Study of drilling of composite material and aluminium stack

Drilling of CFRP/Al or CFRP/Ti, or Al/CFRP/Ti is a challenge to manufacturing engineers. Drilling of CFRP is manageable but the minute drill hits the Al or Ti, those hot and continuous chips destroy the hole. Few studies are carried out in this aspect; CFRP/Al is not reported till date. It is important to select right process parameters when drilling multimaterial stack since each material in the stack requires a different set of machining parameters. Hence, Drilling trials have been carried out in carbon-fibre reinforced plastics (CFRP)/aluminium (Grade 2024) stack without coolant, with plain carbide (K20) drills of various diameters to choose optimum process parameters. The parametric influences on thrust force, torque as well as surface finish were experimentally evaluated. The experimental results show that the quality of holes can be improved by proper selection of cutting parameters. This is substantiated by monitoring thrust force, torque, surface finish, circularity and hole diameter. For the CFRP, the circularity is found to be around 6 μm at low feed rates, when the feed is increased the circularity increases to 25 μm. The wear tests carried out show that, during first 30 holes, thrust force in CFRP undergoes a more important increase (90%) than thrust force of aluminium (6%).     

Cryogenic Drilling of Ti–6Al–4V Alloy Under Liquid Nitrogen Cooling

This article is focused on experimental study of the effects of cryogenic liquid nitrogen (LN₂) coolant during drilling of Ti–6Al–4V alloy material with three different levels of cutting speed (V_c) and feed rate (f) at a constant depth. Cutting temperature (T), thrust force (F_z), torque (M_z), surface roughness (R_a), and hole quality are the output responses investigated by using cryogenic LN₂ coolant compared with a wet coolant. Tool wear and chip morphology were examined with the changes in cryogenic LN₂ coolant. It is found that cryogenic LN₂ coolant results in lowering cutting zone temperature which helps more removal of heat from the cutting zone. Lower thrust forces and surface roughness were observed due to less friction and better chip breaking in cryogenic LN₂ condition. Also better chipping results in improvement in hole quality, viz., circularity and cylindricity in cryogenic LN₂ condition. Less serration and uniform segmentation results in better chip morphology and no damage to the cutting inserts resulted in improved tool life in cryogenic LN₂ condition. The main application of cryogenic LN₂ coolant in the cutting zone provides better lubrication and is more effective than wet coolant. The effects of this investigation show that cryogenic LN₂ coolant is an alternative approach for a wet coolant in the drilling process.     

Assessment of drilling-induced damage in CFRP under chilled air environment

Drilling holes in carbon fiber-reinforced polymer (CFRP) laminates are more prone to incur damage during machining. Surface damage could be considerably minimized through the adoption of cryogenic assisted machining. The economic and safety implications associated with cryogenic technology necessitate the exploration of alternate technologies. In this research work, the effects of cutting velocity (100, 125, and 150?m/min) and feed rate (0.03, 0.06, and 0.09?mm/rev) on thrust force, surface roughness, delamination, and acoustic emissions are studied during the drilling of CFRP laminates under chilled air environment and compared with dry drilling. The output parameters are found to be much influenced by feed rate than cutting velocity. Under high feed rate and cutting velocity, the delamination factor, surface roughness, and acoustic emissions are, respectively, reduced by 13.2, 10.5, and 7.4% for the drilling performed under chilled air environment over dry condition. About 9.9% increased thrust force is observed for chilled air-assisted drilling under the identical machining condition.     

Influence of machining parameters and new nano-coated tool on drilling performance of CFRP/Aluminium sandwich

Drilling and fastening of hybrid materials in one-shot operation reduces cycle time of assembly of aerospace structures. One of the most common problems encountered in automatic drilling and riveting of multimaterial is that the continuous chips curl up on the body of the tool. Drilling of carbon fiber reinforced plastic (CFRP) is manageable, but when the minute drill hits the aluminium (Al) or titanium (Ti), the hot and continuous chips produced during machining considerably damage the CFRP hole. This study aims to solve this problem by employing nano-coated drills on multimaterial made of CFRP and aluminium alloy. The influence of cutting parameters on the quality of the holes, chip formation and tool wear were also analyzed. Two types of tungsten carbide drills were used for the present study, one with nano-coating and the other, without nano coating. The experimental results indicated that the shape and the size of the chips are strongly influenced by feed rate. The thrust force generated during drilling of the composite plate with coated drills was 10–15% lesser when compared to that generated during drilling with uncoated drills; similarly, the thrust force in the aluminium alloy was 50% lesser with coated drills when compared to thrust force generated without coated drills. Thus, the use of nano-coated drills significantly reduced the surface roughness and thrust force when compared with uncoated tools.     

考虑刀具磨损影响的CFRP复合材料钻削轴向力预测

在碳纤维增强树脂(CFRP)复合材料钻削过程中,随着刀具磨损量的累积,轴向力会逐渐增加,轴向力过大会导致CFRP复合材料一系列的加工缺陷。为实现在CFRP复合材料钻削过程中随刀具磨损量的累积轴向力变化的有限元分析及预测,建立了CFRP复合材料钻削仿真模型,通过对ABAQUS仿真软件二次开发,利用Python语言开发子程序,将考虑磨损量累积的轴向力预测模型导入仿真软件,运用ABAQUS软件对CFRP复合材料钻削中轴向力进行研究,实现了随着刀具磨损量累积轴向力变化的预测功能。随后通过CFRP复合材料钻削试验,分析了轴向力随钻削孔数的变化规律,以验证轴向力的预测结果。结果表明:3D钻削有限元模型能够良好地预测实际加工过程中刀具未磨损时轴向力的大小,其误差为9.10%;在考虑磨损量累积后,轴向力预测模型能够较准确地预测实际加工过程轴向力的大小,其最大误差不超过10%。      

基于CFRP层合板钻削轴向力时变曲线的钻头几何形状分析

为探索能够实现碳纤维增强复合材料（CFRP）层合板低损制孔的钻头几何形状,采用4种不同几何形状的钻头,对T800级CFRP层合板进行钻孔实验研究,分析了钻头几何形状对钻削轴向力的影响,探讨了钻削轴向力与分层损伤之间的关系。结果表明:轴向力归零速度与出口分层因子有较好的正相关性,可采用钻削轴向力归零速度来表征钻头几何形状对CFRP层合板钻孔的适用性能。同时,实验发现切削区域具有多阶段几何特征的钻头,在钻出工件底部时轴向力是分阶段缓慢归零,出口分层因子较小。      

Experimental study on mechanical drilling of carbon/epoxy composite-Ti6Al4V stacks

This paper concerns the experimental studies on the drilling process of multilayer carbon/epoxy composite-Ti6Al4V stacks and their individual material layers using tungsten carbide drills. The significance of the current work aims to reveal the impact of tool wear on the drilling process for CFRP/Ti6Al4V, CFRP and Ti6Al4V. Four groups of machining tests including drilling individual CFRP, individual Ti6Al4V, multilayer CFRP/Ti6Al4V stacks with and without a cooling treatment were conducted. Drilling forces, cutting temperatures and hole quality attributes were experimentally investigated in terms of the drill wear extents. The mechanism controlling the tool wear effect on the drilling machinability of CFRP/Ti6Al4V was revealed, providing several implications for the industrial manufacturers. The results highlight the significant impact of the titanium chip ejection on the composite surface quality and the necessity of a rigorous tool wear control to guarantee the damage-free drilling of CFRP/Ti6Al4V stacks.     

双顶角钻头钻削CFRP复合材料的刀具磨损机制

为了研究碳纤维增强树脂基(CFRP)复合材料切削中刀具在不同部位的磨损机制和规律,以典型的硬质合金双顶角钻头作为研究对象,主要研究对出口分层影响较大的横刃和对最终制孔成型影响较大的第二主切削刃的磨损机制及规律。通过减小磨损测量间隔,并引入切削刃钝圆半径以及后刀面磨损带宽度,表征了横刃和第二主切削刃在加工中的衰变过程。基于显微刃口观测和钝圆半径变化,揭示横刃易崩刃和第二主切削刃磨损后又受到重新刃磨的磨损机制,获得了此类型钻头不同部位的磨损规律。同时,基于上述的磨损表征,研究不同切削部位磨损量对钻削轴向力和力矩的影响,横刃轴向力与横刃钝圆半径变化相关性较小,而钻削最大力矩与第二主切削刃后刀面磨损变化规律相一致。     

EXPERIMENTAL INVESTIGATIONS OF DRILLING ON CFRP COMPOSITES

The paper outlines the various problems associated with the drilling of CFRP composites. The technique of dimensional analysis is used to investigate the complex correlation between thrust force, cutting speed, feed, hole diameter, point geometry and material thickness during the drilling of holes in CFRP composites, A new non-dimensional number (t/D), thickness of layered composites to drill diameter, is found to influence the thrust force. Four drill point geometries specifically found effective in drilling of FRP were tried and among them the eight facet drill point geometry was found to give the best results.     

硬质合金台阶钻结构参数及钻削工艺参数对CFRP开孔性能的影响

基于VMC850B立式加工中心和UltraPAC超声C-扫描仪,搭建了碳纤维增强树脂基复合材料(CFRP)钻削试验平台,探讨了台阶钻结构参数及钻削工艺参数对CFRP钻削过程中的钻削轴向力和分层因子的影响。结果表明,钻削工艺参数对第一段钻削轴向力影响较大,台阶钻结构参数对第二段钻削轴向力的影响较大;分层因子的大小与第一段钻削轴向力和第二段钻削轴向力有关,当第一段和第二段直径比d/D0.5时,分层因子主要与第一段钻削轴向力有关;减小分层的优水平组合为第一段直径2.8mm,第二段锋角95°,主轴转速7000r/min,进给速度2.5mm/s。     

A review of modeling and control during drilling of fiber reinforced plastic composites

Drilling induced damage in polymer–matrix composites (PMCs) is a research area of immense engineering importance. Various approaches have been tried worldwide to minimize drilling induced damage. In this study, a review of automated drilling operation has been done. Various mathematical modeling methods used for dynamic phenomenon of drilling in PMCs and conventional materials have been discussed. Drilling of fiber reinforced plastic composites can be modeled using empirical techniques, neural network/fuzzy-logic and transfer function modeling methods. This paper brings state-of-the-art in the control of drilling process. The drilling of fiber reinforced plastic composites can be controlled using neural network, fuzzy logic, supervisory, PI, PID, pole placement and adaptive controllers. Results indicate that thrust force and torque have not been controlled simultaneously for delamination free drilling in PMCs. Critical thrust force has also not been precisely tracked. There is a need to create a combined mathematical model consisting of thrust force, torque and feed rate coupled with a suitable control law for simultaneous control of thrust force as well as torque for delamination free drilling of composites.     

碳纤维增强环氧树脂复合材料层合板干涉连接插钉轴向力建模与分析

碳纤维增强环氧树脂复合材料（CFRP）构件干涉配合连接的插钉轴向力过大会引起层合板弯曲和分层,严重影响产品的安全性。针对CFRP层合板的高锁螺栓干涉连接过程,分析了其制孔、插钉及拧紧等装配连接工艺,将其干涉插钉过程划分为4个阶段,并对各个阶段进行了详细的力学行为分析;对螺栓杆处和倒角处的挤压力和摩擦力分别进行力学建模,并结合各作用力的边界条件与阶段划分,构建了干涉插钉全过程的轴向力模型;通过ABAQUS有限元模拟了CFRP层合板干涉插钉工艺过程,并开展了干涉螺栓安装实验,对比分析了层合板孔周径向挤压应力分布和插钉轴向力变化规律,解析结果与模拟和实验结果吻合较好,为后续CFRP层合板的插钉分层损伤和工艺优化研究奠定基础。      

Influence of process parameters on cutting force and torque during drilling of glass–fiber polyester reinforced composites

This research outlines the Taguchi optimization methodology, which is applied to optimize cutting parameters in drilling of glass fiber reinforced composite (GFRC) material. Analysis of variance (ANOVA) is used to study the effect of process parameters on machining process. This procedure eliminates the need for repeated experiments, time and conserves the material by the conventional procedure. The drilling parameters and specimen parameters evaluated are speed, feed rate, drill size and specimen thickness. A series of experiments are conducted using TRIAC VMC CNC machining center to relate the cutting parameters and material parameters on the cutting thrust and torque. The measured results were collected and analyzed with the help of the commercial software package MINITAB14. An orthogonal array, signal-to-noise ratio are employed to analyze the influence of these parameters on cutting force and torque during drilling. The method could be useful in predicting thrust and torque parameters as a function of cutting parameters and specimen parameters. The main objective is to find the important factors and combination of factors influence the machining process to achieve low cutting low cutting thrust and torque. From the analysis of the Taguchi method indicates that among the all-significant parameters, speed and drill size are more significant influence on cutting thrust than the specimen thickness and the feed rate. Study of response table indicates that the specimen thickness, and drill size are the significant parameters of torque. From the interaction among process parameters, thickness and drill size together is more dominant factor than any other combination for the torque characteristic.     

Investigations into peck drilling process for large aspect ratio microholes in aluminum 6061-T6

Deep or large aspect ratio microholes are needed in products made of aluminum alloys that find applications in space, automotive, and other sectors. In the present work, microholes of 500?µm diameter are produced by mechanical microdrilling. By following peck drilling strategy, microholes having aspect ratio of 6 are drilled in 3-mm thick aluminum 6061-T6 plates. Microdrills being slender and having low rigidity, breakage of these drills is a common occurrence. Hence it is necessary to analyze thrust force as well as torque obtained in microdrilling. For reliable measurement, the thrust force from a dynamometer and torque from a torque sensor is acquired simultaneously using a novel arrangement. For comparison, another set of experiments is also performed to produce 0.5-mm diameter blind holes by direct drilling and the results are further discussed. The causes for increase in forces at some peck steps during microdrilling of holes are explained using the signals and images acquired during the process. By having a threshold on the drilling torque, it is possible to control the microdrilling process and minimize the microdrill breakages.     

Performance evaluation of cryogenic cooling in reaming titanium alloy

Removal of materials in metal cutting operations through drilling and reaming of hard materials is a difficult process. Wear of the tool and high cutting zone temperature have big effect on it. In this study, experiments have been carried out in a reaming operation on titanium alloy material under flood and cryogenic LN₂ cooling separately. Cutting speed, feed rate, and hole depth (constant) are the three input variable parameters. Torque (M_t), thrust force (F_t), cutting temperature (T), quality of the hole, surface roughness (R_a), and chip morphology are the output parameters. In both cooling conditions, each of the nine experiments based on orthogonal array (OA) L₉ were conducted under both cooling conditions. Based on the results obtained, cutting temperature was reduced by 12–21%, thrust force reduction is 17–32%, and torque reduction is 7–30% in cryogenic LN₂ cooling. Surface roughness is increased by 4–15% and hole quality (circularity and cylindricity) parameters are affected in cryogenic LN₂ cooling with respect to flood cooling. Better chip breaking was found in both flood and cryogenic LN₂ cooling. No drastic changes were observed in microstructure under both cooling conditions.     

Investigation of cryogenic cooling effect in reaming Ti-6AL-4V alloy

This research article is based mainly on the investigation of the effect of cryogenic machining, while reaming Titanium grade 5 alloy (Ti-6Al-4V) material. Cutting speed (V_c) and feed rate (f) are two input parameters at three different levels for a constant depth of the hole. The output parameters considered by using a cryogenic LN₂ cooling compared to a conventional flood cooling are torque (M_t), thrust force (F_t), cutting temperature (T), quality of the hole (circularity and cylindricity), surface roughness (R_a) and chip morphology. The results show cryogenic liquid nitrogen (LN₂) cooling resulting in 15–31% reduction in the cutting temperature, 23–57% reduction in the thrust force and 14–65% reduction in torque. Higher surface roughness, circularity (Cir) and cylindricity (Cyl) were observed in the cryogenic LN₂ cooling condition. Furthermore, better chip breakability was observed in the cryogenic LN₂ cooling condition. No drastic change in the microstructure was observed in both flood and cryogenic LN₂ cooling. Increase in microhardness by 10–16% and 8–19% in cryogenic LN₂ cooling over flood cooling was observed.     

Dynamic response of multidirectional composites in hygrothermal environments

Drilling is an essential operation in the assembly of the structural frames of automobiles and aircrafts. The life of the joint can be critically affected by the quality of the drilled holes. The main objective of the present paper is to investigate the influence of some parameters on the thrust force, torque and surface roughness in drilling processes of fiber-reinforced composite materials. These parameters include cutting speed, feed, drill size and fiber volume fraction. The quasi-isotropic composite materials were manufactured from randomly oriented glass fiber-reinforced epoxy, with various values of fiber volume fractions (V_f), using hand-lay-up technique. Two components drill dynamometer has been designed and manufactured to measure the thrust and torque during the drilling process. The dynamometer was connected with a data acquisition, which installed in a PC computer. This set-up enable to monitor and record the thrust force and torque with the aid of a computer program that designed using Lab View utilities.

The results indicate that the start point of torque cycle is delayed by few seconds (depending on the value of feed) than the thrust force. This time is consumed to penetrate the specimen by chiseling edge. After the thrust force reached its maximum value it is gradually decreased during the full engagement of the drill and goes to zero when both the chisel edge and the cutting lips have exit of the laminate. In contrast the torque was gradually increased up to the end of the cycle and sudden jump to a value about 10 times the peak value. Cutting speed has insignificant effect on the thrust force and surface roughness of epoxy resin. For glass fiber-reinforced epoxy composites (GFREC) with V_f=9.8–23.7% the thrust force and torque were decreased with increasing cutting speed. On contrast increasing feed, drill size and fiber volume fractions lead to increase the thrust force and torque. The drilled holes of GFREC with lower V_f ratio at lower feed have greater roughness than that drilled at higher feed. Specimens with high V_f ratio have a contrary behavior. Drill diameter combined with feed has a significant effect on surface roughness.     

A review of mechanical drilling for composite laminates

Composite laminates (CFRP, GFRP, and fiber metal composite laminates) are attractive for many applications (such as aerospace and aircraft structural components) due to their superior properties. Usually, mechanical drilling operation is an important final machining process for components made of composite laminates. However, composite laminates are regarded as hard-to-machine materials, which results in low drilling efficiency and undesirable drilling-induced delamination. Therefore, it is desirable to improve the cost-effectiveness of currently-available drilling processes and to develop more advanced drilling processes for composite laminates. Such improvement and development will benefit from a comprehensive literature review on drilling of composite laminates. This review paper summarizes an up-to-date progress in mechanical drilling of composite laminates reported in the literature. It covers drilling operations (including conventional drilling, grinding drilling, vibration-assisted twist drilling, and high speed drilling), drill bit geometry and materials, drilling-induced delamination and its suppressing approaches, thrust force, and tool wear. It is intended to help readers to obtain a comprehensive view on mechanical drilling of composite laminates.     

Study on vibration drilling of fiber reinforced plastics with hybrid variation parameters method

Delamination is recognized as one of the major causes of damage during drilling of fiber reinforced plastics (FRPs), which not only reduces the structural integrity, but also has the potential for long-term performance deterioration. It is difficult to produce precise quality holes with high efficiency by conventional drilling method. In this paper, a new vibration drilling technology is presented using a hybrid variation parameters method, based on the model for predicting critical thrust forces and the model for predicting thrust and torque during vibration drilling of FRPs. From the drilling experiments, it was found that both precise quality holes and high efficiency could be obtained by this new drilling method.     

Transformation and thickening of chip during high throughput drilling

One of the major difference in drilling process when related to other conventional metal removal processes like turning and milling is that the drill tool has to work beneath harsh environment as the metal cutting region is situated deep inside the work material. Also, the chip flow is restricted only through the flutes, and hence there occurs transformation of chip shape, chip thickening, and changes in force and torque. In the present investigation, high throughput drilling has been performed under a dry and wet environment in an intermetallic titanium aluminide which is an exceptional class of material with superior properties. It is found that the chip shape transformed from spiral to folded ribbon as the depth of hole increased. Also, a substantial increase in chip thickness, thrust, and torque was observed, and toward the end of drilling, chip clogging occurred. An analytical model was established by applying the mechanics of oblique cutting to find the torque and thrust by measuring the thickness of chip, and this model was validated experimentally.