Milling Of Carbon Fiber Reinforced Plastics Research Articles

Effect of Cutting Speed and Feed per Tooth on the Trimmed Surface Roughness and Tool Wear During Milling of CFRP: Aerostructural Part

The machining quality plays a pivotal role in determining the service life of components. In this context, the primary focus of the experimental investigation is centered on the impact of cutting conditions during edge trimming of carbon fiber reinforced plastics (CFRP) material. The ultimate objective of this experiment is to pinpoint the most effective machining parameters, specifically the cutting speed, Vc and the feed per tooth, fz, to minimize damages during the edge trimming process using actual aerostructural sample components composed of CFRP material. Furthermore, the study took into account the issue of tool wear on cutting tools. The Design of Experiment (DoE) technique, specifically the Taguchi L9 orthogonal arrays method, was used to conduct this research. It was shown that the feed per tooth, fz, and the cutting speed, Vc, had the biggest effects on the trimmed surface quality as the longitudinal surface roughness increased. It was demonstrated that the fracture of the pyramidal tooltips in router-type tools happened more frequently at higher cutting speeds, Vc. The optimal machining parameters for minimizing damages during CFRP edge trimming were the combination of the feed per tooth, fz at 0.05 mm and cutting speed, Vc at 50 m/min. The most significant element influencing the tool’s wear was the cutting speed, Vc.

Research on stability of robotic longitudinal-torsional ultrasonic milling with variable cutting force coefficient

With their successful applications in handling, spraying, arc welding and other processing fields, industrial robots are gradually replacing traditional CNC machine tools to complete machining tasks due to the wider working envelope and the higher flexibility. Aiming at the chatter problem, a robotic longitudinal-torsional ultrasonic milling method with variable force coefficient is proposed in this paper. Taking carbon fiber-reinforced plastics (CFRP) as the processing object, the influence of the fiber layup angle on the milling force is analyzed first; then, the robot milling force parameters are determined, and the robot milling kinematics model is established. Furthermore, the ultrasonic function angle is defined, and the cutting layer thickness model, the dynamic milling force model, and the dynamic differential equation under ultrasonic vibration are established to analyze the stability of robotic longitudinal-torsional ultrasonic milling of CFRP. Finally, the full discrete method is used to obtain stability lobe diagrams.

Comparative study on cutting performance of conventional and ultrasonic-assisted bi-directional helical milling of CFRP

Compared with the conventional drilling, the helical milling has obvious advantages in making holes of carbon fiber-reinforced plastic (CFRP). Nevertheless, the rapid wear of cutting edges readily causes some defects in the outlet holes, such as burrs and tearing. In order to improve the hole-making quality of CFRP, a comparative experimental study on conventional and ultrasonic-assisted bi-directional helical milling of CFRP was carried out. The wear mechanism of the forward and reverse cutting edges was analyzed in the two types of machining, and the change laws of cutting forces and hole wall quality were obtained by different machining means. The experimental results indicated that the flank face of forward and reverse cutting edges was dominated by the abrasive wear mechanism in the ultrasonic-assisted milling. With aggravation of the tool wear, no obvious coating peeled off the forward cutting edge, the reverse cutting edge remained relatively intact, and the wear form of neither cutting edge changed. Furthermore, in the ultrasonic-assisted reverse milling, the axial force and hole diameter deviation were restrained better than in the conventional milling, and especially when the tool wear occurred, the cutting force fluctuation varied slowly. In the ultrasonic-assisted milling, the shear fracture predominated over bending fracture. Meanwhile, the time variation of effective rake angles improved the chip breaking and removing performance of cutters, and thus, the machining quality of hole wall was enhanced obviously.

Study on tool wear mechanism and cutting performance in helical milling of CFRP with stepped bi-directional milling cutters

Helical milling, a new machining technology, has obvious advantages in hole making of carbon fiber reinforced plastic (CFRP), and the technology, nonetheless, shows some defects such as hole diameter tolerance and surface damage aggravation caused by fast tool wear. Aiming to improve the hole making quality of CFRP, this paper proposes the bi-directional helical milling strategy, carries out the experimental research on milling CFRP with stepped bi-directional milling cutters, analyzes the wear mechanism of forward and backward cutting edges, and thus obtains the change laws of cutting forces and hole-making quality in different tool wear conditions. The experimental results show that in the initial milling stage, strip-shaped and spoon-shaped wear bands are formed by abrasive wear mechanism on both forward and backward cutting edges; with aggravation of the tool wear, the wear mechanism of forward cutting edge is gradually dominated by the fatigue wear, and subsequently, a large-area coating peels off the tool surface, causing the rapid wear of substrate. Compared with the forward cutting edge, the backward cutting edge produces less and more stable axial cutting force, and causes all the cutting forces to rise more slowly. In comparison with traditional drilling and milling of CFRP, bi-directional hole-making can effectively suppress some defects such as hole diameter shrinking, burrs and tearing, and thus it shows better machining quality.

The design and performance evaluation of assisted chip removal system in helical milling of CFRP/Ti stacks

Hybrid structures consisting of carbon fiber reinforced plastics (CFRP) and metal have been widely applied in aircraft manufacturing. Numerous holes need to be made in order to assemble the structures. Due to the small size of CFRP chips and the dry cutting conditions, improperly dealing with chips can increase tool wear, degrade hole quality, and contaminate to environment and health. In this study, an assisted chip removal system, mainly including an exhaust hood, a vacuum cleaner, and a tool holder, was used for helical milling of CFRP and titanium alloys (CFRP/Ti stacks). The geometry of the chip exhaust hood model was designed and optimized to clear and collect cutting chips using finite element method (FEM). Based on this system, pressurized air was pumped into cutting areas through the inner cooling channels in the tool. Then, the performance of the assisted chip removal system was evaluated in helical milling of CFRP/Ti stacks under different chip collecting conditions. Results showed that this system had a good ability of chip removal and preventing chips returning into the hole. And the pressurized air could promote chips remained in the hole to be removed and provide cooling effect to cutting tool. As a result, tool wear was reduced, the cutting force and cutting temperature were decreased, and hole quality was improved. Results proved the assisted chip removal system can help to further improve the hole-making process of CFRP/Ti stacks.

Application of niobium carbide based cutting materials for peripheral milling of CFRP

Due to its inherent material properties, the implementation of niobium carbide (NbC) as hard phase in cutting materials represents a promising alternative to machining. Recent investigations show equivalent tool life in metal cutting compared with cemented carbides based on tungsten carbide (WC). Besides metal cutting, the machining of high-performance composite materials poses an increasing importance due to its growing demand in the automotive and aeronautical sector. NbC and its wear resistance against abrasion can be suitable for this specific application. Additionally, the low density of NbC indicates an advantageous dynamic behaviour. Thus, this study focuses on the milling of carbon fiber reinforced plastics (CFRP). Complex tool geometries are implemented in a peripheral milling strategy. The machining trials are conducted with uncoated NbC-based cutting materials in CFRP with varying cutting speeds vc. The utilized NbC compositions (NbC-10TiC)-6Ni7.5VC and (NbC-15TiC7N3)-5Ni7.5WC2.5Mo2C embedded in a Nickel (Ni) matrix were applied and compared towards their performance with an industrial available cemented carbide (WC-Co). As tool life criteria, a tool diameter reduction of Δd = 0.1 mm and a cutting path of lc = 10.000 mm were defined. Apart from tool life performance, the workpiece quality was assessed. An inferior performance was identified with (NbC-10TiC)-6Ni7.5VC in terms of tool life compared to WC-Co, which can be attributed to microstructure issues. Yet, (NbC-15TiC7N3)-5Ni7.5WC2.5Mo2C shows a competitive performance in machining with an achieved cutting path lc identical to WC-Co. It can be stated, that NbC-Ni systems can accomplish an equivalent performance in comparison to WC-Co when machining CFRP.

Cryogenic machining of carbon fiber reinforced plastic (CFRP) composites and the effects of cryogenic treatment on tensile properties: A comparative study

Abstract Carbon fiber reinforced plastics (CFRPs) are prone to damage locally during machining due to the applied cutting forced and generated heat. Cryogenic machining can reduce the heat generated damages of CFRPs by utilizing cryogenic liquids instead of conventional cutting fluids. The goal of this study is to investigate milling performance of CFRPs in cryogenic medium. For this, a new cryogenic machining approach was adopted to slot milling of CFRPs by submerging the workpiece within a cryogenic liquid. The CFRPs were fabricated via vacuum assisted resin transfer method by using woven carbon fiber fabric as a reinforcement and epoxy as a matrix. Machining performance was evaluated based on the resulting cutting force, delamination factor, surface roughness, and surface damage. Moreover, the influences of cryogenic coolant on the tensile properties, fracture surface microstructure, and machined surface of the CFRP laminates were analyzed with scanning electron microscopy (SEM). SEM analysis revealed that combination of different damage modes such as debonding, micro matrix crack, fiber pull out, and bundle pull out, delamination, and fiber breakage were observed. The results showed that cryogenic machining approach provided less damage formation on the machined surface, reduced delamination factor and surface roughness but increased resulting cutting force during machining of the CFRPs. On the other hand, there was a slight improvement (about 3%) of the tensile properties for the CFRPs exposed to cryogenic coolant due to matrix hardening and increasing in the fiber strength and shear strength.

Analytical cutting model for a single fiber to investigate the occurrences of the surface damages in milling of CFRP

The edge milling process of carbon fiber-reinforced plastics (CFRPs) is often accompanied by delamination and burrs on slot edges of the top layer. These damages impact on processing quality, processing efficiency, strength, and fatigue life of the materials, etc. To investigate the occurrence of these damages, the analytical cutting model for a single fiber of the top layer is established based on the Winkler elastic foundation beam theory. The critical fiber cutting angles and the corresponding engagement angles with different initial fiber orientations are predicted. Then, the milling experiments with the initial fiber orientations θ0 = 90° are carried out. The results show that the occurrences of the burrs and delamination can be correctly predicted. The suitable initial fiber orientations are chosen in the range from 30 to 60° for the smoother slot edges. There are two burr occurrence zones (BOZs) when θ0 = 90°. The delamination-inhibited zone (DIZ) is usually in the burr occurrence zone (BOZ).

Experimental Study on Milling CFRP with Staggered PCD Cutter

Carbon fiber reinforced plastics (CFRP) have good physical properties, such as high specific strength and high specific modulus. However, cutting delamination, tearing and burr, etc. often occur in the machining process of CFRP, which results in the uncontrollability of machining surface quality and serious tool wear. In this paper, milling of CFRP with a staggered cutter was carried out, the cutting-edge radius was investigated in order to characterize the tool wear; the effect of the cutting-edge wear radius on the milling force and surface quality was found, and the formation mechanisms of the 3D surface topography and surface defects were analyzed under the wear state. Experimental results showed that the wear of the staggered PCD cutter was mainly concentrated in the cutting-edge area. With the increase in milling length, the radius of cutting edge gradually became largeer under the action of abrasive wear mechanism, and the flank wear was not obvious. With the intension of tool wear, milling force gradually increased and the machining surface quality of the CFRP deteriorated distinctly, i.e., defects such as bare fiber fracture, groove and hole appeared, and burrs were gradually generated on the workpiece surface. Finally, through a comparative analysis of cutting performance, it was found that the staggered PCD cutter possessed better performance for wear resistance and burr suppression than the straight-teeth cutter. This finding can provide theoretical and technical support for improving the machining quality of carbon fiber composite materials.

Development of a Staggered PCD End Mill for Carbon Fiber Reinforced Plastic

This work presents a PCD (polycrystalline diamond) end mill with a new staggered structure for the milling of CFRP (carbon fiber reinforced plastic). The magnitude and direction of cutting force is decreased and changed by side-edge re-configuration of the structure. The flute and insert pocket of the staggered PCD end mill are designed considering the tool’s stiffness and welding process. The milling process and machining defects of the staggered PCD end mill are analyzed, and the structural parameters of the staggered PCD end mill are determined. The staggered PCD end mill is fabricated by the process of wire cutting, NC (Numerical Control) machining, high-frequency induction brazing, welding, grinding and passivation. Milling tests of multidirectional CFRP with the staggered PCD end mill is conducted on CNC (Computerized Numerical Control) milling machine. The milling force is measured by a dynamometer. A range analysis of the numerical results of milling force is conducted after milling test, and the influence of milling parameters on milling force is analyzed. A regression model of the milling force is built and verified by experiment. The effects of fiber cutting angle on milling force are obtained through milling CFRP with different fiber orientation angles.

Low Frequency Oscillated Milling of Carbon Fiber-reinforced Plastics

Components made of carbon fiber-reinforced plastics (CFRP) are usually manufactured by near net shape processes. Nevertheless, post processing is necessary and milling is a common technology. In this study, the feasibility of an oscillated milling with a maximum frequency of less than 30Hz for chipping unidirectional CFRP with a thickness of 1.5mm was investigated. The influence of the tool and the fiber orientation on delamination, chip formation and surface quality were studied. It was found that the tool and the fiber orientation angle have a significant influence on delamination. The additional movement could be advantageously for reducing delamination.

Zmogljivost rezilnega orodja pri rezkanju plastike, ojačane z ogljikovimi vlakni

Carbon-fiber-reinforced plastics (CFRPs) are no longer the exclusive domain of aerospace industries and nowadays find more applications in the automotive and consumer industries. The growing volume of these materials increases the need for their efficient machining. However, the machinability of CFRPs is a rather complex task due to the heterogeneity and the considerable number of parameters influencing the cutting process. The cutting tool has long been recognized as an important factor influencing both surface quality and dimensional accuracy. Hence, in this paper, tool performance is investigated in the end milling of CFRPs. The effect of tool geometry and coatings on the cutting forces, dimensional accuracy and surface quality were experimentally examined for side and slot milling.

Effect of Cutting Speed on the Face Milling of CFRP Using a PCD Tool

Carbon-fiber-reinforced plastic (CFRP) is used in various industries such as aerospace and automobile industries because of its high mechanical characteristics. However, this material is difficult to cut. Tool wear and delamination frequently occur during the drilling or cutting of CFRP. In previous studies, we developed a CFRP cutting tool using polycrystalline diamond (PCD). The PCD tool exhibited excellent cutting performance at cutting speeds as low as <120 m/min. In this study, the authors investigated the effect of cutting speed on the face milling of CFRP by using the developed PCD tool.

High-Quality End Milling of CFRP – Inclination Milling with High-Helix End Mill –

Side milling tests of CFRP (carbon fiber reinforced plastics) containing thermosetting resin are carried out by TiAlN/AlCrN-coated, H2-free DLC (diamond-like carbon)-coated, and CVD diamond-coated carbide end mills without coolant. Two types of end mills having different helix angles of 30° and 60° are used. The film thickness and surface smoothness are varied for the DLC-coated end mills. The cutting characteristics are evaluated by tool wear and surface integrity (i.e., 3D profiles of the machined surface, generation of fluffing, delamination, and pull-out of the carbon fibers). The cutting force and tool flank temperature are also examined for the two types of CFRP composites and the helix angle of the end mill. “Inclination milling,”in which the end mill is tilted so that the resultant cutting force acts parallel to the work surface, is proposed as a novel technique to be used with a high-helix angle end mill. This unique approach enables the reduction of tool wear and improves the surface integrity of machined CFRP surfaces.

A comparative study on helical milling of CFRP/Ti stacks and its individual layers

Carbon fiber-reinforced plastics (CFRPs) and titanium alloys have different mechanical properties and show the unique processing characteristics in the cutting process. In order to complete hole-making of CFRP/Ti stacks with larger thickness, a comparative study was conducted on the stacks of CFRP/Ti versus CFRP and titanium alloy single plate in the helical milling process. Experimental results show that cutting performance including cutting force and tool wear pattern and hole quality in helical milling of stacks are all different to single plate. The impact of tool wear on the cutting force is relatively significant while machining of CFRP compared to titanium alloy. While machining of CFRP/Ti stacks, axial forces of titanium alloy suddenly change very larger than single titanium plate due to tool wear, and tool wear state shows combination of several wear pattern. Undersized CFRP holes and oversized Ti plate holes are produced when milling single plate; however, oversized CFRP and undersized Ti plate holes are observed when machining of stacks. The results also indicate that tool wear in helical milling of CFRP will influence the cutting performance of stacks.

Pocket milling of carbon fiber-reinforced plastics using 532-nm nanosecond pulsed laser: An experimental investigation

Non-traditional machining of carbon fiber-reinforced plastics, such as laser machining, has great advantages over mechanical machining in the aspect of machinability and flexibility. In this article, a laser milling method using diode pumped and frequency doubled Nd:YVO4 nanosecond pulsed laser system is presented. The effects of processing parameters including laser power, scanning speed, and hatch distance were analyzed. It was found that machining quality and efficiency are seriously influenced by laser power and pulses overlapping rate. The features of micro-pit and chopped fibers on the machined surface were observed with metallographic microscope, and ablation mechanism involved was studied to explain the phenomenon. Depth-controlled milling strategy was realized in the laser focusing environment. Finally, challenges and suggestions are presented for wide application of the method.

A simplified damage prediction framework for milling of unidirectional carbon fiber-reinforced plastics

This article presents a simple framework for predicting the occurrence of delamination during milling of unidirectional carbon-fiber-reinforced plastics (CFRPs), based on a concept of effective critical cutting zone. To validate the concept, sets of milling experiments were conducted on unidirectional CFRP samples of varying fiber orientations and the delamination signature was measured through microscopic images. By observing the damage extent for different fiber orientation angles and different fiber cutting angles for up-milled and down-milled edges, and correlating them with different material removal mechanisms, it has been shown that the damage mainly depends on the portion of the fiber cutting angles that lie within the effective critical milling zone. Both the delamination and the normal cutting forces were found to be strongly dependent on the range of angles in this zone. In addition, it is shown that the cutting force may be used as a good approximation to determine the effect of machining/process parameters on the ensuing delamination damage during milling of CFRPs. For the tested samples, the normal cutting force decreased with an increase in the cutting speed and it increased with an increase in the feed rate of the cutting tool.

Effects of Fiber Orientation Direction on Tool-Wear Processes in Down-Milling of Carbon Fiber-Reinforced Plastic Laminates

This paper discusses tool-wear processes in the milling of carbon fiber-reinforced plastic (CFRP) laminates. Plane down-milling tests with unidirectional and cross-directional CFRP laminates were performed using two types of cutting tools made of tungsten carbide and polycrystalline diamond. Measurements of the changes in the cutting forces and tool-wear widths over the cutting distance revealed that the fiber orientation direction in the CFRP laminates relative to the tool-traveling direction is an important parameter to determine the tool-wear processes. Additionally, based on obtained experimental results, a wear parameter to characterize cutting tool wear is introduced. This parameter can accurately explain the relationship between the worn tool-edge profiles and the processed-surface quality.

Effect of cutting tool lead angle on machining forces and surface finish of CFRP laminates

Abstract Machining is one of the most practical processes for finishing operations of composite components, allowing high-quality surface and controlled tolerances. The high-precision surface milling of carbon fiber-reinforced plastics (CFRP) is particularly applicable in the assembly of complex components requiring accurate mating surfaces as well as for surface repair or mold finishing. CFRP surface milling is a challenging operation because of the heterogeneity and anisotropy of these materials, which are the source of several types of damage, such as delamination, fiber pullout, and fiber fragmentation. To minimize the machining problems of CFRP milling and improve the surface quality, this research focuses on the effect of multiaxis machining parameters, such as the feed rate, cutting speed, and lead angle, on cutting forces and surface roughness. The results show that the surface roughness and cutting forces increase with the feed rate, whereas their variations are not uniform when changing the cutting speed. Generally, a lower surface roughness was achieved by using a lower cutting feed rate (0.063 mm/rev) and higher cutting speeds (250–500 m/min). It was also found that the cutting forces and surface roughness vary significantly and nonlinearly with the lead angle of the cutting tool with respect to the surface.

Influence of Tool Shape and Coating Type on Machined Surface Quality in Face Milling of CFRP

Since demands for Carbon Fiber Reinforced Plastics (CFRP) are increasing, the number of the studies on machining of CFRP is also increasing. However, since there are already reports on a trimming of a surplus portion or a drilling, we focus on a face machining and a generating the step shape with several cutting tools. Problems in the machining of CFRP include an occurrence of the burr and delamination. Therefore, in this report, we investigate these problems in face milling. And, the machining behavior (Cutting temperature, Cutting force) during the machining is estimated.