小直径铣刀高速铣削淬硬模具钢不同走刀方式下切削力和加工效率的研究

高速加工是制造技术的一次革命性变革,是当今机械加工技术不可抗拒的发展潮流.小直径铣刀高速加工硬质模具钢时不同的切削条件及切削方式又是影响切削力的重要因素之一.本文主要研究刀具以不同走刀方式,在圆弧拐角处改变不同的进给速度铣削淬硬钢带岛屿的型腔时对切削力、及加工时间的影响情况,从而得出在同样的切削条件下摆线式走刀时刀具所受到的切削力较小,但是其加工效率也较低,相比之下圆弧走刀时刀具所受到的切削力较大而切削效率却较高的结论.故在高速加工时从保护刀具的角度出发易选用摆线走刀方式.     

PCBN刀具高速切削镍基高温合金切削力及刀具磨损试验研究

高速切削加工过程中切削参数的选择对刀具切削性能具有较大的影响。镍基高温合金因在高温条件下仍具有较高的抗疲劳强度、屈服强度、抗拉强度等特点,被广泛应用于航空航天、船舶、核电等行业。但是镍基高温合金的切削加工性能差,主要表现在切削力大、切削温度高、刀具磨损现象严重等方面。本文从切削速度、进给量、切削深度等切削参数对切削力的影响进行研究,同时对PCBN刀具磨损形貌进行分析。采用PCBN刀具进行高温合金车削试验,得到PCBN刀具切削高温合金GH4169时切削参数对切削力的影响规律,并探讨不同刀具磨损形貌产生的原因,为高温合金高速切削加工参数制定及工艺优化提供一定参考。     

周铣变曲率曲面铣削力与弯曲误差建模与分析

小直径周铣曲率变化的曲面时,影响铣削力的几何参数都会随着刀具路径而变化,同时小直径刀具加工过程中若f/R(每齿进给量与刀具半径比)不是极小值时其刀齿路径不再近似于圆,传统切削厚度和切削力计算不适用于此类加工时切削厚度和切削力的计算。本文提出了对于f/R不是极小值的小直径刀具圆周铣削曲率变化的曲面时其铣削力的计算模型,对于刀具弯曲模型根据实际情况考虑其受到均布载荷,运用悬臂梁结构对刀具弯曲的误差模型进行建立。     

基于特征的曲面高速加工方法的研究

高速切削技术是大型复杂曲面加工的重要手段.在运用球头铣刀对大型复杂曲面进行整体加工时,由于参与切削的切削刃单元的分布状态和数目的变化使切削载荷不均匀,切削力波动加剧,影响曲面加工质量和刀具寿命.同时,不同形状特征的曲面组合使整体加工很难选择合理的加工工艺.本文在分析了上述问题的基础上,从曲面加工特征的角度出发,提出了对曲面从微分几何理论和实际应用中的刀轴倾角进行分类,根据曲面分类对复杂曲面进行分区域并选择合理的刀具轨迹生成方法,从而提高大型复杂曲面的加工精度和效率.     

虚拟制造中基于刀具变形的复杂曲面加工误差预报

复杂曲面加工过程中刀具的弹性变形是产生曲面加工误差的重要原始误差。着重研究了虚拟制造环境下基于球面铣刀弹性变形的曲面加工误差预报模型。研究并建立了球面铣刀加工复杂曲面的切削力模型和刀具弹性变形模型,在此基础上,分析了曲面生成机理,提出了利用曲面变形敏感系数建立刀具弹性变形对法向加工误差的影响关系。利用该模型可以在实际切削加工前对曲面加工误差进行预报,用以进行误差补偿或切削参数优化。最后,以二维半圆形拉伸曲面为例通过切削实验对本文提出的模型进行了验证。     

考虑节能条件下的自由曲面加工刀具路径优化研究

在数控加工过程中不同的刀具路径所产生的能耗和加工效率不同，为了降低自由曲面在数控加工过程中的能耗，提高加工效率，从节能和高效率两个方面对刀具路径进行优化。建立以节能和高加工效率为优化目标，以主轴转速、每齿进给量、径向切削深度、轴向切削深度和机床设备性能为约束条件的刀具路径数学模型。分析待加工自由曲面的面曲率和残余高度，对加工步长和行距进行合理计算，以此为依据将待加工曲面离散成点云即为刀触点。为避免遗传算法过早陷入局部最优解，引入模拟退火算法对遗传算法进行改进，使用改进后的混合算法对自由曲面刀具路径进行优化。通过仿真加工和实验加工对比了优化路径与传统路径，结果证明了优化方法的有效性。     

高速切削加工稳定性研究

振动是金属加工过程中的一个复杂问题,其形成的颤振不仅限制了机床加工效率的提高,还对机床和切削刀具造成很大的危害。对数控加工特别是高速加工过程中颤振的研究和控制技术是先进制造技术的重要研究课题,本文介绍了切削动力学建模的两个环节:切削力建模和刀具—工件动力学建模;根据切削力建模方式的不同,将其归纳为基于试验的经验公式建模法、解析建模法和基于人工智能及软件技术切削力建模法;根据铣削加工过程中稳定区域的不同预测方式,切削稳定性分析方法分为时域分析方法、频域分析方法、试验分析方法,并对三种方法的优势和不足进行对比分析;对切削颤振的抑制措施进行了总结介绍;展望了高速切削加工稳定性研究的关键技术,为切削加工振动的理论研究与工业应用提供借鉴和参考。     

自由曲面三坐标加工等间距刀具路径规划

为提高自由曲面数控加工的切削效率,改善刀具的受力状态,提出了一种自由曲面三坐标加工等间距刀具路径规划方法.分析了在实际加工过程中可采用的几种刀具路径规划方法及其实现等距加工的约束条件.研究了等间距刀具路径的计算方法,并针对计算过程中出现的逼近误差校验和刀具路径延伸与裁剪问题给出了解决方法.对等参数线法和等距截面法进行了比较,表明应用该方法规划自由曲面刀具路径,可提高走刀路径对曲面形状变化的适应性和切削行间距分布的均匀性.     

高速加工技术的探讨及应用

本文介绍了高速切削的速度，切削力，表面质量及刀具寿命之间的关系，提出了满足高速切削基本条件的合理工艺路线，探讨了MasterCAM软件和PowerMILL软件在高速切削中对刀具路径的优化作用。     

铝合金A6061在金刚石和硬质合金两种刀具下的高速切削研究

铝合金A6061被广泛应用于航天、汽车和模具等领域中,在实际高速加工过程中,却是属于难切削加工材料。硬质合金刀具和金刚石刀具由于都具有高强度、低韧性、较好导热和抗热膨胀等特性,因而,这两种刀具被作为铝合金A6061的高速切削加工的主要刀具。通过ABQUS软件,模拟铝合金A6061分别被金刚石刀具和硬质合金刀具高速切削的加工过程,一方面分析在两种刀具切削下,模拟出铝合金A6061在切削过程切削力和温度变化情况,另一方面通过仿真结果验证金刚石刀具更适合于铝合金A6061的高速切削加工。然后,通过设计实际的车削试验,验证仿真所得到的相应结果和结论。最终为加工企业加工铝合金A6061时,在切削参数和刀具选择这两方面作出一定意义的指导。     

Minimal Realization of Linear Graph Models for Multi-physics Systems

An engineering system may consist of several different types of components,belonging to such physical"domains"as mechanical,electrical,fluid,and thermal.It is t...     

Non-monotonic material contrast in scanning ion and scanning electron images

30 keV Ga⁺ focused ion beam induced secondary electron (iSE) imaging was used to determine the relative contrast between several materials. The iSE signal compared from C, Si, Al, Ti, Cr, Ni, Cu, Mo, Ag, and W metal layers does not decrease with an increase in target atomic number Z₂, and shows a non-monotonic relationship between contrast and Z₂. The non-monotonic relationship is attributed to periodic fluctuations of the stopping power and sputter yield inherent to the ion–solid interactions. In addition, material contrast from electron-induced secondary electron (eSE) and backscattered electron (BSE) images using scanning electron microscopy (SEM) also shows non-monotonic contrast as a function of Z₂, following the periodic behavior of the stopping power for electron–solid interactions. A comparison of the iSE and eSE results shows similar relative contrast between the metal layers, and not complementary contrast as conventionally understood. These similarities in the contrast behavior can be attributed to similarities in the periodic and non-monotonic function defined by incident particle–solid interaction theory.     

Application of Feature Extraction through Convolution Neural Networks and SVM Classifier for Robust Grading of Apples

This paper proposes a novel grading method of apples,in an automated grading device that uses convolutional neural networks to extract the size,color,texture,an...     

分布动态载荷识别的抗噪处理

针对正交多项式频域法在用多种响应对矩形薄板进行载荷识别中抗噪性较差的问题,综合运用平均法、矩阵预处理和奇异值截断法等方法对之进行改善,并引入空间映射的思想,将该方法的应用范围拓展为复杂的模型.利用仿真算例,证实了该方法具有较好的抗噪性.     

基于MELTAC-N平台的核电厂安全级DCS环网研究与测试

针对工程实践中环网通讯相关问题的处理缺乏理论基础及国产化安全级DCS平台的开发缺乏成熟经验借鉴问题,对基于MELTAC-N平台核电厂安全级DCS环网的软硬件实现进行了研究。提出了安全级DCS环网双环网冗余设计、光切换开关设计等硬件设计方法,以及以RPR协议为基础,采用全数据收发策略的软件设计方法。在CPR1000安全级DCS平台上对安全级DCS环网的可靠性及实时性进行了评价,并进行了容错能力、响应时间及响应时间稳定性测试验证实验。结果表明,基于MELTAC-N平台安全级DCS环网软硬件设计具有较好的容错能力及响应时间稳定性。     

The laboratory simulation of abrasive wear

Abrasive wear has long been recognised as one of the most potentially serious tribological problems facing the operators of many types of plant and machinery; several industrial surveys have indicated that wear by abrasion can be responsible for more than 50% of unscheduled machine and plant stoppages. Locating the operating point of a tribological contact in an appropriate operational ‚map’︁ can provide a useful guide to the likely nature and origins of the surface degradation experienced in use, though care must be exercised in choosing the most suitable parameters for the axes of the plot. Laboratory testing of materials and simulations of machine contacts are carried out for a number of purposes; at one level for the very practical aims of ranking candidate materials or surface hardening treatments in order of their wear resistance, or in an attempt to predict wear lives under field conditions. More fundamentally, tests may be aimed at elucidating the essential physical mechanisms of surface damage and loss, with the longer term aim of building an analytical and predictive model of the wear process itself. In many cases, component surface damage is brought about by the ingress of hard, particulate matter into machine bearing or sealing clearances. These may be running dry although, more usually, a lubricant or service fluid is present at the interface. A number of standardised wear test geometries and procedures have been established for both two- and three-body wear situations, and these are briefly described. Although abrasive wear is often modelled as following an ‚Archard’︁ equation (i.e. a linear increase in material loss with both load and time, and an inverse dependence on specimen hardness) both industrial experience and laboratory tests of particularly lubricated contacts show that this is not always the case: increasing the hardness differential in an abrasively contaminated lubricated pair may not always reduce the rate of damage to the harder surface.     

Limits of topographic measurement by the scanning tunnelling and atomic force microscopes

Parameters describing the topographic character of a surface (height, surface wavelength, slope and curvature) can be derived from equivalent sinusoidal profiles. The response of a surface-measuring instrument may be modelled in terms of instrument parameters such as stylus radius, and scanning range and resolution. The performance of the instrument may then be mapped as a zone in amplitude-wavelength (AW) space to show the sinusoidal profiles it is capable of measuring. In a first-order analysis the STM and AFM are considered as equivalent to contact-stylus instruments with a notional stylus radius equal to the tip radius plus the gap. Comparisons between different instruments and types of instrument are readily made by mapping in AW space. The error arising from convolution of the sinusoidal profile with that of the finite tip may be quantified and plotted as contours in AW space.     

Fractional order nonsingular terminal sliding mode control for flexible spacecraft attitude tracking

This paper investigates a fractional terminal sliding mode control for flexible spacecraft attitude tracking in the presence of inertia uncertainties and extern...     

奥氏体不锈钢表面双辉等离子渗锆的动力学

利用双辉等离子渗金属技术在0Cr18Ni9Ti奥氏体不锈钢表面制备了一层均匀、致密、呈良好冶金结合的渗锆合金层,并对1 060℃下的渗锆动力学进行了研究。结果表明:随着距锆合金层表面距离的增加,锆元素的含量呈梯度递减,扩散系数逐渐减小,而扩散激活能逐步增大;在1 060℃采用双辉等离子技术渗锆时,渗锆合金层表层的空位密度为2.945×(1012~1013)cm-2,与相同温度下采用常规渗金属工艺相比,提高了1~2个数量级。     

气化炉三维扫描测量与数据处理

以德士古气化炉耐火砖的内壁蚀损检测设备为基础,对采集到的点云数据做了进一步处理.通过对数据的筛选和剔除,实现了数据点的平滑降噪细化和精简.然后利用点云对整、网格划分和分色显示等方法,最终完成了内壁腐蚀情况的三维建模.重点讨论了点云数据的预处理及后处理的方法,并根据内壁耐火砖的腐蚀阈值,提出了一种气化炉内壁腐蚀区域的识别与分割方法.对耐火砖的腐蚀分析、气化炉的生产与维修提供了可靠依据,并在工程应用中获得了一致认可.