Cutting tool condition monitoring by analyzing surface roughness,work piece vibration and volume of metal removed for AISI 1040 steel in boring

The vibration is one of the intensive problems in boring process. Machining and tool wear are affected more by vibration of tool due to length of boring bar. The present work is to estimate the effect of cutting parameters on work piece vibration, roughness on machined surface and volume of metal removed in boring of steel (AISI1040). A laser Doppler vibrometer (LDV) was used for online data acquisition and a high-speed FFT analyzer used to process the AOE signals for work piece vibration. A design of experiments was prepared with eight experiments with two levels of cutting parameters such as spindle rotational speed, feed rate and tool nose radius. Taguchi method has been used to optimize the cutting parameters and a multiple regression analysis is done to obtain the empirical relation of Tool life with roughness of machined surface, volume of metal removed and amplitude of work piece vibrations.     

Blade geometry effects on the boring of valve seats of internal combustion engines

The boring of valve seats of internal combustion engines is done approximately 25 million times per year in Brazil. Excessive vibrations during this operation are common and can adversely affect dimensional and geometrical tolerances of the valve seats. The sealing of the combustion chamber is prejudiced, resulting in loss of power and higher emission of pollutant gases, harming the environment. The raw material of the valve seats is sintered steel of 370–410 HB hardness and is machined with expensive polycrystalline cubic boron nitride blades. In order to avoid the generation of excessive vibration or chatter during machining, operators reduce cutting speed and feed rate, which consequently causes reduction of productivity. In this context, investigation of the process was performed with the objective of minimizing the vibrations during the valve seat boring through changes in the tool holder design and in geometry of the cutting blades. The proposed modifications resulted in a remarkable reduction in magnitude of the resultant cutting force, vibrations, and roundness deviations of the valve seat. Hence, the sealing between the valve and the seat was improved and the emission of gases from the motor could be reduced, with gains in efficiency. The results also showed that the cutting blade edge must have a 60-μm honing, and the best cutting parameters are in the range: cutting speed 80–100 m/min and feed rate 0.04–0.08 mm/rev/tooth.     

Analysis of dynamic properties of boring bars concerning different clamping conditions

Boring bars are frequently used in the manufacturing industry to turn deep cavities in workpieces and are usually associated with vibration problems. This paper focuses on the clamping properties’ influence on the dynamic properties of clamped boring bars. A standard clamping housing of the variety commonly used in industry today has been used. Both a standard boring bar and a modified boring bar have been considered. Two methods have been used: Euler–Bernoulli beam modeling and experimental modal analysis. It is demonstrated that the number of clamping screws, the clamping screw diameter sizes, the screw tightening torques, the order the screws are tightened has a significant influence on a clamped boring bars eigenfrequencies and its mode shapes orientation in the cutting speed—cutting depth plane. Also, the damping of the modes is influenced. The results indicate that multi-span Euler–Bernoulli beam models with pinned boundary condition or elastic boundary condition modeling the clamping are preferable as compared to a fixed-free Euler–Bernoulli beam for modeling dynamic properties of a clamped boring bar. It is also demonstrated that a standard clamping housing clamping a boring bar with clamping screws imposes non-linear dynamic boring bar behavior.     

Analysis of the vibration characteristics and adjustment method of boring bar with a variable stiffness vibration absorber

In deep hole boring process, long and flexible boring bars are often used. Due to the large length-to-diameter ratio, the stiffness of the boring bars is inevitably reduced, where the boring bars’ vibration effects will occur. The influences of vibration will significantly degrade the accuracy and the surface quality, or even lead failure of the production. Therefore, it is of significant importance to develop techniques to reduce vibration in deep hole boring. In this paper, a new boring bar with a variable stiffness dynamic vibration absorber (VSDVA) is presented, where the basic parameters of the proposed boring bar are measured. Based on the proposed dynamic model, the vibration characteristics of the proposed boring bar are analyzed, and the change laws of the vibration reduction performance are obtained under different excitation frequencies. A new vibration reduction method is proposed, where best vibration reduction performance can be achieved by adjusting the stiffness of the VSDVA. Finally, the vibration reduction performance of the proposed boring bar is validated and evaluated by boring experiments. These works could provide guidance for designing new types of boring bars, selecting cutting parameters, and adjusting the vibration reduction performance of the proposed boring bar, and as a result, it provides a new design idea for the design of boring bar.     

Influence of magnetorheological elastomer on tool vibration and cutting performance during boring of hardened AISI4340 steel

During boring process, tool vibration is a major concern due to its overhanging length, which results in high cutting force, poor surface finish, and increase in tool wear. To suppress tool vibration and improve cutting performance, a novel technique in rheological fluid was designed and developed. In this work, a magnetorheological elastomer (MRE) was developed, and parameters, such as piston location, current intensity, and coil winding direction, were considered. Cutting experiments were conducted to obtain a set of parameters that can efficiently control vibration during boring of hardened AISI 4340 steel. Taguchi method was used to optimize the cutting condition, and findings show that the cutting tool embedded with the MRE reduced tool vibration and effectively increased cutting performance.

     

Accuracy enhancement of a small overhung boring bar servo system by real-time error compensation

This paper is concerned with the work involved in reducing the machining errors of a small overhung boring bar by real-time error compensation. A boring bar developed is made with a pair of concentric bars with an outer diameter of 14 mm and length of 140 mm, representing an overhang ratio of 10:1. A piezoelectric (PZT) actuator was incorporated in the boring bar servo to achieve on-line compensation. Results of cutting tests show that improvement of 40% in the roundness errors can be achieved through on-line compensation of machining errors in precision boring of holes with high aspect ratios.     

Parameter optimization of time-varying stiffness method for chatter suppression based on magnetorheological fluid-controlled boring bar

An innovative chatter suppression method based on a magnetorheological (MR) fluid-controlled boring bar for chatter suppression is developed. The MR fluid, which can change stiffness consecutively by varying the strength of the applied magnetic field, was applied to adjust the stiffness of the boring bar and suppress chatter. The cutting dynamic stability under different natural frequencies of the structure was analyzed by an energy method, which shows that cutting dynamic stability depends on both the natural frequency of the structure and the spindle speed. The chatter suppression mechanism with varying natural frequency is analyzed for further parameter optimization. Furthermore, both theoretical analyses and numerical simulations indicate that a square wave exciting current with a large amplitude and a moderate frequency has a better effect on regenerative chatter suppression. Experiments utilizing a MR fluid-controlled boring bar under an exciting current with different waveforms and frequencies were conducted. The experimental results show that the chatter can be significantly suppressed using MR fluid-controlled boring bar under a square wave exciting current with a frequency of 4–6 Hz and an amplitude of 0–2 A.     

Experimental analysis of boring process on automotive engine cylinders

In this article, mechanics of boring process on cast iron automotive engine cylinders is explored experimentally. In order to shorten the boring cycle time and to improve quality of the cylinder holes, effects of various cutting conditions as spindle speed, feedrate, inserts, and coatings are investigated. Real-time cutting forces are measured with dynamometer during the process. Surface roughness on the engine cylinders, flank, and crater tool wears are measured and compared in various cutting conditions. It is concluded that by selecting proper cutting conditions, cutting forces can be controlled below a threshold value, cycle time can be shortened, tool life and part quality can be increased; therefore, the cost of automotive engine boring process can be reduced significantly.     

CFRP深孔内齿槽镗削专用镗杆的设计

针对碳纤维增强复合材料(CFRP)制件深孔内齿槽镗削的加工,设计了一种具有导向支撑结构和刀尖自动伸缩功能的专用镗杆。利用ANSYS Workbench分别对普通刀杆和专用镗杆进行静力学分析,结果表明专用镗杆的受力变形较小,具有较高的静刚度。联合Hypermesh与ANSYS分别对普通镗杆和专用镗杆进行动力学分析,结果表明专用镗杆的固有频率并没有降低,且能有效减小共振振幅,具有良好的动态性能。     

差动斜楔精密微调镗刀排的研究

采用差动螺距作为微调机构,成功地解决了镗刀直径的精确调节问题。采用差动螺距可以获得比一般螺距更高的微调精度。装置中采用斜楔机构主要实现换向,使差动螺杆的空间布置可以平行于镗杆轴线而不垂直于镗杆轴线,使整个装置安全性高、结构紧凑。装置中设置有两个刀杆安装位置,可以实现高效的镗刀排加工方式。刀杆接口采用莫氏锥实现联接,使刀具安装的通用性较大,可以安装镗刀、钻头、铣刀等多种刀具。     

Modeling the dynamic properties of conventional and high-damping boring bars

Nowadays, the availability of reliable mathematical models of machining system dynamics is a key issue for achieving high quality standards in precision machining. Dynamic models can indeed be applied for tooling system design, preventive evaluation of cutting process stability and optimization of cutting parameters. This is of particular concern in internal turning, where the cutting process is greatly affected by the compliance of the tooling system. In this paper, an innovative hybrid dynamic model of the tooling system in internal turning, based on FE beams and empirical models, is presented. The model was based on physical and geometrical assumptions and it was refined by using experimental observations derived from modal testing of boring bars with different geometries and made of different materials, i.e. alloy steel and high-damping carbide. The predicted modal parameters of the tooling system (tool tip static compliance, natural frequency and damping coefficient of the dominant mode) are in good accordance with experimental values.     

单自由度高频减振镗杆结构的优化设计

随着现代高速切削技术的发展,刀杆的振动严重影响着加工精度和刀具耐用度。对于深孔精加工的镗杆,由于其长径比大,吃刀量小,工件转速高,在切削过程中容易产生高频振动,甚至会产生共振,导致切削无法进行。为了减小镗杆的振动,根据振动学理论,在尽量不降低刚度的同时通过减少镗杆质量来提高其固有频率,利用ANSYS软件对不同结构的镗刀杆进行模态分析和静力分析,提取前四阶固有频率和镗刀尖的位移,从而对镗杆结构做出最佳设计。     

单刀片镗削加工时的力学建模

介绍镗削加工的力学模型.沿切削刃切屑厚度的分布,被作为刀具刃倾角、刀尖圆弧半径、切削深度和进给量的函数被建模.使用机械的和直角到斜角切削转变两种方法,建立该过程的切削力学模型。     

深孔镗杆在推镗和拉镗时的ANSYS受力分析

深孔镗削是提高深孔加工精度的一种方法,它能校正己有孔上的缺陷,如圆度误差、直线度误差,从而获得良好的几何精度和表面粗糙度。深孔镗削的加工方式、运动形式、镗刀的轨迹方程和对镗削的受力分析是深孔镗削加工中各不稳定因素的渊源,在深孔镗削过程中,运用合适的镗削方式可以减小切削系统的振动。针对多刃均布式深孔镗刀,在推镗和拉镗方式下进行受力分析,并利用PRO/E建立镗杆几何模型并生成中性几何文件,通过ANSYS有限元法,计算出推镗和拉镗时镗杆产生的挠度以及最大应力应变曲线,将二者结果进行比较,证明在细长管时拉镗加工的优势。     

多刃均布式镗杆系统振动耦合问题研究

深孔镗削过程中,由于镗杆的悬伸量较大,刚度差,强度低,在镗削过程中易产生振动。自激振动是金属切削过程中产生的振动类型之一,同时其振动机理的揭示以及对它的控制相对于受迫振动的研究而言较为困难。本文针对多刃均布式镗杆系统,在建立其力学模型的基础上,计算镗刀所受的动态切削力,并对镗杆振动系统耦合微分方程进行推导计算,对该耦合系统的稳定性进行分析,最后得出引起该系统产生自激振动的条件。     

内孔环形槽自动进给挖削刀具设计

介绍了斜楔式和偏心式两种内孔环形槽挖削刀具的结构设计和工作原理。通过精心设计,这两种刀具都具有径向自动进给和退刀、轴向位置可调功能,结构简单、工作可靠效率高、适用于各种内孔形环形槽挖削加工。     

Feature signature prediction of a boring process using neural network modeling with confidence bounds

Prediction of machine tool failure has been very important in modern metal cutting operations in order to meet the growing demand for product quality and cost reduction. This paper presents the study of building a neural network model for predicting the behavior of a boring process during its full life cycle. This prediction is achieved by the fusion of the predictions of three principal components extracted as features from the joint time–frequency distributions of energy of the spindle loads observed during the boring process. Furthermore, prediction uncertainty is assessed using nonlinear regression in order to quantify the errors associated with the prediction. The results show that the implemented Elman recurrent neural network is a viable method for the prediction of the feature behavior of the boring process, and that the constructed confidence bounds provide information crucial for subsequent maintenance decision making based on the predicted cutting tool degradation.NSF Industry/University Cooperative Research Center (NSF I/UCRC) forIntelligent Maintenance Systems(IMS).     

精密镗削调刀器的设计与应用

通过对普通镗削敲刀的缺陷分析,结合刀块在镗刀杆刀槽孔中的滑移方式,详细叙述了设计并应用精密镗削调刀器的方法和注意事项。     

Dynamic cutting force modeling and experimental study of industrial robotic boring

In this paper, a new approach based on industrial robotic boring is proposed to solve problems associated with intersection holes during aircraft assembly. A model is established to predict the dynamic cutting force of a robotic machining system. The robot stiffness coupling, chip deformation, and plowing interference affecting the cutting force are considered using the principles of cutting mechanics and the Oxley orthogonal cutting model. By solving a numerical solution of motion differential equation, the cutting force components in the radial, tangential, and feed directions are obtained by the model. In addition, an advanced curve intersection method is developed to identify the instantaneous uncut chip area and cutting edge contact length. Verification tests were performed on an ABB-IRB6600-175/2.55 robot for titanium alloy TC4 to determine the accuracy of the predictions. The results show that the simulated and measured cutting forces were in good agreement under different cutting conditions. By analyzing simulated and experimental results, we show that the model can be applied to predict the occurrence of vibration and has application value in terms of suppressing vibration during robotic boring.     

基于变结构刚度的精密孔镗削颤振抑制新方法

精密孔镗削过程中容易出现颤振现象,它会导致加工精度低和表面质量差等问题。为了解决此问题,首先针对镗削过程中最为常见的再生型颤振建立了动力学模型,并在此基础上,分别讨论了主轴变速方法和变结构刚度方法对切削颤振的抑制机理,对比两种方法发现：它们的抑振机理异曲同工,但是,变结构刚度方法能够避免主轴变速法对刚性较低的切削系统不适用的缺点。其次,为了能对精密孔镗削过程施加变结构刚度法来抑制颤振,本文设计制作了一种基于磁流变液的智能镗杆,通过调节外加磁场强度的大小实现刚度和阻尼特性参数的无级变化,改变机械系统的动态特性,从而达到抑制颤振的目的。最后在车床CA6140上搭建了磁流变智能镗杆的颤振抑制实验系统,通过一系列的实验发现：该方法能够快速高效的抑制镗削过程中产生的颤振,并且使加工表面的粗糙度从Ra 10μm降至Ra 1.5μm,大幅度提高了加工表面质量。