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"Fu-ji, Wang"
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Effects of cutting edge radius and fiber cutting angle on the cutting-induced surface damage in machining of unidirectional CFRP composite laminates
Carbon fiber reinforced polymer composite laminates are anisotropic, inhomogeneous, and mostly prepared in laminate form before undergoing the finishing operations. The edge trimming process is considered as one of the most common finishing operations in the industrial applications. However, the laminate surface is especially prone to damage in the chip formation process, and the most common damage mode is burrs. Burrs may increase cost and production time because of additional machining; they can also damage the surface integrity. Many studies have been done to address this problem, and techniques for reducing burr size in material removal process has been the focus of the research. Nonetheless, the combined effects of the cutting edge radius and the fiber cutting angle on the burr formation have seldom been conducted, which in turn restricts to find out the mechanism of burr formation. The purpose of the present paper is to study the particular mechanism that leads to burr formation in edge trimming of CFRP laminates and investigate the effects of fiber cutting angle and cutting edge radius on burr formation. The results indicate that the burrs are prone to form in the fiber cutting angle range of 0° <
χ
< 90° when a large cutting edge radius of the tool is used for both milling and drilling of CFRP composites.
Journal Article
Analytical model for delamination of CFRP during drilling of CFRP/metal stacks
CFRP/metal stacks are widely used in aeronautical field. Drilling such stack composite in single shot is still challenging because of different machining properties between CFRP and metal. Delamination often occurs at the exit of the composite which can affect the strength of the composite components. Elastic deformation of CFRP and metal plate occurs in drilling process and furtherly affects the drilling character and critical delamination conditions. The aim of this paper is to study the delamination during drilling of CFRP/metal stacks with deformation of CFRP and metal plate. Analytical mechanical models are proposed to predict critical thrust force of CFRP in the drilling process for two stacking sequences, respectively. The elastic deformation of CFRP and metal plate and the local deformation of uncut CFRP laminate in the cutting zone are taken into consideration. The values of critical thrust force and the influences of the deformation of CFRP and metal plate on critical thrust force are obtained based on the solutions of the model. A series of punching experiments with accurate remained uncut plies is conducted to verify the rationality of the proposed models. The results indicate that the prediction of the proposed model shows a close correlation with the experiment measurements.
Journal Article
A mechanistic prediction model for thrust force and torque during drilling of CFRP/Ti stacks
Drilling holes on carbon fiber reinforced plastic/polymer (CFRP) and Ti stack structures is significantly important assembling process in aerospace manufacturing. However, it is quite a challenge that the excessive and completely different drilling loads of two materials with distinguish physical and mechanical properties will lead to frequent CFRP drilling damages and Ti burrs, as well as rapid tool failures. Therefore, understanding and controlling the drilling loads are crucial to ensure low damage and high efficiency drilling of CFRP and Ti stacks. In this paper, a novel mechanistic model was established to predict the thrust force and the torque in the drilling of CFRP and Ti stacks. The cutting loads of a twist drill were discretized along chisel edge, primary cutting edge, and minor cutting edge. An orthogonal cutting model and an oblique cutting model were proposed to represent the discretized cutting load for CFRP and Ti with the consideration of fiber cutting angles, flank face friction, and drilling parameters. Integrating the discretized cutting load, a mechanistic model for predicting thrust force and torque was developed for drilling of CFRP/Ti stack. After the coefficient calibrations, verification experiments showed that the developed model has accurately predicted the thrust force and torque under various spindle speeds/feed rates as well as the changing fiber cutting angles.
Journal Article
Tool path planning and machining deformation compensation in high-speed milling for difficult-to-machine material thin-walled parts with curved surface
Difficult-to-machine material thin-walled parts with curved surface are widely used in industrial applications, and the shape accuracy is a basic requirement for ensuring the usability. Due to the low rigidity of the thin-walled curved surface parts, the cutting force becomes a sensitive factor for the machining deformation. In addition, high speed milling, that has an obvious attribute of small cutting force comparing with the traditional one, provides an effective way to process the thin-walled curved surface parts made by difficult-to-machine materials like titanium alloy. Moreover, the rigidity of the thin-walled curved surface parts is constantly changing along with the machining process, which leads to a more complex machining deformation when choosing different tool paths and affects the machining quality. To reduce the machining deformation, a proper cutting parameters combination which influences the machining deformation directly is obtained based on the established cutting force model, and then a deformation control strategy by planning tool path is put forward. At the same time, an efficient compensation method based on modifying cutter location point is proposed. Taking TC4 thin-walled arc-shaped parts as an example, experimental studies indicate that the largest deformation values reduce to 49 μm after compensation. Compared with the former 104 μm, the deformation degree decreases by 52.88 % when the thickness of the thin wall is 200 μm. The research provides an effective approach to reduce the machining deformation induced error for difficult-to-machine material thin-walled parts with curved surface.
Journal Article
Three-dimensional oblique cutting model for sub-surface damage analysis in CFRP/Ti stack composite machining
Fiber-metal stack composite has been widely used in various aerospace industry due to its enhanced mechanical properties. It is still a challenge to machine such stack composite, for the disparate nature of each stacked constituent and the complex interaction between two constituents. The CFRP (Carbon Fiber Reinforced Plastic) is prone to get sub-surface damage in the chip formation process, which affects the mechanical property of the workpiece. Meanwhile, the sub-surface damage varies obviously under different interaction caused by different stacking sequences, and is also strongly influenced by fiber orientations and cutting parameters. However, only experimental researches on CFRP/Ti stack composite machining cannot reveal the cutting characters of the interface region with the impact of the titanium completely. In contrast, numerical simulation could offer sufficient capabilities to overcome the limitations of the experimentation. In this study, a new contribution is provided to study the sub-surface damage of the interface region versus the interaction of stacked constituents, fiber orientation and cutting parameters via numerical approach. To this aim, a three-dimensional oblique cutting model is developed to simulate the chip formation process of cutting two stacked constituents simultaneously. Different constitutive models and failure criteria are implemented to construct the entire machining behaviors of the stack composite. Simulation results, cutting forces and sub-surface damage depths obtained match well with the experimental ones, which could verify the correctness of the established model. The numerical results highlight the significant effects of fiber orientations, cutting parameters and stacking sequences on the sub-surface damage in the interface region. The variation trends of sub-surface damage are distinct in different fiber orientations and stacking sequences. The research provides a guidance on reduction of the sub-surface damage in machining stack composites.
Journal Article
Evolution laws of fiber-matrix interface cracks in machining of carbon fiber reinforced polymer
Undesirable machining damages exist frequently in the conventional machining processes of CFRP, causing significant decline in the performance of CFRP components. For effectively suppressing various machining damages, this study aims to reveal the evolution laws of the fiber-matrix interface crack, which can be regarded as the origin of majority of the machining damages. In order to accurately and conveniently obtain the evolution laws determined by numerous coupled factors, the study is conducted through a combined method of experiments and machine-learning predictions. Specifically, orthogonal cutting experiments are conducted for analyzing the fiber-matrix interface crack’s types and depth, and upon these characteristics predictive models based on machine learning are established for acquiring sufficient data so that reliable evolution laws can be obtained. From the results, it is found that there are four evolution types in all and when “burrs and cracks” exist, the crack depth increases obviously, and both the evolution types and depth are mainly determined by the fiber cutting angle. According to this, preliminary optimization methods of machining CFRP are proposed. The conclusions of this study are beneficial to facilitate the development of high-quality and high-efficiency machining technologies of CFRP.
Journal Article
Effect of tool wear on drilling unidirectional CFRP laminates in different fiber cutting angles
Drilling performance of carbon fiber reinforced polymer (CFRP) aggravates significantly with serious tool wear caused by highly abrasive fibers. Because of the anisotropy of CFRP, the angle between fiber orientation and cutting direction, namely, fiber cutting angle, also plays a crucial part in the drilling performance. To enhance drilling performance, this paper initially conducts a comprehensive experimental study on the effects of tool wear on thrust force, exit temperature, and hole wall defect in different fiber cutting angles in the drilling of unidirectional CFRP. The results demonstrate that the profile of worn cutting edge is an approximate elliptical arc and the half axis lengths of the elliptical arc are utilized to evaluate cutting edge wear. Tool wear on the cutting edge, flank face, and rake face all deteriorates with the number of drilled holes. Tool wear has a more significant influence on thrust force in the fiber cutting angle region of 0~90° than in the fiber cutting angle region of 90~180°. With increasing tool wear, the exit temperature distribution can still be approximate to an ellipse. The variation of exit temperature caused by tool wear in the major axis direction is still no less than that in other directions. In addition, on hole wall, tool wear causes severe crack defects in the fiber cutting angle region of 0~90° and cavity defects in the fiber cutting angle region of 90~180°.
Journal Article
Effect of geometric feature and cutting direction on variation of force and vibration in high-speed milling of TC4 curved surface
Curved surface parts with difficult-to-machine material are widely used in the industrial applications, and the three-axis NC machining with ball-end cutter is the commonly adopted method for some simple curved surface parts machining due to its high stiffness and simple operation. Due to the geometric feature variation for the curved surface and the bigger cutting force of the difficult-to-machine material, the cutting area and the cutting speed are changing all the time along the determined tool-path which results in a severe variation of cutting force and cutting vibration in high-speed milling process. This may not only affect the machining quality but also the tool life. In this way, the effect of the geometric feature of the curved surface and the cutting direction along the tool-path on the variation of force and vibration in high-speed milling of TC4 curved surface is studied. The experimental results show that both the cutting force and the cutting vibration increase when the tool-path curvature radius increases, while the cutting force decreases when the effective cutting radius increases and the cutting vibration will increase many times when the cutting area increases. Besides, the uphill cutting method for curved surface machining can obtain good machining quality and prolong milling cutter life. It can provide guidance for machining strategy selection especially for the cutting direction selection in the tool-path planning. The achievement, that can make both cutting force and cutting vibration small based on the geometric feature and the cutting direction, provides guidance for the machining planning of TC4 curved surface, which leads to improving machining quality and reducing tool wear.
Journal Article