Form error in diamond turning

The main feature of ultraprecision, single point diamond turning (SPDT) is its ability to produce high quality surface finishes on the order of nanometers while meeting tight form tolerances on the order of micrometers. This capability allows for the production of optical devices with minimum post-processing operations. The issue of form error is critical since it may severely compromise the performance of the designed optical system. Tool-workpiece relative vibration is a major cause of this error. In this article, the authors have demonstrated that imbalance of the spindle is a major cause of form error which eventually leads to a structured error called “spindle star” that appears as straight concentric spokes radiating out from the center of the part. The formation of a spindle star pattern can be explained using Campbell's rotordynamics analysis. This analysis explains how assisted air-hammering instability and cross-coupling effect of the air-bearing spindle can contribute to spindle star. This experimental approach used force and accelerometer data with the help of modal analysis to conclude that spindle star is a synchronous error and is a function of rotational frequency of the spindle and its harmonics. The integer harmonic from the Campbell's waterfall diagram predicts the number of spokes in the spindle star. It was also observed that the height of the spindle star undulations increases with higher rotational speed. It was also observed that cutting material and tool geometry has no influence on the spindle star formation; rather this is an inherent characteristic of air-bearing journals. Finally, the analysis was successfully validated by changing the natural frequency of the spindle by adding mass.     

Measurement of multi-degree-of-freedom error motions of a precision linear air-bearing stage

This paper describes the measurement of straightness error motions (vertical straightness and horizontal straightness) and rotational error motions (pitch, yaw and roll) of a commercial precision linear air-bearing stage actuated by a linear motor. Each of the error motions was measured by two different methods for assurance of reliability. The stage was placed in the XY-plane and moved along the X-direction. The pitch error and yaw error, which were measured by an autocollimator and the angle measurement kit of a laser interferometer, were about 8.7 and 1.6 arc-s, respectively, over a travel of 150 mm with a moving speed of 10 mm/s. The roll error was measured by the autocollimator through scanning a flat mirror along the X-direction. The second method for roll error measurement was to scan two capacitance-type displacement probes along the flat surface placed in the XZ-plane. The two probes with their sensing axes in the Y-direction were aligned with a certain spacing along the Z-axis. The roll error can be obtained by dividing the difference of the outputs of the two probes by the spacing between the two probes. The roll error was measured to be approximately 11.8 arc-s over the 150 mm travel. The horizontal straightness error and the vertical straightness error (Y- and Z-straightness errors) were measured by using the straightness measurement kit of the laser interferometer. The second method for straightness measurement was to scan the flat surface with a capacitance-type displacement probe. The horizontal and vertical straightness errors of the stage over the 150 mm travel were measured to be approximately 207 and 660 nm, respectively.     

大型光学零件金刚石车床

介绍美国LODTM(LargeOpticsDiamondTurningMachine)——大型光学零件金刚石车床的基本结构,重点介绍机床的主要关键技术——测量技术、关键元部件技术、数控技术。     

Surface profile measurement of a sinusoidal grid using an atomic force microscope on a diamond turning machine

This paper describes the surface profile measurement of a XY-grid workpiece with sinusoidal microstructures using an atomic force microscope (AFM) on a diamond turning machine. The sinusoidal micro-structures, which are fabricated on an aluminum plate by fast tool servo-assisted diamond turning, are a superposition of periodic sine-waves along the X- and Y-directions (wavelength (XY): 150 μm, amplitude (Z): 0.25 μm). A linear encoder with a resolution of 0.5 nm is integrated into the AFM-head for accurate measurement of the Z-directional profile height in the presence of noise associated with the diamond turning machine. The spindle and the X-slide of the machine are employed to spirally scan the AFM-head over the sinusoidal grid workpiece. Experiments fabricating and measuring the sinusoidal grid workpiece are carried out after accurate alignment of the AFM cantilever tip with the spindle centerline.     

数控机床螺距误差补偿

螺距误差是造成数控机床加工精度下降的重要原因之一,在分析螺距误差的产生原因之后,给出数控机床螺距误差补偿的原理和补偿步骤。运用此误差补偿方法对一台配备SINUMER IK 802S/C系统数控机床螺距误差补偿后,获得了理想的加工精度。     

Development of an inexpensive, high-accuracy diamond turning machine

A small, numerically controlled, two-axis diamond lathe for parts up to 100 mm diameter has been assembled from commercially available components in two weeks. The machine has exceeded performance expectations; in a test of its accuracy, 25.4 mm diameter hemispherical aluminium parts were cut to an accuracy of 0.25 μm (size and contour band) with a surface finish of 25–40 nm rms     

A/C轴双摆头几何精度误差的预防与补偿方案

通过A/C轴双摆头误差预防与误差补偿工艺方案的研究,设计了A/C轴双摆头装配工艺方案以及两轴回转中心的误差检测与补偿方案.将此研究方案应用于沈阳机床某A/C轴双摆头试制,效果良好.     

齿轮径向跳动测量的误差分析及补偿

针对齿轮径向跳动误差的传统测量方法进行了分析,指出了传统方法存在的缺点;通过分析,提出了一种新的误差分析及补偿的方法,该方法可以用计算机进行辅助误差测量及数据处理,并证明了这种方法的正确性和可行性。     

Investigation and prediction of chip geometry in diamond turning

Management of the chips generated in diamond turning is often critical, because contact between chips and the workpiece can result in superficial damage to the finished surface. Controlling chip motion is not a trivial process as the proper positioning of an oil or air stream requires an understanding of the dynamics of a diamond turned chip and the machining parameters that affect it. Work has been performed to investigate the effects of cutting speed, depth of cut, tool geometry, tool wear, and workpiece material properties on chip motion and geometry. Utilizing radius of curvature data from cutting experiments, a parameter has been proposed that can be used to predict chip radius of curvature for a wide range of machining conditions. This chip curvature parameter, χ, exhibits a power law relationship with chip radius of curvature as a function of tool geometry, depth of cut, cutting speed, and both elastic and plastic properties of the workpiece material.     

Measurement and simulation of regenerative chatter in diamond turning

In this work, the stability of outer diameter turning is explored to extend previous results from the orthogonal turning geometry. The work begins with a numerical approach to the determination of the stability limit using a nonlinear chip area model. A complete experimental verification follows for turning of 6061-T aluminum with single crystal, synthetic diamond tools. Although diamond-turning operations are not particularly susceptible to chatter, the cutting process is well understood, and experimental tests may be conveniently carried out. Recent work to define the specific cutting energy better at small depths of cut is incorporated. The results show qualitative differences from the orthogonal cutting geometry. The role of machine parameters and tool geometry is explored using the verified model.     

金属条材直线度在线测量的新方法

提出了一种测量金属条材直线度的新方法—新组合法.该方法将频域两组两点法与逐次两点相结合,在实现工件直线度无理论误差重构的同时,解决了传统频域法重构短工件时横向分辨率低的问题,能够高精度地测量金属条材的直线度.首先,将所有的采样点通过新组合法分为若干组;其次使用频域两组两点法将其重构为相同数量且横向分辨率较低的曲线,应用...     

Investigation of the direction of chip motion in diamond turning

Management of the chips generated in diamond turning is often critical since contact between chips and the workpiece can result in superficial damage to the finished surface. Controlling chip motion is not a trivial process as the proper positioning of an oil or an air stream requires an understanding of the dynamics of a diamond turned chip and the machining parameters that affect it. Previous work [1] introduced the chip curvature parameter, χ, which is useful in predicting chip radius of curvature over a wide range of cutting speeds, depths of cut, tool geometries and workpiece material properties. To control chip motion, however, an understanding of the direction chips leave the tool/workpiece interface must also be obtained. Cutting experiments were performed investigating the influence of cutting speed, depth of cut, feed rate, tool path angle, tool geometry and tool orientation on the directional characteristics of the motion of diamond turned chips. Flow angle measurements obtained during cutting were found to remain within ± 10° of predictions from a simple geometrical model originally proposed for conventional machining.     

Simple and simultaneous measurement of five-degrees-of-freedom error motions of high-speed microspindle: Error analysis

We have developed a simple and low-cost optical measurement system for the simultaneous measurement of the five-degrees-of-freedom error motions of high-speed microspindles. We demonstrated the usefulness of the system by using it to measure actual spindle rotation errors, and analyzed the major error factors. First, the measurement error due to the form error of the lens was analyzed by ray tracing. Second, we analyzed the measurement error due to a displacement of an irradiation laser point on a 3 mm diameter ball lens. Furthermore, we investigated the effect of the centrifugal force and the crosstalk problem of multiple laser beams. The results indicated that a form error of the rod lens significantly affected the measurement accuracy and that a change in the laser beam irradiation point of the ball lens due to a radial displacement had no significant effect on the measurement accuracy. Finally, we confirmed that, owing to the centrifugal force, the measurement accuracy decreased as the speed of rotation increased, and that there was no crosstalk that the reflected and transmitted laser beams in the X direction were detected by the photodiode in the Y direction for displacements within −10 to 10 μm.     

An empirical survey on the influence of machining parameters on tool wear in diamond turning of large single-crystal silicon optics

We conducted a series of screening experiments to survey the influence of machining parameters on tool wear during ductile regime diamond turning of large single-crystal silicon optics. The machining parameters under investigation were depth-of-cut, feed rate, surface cutting speed, tool radius, tool rake angle and side rake angle, and cutting fluid. Using an experimental design technique, we selected twenty-two screening experiments. For each experiment we measured tool wear by tracing the tool edge with an air bearing linear variable differential transformer before and after cutting and recording the amount of tool edge recession. Using statistical tools, we determined the significance of each cutting parameter within the parameter space investigated. We found that track length, chip size, tool rake angle and surface cutting speed significantly affect tool wear, while cutting fluid and side rake angle do not significantly affect tool wear within the ranges tested. The track length, or machining distance, is the single most influential characteristic that causes tool wear. For a fixed part area, a decrease in track length corresponds to an increase in feed rate. Less tool wear occurred on experiments with negative rake angle tools, larger chip sizes and higher surface velocities. The next step in this research is to perform more experiments in this region to develop a predictive model that can be used to select cutting parameters that minimize tool wear.     

一种新的数控机床热误差实时补偿方法

根据数控机床加工热误差,首先,利用粗集理论方法,分析各变量与热误差之间的相关性,选择出机床热误差补偿的重要特征参数。然后提出一种动态反馈网络建立数控机床加工热误差补偿模型,新的数控机床热误差实时补偿方法具有补偿误差精度高,网络学习收敛速度快,误差补偿实时性好等特点。仿真实验结果证明了该方法的可行性和有效性。     

Annealing treatment of amorphous silicon generated by single point diamond turning

Mechanical material removal during ultraprecision machining of semiconductor crystals normally induces surface damage. In this article, Raman micro-spectroscopy has been used to probe structural alteration as well as residual stresses in the machined surface generated by single point diamond turning. The damage found is characterized by an amorphous phase in the outmost surface layer. In addition, the results of in-situ re-crystallization annealing of micromachined silicon monitored by micro-Raman spectroscopy are reported for the first time. It is also shown that the annealing heat treatment influenced surface roughness, whereby R_max was equal to 24.3 nm and 47.5 nm for the non-treated and annealed surfaces, respectively.     

双刀架曲轴数控车削在线测量及自动补偿的实现

为提高曲轴数控加工自动化程度,采用了双刀架曲轴数控加工与在线检测集成的方法,开发了上、下刀架刀具磨损自动补偿子程序.实际应用表明在线尺寸检测及自动补偿技术改善了加工质量和提高了加工效率.     

Design and performance of a small—scale diamond turning machine

Machining with single-point diamond tools is an area of increasing interest in the manufacture of optics, lens moulds, hard discs and other products Although many materials have been machined with impressive results, questions remain regarding the science of diamond turning. These questions concern the suitability of certain materials for turning, the properties of the tool and machine structure which limit the quality of the final product, and the modelling of the cutting process. To study these phenomena, a laboratory-scale diamond turning machine has been designed and built at the Precision Engineering Center. This machine, PAUL, although simple and compact, has produced excellent results on a variety of static and dynamic cutting experiments. The key points of its design, as well as an evaluation of PAUL's performance, are given in this paper.     

基于神经网络的机床-工件系统热误差补偿技术研究

以机床-工件系统的热变形为研究对象,应用神经网络理论建立机床-工件系统的热误差模型,对热误差神经网络模型的关键输入参数进行了分析讨论,提出了该模型的误差补偿策略。以某型号大尺寸回转支承滚道数控车削加工为例,建立了热误差模型,对回转支承滚道加工实施热误差补偿,结果表明,机床-工件系统的热误差模型有较强的预测能力,提出的补偿方法有较好的补偿效果。     

影响待测物面测量误差的因素及补偿

分析被测物面对激光三角法测量技术的影响,从原理、位移传感器的非线性补偿、被测表面倾角、被测表面特征(颜色、粗糙度、光泽)几方面分析误差产生的原因。探讨各因素的误差补偿方法,对传感器进行非线性误差标定,测量出其非线性误差曲线图;使用标注件标定激光头本身倾角误差,对绘制倾角误差测量结果做曲线拟合;对被测件表面的颜色处理;在非特定条件下,可以忽略表面光泽度和粗糙度;最后综合上述过程,得出测量结果。该方法提高了测量精度。对于小型机电,电子产品外形反求测量,提高其生产过程中的测量精度,具有一定指导作用。