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Investigation on a new type of low-stress cropping system with variable frequency vibration 总被引:2,自引:2,他引:0
L. J. Zhang S. D. Zhao C. J. Hua C. F. Guo J. Lei 《The International Journal of Advanced Manufacturing Technology》2008,36(3-4):288-295
This paper presents a new type of precision cropping system with variable frequency vibration by which the high-quality cutting
surface can be obtained. On the basis of D’Alembert’s principle, the approximate relationship between the exciting force and
the excited frequency in the cropping is acquired through computation. Five types of excited frequency control curves are
designed and applied in the cropping experiments and the influences of these control curves on the cropping cross-section
and the cropping time are investigated by experiment in details. According to the special feature of the cross-section obtained
in the course of variable frequency vibration cropping, a new measurement method is proposed and applied to assess the quality
of the cross-section. The theoretic and experimental results show that the exciting force acted on the bar in the vertical
direction is larger than that in the horizontal direction and the linear decrease control curve, by which the high quality
cross-section is obtained and the cropping time is reduced, is an ideal control mode compared with other control modes mentioned
in the paper. The experiment also proves that the width of the bar instantaneous fracture region is decreased by reducing
the value of every step frequency change, and the cropping time is also shortened by reducing the durative time of every step
variable frequency under the action of the linear decrease frequency curve. 相似文献
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针对金属棒料传统下料工艺存在断面质量差、材料利用率低、能耗高等问题,提出一种综合利用预制环状V型槽缺口效应、起裂微裂纹及扩展宏观裂纹裂尖应力集中效应的新型气动式棒料可控旋弯下料工艺,详细介绍了该下料工艺的工作原理。基于该工作原理研制了金属棒料气动式旋弯下料试验装置,利用材料力学强度理论与线弹性断裂力学理论,建立了弯矩载荷作用下金属棒料下料过程的力学模型,获得了环状“V”型槽根部微裂纹萌生载荷、扩展裂纹起裂载荷及瞬断载荷的理论计算公式。采用三种不同恒应力强度因子幅水平载荷控制曲线对φ30 mm直径的304不锈钢棒料进行下料试验研究,结合所提出的坯料断面评价方法及其评价指标,对下料所得坯料质量进行了量化评价。结果表明,保持裂尖处于恒应力强度因子幅水平,可以实现金属棒料的可控精密下料,断面质量和下料时间随幅值水平提高而降低,当裂尖处△K=0.7Kc时,坯料最终瞬断区最小。该下料工艺利用断裂力学理论建立旋弯下料机理,可以指导实际下料试验,为后续下料工艺数据库的建立提供理论支撑。 相似文献
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非线性耦合同向回转的双偏心转子振动系统同步行为研究 总被引:1,自引:0,他引:1
随着振动系统逐渐朝着大型化、重型化的方向发展,大激振力振动系统是未来发展一个较热的趋势。基于这一特殊背景,提出了非线性(拉簧)耦合同向回转的双偏心转子振动系统及其同步问题。首先基于拉格朗日方程建立了系统动力学方程;随后采用运动分离法建立系统慢变参数的积分方程,推导出了系统实现同步的同步条件和稳定性准则;其次,通过数值分析研究了系统结构参数对系统同步能力及同步特性的影响;继而,采用龙格库塔法建立了非线性耦合同向回转的双偏心转子振动系统的机电耦合仿真模型,开展了系统的同步状态与系统机电耦合的动力特性的仿真分析;最后设计了相关试验装置,开展了同步试验测试。研究结果表明,系统的同步行为主要受拉簧和支撑弹簧的刚度系数、激振电机的位置参数等的影响;激振电机的相位差随着拉簧刚度系数的增加逐渐稳定在零度附近,相应地系统同步状态从反相同步逐渐变成同相同步,理论研究和试验结果能较好吻合。所有研究为研发高效节能的大型振动机械提供指导作用,同时研究成果也对振动同步领域共性问题的解决具有促进作用。 相似文献
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《Precision Engineering》2013,37(1):222-227
A new apparatus for an ultrasonic vibration-assisted glass hot embossing process has been developed. The upper die constitutes the ultrasonic vibrating device, and a cooler is provided to protect the transducer from the high operating temperatures. An ultrasonic horn originally designed for use at room temperature was modified to ensure correct operation of ultrasonic vibrating device for high temperature use. Because the load cell is located inside a vacuum chamber, the detection of the force applied to the glass during the forming process is not significantly impacted by external forces, and thus, a precise force history of the forming glass can be obtained. Flat hot embossing experiments were performed to investigate the effect of ultrasonic vibration on the amount of force required during forming, and Fresnel structure hot embossing experiments were then conducted to investigate the improvement in molding accuracy gained through ultrasonic vibration. The experimental results are taken to validate the manufacturing potential of the developed apparatus and the improvement in formability achieved by applying ultrasonic vibration. 相似文献
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Effects of joint on dynamics of space deployable structure 总被引:2,自引:1,他引:1
Joints are necessary components in large space deployable truss structures which have significant effects on dynamic behavior of these joint dominated structures.Previous researches usually analyzed effects of one or fewer joint characters on dynamics of jointed structures.Effects of joint stiffness,damping,location,number,clearance and contact stiffness on dynamics of jointed structures are systematically analyzed.Cantilever beam model containing linear joints is developed based on finite element method,influence of joint on natural frequencies and mode shapes of the jointed system are analyzed.Analytical results show that frequencies of jointed system decrease dramatically when peak mode shapes occur at joint locations,and there are cusp shapes present in mode shapes.System frequencies increase with joint damping increasing,there are different joint damping to achieve maximum system damping for different joint stiffness.Joint nonlinear force-displacement is described by describing function method,one-DOF model containing nonlinear joints is established to analyze joints freeplay and hysteresis nonlinearities.Analysis results show that nonlinear effects of freeplay and hysteresis make dynamic responses switch from one resonance frequency to another frequency when amplitude exceed demarcation values.Joint contact stiffness determine degree of system nonlinearity,while exciting force level,clearance and slipping force affect amplitude of dynamic response.Dynamic responses of joint dominated deployable truss structure under different sinusoidal exciting force levels are tested.The test results show obvious nonlinear behaviors contributed by joints,dynamic response shifts to lower frequency and higher amplitude as exciting force increasing.The test results are further compared with analytical results,and joint nonlinearity tested is coincident with hysteresis nonlinearity.Analysis method of joint effects on dynamic characteristics of jointed system is proposed,which can be used in optimal design of joint parameters 相似文献
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要使振动平板夯获得最佳振动压实效果,需合理选择其设计参数,这里在对振动平板夯运动分析的基础上,建立了平板夯的振幅值为目标的优化设计模型,以夯机的重量、振动频率、激振力、移动速度、结构限制等为约束条件。通过遗传算法进行优化求解,获得了满足性能要求的结构参数,为提高振动平板夯的性能设计提供了理论依据。 相似文献
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在研究土体塑性变形时力与变形关系的基础上,建立非线性振动压路机模型。结合某型振动压路机选取了系统参数并计算固有频率,根据选定的数值进行在不同激振力频率下的数值仿真。根据振动压路机实验获取并分析实验数据,得出非线性振动压路机的系统响应特点并验证系统模型的可用性,为研究振动压实提供理论依据。 相似文献
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金刚石线锯横向超声振动切割SiC单晶表面 粗糙度预测* 总被引:2,自引:0,他引:2
把横向超声振动应用到金刚石线锯切割硬脆材料加工中,基于冲量原理分析了线锯横截面上不同位置处金刚石磨粒对工件的法向锯切力。应用压痕断裂力学理论,定量分析了在法向和切向载荷共同作用下磨粒下方中位/横向裂纹扩展的长度和深度。研究了振动磨粒在工件上间歇加载和卸载使横向裂纹优先扩展并抑制中位裂纹扩展的屏蔽效应。建立了横向振动线锯切割硬脆材料时线锯横截面不同位置处磨粒的材料去除模式模型,得到了横向振动线锯切割硬脆材料晶片表面粗糙度的预测公式。以SiC单晶为切割对象,进行普通线锯和横向超声振动线锯切割对比试验,测定线锯的锯切力和晶片表面粗糙度,并对表面形貌进行观察。结果表明,横向超声振动线锯切割SiC是以脆性去除为主塑性去除为辅的混合材料去除模式;同等试验条件下,超声振动线锯切割能使晶片表面粗糙度降低25.7%。表面粗糙度测试结果与理论预测具有较好的一致性。 相似文献
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为分析磁轴承激励下转子系统的振动机理,应用一维有限元方法建立了双盘转子系统动力学特性计算模型,研究了不同类型磁轴承激励下转子系统的动力学行为。研究结果表明:同向旋转的扫频激励力激发了转子系统的正进动模态,而反向旋转的扫频激励力激发了转子系统的反进动模态,两种情况下转子系统均以圆轨迹进动;由于单向简谐激励力可以分解为同向旋转激励力和反向旋转激励力之和,因此在单向简谐扫频激励力作用下,转子系统的反进动和正进动模态均被激发,转子系统以椭圆轨迹进动;在双向简谐扫频激励力作用下,转子系统的进动方向和进动轨迹取决于两个激励力的相位差。研究成果为评估高压压缩机转子系统稳定性时磁轴承激励方案的选取提供了理论依据。 相似文献
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大型空间柔性桁架结构模态实验研究 总被引:2,自引:0,他引:2
提出杆系结构的内力脉冲激振法,克服了宽带随机激振法能量分散不易激起各阶模态以及正弦激励慢的缺点,并用半正弦冲击波形完成了大型空间柔性桁架结构的模态实验,得到了系统的固有频率和模态振型。实验结果与理论计算结果非常吻合,验证了理论计算方法的正确性。实验结果表明采用内力脉冲激振的方法能够有效地激起结构的固有频率。实验所得振动参数可为下一步空间柔性桁架结构振动主动控制提供直接依据。 相似文献
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Yang Fulun Yu Junyi Hong LiJinlin University of Technology Changchun University 《机械工程学报(英文版)》1995,(2)
REGULARITYOFVIBRATIONRESPONSEOFMECHANICALSYSTEMUNDERAFFECTOFVARI-FREQUENCYEXCITINGFORCEREGULARITYOFVIBRATIONRESPONSEOFMECHANI... 相似文献
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《Mechanical Systems and Signal Processing》2007,21(1):389-404
A fully rigid–elastic-coupled dynamic model was developed for a vibration isolation system consisting of a rigid vibrating machinery, multiple resilient mounts and a floating elastic panel. This model was applied to investigate the vibration power transmission behavior of an X–Y motion stage-based system used in semiconductor wire-bonding equipment. The natural frequencies and modal characteristics of the system and its subsystems were numerically evaluated. The total power flow from the X–Y motion stage (the vibrating machinery) to the equipment table (the floating elastic panel) through multiple resilient mounts and the contribution of each force component at mounting junctions to the total power flow were analysed in the concerned frequency range for different types of excitations. The total power flow predicted by the developed model was also compared with that calculated using a conventional elastic support model. It was shown that the developed model provides a more accurate prediction of the total power flow in the frequency range of interest. 相似文献
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当测微仪采用接触式测头测量工件尺寸时,测量力的变化会对测量误差的修正造成一定影响,这种影响在大量程高精度测量中更为严重。为了减小这种影响,提高测量结果的精确度,利用弹簧弹力同磁铁磁力之间的动态力平衡原理设计一种恒力结构,并进行理论计算。对计算结果的分析与研究表明,利用该设计方法实现测量力恒定是可行的。 相似文献