Simulation of cutting process in peripheral milling by predictive cutting force model based on minimum cutting energy

The cutting force and the chip flow direction in peripheral milling are predicted by a predictive force model based on the minimum cutting energy. The chip flow model in milling is made by piling up the orthogonal cuttings in the planes containing the cutting velocities and the chip flow velocities. The cutting edges are divided into discrete segments and the shear plane cutting models are made on the segments in the chip flow model. In the peripheral milling, the shear plane in the cutting model cannot be completely made when the cutting point is near the workpiece surface. When the shear plane is restricted by the workpiece surface, the cutting energy is estimated taking into account the restricted length of the shear plane. The chip flow angle is determined so as to minimize the cutting energy. Then, the cutting force is predicted in the determined chip flow model corresponding to the workpiece shape. The cutting processes in the traverse and the contour millings are simulated as practical operations and the predicted cutting forces verified in comparison with the measured ones. Because the presented model determines the chip flow angle based on the cutting energy, the change in the chip flow angle can be predicted with the cutting model.     

Stability lobes for general turning operations with slender tools in the tangential direction

During the turning of large and heavy cases and rings, the tool must be cantilevered over long distances, and chatter due to modes in the tangential direction may occur. This paper proposes a numerical method based on a nonlinear cutting force model, which includes the effects of the cutting parameters to construct precise stability charts for this special machining case. This method has been successfully applied to general cutting geometries in rough and medium longitudinal turning operations, assuming a rigid workpiece and a flexible tool. This study proposes a dynamic model to implement the effects of the tangential mode on chip regeneration in the regenerative plane based on an experimentally obtained dynamic displacement factor. From the simulations and experimental results, the model provides a reliable approach to obtain chatter-free turning conditions.     

Analytical modeling of turn-milling process geometry,kinematics and mechanics

This paper presents an analytical approach for modeling of turn-milling which is a promising cutting process combining two conventional machining operations; turning and milling. This relatively new technology could be an alternative to turning for improved productivity in many applications but especially in cases involving hard-to-machine material or large work diameter. Intermittent nature of the process reduces forces on the workpiece, cutting temperatures and thus tool wear, and helps breaking of chips. The objective of this study is to develop a process model for turn-milling operations. In this article, for the first time, uncut chip geometry and tool–work engagement limits are defined for orthogonal, tangential and co-axial turn-milling operations. A novel analytical turn-milling force model is also developed and verified by experiments. Furthermore, matters related to machined part quality in turn-milling such as cusp height, circularity and circumferential surface roughness are defined and analytical expressions are derived. Proposed models show a good agreement with the experimental data where the error in force calculations is less than 10% for different cutting parameters and less than 3% in machined part quality analysis.     

Contour finish turning operations with coated grooved tools: Optimization of machining performance

This paper presents a new methodology for optimization of machining performance in contour finish turning operations. Two machining performance measures, chip breakability and surface roughness, are considered as optimization criteria due to their importance in finishing operations. Chip breakability covers two major factors: chip shape and size. Comprehensive case studies are presented to demonstrate the determination and application of optimal cutting conditions through experimental validation.     

Dynamic modeling of cutting acoustic emission via piezo-electric actuator wave control

The fundamental understanding of the dynamic behavior of acoustic emission signals in relation to machining process parameters plays an important role in the automation monitoring and control of metal cutting operations. This paper presents an analytical model for acoustic emission dynamics in orthogonal cutting with chip thickness variation. An analytical expression for acoustic emission generated in turning is established as an explicit function of the cutting parameters and tool/workpiece geometry. Based on the theoretical static cutting acoustic emission model, the generation of the RMS acoustic emission is formulated as the function of three process parameters, namely tool displacement, cutting speed, and rake angle. The incremental change of the RMS acoustic emission is related to the chip formation process in an elemental cutting area and it is characterized by the dynamic variation of these process parameters. The analysis of the RMS acoustic emission is then extended into the dynamic transfer function between tool displacement and RMS acoustic emission. Experimental results via simultaneous tool displacement control by piezo-electric actuator and measurement of RMS AE generated during cutting confirm the validity of the analytical acoustic emission model in orthogonal cutting process.     

基于振动传感器的车削加工表面粗糙度预测

文章通过深入研究车床精车外圆时刀具和工件存在相对振动的情况下,加工工件表面轮廓的形成机理,探索出一种建立表面粗糙度值预测模型的新方法。并结合传感器技术,搭建一个能用于测量振动信号的实验平台,通过比较表面粗糙度的预测值和实测值,证明预测模型有一定的准确度。     

Improving tool life by varying resilience and damping properties in close proximity of the cutting edge

During straight turning of workpieces with non-cylindrical geometry or during milling operations on workpieces with hard surfaces such as the scale layer on cast iron the cutting edge has to withstand high recurrent impact loads. These loads can destroy the cutting edge rather spontaneously than by continuous wear. Commonly used criterions such as a flank or crater wear are not suitable. As part of the research presented in this paper mechanical system properties such as resilience and damping are varied and the influence on tool life is presented. Variation was done passively by changing the material of a shim which was positioned directly under the cutting insert and actively by using a piezo actuator to change the pressure of an oil reservoir close to the cutting insert. The results of this research confirm the potential advantages of a properly adjusted resilience close to the cutting edge. However, a single set of optimal properties for different machining operations or workpiece/tool combinations cannot be derived.     

Linear analysis of chatter vibration and stability for orthogonal cutting in turning

The productivity of high speed milling operations is limited by the onset of self-excited vibrations known as chatter. Unless avoided, chatter vibrations may cause large dynamic loads damaging the machine spindle, cutting tool, or workpiece and leave behind a poor surface finish. The cutting force magnitude is proportional to the thickness of the chip removed from the workpiece. Many researchers focused on the development of analytical and numerical methods for the prediction of chatter. However, the applicability of these methods in industrial conditions is limited, since they require accurate modelling of machining system dynamics and of cutting forces. In this study, chatter prediction was investigated for orthogonal cutting in turning operations. Therefore, the linear analysis of the single degree of freedom (SDOF) model was performed by applying oriented transfer function (OTF) and \tau decomposition form to Nyquist criteria. Machine chatter frequency predictions obtained from both forms were compared with modal analysis and cutting tests.     

High-pressure jet-assisted cooling: a new possibility for near net shape turning of decarburized steel

Ultra-high-pressure cooling (UHPC) in turning operations is an effective method for achieving higher productivity. Previous research has demonstrated that the introduction of a high-pressure fluid jet into the gap between the tool and chip interface can control chip form and breakage. The present work shows the effect of UHPC in the turning of near net shape (NNS) decarburized parts. The workpiece material properties are strongly influenced by the loss of carbon atoms to a depth of up to 1 mm, due to the aggressive atmosphere during forming (decarburization). The extremely soft material makes chips difficult to control. Consequently, productivity decreases since the machine must be frequently stopped in order to manually remove the chips from the working area. The results show the influence of UHPC on chip form, surface topography and tool life when turning decarburized parts close to NNS. An interesting observation was that the combination of small cutting depth (near net shape) and soft material (decarburization) allowed for the presence of built-up edge formation, even at a high cutting speed.     

A study on the effects of vibrations on the surface finish using a surface topography simulation model for turning

In this paper, a surface topography simulation model is established to simulate the surface finish profile generated after a turning operation. The surface topography simulation model incorporates the effects of the relative motion between the cutting tool and the workpiece with the effects of tool geometry to simulate the resultant surface geometry. It is experimentally shown that the surface topography simulation model can properly simulate the surface profile generated by turning operations. The surface topography simulation model is used to study the effects of vibrations on the surface finish profile. It is found that the vibration frequency ratio is a more important vibration parameter than the vibration frequency on the characterization of the surface finish profile. The vibration frequency ratio is the ratio between the vibration frequency and the spindle rotational speed.     

Development of a chip flow model for turning operations

A model is presented which predicts the chip flow direction in turning operations with nose radius tools under oblique cutting conditions. Only the tool cutting edge geometry and the cutting conditions (feed and depth of cut) are required to implement the model. An experimental study has verified the chip flow model and shown that the model's predictions are in good agreement with the experimental results.     

Generalized dynamic model of metal cutting operations

This paper presents a unified mathematical model which allows the prediction of chatter stability for multiple machining operations with defined cutting edges. The normal and friction forces on the rake face are transformed to edge coordinates of the tool. The dynamic forces that contain vibrations between the tool and workpiece are transformed to machine tool coordinates with parameters that are set differently for each cutting operation and tool geometry. It is shown that the chatter stability can be predicted simultaneously for multiple cutting operations. The application of the model to single-point turning and multi-point milling is demonstrated with experimental results.     

Modelling and simulation of chatter in milling using a predictive force model

A predictive time domain chatter model is presented for the simulation and analysis of chatter in milling processes. The model is developed using a predictive milling force model, which represents the action of milling cutter by the simultaneous operations of a number of single-point cutting tools and predicts the milling forces from the fundamental workpiece material properties, tool geometry and cutting conditions. The instantaneous undeformed chip thickness is modelled to include the dynamic modulations caused by the tool vibrations so that the dynamic regeneration effect is taken into account. Runge–Kutta method is employed to solve the differential equations governing the dynamics of the milling system for accurate solutions. A Windows-based simulation system for chatter in milling is developed using the predictive model, which predicts chatter vibrations represented by the tool-work displacements and cutting force variations against cutter revolution in both numerical and graphic formats, from input of tool and workpiece material properties, cutter parameters, machine tool characteristics and cutting conditions. The system is verified with experimental results and good agreement is shown.     

Influence of asymmetric cutting edge roundings on surface topography

For finishing operations in machining, hardened steel hard turning can compete with grinding operations by means of accuracy and productivity. In the past research focussed on the effect of process parameters and tool macro geometry on the resulting surface roughness. Recent investigations show, that the cutting edge micro geometry is an important factor to influence surface quality. The knowledge generated by new methods displays the importance of asymmetric cutting edge roundings on cutting forces, chip formation and tool life. It is known, that chip formation also affects the resulting surface quality. Therefore, this paper investigates the effect of asymmetric cutting edge roundings on the resulting surface roughness in hard turning of roller bearing inner rings. Cutting tests with differently shaped cutting edges and two different feed values are conducted. The resulting surface roughness is measured. The consequent surface quality is explained by geometric coherences between uncut chip thickness and stresses along the cutting edge and the effect of material side flow. It is found, that the cutting edge geometry and the resulting stress distribution around the cutting edge affects the generated surface quality.     

A thermo-mechanical model of dry orthogonal cutting and its experimental validation through embedded micro-scale thin film thermocouple arrays in PCBN tooling

Cutting temperature and its distribution in the cutting zone are a critical factor that significantly affects tool life and degrades part accuracy during metal removal operations. However, issues surrounding their modeling and experimental validation in the immediate cutting zone still remain an unresolved issue. A major impediment is the unavailability of adequate temperature measurement methods with sufficient temporal and spatial resolution to measure actual temperatures and validate predictive models. In this paper, a model for the dry orthogonal cutting process with thermo-mechanical coupling effects, i.e., interactions between the stress state, strain rates and the temperature softening of material in the plastic deformation zone, is proposed to predict cutting temperature distribution in the cutting zone. The feasibility and prediction accuracy of the model is verified by experimental measurements through Thin Film Thermocouple (TFTC) arrays embedded at the immediate vicinity of the cutting zone into Polycrystalline Cubic Boron Nitride (PCBN) tooling. The experimental verification is performed under hard turning conditions. It has been shown that the predictions of the proposed model are in very close agreement with the experimentally measured results including the cutting forces, chip thickness and cutting temperature distributions on the rake and flank faces in the cutting zone. Furthermore, the modeling results have also provided an essential understanding on the stress distributions at the tool/chip and work/tool interfaces as well as of the nature of the chip flow velocity along the rake face of the cutting tool.     

A worn tool force model for three-dimensional cutting operations

Previous studies have shown that there is a region on the flank of a worn cutting tool where plastic flow of the workpiece material occurs. This paper presents experimental data which shows that in three-dimensional cutting operations in which the nose of the tool is engaged, the region of plastic flow grows linearly with increases in total wearland width. A piecewise linear model is developed for modeling the growth of the plastic flow region, and the model is shown to be independent of cutting conditions. A worn tool force model for three-dimensional cutting operations that uses this concept is presented. The model requires a minimal number of sharp tool tests and only one worn tool test. An integral part of the worn tool force model is a contact model that is used to obtain the magnitude of the stresses on the flank of the tool. The force model is validated through comparison to data obtained from wear tests conducted over a range of cutting conditions and workpiece materials. It is also shown that for a given tool and workpiece material combination, the incremental increases in the cutting forces due to tool flank wear are solely a function of the amount and nature of the wear and are independent of the cutting condition in which the tool wear was produced.     

Influence of the direction and flow rate of the cutting fluid on tool life in turning process of AISI 1045 steel

High-pressure coolant (HPC) delivery is an emerging technology that delivers a high-pressure fluid to the tool and machined material. The high fluid pressure allows a better penetration of the fluid into the tool–workpiece and tool–chip contact regions, thus providing a better cooling effect and decreasing tool wear through lubrication of the contact areas.The main objective of this work is to understand how the tool wear mechanisms are influenced by fluid pressure, flow rate and direction of application in finish turning of AISI 1045 steel using coated carbide tools.The main finding was that when cutting fluid was applied to the tool rake face, the adhesion between chip and tool was very strong, causing the removal of tool particles and large crater wear when the adhered chip material was removed from the tool by the chip flow. When cutting fluid was not applied to the rake face, adhesion of chip material to the face did occur, but was not strong enough to remove tool particles as it moved across the face, and therefore crater wear did not increase.     

Control of chip flow with guide grooves for continuous chip disposal and chip-pulling turning

This paper presents a new chip control method with guide grooves formed on the rake face to realize continuous chip disposal and chip-pulling turning. Chips are conventionally broken using chip breakers during turning operations for disposal. However, chips of highly ductile materials or thin chips generated in finishing can not be broken easily. In order to prevent the chips from jamming up, the authors propose to continuously guide the chips away from the cutting point. Special tool tips were developed and tested for guiding the chip. Chip controllability and mechanics of the chip-guided cutting are discussed in the present research.     

Simulation of milling tool vibration trajectories along changing engagement conditions

This paper presents a simulation system, which is able to model engagement conditions as a syntactical geometric model along arbitrary NC-programs. This modeling approach allows the feedback of tool deflections into the model of the chip form, which enables the simulation of regenerative tool vibrations along changing engagement conditions. Methods from the field of computer graphics allow a fast analysis of the chip forms as well as a fast cutting force calculation, which is essential to speed up this time-domain simulation system. Experiments show a good agreement of calculated and measured tool trajectories even along sudden changes of the radial immersion. Furthermore, a geometric model of the workpiece is applied, which is able to represent the surface structure resulting from a vibrating cutting tool. Thereby, chatter marks as well as the effects that occur along changing engagement conditions can be modelled and rendered realistically.     

Measurement of specific cutting energy for evaluating the efficiency of bandsawing different workpiece materials

In cutting operations by multipoint cutting tools such as bandsawing, the layer of material removed per tooth (5–30 μm) is usually less than or equal to the cutting edge radius (5–15 μm). Furthermore, the bandsaw tooth is also restricted since it has to accommodate the chip in a gullet of limited size. This situation can lead to inefficient metal removal by a combination of piling up, discontinuous chip formation and ploughing action in contrast to the cutting operations by most of the single point cutting tools (e.g., turning). Specific Cutting Energy (E_SP) is a better way of measuring the efficiency of the metal cutting process compared to the other processes such as determining tool wear, cutting forces, chip ratio, etc. This paper reports on the full bandsawing tests of three different workpiece materials (Ball bearing steel, Stainless steel and Ni–Cr–Mo steel). The increase of E_SP throughout the life of the bandsaw reflected the degradation of the cutting performance due to the wear of the cutting edge geometry for Ball bearing and Stainless steels. However, there was no increase in E_SP when cutting Ni–Cr–Mo steel, which could be explained by the existence of a large protective built-up edge and/or minimal blade wear. The variation of the E_SP in different workpiece materials will also provide valuable information for bandsaw manufacturers and end users to estimate machinability characteristics for selected workpieces.