在五坐标数控机床上对复杂模具曲面的高效加工

把微分几何中曲线与曲面之间的“切触”概念应用于流线型复杂曲面的数控加工,提出用圆柱铣刀和圆锥盘铣刀的外圆在五坐标联动中加工三维自由曲面的最佳切触条件。利用曲线与曲面之间可以比曲面与曲面之间贴合得更紧密的特点 ,把微分几何里的曲线与曲面之间的“切触”概念应用于曲面数控加工     

用圆柱铣刀加工带冠弯扭叶片

本文把微分几何中曲线与曲面之间的“切触”概念应用于叶片复杂曲面的数控加工，提出用圆柱铣刀的外圆在五坐标联动中加工小曲率曲面的最佳切触条件。     

复杂曲面的简易高效数控加工

1　引言文献 [1]提出在五坐标数控机床上用盘状刀具加工复杂曲面的高阶切触原理 ,但五坐标机床属于高挡机床 ,本文提出巧妙方法 ,可在常用的三坐标机床上仍然实现高阶切触。2　用三坐标半加工复杂曲面加工任意曲面的情形如图 1所示 ,有三个坐标系。图 1　高效加工的坐标系1)固定坐标系 :ｘ( 0 ) ｙ( 0 ) ｚ( 0 ) 分别沿工作台纵向横向和铅垂方向 ,π( 0 ) 沿工件回转轴。2 )刀具坐标系 :ｏ(ｓ) 在铣刀底面中心 ,ｚ(ｓ) 为刀具轴线 ,ｘ(ｓ) ｙ(ｓ) ｚ(ｓ) 与ｘ( 0 ) ｙ( 0 ) ｚ( 0 ) 分别平行。3)工件坐标系 :ｘ( 1) 与ｘ( 0 ) 重合 ,绕ｘ( 0…     

三坐标曲面数控加工的刀具轨迹研究

多坐标曲面加工是数控加工中的关键技术，而刀具轨迹的规划是数控编程的基础和关键。文章从提高曲面加工的精度和效率出发，推导和分析了走刀步长和切削行宽度的计算公式，提出了曲面数控加工编程时刀具轨迹规划的原则，并结合实例进行了轨迹验证。     

复杂曲面高效加工的环切刀具路径生成方法

提出一种适用于复杂曲面高效加工的环切刀具路径生成方法,该方法以平面封闭三次B样条曲线族作为导引线,运用复杂曲面笔式加工插补算法实现曲面局部区域的加工.导引曲线由封闭控制多边形顶点,通过逐层内等距,得到内偏置控制多边形的顶点,进而生成B样条导引曲线环.该方法提高了复杂曲面局部加工的效率,而且用B样条曲线描述刀具路径,为实现复杂曲面高效、高精度加工奠定了理论基础,并通过实例验证了算法的有效性.     

自由曲面五坐标端铣加工干涉避免的研究

基于平底端铣刀有效切削轮廓曲率与刀触点曲面法曲率匹配,初定刀具姿态,再通过刀具圆柱面与曲面求交,推导了交线上各点坐标的计算公式.利用交线上干涉点数据,计算并调整刀具姿态,避免切削刃后缘和侧缘过切被加工表面,消除瓶颈干涉.与用刀触点曲率半径计算并消除瓶颈干涉的方法相比,该方法更合理、更实用.     

四元数法改善复杂曲面5轴加工精度研究

提出一种新的刀具轴向设计方法,通过使用四元数法进行刀具轴向规划,以解决曲面5轴数控加工中刀具轴向过度依赖曲面几何特征,造成刀轴剧烈变化所引起的切削恶化问题.在被加工曲面上可能发生过切的区域,指定刀具轴向,再由指定的轴向,直接计算出其他位置的轴向,并与其他刀具轴向设计方法进行对比.实际应用结果表明:采用该方法可以很好地提高复杂曲面切削精度、效率,避免过切.     

影响衣架模具曲面加工精度的工艺分析及对策

通过衣架模具的加工，分析了Cimatron软件在进行曲面数控程序设计时，影响曲面加工质量的相关因素；从刀具、加工方法、进退刀方式和切削参数等方面介绍了提高曲面加工精度所采取的改进措施。     

自由曲面数控加工的直接插补控制方法

提出了集成环境下自由度面数加工的直接插补控制方法。该方法可根据网络上传来的零件几何信息和加工工艺信息，直接生成曲面上的切削轨迹和刀具运动指令。     

圆环面刀五坐标铣削加工复杂曲面干涉避免研究

将圆环面铣刀等效为变直径平底铣刀,基于圆环面铣刀有效切削轮廓曲率与刀触点曲面法曲率匹配,初定刀具姿态,再利用通过圆环面刀圆角中心线的圆柱面与曲面等距面求交,推导了交线上各点坐标的计算公式。利用交线上干涉点数据,计算并调整刀具姿态,避免切削刃后缘和侧缘过切被加工表面,消除瓶颈干涉。此方法比起用刀触点曲率半径计算并消除瓶颈干涉,是一种更全面、合理、可行的实用方法。     

Contact behaviour of the original and substituted real surfaces

Several engineering components transfer load under sliding contact. Between two sliding bodies there are contacts over only small areas of the nominal contact area due to the surface roughness and surface waviness. The nominal contact pressure is therefore much smaller than the real contact pressure acting over the real contact areas inside the contour contact areas.To evaluate the contact parameters (location of the real contact area and contact pressure distribution) different numerical methods have been used in the past decades. The latest ones can consider the real surfaces based on measured surface roughness data.The present study focuses on the characteristic features of the asperities using hemispherical, ellipsoidal and parabolic surfaces as substituting surfaces. In each case the location of the real contact area and contact pressure distribution are evaluated and compared with the results representing the original measured surfaces. The best agreement was obtained if paraboloides were used for substituting asperities.This technique can provide statistical type results characterising the contact behaviour, if the substituting asperities are considered.     

Sink electrical discharge machining of hydrophobic surfaces

The phenomenon of hydrophobicity observed in such surfaces as lotus leaves is typically manifest by hierarchical structures on low-energy surfaces. Sustained interest in fabricating hydrophobic surfaces has resulted in a myriad of processes, which are but limited by their largely referring to soft materials and/or involving multiple process steps. The present work explored the application of electrical discharge machining (EDM) for the single-step manufacture of durable, metallic hydrophobic surfaces. Simple sink EDM in a hydrocarbon dielectric, with no special process kinematic or tooling requirements, is demonstrated to rapidly generate surfaces that are intrinsically water repellent, with contact angles approaching 150°.     

Computer simulation of precision contact with account of microgeometrical and mechanical heterogeneity of surfaces

Computer model of 3D contact based on SPM research of contact surfaces is offered. The main idealizing model feature is linear character and additivity of material deformation on separate contact sites of 3D-images. The model takes into account multilevel topography of surfaces, map of elastic properties of materials, superficial forces effect and non-uniformity of intercontact gap. The map of elastic properties of materials was obtained from the SPM phase contrast images. It is shown, that heterogeneity of micromechanical properties of materials in the contact zone results in essential redistribution of contact spots, contact stresses and adhesive forces. Statistical peculiarities of contact formation depending on probability of mutual collisions of rough surface sites are considered, including during sliding. The efficiency of offered computer model to describe precision contact including multilevel one is considered using examples of interaction between worn TiN coating.     

齿间摩擦对齿轮轮齿表面接触疲劳强度的影响

作者系统地研究了影响齿轮传动中轮齿表面接触疲劳强度的诸因素,并推导出包括齿间滑动摩擦在内的实际外载荷作用下齿轮轮齿表面接触疲劳应力计算公式。研究表明,齿间摩擦对齿轮传动中轮齿表面接触疲劳强度的影响不可忽视。     

Deformations of engineering surfaces under static loads

A computer-aided-system has been developed to provide (i) 3-D assessments of engineering surfaces; (ii) quantifications of surface degradations due to wear and deformation processes; and (iii) predictions of the true area of contact formed between two initially-isothermal, circular cross-sectional surfaces of a soft rough material (duralumin) and a relatively-harder smooth material (titanium) pressed together by a mechanical load. This system is based on a stylus profile-tracing instrument and incorporates an automatically-controlled parallel-profile digitising stage.     

Influence of the meshing clearance on the performance of conjugate helical surfaces

Meshing clearance is significant in both the manufacturing and operating practice of products applying conjugate helical surfaces. Based on the clearance-caused rotation angle of the return stroke for different meshing clearance, the influence of the meshing clearance on the performance of conjugate helical surfaces, such as conjugation interaction, contact area, continuity of the contact line, noise level and smooth running, etc., is explored in depth in this paper. It is concluded that the meshing clearance should be so designed that the resulting clearance-caused rotation angle of the return stroke is as uniform as possible.     

Contact and thermal analysis of bronze and steel machined surfaces in sliding contact

Between engineering components in sliding contact there are usually small real contact areas inside the nominal contact area. The real contact pressure frequently is in the range of the plastic limit pressure.The effect of different machining processes (grinding, milling, spark-erosion and superfinising) on the contact parameters (real contact areas, contact pressure distribution and contact temperature) were analysed and compared between bronze and steel sliding surfaces.The developed contact algorithm can simulate the elastic and also the elastic-plastic sliding contact behaviour in the vicinity of the asperities in an approximate way.Assuming certain sliding speed and coefficient of friction the local contact temperature distribution is also calculated due to the heat generation over the real contact areas for'slow sliding' problems.     

Generative design of joint contact surfaces inspired by biological morphogenesis

Recent knowledge about biological joint morphogenesis opens new perspectives in mechanics to automate joint contact surface design. The present work evaluates the feasibility of a generative design method inspired by the joint morphogenesis process to develop contact surfaces. A finite element model of joint morphogenesis reported in literature was implemented. This morphogenesis process was adapted and implemented for mechanical applications. The results show that the bioinspired joint shaping process adds matter in the zones next to the contact zone decreasing the contact pressure (up to 57%). The results demonstrate the feasibility of implementing biological growing rules in generative design.     

Surface energies and appearances of commonly exposed surfaces of scheelite crystal

Surface energies of five different surfaces of scheelite crystal were calculated using density functional theory (DFT). Based on the calculation results, the predominantly exposed surfaces in the morphologies of scheelite crystals were predicted. {112} and {001} cleavage surfaces and {112} crystal surface are the commonly exposed surfaces, which are consistent with both previous literatures and the present experimental observations based on the XRD. Cleavage generates more easily along {112} surfaces than along {001} surfaces due to their different interlayer spacings. The surface roughness and appearance of different predominantly exposed surfaces were then investigated using AFM. The roughness of smooth {112} cleavage surface is the lowest among these three surfaces. On {001} cleavage surface, terraces are flat and separated by steps of about 10 nm in height. Subsequently, contact angle measurements were adopted to evaluate the wettability and surface energies of these surfaces. The surface energies evaluated directly correspond to the trend calculated with DFT.     

Fabrication of superhydrophobic surfaces on Mg alloy substrates via primary cell corrosion and fluoroalkylsilane modification

The present work reports a simple and safe two‐step process to render magnesium (Mg) alloy surfaces superhydrophobic via primary cell corrosion and subsequently cover it with a fluoroalkylsilane (FAS) film. The surfaces were characterized by scanning electron microscopy (SEM), optical microscopy, energy‐dispersive X‐ray spectroscopy (EDS), Fourier‐transform infrared spectrophotometry (FTIR), X‐ray diffraction (XRD), and optical contact angle measurements. The power generated via the primary cell corrosion of copper and Mg alloys was also measured using a digital multimeter. The results show that micro/nanometer‐scale binary rough structures and an FAS film with a low surface energy were present on the Mg alloy surfaces, both of which confer good superhydrophobicity with a water contact angle of 162.8° and a tilting angle of 2°. The micro/nanometer‐scale binary rough structures consisted of micrometer‐scale grains, cluster‐like structures composed of nanometer‐scale needles, and network‐like structures composed of nanometer‐scale sheets. Superhydrophobicity was analyzed by the Cassie–Baxter theory. Findings show that only about 6.3% of the water surface was in contact with the Mg alloy substrates, while the remaining 93.7% was in contact with the air cushion. The unique advantage of the proposed method is that power can be generated during the machining process of the superhydrophobic surfaces on the Mg alloy substrates.