Chip Formation Mechanism Research Articles

The formation mechanism of discontinuously segmented chip in high-speed cutting of Ti-6Al-4 V

The formation mechanism of discontinuously segmented chip in high-speed cutting of Ti-6Al-4 V

On the transition of failure mechanisms during machining process with varied speeds: A molecular dynamics study

Conventional machining theory states that the machining of a ductile material may create continuous, serrated, and/or fragmented chips with increasing machining speeds. In this study, transitions of failure mode under varied machining speeds in single-crystalline silicon were analyzed based on molecular dynamics (MD) simulations of the ultra-high-speed machining of single-crystalline silicon. The MD simulations employ the periodic boundary conditions along the third direction which can mimic the material failure in cutting plane. The uncut depth reaches 39 nm, which is sufficiently large to accommodate complex atomic evolutions. The simulation results indicate that jetted chips occurred in front of the cutter, when the machining speed is increased to approximately 2.7 × 103 m/s, which is attributed to the shock pressure induced by the chip inertia. Essentially, the Rankine-Hugoniot jump conditions were introduced to explain the influence of the shock pressure. Both the calculations based on Rankine-Hugoniot jump conditions and the MD results imply that the shock wave speed is equal to the machining speed at the steady machining state. In addition, the transition from fragmented-chip to jetted-chip morphology exhibits a stage wherein the two primary adiabatic shear bands are simultaneously activated. The present work sheds light on the underlying mechanism of chip formation at an ultra-high-machining speed beyond 1000 m/s.

Simulation and experimental study of the hole-making process of Ti-6Al-4V titanium alloy for selective laser melting

Towards improving the hole-making accuracy and surface quality of titanium alloy workpieces after selective laser melting (SLM), this paper carried out simulation and experimental research on hole processing. Specifically, it is divided into three process methods: directly milling without preformed holes, milling SLM-formed preformed holes, and drilling SLM-formed preformed holes, compared and studied the dimensional hole accuracy, surface morphology, cutting force, and tool wear, analyzing chip and burr formation mechanism. Firstly, the geometric model of SLM titanium alloy workpiece containing features such as collapse, sticky powder, and lack of fusion hole was established by ABAQUS finite element software, and cutting simulation analysis was conducted based on Johnson-Cook failure criterion to investigate the stress distribution and cutting force variation law under different hole diameter and cutting speed; Then hole-making experiments with hole diameters ∅1 mm-∅3 mm were conducted, and the experiment results showed that: The surface quality of milling SLM-formed preformed holes is better, as shown by smaller burr size, stable chip pattern, less tool wear, better hole size, and best overall forming quality; the average error rate of drilling SLM-formed preformed holes was the smallest 1.458 %, and dimensional accuracy improved by 67.3 %, but they had larger burr sizes and slightly poorer surface quality. The axial force obtained by a higher cutting speed and lower material removal rate at the same bore diameter is small. The experiment results verify the accuracy and validity of the simulation analysis, and the average error of the simulation results is 8.4 %.

Serrated chip formation mechanism in orthogonal cutting of cortical bone at small depths of cut

Serrated chip formation mechanism in orthogonal cutting of cortical bone at small depths of cut

Analysis of chip formation mechanism in turning of AA 7075/SiCp MMCs

Purpose The purpose of this paper is to examine the quality of the turned surface. The quality of the surface produced depends on the nature of the chips, which are produced while turning metal matrix composites. This quality is a function of the machining parameters, tool material, tool configuration and elements of the composites. Design/methodology/approach In this study, the turning of AA7075/15 wt.% SiC (particle size 20–40 µm) composites is investigated. Thirty experiments were conducted, and the chip-formation mechanism in turning AA7075/SiCp composites at various combinations of cutting speeds, feed and depth of cuts was studied. Findings It is observed from the response surface methodology-based experimentation that in turning of coarser reinforcement (particle size 20–40 µm) composites, total gross fracture occurs. This causes small slices of chips and a higher shear plane angle. The nature of chips produced at various combinations of cutting speeds, feed and depth of cuts is different. The chips generated were segmented, spiral in cylindrical form, connected C type, chips with saw tooth, curled chips, washer C type chips, half-curved segmented chips and small-radii segmented chips. Originality/value The novelty of this research is that, so far, very little work has been published on the detailed analysis of chips produced during turning of AA7075/15 wt.% SiC (particle size 20–40 µm) composites.

Experimental Investigation of Temperature Distribution in the Chips, Workpiece and Cutting Tool During Machining Operations

High temperature values are encountered during machining processes and these high temperature values have negative influences on the tool, workpiece, chip formation mechanisms, the process efficiency and the quality of surface of the machined parts. These negative influences can be reduced drastically with the use of appropriate cutting tool with suitable depth of cut during machining operations. The studies of these thermal fields in machining are necessary and very important for the development of new technologies aiming to increase the tool lives and to reduce production costs. This work centers on measurement of temperatures in the chips, cutting tool and workpiece during turning and drilling operations using uncoated high-speed steel and coated cemented carbide cutting tools at different cutting speeds and depths of cut to ascertain the more suitable cutting tool and feed rate during machining operations. Although, the direct temperature measurement at the chip-tool interface are very complex, the turning experiments were performed on a lathe machine at varying turning speeds and depths of cut, while the drilling operation was performed on a drilling machine at different turning speeds and depths of cut. All the experiments were carried out at the mechanical Engineering workshop of Federal University of Technology, Owerri. The temperature values of chip, cutting tool and workpiece when working on brass, high-carbon steel and stainless steel were measured using digital thermocouples. The results obtained showed that uncoated high-speed steel cutting tool could not cut stainless steel and high-carbon steel at very high turning speed and depth of cut due to the excessive heat it generated at the contact area, and at very low cutting speed the temperature of the cutting tools were higher than the workpiece irrespective of the cutting tool till an increased cutting speed where temperature of workpiece became higher than the cutting tool. It is recommended that coated cemented carbide on hard materials be used during turning and drilling to ensure a negligible increase in temperature while machining, also monitor speed for required finishing and extended tool life.

VIBRATION-ASSISTED TURNING SIMULATION WITH TEXTURED TOOLS: A NUMERICAL INVESTIGATION

In this study, through numerical simulation, an effort has been made to acknowledge the efficiency of machining Titanium grade 23 under vibration assistance with textured cutting tools. Dry turning experiments with commercially available carbide inserts without texturing were carried out without vibration assistance. Cutting forces ([Formula: see text][Formula: see text], [Formula: see text][Formula: see text], [Formula: see text][Formula: see text]) were observed during experimentation, which were further validated using DEFORM 3D. The forces were validated using DEFORM 3D. Closer to the cutting edge, dimple type 1, dimple type 2, horizontal, and vertical patterns were made on cutting inserts using SOLIDWORKS software. A numerical model based on experimentation was developed employing DEFORM 3D software for conventional and vibration-assisted turning. Cutting forces ([Formula: see text][Formula: see text], [Formula: see text][Formula: see text], [Formula: see text][Formula: see text]), cutting temperature, tool wear, and the mechanism of chip formation were also explored through FEM investigation. Micro-textured inserts were found to be enhancing machinability. Machining with vibration assistance also improved machinability. The study found that textured tools improved machinability in conventional and vibration-assisted machining modes. The effect of textured tools on machinability improved with vibration-assisted machining. The numerical analysis revealed that dimple type 1 and vertical grooved tool improved the machinability of Titanium grade 23.

Machinability improvement of titanium alloys in ultra-precision machining with micro-structured surface

Titanium alloys get wider applications in different areas due to its excellent mechanical properties. However, poor thermal conductivity and low elastic module of titanium alloy induce high tool wear and make it being one of hard-to-machine materials; especially the segmented chip formation accelerates the diamond tool wear in ultra-precision machining (UPM) of precision parts. This study applies micro-structured surface to improve machinability of titanium alloys in UPM by reducing the chip segmentation induced cutting forces fluctuations. Finite element (FE) model is built to study chip formation mechanism and characterize geometries of segmented chips in orthogonal diamond cutting of Ti6Al4V alloy with the aims at the design of micro-structures array. Turning experiments are conducted to compare cutting force, surface roughness, and tool wear for diamond turning of Ti6Al4V alloy on smooth surface and micro-structured surface. The results show that the FE simulated saw chips agree well with the measured ones. Moreover, the micro-structured surface helps to decrease cutting force, reduce diamond tool wear, and improve surface quality for UPM of titanium alloy. Especially, the new method fabricates micro-grooves array on the machined surface in half-finishing process of UPM without the need of any material pre-processing and extra manufacturing equipment, which can also provide the guidance for efficient and sustainable UPM of titanium alloys parts with high surface quality.

Effects of feed direction on material removal behavior in belt grinding of titanium alloys

For abrasive belt grinding, although machine processing selection has been well studied to achieve good machinability, there is still a lack of understanding regarding the influence of feed direction and its mechanism, even though it is a common matter. This paper investigates the differences between up- and down-grinding in belt grinding of TC4, where the grinding forces, material removal performance, surface quality, and chip morphology are captured for the grinding process evaluation and mechanistic analysis In up grinding, it was observed that approximately 21.1 % more material removal can be achieved due to the larger penetration depth of scratching grains when maintaining a constant normal grinding force. Furthermore, the higher tangential grinding force resulting from increased cutting behavior and an additional sliding phase leads to more severe abrasive belt wear, as evidenced by a 22.7 % higher grinding ratio. Comparatively, down grinding mode generates a machined surface with lower roughness in the transverse and longitudinal direction, which can be explained by the minimum chip thickness effect and undeformed chip thickness model. The microscopic characteristics of chips and ground surface provide more evidence on the different chip formation mechanisms between two grinding modes.

Accurate modeling and controlling of weak stiffness grinding system dynamics with microstructured tools

The weak stiffness grinding system often produces uncontrollable vibration, which directly reduces the machining quality. In order to accurately predict and control the weak stiffness grinding system dynamics, an accurate dynamics modeling and the controlling method with microstructured tools are presented innovatively. Based on the real random abrasive grain model, an instantaneous undeformed chip thickness model considering the phase deviation, time accuracy and grinding wheel-workpiece separation caused by vibration is established. On this basis, the controlling principle of microstructured grinding wheel on chip formation mechanism and grinding forces is studied. Then, combined with the element division principle and dynamics parameters of grinding system, the dynamics model of weak stiffness grinding system is established. According to the grinding experimental results based on vibration monitoring, the error rate of the established dynamics model is less than 9.8 %. Compared with the non-structured grinding wheel, the microstructured grinding wheel can control the vibration amplitude, the vibration frequencies and the wheel deflection. Based on the workpiece surface machining results, the addition of microstructures suppresses the phenomena of overcutting and the wheel bounce, and the profile protrusion height caused by grinding vibration is decreased by 77 %. The established dynamics model is of great significance for understanding and control the dynamic behavior of weak stiffness grinding systems.

Mechanics of chip, delamination, and burr formation in drilling supported woven GFRP composites

A new approach was used in drilling woven glass fiber reinforced polymer (GFRP) composites to clamping the specimen by a controllable force at drill entry and exit sides. The influence of cutting and support conditions on thrust force, push-out and peel-up delaminations, and burr factor was investigated. A series of ASTM tests were implemented to determine tensile, in-plane shear, Mode I and Mode II fracture toughness properties, which were used to predict the critical thrust force (CTF) at delamination initiation. The delamination and burr areas were accurately measured via inexpensive, easy, and accurate image processing technique. Result from drilling processes revealed that the supported specimens are approximately free from burr accompanied with insignificant peeling within the drill (10 mm)/support hole (12 mm) tolerance. By using support plates, the thrust force was increased up to 8.3% compared to the unsupported conditions. On the other hand, the delaminations were decreased by about 65.5%. The delaminations were dominated by Mode I fracture toughness, which is lower than that of Mode II by 41%. The predicted CTF using concentrated load models are slightly lower than the measured values, which interpret the occurrence of delamination damage on the cutting zone.

Revisiting the Influence of Contact Length and Surrounding Medium on Metal Cutting Tribology

Metal cutting processes involve severe frictional conditions at the tool-chip contact interface, physico-chemical phenomena that are not fully understood and theoretical models with a strong empirical basis. In the literature, it is common to find values for the friction coefficient which are higher than the unit, despite the inconsistency of these findings with the mathematical theory of plasticity used for accurate modelling of the chip formation mechanics. Thus, the present work seeks to contribute to a better understanding of metal cutting tribology based on well-controlled and specially designed experimental conditions. To enable the stress state at the contact interface to be determined and to provide a known real contact area, polished cutting inserts with prepared rake faces were used to restrict the contact length in orthogonal cutting tests under controlled atmospheres. These conditions also allowed the contribution of the sticking mechanisms to be minimized. Cutting tools of restricted contact lengths have been found to reduce process forces and the friction coefficient, while industrial standard inserts make cutting operation sensitive to the chemical composition of the surrounding atmosphere.

Numerical assessment of transition in cutting mode and its effect on roughness creation

Ductile-to-brittle transition in cutting mode is an important phenomenon in the ultra-precision machining and surface finish of brittle materials. Using a newly-developed coarse-grained molecular dynamics technique, we systematically explore the effect of depth of cut on the cutting mode and the evolution of roughness. Our simulations demonstrate that the transitional depth of cut (TDoC) model accurately predicts the material removal mechanisms, which are affected by both the material’s properties and the cutting depth. When the cutting depth increases, the operating mechanism shifts from shearing-induced serrated chip formation to cleavage-cracking chip breakage. The RMS roughness study demonstrates that the roughness is a direct outcome of the chip formation mechanism and is, in general, higher when chip breakage occurs.

Modeling and analysis of chip segmentation in micro-cutting of Zr-based bulk metallic glass (BMG)

Bulk metallic glasses (BMG) exhibit an amorphous structure and possess excellent properties, such as high hardness (∼8 GPa), high elastic and strain limit (∼2 %), and wear/corrosion resistance. Chip formation behavior of BMG during machining is distinct from the crystalline materials, and is not very well understood. Hence, this paper presents experimental and analytical investigations to explore the underlying chip formation mechanism in the micro-cutting of BMG. The experimental study was carried out by analyzing the chip morphology, force signature, and hardness of the workpiece. BMG machining yields segmented chips due to the shear localization. The shear localization is clearly observed in terms of periodic primary shear bands and multiple secondary shear bands. The machined surface also shows work softening due to machining-induced deformation. It has been observed that free volume and the shear zone temperature affect the shear localization, which is reflected in the chip segmentation. A shear localization model has been developed, which includes the effects of new surface creation energy, shear energy, and friction energy. Based on a bifurcation analysis, critical free volume and temperature flow coefficients have been calculated. Based on the critical free volume and temperature flow coefficients, four distinct regimes of shear localization have been identified. The shear localization dampens out if the free volume coefficient is less than the critical free volume flow coefficient. Substantial shear localization is observed if the free volume flow coefficient exceeds the critical value. This study shows that free volume generation primarily drives the chip segmentation and shear localization, and the temperature effects play a secondary role.

Machinability analysis during finish turning Ti6Al4V with varying cutting edge radius

ABSTRACT The effect of cutting edge radius (rβ) on the chip formation mechanism during the finish turning of Ti6Al4V is studied. An increase in rβ decreases the cutting to thrust force ratio and produces lower chip thickness due to the increase in plowing zone depth. Larger radius tools produce thinner loosely curled chips whereas tightly curled thicker chips are formed for the unprepared edge tool (36 µm). As rβ increases, the chip flow angle (β) increases and free-flowing chips with reduced up-curl but increased side and lateral curl and consequently larger resultant chip curl radius are produced. The chip serration height to overall chip thickness ratio increases whereas chip core thickness reduces owing to the increased plowing action as rβ increases. Chip segmentation analysis reveals increased serration height, thermal instability, and shear localisation in the shear zone due to the increased ploughing effect beyond ~60 µm edge radius.

Mechanism and force modeling for cross-edges in the flank-end milling process based on the constrained cutting theory

Flank milling is one of the most important processes in modern industries. Traditionally, flank edges are taken as the main part to remove materials. However, cross-edges additionally have a great rule on the machining process. This paper studies the mechanism of removing materials for cross-edges. First, the mathematical model for cross edges is built. Then, angles for an arbitrary point on a cross-edge embracing the rake, clearance, and inclination angles are deduced. The constrained cutting situation is found in the zone between cross-edges and corresponding their connecting flank-edges. Based on this, the chip-formation mechanism for cross-edges is discussed in deep. Using mechanical principles, cutting forces model due to chips forming is put forward utilizing parameters such as the shear strength, the friction angle, and the shear angle, etc. To combine the effect of environment, tool wear, machine tools error, and so on, an empirical model is obtained from the mechanical one. This paper adopts two methods to verify the validity of the proposed theory. The first one is using FEM software to simulate the milling process to observe the deformation zone in the cutting area using two groups of parameters, the results of the shearing zones for flank- and cross-edges shows that the constrained theory can be used in the cross-edge milling process. Some experiments conducted are the other way to prove the correctness of the cutting forces model. The results also tell us that the model in this paper is valid and of high accuracy.

Low-speed orthogonal cutting of large Zr-based metallic glasses: A shear angle model considering internal friction and serrated chip formation

Metallic glasses have high hardness, low cutting force, and serrated chip formation, which pose significant challenges for cutting. The chip formation mechanism of metallic glasses under low-speed cutting has been studied, but the effects of compression and internal friction have been neglected. In this study, a shear angle model that considers internal friction was proposed and compared with classical shear angle models. Low-speed orthogonal cutting experiments on Zr-based metallic glasses were conducted and the cutting forces, chip morphology, shear angle, external and internal friction angle under different cutting parameters were measured and calculated. The results show that the internal friction angle ranges from 21.3° to 36.0° and the shear angle ranges from 29.9° to 38.0°. The improved model can better characterize the cutting properties of metallic glasses. This study presents a new method and model for low-speed cutting of metallic glasses and provides insights into their deformation and fracture behaviors.

Time-Varying Tool-Chip Contact in the Cutting Mechanics of Shear Localization

Abstract Shear localization is the dominant chip formation mechanism in machining of high performance metallic components, such as those made of titanium and nickel-based alloys. This paper presents an analytical thermo-mechanical model considering a new tool-chip contact mechanism due to shear localization. First, it is experimentally shown that the sticking and sliding contact lengths fluctuate with the frequency of shear localization. Second, a cutting mechanics model is developed considering the shear band formation, its rolling on the tool’s rake face, and the time-varying tool-chip contact length with experimental validation. Finally, the transient temperature at the tool-chip interface is predicted by taking the rolling phenomenon and the time-varying heat sources at the tool-chip interface into account. The proposed model shows that at the beginning of each segmentation cycle, the entire tool-chip contact length is dominated by sliding condition with negligible sticking length. When the tool advances, new workpiece material piles up in its front with an increase in the sticking length. Meanwhile, the sliding length decreases due to the drop in the load-bearing capacity of the shear band. When enough material piles up in front of the tool, a new shear band forms, and the entire contact length returns to the sliding condition. This process repeats each time a shear band occurs, causing the cyclic formation of shear bands and time-varying nature of the tool-chip contact length, therefore influencing the temperature and stress evolution at the tool-chip interface.

Research on the influence of stress wave on crack and chip formation mechanism in radial ultrasonic vibration assisted grinding

The propagation of stress waves in the ultrasonic vibration grinding zone was studied and analyzed in this paper and the microscopic mechanism of ultrasonic vibration assisted grinding is clarified by combining the method of finite element analysis (FEA). The creation of an experimental platform for ultrasonic vibration assisted grinding allowed for a comparative experimental evaluation of radial ultrasonic vibration assisted grinding (RUVAG) and conventional grinding (CG). Experiments analysis show that: (a) Compared with conventional grinding, the alternating impact of stress waves in ultrasonic vibration grinding is beneficial to the propagation of microcracks and the removal of materials. Meanwhile, there is no burn on the machined surface, so the quality of the machined surface is better. (b) Under the alternating and superimposed action of stress waves, dislocation emission becomes difficult due to the suppressed thermal activation process. Therefore, the plastic deformation of the material is suppressed and reduced in the grinding zone, and the material is more likely to break than during conventional grinding. Therefore, compared with conventional grinding, both cracks and chips are easier to form in it..

Grinding performance study of CF/epoxy and CF/PEEK composites

AbstractIn order to distinguish the grinding performance of the thermoset and thermoplastic carbon fiber‐reinforced plastic (CFRP) composites, carbon fiber‐reinforced epoxy resin (CF/epoxy) and carbon fiber‐reinforced poly‐ether‐ether‐ketone (CF/PEEK) composites were employed in this study. Different process parameters were set to grind the two materials. Then the surface morphologies and roughness of the workpieces with different process parameters were observed and measured. Experimental results indicated that the grinding forces were positively correlated with the grinding depth and feed speed, and negatively correlated with the wheel speed. The grinding depth was the main influencing factor of the maximum temperature of the grinding. The heat distribution of the grinding process was dependent on the fiber direction. In addition, the chip formation mechanism of CF/epoxy and CF/PEEK were investigated. Compared with CF/epoxy, the grinding forces and temperature were higher and the wheel was more prone to be clogged under the same grinding parameters, indicating that it was more difficult to process CF/PEEK. However, the surface quality of CF/PEEK with high ductility was much better than CF/epoxy.