采煤机端盘截齿载荷特性研究

为研究采煤机端盘截齿的载荷特性,以MG500型采煤机滚筒为研究对象,采用非线性动力学仿真软件LSDYNA建立采煤机螺旋滚筒与被截割煤岩的有限元模型,利用该模型研究了斜切工况下端盘截齿的受力特点和截齿载荷特性随安装参数的变化规律。研究表明:斜切进割过程中,端盘截齿截割阻力和滚筒截割阻力矩随端盘截齿圆周切向安装角的增大而减小,随端盘截齿截距的增大而增大;滚筒截割阻力矩的特征值均随圆周切向安装角的增加其减小的趋势随之减缓,随截距的增大其增加的趋势也随之增强;为使滚筒拥有良好的截割性能,端盘截齿宜选用较大的圆周切向安装角和较小的截距。     

滚筒采煤机负载的波动性分析

为了寻求滚筒采煤机正常工作时自身产生振动与冲击的原因,经过对滚筒上截齿受到的截割阻力与牵引阻力以及该两力在采煤机的牵引方向和竖直方向分力进行分析,得知两分力大小与截齿的切削厚度和旋转角度位置有关;研究了滚筒上受到的瞬时力与平均力的计算方法,推导了综合旋转角度和切削厚度的载荷波动系数的计算公式,并对所建立的公式进行了仿真模拟。结果表明:截齿数目从偶数增加1变为奇数时,载荷的波动系数的值明显减小;截齿从奇数增加1变为偶数时,载荷的波动系数不一定减小;适量的增加滚筒上同一螺旋线上截齿的数目可以有效的减小载荷的波动系数;为了提高截齿的使用寿命和可靠性以及滚筒的稳定性,减小滚筒和整个采煤机的冲击性,同一螺旋线上一周内截齿的数目应该尽量选用奇数。     

采煤机截齿截割阻力试验研究

为研究采煤机工作状态下截齿截割阻力变化特性,设计了截齿截割阻力试验方案,并应用该试验方案,进行了斜切进刀工况和正常工况下的模拟截割试验,得到了截割阻力试验变化曲线。分析试验结果可知:在斜切进刀和正常工况下各截齿截割阻力均为间歇周期分段变化,且在单个周期内会出现波动;截割阻力在斜切进刀工况下整体上先增大后减小,但在正常工况下,整体较稳定;在斜切进刀工况和正常工况下,截齿截割阻力均会出现一些突变,斜切进刀工况下最大截割阻力可以达到6 700 N左右;在斜切进刀工况下,各截齿开始参与截割的位置差异性较大,最大相差约1.10×104mm;能为采煤机斜切进刀工况下事故频发的原因提供试验依据,为截割部的设计提供试验数据。     

运动参数对螺旋滚筒截割过程的动力传递问题影响分析

利用ANSYS/LS-DYNA软件建立了复杂煤层条件下螺旋滚筒与煤岩的耦合模型,基于不同工况进行截割过程的动态模拟,提取了滚筒与截齿的工作载荷,并分析了载荷的变化规律。通过对螺旋滚筒截割煤岩的动力学分析得到了由煤到岩变化时螺旋滚筒的应力云图及载荷变化曲线,获取了滚筒与截齿的应力应变等参数的时间历程曲线。研究表明:螺旋滚筒截割煤岩混合界面时,煤岩出现大量崩落,工作载荷波动变大;截齿的最大应力主要集中在合金头齿尖局部接触区域及齿柄头部的轴肩处,齿座最大应力主要集中在其根部;改变牵引速度比改变滚筒转速对滚筒载荷与应力影响更明显。研究成果为薄煤层采煤机螺旋滚筒的结构设计及其截割性能的提高提供了重要参考。     

斜切工况下刮板输送机销排载荷分析

根据对滚筒的受力分析,推导出滚筒在截割过程中所受三向力方程组,结合MATLAB编程,计算得到斜切工况下前后滚筒载荷随滚筒旋转角度变化曲线;以采煤机整机为研究对象,列出整机受力方程组,建立了数学计算模型;基于MATLAB编程,结合斜切工况下前后滚筒载荷变化曲线获得了在斜切工况下前后滑靴载荷变化曲线,由滑靴与销排的接触关系和力的作用是相互的原理,得到斜切工况下作用在销排载荷曲线,并通过ANSYS Workbench仿真分析,获得了刮板输送机销排的应力分布和变形情况。为今后刮板输送机销排的设计及损坏原因分析提供参考。     

重型掘进机截割机构的优化分析

应用Matlab仿真分析软件对截割机构上截齿排布对截割时的动力学特性的影响进行了分析,通过对截齿各排列因素的分析选定以不同的截齿截线间距为研究对象[1],根据现有截齿的截线等间距分布规律及截齿截割作业时的截割规律设置优化后的截线间距为由前到后逐渐增加,使截线的间距分布规律和截割机构截割作业时的截割阻力分布规律及截割作业时的煤层的压张效应相符合,从而分析优化前后的截线间距。该优化方案极大地提升了掘进机掘进作业时的稳定性,减轻了截割作业时对截齿的磨损,增加了掘进机截割机的使用寿命。     

基于实验的采煤机截割比能耗特性分析

为研究复杂工况下采煤机截割效率,采用截割比能耗的方法对不同工况下采煤机能耗利用率进行研究,通过建立截割比能耗模型,并基于实验检测实时测出摇臂传动系统中惰轮轴和行走系统齿轨销轴的应变,利用MATLAB编程计算出惰轮轴和齿轨销轴的圆周力,并对其进行小波降解排除振动和噪音等高频信号的影响,最终在MATLAB中根据能耗计算公式、体积计算公式和比能耗计算模型式子计算出不同工况下的截割比能耗,并对其进行研究,研究结果为:其他工况保持不变的情况下,直行截割的比能耗随着牵引速度的增加而减少;斜切截割比直线截割的比能耗大;截割比能耗随着煤岩硬度的增大而增加。研究结果为采煤机的使用和研发、滚筒结构设计及优化和滚筒截齿分布方式等提供理论基础。     

连续采煤机截齿随机载荷的数学模型

截齿的载荷是确定连续采煤机截割工况和研究其截割性能的依据,根据对连续采煤机截割滚筒结构特殊性和工作条件复杂性的分析,通过假设单个截齿平均载荷与随机载荷的关系、截齿的受力分布类型以及硬质包裹体的接触概率,利用叠加原理,建立了在复杂煤层截割时,连续采煤机上处于截割断面不同位置的截齿的随机载荷的数学模型.     

采煤机截割参数对截齿受力情况的影响研究

针对某煤炭企业服役中的采煤机存在振动的问题,采用仿真计算的方法,完成了采煤机截割滚筒半径尺寸、工作过程截割滚筒牵引速度和截割滚筒转速变化对截割力的影响规律分析.结果表明,采煤机截割滚筒半径尺寸的变化对滚筒截割齿的作用力影响较小,截割滚筒工作时牵引速度和旋转速度的变化对滚筒截齿作用力影响明显,采煤机工作过程中出现振动问题...     

采煤机斜切进刀工况下截割阻力特性研究

针对现有比例算法与功率算法等在计算采煤机斜切进刀工况下截割阻力的不足,从截齿截入煤壁深度入手,分析了截齿参与截割的判断条件,推导了截齿切削厚度、截割阻力的理论计算方法,并利用MATLAB进行了模拟;设计了截割阻力的试验测试方案,进行了试验研究;对比分析了理论模拟与试验结果,两者在周期性、变化趋势、数值特性等方面基本一致,验证了理论分析的正确性和试验的可行性;依据对边界位置关键截齿的分析,确定了斜切进刀工况下采煤机危险截割位置为S=1.25×10~4~1.31×10~4mm。能为分析斜切进刀工况下采煤机滚筒载荷的变化情况,改善采煤机实际操作、预测事故发生等提供理论和试验依据。     

慢走丝电火花线切割粗加工仿真系统的开发

为对电火花线切割加工机理有更深刻的认识,了解加工参数对加工精度的影响规律,介绍了一个电火花线切割加工粗加工的仿真系统。仿真系统通过对放电点的探索、工件的去除以及对线电极丝振动的分析,将实际的加工现象形象地再现于计算机上。为证实仿真系统的正确性,将仿真结果与试验结果进行了比较。在试验结果的获取中,为能够得到很难测量的线电极周围的放电间隙和工件形状数据,提出一种新的三维形状测量方法。通过对仿真结果和试验结果的比较,定性地证明了仿真方法的正确性。研究结果表明:改变线电极张力及伺服电压值时,从仿真过程得到的加工形状结果与试验得到的加工形状结果其倾向基本一致;加工缝端部的形状呈凸形还是呈凹形,取决于加工过程中放电爆发力和静电引力的相对大小。     

快走丝线切割机工艺参数自动选择

建立了线切割加工中放电参数与加工效果之间的神经网络模型,给出了放电参数的优化方法。该方法已用于线切割ＣＡＤ／ＣＡＭ系统,实现了放电参数的自动选择。     

CONSIDERATION OF THE FORM OF THE UNDEFORMED SECTION OF CUT IN THE CALCULATION OF MACHINING FORCES

For the calculation of machining forces in turning processes, the empirical equation of Victor and Kienzle has been established as a common model. However, the model has some constraints. The undeformed chip thickness has to be higher than 0.1 mm and the ratio of undeformed chip width and undeformed chip thickness has to be higher than four. This means that the equation cannot be used for several combinations of process parameters. This paper shows an approach to calculate the machining forces for any form of undeformed sections of cut based on the approach of Victor and Kienzle. In order to achieve this, the undeformed chip thickness and the undeformed chip width are defined in a new way. Furthermore, the direction of chip flow is considered to determine the feed and passive force components.     

超声波振动金刚石刀具对脆性材料临界切削深度的影响

通过脆性材料沟槽切削试验,研究了超声波直线振动金刚石刀具和超声波椭圆振动金刚石刀具对脆性材料临界切削深度的影响,与没加超声波振动的金刚石刀具相比,超声波振动金刚石刀具能增大对脆性材料塑性切削的临界切削深度。提出了超声波振动金刚石刀具切削脆性材料临界切削深度计算公式,分析了导致超声波振动金刚石刀具增大脆性材料塑性切削的临界切削深度的原因。     

新型限速切断阀的流量关断特性分析

建立了限速切断阀在液压电梯系统中的数学模型,利用MATALAB中的SIMULINK工具对限速切断阀的流量关断特性及其在液压电梯系统中的阶跃特性进行了仿真分析,并在模拟试验平台及液压电梯试验台上对限速切断阀进行了系统全面的试验研究,仿真结果和试验结果相比较,两者基本相符。为以后同类阀的设计提供了理论和试验参考依据。     

基于有向割集分解的装配序列生成方法

基于有向图理论,提出了装配序列规划新方法。把有向图理论引入到装配模型表达,提出了有向装配连接图模型,并给出了有向装配连接图的性质。通过对有向装配连接图的割集分解计算,实现了装配序列生成。此方法比无向割集分解方法计算量小、产生无效序列少。为进一步剔除无效序列研究了单调非线性装配意义下基于有向割集分解的装配序列生成算法,并讨论了约束的加入和表达方法。最后给出了一个装配实例,证明了算法的有效性。     

CUTTING TEMPERATURE OF TEMPERING BEARING STEEL GCr15 CUT BY PCBN CUTTER

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A SIMPLIFIED SOLUTION FOR THE DEPTH OF CUT IN MULTI-PATH BALL END MILLING

Abstract

The axial depth of cut is an important factor in the dynamic cutting force analysis of milling. In multi-path ball end milling, it varies with the cutting edge position angle. General equations are derived from which the instant depth of cut in ball end milling can be calculated. Examples are given for four path increment modes. The cutting condition in each mode is discussed with respect to the depth of cut. The conditions needed to disengage the tip of the ball end mill from the cut are determined. The "step-up" increment mode has the most favorable cutting condition for cutter tip relief and high cutting velocity. In order to obtain an instant evaluation of the cutting stability, the equations of maximum depth of cut in ball end milling are derived. The exact solutions are obtained from the general equations for the instant depth of cut. More conservative estimates are obtained from the simplified solutions. The results in this paper can be used as a guide in NC part programming to select an optimal cutting strategy and to ensure a stable cutting process in ball end milling.     

A SIMPLIFIED SOLUTION FOR THE DEPTH OF CUT IN MULTI-PATH BALL END MILLING

The axial depth of cut is an important factor in the dynamic cutting force analysis of milling. In multi-path ball end milling, it varies with the cutting edge position angle. General equations are derived from which the instant depth of cut in ball end milling can be calculated. Examples are given for four path increment modes. The cutting condition in each mode is discussed with respect to the depth of cut. The conditions needed to disengage the tip of the ball end mill from the cut are determined. The "step-up" increment mode has the most favorable cutting condition for cutter tip relief and high cutting velocity. In order to obtain an instant evaluation of the cutting stability, the equations of maximum depth of cut in ball end milling are derived. The exact solutions are obtained from the general equations for the instant depth of cut. More conservative estimates are obtained from the simplified solutions. The results in this paper can be used as a guide in NC part programming to select an optimal cutting strategy and to ensure a stable cutting process in ball end milling.     

ENHANCING THE DEPTH OF CUT IN ABRASIVE WATERJET CUTTING OF ALUMINA CERAMICS BY USING MULTIPASS CUTTING WITH NOZZLE OSCILLATION

An experimental investigation is presented to increase the depth of cut in abrasive waterjet (AWJ) cutting of alumina ceramics by introducing a new cutting technique combining multipass operations with controlled nozzle oscillation. Plausible trends of the depth of cut per pass and total depth of cut with respect to the number of passes and the parameters in each pass are discussed. It shows that cutting with nozzle oscillation can significantly increase the depth of cut in the single-pass cutting mode, while further gains in the depth of cut can be made by using multipass cutting with nozzle oscillation. While multipass cutting can be used to increase the total depth of cut for machining thicker materials, it has been found that an average increase of 50.8% in the total depth of cut can be expected by using multipass cutting with nozzle oscillation as compared to single-pass cutting without nozzle oscillation within the same cutting time. Recommendations are finally made as a practical guide for the selection of process parameters in multipass AWJ cutting of alumina ceramics with controlled nozzle oscillation.