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.     

Machinability of Kevlar® 49 Composite Laminates While Using Standard TiN Coated HSS Drills

This article addresses the machinability of plain weave Kevlar® 49 prepeg composite laminates of different thickness while using 135° split-point TiN coated 6 mm diameter HSS drills. The effect of composite preparation parameters and the drilling conditions on the machinability of the laminates is assessed using the drilling thrust force, cutting torque, and specific cutting energy. The thickness and processing time of the laminates as well as the drilling process parameters were found to influence the maximum value of thrust force and torque as well as the quality of drilled holes. The wear features of the drills used in machining Kevlar composites have been found to be different from the conventional wear patterns that occur during drilling metals and alloys.     

Machinability of Kevlar® 49 Composite Laminates While Using Standard TiN Coated HSS Drills

Abstract

This article addresses the machinability of plain weave Kevlar® 49 prepeg composite laminates of different thickness while using 135° split-point TiN coated 6 mm diameter HSS drills. The effect of composite preparation parameters and the drilling conditions on the machinability of the laminates is assessed using the drilling thrust force, cutting torque, and specific cutting energy. The thickness and processing time of the laminates as well as the drilling process parameters were found to influence the maximum value of thrust force and torque as well as the quality of drilled holes. The wear features of the drills used in machining Kevlar composites have been found to be different from the conventional wear patterns that occur during drilling metals and alloys.     

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).     

Characteristics of laser assisted machining for silicon nitride ceramic according to machining parameters

This paper describes the Laser Assisted Machining (LAM) that cuts and removes softened parts by locally heating the ceramic with laser. Silicon nitride ceramics can be machined with general machining tools as well, because YSiAlON, which was made up ceramics, is soften at about 1,000°C. In particular, the laser, which concentrates on highly dense energy, can locally heat materials and very effectively control the temperature of the heated part of specimen. Therefore, this paper intends to propose an efficient machining method of ceramic by deducing the machining governing factors of laser assisted machining and understanding its mechanism. While laser power is the machining factor that controls the temperature, the CBN cutting tool could cut the material more easily as the material gets deteriorated from the temperature increase by increasing the laser power, but excessive oxidation can negatively affect the quality of the material surface after machining. As the feed rate and cutting depth increase, the cutting force increases and tool lifespan decreases, but surface oxidation also decreases. In this experiment, the material can be cut to 3mm of cutting depth. And based on the results of the experiment, the laser assisted machining mechanism is clarified.     

基于Pareto遗传算法的螺旋铣加工参数优化

螺旋铣是主要针对航空领域中难加工材料的先进制孔工艺技术。在螺旋铣孔过程中,主轴转速、每齿进给量和每转轴向切削深度是3个最主要的加工参数。以材料去除量和刀具耐用度为优化目标,基于Pareto多目标遗传算法,针对螺旋铣削钛合金材料在稳定性切削条件下的切削参数进行了优化,主要考虑铣削参数对孔表面质量的影响。最终通过切削实验进行了验证。     

MACHINING STUDIES OF UD-FRP COMPOSITES PART 2: FINITE ELEMENT ANALYSIS

ABSTRACT

A number of parameters and an exhaustive material development and experimental procedure to determine the response variables like cutting forces, surface damage restricts the expensive experimental research. In this context, Finite Element Method (FEM) analysis can be used as a tool for the prediction of the various machining responses. A finite element analysis of the orthogonal machining of Uni-directional Glass Fiber Reinforced Plastic (UD-GFRP) laminates is presented in this study to understand the complex relation between fiber orientation, tool geometry, depth of cut on cutting forces and sub-surface damage.     

激光超声复合切削硬质合金的刀具磨损及其对工件表面质量的影响

基于激光加热辅助切削和超声椭圆振动切削提出了激光超声复合切削加工工艺。采用聚晶立方氮化硼(PCBN)刀具对YG10硬质合金进行了常规切削,超声椭圆振动切削,激光加热辅助切削和激光超声复合切削对比试验。检测了刀具磨损量、刀具磨损形貌、工件表面粗糙度以及工件表面形貌,并通过扫描电镜(SEM)对刀具磨损区域进行了能谱分析,同时研究了激光超声复合切削硬质合金时PCBN刀具的磨损及其对工件表面质量的影响。最后,与常规切削、超声振动切削及激光加热辅助切削进行了对比试验。结果表明:激光超声复合切削时刀具使用寿命显著增加,加工后的工件表面粗糙度平均值分别降低了79%、60%和64%,且工件表面更加平整光滑。激光超声复合切削硬质合金时,PCBN刀具的前刀面磨损表现为平滑且均匀的月牙洼磨损,后刀面磨损表现为较窄的三角形磨损带和较浅的凹坑和划痕;刀具的失效机理主要为黏接磨损、氧化磨损和磨粒磨损的综合作用。     

激光加热辅助铣削氮化硅陶瓷试验研究

激光加热辅助切削是加工工程陶瓷材料的一种有效方法,关于辅助车削的研究较多,而激光加热辅助铣削的研究较少。本文搭建了激光加热辅助铣削试验系统,对氮化硅陶瓷进行了加工试验研究。随着激光能量升高,切削力降低,刀具磨损减少,切屑尺寸增加。工件表面粗糙度、表面形貌、表面组织与表面硬度的测量结果表明加工质量好、激光对工件不造成损伤。此外,研究了加工过程中产生的边缘碎裂现象,分析了工艺参数对碎裂宽度的影响规律。     

高温合金蜂窝芯高速铣削材料去除机理与损伤行为

高温合金蜂窝芯材料具有高比刚度、轻质和能量吸收特性好等优异性能,被视为下一代高超声速飞行器热防护结构极具潜力的材料。高速铣削是高温合金蜂窝芯零件成型过程中重要的减材制造工艺,在蜂窝芯材料高速铣削时,蜂窝芯材料面内刚度低且高温合金塑性好,较小的切削力就会使蜂窝壁产生较大的塑性变形,导致蜂窝芯加工精度较低、加工损伤难以控制,对后续焊接、装配等工序产生不利影响。基于有限元仿真对蜂窝壁切削材料去除机理进行了深入研究,探索了铣削参数、刀具类型和铣削方式对铣削过程中铣削力和加工损伤的影响。研究结果表明,蜂窝壁切入角是影响蜂窝芯材料切削加工过程中瞬时应力分布和成屑机理的关键性因素。得到了铣削参数、刀具类型和铣削方式对高温合金蜂窝芯加工过程中加工损伤的影响规律。对于铣削参数,过大的进给量会导致芯格变形等加工损伤,降低切削速度会提高微小毛刺等加工损伤发生的频率;本文采用的三种刀具的对比结果表明,立式铣刀加工质量最好。插铣方式会产生明显的轴向冲击,而侧铣方式可以有效避免轴向冲击。研究成果为高温合金蜂窝芯低损伤高性能加工提供了理论依据和工艺技术储备。     

Modeling of vapor-to-melt ratio in laser cutting aluminum alloy sheet

To study the regular pattern of vapor-to-melt ratio in laser cutting sheet metal, a physical model of vapor-to-melt ratio is developed to demonstrate the material remove forms of vaporization-melt in cutting area and the state of energy and mass flow in the molten layer. Variation of vapor-to-melt ratio with laser power and cutting velocity is obtained by laser cutting of 6063 aluminum alloy sheet. The 0.5-mm sheet thickness is carried out on a JK701H Nd:YAG pulse laser cutting system by simulating under the regression correction of cut radius. Observation on the cut samples with different parameters (65 W, 85 W, 105 W varied with laser power increasing, and 2.2 mm/s, 2.0 mm/s, 1.8 mm/s with decreasing of beam cutting speed) and the calculations show that vapor-to-melt ratio increases (0.595–1.995, 0.672–2.631, 0.787–4.171) with laser power (65 W–110 W) and decreases with cutting velocity (1.8 mm/s–2.4 mm/s). At the same time, the laser cutting quality increases with vapor-to-melt ratio and the decrease with thickness of residual molten layer. The results show good agreement between vapor-to-melt ratio model and experiments. The analysis verifies that this model is feasible and it makes contribution to laser precision cutting.     

Position-oriented process monitoring in freeform abrasive machining

Process monitoring is necessary for the identification and avoidance of process disturbances that could cause poor surface integrity at selected machining parameters. In this paper, a position-oriented process monitoring strategy is introduced which enables determination of process characteristics for freeform abrasive machining. Through correlation of internal machine data of position and power during machining with laser displacement measurement, position-orientated maps of power and specific energy can be generated to enable an evaluation of the machining efficiency of the abrasive machining process. Measurement chains are described, and experimental results reveal that the measurement system provides a significant insight into the process by identifying regions of high power, depth of cut, engagement and specific energy on freeform parts.     

MACHINING STUDIES OF UD-FRP COMPOSITES PART 2: FINITE ELEMENT ANALYSIS

A number of parameters and an exhaustive material development and experimental procedure to determine the response variables like cutting forces, surface damage restricts the expensive experimental research. In this context, Finite Element Method (FEM) analysis can be used as a tool for the prediction of the various machining responses. A finite element analysis of the orthogonal machining of Uni-directional Glass Fiber Reinforced Plastic (UD-GFRP) laminates is presented in this study to understand the complex relation between fiber orientation, tool geometry, depth of cut on cutting forces and sub-surface damage.     

Using a Nd:YAG laser and six axes robot to cut zinc-coated steel

Zinc-coated steel sheets are important materials in the automobile and home appliance industries. Currently, lasers are the preferred tools for metal cutting because of their good cutting quality, flexibility and excellent features and results, as compared to traditional tools. The solid-state Nd:YAG laser has successfully replaced the gaseous CO₂ laser for metal cutting; its small size and short wavelength makes it suitable for cutting bright and metal-coated materials, as well as being able to be transmitted via optical fibers and robots to cut complicated three dimensional and curved shapes. In this work, the Nd:YAG laser is used to cut 1 mm zinc coated steel sheets. We demonstrate the effects of different cutting parameters such as laser power, cutting speed, different gas types and pressures, and focus position on the cutting quality characteristics of attached dross, kerf width and cut surface roughness. Using a six axes robot, cutting speed was limited to 6 m/min because of the noticeable vibration at higher speeds. Results showed that the cutting surfaces achieved were very sharp and smooth. In cutting, Nd:YAG required less power and attained higher speeds than the published results of a CO₂ laser, which makes Nd:YAG an economical alternative to cut zinc and metal-coated materials. In addition, laser cutting using robots provided efficient and consistent cutting quality, especially in the case of 3D and countered cutting. Apart from using low speed, robots proved to be more economical than costly, specially designed CNC tables.     

Finite element analysis of laser inert gas cutting on Inconel 718

Inconel 718 has high strength, which makes it difficult to cut using conventional cutting methods. In the present study, the laser inert gas cutting of Inconel 718 was simulated by finite element analysis software ANSYS. Finite element method was used to predict thermal stress and kerf width formation during the laser cutting process. ANSYS Parameter Design Language was used to model the Gaussian-distributed heat flux from the laser beam acting on the workpiece. The removal of melted material during laser cutting to form the kerf width was modeled by employing the element death methodology in ANSYS. In addition, laser cutting was simulated at continuous wave (CW) and the effects of laser power and cutting speed on kerf width were investigated. A series of experiments were carried out to verify the predictions. The temperature fields on the workpiece were measured using thermocouples. The kerf width size was measured using a profile projector, whereas the metallurgical and morphological changes at the cutting edge were examined using scanning electron microscopy. A good correlation was found between the simulation and experimental results.     

Micro-burr formation and minimization through process control

This paper presents an investigation on micro-burr formation in machining. Micro-cutting is compared with conventional cutting in terms of cutting process characteristic and cutting conditions. In this paper, tungsten–carbide micro-mills were used to cut holes (in a drilling-like process) to investigate top burr formation. The size and type of burr created in stainless steel 304 are studied as a function of machining variables, which are feed, cutting speed and cutting edge radius, to help illuminate the micro-burr formation mechanisms. A series of experiments was conducted to study tool life as a function of cutting conditions. Tool life, here, is defined as the number of holes created before a significant increase in burr height. Based on experimental results, contour charts for predicting burr formation as well as tool life are developed to minimize burr formation and to improve tool life. The model, which includes the effect of feed, cutting speed, and the interaction between the two, predicted the burr height and tool life values with an accuracy of about ±15%.     

基于钝圆尺寸效应的微细切削机理试验研究

通过微细车削试验,研究了微细切削加工参数对切削力、表面质量、切屑形成的影响,发现切削厚度与刃口半径的比值是影响微细切削的关键因素,当该比值过小时,刃口尺寸效应作用极其显著,导致切削比能迅速增大,表面质量恶化,切屑形成困难。根据这一结论可确定微细切削加工参数选择的下限范围,从而为微细切削加工参数选择提供理论依据。     

Some studies on hard turning of AISI 4340 steel using multilayer coated carbide tool

Hard turning with multilayer coated carbide tool has several benefits over grinding process such as, reduction of processing costs, increased productivities and improved material properties. The objective was to establish a correlation between cutting parameters such as cutting speed, feed rate and depth of cut with machining force, power, specific cutting force, tool wear and surface roughness on work piece. In the present study, performance of multilayer hard coatings (TiC/TiCN/Al₂O₃) on cemented carbide substrate using chemical vapor deposition (CVD) for machining of hardened AISI 4340 steel was evaluated. An attempt has been made to analyze the effects of process parameters on machinability aspects using Taguchi technique. Response surface plots are generated for the study of interaction effects of cutting conditions on machinability factors. The correlations were established by multiple linear regression models. The linear regression models were validated using confirmation tests. The analysis of the result revealed that, the optimal combination of low feed rate and low depth of cut with high cutting speed is beneficial for reducing machining force. Higher values of feed rates are necessary to minimize the specific cutting force. The machining power and cutting tool wear increases almost linearly with increase in cutting speed and feed rate. The combination of low feed rate and high cutting speed is necessary for minimizing the surface roughness. Abrasion was the principle wear mechanism observed at all the cutting conditions.     

The influence of the cutting tool microgeometry on the machinability of hardened AISI 4140 steel

The aim of this work is to define the cutting conditions that allow the dry drilling of carbon fiber reinforced epoxy (CFRE) composite materials taking into consideration the quality of the drilled holes (the exit delamination factor and the cylindricity error) and the optimum combination of drilling parameters. A further aim is to use grey relational analysis to improve the quality of the drilled holes. The machining parameters were measured according to 3³ full factorial parameter designs (27 experiments with independent process variables). The experiments were carried out under various cutting parameters with different spindle speeds and feed rates. Drilling tests were done using WC carbide, high-speed steel (HSS), and TiN-coated carbide drills. The experiment design was accomplished by application of the statistical analysis of variance (ANOVA). Results show that the thrust force is mainly influenced by the tool materials and the feed rate, which has a strong influence on the exit delamination factor. On the other hand, the spindle speed particularly affects the cylindricity error of the holes. Correlations were established between spindle speed/feed rate and the various machining parameters so as to optimize cutting conditions. These correlations were found by quadratic regression using response surface methodology (RSM). Finally, tests were carried out to check the concordance of experimental results.     

Effect of Chilled Air on Machining Performance in End Milling

Flood coolant is customarily used to increase tool life and to improve workpiece surface finish in machining. It is also responsible for some adverse effects on the environment and users’ health, and hence the interest in chilled air assisted machining as an alternative to flood coolant. The effect of chilled air on machining performance was carried out using an end-milling operation on ASSAB 718HH mould steel using uncoated tungsten carbide inserts at different depths of cut, feedrates and cutting speeds under three different lubrication modes, i.e. chilled air, conventional coolant, and dry cutting. The relative performance of these modes is evaluated in terms of tool wear, surface finish, cutting force, and quality of the chips. Lower tool wear was observed using chilled air compared to that for the conventional flood coolant at a lower depth of cut, lower feedrate and lower cutting speed. The surface roughness was found to reduce at higher depths of cut, higher feedrates and higher cutting speeds for chilled air as compared to dry cutting and flood coolant. It is also observed that the cutting force experienced with chilled air is comparable and, in many cases, lower than that when using flood coolant. Stress lines on the chip surfaces show that the chips experienced the highest shear stress in dry cutting, followed by cutting with chilled air and lastly, with flood coolant.