飞机整体结构件加工变形的产生和对策

分析了整体结构件加工变形的产生机理。通过两个实例，说明了整体结构件已去除材料残余应力的释放和切削加工表面残余应力对工件变形的影响。提出了深冷处理消除毛坯残余应力、高速切削和切削加工工艺优化等抑制整体结构件加工变形的策略。针对整体结构件弯曲变形，提出了校正需要满足的基本曲率关系．     

金属切削变形对已加工表面质量的影响

当工件进入装配成为机器零件后,已加工表面质量对该零件的使用性能会造成很大的影响。表面质量的主要标志是表面粗糙度、加工硬化和残余应力。根据金属切削原理中对切削变形的研究理论,分析了金属切削变形对表面形成过程的内在影响:积屑瘤的生成增加了表面粗糙度值;刀具刃口和后刀面的挤压及摩擦使表面产生加工硬化;机械应力和热应力引起的变形使加工表面产生残余应力。     

基于热力耦合模型的切削加工残余应力的模拟及试验研究

航空精密薄壁零件具有复杂的型腔结构,切削加工残余应力是薄壁零件精度稳定性的重要影响因素,因此必须对切削加工残余应力进行研究。根据热—弹塑性有限元理论,建立切削加工三维有限元模型,对航空铝合金材料Al2A12进行切削加工非线性弹塑性有限元模拟分析,对切削加工表面残余应力进行预测和计算。通过有限元分析,得到不同切削参数、刀具参数条件下的已加工表面残余应力的模拟结果,并对结果进行比较分析,得到各个因素对工件已加工表面残余应力的基本影响规律;进行不同加工工序条件下的切削加工残余应力的有限元模拟,在加工表面已有一次切削加工残余应力分布的情况下,进行二次切削加工有限元模拟,得到二次切削加工对工件已加工表面残余应力的影响规律;并且进行不同切削参数对残余应力影响的试验研究,验证有限元模型的正确性。     

复合材料的切削加工表面质量

从已加工表面几何特性，加工硬化和残余应力几方面探讨了复合材料的切削加工表面质量问题。研究结果表明，复合材料的已加工表面包含大量的加工所致缺陷，增强体的特性和取向分布，刀具条件是决定复合材料已加工表面形貌的主要因素；复合材料已加工表面硬度甚至低于加工材料，而皮下层材料通常发生显著的加工硬化；微观上复合材料切削变形区的应力状态很复杂，实践上，复合材料的已加工表面常残余压应力，或表面加工缺陷使大部分热应力和弹性恢复应力均被释放。     

端面车铣加工表面粗糙度预测模型的研究

在对车铣复合加工表面粗糙度的形成机理进行理论分析的基础上,建立了端面车铣复合加工粗糙度的预测模型。根据残留面积高度的几何分析,进行了残留面积高度的三维仿真计算。对计算结果进行分析可知车铣加工中端面的表面粗糙度值并不一致,零件直径越大处残留高度越大;粗糙度值越大,随着径向尺寸的减小,粗糙度值逐渐降低。     

铝合金7475已加工表面残余应力的数值模拟

为了揭示铝合金材料已加工表面残余应力的分布规律,建立了三维有限元模型对铝合金材料7475的切削加工过程进行了数值模拟,获得了铝合金材料7475已加工残余应力的分布规律,同时也研究了不同切削深度对已加工表面残余应力的影响规律。模拟结果表明：已加工表面层残余应力为拉应力,沿深度方向由拉应力逐渐过渡到压应力;而切削深度对铝合金7475已加工表面残余应力的影响较小。     

精密切削钛合金TC4表面残余应力的模拟研究

本文建立钛合金正交切削热一力耦合有限元仿真模型,采用自适应网格(ALE)技术及Johnson-Cook强化模型和剪切失效模型定义切削.通过对TC4切削过程的有限元模拟,分析了刀具刃口半径及材料的变形对已加工表面残余应力分布和表面质量的影响,并提出在切削钛合金时需采用较小的切削深度、较高的刀具锋锐度、较高的切削速度进行切削,以得到较好的表面加工质量.     

金属切削变形对已加工表面质量的影响

工件加工处理后成为机器零件,而已加工表面质量会影响零件的使用性能。表面质量判断依据包括表面粗糙度、残余应力和加工硬化。按照金属切削原理,基于切削变形理论,对切削变形的影响问题进行分析,主要探讨金属切削变形对已加工表面质量的影响,希望能够为相关人员提供参考。     

磁盘基片加工平面度超差的原因及对策

计算机磁盘基片,直径为130毫米的,按一般国际标准,加工表面粗糙度Ra<0.015μm,加工平面度要小于6.32微米。在建南机器厂实际生产制造中,使用美国制造的MVP—ST200超精密磁盘车床,采用真空吸盘装夹,用硬质合金车刀进行粗加工和半精加工。用天然单晶金刚石车刀进行精加工。磁盘基片是圆薄板形零件,刚性很差。且在车削加工时,已加工表面将产生残留应力,其残留应力随切削条件的改变而变化。因此,当一个磁盘基片两面的切削条件不一致时,就会造成磁盘基片两面的残留应力的大小和分布不一致,从而使磁盘基片产生变形。磁盘基片两面的残留应力相差越大,产生的变形就越严重。根据测试,在实际生产中,粗加工和半精加工之后产生的磁盘基片变形,一般达数十微米。另外,磁盘基片的厚度只有1.88毫米,所以其刚性极差,虽用真空吸盘装夹,也会变形,所以磁盘基片在半精加工之后的变形在精加工之后仍将被大部分继承下来。正由于上述两个原因,在实际生产中,磁盘基片的平面度公差要满足要求,必须采取两个措施。即:     

关于机械切削加工时残留面积高度R的理论计算公式推导

在机械切削加工中，当刀具无修光刃的情况下，加工后的工件表面上会残下类似于螺纹一样的表面，即残留面积，它在很大程度上影响着已加工表面质量。本文将分析在不同的切削条件下残留的形状，并着重推导各种形态的残留面积高度Ｒ的理论计算公式。     

A study on the five-axis end milling for sculptured surfaces

The direction vector of milling cutter for CL-data of five-axis milling is obtained by the fact that the bottom part of the milling cutter rides on free-form surfaces using the z-map method. Since the direction vector is known, CL-data can be transformed to the NC-code with regard to the geometry of the five-axis machine and post-processing. For uniform surfaces, the tool path is created from the prediction of cusp heights. After generating the NC-code, a sculptured surface was machined by five-axis end milling and cusp heights on the machined surface were measured by a three-dimensional CMM with laser scanner. From this machining test, it was found that this machining method is effective.     

Dispatching rules for unrelated parallel machine scheduling with release dates

A simplified procedure is proposed to predict the surface integrity of complex-shape parts generated by ball-end finishing milling. Along a complex cutting path, the tool inclination may vary within a large range. A geometrical study is performed to predict the effect of the tool inclination (lead angle) on the micro-geometry of the machined surface and on the effective cutting speed. This geometrical study brings out a range of values of the lead angle for which the machined surface is damaged by cutting pull-outs. This geometrical study also brings out a range of values of the lead angle for which the effective cutting speed is null. This case corresponds to extreme values of the cutting forces and to high compressive residual stresses. These predictions are verified for a selection of tool inclinations and other cutting parameters such as cutting speed, feed per tooth and cusp height. These machining tests are performed on a high-strength bainitic steel. The experimental campaign includes milling tests with cutting forces measurements, 2-D optical micro-geometry measurements and X-ray diffraction measurements.     

Five-Axis NC Machining of Sculptured Surfaces

This paper presents a new method for the determination of tool position and orientation for NC milling of sculptured surfaces with a five-axis NC machine. This method uses an analysis of local curvatures of the surface and the tool geometry. Based on matching these local properties, optimal tool axis orientations are selected so that the gouging error in machining is eliminated or controlled within a specific tolerance. An accurate technique is also proposed for the computation of cusp height of the machined surface. By eliminating gouging and controlling scallops within a specified tolerance, it is expected that the time-consuming manual grind-ing process could be greatly reduced or completely eliminated in the finish machining of complex die or mould surfaces.     

基于Bauschinger效应的逆向精切削变形机理

基于工件材料Bauschinger效应,从已加工表面变质层的形成入手,建立了逆向精切削法的切削变形模型。利用金相显微试验技术对比研究了正、逆向精车削条件下工件材料晶粒流动情况,用位错理论对可逆向精切削的变形机理进行了论述。研究表明,可逆向切削时,可以采用首切时正向切削,复切(半精加工或精加工)时逆向切削的工艺路线,这样既可提高加工效率和加工精度,又可减小工件表面变质层。     

基于薄板单元函数的切削仿真算法

提出了一种基于薄板单元函数的切削仿真算法.通过在曲面的投影平面内建立规则或不规则的投影网格,再借助节点的挠度和转角参数,并参考有限元法中薄板弯曲单元所用到的形函数,在每个单元中建立单元内的高度场函数来描述被加工曲面.该算法可使曲面求交仍然是一维运算,不仅精度高,而且有非常高的效率.     

Plastic deformation analysis in machining of Inconel-718 nickel-base superalloy using both experimental and numerical methods

Surface region plastic deformation of Inconel-718 nickel-base superalloy workpieces was evaluated when machined under orthogonal cutting conditions at various cutting speeds. Plastic deformation analysis was accomplished by determining the residual stress and plastic strain distributions in the surface region. The residual stresses were tensile and maximum near the surface and decreased in magnitude with an increase in depth beneath the machined surface. Similarly, the plastic strains were maximum near the surface and decreased with an increase in depth beneath the machined surface. In addition, a finite element simulation of orthogonal machining was carried out for predicting the residual stress and plastic strain distribution. In general, the trend of the curves predicted by the finite element model was similar to those found experimentally.     

The effect of characteristics of free<Emphasis Type="Bold">-</Emphasis>form surface on the machined surface topography in milling of panel mold

In the milling process of automobile panel mold of hardened steel, the characteristic of free-form surface is one of the dominant factors for surface topography. In this paper, the trajectory of cutting edge is firstly modeled to analyze the residual height of the free-form surface in ball-end milling of hardened steel. Furthermore, the non-uniform rational B-splines (NURBS) surface reconstruction is utilized to generate the surface topography. Subsequently, the influences of surface curvature, lead angle, milling vibrations on the machined surface topography, and residual height are investigated, respectively. Finally, the accuracy of the surface topography and the roughness prediction model are validated by the milling experiments of free-form surface, where two-dimensional contour maps could be obtained. The simulation and experimental results demonstrate that the machined surface topography of hardened steel is fitted by means of NURBS surface reconstruction. In that manner, the effects of surface characteristics on the machined surface topography can be accurately predicted.     

基于UG的正交车铣加工回转体表面微观残留仿真

正交车铣加工的回转体表面由铣刀与工件的复合相对运动形成,其形成机理独特,多个参数影响其表面微观形貌。为研究切削参数对正交车铣回转体表面微观残留的影响,基于UG建立了正交车铣回转体表面的仿真加工方法,并通过Vericut构建了虚拟五轴车铣加工环境,由此仿真研究了周向每齿进给量对正交车铣回转体表面微观残留的影响,发现已加工表面微观残留高度随周向每齿进给量增加显著增大。     

Some aspects in the surface integrity associated with turning of powder metallurgy compacts

The shape of the tool insert geometry, particularly the size of the tool nose radius, plays a significant role in influencing a variety of surface integrity characteristics such as surface finish, roundness, tool life, edge frittering etc. It has been found in previous work that a large tool nose radius is beneficial in improving the component quality. This paper substantiates these facts and shows that increasing the feed rate generally debilitates the surface integrity but, probably due to some elasticity in the porous compact's surface, this does not cause residual hardening to the machined surface. Abrasion during secondary machining suggests that flank, rather than crater, wear determines the end point during cutting operations. Tool nose geometry plays a significant role in improving surface topography, by reducing the cusp height—when the nose radius is large. The manufacturing envelopes defined by skewness and kurtosis for the machined surfaces suggest that there is a general drift either from a bearing to a locking surface or vice versa. Furthermore, the dispersion of these envelopes reduces with increasing feed rate. These conditions can be attributed to the tool nose geometry, feed rate and depth of cut which modifies the machined surface topography.     

Measurement of equivalent residual stresses generated by milling and corresponding deformation prediction

We introduce a method to measure the equivalent residual stresses and depths of the affected layers, which are generated in the workpiece during the milling process. These layers lie immediately under the milled surface. After machining, two material layers on the opposite side from the machined surface were chemically removed, and strain changes on the machined surface were measured after each layer removal. Based on the strain changes and the thickness of each removed layer, the equivalent residual stresses and depths of the affected layers in different directions were obtained. Based on the measured results, the corresponding deformations caused by the milling induced residual stresses can be predicted in workpieces with different rigidities. The predicted deformations were validated by the experimental results. We found that our measuring method can be successfully used in practice to evaluate the machined surface properties and predict the deformations caused by milling induced surface residual stresses accurately.