Chip Formation Process Research Articles

Research on the carbon fibre-reinforced plastic (CFRP) cutting mechanism using macroscopic and microscopic numerical simulations

The essence of cutting carbon fibre-reinforced plastic (CFRP) composites is a process of material failure and chip formation. The mechanism of cutting CFRPs can be explained from the perspective of local removal of material on the microscopic level. The morphology of the chips resulting from the cutting process can be determined from the perspective of the overall failure of the material on the macroscopic level. To reveal the mechanism of cutting CFRPs at both levels, a macroscopic model and a microscopic model are established in this study. Orthogonal cutting is applied in both of the models to illuminate the removal process. Combined with experimental observations, the results that obtained from both the macroscopic and microscopic level revealed the different mechanics of cutting CFRPs for different fibre orientations. For example, the forms of fracture that occur at 0° fibre orientation are primary interface cracking and fibre bending; the resulting chips have long shapes.

Effect of microstructure evolution on chip formation and fracture during high-speed cutting of single phase metals

Microstructure evolution of materials has an important effect on chip formation and fracture process, which is also essential for revealing the mechanism of high-speed cutting. Complex microstructures would make it difficult in analyzing the deformation procedure during cutting process. As a result, in this study, oxygen-free high-conductivity (OFHC) copper, including coarse grains and single phase, is chosen for workpiece material to be machined with high-speed cutting experiments for revealing the cutting mechanisms. Chips and chip roots of OFHC copper under orthogonal cutting conditions with increasing cutting speeds from 750m/min to 3000m/min are collected. The microstructure and fracture characteristics of collected chips are observed by electron backscatter diffraction (EBSD) and scanning electron microscope (SEM), respectively. The results show that the grain refinement and dynamic recrystallization (DRX) are both generated during the cutting process, which lead to the strengthening of mechanical properties and the fracture transformation from ductile to brittle. This research explains the effect of microstructure evolution, especially the transformation of grain itself, on the chip formation and fracture mechanisms.

Interaction between the local tribological conditions at the tool–chip interface and the thermomechanical process in the primary shear zone when dry machining the aluminum alloy AA2024–T351

In this work, a predictive machining theory, based on a finite element model, were applied to dry orthogonal cutting of aluminum alloy AA2024–T351. In order to analyze the effects of chip formation process and local friction coefficient on the thermomechanical load along the tool rake face and the round cutting edge, an Arbitrary Lagrangian Eulerian (ALE) model was developed. To validate the present model, the FE results have been compared to the experimental data for a wide range of cutting speed. This shows a good agreement in both trends and values for cutting forces and tool–chip contact length. The ALE approach appears as an appropriate formulation to reproduce: (i) the tribological conditions corresponding to large values of friction coefficient such as in dry machining of aluminum alloys, and (ii) the material flow process around the round cutting edge. It was observed that a transition from a sliding contact to a sticking–sliding contact occurs when the local friction coefficient and the thermal softening are large enough. Predicted results show also that the decrease of the cutting forces as the cutting speed increases is mainly due to the variation of the tool–chip contact length in terms of cutting velocity. The effect of material flow around the round cutting edge on the distributions of frictional stress and pressure has also been analyzed.

Symulacja procesu formowania wióra z użyciem metody elementów skończonych

Symulacja procesu formowania wióra z użyciem metody elementów skończonych

Dry Machining Aeronautical Aluminum Alloy AA2024-T351: Analysis of Cutting Forces, Chip Segmentation and Built-Up Edge Formation

In this paper, machining aeronautical aluminum alloy AA2024-T351 in dry conditions was investigated. Cutting forces, chip segmentation, and built-up edge formation were analyzed. Machining tests revealed that the chip formation process depends on cutting conditions and tool geometry. So continuous and segmented chips are generated. Under some cutting conditions, built-up edge formation occurs. A predictive machining theory, based on a finite elements method (FEM), was applied to reproduce and explain these phenomena. Thermomechanical behaviors of the work material and the tool-work material interface were considered. Results of the proposed modelling were compared to experimental data for a wide range of cutting speed. It was shown that the feed force is well reproduced by the ALE-FE (arbitrary lagrangian-eulerian finite element) formulation and highly underestimated by the lagrangian finite element (LAG-FE) one. While, the periodic localized shear band, leading to a chip segmentation, is well reproduced with the Lagrangian FE formulation. It was found that the chip segmentation can be correlated to the cutting force evolution using the defined chip segmentation intensity parameter. For the built-up edge (BUE) phenomenon, it was shown that it depends on the contact/friction at the tool-chip interface, and this is possible to simulate by making the friction coefficient time-dependent.

Numerical investigation of the evolution of grit fracture and its impact on cutting performance in single grit grinding

The study of single grit grinding with different geometries is important for understanding the micro-cutting behavior and material removal mechanism during grinding. However, the geometry of the grit changes during the wear process. The most fatal wear form responsible for the change in geometry is grit fracture as it causes considerable material loss instantaneously. This paper presents a new method to simulate single grit grinding with the fracture wear effects incorporated. The simulation procedure consists of three phases. The grinding force is calculated in phase 1, the grit fracture wear is simulated in phase 2, and the geometry of the grit after fracture wear is updated in phase 3. The evolution of grit fracture and its impact on cutting performance are studied by recycling the simulation procedure until the grit wears out. The results obtained reveal that the fracture wear is primarily caused by the maximum tensile stress along the rake surface or inside the grit. The resultant grinding force fluctuates during the chip formation process and is controlled by the number of cutting edges and the effective area of the flank surface. It decreases rapidly at the initial wear stage and varies with the dulling and self-sharpening action induced by the fracture wear. The volume of grinding chip decreases with an increase in the number of micro-cutting edges, which may result from a decrease in the ploughing effect.

Controlling the type and the form of chip when machining steel

The type of the chip produced in the process of machining influences many factors of production process. Controlling the type of chip when cutting metals is important for producing swarf chips and for easing its utilization as well as for protecting the machined surface, cutting tool and the worker. In the given work we provide the experimental data on machining structural steel with implanted tool. The authors show that it is possible to control the chip formation process to produce the required type of chip by selecting the material for machining the tool surface.

Treatment of products made of polymeric materials

The properties of polymeric materials are considered from the point of view of processability. The differences of the chip formation process during the treatment of products made of polymeric materials compared to the treatment of metal products are shown. The types of chips formed in the process of cutting plastics are studied, which, as during the treatment of metals, yield information on the phenomena occurring in the zone of cutting (deformations and temperatures) and the quality of the treated surfaces. The empirical dependences of the forces of cutting on the treated material, the material of the cutting edge of a tool, and its geometrical parameters are given. The problems of the wear of tools during the treatment of polymeric materials and the features typical for the treatment of polymeric materials by cutting are considered.

Influence of friction models on FE simulation results of orthogonal cutting process

It is well-known that the reliability of finite element (FE) simulation results of cutting processes depends mainly on two factors: implementation of a well-defined constitutive model which can properly represent the severe deformation in chip formation process as well as the viability of the relation adopted to simulate the frictional condition at the tool-chip interface. In the current study, a systematic approach is presented to evaluate the performance of various friction models in three different FE commercial codes: Deform 2D, Abaqus/Explicit and AdvantEdge. The frictional condition was analysed for two uncoated cemented carbide-plain carbon steel combinations: K10/AISI 1045 and H13A/AISI 1080. The results indicated that approximately similar ranges of minimum average error in simulation responses can be achieved, independently of the FE code used for simulation of the chip formation process and for both tool-work material combinations. The reasons for this observation were critically discussed.

Specific Features of Chip Making and Work-piece Surface Layer Formation in Machining Thermal Coatings

A wide range of unique engineering structural and performance properties inherent in metallic composites characterizes wear- and erosion-resistant high-temperature coatings made by thermal spraying methods. This allows their use both in manufacturing processes to enhance the wear strength of products, which have to operate under the cyclic loading, high contact pressures, corrosion and high temperatures and in product renewal. Thermal coatings contribute to the qualitative improvement of the technical level of production and product restoration using the ceramic composite materials. However, the possibility to have a significantly increased product performance, reduce their factory labour hours and materials/output ratio in manufacturing and restoration is largely dependent on the degree of the surface layer quality of products at their finishing stage, which is usually provided by different kinds of machining. When machining the plasma-sprayed thermal coatings, a removing process of the cut-off layer material is determined by its distinctive features such as a layered structure, high internal stresses, low ductility material, high tendency to the surface layer strengthening and rehardening, porosity, high abrasive properties, etc. When coatings are machined these coating properties result in specific characteristics of chip formation and conditions for formation of the billet surface layer. The chip formation of plasma-sprayed coatings was studied at micro-velocities using an experimental tool-setting microscope-based setup, created in BMSTU. The setup allowed simultaneous recording both the individual stages (phases) of the chip formation process and the operating force factors. It is found that formation of individual chip elements comes with the multiple micro-cracks that cause chipping-off the small particles of material. The emerging main crack in the cut-off layer of material leads to separation of the largest chip element. Then all the stages of chip element formation are cycled. Fluctuations of the cutting force components completely repeat all the stages of local destruction and formation of individual chip elements. Studies have shown that with increased thickness of the cut-off layer the main crack develops below the cut-off line thus significantly affecting the quality of the machined surface: emerging cracks, cavities, chips, and other defects that significantly reduce the product performance. In machining the plasma-sprayed coatings, their high tendency to strengthening and rehardening because of the cutting action has a great impact on the surface quality. This is evident as a loss of the elastic equilibrium state stability and as a destruction of the work-piece surface layer (chipping, peeling, flaking). With increasing curvature of the machined surface (e.g., decreasing radius of cylindrical billet) the surface layer is increasingly prone to destruction. Specific problems are cutting fluids used in grinding the plasma-sprayed coatings. Machining in this case comes with saturated liquid vapours formed in the surface layer of a billet under high pressure. With a pressure drop on the tool-side in cutting there is such an intensity of vaporization that micro- and macro-fractures of the machined work-piece surface can be initiated.

Processing outcomes of the AFM probe-based machining approach with different feed directions

We present experimental and theoretical results to describe and explain processing outcomes when producing nanochannels that are a few times wider than the atomic force microscope (AFM) probe using an AFM. This is achieved when AFM tip-based machining is performed with reciprocating motion of the tip of the AFM probe. In this case, different feed directions with respect to the orientation of the AFM probe can be used. The machining outputs of interest are the chip formation process, obtained machined quality, and variation in the achieved channel depth. A three-sided pyramidal diamond probe was used under load-controlled conditions. Three feed directions were first investigated in detail. The direction parallel to and towards the probe cantilever, which is defined as “edge forward”, was then chosen for further investigation because it resulted in the best chip formation, machining quality, and material removal efficiency. To accurately reveal the machining mechanisms, several feed directions with different included angles for the pure edge-forward direction were investigated. Upon analysis of the chips and the machined nanochannels, it was found that processing with included angles in the range 0–30° led to high-quality channels and high material-removal efficiency. In this case, the cutting angles, such as the rake angle, clearance angle, and shear angle, have an important influence on the obtained results. In addition, a machining model was developed to explain the observed machined depth variation when scratching in different feed directions.

A numerical approach on parametric sensitivity analysis for an aeronautic aluminium alloy turning process

The understanding of physical parameters of machining processes of aerospace grade aluminium alloy is always of prime importance. The main concern is always to understand the chip formation process and the resultant cutting force experienced by the tool due to different parameters like cutting speeds, feed rate, friction coefficient and tool rake angle etc. The finite element analysis has replaced many expensive and time consuming physical machining processes. In the present work, an extensive study of different parameters affecting the turning process of aluminium alloy (A2024-T351) is performed using finite element analysis. The Johnson-Cook ductile material model based on coupled plasticity and damage evolution is employed to simulate the cutting process. The authenticity of the performed simulation work is verified by comparing the simulation results with available experimental data on machining of aluminium alloy (A2024-T351). DOI: http://dx.doi.org/10.5755/j01.mech.22.2.12825

Analysis of chip morphology and surface topography in modulation assisted machining

Modulation assisted machining (MAM), superimposing a controlled tool modulation in the feed direction of conventional machining process, can change the chip morphology and the surface topography of machined components, and finally affect the functional performances of the components. This paper is dedicated to gaining a better understanding of the chip and surface formation processes in MAM. Geometrical analysis of the tool path in face turning configuration with MAM is performed, revealing how discrete chips are generated and presenting the effects of modulation conditions on chip morphology and undeformed chip thickness. Based on the chip formation analysis, an analytical model for prediction of surface topography is developed, which takes into account tool geometries, cutting conditions, modulation conditions and the effects of plastic side flow. By using the proposed model, the influences of modulation conditions on surface topographies are shown qualitatively by laser microscope, and are analyzed quantitatively through a set of three-dimensional (3D) surface amplitude parameters. Finally, a series of turning experiments is carried out to verify the prediction of surface topography. Errors between the measured results and the predicted results are within 20% for most conditions, and the underlying sources of these errors are analyzed. This paper can serve as a theoretical basis for the further controlling of chip morphology and surface topography.

Morphology of the Chip Formation at Orthogonal High Speed Milling of AISI H13

High-speed cutting (HSC) or high-speed machining (HSM) is an issue that the scientists deals with in long-term. To demonstrate the explicitness, that a full HSC machining process is considered, it is necessary to monitor the series of factors. In particular, the process of chip formation, cutting forces, cutting temperature, vibration, tool life and surface finish quality in relation to the method of machining, machined material and its properties. The article deals with the detailed analysis and evaluation of the chip formation in order to determine the hard area, transition area and veritable HSC machining. The evaluation process is based on the proposed experimental model, which is confronted with the measurement results.

Dynamic simulation of chip formation in the process of cutting

This work examines the simulation of chip formation during the process of cutting. An analysis of complex rheological models enabled a set of assumptions to be considered, thereby substantiating a hypothesis relating to the chip formation process. The studies demonstrated that the chip formation process, taking into account the plastic deformation and destruction of metal in the local zone, is most appropriately represented by a rheological model in the form of a series connection of elastic-ductile-plastic relaxing medium of Ishlinskiy (reflecting the process of primary deformation of metal from the cut off layer) and the medium of Voigt with two elastic-dissipative elements (representing the process of deformation and frictions from the convergent shaving). The attained complex rheological model served as the basis for constructing a representative dynamic model for chip formation process.

Effects of External Hydrostatic Pressure on Orthogonal Cutting Characteristics

In this paper, effects of external hydrostatic pressure on the cutting characteristics are investigated. Orthogonal cutting experiments are conducted in a high pressure chamber using four kinds of materials; two of them are brittle materials and the others are ductile materials. Chip formation processes of soda glass specimen are studied by in-situ observation. It is confirmed that chip formation style changes from the crack type to the segmented chip type, then to the continuous chip type with the increase of hydrostatic pressure. Furthermore, cutting forces under various hydrostatic pressures are measured, and effects of hydrostatic pressure on the cutting forces are studied. It is found that hydrostatic pressure increases the cutting force in the brittle mode cutting of glasses, but does not affect the cutting force in ductile mode cutting. In case of ductile materials, hydrostatic pressure increases the cutting force of polycarbonate too, but does not affect the cutting force of pure aluminum. Based on those experimental results, mechanism of hydrostatic pressure effects on cutting characteristics is discussed.

Numerical modeling of stacked composite CFRP/Ti machining under different cutting sequence strategies

Stacked composite CFRP/Ti is identified as an innovative structural configuration for manufacturing the key aircraft components favoring energy saving in the modern aerospace industry. Machining of this composite-to-metal alliance exhibits the most challenging task in manufacturing community due to the disparate natures of each phase involved and their respective poor machinability. Since the experimental studies are highly cost and time consuming, the numerical approach should be a capable alternative to overcoming the several technical limitations involved. In this research, an original FE model was developed to simulate the complete chip formation process when orthogonal cutting (OC) of hybrid CFRP/Ti stacks. Different constitutive models and failure criteria were implemented into the Abaqus/Explicit code to construct the entire machining behavior of the stacked composite material. The stack model was built to replicate accurately the key physical phenomena activated in the hybrid cutting operation. Special concentration was made on the comparative studies of the effects of different cutting-sequence strategies on the machining responses induced by CFRP/Ti cutting. The numerical results highlighted the significant role of cutting-sequence strategy in affecting the final machined surface morphology and subsurface damage extent, and hence emphasized the importance of selecting reasonable cutting-sequence strategy for hybrid CFRP/Ti machining.

Tool Life Extension Methods for Cut-off Tools Made of High-speed Steel

The paper presents tool life extension methods applied to cut-off tools made of high-speed steel. Despite the wide application of cutting tools made of sintered carbides, which is becoming the main cutting material, including the coated tools, there still remain the applications of high-speed steel cutting tools for low cutting speed machining (i.e. screw taps, reamers, broaching tools, cutting off tools). Therefore the improving of their cutting ability is important to be researched. The paper involves the application of selected modification methods for the increasing of the tool life in operating conditions, i.e. in manufacturing of ball bearing rings from the bar raw product. Moreover, the paper introduces and evaluates the results obtained by individual methods (tool mechanical and physical modifications) finding the reasons of longer tool-lives for example by analysing the metallographic microsections of chip formation process.

Current Trends in Machinability Research

The manufacturing index of a country relies on the quality of manufacturing research outputs. The emergence of new materials such as composites and multi component alloy has replaced traditional materials in certain design application. Materials with properties like high strength to weight ratio, fatigue strength, wear resistance, thermal stability and damping capacity are a popular choice for a design engineer. Contrary, the manufacturing engineer is novice to the science of machining these materials. This paper is an attempt to focus on the current trends in machinability research and an addition to the existing information on machining. The paper consist of information on machining Austempered Ductile Iron (ADI), Duplex Stainless Steel and Nano-Structured Bainitic Steel. The various techniques used to judge the machinability of these materials is described in this paper. Studying the chip formation process in duplex steel using a quick stop device, metallographic analysis using heat tinting of ADI and cutting force analysis of Nano-structured bainitic steel is discussed.

SPH Meshless Simulation of Orthogonal Cutting of AA6060-T6

A modern meshless method known as Smooth Particle Hydrodynamics (SPH) was involved in achieving numerical simulation of chip formatting during the orthogonal cutting of AA6060-T6 alloy with the aim of finding a convenient method for investigating the chip formation and reducing the costs of experimental research by involving numerical simulation in order to get information about the parameters describing the process. Based on a few experimental orthogonal cutting results the procedure to achieve a proper numerical simulation of the chip formation process is presented. The procedure and the results may be applied when simulation data and prognosis data about machining AA6060-T6 data are needed.