Analytical study of maximal tapping torque during forming screw process

Forming screws lead to a bolted assembly forming the threads of the work-piece by displacing material. The automotive industry is one of the largest markets for forming screws, which have been developed in the last ten years. One of the problems facing the designer of bolted assemblies using forming screws is the knowledge of the forming torque during the process.This study proposes an analytical model based on a previous study concerning radial penetration of a rigid acute wedge into a perfectly plastic material. The method uses the slip-line method with a model taking into account the interaction between two consecutive formed threads and enables the mean pressure on the thread flank to be obtained as a function of the formed thread height. From these results and a knowledge of the forming screw end geometry, an analytical method is proposed for the maximum forming torque, the physical phenomena of the displacement of material in the tapping process is illustrated and the significantly influential parameters highlighted. An experimental study seeks to determine the optimal lead hole on the work piece for an M8 screw. This sets limits on the forming torque and conserves a sufficiently well formed thread shape for good stripping resistance. The experimental results are compared favorably with the results of the analytical study in order to validate the forming screw model.     

基于AdvantEdge的直槽丝锥工艺参数优化

为改善316 L不锈钢材料的攻丝性能,研究以性能指标轴向力、扭矩、温度最低为优化目标,采用单因素试验和全因素试验设计相结合的方法,对影响攻丝性能的直槽丝锥工艺参数(主轴转速、丝锥涂层、切削液种类)进行优化;基于AdvantEdge软件进行攻丝数值模拟,采用熵权分析法确定最佳工艺参数组合,并通过对比试验验证了优化工艺后的...     

Investigation of thread tapping load characteristics through mechanistics modeling and experimentation

A mechanistic model for the prediction of tapping torque and axial force is developed. The model is capable of predicting tapping torque and axial force resulting from chip formation and tool flank/workpiece friction under various machining conditions, including dry tapping and tapping with different cutting fluids. Extensive tests on tapping torque and axial force measurements are conducted to verify the predictive model. Characteristics of the measured tapping loads are studied. It is found that the total tapping load consists of a base load and a chip packing load. The base load results from chip formation and tool/workpiece friction. The predicted tapping load is found to be in good agreement with measured base load. The chip packing load is the result of chip clogging in the flutes, and is random in nature. The chip packing load may be many times that of the base load, depending on tap geometries and the machining conditions. Factors causing severe chip clogging and excessive torque leading to tap breakage are also reported.     

Investigation of the torque characteristics in vibration tapping of hardened steel

Vibration tapping is presented in this paper to solve this problem, as high-speed steel tap is incapable of tapping small-hole (M3) in hardened steel (50HRC). Theoretical analysis with fracture mechanics indicates that the impact effect of the tap on the workpiece results in increased II-type stress intensity factor and extended micro cracks, leading to lower plastic deformation, reduced cutting forces and a much lower tapping torque, and the torsional rigidity of the tap is enhanced in vibration tapping as proved by dynamic analysis. The experimental results show that with well chosen amplitudes, tapping torque decreases as vibration frequency increases, and tapping torque increases as net cutting time ratio increases, where net cutting time ratio influences the tapping torque more significantly. Vibration tapping is then proved to be a practical solution to the problem of small-hole tapping in hardened steel.     

Mechanistic model for the reaming process with emphasis on process faults

A mechanistic model is developed to predict the cutting forces for an arbitrary reamer geometry. Inputs to the model include: tool geometry, feed, speed, initial hole geometry, and process faults including parallel offset runout, spindle tilt, their respective locating angles, and tool/hole axis misalignment. Given these input parameters, the model predicts torque, thrust, and radial forces. The cutting edges of the reamer are divided into elements and the elemental forces are determined from a fundamental oblique cutting model. The model is calibrated over a range of feed, speed, and varying tool geometry. Model validation tests were conducted and model predictions match experimental data well. The effects of process faults on cutting forces are examined through model-based studies. It was found that parallel offset runout, spindle tilt, spindle tilt locating angle, and tool/hole axis misalignment have significant effects on the radial forces. These radial forces are shown to be correlated to hole quality.     

工艺参数对振动攻丝扭矩的影响

结合试验结果，分析了在结构钢和合金钢的振动攻丝过程中，基本工艺参数对攻丝扭矩的影响，得出了不同参数对扭矩的影响规律，对于优化工艺参数、减小攻丝扭矩、改善攻丝效果具有一定的借鉴意义。     

Some investigations on vibratory tapping process

This paper reports the results of an experimental program to study the influence of torsional vibrations on the tapping process. An attachment has been designed and developed to produce controlled torsional vibrations on the tap while tapping. Investigations have been carried out to study the influence of different process conditions, such as tap size, work material, vibration amplitude and frequency, etc., on the tapping torque and thrust during machining. Optimal process conditions which enhance the tap life are reported.     

一种永磁同步电主轴转矩脉动和电磁力波的抑制方法

针对磁极为平行充磁且两边平行的表面式永磁同步电主轴存在转矩脉动和径向电磁力波的问题,提出一种磁极结构优化方法以抑制转矩脉动和径向电磁力波。基于等效面电流法建立磁极表面半径为任意值的永磁同步电主轴转子气隙磁场的解析模型;综合研究转子气隙磁场对定子开槽电主轴转矩脉动、径向电磁力波的影响;在最小气隙长度不变的前提下,确立优化目标(气隙磁通密度的谐波和幅值),并通过迭代计算的方式得到满足不同优化目标的永磁体磁极结构方案(方案一结构和方案二结构);最后,通过有限元法验证转子气隙磁场解析模型的有效性,并对原结构电主轴、方案一结构电主轴和方案二结构电主轴的转子气隙磁场谐波、转矩脉动、齿槽转矩、平均转矩和径向电磁力波进行对比分析。结果表明:该优化方法可以得到满足不同优化目标的永磁体磁极结构方案,实现原电主轴指定阶次磁通密度谐波、转矩脉动和径向电磁力波的综合抑制。     

步进式振动攻螺纹优越性的理论证明

建立了步进式振动攻螺纹的理论模型，证明了步进式振动攻螺纹相对于普通攻螺纹能够降低平均切削扭矩和提高丝锥的动刚度。     

Predictive Cutting Models for the Forces and Torque in Machine Tapping with Straight Flute Taps

In this paper the development of predictive cutting models for the forces and torque in machine tapping operations with straight flute taps is outlined. The models, based on the ‘Unified-Generalised Mechanics of Cutting Approach’, allow for the many tap and cut geometrical variables, the cutting speed and the toolcoating-workpiece material combinations. The models have been verified by extensive computer simulation studies as well as comprehensive experimental testing programmes. This investigation has provided a deeper understanding of the basic cutting action as well as predictive force models of tapping, renowned as “one of the most neglected operation in machining research”.     

移动机器人神经网络补偿计算力矩控制

针对存在动力学不确定建模项、建模误差及外界干扰的移动机器人,设计RBF神经网络补偿计算力矩控制算法。基于反步法设计运动学辅助速度控制率。根据动力学理想名义模型,基于计算力矩法设计一般的力矩控制器。在此基础上,建立具有不确定建模项、建模误差及外界干扰的移动机器人动力学模型,基于计算力矩法设计带有RBF神经网络补偿的力矩控制器,神经网络的权值由自适应律给出。最后,利用Lyapunov理论证明了系统的稳定性。仿真结果表明：神经网络对系统不确定项具有良好的逼近性能,相比于一般的计算力矩控制,所提出的神经网络补偿计算力矩控制算法具有更好的跟踪性能,控制系统具有更好的鲁棒性。     

Effects of Synchronizing Errors on Cutting Performance in the Ultra-High-Speed Tapping

Synchronizing errors between the spindle motor and the z-axis motor directly influences the cutting characteristics in tapping, because the tapping process is accomplished by synchronizing the movement of the z-axis with the revolutionary spindle motion. The excessive synchronizing error can cause tap breakage due to the abrupt increase of cutting torque or damage the thread accuracy by overcutting the already cut threads. This paper describes the effects of the synchronizing errors on the cutting performance in the ultra high-speed tapping and presents a minimum level of synchronizing errors necessary to maintain the quality of the cut thread.     

Analysis of form threads using fluteless taps in cast magnesium alloy (AM60)

Threads are used in the most assemblies of industrial products. Commonly, mechanical components need to have threaded parts allowing fast and accurate assemblies and disassemblies. Internal tapping is one of the most demanded machining operations, and threads obtained by forming have been a good alternative. This work investigates the effect of the factors the hole diameter, the forming speed and types of tool on the responses: torque, hardness, fill rate, and thrust force of the form tapping process. The experiments were carried out with three diameters, three forming speeds, and two coatings. The material used was the AM60 alloy due to its high ductility and wide application as head engine. The results revealed torque is more affected by the hole diameter than thrust force, and little hardening occurred using high forming speed with a small diameter. The fill rate of the thread profile was not significantly affected by the intermediate and large diameters. Finally, it can be stated that the recommended hole diameter provided by the tool's supplier can be modified to achieve more accurate thread profiles.     

基于EMD的非线性扭矩激励作用下单跨转子横向振动响应

针对单跨转子在非线性扭矩激励作用时横向振动的响应,建立在某一频率的扭矩激励作用时单跨转子运动微分方程;分别对转子系统在有、无扭矩激励两种运行状态下的方程求解仿真,运用EMD方法对求解的结果进行分析。结果表明:在扭矩激励作用下横向振动信号中包含多个与激励频率相关的振动信号;并且能量发生了分流,对系统的稳定性有重要影响。最后,建立与仿真模型相同条件的试验台,试验结果验证了数值仿真的正确性;另外试验分解结果中存在不对中故障分量,试验发现不对中故障的存在使得扭矩激励对转子横向振动更突出。     

Intelligent monitoring of tapping tools

On-line monitoring of tapping tools is essential for factory automation and productivity enhancement. Three indirect indexes, namely, average peak-topeak torque, modified RMS (root-mean square) torque, and prediction errors of torque signals, were used to monitor the tap wear conditions. In order to further process these three indirect indexes, a multilayer, feedforward neural network with a total of 18 neurons was used. The three indirect indexes are the inputs of the neural network while the wear states are its outputs. The information contained in the inputs is recoded into an internal representation by the hidden neurons which perform the mapping from input to output.     

负载对数控转台精度影响的研究及试验设计

分析数控转台工作时力和力矩载荷的工况特点,以及YRT转台轴承和抱闸机构承受工作载荷作用时的工作原理。推导六自由度载荷作用下转台主轴形变的计算公式,并总结工况载荷对转台变形和精度的影响。设计了在轴向载荷、径向载荷、弯曲载荷、扭转载荷下检验转台变形的方法。研究内容为数控转台轴承支撑结构和抱闸机构的设计计算提供参考,为数控转台的载荷试验提供试验和检验方法。     

Diagnosis of tapping process using spindle motor current

A two-stage pair-wise feature selection and classification method is proposed to diagnose the tapping process using the electrical current signal of the spindle motor. The motor current is measured with a non-intrusive Hall effect sensor. The diagnostic process is divided into two stages. In the first stage, wavelet coefficients of the current signals are computed and a subset of these coefficients is chosen as the initial diagnostic features based on their discriminatory powers for each pair of the fault classes. At the second stage, principal component analysis (PCA) is applied to reduce the dimensionality of the initial diagnostic features. Non-linear radial basis probabilistic neural networks (RPNNs) are employed for pair-wise feature classification. The final diagnostic decision is made based on a statistical voting procedure. The proposed method has been demonstrated with experimental data. On average a 93% success rate has been achieved.     

Effectiveness and resolution of tests for evaluating the performance of cutting fluids in machining aerospace alloys

The paper discusses effectiveness and resolution of five cutting tests (turning, milling, drilling, tapping, VIPER grinding) and their quality output measures used in a multi-task procedure for evaluating the performance of cutting fluids when machining aerospace materials. The evaluation takes into account the following process output measures: tool wear, cutting forces, torque, spindle power, geometrical accuracy, texture and integrity of workpiece surface. Using statistics, through calculation of the Hellinger distance, the resolution given by experimental data was evaluated and a comparison of robustness in ranking the performance of cutting fluids based on different output measures and cutting tests is presented.     

Stainless steel thread forming screws and their susceptibility to stress corrosion cracking

Abstract

Thread forming fasteners incorporate both drilling and hole tapping features and are commonly used in the construction industry to fix together steel sheets of different material types. With this practical application in mind, fasteners manufactured from martensitic and austenitic stainless steels have been subjected to alternating corrosion conditions in accordance with test standards DIN 50021-SS and DIN 50018-K WF 2·0. The torque applied to the screws during these tests was controlled to place the fasteners under equal tensile loads, independent of their tensile strength. Thus, the results provided information on their relative susceptibilities to stress corrosion cracking. At the end of the tests, up to 80% of the martensitic stainless steel drilling and tapping screws had failed due to hydrogen induced stress corrosion cracking. The fasteners manufactured from austenitic materials withstood identical test conditions without any evidence of cracking or crack initiation. It is concluded that fasteners manufactured from modified martensitic stainless steel are more susceptible to stress corrosion cracking under the conditions of test than those made from cold worked austenitic stainless steels. This suggests that in practical applications the potential for catastrophic failure due to stress corrosion cracking could be considerably higher in modified martensitic fasteners in comparison with austenitic stainless steel fasteners, including those with hardened carbon steel drill points.     

液力变矩器总成点固焊焊接变形有限元分析

液力变矩器总成电子束环焊缝焊前先要6点点固焊,3焊枪对称同时先焊3点,然后工件转60°再焊另外3个焊点。液力变矩器上盖和泵轮之间的焊后间隙有严格要求。应用热弹塑性有限元法对液力变矩器点固焊过程夹持力和焊接变形进行全面分析,定量得出了焊接预留间隙,为夹具设计提供了依据。总成点固焊的同心精度是重要的考核指标之一,计算结果与实验结果显示径向变形主要由点固焊的前3点决定,点固焊同步性对同心精度有重要影响。