Application of grey fuzzy logic for the optimization of drilling parameters for CFRP composites with multiple performance characteristics

Carbon Fibre Reinforced Plastic (CFRP) composite materials have potential applications in various domains. In machining, drilling is essentially required to join different structures. But CFRP drilling poses many problems that decrease the quality of holes. In this paper, Taguchi’s L₂₇ orthogonal array is used to perform drilling of CFRP composite plates. To improve the quality of the holes drilled, the optimal combination of drilling parameters is chosen using grey relational analysis. Grey fuzzy optimization of drilling parameters is based on five different output performance characteristics, namely, thrust force, torque, entry delamination, exit delamination and eccentricity of the holes. Analysis of variance (ANOVA) is used to find the percentage contribution of the drilling parameters and found that feed rate is the most influential factor in drilling of CFRP composites.     

Tool life evaluation of CFRP drilling with three kinds of drill

Serious tool wear in CFRP drilling is one of the key problems to be solved urgently. Firstly, a suitable indirect evaluation index of tool life is selected according to the literature. The critical delamination force was obtained by blind hole pushing experiment. Then, tool wear experiments were carried out with double point angle drill, stepped drill and reverse edge compound drill to analyze the variation rules of the thrust force, exit burr, exit delamination and tear with tool wear. Threshold values of exit delamination, tearing and critical thrust force were compared with each evaluation index one by one to study the causes of drills failure. The results indicated that the maximum tool wear position was the outer corner. Among the three types drills, the thrust force, delamination factor and burr angle of the reverse edge compound drill are smaller. The double point angle drill fails due to the excessive thrust force, while the stepped drill and the reverse edge compound drill fail due to the hole exit delamination exceeding the threshold. The number of drilled holes of the reverse edge compound drill is 100 % and 25 % higher than that of the double point angle drill and the stepped drill, respectively. Therefore, the reverse edge compound drill is suitable for drilling CFRP.

     

Characterization of hole circularity in pulsed Nd:YAG laser micro-drilling of TiN–Al2O3 composites

In micro-manufacturing, circularity of a drilled hole at entry and exit are important attributes which greatly influence the quality of a drilled hole. This study investigates the effect of five parameters in the circularity of drilled holes in pulsed Nd:YAG laser micro-drilling process. The drilling operation has been carried out on titanium nitride–alumina (TiN–Al₂O₃) composite, an important electroconductive ceramics suitable for wear and heating applications. The effect of various process parameters like lamp current, pulse frequency, pulse width, air pressure, and focal length of Nd:YAG laser micro-drilling on hole circularity at entry and exit has been investigated through response-surface-methodology-based experimental study. The parametric combination for optimal hole circularity at entry and exit has also been evaluated.     

TiSiC涂层钻头钻削CFRP/TC4钛合金叠层材料的研究

为解决碳纤维复合材料/钛合金叠层材料制孔刀具使用寿命短的问题,本文提出采用Ti Si C涂层来提高刀具耐用度,并研究了Ti Si C涂层钻头钻削碳纤维复合材料/钛合金叠层材料时的轴向力、刀具磨损和孔出口质量。结果表明,Ti Si C涂层刀具能减小钻削钛合金的轴向力,延长刀具寿命和改善孔出口质量,且制孔一致性良好,有利于提高钻孔质量和刀具寿命。     

CFRP及叠层结构螺旋铣孔专用刀具切削性能评价

碳纤维增强复合材料(CFRP)及由钛合金Ti-6Al-4V和CFRP组成的金属复合材料叠层结构广泛应用于现代航空工业。大型客机结构件之间主要通过铆接和高锁螺栓连接,根据波音与空客公司发布的数据显示,最新一代B787与A380上装配孔的数量已超百万,装配过程中的制孔效率与质量直接决定了客机整体装配效率及关键结构件的疲劳寿命,从而间接影响了客机的生产成本以及飞行可靠性。随着飞机数字化装配的快速发展,传统的钻孔工艺会产生很多加工缺陷,工序复杂,加工孔质量不能满足要求,因此,有必要优化制孔工艺,设计新型专用刀具。本文通过研究螺旋铣孔运动学特性,分析螺旋铣孔的工艺特点,设计了一种新型螺旋铣孔专用刀具,并以加工过程的轴向切削力、出入口加工质量以及刀具磨损为评价指标,验证该新型专用刀具的切削性能。结果表明,专用刀具在干切削条件下能够实现复材孔无分层、钛合金孔无毛刺加工,大幅提高刀具寿命,解决了传统立铣刀对CFRP及CFRP/钛合金叠层结构进行螺旋铣孔时刀具寿命低、加工质量差等问题。     

Micro-drilling of Ti–6Al–4V alloy: The effects of cooling/lubricating

This paper presents a series of experimental investigations of the effects of various machining conditions [dry, flooded, minimum quantity lubrication (MQL), and cryogenic] and cutting parameters (cutting speed and feed rate) on thrust force, torque, tool wear, burr formation, and surface roughness in micro-drilling of Ti–6Al–4V alloy. A set of uncoated carbide twist drills with a diameter of 700 μm were used for making holes in the workpiece material. Both machining conditions and cutting parameters were found to influence the thrust force and torque. The thrust force and torque are higher in cryogenic cooling. It was found that the MQL condition produced the highest engagement torque amplitude in comparison to the other coolant–lubrication conditions. The maximum average torque value was obtained in the dry drilling process. There was no substantial effect of various coolant–lubrication conditions on burr height. However, it was observed that the burr height was at a minimum level in cryogenic drilling. Increasing feed rate and decreasing spindle speed increased the entry and exit burr height. The minimum surface roughness values were obtained in the flood cooling condition. In the dry drilling process, increased cutting speed resulted in reduced hardness on the subsurface of the drilled hole. This indicates that the surface and subsurface of the drilled hole were subject to softening in the dry micro-drilling process. The softening at the subsurface of drilled holes under different cooling and lubrication conditions is much smaller compared to the dry micro-drilling process.     

Experimental evaluation of polycrystalline diamond tool geometries while drilling carbon fiber-reinforced plastics

Polycrystalline diamond (PCD) drills are commonly employed in carbon fiber-reinforced plastic (CFRP) drilling to satisfy hole quality conditions with an acceptable tool life and productivity. Despite their common use in industry, only a small number of studies have been reported on drilling CFRPs with PCD drills. In this study, drilling performances of three different PCD drill designs are investigated experimentally using thrust force, torque, and hole exit quality measurements. Results show that work material properties, drilling conditions, and drill design should all be considered together during the selection of process parameters, and the relationships among these factors are quite complex.     

CFRP/TC4叠层材料低频振动钻削试验研究

低频振动辅助切削技术是基于传统切削给刀具加上有规律并可控的振动,从而达到减小切削力、提高加工精度和延长刀具寿命的目的。将低频振动辅助切削技术应用到CFRP/钛合金叠层材料制孔中,在孔径、孔壁粗糙度和入口质量等制孔质量方面与传统钻削进行对比试验研究。结果表明,振动钻削在制孔质量上具有明显的优势。     

Investigation on drilling-grinding of CFRP

It is difficult to machine polymer matrix composites reinforced by carbon fibre, and the holemaking process is the most necessary machining process for composite plate products. Conventional drills have a very short life in the drilling of this kind of composites and the quality of the hole is very poor. In this paper, the cemented or plated diamond core tools are tested to make holes in carbon fibre/epoxy composite plates. The effects of machining parameters, cooling and chip removal on the tool life, and the hole quality are investigated. The results indicate that the material removal mechanism of the two kinds of diamond tools is not like the cutting effect of the conventional drilling but similar to that of grinding. Satisfactory effects in making holes in the composites are obtained—quite acceptable machined hole quality, low costs, and long wear-resistant endurance.     

Experimental investigation of surface and geometrical characteristics of rotary ultrasonic drilling of soda glass

Edge-chipping, surface roughness and dimensional accuracy are crucial quality aspects of drilled holes in hard-to-cut material such as glass, ceramics and carbon fiber reinforced plastics. In this article, an experimental study was conducted to investigate the quality measures of holes produced by rotary ultrasonic drilling (RUD) and conventional drilling. Edge-chipping width at tool exit side, the surface roughness (Ra and Rz), out-of-roundness, cylindricity error and hole conicity were the main responses when drilling soda glass using diamond abrasive tools and a cutting fluid. Statistically designed experiments were carried out for rotary ultrasonic and conventional drilling (CD) at two levels of tool feed rate (0.6 and 6?mm/min), spindle speed (3,000 and 8,000?rpm) and tool particles-concentration. Analysis of variance was used to define the significant factors and their interactions and build models for predicting the responses. The results showed that reducing the chipping, surface roughness and roundness error. The normal tool concentration showed a substantial effect in improving the surface quality and reducing the hole-geometrical errors.     

CFRP/钛合金叠层构件制孔孔径分布规律研究

为了研究CFRP/钛合金叠层构件一体化制孔加工后的孔径几何精度变化规律及主要影响因素,在CFRP/钛合金制孔基础上,利用三坐标测量机对孔径几何精度进行检测,并分别对单个孔及系列孔的孔径几何精度进行分析,得到孔径几何精度的变化规律及主要影响因素。结果表明:叠层材料制孔加工过程中材料加工性能的巨大差异,使加工至材料界面时产生的切削振动较大,是影响CFRP与钛合金孔径几何精度的主要因素,且对CFRP孔径影响较大,对钛合金孔径影响较小。     

Robotic drilling system for titanium structures

Manual drilling in titanium structures is a tedious and labor-intensive work. To reduce man-hour requirements while concurrently improving hole quality, we developed a robotic drilling system for this application. The lean system contains the product holding fixture, the industrial robot, the end effector, the control and sensor system, and the offline programming. The system functions include locating workpiece with a calibration stick or the vision system, weld mark inspection, one-sided clamping, drilling and reaming hole in material stack combinations of titanium and aluminum, and real-time thrust force feedback. The positional accuracy and the repeatability of the system have successfully been placed within the specification’s 0.3 mm tolerance and 0.2 mm tolerance, respectively. The dimensional accuracy of drilled holes in both Ti alloy and Al alloy materials is within H9 tolerance.     

A method for the localization of damage in a CFRP plate using damping

In the past 25 years, the scientific and industrial communities have made great efforts on the fields of damage detection and structural health monitoring (SHM). However, no single approach has proven appropriate for all situations. Composite materials, which are receiving an increasing attention in the aeronautical industry, namely carbon fibre reinforced plastics (CFRP), are very sensitive to impacts of medium and low energy. Typically, barely visible impact damage (BVID) will occur, constituting an unsafe failure of difficult assessment. To assess (detect, locate and quantify) damage in this kind of material is still a challenge, especially if a huge amount of sensors or expensive equipments at hand are not used. In this work, a methodology that makes use of a reduced amount of conventional sensors is explored, with the aim of locating damage for a low cost on components that are subjected to impacts during service. This represents a considerable benefit, namely for the assessment of damage in aeronautical components, compared to most methods used today. This work can also give a major contribution to the research community since uncommon approaches will be used to model damage in composite materials, namely the modal damping factor as the main feature for damage localization.     

碳纤维复合材料孔加工研究现状

根据碳纤维复合材料的特性和制造加工中存在的问题,综述了碳纤维复合材料孔加工时加工工艺、钻头几何参数及其材料、机床振动、材料制备缺陷等因素对钻削加工损伤(尤其是分层损伤)的影响和抑制方法、钻削建模与仿真以及叠层孔加工等方面的研究最新进展,重点关注了钻削诱导的分层损伤形成机理以及一些特殊工艺,如振动辅助钻削、螺旋铣削孔加工、磁性胶体垫板孔加工技术和高速钻削技术等对碳纤维复合材料孔加工质量改善效果。     

Evaluation of a novel approach to a delamination factor after drilling composite laminates using a core–saw drill

Drilling is the most commonly applied method for hole making of fiber-reinforced materials owing to the need for structure joining. Delamination is the most common defect during drilling because of the heterogeneity of both the fibers and the matrix. The delamination, in general, is an irregular shape and size, containing long and fine breaks and cracks at the exit of the drilled hole, especially in the drilling of carbon-fiber-reinforced plastic (CFRP). On the other hand, a core–saw drill is designed to reduce the threat of chip removal in drilling composite materials. Since the thrust force of core–saw drill is distributed toward the periphery, the core–saw drill allows a larger critical thrust force than the twist drill at the onset of delamination when drilling composite materials. The aim of this paper is to present a novel approach of the equivalent delamination factor (F _ed) to characterize drilling-induced delamination using a core–saw drill and compare it with the adjusted delamination factor (F _da) and the conventional delamination factor (F _a). The experimental results indicated that the F _ed obtained is considered suitable for characterizing delamination at the exit of a hole after drilling CFRP.     

Analytical models of composite material drilling

Drilling of composite material structures is widely used for aeronautical assemblies. When drilling, damage to the composite laminate is directly related to the cutter geometry and the cutting conditions. Delamination of the composite materials at the hole exit as directly related to the axial force (F _Z) of the cutter is considered to be the major such defect. To address this issue, an orthotropic analytical model is developed in order to calculate the critical force of delamination during drilling and a number of hypotheses for loading are proposed. This critical axial load is related to the delamination conditions (propagation of cracks in the last layers) and the mechanical characteristics of the composite material machined. A numerical model is also drawn up to allow for numerical validation of the analytical approach. A comparison between these analytical and numerical modellings and experimental results from quasi-static punch tests led to the choice of the loading hypothesis closest to the experimental conditions. The selection of corresponding load permits to model the drilling critical thrust force on delamination and then to optimise the cutting conditions. The dimensions and geometrical shape of the cutter are of considerable importance when it comes to choosing this load. The present article focuses on the case of the twist drill, which is commonly used to drill thick plates. However, this work can be adapted to different cutter geometries.     

Artificial neural network based tool condition monitoring in micro mechanical peck drilling using thrust force signals

Micro scale machining process monitoring is one of the key issues in highly precision manufacturing. Monitoring of machining operation not only reduces the need of expert operators but also reduces the chances of unexpected tool breakage which may damage the work piece. In the present study, the tool wear of the micro drill and thrust force have been studied during the peck drilling operation of AISI P20 tool steel workpiece. Variations of tool wear with drilled hole number at different cutting conditions were investigated. Similarly, the variations of thrust force during different steps of peck drilling were investigated with the increasing number of holes at different feed and cutting speed values. Artificial neural network (ANN) model was developed to fuse thrust force, cutting speed, spindle speed and feed parameters to predict the drilled hole number. It has been shown that the error of hole number prediction using a neural network model is less than that using a regression model. The prediction of drilled hole number for new test data using ANN model is also in good agreement to experimentally obtained drilled hole number.     

Effect of backstitch tool path on micro-drilling of printed circuit board

As electronic components have become smaller, micro-drilling tools have been developed and used to drill holes in the hundred-micrometer range on printed circuit boards. To improve the productivity of the drilling process, printed circuit boards are generally stacked in several layers and drilled simultaneously. In this process, however, misalignment of the drilled holes on the top and bottom layers occurs, and this consequently degrades the overall product quality. To solve this problem, a new tool path strategy is proposed, which we refer to as the backstitch tool path. The basic scheme of the suggested strategy is to make a balance on the substrate. We compared this approach with a conventional tool path by examining the hole positioning error, drilling thrust force, drilling torque, and drilling duration under various drilling conditions. The effects of each process parameters were analyzed, and the suggested backstitch tool path has a positive effect on low bending stiffness tool, too much adjacent holes, and higher in-feed rate, respectively. Applying the backstitch tool path strategy to a micro-drilling operation improved the productivity and product quality.     

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.     

碳纤维复合材料/钛合金叠层钻孔质量研究

碳纤维复合材料(Carbon fiber reinforced plastic,CFRP)/钛合金叠层的钻孔机理不同于单层材料钻孔,钛合金切屑在排出孔外过程中会对CFRP孔质量造成损伤。为了探究CFRP在叠层钻孔时的质量特性,设计正交试验分析了钛合金切屑和切削参数对CFRP层钻孔质量的影响。观察了轴向切削力和力矩的变化以及钛合金切屑形态,分析CFRP层孔径超差和入口撕裂的机理。结果表明:大进给量条件下,高温、高硬度的钛合金切屑会对CFRP产生严重的侵蚀,是导致CFRP孔径超差的主要原因,并会增大入口撕裂程度;CFRP入口撕裂主要产生在切削速度和纤维方向夹角θ=45°的位置,低切削速度不利于切削CFRP,会加大入口撕裂程度。因此,应使用小进给量钻削钛合金层,使用大切削速度钻削CFRP层;在保证钻头强度的前提下,推荐使用具有较大容屑空间的钻头。