Laser cutting of Kevlar laminates: First and second law analysis

Kevlar laminates are difficult to machine using conventional machining methods because of their thermal and mechanical properties. Laser cutting offers advantages over conventional machining methods, such as precision of operation, non-frictional processing, and operational cost. This provides the motivation for the present study, which reports on laser cutting of Kevlar laminates of different thicknesses. The first and second law efficiencies of the cutting process are formulated and predicted in line with the experimental parameters. The laser cut surfaces are examined using optical and electron scanning microscopes. It is demonstrated that the first and second law efficiencies improve at high laser cutting speeds and low laser output power levels. For these conditions parallel sided kerfs with no sideways burning are produced.     

Laser cutting of small diameter hole in aluminum foam

The International Journal of Advanced Manufacturing Technology - Laser cutting of a small diameter hole into aluminum foam is carried out, and thermal stress field developed in the cutting section...     

Laser hole cutting into Ti-6Al-4V alloy and thermal stress analysis

Laser hole cutting into Ti-6Al-4V alloy is carried out. Temperature and stress fields during the cutting process are predicted using the finite element code. Temporal variation of surface temperature in the region close to the kerf edge is monitored by a thermocouple and compared with the predictions. The residual stress formed in the cutting region is obtained from the XRD technique and compared with the predictions. The morphological changes around the kerf surfaces are examined incorporating optical and scanning electron microscopes. It is found that von Mises stress attains slightly higher values at the top circumference as compared to that corresponding to the bottom circumference of the hole cut. The prediction of temperature variation agrees well with the thermocouple data. The residual stress predicted also agrees with the results of the XRD technique.     

CO2 laser cutting of Kevlar laminate: influence of assisting gas pressure

In the present study, laser cutting of Kevlar laminate is considered, and the effect of assisting gas pressure and laser output power on the end product quality is examined. The end product quality is judged via measurement of out-of-flatness and kerf width ratios. Experimental tests are carried out using a CO₂ laser beam with pulse repetition rate of 300 Hz. The cutting model introduced previously is accommodated to predict the kerf size for various laser output power and assisting gas pressures. The predictions are compared with the experimental results. It is found that the predictions of kerf size are in good agreement with the experimental results. The influence of assisting gas pressure is significant on the resulting cut quality, in which case, out-of-flatness and kerf width ratio improve considerably at high assisting gas pressures (500 kPa).     

多刃均布式深孔镗刀的建模及切削参数的确定

深孔镗削过程中,设置合理的切削参数可有效减小切削系统的振动.基于矢量法建立多刃均布式深孔镗刀的切削角度模型,利用Pro/E建立几何模型并生成中性几何文件,通过Ansys有限元法,计算不同切削条件下,镗刀的受力情况,分析其最大应力应变曲线,确定出合理的切削参数.     

深孔加工中切削参数的选择

笔者主要阐述了数控深孔钻床在使用枪钻进行深孔加工时工艺参数的选择,寻求最佳加工性能,以求达到快速加工、提高效率的目的。     

Roundness modeling in BTA deep hole drilling

The modeling of deep hole geometry which was generated for boring and trepanning association (BTA) drilling was performed and its characteristics was discussed, also the effects of internally BTA drilled round profile are analyzed and its geometric modeling reliability was verified by the experiments of roundness testing, especially in BTA drilling operation. In this study, a harmonic geometric round model with the parameter of harmonic function was established. This relationship is also used to provide physical meanings to harmonic lobes generated by the proposed roundness model for a profile of BTA drilling, especially those caused by the spindle error motions of the BTA tool. In general, the theoretical roundness profile of a hole with an arbitrary multi-lobe can be calculated. But in real experiments, the two- to six-lobe hole profile was frequently measured. The most frequently measured one is three- and five-lobe profile in experiments. With these results, It was predicted that the reliability of proposed harmonic model has been verified theoretically and experimentally by a large number of real profile estimation of the hole and the experimental results that was produced by BTA drilling operation in deep hole making operation. This new modeling method is expected to provide desirable insights into the advanced tolerance analysis of circular hole making in BTA drilling process.     

平纹编织碳纤维/Kevlar纤维增强混杂复合材料微-宏观切削去除机理研究

由于碳纤维和Kevlar纤维力学性能相差迥异,在C-K纤维混杂增强复合材料(Carbon-Kevlar fiber hybrid composite,CKFH)加工中易产生加工缺陷,比单种纤维复合材料的加工缺陷更难控制。由此,从微观和宏观角度,构建CKFH三维有限元切削模型,分析CKFH的切削去除机理及平纹编织结构对切削过程的影响机制。结果表明,在不同纤维取向下,Kevlar纤维均易产生抽丝拉毛现象,尤其当纤维取向θ=0°/180°时最为明显;纤维取向θ=0°/180°时,切屑多为卷曲片状切屑,纤维取向θ=45°、90°、135°时,两种纤维的断裂相互影响,切削表面、切屑形态均与切削方向存在密切关系,当纤维取向θ=45°时,多为细小片状切屑,纤维取向θ=90°时,切屑多为絮状块状切屑,纤维取向θ=135°时,切屑多为成块状切屑;从碳纤维切向Kevlar纤维时,Kevlar纤维出现松散、抽丝拉毛现象明显,从Kevlar纤维切向碳纤维时,在Kevlar纤维的韧性弯曲区碳纤维发生弯曲脆断、碎裂,易出现凹坑;平纹编织结构对切削应力的传递具有明显的阻断作用,有限元仿真结果与试验观测结果基本吻合。     

Laser straight cutting of alumina tiles: thermal stress analysis

In the present study, laser straight cutting of alumina tiles is carried out. Temperature and thermal stress fields developed in the cutting section are modeled and predicted through the finite element method. The geometric features of the cut sections are examined using optical and scanning electron microscopes. Temperature predictions are validated with the thermocouple data. The X-ray diffraction technique is incorporated to measure the residual stress at the cut surface vicinity. It is found that the residual stress predicted agrees with that obtained from the X-ray diffraction technique. Striation patterns formed at the kerf surface have shallow depths because of the low thermal conductivity and high melting temperature of the workpiece. Dross attachment is observed at the bottom surface of the cut edges.     

Finite element modeling of ultrasonic-assisted turning: cutting force and heat generation

Abstract

Adding ultrasonic vibrations to conventional turning can improve the process in terms of cutting force, surface finish and so on. One of the most important factors in machining is the heat generation during the cutting process. In ultrasonic-assisted turning (UAT) the tool tip also vibrates at very high frequency and this sinusoidal motion causes complexity in heat modeling of the cutting system. Modeling and simulation of cutting processes can help to understand the nature of process and provides information to select optimum conditions and machining parameters. In this article, a finite element model has been developed for predicting tool tip temperature in UAT. The effect of machining parameters including cutting speed, feed rate and amplitude of vibration on the tool tip temperature has been investigated. In order to simplify the machining process, the cutting experiment has been carried out in dry condition. The results showed that by applying ultrasonic vibration to the cutting tool, the tool tip flash temperature increases but in some condition its average value could be less than the conventional machining.     

Bystronic激光切割机加工质量分析与控制

分析激光切割的加工原理，以及影响加工质量的诸多因素，阐述如何控制提高加工质量的方法。     

On modeling of cutting forces in micro-end milling operation

Micro-end milling is used for manufacturing of complex miniaturized components precisely in wide range of materials. It is important to predict cutting forces accurately as it plays vital role in controlling tool and workpiece deflections as well as tool wear and breakage. The present study attempts to incorporate process characteristics such as edge radius of cutting tool, effective rake and clearance angles, minimum chip thickness, and elastic recovery of work material collectively while predicting cutting forces using mechanistic model. To incorporate these process characteristics effectively, it is proposed to divide cutting zone into two regions: shearing- and ploughing-dominant regions. The methodology estimates cutting forces in each partitioned zone separately and then combines the same to obtain total cutting force at a given cutter rotation angle. The results of proposed model are validated by performing machining experiments over a wide range of cutting conditions. The paper also highlights the importance of incorporating elastic recovery of work material and effective rake and clearance angle while predicting cutting forces. It has been observed that the proposed methodology predicts the magnitude and profile of cutting forces accurately for micro-end milling operation.     

花键回转切削的运动学建模及轨迹仿真

提出了一种全新的用于花键切削加工的回转车削方法,分析了用回转车削方法加工花键的运动情况,建立了花键加工时刀具切削刃相对工件的矢量模型。运用MATLAB软件对花键加工轨迹进行了仿真,并且在回转车床上加工了花键样品,获得了理想的形状,为使用回转车削方法进行花键加工的推广应用奠定了基础。     

Laser cutting of thick-section circular blanks: thermal stress prediction and microstructural analysis

Laser cutting of thick-section circular mild-steel blanks of 10 mm thickness is examined. Thermal and stress fields developed in the cutting zone are predicted using finite element method and the simulation conditions are selected in line with the experimental parameters. An experiment is carried out to assess the geometric features of the cut surfaces. The morphology of the cut sections are examined using optical and scanning electron microscopes and energy dispersive spectroscopy is carried out for elemental composition of the cut surface. It is found that laser cutting of thick steel blanks results in substantial conduction loss from the cutting zone, which results in high-temperature gradients and large stress levels in the cutting section. The cut edge features such as local dross attachment, striation patterns, and microcrack formation in the cut section are also examined.     

薄壁筒件内孔车削振动建模与分析

分析了车削薄壁筒件内孔表面时影响振动的主要因素,以切削加工中工件过渡表面的法线方向为建模方向,重点考虑车削加工中动态切削力的影响,依据振动基本理论建立了薄壁筒件动态车削过程的振动模型方程,通过对方程的数值分析探讨加工过程中的振动问题。分析结果表明:切削用量三要素对动态切削力的影响起主导作用,进而对切削振动产生较大影响。刀具主偏角对动态切削力也有一定影响,车削产生的振动与主偏角之间是非线性的关系。这些结论为薄壁筒件加工中的振动研究提供有益的参考。     

Laser micro-welding of aluminum alloys: experimental studies and numerical modeling

Experimental and numerical studies were conducted on the effects of the laser beam pulse shaping in the time domain on the quality of the welding seam in laser micro-welded AlMg3 with a thickness of 0.2 mm and 1 mm thick AlMg4.5 Mg foils, respectively. The pulse shaping was realized by a time sequence of three different rectangular pulses with different duration and power level. The first pulse was used to pre-heat the sample, welding occurred with the second pulse and the third pulse controlled the melt pool behavior. The power level and the duration of the single pulses were varied systematically and the resulting microstructure was analyzed by scanning electron microscope. The experiments were accompanied by numerical simulations based on a finite volume model which considers the transient heat flow, melt convection and the evolution of a gas capillary during the deep penetration welding process.     

SPH modeling of chip formation in cutting unidirectional fiber-reinforced composite

The machining of composites is of great interest in manufacturing today. To that end, it is necessary to calculate the cutting forces required and to predict the surface quality obtained. In the present work, the cutting zone of a unidirectional fiber-reinforced composite is simulated by the SPH method. The calculation results—specifically, the equivalent stress and the strain distribution—are compared with results obtained previously by the finite-element method and also with experimental data. The good agreement with experimental data indicates that the SPH method may expediently be used in simulating the cutting of composites.