Search Results (11)

Hybrid machining has considerable potential for industrial applications. The process allows the limitations of additive manufacturing to be reduced and high-precision components to be produced. This article discusses tests determining the impact of 3D printing parameters, machining parameters, and selected milling tools on achieving defined surface roughness values in parts made of PETG (polyethylene terephthalate glycol). Perpendicular-shaped samples were printed by fused deposition modelling (FDM) using variable layer heights of 0.1 mm and 0.2 mm and variable feed rates of 90, 100, 110, and 120 mm/s. Surface roughness values, topography, and Abbott–Firestone curves were determined using a Keyence VR-6000 profilometer. Straight grooves were machined in the test samples using a DMG MORI CMX 600V milling machine with a rotary burr, single-edge spiral burr cutter and spiral endmill. The microstructure was examined using a Motic inverted microscope. The surface roughness parameters of the grooves were investigated. The results confirmed that the use of hybrid machining (with a printed layer height L_h = 0.1 mm, V_feed = 120 mm/s, and a cutter–rotary burr) allows for lower surface roughness parameters, i.e., Ra = 1.54 μm. The relationships developed between printing, cutting, and milling tool parameters can be employed to predict the roughness parameters of filaments with similar characteristics. Full article

Titanium alloys are widely used in various fields, but milling titanium alloy materials often leads to problems such as high milling forces, increased milling temperatures, and chip adhesion. Thus, the machinability of titanium alloys faces challenges. To improve the milling performance of titanium alloy materials, this study analyzes the effective working area on the surface of the milling cutter through mathematical calculations. We design micro-grooves in this area to utilize their friction-reducing and wear-resisting properties to alleviate the aforementioned issues. The effective working area of the ball end milling cutter’s cutting edge is calculated based on the amount of milling and the installation position between the milling cutter and the workpiece. By observing the surface structure of seashells, micro-grooves are proposed and designed to be applied in the working area of the milling cutter surface. The impact of the micro-groove area on the milling cutter surface and spindle speed on milling performance is discussed based on milling simulation and experimental tests. Experimental results show that the cutting force, milling temperature, and chip resistance to adhesion produced by micro-groove milling cutters are superior to conventional milling cutters. Milling cutters with three micro-grooves perform best at different spindle speeds. This is because the presence of micro-grooves on the surface of the milling cutter improves the friction state, promoting a reduction in milling force, while the micro-grooves also serve as storage containers for chips, alleviating the phenomenon of chip softening and adhesion to the cutter. When conducting cutting tests with a milling cutter that has three micro-grooves, the milling force is reduced by 10% to 30%, the milling temperature drops by 10% to 20%, and the surface roughness decreases by 8% to 12%. Full article

The slot milling cutter is primarily used for machining the tongue and groove of the steam turbine rotor, which is a critical operation in the manufacturing process of the steam turbine rotor. It is challenging to predict the milling force of a groove milling cutter due to variations in rake, rake angles and cutting speeds of the main cutting edge. Firstly, based on a limited amount of experimental data on turning, we have developed an equivalent turning force model that takes into account the impact of the rounded cutting edge radius, the tool’s tip radius and the feed rate on tool’s geometric angle. It provides a more accurate frontal angle for the identification method of the Johnson–Cook material constitutive equation. Secondly, the physical parameters, such as shear stress, shear strain and strain rate on the main shear plane, are calculated through the analysis of experimental data and application of the orthogonal cutting theory. Thirdly, the range of initial constitutive parameters of the material was determined through the split Hopkinson pressure bar (SHPB) test. The objective function was defined as the minimum error between the theoretical and experimental values. The optimal values of the Johnson–Cook constitutive equation parameters A, B, C, n and m are obtained through a global search using a genetic algorithm. Finally, the shear stress is determined by the governing equations of deformation, temperature and material. The axial force, torque and bending moment of each micro-segment are calculated and summed using the unit cutting force vector of each micro-segment. As a result, a milling force prediction model for slot milling cutters is established, and its validity is verified through experiments. Full article

This paper presents a longitudinal–torsional transducer for use during the ultrasonic vibration-assisted milling (UVAM) of honeycomb aramid material. The mechanism of longitudinal–torsional conversion was analyzed to guide the design of a vibration transducer. The transducer features five spiral grooves around the front cover plate, which function under the excitation of a group of longitudinal piezoelectric ceramics. A portion of the longitudinal vibration was successfully converted into torsional vibration. The resonant frequency, longitudinal vibration displacement and torsional amplitude at the top of the disk milling cutter were 24,609 Hz, 19 μm and 9 μm, respectively. In addition, the directivity of the longitudinal–torsional transducer was theoretically analyzed. Compared with conventional milling, UVAM with the longitudinal-torsional could significantly reduce the cutting force (40–50%) and improve the machining stability. Full article

The damping performance of unequal tooth milling cutters is controlled by the pitch parameters. How to improve the vibration damping and dynamic balance of milling cutters needs to be further studied. This paper analyzes the pitch angle through the stability of the lobe diagram and the spectral characteristics, and unequal-pitch end mills with asymmetric structure were determined to have better cutting stability. Due to the principle error of the asymmetrical tool, dynamic balance accuracy is poor. The dynamic balance of the tool is analyzed, and the centroid model of the tool is established. In order to improve the dynamic balance accuracy of tools, the parameters of the groove shape are analyzed and optimized, and balance accuracy is improved. Through modal and milling-force analysis, the relative vibration displacement and cutting force of the optimized tool were reduced by 17% and 10%, respectively, which determined that such tools have better dynamic performance. Here, unequal tooth end mills could reduce vibration and had higher accuracy in dynamic balance by adjusting the parameters of the pitch angles and chip pockets, so that the tool could have higher cutting stability. Full article

Deep-and-narrow micro-grooves are the common functional structures of miniature parts. The fabrication of the micromilled grooves with high quality and accuracy is the essential guarantee of the causative performance for these miniature parts, and micromilling is the most versatile process to machine such micro-grooves. However, micromilling technology is a highly tool-dependent process, and the commercial carbide micromilling cutter has shown obvious deficiencies in terms of rapid tool wear and inferior machined quality during the machining process. In this paper, a polycrystalline diamond (PCD) micromilling cutter with a large-aspect-ratio (LAR) was designed and prepared by the self-proposed hybrid fabrication method of laser and precision grinding. Micromilling experiments on oxygen-free copper were conducted, and the carbide micromilling cutter was selected in the comparative experiments. The variations of milling forces and specific energy were analyzed through the parameter experiments. Then, the surface quality, machined accuracy and tool wear were further investigated. Results showed that the PCD micromilling cutter with an aspect ratio of 3.25 was successfully manufactured by the proposed hybrid method. The self-fabricated PCD micromilling cutter presented remarkable superiority in terms of the surface quality, machined accuracy, and tool wear when preparing deep-and-narrow micro-grooves. Finally, a satisfactory micromilled groove with an aspect ratio of 2.5 was achieved with the self-fabricated LAR PCD cutter under the optimized conditions. Full article

Milling cutters belong to a widely used category of cutting tools. In this category, modular milling cutters are a narrow niche, less studied, and developed. Usually, they are symmetrical cutting tools. A milling cutting tool that can be reconfigured due to its modularity and still keeps its symmetry becomes more interesting and useful for machining. The paper presents such a new concept in a computer aided design (CAD) model of a cutting tool based on some novel features. The tool itself is designed as a modular complex. The way the torque is transmitted from the shaft to the elementary cutters is an original one, as they are joined together based on a profiled assembling. The profile is one formed of filleted circular sectors and segments. The reaming of the elementary cutters has two sections each of them assuming a task: transmitting the torque, and precisely centring, respectively. The cooling system, which is a component of the tool, provides the cutting area with coolant both on the front and side face of the cutting tool. Some nozzles placed around the cutting tool send jets or curtains of coolant towards the side surface of the cutter, instead of parallel, as some existing solutions do. The source of the coolant supply is the inner cooling system of the machine tool. This provides the tool with coolant having proper features: high enough flow and pressure. The output of the research is a CAD-based model of the modular milling cutter with a high performance cooling system. All of this model’s elements were designed taking into account the design for manufacturing principles, so it will be possible to easily manufacture this tool. Several variants of milling cutters obtained by reconfiguring the complex tool are presented. Even if the tool is usually a symmetric complex, it can process asymmetric parts. Symmetry is intensively used to add some advantages to the modular cutting tool: balanced forces in the cutting process, the possibility of controlling the direction of the axial cutting force, and a good machinability of the grooves used to assemble the main parts of the cutting tool. Full article

Disk milling strategy has been applied in grooving for decades for its capacity to provide huge milling force on difficult-to-cut material. However, basic research on the tool orientation of the disk milling cutter for the disk milling process on the milling free surface, especially on the free surface of the blisk, is still lacking in previous studies. In this study, the minimum residual amount after the disc milling process is used as an optimization target to obtain the optimal tool orientation of the disc cutter. To address the problem mentioned above, a torque balance method, including a torque balance algorithm and concentric circle ray point (CCRP) method is proposed. The torque calculation and torque balance problem are solved by the torque balance algorithm and the problem of generating random points to cause torque symmetry is solved in the CCRP method. Based on the secondary development of UG NX software, a series of tool orientation of disk milling cutter are calculated. Finally, the torque balance method is compared with steepest descent method, Newton method, and conjugate gradient method in the aspects of calculation accuracy, operation speed, and convergence speed. However, both the calculation speed and the convergence speed are better than the other three algorithms. Compared with the other three methods, the operation speed of the torque balance method is reduced by 0.35 times, 1.5 times, and 2.25 times. The results prove the feasibility of the torque balance method in solving the problem of tool orientation optimization of the disk milling cutter. Full article

Micro-milling is an emerging processing technology for machining micro- and high-precision three dimensional parts that require the use of various materials (with sizes ranging from tens of micrometers to a few millimeters) in the field of advanced manufacturing. Therefore, it can be applied to manufacture the micro parts, but new challenges are raised about parts with high surface quality. Herein, both surface formation and micro machined surface roughness models are studied, with the aim of solving complicated problems regarding the quality of surface finish when micro-milling metallic materials. From a theoretical point of view, the first model for surface formation processes considering the strain gradient plasticity theory was built in the area around the cutting edge, and the minimum uncut chip thickness equation was derived. The model accounts for the properties of the work material in tertiary and quaternary zones on the minimum chip thickness. A second model for micro machined surface roughness based on the relationship of kinematics between cutting process and cutter edge was also developed, which takes the influences of tool run out into account. Both proposed models were introduced to analyze the tendency of surface roughness for micro grooves. Both models were also used to justify experimental results. The results show that the developed surface roughness model could be useful in predicting both roughness parameters and trends as a function of cutting parameters. Full article

Carbon fiber reinforced plastic (CFRP) is typically hard to process, because it is easy for it to generate processing damage such as burrs, tears, delamination, and so on in the machining process. Consequently, this restricts its wide spread application. This paper conducted a comparative experiment on the cutting performance of the two different-structure milling cutters, with a helical staggered edge and a rhombic edge, in milling carbon fiber composites; analyzed the wear morphologies of the two cutting tools; and thus acquired the effect of the tool structure on the machined surface quality and cutting force. The results indicated that in the whole cutting, the rhombic milling cutter with a segmented cutting edge showed better wear resistance and a more stable machined surface quality. It was not until a large area of coating shedding occurred, along with chip clogging, that the surface quality decreased significantly. At the stage of coating wear, the helical staggered milling cutter with an alternately arranged continuous cutting edge showed better machined surface quality, but when the coating fell off, its machined surface quality began to reveal damage such as groove, tear, and fiber pullout. Meanwhile, burrs occurred at the edge and the cutting force obviously increased. By contrast, for the rhombic milling cutter, both the surface roughness and cutting force increased relatively slowly. Full article

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. Full article