Drilling of composite structures (original) (raw)
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Analytical models of composite material drilling
The International Journal of Advanced Manufacturing Technology, 2011
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.
Optimization for drilling process of metal-composite aeronautical structures
Science and Engineering of Composite Materials, 2021
Metal-composite laminates and joints are applied in aircraft manufacturing and maintenance (repairing) using aluminum alloys (AA) and glass fiber-reinforced polymer (GFRP). In these applications, drilling has a prominent place due to its vast application in aeronautical structures’ mechanical joints. Thus, this study presents the influence of uncoated carbide drills (85C, 86C, H10N), cutting speeds (v c = 20, 40, and 60 m min−1), and feed rates (f = 0.05, 0.15, and 0.25 mm rev−1) on delamination factor, thrust force ( F t {F}_{\text{t}} ), and burr formation in dry drilling metal-composite laminates and joints (AA2024/GFRP/AA2024). Experiments were performed, analyzed, and optimized using the Box–Behnken statistical design. Microscopic digital images for delamination evaluation, piezoelectric dynamometer for thrust force acquisition, and burr analysis were considered. The major finding was that the thrust force during drilling depends significantly on the feed rate. Another signific...
Composites Part B: Engineering, 2017
Fibre reinforced polymer (FRP) composite laminates are employed in many industrial applications due to their attractive mechanical and structural properties. Machining operation, such as drilling of FRP laminates, plays a significant role in the assembly of parts in aircraft and spacecraft production. Among other production bottlenecks, drilling-induced delamination remains a major defect which adversely affects the quality of assembly parts. An efficient strategy in preventing this problem is the calculation of the critical thrust force above which delamination is initiated. Therefore, in this study, a new analytical model is proposed to predict the critical thrust force for delamination. Unlike the general models in the literature which derived only mode I strain energy release rate based on the assumption of classical laminate plate theory (CLPT) combined with linear elastic fracture mechanics (LEFM) mode I considerations in the elliptic delamination zone, the proposed analytical model is derived based on first-order shear deformation theory (FSDT) and accounts for mode I and mode II strain energy release rates in the delamination zone. This strategy allows to activate mixed mode criteria for delamination initiation which is a valid assumption for laminates with layers of different orientations. The present model is partly derived for general laminates subject to distributed loading and further extended to cross-ply laminate sequence subject to a mixed load condition. The results show that the effect of shear deformation in the prediction of the critical thrust force is influential with increasing ply thickness and the effect of chisel edge on shear deformation is more profound in the distributed load regime.
Comparative analysis of drills for composite laminates
Journal of Composite Materials, 2012
The characteristics of carbon fibre reinforced plastics allow a very broad range of uses. Drilling is often necessary to assemble different components, but this can lead to various forms of damage, such as delamination which is the most severe. However, a reduced thrust force can decrease the risk of delamination. In this work, two variables of the drilling process were compared: tool material and geometry, as well as the effect of feed rate and cutting speed. The parameters that were analysed include: thrust force, delamination extension and mechanical strength through open-hole tensile test, bearing test and flexural test on drilled plates. The present work shows that a proper combination of all the factors involved in drilling operations, like tool material, tool geometry and cutting parameters, such as feed rate or cutting speed, can lead to the reduction of delamination damage and, consequently, to the enhancement of the mechanical properties of laminated parts in complex structures, evaluated by open-hole, bearing or flexural tests.
Critical thrust and feed prediction models in drilling of composite laminates
Composite Structures, 2016
Drilling induced delamination has been recognized as a major problem during drilling of composite materials. The size of the delamination zone has been shown to be related to the thrust force. However, thrust force strongly depends on drilling parameters and it is not possible to control it directly. Thrust force can be correlated with feed rate, the most important parameter affecting thrust force. This paper presents analytical models to predict critical thrust force and feed rate at the onset of delamination. The model proposed is based on elastic fracture mechanics, classical plate bending theory and the mechanics of oblique cutting. An advantage of this model over other proposed models is that to avoid delamination via thrust monitoring, the thrust force will need to be sensed and used in adaptive control, while optimal feed rate can be used directly in CNC command generation to maximize productivity.
Experimental Investigation of Composite Materials Drilling Using a Step Gundrill
2017
The composite materials are nowadays widely used in the aeronautical field. Drilling of the aeronautical composite parts is required in the assembly process. The study of this operation is very important for composite materials since it generates a number of defects. These defects decrease the structure resistance against failure. A solution, to reduce these defects, is to drill using a special tool. In this paper, an experimental study on the drilling of thick composite plates using a step gundrill is conducted. This tool has a special geometry designed to drill thick composite materials and hybrid materials. More particularly, it allows the drilling chips to easily feed out of the hole. A number of drilling tests is performed in this paper. The drilling thrust force of each zone of the tool is measured, as well as the total drilling thrust force. The delamination at the exit of the hole is directly related to this thrust force. It is then interesting to decrease this drilling forc...
Composite materials have become valuable construction materials in aerospace, defense and in recent years in automotive industry. The advantage of composite materials over conventional materials stems largely from their higher specific strength, stiffness and fatigue characteristics. Composite components are joined by mechanical fasteners, accurate, precise high quality holes need to be drilled to ensure proper and durable assemblies. Drilling of composite materials causes several damages, such us: delamination, fibre-pull out, edge chipping, uncut fibers and others. Delamination is a major problem associated with drilling fiber reinforced composite materials. It causes poor assembly tolerance, reduces structural integrity of material and the potential for long term performance deterioration. The thrust force has been cited as main cause of delamination. In this paper the objective was to establish correlation between cutting parameters and thrust force, drilling torque and delamination. Drilling tests were carried out on carbon epoxy composite material using three different drills, HSS-Co twist drill, Multi Constructional twist drill and "Brad & Spur" drill. The data have been processed by the "DesignExpert" software package which generated the mathematical models.
Materials, 2016
Composite materials are widely employed in the naval, aerospace and transportation industries owing to the combination of being lightweight and having a high modulus of elasticity, strength and stiffness. Drilling is an operation generally used in composite materials to assemble the final product. Damages such as the burr at the drill entrance and exit, geometric deviations and delamination are typically found in composites subjected to drilling. Drills with special geometries and pilot holes are alternatives used to improve hole quality as well as to increase tool life. The present study is focused on the drilling of a sandwich composite material (two external aluminum plates bound to a polyethylene core). In order to minimize thrust force and burr height, the influence of drill geometry, the pilot hole and the cutting parameters was assessed. Thrust force and burr height values were collected and used to perform an analysis of variance. The results indicated that the tool and the cutting speed were the parameters with more weight on the thrust force and for burr height they were the tool and the interaction between tool and feed. The results indicated that drilling with a pilot hole of Ø4 mm exhibited the best performance with regard to thrust force but facilitated plastic deformation, thus leading to the elevation of burr height, while the lowest burr height was obtained using the Brad and Spur drill geometry.
Experimental and Analytical Investigation of Drilling of Sandwich Composites: A Review
A composite material is made out of a mixture or a combination of two or more distinctly differing materials which are insoluble in each other and differ in form or chemical composition. The technological and commercial interest in composite material lies in their superior properties of strength-to-weight, stiffness-toweight, fatigue and thermal expansion compared to metals. Extensive use of composite in application such as rockets, satellites, missiles, light combat aircraft, advanced light helicopter and trainer air craft has shown that India is on par with the advanced countries in the development and use of composites in this area.
Investigation of the Effects of Drilling on Mechanical Joints in Composite Structures
International Conference on Sustainable Future and Environmental Science, 2021
The use of a variety of composites due to their superior properties, which include low weight, high strength, and high corrosion resistance, which are generally many applications in the aerospace, automotive, and marine structures have increased significantly. Fiberglass reinforced composites have several industrial applications due to their suitable mechanical and physical properties. Drilling is one of the common methods for connecting structures made of reinforced materials with fibers. Composite structures usually result from the joining of members to transmit and tolerate incoming forces. One of the methods of connecting the members, due to the ease of maintenance and repair, is the mechanical connection through screws or rivets, which inevitably must create holes in these members. Composites as materials that are difficult to machining, drilling these materials can lead to delamination and, in some cases, degradation. In this paper, the effects of drilling on mechanical joints in composite structures and solutions to prevent damage to them due to drilling are investigated.