表面粗糙度S_a值的影响规律。结果表明:超声振动研磨后的工件表面粗糙度S_a值相较于普通研磨后的79 nm下降为45 nm;超声振动研磨后工件表面粗糙度随n的增大先减小后增大,转速为1 800 r/min时,粗糙度值最小;工件表面粗糙度随v和a_p的增大而增大,随着d的减小而减小。并得出试验参数内的最优参数组合为:n=1 800 r/min,v=5 mm/min,a_p=1 μm,d=4.5 μm。      

支承偏移的轴承套圈定位误差及补偿方法分析

提出一个关于测力传感器变形引起的定位误差补偿方法。针对磨削轴承套圈的电磁无心夹具,在前后两个支撑上分别安装测力传感器,当支撑径向定位轴承套圈时,测力传感器精确测量轴承套圈所受支撑力并发生相应偏移。通过分析无心磨削支撑与工件的位置关系和定位误差的变化规律,推导出测力传感器受力变形导致支撑发生偏移引起的定位误差的计算公式,并提出通过控制砂轮架进给的方法补偿定位误差。结果表明：测力传感器变形会影响套圈的加工精度,此方法能够补偿该定位误差。且通过对比补偿前后的磨削时间表明,此方法能提高轴承套圈外圆磨削效率。     

Continuous workpiece speed variation (CWSV): Model based practical application to avoid chatter in grinding

The continuous variation of rotation speeds provides a means of avoiding chatter instability in different machining processes. This paper presents a time domain dynamic model that simulates chatter vibration during infeed centerless grinding for any continuously variable work rotation speed strategy. As a result of taking machine dynamics and main non-linear effects of the process into account, part roundness error is predicted for the whole grinding cycle. Lastly, experimental results have validated the model and verified that adequate speed variation strategies are capable of avoiding chatter and improving workpiece roundness and roughness, both for infeed and throughfeed centerless grinding.