Deformation in bar cropping investigated by visio-plasticity

Plane-strain cropping experiments were carried out on specimens made of lead and of aluminium. The use of the former material allowed close satisfaction of the normal plasticity theory assumption of a non-work-hardening materials, and at the same time effectively simulated hot cropping (since the recrystallization temperature of lead is less than room temperature), whilst the use of the latter material enabled a direct comparative assessment of the effect of work hardening.It has been found that the simple cropping process includes three distinct stages of deformation, namely, indentation-rotation, deep penetration, and shearing. The slip-line fields for various stages of deformation during the cropping process were obtained by the visio-plasticity method; these fields enable the determination of the cropping pressure and of the modes of deformation. The visio-plasticity method, essentially, involves measuring the distortion of a grid printed on the plane of the specimen normal to the axis on which no deformation occurs.The coefficient of friction was determined for each point along the face of the moving blade, and its value was found to vary inversely with distance from the freedge. At the cutting edges of both the moving and the fixed blades, full sticking friction was noted, and as these edges are therefore expected to suffer from excessive wear, the recommendation is made that only materials possessing excellent wear-resisting properties should be used in their manufacture.The strain of the test specimens was also determined, qualtitatively, from measurement of the distorted grids, and contours of effective strain were then drawn. These give an indication of local work hardening, as well as of the homogeneity of the billets in respect of hardness and ductility, and are seen to be close in shape to the experimentally observed fracture path.Experimental results show that distortion of the offcuts is inevitable with open cropping blades, and can only be eliminated by the use of mechanical support.     

Research of stress intensity factor of V-shaped notch tip in precision cropping

For carrying out the precise cropping of metal bar with different geometrical sizes, it is very important to obtain the reasonable stress intensity factor of V-shaped notch tip rapidly and accurately. At first, a new precise cropping method, which is the high-speed peripheral low-stress bending fracture cropping is presented in the paper, and its working mechanism is also given in detail. The stress field near V-shaped notch tip is analyzed, and the stress extrapolation method is presented to compute the stress intensity factor of V-shaped notch tip. Based on it, the correctional expression of theoretical stress intensity factor in a handbook of stress intensity factor is also given. The contrasts between stress intensity factor results obtained by means of the stress extrapolation method and the corresponding theoretical results in the handbook of stress intensity factor are also carried out in detail. The results show that the two errors are not more than 5 % and are within a reasonable engineering range. The cropping experimental results for initial loading force and crack propagation life have also confirmed that the correctional expression of theoretical stress intensity factor is feasible.     

基于自由运动的刚性球棒的像机内外参数标定

制作一种两端及中间各安装一个红外反光标志球的刚性球棒,不需要其它复杂标定装置,只要将这种特制的刚性球棒在测量空间内多次随意移动并摄取其图像,即可实现双像机标定。标定算法首先假定主点位于像面中心附近的某个位置,通过Hartley改进八点法求出基本矩阵,继而求出半标定矩阵并对其奇异值分解,再线性地求出焦距。接着求出本质矩阵,奇异值分解后得到旋转矩阵和比例因子意义下的平移向量。利用三角法确定刚性球棒两端点的重建坐标和距离,与标准距离对比确定比例因子。通过评价函数将像机标定转换成寻找两像机最佳主点配对的非线性最小化问题。运用改进的模拟退火进化策略算法迭代优化求解出最佳主点配对,继而求解出像机其它内外参数。与传统方法相比,本文方法不需要对球棒的运动做任何限制,并且能够同时求解出像机内、外参数,改进的模拟退火进化策略算法改善了全局收敛性能并加快了收敛速度。     

外圆磨削强化技术及其磨削力的研究

提出了外圆磨削方式的磨削强化技术,并在M1432B型磨床上进行了试验.针对参量为磨削深度0.3mm、工件速度0.2m/min的试件强化层进行金相分析与硬度测量,发现组织为马氏体且硬度最高达到754HV(约62.3HRC),验证了其切实的可行性及良好的强化效果.对于外圆磨削强化过程中的磨削力,建立了磨削力模型并提供了使用自制弹性顶尖的测量方法,实测后发现切向力与法向力数值随着磨削深度的增大而增大,在磨削深度0.4mm处分别达到了146N和656N,且法向力的数值与增长速度比切向力高.     

参数设定对原子力显微镜测试的影响

研究了不同的测试模式、线扫描点、扫描速率、积分增益和振幅设置对原子力显微镜测试的影响,比较了在不同的测定参数下样品的成像质量、槽深和粗糙度.结果表明,随着线扫描点的增加和扫描速率的降低,成像所需的扫描时间也随之增加,但扫描点越多,图像越精细.积分增益越大,系统响应的越快,但系统的噪音也会随之增加.振幅设置对软样品的影响比对硬样品的大.结合实际操作,还简单介绍了一些原子力显微镜测试的经验.     

影响轧制差厚板冲压成形性能的几何参数研究

轧制差厚板的出现使得汽车行业能够获得更轻的车身重量以及更低的生产成本。为了推动轧制差厚板的应用进程,需要对其冲压成形性能进行深入研究。对轧制差厚板方盒形件进行了冲压成形仿真,以进料量之差、最大厚度减薄率以及厚度过渡区中心移动量为评价标准,分析了不同板厚比及厚度过渡区位置对差厚板成形性能的影响。研究结果表明:板料厚度差越小,过渡区越接近薄侧端部,差厚板的冲压成形性能越好。     

Verifying the geometric precision of machine tools

A method is proposed for determining the basic tests of the geometric precision of a metal-cutting machine so as to assess the influence of its error on the precision of the manufactured parts.     

Monitoring force in precision cylindrical grinding

Aerostatic spindles are used in precision grinding applications requiring high stiffness and very low error motions (5–25 nm). Forces generated during precision grinding are small and present challenges for accurate and reliable process monitoring. These challenges are met by incorporating non-contact displacement sensors into an aerostatic spindle that are calibrated to measure grinding forces from changes in the gap between the rotor and stator. Four experiments demonstrate the results of the force-sensing approach in detecting workpiece contact, process monitoring with small depths of cut, detecting workpiece defects, and evaluating abrasive wheel wear/loading. Results indicate that force measurements are capable of providing useful feedback in precision grinding with excellent contact sensitivity, resolution, and detection of events occurring within a single revolution of the grinding wheel.     

Numerical investigation of the effects of geometric parameters on transverse motion with slanted-groove micro-mixers

Journal of Mechanical Science and Technology - We investigated hydrodynamic phenomena inside several passive microfluidic mixers using a Lattice Boltzmann method (LBM) based on particle mesoscopic...     

基于MALTLAB的等速万向节几何精度的分析

本文在万向节检测装置中运用MATLAB软件对等速万向节的圆周间隙进行了可视化分析,根据圆周间隙的变化规律,找出了引起圆周间隙变化的主要因素及产生振动的原因.为减小等速万向节的误差、降低噪声提供了可靠的依据.     

影响TRB单向拉伸的几何参数研究

将连续变截面辊轧板(Tailor Rolled Blanks,TRB)厚度过渡区离散为有限数量的等厚度区域,采用线性插值的方法描述TRB材料的非均匀性,建立TRB材料的应力应变场。参照等厚度板的单向拉伸试验国家标准,提出TRB单向拉伸试验的概念,在有限元软件ABAQUS中建立TRB单向拉伸的数学模型。以影响TRB单向拉伸的板料过渡区长度、板料厚度比等为参数,以厚度过渡区伸长率和厚度过渡区移动量等为评价标准,通过数值模拟和回归分析对不同方案下的厚度过渡区伸长率和厚度过渡区移动量进行比较。最后得到板厚比和伸长率之间关系的三次拟合曲线,分析厚度过渡区长度、板厚比对厚度过渡区移动量的影响。其结果为TRB拉伸性能标准的制定以及推动TRB在车身轻量化上的应用提供了重要的技术参考。     

切削参数对东非黑黄檀木材铣削力的影响研究

东非黑黄檀是一种常用的红木家具材料 . 以雕铣东非黑黄檀的铣削力为研究对象,采用Box -Behnken响应面分析法设计实验, 研究了切削参数对铣削力的影响,并构建了铣削力的二阶响应回归模型. 试验结果表明:x和y方向的铣削分力,都随着模型中的轴向切深、径向切深、每转进给量的增大而增大.x方向分力随着主轴转速的升高而降低,y方向分力随着主轴转速的升高而升高. 构建的二阶响应模型对铣削分力预测得到的结果与实验结果基本一致,使用该二阶响应模型可以正确预测铣削分力的变化.     

Investigation of a new-type precision cropping system with variable-frequency vibration

To investigate a new-type precision cropping system with variable-frequency vibration, it is necessary to obtain the characteristics of vibrating force and displacement of shearing die in different exciting frequencies. The model and equations of a six-degree-of-freedom vibrating system are established, and the six natural frequencies of the system are achieved by means of classical analysis method, the amplitude-frequency characteristics are described according to Cramer's rule, and the theoretical analysis results are verified by experiments. The approximate relationship between the vibrating force and exciting frequency are achieved and the experimental results show that crack will propagate along z direction, which is in agreement with the theoretical results. The work-piece cross-section obtained by the experiments has no radial distortion and deviation angle, moreover, the cutting force is lower and the die lifetime is longer compared with common bar cropping method. A new cross-section quality assessment method is proposed for the work-piece obtained under the control of different frequency-time characteristic curves. The assessment results show that the linear decrement control mode is better for producing good-quality work-piece.     

齿轮几何参数的选择对传动效率影响的研究

采用单参数齿轮台架试验的方法，基于对试验的曲线和结果分析，揭示了齿轮各几何参数对其传动效率的影响。针对低速重载工况下选择高传动效率、高啮合质量的齿轮副几何参数，提出了几何参数选择原则。研究结果表明，在产品的设计过程中齿轮几何参数的选择，是影响产品具有良好的啮合和节能低耗效果的重要因素。     

仪表测力及测力变化与其精度

针对仪表测力及测力变化对其精度的影响,提出改进措施,从而提高了仪表的测量精度,延长了其使用寿命,满足了检测精密产品的要求。     

一种基于D-H参数的7自由度机械臂机构精度综合方法研究

提出了一种基于最佳精度模型的机械臂机构精度综合的方法,利用遗传算法对D-H参数公差优化分配,为机械臂的精度设计提供理论依据。以一种基于双电机伺服驱动关节的7自由度协作机械臂为研究对象,机械臂的几何定位精度的设计目标为1.4 mm,建立该型机械臂末端执行器的几何定位误差模型;对参数误差进行敏感性分析,找出对机械臂末端执行器几何定位误差影响相对较大的参数误差;根据最佳精度数学模型,利用遗传算法对D-H参数公差优化分配;经过对误差仿真计算分析,机械臂的最大几何定位误差为1.226 7 mm,均值为0.485 9 mm,方差为0.216 5 mm,满足设计要求。为该机械臂的制造装配提供了理论参考依据。与基于最小成本模型的精度综合法相比,提出的精度综合方法不需要统计加工制造成本信息,能够确保机械臂的设计精度满足设计要求,可用于单个或者小批量生产制造机械臂的精度设计。     

关键几何参数对药柱贮存刚度的影响分析

基于粘弹性理论,利用ANSYS有限元软件,建立药柱结构的有限元模型,确定影响药柱贮存刚度的关键几何参数,对不同药柱结构贮存期内的药柱刚度进行分析,研究不同几何参数对药柱贮存刚度的影响敏感度,为药柱结构完整性设计提供理论分析与研究基础。     

Improving the precision of complex parts in external turning

The use of cut-layer simulation to determine the cutting forces is considered.