Chip Segmentation Research Articles

A new damage evolution criterion for the coupled Eulerian-Lagrangian approach: Application to three-dimensional numerical simulation of segmented chip formation mechanisms in orthogonal cutting

A damage evolution law is proposed to consider the frictional behavior within an Eulerian material after full damage as a Lagrangian material, where the mesh explicitly describes the newly born interface interactions. This approach is prominent for simulating severe plastic deformation (SPD) processes during which material separation can occur. Among these, orthogonal cutting represents the simplest process for comparison with the simulation because it offers accessibility for measuring physical quantities in situ in the vicinity of the tool. Therefore, a numerical model based on a coupled Eulerian-Lagrangian formulation to simulate segmented chip formation mechanisms during orthogonal cutting was developed. A simple damage initiation criterion was used, and the damage evolution criterion was coded in the ABAQUS subroutine VUSDFLD. The model can simulate both segmented and continuous chip formation, depending on the experimental configuration, while satisfactorily predicting chip morphology and physical quantities such as temperature, primary shear band and cutting forces. Additionally, a non-negligible material side flow observed experimentally was successfully predicted by simulation. The model accuracy in predicting the material plastic behavior is auspicious for its subsequent extension to the three-dimensional model of SPD processes (i.e., milling, friction stir welding, etc.).

NUMERICAL METHODS FOR THE SIMULATION OF SEGMENTED CHIPS AND EXPERIMENTAL VALIDATION IN MACHINING OF TI-6AL-4V

The simulation of machining processes holds the opportunity for process improvement on many levels. Possible benefits that can be derived from accurate representations of the real processes on the tool from simulations include a prediction of tool wear, the shape of the chips produced, the forces, frictions and temperatures that arise and the residual stresses in the workpiece. These predictions can be used to improve the process in terms of its economic and ecological behaviour: Increasing the service life of the tools used through an improved understanding of the tool-workpiece interaction. The finite element method (FEM), among others, has emerged as a common method for simulating these processes. When simulating machining processes using FEM, a major challenge is to avoid or compensate for the mesh distortions caused by the massive, fast-moving deformation processes, but at the same time to allow the mesh to be discretised in some way to ensure chip removal. To this end, various approaches will be presented in the course of this work and the mesh-based approaches will be explored in depth. Among other things, a remeshing approach for these investigations was developed. The machining of TI6AL4V is used to illustrate these approaches, as its tendency to form segmented chips is particularly challenging to model.

High-pressure flank cooling and chip morphology in turning Alloy 718

The use of cutting fluids is commonly considered a necessity while machining Heat Resistant Super Alloys (HRSA). Specifically, cutting fluids applied under high-pressure, which for many decades have been the solution for the most demanding applications. The results might be diverse and vary between applications, but typically leads to improved tool life, enhanced chip breakability, lower temperature in the cutting zone and better surface quality of the finished product. The available high-pressure cutting fluid delivery systems are usually designed with the intention to improve the cutting fluid penetration at the vicinity of the cutting edge on the rake face side of the insert. However, there has been limited interest in investigating high-pressure cutting fluid applied to its flank face. Both specifically and in combination with cutting fluid directed to the rake face. In this study, the focus has been to investigate the chip formation process during the turning of Alloy 718 (Inconel 718). Particularly, for a defined turning operation where high-pressure cutting fluid is applied to the flank side as well as the rake side of an uncoated carbide insert. Several combinations of pressure levels and jet directions were investigated. The corresponding effects on the tool-chip contact zone and chip characteristics were studied for two cutting speeds. The results of the investigation showed a substantial improvement in lowering the tool-chip contact area at a rake pressure of 16 MPa. At which pressure, additional cutting fluid applied to the flank at a moderate pressure of 8 MPa had no dominant effect on chip formation (chip break). However, flank cooling of the cutting zone supports chip segmentation and thus indirectly chip breakability. For cutting fluid applied to the rake side at a more moderate pressure of 8 MPa, more prominent effects on the insert became apparent when additional cutting fluid was applied to the flank side. This was particularly noticeable when cutting fluid was directed towards the flank side of the insert at the same pressure level as the cutting fluid applied towards its rake face. The additional thermal transfer was seen to have a significant effect on the material deformation phenomena in the primary shear zone (lowering shear angle) as well as the sliding and sticking conditions of the tool-chip interface. Based on the evidence from this study, it can be concluded that cutting fluid applied towards the flank side of the insert has a significant impact on the cutting process. In particular, if applied in combination with a rake pressure at a similar level, in this case, 8 MPa.

Chip formation and wear mechanisms of SiAlON and whisker-reinforced ceramics when turning Inconel 718

Inconel 718 has found use in many demanding applications due to its high temperature fatigue strength, hardness and low thermal conductivity. These material properties present a challenge to productive and high quality (surface finish) machining and promote rapid tool wear. The work presented here describes the chip formation and wear mechanisms of silicon nitride (Si3N4) based ceramic SiAlON and silicon carbide whiskers reinforced alumina (WRA) (Al2O3 + SiCw) round (RNGN) inserts, when turning solution-annealed Inconel 718 (27<HRC<30) with a 10% concentration cutting fluid. Four sets of cutting trials were conducted at a cutting speed of 250 m/min and another four at 300 m/min. The results show that using SiAlON turning inserts at a cutting speed of 300 m/min delivered the best results in terms of tool flank wear, total tool life, and work-piece surface finish. The morphology of the Inconel 718 chip, at cutting speeds above 250 m/min, presents an intense shear band localisation in the primary shear zone of the chip/tool interface, which leads to chip segmentation.

Analytical Modeling of Shear Localization in Orthogonal Cutting Processes

AbstractThis paper presents an analytical thermo-mechanical model of shear localization and shear band formation in orthogonal cutting of high-strength metallic alloys. The deformation process of the workpiece material includes three stages: homogeneous deformation, shear localization, and chip segmentation. A boundary layer analysis is used to analytically predict the temperature, stress, and strain rate variations in the primary shear zone associated with the shear localization. The predictions of shear band spacing and width from the proposed model are verified by experimental characterization of the chip morphology. The rolling of shear bands on the tool rake face is discussed from the experimental observations. The cutting tool temperature, which is influenced by the heat generated during the shear band formation, is simulated and compared with finite element simulations. The proposed analytical model reveals the fundamental mechanism of the complete shear localization process in orthogonal cutting and predicts the stress and temperature variations with high computational efficiency.

Research on cutting performance of coated cutting tools by a new impact test method considering contact stress condition caused by segmented chips

The generation of segmented chip will cause unstable vibration of cutting force and produce high-frequency stress impact on the cutting tool. The segmented chip morphology and contact stress between chip and flank face of coated cutting tool were studied by cutting experiments. It was found that the average contact stress of the coated tool was 4.9 GPa and the alternating frequency reached 22 kHz. A new high-frequency impact test method was used to simulate the loading condition of coated tools in the cutting experiments. The results showed that the cutting performance of the coated tool was related to the impact fatigue resistance. In the case of a high feed rate (above 0.1 mm/rev) or high preloading depth (7.51 μm and 9 μm), TiSiN/TiAlN bilayer coating shows better performance, compared with TiSiN/TiAlN nanolayer coating. However, in the case of low feed rate (less than 0.1 mm/rev) or low preloading depth (18 μm), TiSiN/TiAlN nanolayer coating shows better performance. Cutting conditions and coating structure could match to get optimized cutting performance of coated cutting tools.

A new quick-stop device to study the chip formation mechanism in metal cutting: Computational and experimental investigation

Understanding the chip formation mechanisms during machining is an important factor to facilitate the choice of cutting tools and machining parameters. Despite the appearance of new sophisticated methods and advanced equipment, the technique so called quick-Stop Test (QST) remains efficient, less costly, and easier to apply in the investigation of chip formation in cutting process. In present paper a new Quick-Stop Device QSD is designed, numerically simulated, implemented, and tested. The reformed QST technique uses a QSD device which operates on the modified Charpy pendulum. Accordingly, design of new QSD is presented and deeply described, and 2D FE modeling of the new QST, including the application of the appropriate boundary conditions, has been carried out. Moreover, chip formation and morphology for different cutting conditions have been effectively simulated. Subsequently, quick stop cutting operations including metal cutting tests of high alloyed tool steel (AISI D2) using fabricated new QSD are performed. Preliminary results of quick-stop experiment from current investigation prove the effectiveness of the new designed QSD in matter of rigidity, safety, and absence of vibration, while providing a fast set up time and allowing extremely short workpiece-cutting tool separation time and guarantee the generation of chip with its root. The photomicrographs of chip root samples gathered from hard metal cutting experiments including various cutting speeds machining conditions, enables clear observation of segmented chip formation mechanisms, thereby, highly promising the new designed QSD for the purpose of investigation of the different cutting parameters influencing the chip formation and morphology.

Inverse Identification of the Ductile Failure Law for Ti6Al4V Based on Orthogonal Cutting Experimental Outcomes

Despite the prevalence of machining, tools and cutting conditions are often chosen based on empirical databases, which are hard to be made, and they are only valid in the range of conditions tested to develop it. Predictive numerical models have thus emerged as a promising approach. To function correctly, they require accurate data related to appropriate material properties (e.g., constitutive models, ductile failure law). Nevertheless, material characterization is usually carried out through thermomechanical tests, under conditions far different from those encountered in machining. In addition, segmented chips observed when cutting titanium alloys make it a challenge to develop an accurate model. At low cutting speeds, chip segmentation is assumed to be due to lack of ductility of the material. In this work, orthogonal cutting tests of Ti6Al4V alloy were carried out, varying the uncut chip thickness from 0.2 to 0.4 mm and the cutting speed from 2.5 to 7.5 m/min. The temperature in the shear zone was measured through infrared measurements with high resolution. It was observed experimentally, and in the FEM, that chip segmentation causes oscillations in the workpiece temperature, chip thickness and cutting forces. Moreover, workpiece temperature and cutting force signals were observed to be in counterphase, which was predicted by the ductile failure model. Oscillation frequency was employed in order to improve the ductile failure law by using inverse simulation, reducing the prediction error of segmentation frequency from more than 100% to an average error lower than 10%.

An accurate transient model for temperature fluctuation on localized shear band in serrated chip formation

The temperature fluctuation process on localized shear band is an important foundation of the chip formation mechanism in mesoscopic scale of time (700-70ms) and dimension (65-500um). An accurate transient temperature fluctuation modeling of localized shear band is proposed by using the classic method of moving heat source and thermal convection in mesoscopic scale. Where, chip geometry, time coefficient of the coupling effect from relative chip segment, temperature rise from different heat sources and thermal convection model for chip segmentation process are developed, respectively. A novel measuring method are applied for thermal distribution in shear band and its evolution in chip generation progression. The given experimental and numerical results can show that the proposed temperature model can get the efficient predictions of temperature and physical phenomena at various chip segmentation stage. Physical phenomena in chip formation process, such as instable chip flow, crack generated and propagation, from the viewpoint of temperature fluctuation and its instable evolution, and cutting force are addressed and analyzed. The innovative model can determine the temperature fluctuation and evolution, area of maximum temperature of shear band in chip segmentation process in mesoscale of time and dimension.

Experimental and numerical investigation of the effects of preheating temperature on cutting force, chip shape and surface roughness in hot turning of AISI630 hardened stainless steel

Hot machining is a type of cutting operation that an external heat source is used to pre-heat and consequently reduce the yield strength of the workpiece material. In this study, the conventional and hot turning of AISI630 hardened stainless steel, which is widely used in energy equipment, aerospace, and petrochemical industries, have been evaluated in both numerical and experimental methods. Simulation of the turning process is carried out by finite elements method (FEM) using AdvantEdge software. To predict chip morphology and cutting forces, the 2D and 3D FEM analyses have been used, respectively. The numerical analysis showed that hot turning in 300°C causes a reduction of 28% in cutting forces and consequently decreases stressed on the cutting tool. It is found that the main factor affecting the fluctuations of the cutting forces in turning of hardened AISI630 is the saw-tooth formation phenomenon (chip segmentation) as well as the shear band generation due to thermal softening of the workpiece material. Furthermore, the relation between cutting force fluctuation and the machined surface roughness has been investigated applying numerical analysis and experimental data. The results of roughness measurement revealed that hot turning in 300°C reduces the machined surface roughness up to 23%. In addition, it has been observed that hot turning technique decreases side flow and surface damages in comparison to conventional turning.

Analysis of Hole Quality and Chips Formation in the Dry Drilling Process of Al7075-T6

Millions of holes are produced in many industries where efficient drilling is considered the key factor in their success. High-quality holes are possible with the proper selection of drilling process parameters, appropriate tools, and machine setup. This paper deals with the effects of drilling parameters such as spindle speed and feed rate on the chips analysis and the hole quality like surface roughness, hole size, circularity, and burr formation. Al7075-T6 alloy, commonly used in the aerospace industry, was used for the drilling process, and the dry drilling experiments were performed using high-speed steel drill bits. Results have shown that surface roughness decreased with the increase in spindle speed and increased with the increase in the feed rate. The hole size increased with the high spindle speed, whereas the impact of spindle speed on circularity error was found insignificant. Furthermore, short and segmented chips were achieved at a high feed rate and low spindle speed. The percentage contribution of each input parameter on the output drilling parameters was evaluated using analysis of variance (ANOVA).

Effect of anisotropy and cutting speed on chip morphology of Ti-6Al-4V under high-speed cutting

The Ti-6Al-4V with significant anisotropy was taken as the research object to analyze the influence of sampling direction and cutting speed on the chip morphology. Based on the fracture damage model of Ti-6Al-4V which was constructed in the previous stage, high-speed orthogonal cutting simulation was carried out in finite element software. The accuracy of the model was verified by cutting experiments. The chip morphology was quantitatively characterized by the chip segmentation degree and chip segmentation frequency. The results showed that the accuracy of the model was high, and it could accurately reproduce the chip formation process of the material in the high-speed cutting process. It was found that material direction and cutting speed had significant effects on chip morphology. When the cutting speed was constant, the chip morphology under different directions was different. The critical cutting speed of chip changing from serrated chips to fragmented chips was different when the direction ranged from 0° to 90°.

A new geometric model of serrated chip formation in high-speed machining

• The serrated chip geometry can be predicted effectively with average value. • The serrated chip formation can be modeled effectively in time domain without measurement of chip geometry. • The critical shear strain rate for the disappear of crack in machining of cast aluminum alloy are presented. The geometry of serrated chip is of paramount importance to the analysis of physical and thermal phenomena in chip formation process, and it can affect tool fatigue life, surface finish and geometric accuracy of the machining part. This paper presents a novel geometry model of serrated chip segment based on chip formation and cutting force in metal cutting by considering the difference between deformation of shear band and primary shear zone. Where, focusing on the high-speed machining, it key points about the geometry of chip segment, shear band angle, secondary shear angle, third shear angle (curvature angle of second shear band), the strain and its rate, and their evolutions in chip formation process are developed, respectively. Finally, the experimental and simulated instances can verify the proposed method. The results can show that this proposed model having a high accuracy can effectively reflect the evolution of chip segment. The shear angle is silent increased with increase of feed rate, while the difference between shear angles is decreasing with increase of feed rate. While the shear strain is increasing with the increasing feed rate and decreasing with increase of cutting depth, the cutting velocity can enlarge the difference. The critical shear strain rate and cutting velocity for the disappear of crack in chip for feed rate of 0.117mm, 0.14mm and 0.187mm are 1.566e 5 1/s and 32.71m/s, 1.486e 5 1/s and 35.98m/s, 1.279e 5 1/s and 39.25m/s, respectively, which decreased with increased of feed rate.

Study of segmented chip formation in cutting of high-strength lightweight alloys

Chip segmentation results in fluctuation of the cutting force, deteriorated tool wear and surface finish, thereby plays an important role in the machining process. Although extensive research has been carried out on studying the segmented chip formation, the mechanism of chip segmentation has remained under debate. This paper aims to investigate the mechanism by combining numerical and experimental methods. Finite element (FE) models of the orthogonal cutting process of A2024–T351 aluminum alloy and Ti6Al4V titanium alloy were developed with three numerical formulations: Lagrangian (LAG), arbitrary Lagrangian–Eulerian (ALE), and coupled Eulerian and Lagrangian (CEL). The appropriate model for predicting the segmented chip formation process was selected by systematic comparison. The mechanism of chip segmentation was thoroughly investigated by the selected numerical model. It revealed that the adiabatic shear band (ASB) is generated not only from the chip root but also from the free chip surface. The finding was then validated by observing the microstructure of chips from high-speed dry-cutting tests.

Effect of microstructural change on cutting force fluctuation

Machining of aerospace and biomedical grade titanium alloys such as Ti6Al4V is always a challenge due to their low thermal conductivity and elastic modulus. Formation of localized shear bands during machining of Ti6Al4V alloy results in chip segmentation, which causes force variation on the cutting tool. An unconventional way is followed to study the effect of microstructural changes on cutting forces while machining Ti6Al4V alloy. Microstructure of the material was altered using static annealing and laser heat treatment. For static annealed material the study was focused on the effect of microstructure on machinability of Ti6Al4V alloys at different cutting speeds. The variation in force was observed to be smallest in the case of lower grain size samples subjected to machining.

Advanced modelling for grinding - from friction to ploughing and dynamic chip formation with temperatures

There is a lot of discussion and interest in the “Industry 4.0 project”. But before we start teaching a computer for creating AI, the adequate mathematics of the process must be systematic developed and known. This paper presents every phenomenon from the dressed micro geometry of the spherical wheel space, with average edge contour, average undeformed chip thickness and distance from each other. These dynamic cutting edges create friction, ploughing with a frontal bulge and a segmented chip. To advance the field of modelling chip formation it is necessary to find the relevant friction and contact conditions with corresponding process mechanics. The knowledge of the existing stress and strain-rate situation delivers the metal deformation in the plastic zone. The plastic deformation is the only parameter that will not disappear after completing the operation. Therefore, this will be the base to compare the developed theoretical material deformation with the experimental results during the grinding process.

Chip segmentation frequency based strategy for tool condition monitoring during turning of Ti-6Al-4V

Tool condition monitoring in machining reduces downtimes, maximizes productivity rate and improves the quality of the end-product. However, it still poses a challenge due to the complex non-stationary character of the tool wear and the several uncertainties coming from the machining processes. Recent studies provide new strategies for indirect tool monitoring. Unfortunately due to the unbalance between big amounts of data, low accuracy and high complexity they are not feasible in an industrial environment. The present research work proposes a strategy for tool condition monitoring during turning of Ti-6Al-4V using acoustic emission signals and the chip segmentation frequency as measurement variable. Three different approaches for wear estimation using different AE-data processing methods are presented. Through their combination, a strategy for qualitative and quantitative tool wear monitoring is proposed.

Simulative design of constraints for targeted restriction of chip thickness deviations when machining titanium alloy Ti6Al4V

When machining the titanium alloy Ti6Al4V, segmented chip formation is a major challenge as it leads to chatter-vibrations of the tool-machine-system. In this paper a counter element to suppress segmentation, the constraint, is designed by simulations. Therefore, the segmented chip formation of Ti6Al4V has been modelled in a finite element simulation using different approaches for flow stress modelling. The simulation results were validated with the help of orthogonal cutting experiments. Based on a suitable choice of a flow stress model, different geometries and positions of the constraint are analysed and discussed in this paper.

The effectiveness of the use of a water repellent emulsion when turning machining of carpolon

The article presents the results of experimental studies of caprolon turning machining with the cutting fluid use. It is scientifically substantiated the use of an aqueous emulsion with the addition of a water repellent as a cutting fluid during caprolon turning machining. On this basis a new method for turning caprolon blanks was developed and patented. The fact of decrease in the water absorption capacity of caprolon in the case of its turning with the supply of an aqueous emulsion of potassium palmitate to the cutting zone has been established experimentally. At the same time, turning caprolon in the traditional way leads to the activation of the water absorption process. It has been experimentally proven that turning caprolon with the supply of an aqueous emulsion of potassium palmitate to the cutting zone provides a better processed surface of the part compared to the traditional turning method. This is evidenced by a more uniform deviation profile of the depressions and protrusions of the treated surface and the numerical values of the roughness parameters. The results of microstructural studies of caprolon shavings are presented. It has been established experimentally that turning machining of caprolon using an aqueous emulsion of potassium palmitate contributes to the formation of continuous flow chips whereas turning caprolon in the traditional way leads to the formation of segmented chips.

Ultrasonic-assisted drilling of nickel-based super alloy in conel 601: An experimental study

In this study, a comparison between ultrasonic-assisted drilling (UAD) and conventional drilling (CD) is presented under different feed rates using thrust force, torque, and hole geometrical errors as output responses. The experiments were done on plates of Inconel 601 (nickel-based superalloy), which is classified as a difficult-to-cut alloy due to its high Nickel content (60%), high hardness (43 HRC), and low thermal conductivity. The experiments were performed using DMG Mori Ultrasonic 20 linear, which is equipped with ultrasonic tool holderoscillating at 20 kHz with 7 μm amplitude. A coated carbide single margin twist drill had been used in the experiments. Full factorial design of experiments approach was employed, and the results had been statistically analyzed to find the most significant factor affecting the process responses. The results showed that the ultrasonic assistance had reduced the thrust force, and torque compared to conventional drilling (CD). Also, a reduction in holecylindricity error was detectedduring UAD, whichimprovesthe hole quality. In case of UAD, twist drills did not suffer from a physical wear, however notch wear was observed in CD drills. Chip morphology was also studied. Short segmented chips were obtained when using UAD which improved chip evacuation and reduced the chance of chip jamming in the drill flutes.