Chip Formation In Machining Research Articles

A framework to efficiently simulate the cyclic variation of the residual stresses induced by chip formation in machining of Ti-6Al-4 V alloy

Residual stresses is a key part of surface integrity, having a strong influence on the functional performance and lifespan of components. Advances in modeling of machining-induced residual stresses are fundamental to achieve more accurate predictions. Due to the low computational efficiency and the lack of consideration of the whole residual stress formation process, a framework to simulate the residual stress in the machining of Ti-6Al-4 V titanium alloy using CEL (Coupled Eulerian and Lagrangian) and Lagrangian approaches is proposed. A model of the cutting and workpiece unloading processes is simulated using CEL approach and explicit time integration scheme. Then, a model of the cooling process of the workpiece is developed in order to calculate the residual stresses. To improve computation efficiency and to reduce the effects of cumulative errors, this model is simulated using Lagrangian approach and implicit time integration scheme. Data transfer between these two models is performed by combining a strategy of data transfer and mesh rebuilding. The cutting force and residual stress are obtained by simulation with average errors of 18% and 21%, respectively. The predicted and measured thicknesses of the layer are reasonable well predicted. The computational time of proposed approach can be greatly reduced from 81 h to 5.3 h by comparison with traditional one. This framework was then used to investigate the cyclic variation of the residual stress along the cutting direction, which is due to the cyclic nature of the chip formation process.

An experimental study based on Six Sigma approach to optimize chip formation in machining

Quality and productivity have been distinguished as a significant role in any organization, especially for the manufacturing industry to gain more profit that prompts achievement of a company. In the manufacturing of pistons, the makers who are competing in the market want their products to be manufactured at less expense. In a large-scale manufacturing organization, which intends to produce around 600 to 800 parts per shift per line each and every single rejection record to the deficiency of Productivity. Defectives are investigated again and rework has to be done to bring down the number of damaged pistons, hence it reduces the quality of the product manufactured, devouring additional man and time. This paper reports a work improvement project in Federal-Mogul Goetze India limited. It involves Problem Identification in the production of pistons and proposing an effective framework to improve the current situation effectively. Based on the observation and data collection on day-to-day productivity, the major problem has been identified. To study and improve the problems identified methodology adopted is Six Sigma. DMAIC helps in understanding the process and the variables that affect it so that can be optimized the processes. The main objective of this case study is to reduce the number of defective pistons produced in the Piston Machine Shop. The outcome of this study is a suggestion to improve the process efficiency by parameter optimization that identifies and determines the root cause and controls the factors leading to desired output by following six sigma approaches.

Investigations on tool wear, surface roughness, cutting temperature, and chip formation in machining of Cu-B-CrC composites

Investigations on tool wear, surface roughness, cutting temperature, and chip formation in machining of Cu-B-CrC composites

Analysis of slip-line model for serrated chip formation in orthogonal machining of AISI 304 stainless steel under various cooling/lubricating conditions

In the past, numerous slip-line models have been developed and presented for continuous chip formation. However the authors of this paper recently proposed a new slip-line model for serrated chip formation in machining with rounded cutting edge. In that model, Oxley’s predictive machining theory was integrated for machining of stainless steel material and the model was validated under dry cutting. The current study extends the previously developed slip-line model for orthogonal turning of AISI 304 austenitic stainless steel for various cooling/lubricating conditions. The orthogonal machining experiments were performed under dry, flood cooling, MQL (Minimum Quantity Lubrication) and cryogenic cooling conditions. Good correlations are observed between experimental work and predictions under various cooling/lubricating conditions for cutting force components and maximum and minimum chip thickness values. After achieving the good correlation, several important outputs such as the shear stress, flow stress, ploughing force, stagnation point angle, chip up-curl radius, which are difficult or impossible to measure experimentally were determined by solving the extension of the previously developed model. The lowest tool-chip frictional shear stress was achieved under MQL method whereas the highest was obtained in dry cutting. In addition, the minimum ploughing force was obtained in cryogenic cooling while the maximum value occurred in dry cutting. The stagnation point angle decreased when applying lubricant or coolant and increased with increasing cutting speed. The tool-chip contact length slightly decreased, the chip up-curl radius increased and the thickness of the primary shear zone reduced with increasing cutting speed. Additionally, lower tool-chip contact length, larger chip up-curl radius and larger primary shear zone thickness occurred while using lubricant or coolant. Higher cutting speed caused lower shear strain and flow stress and higher shear strain-rate. The highest and lowest flow stresses were obtained under cryogenic cooling and dry cutting, respectively.

Chip formation in machining of anisotropic plastic materials—a finite element modeling strategy applied to wood

This paper presents an FEA modeling strategy for predicting the cutting forces generated during linear wood machining. The objective is to determine both the forces and paths of cracks propagating in elastoplastic and anisotropic materials. The model combines a bilinear representation of the material strain-stress relation and the Hill yield function. The proposed procedure also integrates the displacement extrapolation method to evaluate the stress intensity factors. It establishes the cutting forces from the contact pressures between the tool and the chip. These pressures are determined using the penalty method. The validation phase compares the model predictions with average experimental forces and shows correspondence levels higher than 91% and 92% for low (0.085e10−3 m/s) and high (6.8 m/s) wood-feeding speeds, respectively. The developed model maintains a high precision degree over a large range of feeding-velocity. This study demonstrates that the resistive force between the chip and the tool surface is a function of both the rake angle φ and the coefficient of friction (COF). The friction force prompts a self-energizing effect, which increases the resistive force. On the other hand, larger φ amplitudes reduce this effect. Furthermore, the rake angle φ defines the crack propagation mode. Larger φ amplitudes favor the opening mode, whereas smaller values promote the shear mode. The COF amplitude also influences the surface quality, with larger COFs producing more profound cutting dimples. Thus, reducing the COF should result not only in lower cutting forces but also in a better surface quality of machined parts.

Chip formation mechanism in machining of Al/SiCp composites based on analysis of particle damage

Particles cracking and debonding are important damage modes that affect the manufacturing processes of Al/SiCp composites. The study of chip formation is the most effective and cheapest way to understand the machining characteristics of a material. Therefore, a comprehensive investigation of the effects of particle damage on the chip formation is of great significance for optimizing the manufacturing processes of Al/SiCp composites. This paper aims to investigate the forming mechanism of particle damage and the effects of particle damage on the chip formation in machining of Al/SiCp composites. The followings are the contributions of this study: (1) According to microscopic observations of chip roots, the forming mechanism of particle damage was revealed. (2) Based on the microscopic observations of cross-section and fracture surface of chips, the effect of particle damage on chip formation was investigated systematically in machining of Al/SiCp composites with varying particle contents and sizes under different cutting conditions. (3) Based on different degrees of particle damage in the chip formation, three novel conceptual models of the chip formation for various fracture types were proposed to visually describe the forming process of chips in machining of Al/SiCp composites.

Digital Twin of Chip Formation

Chip formation in machining is investigated. A relation is established between the type of chip, the type of crystal lattice, and the number of slip systems. A neural-network model of chip formation permits prediction of the type of chip. A smart control system for chip formation is proposed.

Experimental study on the cutting temperature, vibration and chip formation in machining of 316L under dry and flood process

Experimental study on the cutting temperature, vibration and chip formation in machining of 316L under dry and flood process

Chip formation in machining of unidirectional carbon fibre reinforced polymer laminates: FEM based assessment

Finite-element (FE) method offers a low cost virtual alternative to assist in optimisation of critical process parameters in machining of composites. This study is focussed on understanding the mechanics of chip formation in orthogonal cutting of unidirectional (UD) carbon-fibre-reinforced polymer (CFRP) laminates through development of FE models. Machining responses of UD CRFP laminates with fibre orientation of 45° (measured with respect to the cutting direction) are assessed. Modelling of material removal in the form of fragmented chips is considered. Damage initiation is determined using the Hashin stress criterion for the fibre component, while matrix failure predicted using Puck criteria. Subsequent damage evolution events are modelled using a strain-based softening approach to degrade relevant material properties linearly. Primary numerical results compared with experimental data revealed that developed FE models are able to predict global machining responses (i.e. cutting forces) and characterise various discrete damage modes associated with machining response of quasi-brittle CFRP laminates successfully. The models also provide a valuable insight into variation in chip morphology.

A slip-line model for serrated chip formation in machining of stainless steel and validation

Machining of difficult-to-cut materials producing serrated chip formation has generated a significant interest among academic researchers and industry groups because of the need for understanding the fundamental mechanisms to model the process. Therefore, various analytical and numerical models have been developed in the recent past to investigate such machining operations. The slip-line theory is one of the established modeling methods, but slip-line modeling of serrated chip formation has not been investigated adequately. In this study, a new slip-line model for serrated chip formation in machining with rounded cutting edge tool is presented along with its associated hodograph. In addition, Oxley’s theory was integrated to the proposed slip-line model for stainless steel material, and the model was validated by experimental results. A good agreement between the experimental and analytically predicted results was obtained. The proposed slip-line model offers predictions of cutting and thrust forces, ploughing force, maximum and minimum chip thickness values, tool–chip contact length, chip up-curl radius, thickness of the primary shear zone, angular position of the stagnation point, shear strain, shear strain rate at the shear plane, and the prevalent flow stress.

Chip Formation Mechanism in Machining of Carbon Fiber Reinforced Plastic

Machining of carbon-fiber-reinforced plastic (CFRP) is still a challenging due to its inhomogeneous and anisotropic properties, which often lead to damage such as the delamination and the fiber pullout. The chip formation mechanism in machining of CFRP is completely different from the mechanism in metal cutting. In this paper, a two-dimensional macro equivalent homogeneous finite element model is established to simulate the dynamic cutting processes of unidirectional CFRP (UD-CFRP). The anisotropic material constitutive, the initial failure criterion and the damage evolution rule are defined in this model to investigate the material responses under the cutting load. Furthermore, the specific stiffness degradation variables are set to calculate the residual stiffness in cutting process. Failure mechanisms in chip formation in machining of CFRP for 0°, 45°, 90°and 135° fiber orientations are investigated by this model. And the effect of rake angle and the depth of cut on the chip formation are also analyzed. Cutting experiments of CFRP are obtained to observe the chipping process by microscopic observation accordingly. Finally, the chip formation mechanisms in machining of CFRP are summarized as the debonding-bending type and the cutting type. There is serious sub-surface damage in machining of CFRP for 135° fiber orientation.

Finite Element Modeling and Validation of Chip Segmentation in Machining of AISI 1045 Steel

The finite element (FE) method based modeling of chip formation in machining provides the ability to predict output parameters like cutting forces and chip geometry. One of the important characteristics of chip morphology is chip segmentation. Majority of the literature within chip segmentation show cutting speed (vc) and feed rate (f) as the most influencing input parameters. The role of tool rake angle (α) on chip segmentation is limited and hence, the present study is aimed at understanding it. In addition, stress triaxiality's importance in damage model employed in FE method in capturing the influence of α on chip morphology transformation is also studied. Furthermore, microstructure characterization of chips was carried out using a scanning electron microscope (SEM) to understand the chip formation process for certain cutting conditions. The results show that the tool α influences chip segmentation phenomena and that the incorporation of a stress triaxiality factor in damage models is required to be able to predict the influence of the α. The variation of chip segmentation frequency with f is predicted qualitatively but the accuracy of prediction needs improvement.

An enhanced constitutive material model for machining of Ti–6Al–4V alloy

Material failure due to adiabatic shear banding is a characteristic feature of chip formation in machining of Ti–6Al–4V material. In this paper, an enhanced Zerilli–Armstrong (Z-A) based material flow stress model is developed by accounting for the effects of material failure mechanisms such as voids and micro-cracks on the material flow strength during shear band formation. These effects are captured via a multiplicative failure function in the constitutive material flow stress model. The strain and strain rate dependence of the material failure mechanism are explicitly modeled via the failure function. The five unknown constants of the failure function are calibrated using cutting force data and the entire model is verified using separate force, chip segmentation frequency and tool–chip contact length data from orthogonal cutting experiments reported by Cotterell and Byrne (2008a,b). Model predictions of these quantities based on the enhanced material model are shown to be in good agreement with experiments over a wide range of cutting conditions.

Chip Flow and Scaling Laws in High Speed Metal Cutting

Chip formation in machining plays an important role in the cutting process optimisation. Chip morphology often reflects the choice of cutting conditions, the tool wear and by consequences the integrity of the machined surface and tool life. In this study, photographs of the chip morphology during high speed machining of a middle hard steel (C20 similar to AISI 1020) are taken by using a ballistic setup. From these recordings, the evolution of the chip morphology is presented and analysed in terms of cutting conditions. A simplified modeling is then proposed by considering the workpiece material as elastic perfectly plastic. The existence of a scaling law governing the chip morphology in high speed machining is demonstrated. The cutting velocity is shown to have a weak effect at high speed machining as opposed to the well known strong influence of the velocity in the range of low cutting speeds.

Cutting Model in Machining of Al/SiC<sub>p</sub> Metal Matrix Composite

Prediction of shear plane angle is a way for prediction of the mechanism of chip formation, machining forces and so on. In this study, Merchant and Lee-Shaffer theories are used for prediction of shear plane angles and cutting forces in machining of Al/SiCpMMC with 20% of SiC as reinforcement particles. The experimental cutting forces are compared with the calculated cutting force based on shear plane angles extracted from Merchant and Lee-Shaffer theories. The variation of these cutting forces with cutting speed, feed rate and depth of cut has been discussed. The results showed that Merchant theory may be used as a good method for prediction of chip formation in machining of Al/SiCpMMC.

Investigation of Cutting Model in Machining of Al/SiC<sub>p</sub> Metal Matrix Composite

Prediction of shear plane angle is a way for prediction of the mechanism of chip formation, machining forces and so on. In this study, Merchant and Lee-Shaffer theories are used to predict the shear plane angles and cutting forces in machining of Al/SiCpMMC. The experimental cutting forces are compared with the calculated cutting force based on shear plane angles extracted from Merchant and Lee-Shaffer theories. The variation of these cutting forces with cutting speed, feed rate and depth of cut has been discussed. The results show that Merchant theory may be used as a good method for prediction of chip formation in machining of Al/SiCpMMC.

Unusual Applications of Machining: Controlled Nanostructuring of Materials and Surfaces

Abstract A class of deformation processing applications based on the severe plastic deformation (SPD) inherent to chip formation in machining is described. The SPD can be controlled, in situ, to access a range of strains, strain rates, and temperatures. These parameters are tuned to engineer nanoscale microstructures (e.g., nanocrystalline, nanotwinned, and bimodal) by in situ control of the deformation rate. By constraining the chip formation, bulk forms (e.g., foil, sheet, and rod) with nanocrystalline and ultrafine grained microstructures are produced. Scaling down of the chip formation in the presence of a superimposed modulation enables production of nanostructured particulate with controlled particle shapes, including fiber, equiaxed, and platelet types. The SPD conditions also determine the deformation history of the machined surface, enabling microstructural engineering of surfaces. Application of the machining-based SPD to obtain deformation-microstructure maps is illustrated for a model material system—99.999% pure copper. Seemingly diverse, these unusual applications of machining are united by their common origins in the SPD phenomena prevailing in the deformation zone. Implications for large-scale manufacturing of nanostructured materials and optimization of SPD microstructures are briefly discussed.

Modelling orthogonal machining of carbon steels. Part I: Strain hardening and yield delay effects

Previous models of how a metal's flow stress behaviour influences continuous chip formation in machining have described flow stress dependence on strain purely in terms of a strain-hardening exponent. For ferrous metals in their softened state but not for non-ferrous metals there have been systematic differences between predicted and experimental process forces and chip forms. This paper adds yield delay, with its consequent upper yield point and yield drop, to the description of flow stress dependence on strain within a finite element analysis of chip formation. It shows that this reduces the differences between simulated and experimental observations in ferrous machining. However, the size of the yield drop required for complete agreement is perhaps larger than could realistically be expected to occur. More work is still required to model the process with complete accuracy. It is believed to be the first time that yield drop effects have been included in a finite element analysis of the machining process. Further, developments are reported in the radial return method of updating the flow within the finite element method.

Characteristics of cutting forces and chip formation in machining of titanium alloys

Chip formation during dry turning of Ti6Al4V alloy has been examined in association with dynamic cutting force measurements under different cutting speeds, feed rates and depths of cut. Both continuous and segmented chip formation processes were observed in one cut under conditions of low cutting speed and large feed rate. The slipping angle in the segmented chip was 55°, which was higher than that in the continuous chip (38°). A cyclic force was produced during the formation of segmented chips and the force frequency was the same as the chip segmentation frequency. The peak of the cyclic force when producing segmented chips was 1.18 times that producing the continuous chip. The undeformed surface length in the segmented chip was found to increase linearly with the feed rate but was independent of cutting speed and depth of cut. The cyclic force frequency increased linearly with cutting speed and decreased inversely with feed rate. The cutting force increased with the feed rate and depth of cut at constant cutting speed due to the large volume of material being removed. The increase in cutting force with increasing cutting speed from 10 to 16 and 57 to 75 m/min was attributed to the strain rate hardening at low and high strain rates, respectively. The decrease in cutting force with increasing cutting speed outside these speed ranges was due to the thermal softening of the material. The amplitude variation of the high-frequency cyclic force associated with the segmented chip formation increased with increasing depth of cut and feed rate, and decreased with increasing cutting speed from 57 m/min except at the cutting speeds where harmonic vibration of the machine occurs.

Novel microstructures from severely deformed Al–Ti alloys created by chip formation in machining

We present some consequences of Severe Plastic Deformation (SPD) of Al–Ti alloys by chip formation in machining that can enable opportunities for creating novel microstructures. Chips cut from Al-6wt%Ti are composed of a refined dispersion of the fragmented remains of a hitherto coarse Al3Ti embedded in a nanostructured matrix. This multi-phase nanostructured chip material demonstrates considerable resistance to coarsening owing to the thermally stable dispersion of ultra-fine Al3Ti dispersions and thus has promise in structural alloy applications. Furthermore, the Al–Ti machining chips are shown to possess excellent grain refining characteristics, leading to microstructurally refined and homogeneous Al alloy castings. This realization enables a low-cost route for enhancing the efficiency of the grain refiner master alloy systems by exploiting SPD during chip formation.