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。     

Neural network approach for estimating the residual tensile strength after drilling in uni-directional glass fiber reinforced plastic laminates

The drilling of fiber reinforced plastics (FRP) often results in damage around the drilled hole. The drilling induced damage often serves to impair the long-term performance of the composite products with drilled holes. The present research investigation focuses on developing a predictive model for the residual tensile strength of uni-directional glass fiber reinforced plastic (UD-GFRP) laminates with drilled hole which has not been developed worldwide till now. Artificial neural network (ANN) predictive approach has been used. The drill point geometry, the feed rate and the spindle speed have been used as the input variables and the residual tensile strength as the output. The results of the predictive model are in close agreement with the training and the testing data.     

Machinability analysis in drilling woven GFR/epoxy composites: Part I – Effect of machining parameters

The present paper deals with the effect of machining parameters (feed, speed and drill diameter) on the thrust force and machinability of woven glass fiber-reinforced epoxy (GFRE) composites. The selected machinability parameters were delamination size, surface roughness, and bearing strength. The results show that, delamination-free in drilling GFRE composites was not observed, in the range of the investigated cutting parameters. Surface roughness instrument can be used as an indication for the position of the internal delamination damage in drilling GFRE composites. The high values of correlation coefficients between thrust force and the machinability parameters confirm the importance of reducing the thrust force to improve the load carrying capacity of composite structure assembled by rivets or bolted joints.     

Drilling tool geometry evaluation for reinforced composite laminates

In this work, a comparative study on different drill point geometries and feed rate for composite laminates drilling is presented. For this goal, thrust force monitoring during drilling, hole wall roughness measurement and delamination extension assessment after drilling is accomplished. Delamination is evaluated using enhanced radiography combined with a dedicated computational platform that integrates algorithms of image processing and analysis. An experimental procedure was planned and consequences were evaluated. Results show that a cautious combination of the factors involved, like drill tip geometry or feed rate, can promote the reduction of delamination damage.     

Optimization of process variables in drilling of carbon fiber reinforced plastics using various multi criteria decision making approaches

Carbon fiber-reinforced polymers are one of the lightweight materials used in structural design due to their exceptional mechanical performances. The drilling operation is indispensable as it facilitates the assembling of various manufactured components. However, drilling of fibrous laminates is deemed difficult in comparison to the traditional metals because of the anisotropic and non-homogeneous nature. The present work addresses the parametric effect on the drilled hole delamination and further reduces it with an optimal combination of parameters for multi-objectives using different multi-criterion decision-making techniques. Initially, the response surface-based regression model of delamination as a function of three static inputs has been developed, further revised with induced thrust as well as mean torque for the improvisation of the prediction capability. Finally, for the overall improvement, a decision-making model has been used that includes grey relation analysis, technique for order performance by similarity to ideal solution, and VIšekriterijumsko Kompromisno Rangiranje method. The delamination was found to be minimum at a low drill point angle (100°), high spindle rotation (2150 min⁻¹ ), and low feed rate (0.025 mm/rev) due to reduced thrust force. The mean absolute prediction error was significantly improved considering root mean square torque rather than axial thrust with process variables.     

Optimization of delamination factor in drilling GFR–polypropylene composites

Glass fiber-reinforced polypropylene composites often replace the conventional materials due to their special or unique mechanical properties. As the applications of these composites increase for a number of industries, drilling of these composites is inevitable for subsequent composite product manufacturing stage. In the drilling of composites, the thrust force is induced during the drilling operation; as a result, it causes damage. This damage is characterized by the delamination factor, which depends on the machining parameters such as speed of the spindle, feed rate, and drill diameter. The study on the delamination in the drilling of glass fiber-reinforced polypropylene is limited and has been carried out comprehensively. The effect of machining parameters on delamination in the drilling of glass fiber-strengthened polypropylene (GFR-PP) composites is studied through the Box–Bhenken design. Response surface method, along with the desirability analysis, is used for modeling and optimization of delamination factor in the drilling. The result proves that the models are effectively used to forecast the delamination in the drilling of GFR-PP composites. Also, the result indicates that the foremost issue that influences the delamination is the feed rate.     

Investigations on Drilling of Bidirectional Cotton Polyester Composite

Cotton fiber composites are currently used in the interior parts of automobiles, insulation boards, fiber boards, and various parts of high-friction mechanical assemblies. These composites are subjected to machining operations. Drilling is an indispensable machining operation for assembly of different parts. The present work aimed to carry out experimental and analytical investigations on drilling of bidirectional cotton polyester composite. Influence of feed, spindle speed, and drill point angle on machining characteristics like thrust force, torque, and delamination factor was studied by conducting experiments derived from Taguchi's L27 orthogonal array. To determine the significance of each drilling process parameters and their interactions, analysis of variance (ANOVA) test was conducted. Modeling of drilling parameters was carried out through multiple regression analysis and their optimization for minimizing cutting forces and machining induced damage was carried out using signal to noise ratio analysis.     

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 investigation on drilling of natural flax fiber-reinforced composites

Natural fiber composites (NFCs) have strong potential to replace glass fiber-reinforced plastics. An instrumental operation in machining composite structures is hole making which facilitates assembly of parts. Understanding the effects of drilling process parameters on feature properties of NFCs has great benefits. In this regard, to make a good quality and accurate hole in composite structures, appropriate selection of drill bit and cutting parameters is important. This paper investigates delamination behavior and hole quality of flax/epoxy composite laminates in response to feed, spindle speed, and three different types of drill bit. As indicated by analysis of variance results, drill bit type and feed have greater influences on the thrust force. It appeared that delamination factor and surface roughness were significantly influenced by drill bit, but not by feed and spindle speed. The choice of drill bit has great impact on the delamination factor (67.27%) and surface roughness (74.44%), respectively.     

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.     

An approach towards damage free machining of CFRP and GFRP composite material: a review

Over the last decade, the use of polymeric composite material has increased considerably, and as a result, machinability of such material has also increased. The main aim of this work is to emphasize on the conventional and unconventional machining of composite materials, more specifically on drilling of carbon fiber-reinforced polymer and glass fiber-reinforced polymer. Additional concentration on tool materials and geometry, roughness of drill surface, thrust force and delamination at entry and exit with influence of point angle of tool, variable feed rate, and variable spindle speed. Over the last few years, many studied on the effect of cutting parameters and tool geometry using conventional machining, the phenomena associated with unconventional machining of composite material requires some supplementary studies in order to make damage free machining of composite materials.     

CFRP管面钻削缺陷形成机制

碳纤维增强复合材料(CFRP)传动轴因性能优越广泛应用于汽车、航空航天、船舶、冷却塔风机等轻量化领域,但其钻削过程中容易出现毛刺、分层等缺陷。为了揭示CFRP管面钻削缺陷形成机制,选择双锋角钻头和三尖二刃钻对CFRP管面钻孔,利用分步钻削盲孔和通孔的方法,分析了损伤部位的受力情况,揭示了入口撕裂、出口毛刺和分层产生原因。根据实验结果,发现双锋角钻头钻孔时入口撕裂损伤较大,损伤位置在钻头与管面接触最低点,且主要是那部分水平缠绕CFRP管的纤维,原因是水平缠绕的纤维屈曲变形最大,对切削力更加敏感。双锋角钻头和三尖二刃钻的横刃对孔最终出口分层没有影响,主切削刃的切削行为决定孔最终出口分层。相同钻头钻孔时,轴向力不是唯一影响分层因子的因素,还需考虑切削热。相比双锋角钻头,三尖二刃钻因锋利的外缘尖角能有效划断纤维,使出口分层较小。     

Selection of drilling conditions for glass fibre reinforced plastics

An experimental investigation has been carried out into the drilling of glass fibre reinforced plastics using HSS twist drills. A test series was conducted using a wide range of cutting conditions and drill geometry, namely cutting speed, feed rate, point angle and helix angle. Decisions relating to the ‘optimum’ drilling conditions were based on the geometrical accuracy and appearance of the produced holes. Drill wear was measured during the test trials and used as a further constraint in ‘optimum’ cutting conditions selection. Speed, feed rate and drill point angle were found statistically to be the most significant parameters influencing hole quality. Drill wear can be successfully correlated to the level of the thrust force. A simple nomogram is included to predict drill wear level from the thrust level or the amount of material removed.     

Experimental thrust forces and delamination analysis of GFRP laminates using candlestick drills

Drilling is usually performed using twist drills while assembling the composite components. However, it is necessary to adopt appropriate tool as the risk of delamination damage is high. Many researchers have performed experimental and theoretical study concerning drilling-induced delamination damage in composites utilizing special drills. The article performed drilling experiments of glass fiber reinforced plastic laminates utilizing candlestick drills. Ten candlestick drills with different drill tip geometries were compared in thrust forces and push down delamination. The results revealed the drilling behavior of the outer cutting edges and the outer drill tips for candlestick drill, and also indicated that the push down delamination depended on exit thrust force instead of maximum thrust force. What is more, thrust forces and push down delamination were significantly reduced when holes were produced using reasonable candlestick drill tip geometry. Finally, the analysis was useful for selecting appropriate candlestick drill tip geometry and conducting candlestick drill tip geometry optimization.     

Parametric optimization studies on drilling of sandwich composites using the Box–Behnken design

This study was carried out to investigate the parametric influence on the performance of drilling newly made sandwich composites. Sandwich composite was prepared by using steel and jute as reinforcements and polyester as the matrix material. Drilling experiments were carried out by considering input factors such as spindle speed, feed rate of the spindle, point angle of the drill and tool diameter. Three output factors, namely thrust force developed during drilling, surface roughness of the drilled hole and damage at the entrance surface, were studied. All output factors were optimized by using the Box–Behnken approach, and the best machining conditions were taken on the basis of the desirability approach. Confirmatory experiments were conducted and compared against the Box–Behnken model. The comparison showed only a minor error, and hence the optimization is satisfactory.     

Delamination analysis of carbon fibre reinforced laminates: Evaluation of a special step drill

Drilling of carbon fibre/epoxy laminates is usually carried out using standard drills. However, it is necessary to adapt the processes and/or tooling as the risk of delamination, or other damages, is high. These problems can affect mechanical properties of produced parts, therefore, lower reliability. In this paper, four different drills – three commercial and a special step (prototype) – are compared in terms of thrust force during drilling and delamination. In order to evaluate damage, enhanced radiography is applied. The resulting images were then computational processed using a previously developed image processing and analysis platform. Results show that the prototype drill had encouraging results in terms of maximum thrust force and delamination reduction. Furthermore, it is possible to state that a correct choice of drill geometry, particularly the use of a pilot hole, a conservative cutting speed – 53 m/min – and a low feed rate – 0.025 mm/rev – can help to prevent delamination.     

Study of the Effect of Tool Wear on Hole Quality in Drilling CFRP to Select a Suitable Drill for Multi-Criteria Hole Quality

In recent years the use of carbon fiber composites in aerospace industries has been on the rise due to their unique properties like high specific strength, high stiffness, and fatigue characteristics. The machining behavior of these materials differs from machining homogenous metals because the drill bit encounters fiber and matrix alternatively which have widely different properties. Among the various machining operations, drilling is very common to facilitate assembly using fasteners to others parts in the structure. Rapid wear of the tool due to the abrasive carbon fibers is an important reason for damage occurrence. This results in frequent drill changes affecting the production cycle and increasing the final cost. Drill geometry is an important factor which decides the quality of the drilled hole. Hole quality is decided by a number of parameters like fiber pullout, delamination, surface finish, etc., among others. It is therefore necessary to evaluate the performance of the different drills available based on the quality of the holes they produce and drill life time. Three tool geometries are evaluated for thrust force, tool wear, surface roughness, fiber pullout, hole oversize, and eccentricity. Recommendations are given to aid in the selection of appropriate drill for the desired hole quality parameter.     

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.     

Some experimental investigations on drilling AA (6351)-SiC-B4C composite

This study is performed to assess the drilling of silicon carbide (SiC) and boron carbide (B₄C) particles reinforced with 6351 aluminum matrix. Stir cast specimens were prepared using an electrical resistance furnace, and the mechanical properties were revealed. Experiments were carried out with varying spindle speed, feed rate, and point angle to analyze the drill tool temperature, thrust force, and surface roughness. Analysis of variance (ANOVA) was performed to determine the significance and the percent of influence of each input process parameter on the quality response. The results show that the increasing spindle speed reduces the thrust force and surface roughness, but increases the tool temperature. Furthermore, the point angle tool of 90° reduced the thrust force significantly but negatively influenced the other output responses. The spindle speed contributes more to the thrust force and surface roughness by 63.53% and 44.01%, respectively, and the point angle contributes 48.88% to the tool temperature.     

Fracture and damage mechanics modelling of thin-walled structures - An overview

This paper reviews the most important current approaches for residual strength prediction of thin-walled structures. Crack driving force parameters such the linear elastic stress intensity factor and its plastic zone corrected extension for contained yielding conditions, the crack tip opening displacement δ₅, the crack tip opening angle CTOA, the cohesive zone model parameters, separation energy, critical tensile stress and critical separation and the parameters of the damage models of Gurson-Tvergaard-Needleman type are introduced and discussed with respect to their benefits and limitations for the simulation of plane and stiffened panels. In addition, specific aspects of modern non-integral and integral structures which pose a challenge are addressed. These comprise multi-site damage, crack deviation and branching, welding residual stresses, strength mismatch in material compounds and problems in bonded structures, such as delamination. A number of examples are provided to illustrate the potential of the various approaches.