Minimum Undeformed Chip Thickness Research Articles

Non-destructive measurement of MUCT in micro-milling using surface topography generated by bi-planer size effects

In mechanical micro-cutting, a Minimum Undeformed Chip Thickness (MUCT) is desired to ensure chip formation by the round-edged tool. Although the MUCT controls several machinability, productivity, and sustainability attributes, its measurement using output responses is a challenging task. This article, for the first time, demonstrates a non-destructive methodology to measure MUCT in micro-milling using the topographical pattern that inherently remains embedded on the micro-milled floor surface in the form of a microscopic step at the ploughing-shearing transition boundary. Simultaneous action of two Size Effect phenomena that occur concurrently in two mutually perpendicular planes owing to rounded-nose and rounded-edge produce microscopic step during surface generation. A methodology to quantify MUCT using this inconsistent surface topography is also demonstrated. MUCT remains within 36–41 % of the edge radius during dry micro-milling of Ti-6Al-4V using TiAlN-coated WC-6Co tool. The same reduces to 33–40 % of the edge radius when cutting fluid is delivered through sustainable Minimum Quantity Lubrication (MQL) strategy. Proportionality between MUCT and edge radius remains valid during abrasive wear regime of the cutting tool. Tool wear significantly deteriorates surface quality, causing Ra roughness to increase from 40 to 350 nm when adhesion deposits on cutting edge. Consequently, the proposed surface-dependent methodology fails to provide precise MUCT data when cutting tool experiences aggressive wear.

Influence factors and prediction model of surface roughness in single-point diamond turning of polycrystalline soft metal

Ultrasmooth surface of soft metals is required in the field of advanced technology. However, the strong plasticity of soft metals makes it hard to achieve high surface finishing in ultraprecision machining. In this paper, the ultraprecision machining experiments of polycrystalline tin are carried out, and the factors including tool nose radius, cutting parameters, and material properties affecting the surface roughness in single-point diamond turning are investigated. Side flow, anisotropy, and grain boundary step are identified as the main causes of increasing of surface roughness, with grain boundary step demonstrating the largest impact. A surface roughness prediction model of tin in single-point diamond turning is established, which takes the minimum undeformed chip thickness, side flow, anisotropy and grain boundary step into consideration. The experiments show that the maximum prediction error of this prediction model is 6.51%.

Modelling of surface roughness in elliptical vibration cutting of ductile materials

Elliptical vibration cutting (EVC) is a widely used ultra-precision machine technology. However, the surface roughness prediction of EVC is difficult for the complicated surface generation process. In this paper, the surface generation mechanism of EVC is elucidated. A new surface roughness model is proposed considering the roughness in the nominal cutting direction (NCD) and feed direction (FD). The roughness in the NCD is determined by kinematics, tool edge radius, tool flank face interference, and material spring back. For the first time, the influence of material spring back in previous cutting cycle on surface roughness generation is considered in EVC along the NCD. The roughness in the FD is determined by kinematics, tool nose radius, shift distance, tool interference, material spring back and material pile-up. The material spring back is determined by using a function of the plastic strain of workpiece material in the third deformation zone and the minimum undeformed chip thickness. For calculating the roughness component of material pile-up, a function related to tool edge radius, depth of cut, residual height caused by tool nose radius and feed rate is constructed. The experimental results show that the proposed model has a high prediction accuracy. According to the model, the influencing mechanism of various machining factors on the surface roughness variation is clarified and a high-efficiency machining method without deteriorating surface roughness is obtained.

Investigation on the size effect in micro end milling considering the cutting edge radius and the workpiece material

Abstract. Previous research has found that the peripheral and end cutting edges of the cutter had different cutting mechanisms in the micro end cutting process considering the size effect. This investigation is a further study on this point considering the cutting edge radius of the cutter and the material of the workpiece based on the methods of finite element simulation and the micro end cutting experiment. This study adopts a combination of simulation and experiment research methods and the cutting edge radius and the workpiece material as two variables. Considering the cutting mechanisms of the peripheral cutting edge and the end cutting edge are different, the peripheral cutting edge and the end cutting edge are studied respectively. Meanwhile, the minimum undeformed chip thickness (MUCT) value is determined in three ways, chip morphology, cutting force, and surface roughness, so the final result obtained by comparing three kinds of results has a very important reference value. Not only are the chip morphology obtained by finite element simulation and the surface roughness obtained by the micro end cutting experiment used to identify the MUCT value, but also the cutting force. The simulation and experimental results show that the cutting force can be used to identify the MUCT value for the peripheral cutting edge, but it cannot be used for the end cutting edge. The MUCT value increases with the increase of the cutting edge radius, no matter which process it is. The material property has some effects on the MUCT value; even the cutting parameters and the cutting edge radius remain unchanged for the peripheral cutting edge. However, the material property has no effect on the MUCT value for the end cutting edge. In this study, the influence of important variables on MUCT is studied as much as possible to reflect a real application situation.

Prediction of surface roughness in diamond turning of Al6061 with precipitation effect

Aluminum alloy 6061(Al6061) is one kind of precipitation hardening alloy, and its precipitate generation highly influences the mechanical properties and finished surface quality in diamond cutting. To accurately estimate the surface roughness in diamond turning of Al6061, an improved surface roughness prediction model is proposed in this study with the full consideration of the minimum undeformed chip thickness, the materials plastic side flow, elastic recovery and precipitation effect. Pre-heating treatments and diamond turning experiment are conducted on Al6061 samples to build the relationship between pre-heating conditions, precipitation generation and surface roughness in single point diamond turning (SPDT). The experimental results show that precipitation effects are found on both the deformed chips and the fresh generated surface. The effect of pre-heating conditions on precipitates generation agrees well with its effect on surface roughness of Al6061 in SPDT. Compared with the previously proposed models, the developed model considering the precipitation effect of Al6061 remarkably improves the prediction accuracy by 26 %.

Experimental Study on the Minimum Undeformed Chip Thickness Based on Effective Rake Angle in Micro Milling.

Micro milling is widely used to manufacture micro parts due to its obvious advantages. The minimum undeformed chip thickness, the effective rake angle, and size effect are the typical characteristics and closely related to each other in micro milling. In this paper, the averaging method is proposed to quantitatively estimate the effective rake angle in the cutting process. The minimum undeformed chip thickness is explained based on the effective rake angle and determined to be 0.17 rn (tool cutting edge radius). Then, micro milling experiment was conducted to study the effect of the minimum undeformed chip thickness. It is found that the minimum undeformed chip thickness results in the unstable cutting process, the uneven peaks on cutting force signal, and the dense characteristic frequency distribution on frequency domain signal. The dominant ploughing effect induces the great specific cutting energy and the deteriorated surface roughness due to the minimum undeformed chip thickness.

Study on micro cutting fundamentals considering the cutting edge radius and the workpiece material in micro end milling

Previous studies found that the peripheral cutting edge and end cutting edge in micro end milling had different cutting phenomena considering the size effect in micro cutting processes. This paper is a further study on this point considering different workpiece materials and cutting edge radii. Finite element simulations have been conducted to determine the minimum undeformed chip thickness (MUCT) by the chip morphology and the results are verified by micromilling experiments. Both the simulations and experiments show that the MUCT of the peripheral cutting edge and the end cutting edge are different even if the cutting edge radii remain unchanged. The MUCT is directly proportional to the cutting edge radius. Material properties also have some effects on the MUCT of the peripheral cutting edge. But it has limited effects on that of the end cutting edge. The results indicate that the feed engagement other than the axial depth of cut should be carefully selected in micro end milling when considering different workpiece materials.

Modeling Dynamic Stability and Cutting Forces in Micro Milling of Ti6Al4V Using Intermittent Oblique Cutting Finite Element Method Simulation-Based Force Coefficients

Abstract Tool breakage is a significant issue in micro milling owing to the less stiffness of the micro tool. To cope up with such limitation, precise predictions of dynamic stability, and cutting force have the utmost importance to monitor and optimize the process. In this article, dynamic stability and cutting force are predicted precisely for micro milling of Ti6Al4V by obtaining force coefficients from a novel 3D intermittent oblique cutting finite element method (FEM) simulation considering the influence of tool run out. First, the stability model is modified by incorporating the appropriate values of limiting angles obtained analytically accounting the trajectories of the flutes due to tool run out. This stability model is utilized to select chatter-free parametric combinations for micro milling tests. Next, an improved cutting force model is developed by incorporating the force coefficients obtained from oblique cutting simulation in the mechanistic model and differentiating the whole machining region into three distinct region considering size effect. The force model also considers the effect of increased edge radius of the worn tool, run out, elastic recovery, ploughing, minimum undeformed chip thickness (MUCT), and limiting angles, cumulatively. The proposed dynamic stability and cutting force models based on the oblique cutting simulation show their adequacy by predicting the stability limit and cutting force more precisely, respectively, as compared to those obtained by orthogonal cutting simulation. Besides, the proposed force model for the worn tool is found to be viable as it is closer to the experimental forces, whereas force model without the incorporation of tool wear underestimated the experimental forces.

Study of High-Speed Mechanical Micro Drilling Process Fundamentals for Small Holes

High-speed mechanical micro drilling would be a promising process for small hole fabrications with high productivity and high quality. But there are limited studies on this topic. Fundamental questions such as the minimum undeformed chip thickness (MUCT) due to the size effect in microcutting, burr size, cutting force, and optimal parameters are discussed for high-speed mechanical micro drilling in this paper. Based on finite element method (FEM) modelling, the MUCT is identified as 0.86 μm for copper C26000 with the cutting edge radius of 5 μm from both chip generation and force variation analyses. The ratio of MUCT to the cutting edge radius is 0.17, which is smaller than that (usually 0.2 or 0.25 for copper) in micro shaping and micromilling processes. This result has been successfully verified by experiments with the drill with a diameter of 1 mm and the spindle speed of 80,000 min-1. Burr width at the hole entrance reaches the maximum value when the undeformed chip thickness (UCT) is smaller than the MUCT. Experimental optimizations with the integrated considerations of cutting forces and burrs have been conducted. The optimal high-speed micro drilling parameters have realized a material removal rate (MRR) of 25% increasement compared with conventional micro drilling.

Finite Element Simulations for Micromilling of Oxygen-free Copper

Micromilling mechanism studies are the fundamentals for high-quality micro components fabrications. Based on the finite element method (FEM), the simulation model for micromilling of the oxygen-free copper (OFC) was established in this paper. The influences of the key process parameters (feed engagement fz, axial depth of cut ap, radial depth of cut ae, and spindle speed n) on the milling forces were investigated. According to the simulation results, to achieve the minimum undeformed chip thickness, the critical feed engagement was identified to be 2.5 μm/z. when the axial depth of cut increased, the milling force was increasing linearly, but at the same time the milling force took an oscillator decreases due to the increasing of spindle speed. The overall trend of milling force under different radial depths of cut is upward. Therefore, the feed engagement should be greater than 2.5μm/z for micro milling of oxygen-free copper. Small radial depth of cut, small axial depth of cut, and appropriate spindle speed should be selected to obtain a high machining quality. Introduction As an excellent metal with extremely low oxygen content, high conductivity and high corrosion resistance, oxygen-free copper C10100 is widely used in the manufacturing of audio-visual equipment and communication components. With good ductility and no hydrogen embrittlement, it can also be processed into various precision micro parts. Compared with traditional cutting, high-speed micromilling is more suitable for machining micro-small parts. In order to obtain higher dimensional accuracy and better surface quality, it is necessary to study the milling parameters of OFC in the processing of precision parts. In the actual machining process, the changes of milling force caused by the changes of milling parameters can reflect the quality of the final machined parts more intuitively. Therefore, the adjustment of milling parameters can be guided by measuring the milling force in the milling process. In order to reveal the difference in mechanism between traditional cutting and micromilling, scholars have conducted a lot of studies. In the study of cutting poly-crystalling OFC with single crystalline diamond (SOD) micro-tools, X. Ding has proposed that the cutting strategy of reducing cross-feed can improve the cutting performance with using micro-tools. Constant cutting forces, burr size and an improved roughness of the machined surface have been obtained by employing this cutting strategy [1]. Niu has presented an innovative cutting force modeling concept by taking account of micro-cutting dynamics. Experimental cutting trial is conducted to validate the modeling approach and the cutting force model [2]. Qu has studied the impact of MQCL method on the machining results and mechanical properties of the component [3]. Yuan has proposed an innovative uncut chip thickness algorithm and developed the model for determining the instantaneous uncut chip thickness in micro end-milling processes [4]. D.DAS has studied the effect of stress parameters on ratcheting deformation stages of polycrystalline OFHC copper [5]. For the micromilling of pure copper, M. Rahman has studied the failure mechanism and factors which affect the micro end mill [6]. Liu has studied the relationship between size effect and burr in micromilling OFC and constructed a geometric model of exit burrs [7]. Liu has established SPH simulation model and carried out systematic research on formation mechanism of chip [8].For oxygen-free copper materials, Tian has established a constitutive model and carried out simulation analysis based on Abaqus [9]. Cheng has proposed 211

Study of microcutting fundamentals for peripheral and end cutting edges in micro-end-milling

In the micro-end-milling of surfaces, thin walls, and micro channels, etc, both peripheral and end cutting edges of micro end mills are engaged in cutting. However, the microcutting fundamentals for end cutting edges have not been well studied, even though those for peripheral cutting edges have been studied widely. Key micromilling variable analyses show that the order of significance is the axial depth of cut (ap), feed per tooth (fz), and radial depth of cut (ae). It means that the microcutting mechanisms of the end cutting edge need to be studied and compared with that of the peripheral cutting edge in order to understand micro-end-milling mechanisms more thoroughly. Simulations using the finite element method (FEM) show that the minimum undeformed chip thickness (MUCT) is different for peripheral and end cutting edges, even though the cutting edge radius remains unchanged. The results of those simulations have been experimentally validated. It shows that the MUCT of the end cutting edge is larger than that of the peripheral cutting edge. That means the MUCT is not only the size of a certain proportion of the cutting edge radius, as mentioned in previous studies, but also has a close relationship with the location of the cutting edge. Therefore, ap could be several times larger than fz according to the relationship between MUCT and the micromilling parameters. It creates a solid basis for the selection and quantization of micro-end-milling parameters in the fabrication of complicated geometries as thin walls and micro channels.

Research in minimum undeformed chip thickness and size effect in micro end-milling of potassium dihydrogen phosphate crystal

Micro-milling is a promising approach to repair the micro-defects on the surface of potassium dihydrogen phosphate (KDP) crystal. However, KDP crystal is difficult to machine due to its properties of soft-brittle and easy deliquescence. This study investigates the minimum undeformed chip thickness hm and the size effect in micro end-milling of KDP crystal by comprehensively analyzing cutting force, specific cutting force and machined surface quality. A model of the chip formation, which is capable of connecting the minimum undeformed chip thickness, the undeformed chip thickness and the periodicity of cutting force together, is developed to predict the value of minimum undeformed chip thickness. The normalized minimum undeformed chip thickness λe in terms of the ratio of the minimum undeformed chip thickness to the cutting edge radius re, is estimated to be 0.43 ≤ λe ≤ 0.48. The significantly non-proportional increase of specific cutting force indicates the existence of size effects when the ratio of feed per tooth to cutting edge radius ft/re is less than 0.7. The machined surface quality also reflects severe size effect by the phenomenon that the micro cracks and brittle pits appear on the groove base, and the value of surface roughness Ra is large when the ratio ft/re is less than 0.5. Furthermore, the surface quality deteriorates and the brittle cutting appears when the ratio ft/re is much larger than 1 which seems similar to macro-milling. The perfect machined surface with almost no ploughing effect and brittle cutting is achieved at a ratio ft/re of 0.7. Therefore, a feed per tooth, slightly larger than the minimum undeformed chip thickness but smaller than cutting edge radius, is recommended for micro-milling of KDP crystal or soft-brittle crystal.

Cutting surface quality analysis in micro ball end-milling of KDP crystal considering size effect and minimum undeformed chip thickness

Potassium dihydrogen phosphate (KH2PO4 or KDP) crystal is a typical soft-brittle optical crystal, and the size effect and brittle cutting mode are easy to appear in micro ball end-milling of KDP crystal. In this paper, micro-grooving experiments are conducted to study the size effect and brittle cutting in micro ball end-milling of KDP crystal with different feed rate and depth of cut. The cutting force, machined groove base quality and chip morphology are collected and analyzed carefully. The size effect is discovered by the phenomena of the existence of oscillations and relaxations in cutting force and hyper-proportional increase of specific cutting force, when the ratio of feed per tooth to cutting edge radius ft/re is less than 1. While the brittle cutting mode is detected through the existence of sharp fluctuations in cutting force and cracks on the groove base when the ratio ft/re is larger than 2. From the further comprehensive analysis of cutting force, specific cutting force, machined groove base quality and chip morphology, the cutting parameters with ratios of the maximum undeformed chip thickness in one cutting circle to cutting edge radius hmax/re around 0.14, 0.2 and 0.4 are regarded as size effect, optimal and brittle cutting points, respectively. The size effect, ductile cutting and brittle cutting zones are divided by the size effect and brittle cutting boundaries (points). Among the optimal points, the depth of cut of 2μm with the ratio ft/re of 1 is the optimal cutting parameter for micro ball end-milling of KDP crystal.

Modeling and Simulation for Micromilling Mechanisms

In order to study the micromilling mechanisms, FEM (finite element method) has been used to create models and to conduct simulations for micromilling process. The aluminum alloy material 7075-T6 is selected as the workpiece material for its advantages to make miniaturized components. By analyzing the variation of the milling force and the chip formation in this simulation, the result shows that the critical process parameter of the MUCT (minimum undeformed chip thickness) is that the feed engagement fz=2μm/z. Simulations with different radial depth of cut ae have been conducted. According to the chip formation and the cutting force, it can be noticed that the milling force increases with the increase of the radial depth of cut. This study lays a theoretical foundation for further optimizations and experiments of micromilling.

Micromilling Simulation for the Hard-to-cut Material

Micromilling of the hard-to-cut material has many challenges such as the relatively weak stiffness of the machining system and the deep understanding of the micromilling mechanism. Aiming at the typical hard-to-cut material Inconel 718, the model of micromilling process has been created based on FEM (finite element method). The analytical results of the FEM model show that the critical process parameter of minimum undeformed chip thickness (MUCT) is the critical feed engagement fz =1.5 μm/z for Inconel 718. The milling force shows a trend to increase with the increasement of feed engagement. The radial depth of cut ae has directed effects on the cutting force and it shows that the milling force has an obviously trend to increase with the increasement of radial depth of cut. Therefore, in micromilling of Inconel 718, the feed engagement should be larger than the critical value and the radial depth of cut is better to select a relatively smaller one in order to reduce the cutting force.

Origins for the size effect of surface roughness in diamond turning

In this work, a novel surface roughness prediction model, in which the kinematics, plastic side flow, material spring back and random factors are considered, is theoretically formulated to reveal the underlying mechanisms for the observed size effect of surface roughness in diamond turning. In this newly developed model, the copy effect of tool edge waviness is successively integrated into the kinematic component, and a yield stress and minimum undeformed chip thickness related function is constructed for calculating the material spring back. For the component of plastic side flow, the effects of minimum undeformed chip thickness, tool nose radius, feed rate as well as cutting width are took into account. Moreover, the component of random factors is assumed to follow a Gaussian distribution. Theoretical predictions and experimental validations show that the feed rate dependent size effect of surface roughness as observed on the fine grain substrate is derived from the decrement of the kinematic component being less than the increment of the plastic side flow component. For the coarse grain substrate, the large and hard inclusion inevitably appears in the matrix. Therefore, the size effect of surface roughness can be attributed to the formation of pit defect and deep groove on the finished surface at large feed rate and the protrusion of hard inclusion from the finished surface at low feed rate.

Theoretical and empirical coupled modeling on the surface roughness in diamond turning

Abstract In this work, a theoretical and empirical coupled method is proposed to predict the surface roughness achieved by single point diamond turning, in which the surface roughness is considered to be composed of the certain and uncertain parts. The certain components are directly formulated in theory, such as the effects of the kinematics and minimum undeformed chip thickness. The uncertain components in relation to the material spring back, plastic side flow, micro defects on the cutting edge of diamond tool, and others, are empirically predicted by a RBF (radial basis function) neural network, which is established by referring to the experimental data. Finally, the particle swarm optimization algorithm is employed to find the optimal cutting parameters for the best surface roughness. The validation experiments show that the optimization is satisfied, and the prediction accuracy is high enough, i.e. that the prediction error is only 0.59–10.11%, which indicates that the novel surface roughness prediction method proposed in this work is effective.

Conservation law of surface roughness in single point diamond turning

In this work, a comprehensive model is established to predict the surface roughness achieved by single point diamond turning. In addition to the calculation of the roughness components in relation to the kinematics and minimum undeformed chip thickness, the newly developed model also takes the effects of plastic side flow and elastic recovery of materials as machined into account. Moreover, the ‘size effect’ has also been successfully integrated into the model, i.e. an inflection point appears in the trend line of predicted surface roughness as the ratio of maximal undeformed chip thickness to cutting edge radius (hDmax/rn) is equal to one unit. Face turning experiments validate that the maximal prediction error is only 13.35%. As the ratio of hDmax/rn is higher than one unit, both the prediction and experiments reveal that a conservation law exists in diamond turned surface roughness, owing to the competitive effects of kinematics, minimum undeformed chip thickness, plastic side flow and elastic recovery of materials on surface formation. Under the conservation law, the freedom control for an invariable surface roughness can be fulfilled in response to a quantitative ratio of hDmax/rn, either through an accurate configuration of feed rate and depth of cut with fixed tool nose radius and cutting edge radius, or by a reasonable selection of tool nose radius and controlled cutting edge radius with designed feed rate and depth of cut.

Observations on chip formation and acoustic emission in machining Ti–6Al–4V alloy

Orthogonal cutting tests were undertaken to investigate the mechanisms of chip formation for a Ti–6Al–4V alloy and to assess the influences of such on acoustic emission (AE). Within the range of conditions employed (cutting speed, v c =0.25–3.0 m/s , feed, f=20–100 μm ), saw-tooth chips were produced. A transition from aperiodic to periodic saw-tooth chip formation occurring with increases in cutting speed and/or feed. Examination of chips formed shortly after the instant of tool engagement, where the undeformed chip thickness is slightly greater than the minimum undeformed chip thickness, revealed a continuous chip characterised by the presence of fine lamellae on its free surface. In agreement with the consensus that shear localisation in machining Ti and its alloys is due to the occurrence of a thermo-plastic instability, the underside of saw-tooth segments formed at relatively high cutting speeds, exhibiting evidence of ductile fracture. Chips formed at lower cutting speeds suggest that cleavage is the mechanism of catastrophic failure, at least within the upper region of the primary shear zone. An additional characteristic of machining Ti–6Al–4V alloy at high cutting speeds is the occurrence of welding between the chip and the tool. Fracture of such welds appears to be the dominant source of AE. The results are discussed with reference to the machining of hardened steels, another class of materials from which saw-tooth chips are produced.

A revised model for predicting surface roughness in turning

The objective of this paper is to demonstrate how tribological interactions at the interface between the chip and the tool control the surface roughness generation in finish turning with a single-point tool. It was assumed that one of the major sources which cause visual differences between the theoretical and natural surface roughness is relatively strong adhesion at the rake-chip interface. By considering this exceptional tribological effect, expressed mathematically in the form of the condition for the transition from ploughing to micro cutting, the minimum undeformed chip thickness was estimated. Consequently, the theoretical surface roughness was calculated based on Brammertz's formula. From the obtained data it is evident that the proposed methodology results in a better evaluation of the natural surface roughness produced by turning.