起落架着陆过程建模与多目标参数优化设计

飞机起落架着陆性能的优化主要取决于系统多参数优化匹配。建立飞机起落架着陆过程的动力学模型，分析各模型参数对优化指标的灵敏度，获得起落架优化设计组合变量。利用综合加权法计算各目标函数权重，建立起落架参数多目标优化模型。采用自适应遗传算法对起落架着陆过程模型进行多目标寻优，获得综合目标最优的起落架参数组合，实现了起落架系统参数的优化设计。优化结果表明：着陆过程缓冲支柱最大轴向载荷减少了35.79%,机轮最大垂直载荷减少了24.08%,缓冲器的行程变化大小减少了17.99%和垂直阻尼振动的次数减少了15.38%。     

助航灯具干冰清洗多目标参数混合优化

目的 采用干冰清洗技术对助航灯具进行自动清洗,并对清洗参数进行多目标混合优化。方法 以清洁度为评价指标,使用单一变量控制法进行试验,分析清洗工艺参数影响力,获得清洗距离、角度、流量、时间等参数的最佳范围。提出以提高清洁度,节约清洗原料,降低发光口磨损度,提升清洗效率为目标,构建多目标参数优化模型,以清洗参数为决策变量,通过GA-SA混合算法求解优化参数。最后,对设定权重下的子目标优化结果进行试验验证。结果 在仅考虑清洁度这一目标时,试验结果表明,清洗距离范围为8.5～12 cm,清洗角度范围为70°～83°,清洗流量范围为0.6 L/min及以上,清洗时间范围为2 s及以上。通过求解多目标优化模型,获得清洗工艺参数组合,距离为10.801 7 cm,角度为77.459 5°,流量为0.630 1 L/min,时间为2.207 0 s。结论 相较于传统助航灯具清洗方式,干冰清洗多目标参数混合优化获得的工艺参数组合在保证清洁度的前提下,可以实现同时使节约清洗原料、降低发光口磨损度、提升清洗效率达到理想效果的最优解,解决了人工手动清洗费时、耗力、成本高等问题。     

大尺寸硅片自旋转磨削的试验研究

利用基于自旋转磨削原理的硅片超精密磨床,通过试验研究了砂轮粒度、砂轮转速、工件转速及砂轮进给速度等主要因素对材料去除率、砂轮主轴电机电流以及磨削后硅片表面粗糙度的影响关系。研究结果表明,增大砂轮轴向进给速度和减小工件转速,采用粗粒度砂轮有利于提高磨削硅片的材料去除率,砂轮轴向进给速度对材料去除率的影响最为显著;适当增大砂轮转速,减小砂轮轴向进给速度,采用细粒度砂轮可以减小磨削表面粗糙度;在其它条件一定的情况下,砂轮速度超过一定值会导致材料去除率减小,主轴电机电流急剧增大,表面粗糙度变差;采用比#2000粒度更细的砂轮磨削时,材料去除率减小,硅片表面粗糙度没有明显改善。     

加工电熔锆刚玉砖用电镀金刚石磨轮的研制和应用

电熔锆刚玉砖是玻璃熔窑最重要的耐火材料,该砖结构致密、热稳定性高、耐磨性好、抗蚀能力强,只有超硬磨料才能对锆刚玉砖表面进行有效磨削。本文通过复合电镀方法研制和生产金刚石磨轮,并给出了复合电镀金刚石磨轮的工艺流程。在研制过程中,对金刚石磨轮的基体和胎体进行了优化设计,分析了金刚石质量、金刚石浓度、金刚石粒度对磨削过程的影响,采用两种品级、四种粒度的金刚石按一定比例混合使用,扩大了磨轮的适用范围,提高了磨轮的自锐性,研制的电镀金刚石磨轮用于磨削锆刚玉砖耐火材料,其平均使用寿命达到168．36m^2,与热压焊接金刚石磨轮比较,平均寿命和磨削效率分别提高16．5％和20％。使用结果表明：电镀金刚石磨轮是最适合磨削加工电熔锆刚玉砖的金刚石工具,加工后的锆刚玉砖具有精确的几何形状和高光洁度的表面,同时,选择合适的金刚石磨轮和合理的磨削参数,对电镀金刚石磨轮的使用寿命和磨削效率以及锆刚玉砖的加工质量有重要影响。     

Multi-objective optimization of process parameters during low-pressure die casting of AZ91D magnesium alloy wheel castings

Multi-objective optimization has been increasingly applied in engineering where optimal decisions need to be made in the presence of trade-offs between two or more objectives. Minimizing the volume of shrinkage porosity, while reducing the secondary dendritic arm spacing of a wheel casting during low-pressure die casting(LPDC) process, was taken as an example of such problem. A commercial simulation software Pro CASTTM was applied to simulate the filling and solidification processes. Additionally, a program for integrating the optimization algorithm with numerical simulation was developed based on SiPESC. By setting pouring temperature and filling pressure as design variables, shrinkage porosity and secondary dendritic arm spacing as objective variables, the multi-objective optimization of minimum volume of shrinkage porosity and secondary dendritic arm spacing was achieved. The optimal combination of AZ91 D wheel casting was: pouring temperature 689 °C and filling pressure 6.5 kPa. The predicted values decreased from 4.1% to 2.1% for shrinkage porosity, and 88.5 μm to 81.2 μm for the secondary dendritic arm spacing. The optimal results proved the feasibility of the developed program in multi-objective optimization.     

单颗钎焊金刚石磨粒磨损试验研究

采用单颗磨粒试验方法,以碳钢碟轮为修整工具,研究金刚石和CBN磨粒修整过程中的磨损特征。结果表明:砂轮和修整碟轮的相对速度对金刚石磨粒的磨损有重要影响;相对速度为51.9 m/s时,金刚石磨粒的磨损高度为50.1 μm;相对速度为17.3 m/s时,金刚石磨粒的磨损高度显著减小,为19.5 μm。通过相同条件下金刚石与CBN磨粒的磨损特征对比,表明金刚石磨粒在磨损过程中同碟轮之间发生化学作用,加速金刚石磨粒的磨损;对试验后金刚石磨粒进行拉曼光谱分析,并未检测到石墨物质。      

磨削印刷线路板铣刀时的锯齿现象及其消除

本文针对金刚石砂轮磨削印刷线路板(PCB)铣刀过程中铣刀切削刃产生的锯齿现象进行了分析,研究了砂轮粒度、砂轮转速以及切沟速度对铣刀切削刃锯齿的影响.研究结果表明,随着砂轮粒度的减小,切削刃质量得到提高,砂轮转速和切沟速度对切削刃质量都有影响,其中砂轮粒度对切削刃质量的影响最为重要.     

A multi-objective genetic algorithm (GA) approach for optimization of surface grinding operations

A genetic algorithm (GA) based optimization procedure has been developed to optimize grinding conditions, viz. wheel speed, workpiece speed, depth of dressing and lead of dressing, using multi-objective function model with a weighted approach for surface grinding process. The procedure evaluates the production cost and production rate for the optimum grinding condition, subjected to constraints such as thermal damage, wheel wear parameters, machine tool stiffness and surface finish. New GA procedure is illustrated with an example and optimum results such as production cost, surface finish, metal removal rate are compared with quadratic programming techniques.     

基于SPA的6061铝合金脉冲激光焊接工艺参数优化

以激光峰值功率、焊接速度、脉冲宽度、离焦量为优化工艺参数，以焊接接头的抗拉强度、断后伸长率、焊缝熔深、焊缝宽度为综合优化工艺目标，运用正交试验与集对分析相结合的方法对6061铝合金脉冲激光焊接工艺进行了多目标优化. 通过正交试验获得数据样本，利用集对分析法对数据分析以实现工艺参数的优化. 首先确定单工艺目标与理想解的同一度、对立度、贴近度，然后以单工艺目标贴近度的权重和表示综合工艺目标的贴近度. 最后根据不同工艺参数、不同工艺水平的综合工艺目标的平均贴近度确定最佳工艺. 优化结果为:激光功率3.5 kW、焊接速度2.4 m/min、脉冲宽度4.0 ms、离焦量-1 mm.     

Modified PSO algorithm for multi-objective optimization of the cutting parameters

Economic profit of machining is essentially based on the optimal selection of cutting parameters. In this paper, a multi-objective particle swarm optimization approach is introduced to optimize the cutting parameters in turning processes: cutting speed, feed rate and cutting depth. The proposed model presents the problem in form of a multi-objective problem with production rate and used tool life objectives and has a set of constraints that represent the important limitations to be satisfied. To obtain the non dominated solutions and build the Pareto front graph, a modified dynamic neighborhood particle swarm optimization (DNPSO) technique is used. In addition, a fuzzy-based mechanism is employed to extract the best compromise solution. The results on an illustrative sample reveal the capabilities of the proposed DNPSO approach to generate well-distributed Pareto optimal solutions. Comparison with multi-objective deterministic approach (Min?CMax) shows the superiority of the proposed approach and confirms its potential for solving multi-objective problems.     

钎焊单层金刚石砂轮的现存问题及其对策

概述了用活性钎料将金刚石磨料钎焊到钢基体表面制作单层金刚石砂轮 ,比传统的单层电镀金刚石砂轮具有明显的工艺优势。分析指出了钎焊工艺的现存问题 ,即如何实现金刚石磨料与合金钎料层高的结合强度、钎料层厚度的均匀性和金刚石磨料的有序排布。给出了可行的解决方案 ,即利用Ag -Cu -Cr或Ni-Cr等活性钎料与金刚石界面化学反应生成的Cr7C3 和Cr2 3 C7实现钎料层与金刚石间的高强度结合 ;通过砂轮地貌优化 ,优化出磨粒排布方式 ,然后按优化的结果排布磨料。研制出了具有磨料出露高度高、有序排布、钎料层厚度一致性、高结合强度、高锋利度的单层钎焊金刚石砂轮。     

A study on ELID ultra precision grinding of optical glass with acoustic emission

ELID grinding of BK7 glass and Zerodur was investigated using acoustic emission. Experiments showed that the contacting area between the wheel and workpiece in a grinding process was critical to influence wheel loading for a fine grit size resin-bonded cup wheel. ELID can be used for efficient material removal when the wheel/workpiece contacting area is large. Correlations were observed between the dressing intensity on the ELID wheel and the detected AE signals. Aggressive ELID dressing parameters for grinding with finer grit size wheels corresponded to a lower AE level. With an increase in the processing time of an ELID wheel, low and stable AE amplitudes became large with fluctuations due to the deterioration of the grinding wheel. Results indicate that the AE sensing technique has the potential to be adopted as an effective method for monitoring an ultra precision grinding process, identifying the condition of the grinding wheel and investigating the mechanism of ELID grinding.     

精密轴承磨削金刚滚轮修整工艺优化研究

目的 通过对轴承套圈表面修整工艺优化的研究,实现对轴承套圈表面优质高效的磨削加工.方法 首先基于金刚滚轮修整原理和力学原理,建立修整过程系统简化模型,根据模型求得系统固有频率,再根据频响函数曲线图确定主轴最佳转速.然后建立砂轮与滚轮的运动轨迹方程,根据方程求得曲率半径,再根据曲率半径求得使砂轮表面粗糙度较低的修整速比.接着引入一个新的物理量干涉角,根据经验确定一个较优的干涉角,将修整速比代入,求得最后的滚轮进给速度.最后通过间接获得的磨削力大小来优化整个修整过程,若磨削力偏大,则重新选择主轴转速.结果 根据该方法得到优化结果,选用砂轮转速为23994 r/min、滚轮转速为5473 r/min、修整进给速度为1.77 mm/min、磨削力为37.2 N时,轴承套圈表面能获得较高的质量.对比优化前后轴承套圈沟形,由优化前的不合格变为优化后的合格,有了显著的改善.结论 将修整参数运用多个方法进行确定,并通过磨削力进行最后的优化.根据加工产品表面呈现出的问题,可以找到对应的参数,进而对参数进行单独优化,为企业优化轴承套圈表面质量提供了一套科学有效的方法.     

石材加工中的磨轮磨削工艺

本文是通过实验的方法研究花岗石磨抛工艺,分析磨轮磨损的原因和影响光泽度的因素,探讨磨轮在花岗石磨削过程中的半径补偿,以指导实际生产,提高生产效率和加工精度。通过实验可以得到以下结论：磨轮的磨损主要取决于石材的硬度和石材去除量,石材硬度愈高,磨轮寿命愈短;去除量愈大,磨轮磨损愈大。树脂型磨轮磨抛花岗石,磨轮半径每米要补偿0．01-0．02mm。光泽度与磨粒的粒度和主轴转速有关,磨粒的粒度越小,转速愈高,光泽度愈高。     

碟轮修整单层钎焊金刚石砂轮的试验研究

单层钎焊金刚石砂轮在制作完成之初由于砂轮基体加工存在误差以及磨粒粒径大小不一等原因造成磨粒等高性不一致,这使其难以在硬脆材料的精密磨削中得到广泛的应用。采用自制的钎焊碟轮对80/100#单层钎焊金刚石砂轮进行了修整试验研究。在修整试验前后跟踪了砂轮磨粒等高性的变化,进行了SiC陶瓷的磨削试验,并观测了工件表面质量的变化情况。试验结果表明:采用此方法能够实现单层钎焊金刚石砂轮的高效精密修整。修整试验结束后砂轮磨粒等高性较好,磨削SiC陶瓷的表面质量得到明显改善,表面粗糙度Ra值达到了0.1μm以下。     

On the study of creep feed grinding of alumina

Several issues involved in creep feed grinding of alumina with diamond wheels were studied. Influences of variables on responses were investigated. Off-line optimization was performed by formulating the grinding process as a multi-objective nonlinear mixed integer problem. The dominant mechanism of material removal was determined. The grinding process was simulated to obtain the number of active cutting edges and the grinding parameters such as cutting length, maximum undeformed chip thickness, etc. Unit load distribution was characterized and then used to estimate the percentage of cutting edges that fracture or plastically cut the material and to derive the probability distribution function for substance cracks. Fractal concept was applied to characterize wheel profiles. Findings from these studies are reported in this paper. These studies are definitely not complete, but surely shed some light on the creep feed grinding process of ceramic materials.     

Ni-Cr合金真空单层钎焊金刚石砂轮

单层高温钎焊超硬磨料砂轮具有传统电镀砂轮无法比拟的优异磨削性能 ,国内应及早研制开发应用此种砂轮。本文利用真空炉中钎焊的方法 ,用Ni Cr合金钎料 ,适当控制钎焊温度、保温时间和冷却速度 ,实现了金刚石与钢基体间的高强度连接。扫描电镜X射线能谱 ,结合金相及试样逐层的X射线结构分析 ,剖析了Ni Cr合金与金刚石和钢基体钎焊界面的微区组织结构 ;揭示了Ni Cr合金对金刚石和钢基体表面的浸润和钎焊机理。即在钎焊过程中会在金刚石界面形成富Cr层并与金刚石表面的C元素反应生成Cr7C3,在钢基体结合界面上Ni Cr合金和钢基体中的元素相互扩散形成冶金结合 ,这是实现合金层与金刚石和钢基体都有高结合强度的主要因素。最后重负荷磨削试验表明金刚石为正常磨损 ,没有整颗金刚石脱落 ,说明金刚石确有高的把持强度     

Influence of surface topography evolution of grinding wheel on the optimal material removal rate in grinding process of cemented carbide

Most of the reported studies on the optimization of grinding parameters do not consider the evolution of the surface topography of grinding wheels, and the established empirical models will no longer apply when the surface conditions of the grinding wheel changes. In this paper, an integrated model based on the surface topography of grinding wheel is established. The grinding process of cemented carbide is simulated using the established model, and the simulation results are analyzed to obtain the surface roughness model and the specific grinding energy model based on the undeformed chip thickness distribution. Subsequently, the grinding constraint models are defined according to the two grinding constraints—surface roughness and specific grinding energy. Through inversion analysis, the maximum material removal rate of the given grinding wheel surface conditions satisfying the defined grinding constraints are obtained, and the influence rules of the grinding wheel surface conditions on the maximum material removal rate are analyzed. Then the grinding wheel surface conditions are adjusted by changing the radial dressed height of the grinding wheel and the arrangement distance of the grains in wheel circumferential direction to improve the maximum material removal rate of the grinding wheel. Finally, the optimization results are verified through grinding tests of cemented carbide.     

A systematic approach to design high-performance feed drive systems

A systematic design methodology for the mechatronic system composed of mechanical and control subsystems is proposed to design high-speed and high-precision feed drive systems. Strict mathematical modeling and identification processes of the subsystems are performed in this paper. Parametric studies and circular motion experiments in the x–y table are conducted to investigate the influence of interactions on the performance of feed drive systems. Based on analyses of the system performance according to design and operating parameters, a nonlinear constrained optimization problem including the relevant subsystem parameters of the feed drive system is formulated. The multi-objective optimization procedure and normalization technique are introduced in the design process. A Pareto optimum solution set is applied to investigate the relationships between objective functions. The effectiveness of the proposed design methodology is verified through numerical case studies.     

应用弹性砂轮对铝合金镜面磨削工艺研究

目的解决铝合金手机外壳传统抛光工艺中存在的抛光效率低等问题。方法采用聚氨酯弹性砂轮对6061铝合金进行了磨削加工,使用正交试验研究了磨料粒度、进给速度、切削深度、砂轮线速度对加工表面粗糙度及材料去除率的影响。试验中使用折线走刀方式进行加工,可减轻磨料分布不均带来的影响。使用白光干涉仪测量了加工后表面的粗糙度,通过计算单位时间内工件的质量变化得出了去除率,并通过对结果的综合优化得出了最优工艺参数。结果在选取的16组磨削工艺参数中,可获得的最低表面粗糙度为44.87 nm,最大去除率为0.329 g/min。对表面粗糙度影响最大的因素为磨料粒度,影响最小的因素为进给速度;对材料去除率影响最大的因素为切削深度,影响最小的为进给速度。经过综合优化,最佳工艺参数组合为:砂轮600#,转速2000 r/min,切削深度0.04 mm,进给速度20 mm/min。结论弹性聚氨酯砂轮应用于铝合金磨削可提高加工表面质量,可简化工艺流程,节省备料和安装调整时间,从而提高效率。