Small Feed Rate Research Articles

An insight into the influence of precipitation phase on the surface quality in diamond turning of an Aluminium alloy

Diamond turning is an effective technology for processing metal mirrors used in photoelectric communications, radar, and other fields. In diamond turning, the precipitated phase is an essential factor that influences the surface quality of the metal mirrors. However, in previous studies, the precipitation phase has typically been handled as a random variable in a surface morphology model to evaluate its influence on the surface roughness, instead of determining the formation mechanism and proposing suppression solutions. In this study, a new phenomenon is observed in the diamond turning of metal mirrors, that is, the micro diamond tool can reduce the protrusion of the precipitated phase under a small feed rate and improve the surface quality. Investigating the turning process using diamond tools with varying tool nose radii at small feed rates (<1 μm/r), the underlying transformation mechanism of the precipitation phase is determined with the advanced material characterization technologies. The growth of the precipitated phase with an increase in the tool nose radius is explained using the energy gradient theory. The results showed that the increased material strain on the machined surface decreased the activation energy of solute diffusion in the material, causing solute accumulation and precipitate phase growth. With a further increase of tool nose radius to around 1000 μm, the β'' phase breaks and rotates. The representative volume element method shows that when undergoing severe plastic deformation, dislocations and grain boundaries quickly aggregate and slide on the precipitated phase, which will lead to the fracture and rotation of β'' phase. These findings provide a theoretical basis for the development of highly smooth mirrors.

Surface and subsurface analysis of TC18 titanium alloy subject to longitudinal-torsional ultrasonic vibration-assisted end milling

Longitudinal-torsional ultrasonic vibration-assisted milling is a machining method that can effectively improve the quality of the machined surface. When this method is used for the end milling of TC18 titanium alloy, however, the law of influence on the machined surface and subsurface remains unclear. In this study, we examined the effects of the ultrasonic amplitude, feed rate, and cutting speed on the machined surface morphology, roughness, surface residual stress, and subsurface microstructure in the longitudinal-torsional ultrasonic vibration-assisted end-milling process. According to the results, longitudinal-torsional ultrasonic vibration-assisted end milling can help form more obvious surface microtextures with a more distinct surface texture regularity at large amplitude, small feed rate, and high cutting speed. Compared with conventional milling, longitudinal-torsional ultrasonic vibration-assisted milling generates a larger roughness and surface residual stress and a deeper plastic deformation layer of the subsurface in the case of an obvious highly perturbed layer. In addition, the surface residual stress becomes greater and the plastic deformation layer gets deeper at a larger amplitude. When the amplitude was 5 µm, the surface residual stress was − 450.625 MPa and the depth of the deformation layer was 5.4 µm. The stress and depth increased by 21.55 % and 134.78 %, respectively, compared with those of conventional milling. The increase in the feed rate enhanced the roughness, decreased the surface residual stress, and did not significantly alter the depth of the plastic deformation layer. When the feed rate was 0.01 mm/z, the roughness was 0.383 µm and the surface residual stress was − 479.1 MPa. The feed rate and roughness increased by 42.63 % and 20.62 %, respectively, compared with those of conventional milling. With the increase in the cutting speed, the roughness increased, and the surface residual stress and the depth of the plastic deformation layer decreased. When the cutting speed was 15 m/min, the roughness was 0.31 µm, the surface residual stress value was − 454.7 MPa, and the depth of the plastic deformation layer was 5.7 µm. These three parameters increased by 17.8 %, 18.79 %, and 92.5 %, respectively, compared with those of conventional milling. This research has certain application prospect in surface machining of titanium alloy and quality control of machined surface.

Ductile machining of single-crystal germanium for freeform surfaces diamond turning based on a long-stroke fast tool servo

Freeform surfaces of single-crystal germanium are required increasingly in advanced infrared optics, but there are difficulties in processing due to the high hardness, brittleness and low fracture toughness of germanium itself. In the present study, the machining mechanisms and parameters of single-crystal germanium were investigated via ultra-precision diamond turning based on a long-stroke fast tool servo. To realize ductile regime machining, a ductile machining model in ultra-precision turning of germanium considering both feed rate, cutting depth and surface slope of freeform surface was proposed and discussed. A novel taper cutting test was adopted to determine the critical ductile–brittle transition depth. Subsequently, XYPFS were fabricated under different cutting parameters to demonstrate the effectiveness of proposed model. The morphologies of machined surfaces and cutting chips were identified and compared. Finally, a smaller feed rate and cutting depth should be used to reduce its maximum undeformed chip thickness and realize the ductile machining for a freeform surface having a large surface slope. The freeform surface of single-crystal germanium with a form error of ~1258 nm PV and surface roughness of ~1.92 nm Ra was successfully fabricated. In summary, this research provides a comprehensive understanding of ductile machining mechanisms of diamond turning based on a LFTS as well as is meaningful in the manufacturing of freeform surfaces on germanium or other brittle materials with optically qualified surfaces and high-precision.

Study on the temperature field of stone processed by diamond tools

Abstract The experiments were designed by testing methods and orthogonal single factor experimental design. XK5032C CNC milling machine, the equipment to achieve X-axis, Y-axis and 3-axis Z direction of the automatic feed, spindle cooling method using water-cooled. In different processing parameters (spindle speed, depth of cut and feed rate), measurement of the surface temperature of diamond tools. In the testing experiment result analysis, we conclude, the depth of cutting is the biggest influence on the surface temperature. From the orthogonal experiment data analysis, we found that, the temperature was reduced with spindle rotation but opposite with two other factors. By linear regression analysis. We get the best cutting results by choosing a large spindle rotation and a small feed rate.

Machinability Investigation for Cellulose Nanofiber-Reinforced Polymer Composite by Ultraprecision Diamond Turning

Cellulose nanofiber (CeNF)-reinforced polymer composites have wide potential applications in the manufacturing of optical and mechanical parts owing to their light weight, high mechanical strength, and optical transparency. In this study, CeNF-reinforced homogeneous polypropylene (PP-CeNF) was machined under various conditions by ultraprecision diamond turning, and the results were compared with those of pure PP without CeNF addition. The influence of CeNFs on material removal was investigated by examining the surface topography, chip morphology, cutting forces, and cutting temperature. It was found that the surface defects in pure PP cutting were surface tearing, while the surface defects of PP-CeNF were surface tearing and micro-holes induced by the pulling-outs of CeNFs. Surface tearing increased with cutting speed; pulling-outs of CeNFs were slightly affected by cutting speed but strongly dependent on the tool feed rate. Under a small tool feed rate, the surface roughness could be reduced to ∼10 nm Ra for PP-CeNF. The thermal effect was insignificant in the experiments, whereas the effect of strain rate-induced material hardening was dominant for both workpiece materials at a high cutting speed. This study helps to understand the mechanisms for ultraprecision cutting of CeNF-reinforced polymer composites and provides guidelines for improving the machined surface quality.

Surface modeling and analysis of high-speed ultrasonic vibration cutting

High-speed ultrasonic vibration cutting has been proven to be effective in prolonging tool life, as well as reducing cutting force and cutting temperature at certain cutting speeds, which is higher than both the critical cutting speed of traditional ultrasonic vibration cutting and the range of conventional high-speed cutting in recent research. However, the surface topography results from the periodic sinuous tool vibration trajectory, and its influence on machined surface roughness, remains unclear. Therefore, in this article, the modeling and analysis of the surface topography and roughness are developed first. Then, simulations conducted through MATLAB calculations, SOLIDWORKS modeling, and cutting experiments are conducted to investigate the influences of the feed rate and the phase shift between the adjacent tool trajectories on the surface roughness. The results indicate that optimal surface roughness can be obtained under the conditions of a small feed rate (0.005 mm/r) and a phase shift of 180°. In this condition, the surface finish can reach Ra < 0.4 μm and realize finishing machining. In addition, compared with conventional cutting, high-speed ultrasonic vibration cutting can achieve the same quality at a cutting speed two times that of conventional cutting. Consequently, a better surface quality can be obtained through high-speed ultrasonic vibration cutting, due to the decrease of surface roughness compared with that of conventional cutting.

Optimization method of manufacturing for diamond turning soft-brittle materials' harmonic diffractive optical elements.

Single-point diamond turning is a high-efficiency, low-cost method for manufacturing harmonic diffractive optical elements (HDOEs). Generally, in order to ensure high diffraction efficiency of HDOEs, a half-round tool is used to reduce surface-relief profile errors and a super small feed rate is selected to control surface roughness when hard-brittle materials are turning. However, this method is no longer suitable for soft-brittle materials, which have a strict requirement for the range of the feed rate. It limits the types of materials available for HDOEs. Therefore, according to the range of the feed rate and the cutting depth for soft-brittle materials, an optimized turning model is proposed in this paper. It overcomes the high surface roughness caused by the half-round tool; meanwhile, the advantage of the half-round tool is kept in terms of surface-relief profile errors. On this basis, a mathematical model is proposed to reveal the relationship among diffraction efficiency, period widths, tool radius, and feed rate with different soft-brittle optical materials. As a typical soft-brittle material, barium fluoride (BaF2) was selected to be the material for manufacturing HDOEs. By using the optimized model, the turning experiment of BaF2 HDOEs was completed, and then the BaF2 HDOEs with Ra=2.75nm were obtained. The optimized model is verified to be effective and further provides theory guidance and engineering application in the optical manufactory field of soft-brittle materials for HDOEs. The range of application materials for HDOEs is enriched, and the freedom of advanced optical design is broadened.

Effect of ultrasonic impact treatment on the surface integrity of nickel alloy 718

Ultrasonic impact treatment (UIT) is a type of surface strengthening technology that can improve the fatigue properties of materials by improving the surface quality, residual stress, and other aspects. In this study, the influence of ultrasonic impact parameters on the surface integrity of nickel alloy 718 was studied. The micro stress concentration caused by the surface morphology was also explored. The cosine and exponential decay functions were used to fit and characterize the distribution of residual stress and work hardening in the surface material. The results showed that the feed rate had the greatest influence on surface roughness, stress concentration, and surface residual stress. It was not appropriate to evaluate the surface hardening effect only by the number of impacts per unit area, the ultrasonic impact parameters such as feed speed and pre extrusion depth should also be considered. The grain refinement was obvious after UIT. The multi-objective optimization of machining parameters was performed with the objective of surface stress concentration and residual stress. A surface with a smaller surface stress concentration factor and larger compressive residual stress can be obtained simultaneously using medium linear velocity, medium pre extrusion depth, and smaller feed rate.

Surface quality of cemented tungsten carbide finished by direct cutting using diamond-coated carbide end mill

• Superiority of direct cutting of cemented carbide with diamond-coated tool was shown. • Surface quality in direct cutting, electrical machining, and polishing was compared. • Specularity of finished surface similar to polishing was obtained via direct cutting. • Large compressive residual stress can also be obtained via direct cutting. • Higher transverse rupture strength can be achieved compared with polishing. This study addresses the finished surface quality of cemented tungsten carbide obtained via direct cutting with a diamond-coated carbide end mill under ultrasmall feed rates. The surface appearance, composition distribution, profile, roughness, residual stress, and transverse rupture strength were experimentally investigated. The finished surfaces obtained via electric discharge machining with two types of machining conditions and mechanical polishing processes were also evaluated to compare the surface quality. Two types of cemented tungsten carbide materials, TAS VC-70 and VM-40, were applied as the workpiece materials. A mirror surface can be obtained via direct cutting and mechanical polishing with both materials. The microstructure morphologies of the finished surface obtained via direct cutting were different from those obtained via mechanical polishing. In the case of VC-70 which has larger tungsten carbide grain size and higher cobalt content, the flat cross-section of the tungsten carbide grain under ductile mode cutting was conspicuous in direct cutting under small feed rate and depth of cut. In contrast, an extremely thin layer composed of fine grains of tungsten carbide and cobalt was observed on the finished surface in direct cutting under comparatively large feed rate and depth of cut. The surface roughness and profile of the finished surface resulting from direct cutting were comparatively rougher than those resulting from mechanical polishing, although the finished surface was significantly smoother than that resulting from electric discharge machining. The residual stress of the subsurface obtained via direct cutting showed larger compressive stress than that obtained via electric discharge machining and mechanical polishing under all cutting conditions and materials. Moreover, satisfactory transverse rupture strength can be obtained via direct cutting in both materials compared with other processes, and two times more transverse rupture strength can be achieved via direct cutting compared with the case of electric discharge machining in VM-40 cutting.

Effects of spinning parameters on microstructures of ellipsoidal heads during marginal-restraint mandrel-free spinning

Marginal-restraint mandrel-free spinning is an advanced technology for manufacturing ellipsoidal heads with large diameter-thickness ratios. The effects of spinning parameters on the forming accuracy of ellipsoidal heads have been studied, and optimized spinning parameters have been obtained. The microstructure evolution of a workpiece is usually very complicated in the spinning process. In this work, the influence of spinning parameters on the microstructures of two-pass spun ellipsoidal heads is studied. It is found that the forming angle and feed rate of the first pass, angle between passes, and feed rate of the second pass significantly affect the microstructures. Meanwhile, the evolution rule of the microstructures near the inner and outer surfaces of the spun parts is almost consistent. A large forming angle, large angle between passes, or large feed rate of the second pass are beneficial to obtain uniform microstructures. A small or large feed rate of the first pass reduces the microstructure uniformity. To improve the microstructure uniformity between the inner and outer surfaces, the optimized spinning parameters are determined.

Micro-drilling of Mg-based MMCs reinforced with SiO2 nanoparticles: An experimental approach

Mg-based metal matrix composites reinforced with nanoparticles are promising biomaterials due to their biocompatibility and high hardness and because they are local and systemic toxicity free. Nano-metal matrix composites are considered to be hard-to-machine materials due to the high strength and high abrasiveness of the reinforcing nanoparticles. In this article, the micro-drilling mechanisms of Mg-based metal matrix composites reinforced with different volume fraction of SiO2 nanoparticles (0.5, 1.0, 1.5, 2.0 vol.%) were investigated experimentally. Results obtained were also compared with pure Mg. First, it was found that the volume fraction and drilling parameters played an important role in the chip formation mechanism. Second, the influence of drilling parameters on hole surface morphology and cutting force were studied, in which both the rotation speed and feedrate affected the surface morphology, and the main factor affecting cutting force was found to be the feedrate. Furthermore, the formation of burrs was investigated. The height of the burr could be reduced by using small feedrate and low rotation speed. Finally, the size effect of micro-drilling was studied. The variation of surface roughness and cutting force of pure Mg and Mg-based metal matrix composites had three changing trends with the uncut chip thickness. The minimum chip thickness of Mg/SiO2 metal matrix composites was determined to be 1.1 μm.

An experimental study on single-point diamond turning of a 55 vol% SiCp/Al composite below the ductile brittle transition depth of SiC

To achieve excellent surface quality, this paper presented an experimental study on single-point diamond turning of a 55 vol% SiCp/Al composite below the ductile brittle transition depth of SiC. The dry and mist cutting results indicated that the surface roughness generated by dry turning is much higher than those generated by mist turning. Surface roughness decreased with the increasing rotation speed and increased with the increasing feed rate, while the influence of depth of cut was insignificant. The minimum surface roughness Sa could be achieved around 0.05 μm. Besides, the roughness rebounded obviously under much small feed rate (0.5 μm/z) or depth of cut (0.25 μm). Machined surface examined by SEM indicated that many SiC particles were cut in ductile mode, while there were still numerous defects, such as holes, pits, tearings, grooves, and voids. The chipping, cleavage, and abrasive wear were the dominating wear patterns of diamond tools. In the end, the main influential factors on the cutting process of SiC and approaches for enhancing the probability of ductile cutting SiC were discussed.

Experimental Vibration Study in Milling Thin-Walled Ti6Al4V under MQL using Coconut Oil as Cutting Fluid

In thin-walled Titanium Ti6Al4V machining, vibration is the dominant factor affecting the quality of components. Excessive vibrations can generate chatter, this condition occurs because it is not suitable in choosing machining parameters. Chatter is not expected because it causes dimensional errors, rapid tool wear and poor surface finish. This experiment tries to identify chatter-free conditions with the appropriate parameters. Uncoated carbide is used as a cutting tool with a diameter of 10 mm and machining under the MQL system with coconut oil as a cutting fluid. In the result of the milling showed if this machining is free of chatter, where from frequency was achieved is not equal to the natural frequency from simulation, then this is also approved from result surface roughness and surface photography. In surface roughness result, the value is smaller than minimum critical amplitude, where good result in high value of the cutting speed and small feed rate and result of the surface photography was identified no severe surface condition along thin-walled. The experiment also calculated for non-thin-walled Ti6Al4V as evaluation, where the result of both acceleration and surface roughness was obtained smaller than milling thin-walled.

Experimental study on the low-feed grooving process with different grooving tools

The requirement of grooved surface and grooving forces is improved for the machining of precision and small parts in the modern industry. Reducing the grooving feed rate is an effective method to improve the surface quality and lower the cutting forces. But small feed rate results in the problems of chip breaking and cutting vibration. Improvement of tool geometry is the solution to the problems, however, The matching relationship between the tool geometry and the feed rate is not clear. In this paper, three grooving tools (N123G5-0300-0002-CM, GZD3002-MC, and N123G5-0300-0001-CF respectively) with different parameters have been selected and a series of grooving experiments have been performed. The experimental results show that the initial state and the steady state will produce two different kinds of chips during the grooving process. For CF tools, chip breaking occurs when the feed rate is higher than 0.04 mm/rev, and the feed rate should be higher than 0.06 mm/rev for the other two tools. An analytical model for calculating surface roughness considering the tool geometry parameters and feed rate has been proposed. The elastic recovery of the grooved surface has been analyzed to explain the error between analytical results and experimental results.

Investigation on the material removal and surface roughness in ultraprecision machining of Al/B4C/50p metal matrix composites

Metal matrix composites (MMCs) are increasingly applied in various engineering industries because of their distinct physical and mechanical properties. While the precision machining of MMCs is less understood due to their complex microstructure and poor machinability, a comprehensive scientific understanding on their machining mechanics and the associated surface generation mechanisms is of great importance particularly for industrial scale applications of MMCs. This paper presents a simulation and experimental-based holistic investigation on cutting mechanics, material removal and surface roughness in ultraprecision machining of MMCs. B4C/Al2024 is selected as the targeted MMC material in this research. The thermal-mechanical-tribological integrated modelling and analysis are presented to investigate the effects of cutting speed, feed rate and depth of cut (DOC) on the material removal, chip formation mechanics and surface generation process. The simulation results indicate that the machined surface roughness in precision machining of particle reinforced MMCs can be reduced by increasing the cutting speed and decreasing the depth of cut. The surface flow waviness decreases, which contributes to a higher surface quality, while machining with a smaller feed rate. The well-designed machining trials are conducted under the same cutting conditions and process variables as those in simulations, which perform a good agreement with simulation results.

Investigation on plastic deformation behaviors in hard milling of H13 steel

Plastic deformation layer, as the topmost layer of machined surface, has a significant impact on the surface integrity. This research focuses on the plastic deformation behaviors in milling surface. First, the thermal model of machined surface and the classical infinitesimal milling force in hard milling process are developed, which were verified by a series of experiments. Secondly, the microstructure of plastic deformation layer is observed by a hard milling experiment and the scanning electronic microscopy analysis. Thirdly, based on the force model and thermal model, the reason that resulted in the nonuniformity of plastic deformation is analyzed by considering the mechanism of plastic deformation. Finally, the effect of cutting parameters on the thickness of plastic deformation is investigated; the results indicate that the more uniform plastic deformation can be obtained by employing the higher cutting speed and smaller feed rate in milling process. This research reveals the variation of plastic deformation layer, it is also helpful to optimize the cutting parameters so as to obtain the desired surface integrity.

Study on the surface damage mechanism of monocrystalline silicon in micro ball-end milling

This paper investigates the surface damage mechanism of monocrystalline silicon in micro ball-end milling with polycrystalline diamond (PCD) and natural diamond tools. Machining-induced surface damages such as surface fracture, phase transition, and residual stress are studied under different machining conditions. It is found that under a small feed rate and cutting depth and high spindle speed, PCD micro ball-end mill is a potential candidate in manufacturing low-damage surfaces that are distributed uniformly with the amorphous layer of several-nanometer thickness and the average compressive residual stress that does not exceed 150 MPa. Additionally, the influences of feed rate on surface damages in PCD micro milling are more significant than those in micro milling with a natural diamond tool. The experimental results reveal the surface damage mechanism: (i) the current cutting region comprises the subsurface layer after machining in the last tooth period, the previously produced surface/subsurface defects can affect the damages of the current machined surface, (ii) the cutting edge closer to the tool tip acts primarily on amorphous silicon generated in the previous tooth period, part of the amorphous phase remains on the machined surface, and the formation of metastable phases (Si-III, Si-XII, and Si-IV) occurs away from the machined surface.

Micro-machinability and edge chipping mechanism studies on diamond micro-milling of monocrystalline silicon

Excessive generation of undesirable surface and subsurface damages such as surface edge chipping often occurs when monocrystalline silicon, a hard and brittle material, is machined at tens to hundreds of microns in thickness. However, before developing strategies to reduce edge chipping and improve the machining efficiency by micro-milling, understanding of its cutting mechanism is required. In this study, the micro-machinability and edge chipping mechanism on a (001) silicon were investigated by full slot milling using the natural diamond tool. A volumetric measurement technique was also proposed to quantify edge chipping better. Three chipping types: 45°, 90° and mixed mode (dominant type) were observed, and its mechanism is attributed to cleavage and slip structure within silicon’s crystal architecture. The cutting forces, surface and edge quality were examined and characterised accordingly. From the reported results, the size effect on the specific cutting energy is greatly influenced by the shear strain work hardening of the workpiece. Enhancement of the strain work hardening effect is attributed and demonstrated using small feed rate, high cutting speed and cutting along the [100] feed direction. As a result, good surface quality of Ra = 20 nm and small edge chipping volume of 80 μm3 were achieved.

Optimizing Machining Process of E31 Steel for Improved Surface Roughness

End milling (EM) and electric discharge machining (EDM) are frequently used for machining high chromium steel. The superior surface finish is among the key requirements for the improved functional behavior, wear resistance, and fatigue life high chromium steel components. The present work includes optimization of EM (using Taguchi method) and EDM processes (by selecting appropriate electrode) for machining of the high chromium steel keeping high material removal rate (MRR) and superior surface finish as the objectives. Additionally, the effect of coolant on surface roughness was evaluated. For EM, the feed rate was found the most influential parameter and the high spindle speed, small feed rate result-in better surface finish whereas the depth of cut has the insignificant effect on the surface roughness for the selected rages of process parameters. The scanning electron microscope (SEM) micrographs revealed that flood cooling decreases the surface defects and mostly high chromium steel samples were having a lower surface roughness when coolant was used. For EDM, the brass electrode results in a superior surface finish but a lesser MRR than the copper electrode while machining high chromium steel.

Research on Cutting performance of 316L Stainless Steel Based on Microstructure Tool

Based on carbide (YW1) as the material of surface texture cutting tool to conduct the basic experimental research on the micro-groove tool cutting 316L stainless steel under the condition of dry cutting and cutting fluid lubrication. The results show that the improved cutting effect of microstructure is not only related to texture type, but also to feed rate, spindle speed and cutting lubrication condition. Under the condition of small feed rate and fluid lubrication cutting, vertical groove has the most obvious effect, which can reduce cutting force, average friction coefficient to 19.01% and 13.39% respectively.