Design for variable pitch end mills with high milling stability

The strong demand for increasing productivity and workpiece quality in milling process makes the machine?Ctool system operate close to the limit of its dynamic stability. Besides predicting accurately chatter stability, it is required that some optimizations should be conducted, e.g., cutter structure, for improving the dynamic stability limits. Milling cutters with variable pitch angles can be very effective in improving stability against chatter for certain speed ranges, which will be predicted by the model presented here. The present paper deals with the design of structural geometry of variable pitch end mills in detail. Based on the analysis of tooth engagement factor, which is expressed and extended in the paper, an approach is proposed to design variable pitch end mill with high milling stability. The certain speed ranges with high milling stability are given. An example of the design of variable pitch end mills is illustrated to demonstrate the validity of this method.     

Modeling dynamics and stability of variable pitch and helix milling tools for development of a design method to maximize chatter stability

Chatter is one of the major limitations in milling operations causing poor quality and reduced productivity. Stability diagrams can be used to identify deep stable pockets which usually occur at high spindle speeds. However, the required high cutting speeds may not be applied in some cases due to machinability or machine tool limitations. It is known that variable pitch and helix tools help suppressing chatter even at low cutting speeds. These tools may offer high productivity if they are properly designed. The literature on variable geometry milling tools is mainly limited to modelling and simulation whereas for industrial applications design guidelines are needed for selection of variation pattern and amount which is the focus of this paper. Dynamics and stability of variable pitch and helix tools are modelled and solved in frequency domain as well as using Semi-Discretization Method employing multiple delays. A practical but accurate design method is presented for selection of the best variation combination to maximize chatter free material removal rate without using time consuming computer simulations. Increased stability with the tools designed using the proposed method is demonstrated by several examples which are verified experimentally.     

Study on vibration reduction mechanism of variable pitch end mill and cutting performance in milling titanium alloy

The vibration reduction mechanism of variable pitch end mills was analyzed by the theory of energy balance of the frequency spectrum line. The variable pitch mill can reduce the forced vibration in the cutting process due to the uniform distribution of frequency spectrum line energy and lower peak energy of the cutting force. Aimed at the vibration phenomenon which restricted the efficiency in cutting aero material titanium alloy, high-speed cutting experiments of titanium alloy Ti6Al4V were set with variable and equal pitch mills under dry and down-milling environment. The influences of cutting speeds on cutting forces and tool vibration were analyzed at time domain and frequency domain, respectively, by which the vibration reduction mechanism of variable pitch mill was verified. Due to the misalignment of end mill no. 3, high-level cutting forces and tool vibration were caused by the unequal cutting load on each edge. It is found that severe tool vibration was produced under the cutting speed of 150 m/min because of low-frequency resonance in the cutting process.     

The reconstruction of helical particles with variable pitch

In the reconstruction of helical particles, it is normally assumed that translation along the length of a particle is coupled to rotation about its axis. This assumption is not valid for particles whose pitch varies along the particle length (e.g. actin, HbS fibers), and application of the usual algorithms results in significant errors in both the shape and coordinates of subunits in the reconstructed density map. We have developed an iterative procedure for reconstructing particles with variable pitch. The goal of this procedure is to obtain an accurate estimate of the local pitch of the particle which can then be incorporated into the reconstruction algorithm. This involves synthesis of trial model structures which have constant pitch. The local pitch is derived from a cross-correlation analysis between these trial models and the variable pitch particles. The constant pitch models are constructed using coordinates measured from the reconstructed density maps. Each iteration of the procedure provides an improved estimate of the pitch which is incorporated into the succeeding iteration. The fidelity of the reconstruction is determined from cross-correlation between the original micrograph and a variable pitch model. The iterations are continued until the cross-correlation coefficient between the variable pitch model and the micrograph of the particle is maximized. The implementation of the iterative procedure is described and its behavior is evaluated using model structures which incorporate variations in pitch similar to those actually occurring in sickle hemoglobin fibers. The results indicate that the iterative reconstruction procedure considerably reduces the errors associated with constant pitch reconstructions. These tests provide a basis for applying this procedure in the structural analysis of micrographs of helical particles which display variable pitch. Application to sickle hemoglobin fibers resulted in an improvement in the accuracy with which the hemoglobin S molecules can be located in the density maps.     

基于UG的变螺距螺旋面的研究与开发

通过对螺旋面生成原理的分析 ,建立变螺距直母线螺旋面的数学模型 ,并基于UG环境进行二次开发 ,成功地扩展了UG的螺旋面生成功能。介绍利用UG OpenAPI建立螺旋面的开发技术和实现方法     

CNC2190数控龙门铣床螺距误差补偿与重建

对数控机床反向间隙补偿和螺距误差补偿原理及测量方法进行了深入研究和分析,并针对CNC2190数控铣床FANUC 18-M系统的螺距误差进行实际补偿和重建,取得了良好的补偿效果,说明对滚珠丝杠传动机构的反向偏差与螺距误差进行补偿是恢复和提高机床精度的一种重要手段.     

考虑变时滞效应的弱刚度球头铣刀铣削稳定性研究

弱刚度球头铣刀广泛应用于深腔模具零件的铣削中,加工过程中容易发生颤振,确定加工稳定域是实现稳定铣削的重要手段,但该铣削系统具有变时滞特点,稳定性分析的难度较大,制约着加工质量的提高。为此,提出一种弱刚度球头铣刀铣削稳定性分析方法。首先,建立弱刚度刀具系统的动力学方程;接着,基于Newton-Raphson求解出刀齿选定点的时滞量;最后,基于全离散法提出考虑变时滞再生效应的稳定性分析方法,并利用Floquet定理获得了不同转速所对应的临界切深,构建出铣削稳定性叶瓣图。实验结果表明在叶瓣图的非稳定域铣削时铣削力中含颤振频率成分,所加工表面的S_y和S_a比稳定域内加工表面增大35%和42%,说明该分析方法是可靠的,可为切削参数的选择和优化提供依据。     

The influence of end mill helix angle on high performance milling process

The results of experimental research on the influence of the helix angle on high performance milling of AlZn5.5MgCu alloy are presented. End mills with a wavy shape of a cutting edge, dedicated to rough high performance machining, were used. The helix angle was changed in the range of 20° to 50° with a step of 5°. During the milling tests, three cutting force components were measured. After each test cutting, chips were collected and analyzed. A recording of the chip evacuation process using a high-speed camera was also conducted. The influence of the helix angle on cutting force components was determined and the mathematical models of the forces were calculated. The significance of coefficients in the obtained equations was analyzed as well. The recorded images of the chip evacuation were analyzed. The displacement and the angle of the chip evacuation were determined. Based on the analysis of the selected images the impact of the helix angle on the direction and evacuation velocity of chips was determined. The size and shape of the obtained chips was also analyzed.

     

变截面变螺距螺杆的四轴数控编程、仿真及加工(下)

正6 UG后处理器与机床参数的匹配6.1设置机床参数本文使用的设备是一台三菱M64控制器的四轴(X轴、Y轴、Z轴和A轴)加工中心。为了避免数控分度头的返程误差,在加工过程中要求数控分度头始终正转,因此,设置机床第四轴(即旋转轴A轴)的1089号参数为0(该参数用来设定旋转轴的捷径控制,0表示没有捷径,正负号用来确定旋转轴的转向;1表示使用捷径,当使用绝对值指令时,将按移动量小于180°的方向移动);设置1090号参数为1(该参数用来设定超过360°的旋转轴移动量,设置为0时,表     

非均匀螺旋角铣刀的结构分析和稳定性预测

高速铣削加工中,传统均匀螺旋角刀具不能有效抑制铣削过程中的再生颤振,但非均匀螺旋角铣刀却可以解决此类问题。本文通过分析各个铣削刃螺旋角和容屑角的空间结构关系,并结合"再生因子"探究其与再生颤振之间的关系。确定非均匀螺旋角与容屑角之间的控制方程,并建立铣削动力学模型。通过增强摄动同伦法(EMHPM)计算出非均匀螺旋角铣削加工过程中的稳定性叶瓣图。采用试验验证非均匀螺旋角刀具的有效性,利用本文方法与全变量插值法进行比较(对比试验1);利用均匀螺旋角刀具模型与非均匀螺旋角刀具模型进行比较(对比试验2)。试验结果表明,本文方法可以准确预测铣削稳定性,非均匀螺旋角可以有效提高铣削稳定性。     

异形瓶分件供送变螺距螺杆的三维实体建模

提出了一种绘制异形瓶变螺距螺杆螺旋槽的解析作图法,并对传统的设计方法进行了修改.利用PRO/E的扫描混合功能,构造了变螺距螺杆的三维实体模型,并通过ADAMS进行了运动仿真分析,证明了按本方法设计的变螺距螺杆与供送件不会发生干涉,运行平稳,仿真结果与理论曲线相吻合,验证了模型建立的正确性.解决了复杂形体供送件螺杆的参数化设计,完善了其设计理论与设计方法.     

变螺距不等深异形螺杆的几何建模及数控加工

基于变螺距不等深异形螺杆几何成形原理,分析几何建模难点,建立数学计算模型.生成轨迹曲线,巧妙控制扫掠方法构建精准几何模型;在此基础上,根据变螺距不等深异形螺杆螺旋槽型面要求,设计工艺方案,提出刀具轨迹计算方法.完成了复杂异形螺杆的几何建模及数控加工,实现了CAD与CAM无缝连接.     

风力机独立液压变桨距控制系统建模与仿真分析

建立独立液压变桨距控制系统的数学模型,并对变桨距控制系统进行稳定性分析,确定独立液压变桨距控制系统的设计参数;通过对风力机系统进行SIMULINK仿真分析,验证了风力机能在超额定风速状态下正常工作,说明此独立液压变桨距控制系统模型的可行性和设计参数的准确性,为开发液压变桨距控制器提供了依据。     

粒子群优化变论域模糊PID控制在风电机组变桨距中的应用

风力发电机变桨距系统采用传统PID控制,不仅超调大、调节时间长、精度低,而且在超过额定风速时,风电机组的输出功率波动比较剧烈,误差较大。该文采用粒子群优化算法改进变论域模糊PID控制器,仿真结果表明:粒子群优化变论域的模糊PID控制器具有良好的动态性能及对风速扰动的鲁捧性,可以平稳地输出功率。     

力觉临场感遥操作机器人系统的时延稳定性分析

在力觉临场感遥操作系统中,通讯时延的存在严重影响系统的稳定性,对时延稳定性的分析集中在定常时延,很少述时变时延的情况,本文从分析系统的动力学方程入手,构造适当的Lyapunov V函数,并据此来分析时变时延下系统处于约束运动状态下的稳定性。     

自抗扰控制技术在风电变桨控制系统中的应用

研究了自抗扰控制技术在风力发电变桨距控制系统中的应用。首先介绍了风力发电机组的机理模型,然后介绍了自抗扰控制的基本原理。最后,设计了自抗扰控制器,并介绍了其参数整定方法,并应用在了风力发电的变桨距控制系统中。仿真结果表明这种方法可以有效抑制随机风扰动下电机转速偏差,实现恒功率控制。     

Stability of shaping trajectories in milling: Synergetic concepts

The use of synergetic concepts in studying the steady shaping trajectories of the tool relative to the workpiece in end milling is discussed, with allowance for elastic displacements and their stability. A two-level hierarchy of dynamic equations is employed. At the first level, steady trajectories are considered. At the second, their stability is analyzed on the basis of variational equations for these trajectories. The case in which the pulsed reaction of the system is an order of magnitude less than one period of the displacement cycle is considered.     

轮槽加工中铣削力与铣削温度分布规律研究

轮槽铣刀的改进往往是推动轮槽加工技术进步的最直接动力,而轮槽铣刀不同点的切削用量不同,很难测量出刀具不同点的力和温度。基于微元思想并利用标准盘铣刀和等效方法进行了铣削试验,得到了轮槽铣刀相应型线上铣削力与铣削温度的分布曲线并关注了危险点。     

浅谈仿真工具对控制系统稳定性的分析

介绍Simulation Program with Integrated Circuit Emphasis(SPICE)-PSPICE、MATLAB仿真软件在自动控制模拟仿真分析中的应用,更新了传统的设计与分析的模式,并给出了实用的电路仿真实例。充分利用功能强大的数据分析软件PSPICE对系统函数进行仿真,并用另一软件MATLAB对此系统进行了系统仿真,对其仿真结果进行了分析和比较。