Development of a thermo-viscoplastic cutting model using finite element method

In this paper, a cutting model is developed by applying the thereto-viscoplastic FEM (finite element method) to analyze the mechanics of steady state orthogonal cutting process. The model is capable of dealing with free chip geometry and chip-tool contact length. The coupling with thermal effects is also considered. In calculating temperature distributions, the “upwind” scheme is employed to remove spurious oscillations that occur in the solution and therefore it is possible to analyze high speed metal cutting. Orthogonal cutting experiments are performed for 0.2% carbon steel to validate the cutting model. Tool forces are measured and the results are discussed in comparison with the results of the FEM analysis.     

A thermo-elastic-plastic model with special elements in a cutting process with tool flank wear

A coupled model of the thermo-elastic-plastic material under large deformation for orthogonal cutting with a pre-honed land simulating tool flank wear is constructed. The stress concentration of workpiece at tool tip is especially considered. The singular elements are utilized in the workpiece around the tip of the tool to simulate the stress concentration. The elastic-plastic and the geometric stiffness matrices were derived based on the special shape function. The cutting tool is incrementally advanced forward in a step-by-step process from an incipient stage of tool-workpiece engagement to a steady state of chip formation. A numerical technique gradually reducing displacement was developed to deal with a new generative node to contact with the tool flank.     

Experimental and numerical characterisation of heat flow during flame cutting of thick steel plates

Temperatures measurements during flame cutting of a thick steel plate and measurements of the extension of the fusion and heat affected zones and Vickers hardness after cutting have been performed. Additionally, a 3-D thermal model for simulation of flame-cutting has been developed. For the sake of simplicity, the model depends only on two parameters: (i) the heat density within the flame, and (ii) the heat transfer coefficient within the air gap that forms behind the cut. The results show that the model is able to properly reproduce the measured temperature curves and the heat affected zone with an input power in the same range of those reported in the literature. A process efficiency of 26.5% is found in the steady state regime of flame-cutting.     

Development of a virtual machining system, part 3: cutting process simulation in transient cuts

In Parts 1 and 2 of this three-part paper, a mechanistic cutting force model was developed and machined surface errors for steady cuts under fixed cutting conditions were predicted. The virtual machining system aims to simulate and analyze the machining and the machined states in a general flat end-milling process. This frequently involves transient as well as steady cuts. Therefore, a method for simulating the cutting process of transient cuts needs to be developed to realize the virtual machining system concept. For this purpose, this paper presents a moving edge-node (ME) Z-map model for the cutting configuration calculation. The simulation results of four representative transient cuts in two-dimensional pocket milling and an application of off-line feed-rate scheduling are also given.

In transient cuts, the cutting configurations that are used to predict the cutting force vary during the machining operation. The cutting force model (Part 1) and surface error prediction method (Part 2) were developed for steady cuts; these are extended to transient situations using the ME Z-map model to calculate the varying cutting configurations efficiently. The cutting force and surface errors are then predicted. To validate the feasibility of the proposed scheme, the measured and predicted cutting forces for transient test cuts were compared. The predicted surface error maps for transient cuts were constructed using a computer simulation. Also, off-line feed-rate scheduling is shown to be more accurately performed by applying the instantaneous cutting coefficients that were defined in Part I.     

The effect of tool nose radius in ultrasonic vibration cutting of hard metal

A tool edge with a small nose radius can alleviate the regenerative chatter. In general, it is important for conventional cutting to use the smallest possible tool nose radius. However, a sharp tool shape has an adverse effect on tool strength and the instability of machining process still occurs. Previous researches have shown that vibration cutting has a higher cutting stability as compared with conventional cutting. In the present paper, the influence of tool nose radius on cutting characteristics including chatter vibration, cutting force and surface roughness is investigated by theory. It is found from the theoretical investigation that a steady vibration created by motion between the tool and the workpiece is still obtained even using a large nose radius in vibration cutting. This article presents a vibration cutting method using a large nose radius in order to solve chatter vibration and tool strength problem in hard-cutting. With a suitable nose radius size, experimental results show that a stable and a precise surface finish is achieved.     

An approach for on-line cutting edge stress estimation

Cutting edge deteriorations are attributed to higher mechanical and thermal stresses working on it during metal cutting. However, the stress estimation is a difficult task, especially when on-line estimation is desired. This paper presents a new approach for cutting edge mechanical stress estimation and load simulation. The approach can be applied in the implementation of on-line stress estimation to the study of stress state at the cutting edge and the strategy of real-time edge deterioration monitoring. The approach is based upon cutting force measurement and cutting edge load analysis. The concept of load function and related stress are introduced to estimate stresses working on the cutting edge. With multiple regression, the related stresses can be estimated on-line, from which the actual stresses can be estimated. The method for two-dimensional stress estimation of a cutting edge is illustrated and the principle can also be applied to three-dimensional stress estimation of a cutting edge. The experimental results, obtained with a developed real-time monitoring system and their analysis with respect to cutting edge stress estimation and analysis under different processing phenomena are also reported.     

Relationship between plasma arc cutting acoustic and cut quality

Abstract

The tremendous acoustic signal exiting during the plasma arc cutting process includes a lot of information about this process and has a close relation with cut quality. To investigate the relationship between the plasma arc cutting acoustic and cut quality, a number of experiments have been carried out. In the present study, cut quality by plasma arc is described by top and bottom kerf widths, bevel angle, and attached dross state, and the relationship between the evaluation items for cut quality and the SPL (sound pressure level) of the cutting acoustic is investigated in detail. It is shown that the SPL reaches a maximum as the bottom kerf width equals the diameter of the plasma arc potential core. The attached dross and kerf widths in a state of free dross obviously affect the low and high frequency components of the plasma arc cutting acoustic, respectively. These results also suggest the possibility of designing an acoustic-based monitoring system for the plasma arc cutting process.     

Significance of residual stress in PVD-coated carbide cutting tools

The performance of PVD-coated carbide cutting tools is influenced by their residual stress state, where coating and substrate subsurface have to be considered. The substrate stress is the result of different impacts caused by pre-coating processes and the PVD-coating itself. This presentation demonstrates the significance of residual stress in coating and substrate as well as the influence of each step of a conventional commercial process chain on the respective residual stress state for the manufacture of PVD-coated carbide cutting tools. Alterations of the process chain for tool micro geometry preparation by laser beam removal are considered.     

Three-dimensional cutting process analysis with different cutting velocities

This paper uses the large deformation large strain finite-element theory, the updated Lagrangian formulation and the incremental theory approach to develop a 3D elastic-plastic analytical model that examines metal cutting on the tool tip and twin nodes on the machined face. The geometric position and the critical value of strain energy density, combined with twin node treatment, are also introduced to serve as the continuous chip separation criterion.

Finally, the 3D low-velocity cutting condition of mild steel was explored to analyze changes in the appearances of the workpiece and the chip, the distribution of stress and strain, and the progress of changes in the cutting force. The impact of different cutting velocities and the initial conditions of the residual stress were studied to understand the impact of various cutting conditions on the machined workpiece. The numerical average cutting forces are compared with the experimental cutting forces with the different low-cutting velocities to verify that the 3D cutting model that has been developed is reasonable.     

Influence of a defined pre-load on the stress state in the precision cutting process

Precision cutting is a single stroke shear cutting process to achieve a flush-cut amount between 60 and 90% of the sheet thickness by using a single-acting standard press. This paper presents a method to quantify the amount of required compression stresses based on theoretical and experimental precision cutting tests in which the stress state is overlaid by an additional radial pre-load on the strip. It was found that even a minimal pre-load of 30% of the yield stress can move the stress level to a state with lower tensile stress.     

The effect of vibration cutting on minimum cutting thickness

In the ultra-precision diamond cutting process, the rake angle of the tool becomes negative because the edge radius of a tool is considerably larger compared to the sub-micrometer depth of the cut. The effects of plowing due to the large negative rake angle result in an unstable cutting process without continuous chip. For this reason, it is important to determine minimum cutting thickness in order to enable greater machining accuracy to be obtained by fine and stable machining. It was previously reported that the critical depth of cut with a continuous chip was determined by the tool sharpness and the friction coefficient between a workpiece and a tool [S.M. Son, et al., Effects of the friction coefficient on the minimum cutting thickness in micro cutting, International Journal of Machine Tools and Manufacture 45 (2005) 529–535]. For the same edge radius of a tool, the higher the friction coefficient of the tool–workpiece, the thinner the minimum cutting thickness becomes. Therefore, it is believed that increasing the friction coefficient by a physical method would be effective to achieve thinner stable cutting. In this study, the possibility of reducing the minimum cutting thickness was investigated through changing the friction coefficient of a tool–workpiece. The vibration cutting method is applied to increase the friction coefficient. Experimental results show that the cutting technology is efficient for increasing the friction coefficient and decreasing the minimum cutting thickness. The minimum cutting thickness was reduced by about 0.02–0.04 μm depending on materials and vibration conditions.     

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.     

Hybrid cutting of granite by use of ultrasonic assistance

Hybrid technologies offer an important approach to enhance existing limits of conventional cutting manufacturing processes. Superposition of the infeed with adapted ultrasonic vibrations enables reductions of machining forces. This results in diminished tool wear and longer tool life. Furthermore, an increase of removal rates can be achieved. Successful machining of recalcitrant metal-based materials by ultrasonic assisted systems creates a high potential to gain similar effects in machining of mineral-based materials. This will be studied in this article. The state of the art for the machining of stone uses geometrically undefined cutting edges. This paper focuses on the geometrically defined cutting of granite with additional ultrasonic assistance. Cutting tests at a test station with linear cutting motion are being performed. The ultrasonic frequency is maintained at 20 kHz. Different oscillation amplitudes are applied to influence process forces and the wear of the used carbide metal and polycrystalline diamond cutting segments (PCD). A method to observe the wear is developed by use of a stereomicroscope and a 3D measurement system. This will enable conclusions about the applicability of the geometry of the cutting segments and the process parameters. Due to the significant different wear rates of both cutting materials, the cutting force progression by using PCD tools shows completely different characteristics compared to the machining with carbide metal tools.     

Dynamics of shear band instabilities in cutting of metals

We study the dynamics of flow instability and shear localization in cutting using direct high-speed imaging and low melting point alloy as a model material system. The onset of instability and departure from steady laminar flow is triggered by nucleation of shear band at the tool tip and subsequent propagation towards the free surface. The stress at the onset of shear band formation is found to be constant and a physical characteristic of the material. The shear band velocity and inhomogeneous strain field arising from the banding are quantitatively characterized using an image correlation method.     

Statistical investigation of modal parameters of cutting tools in dry turning

It is very important that optimized cutting parameters be selected in controlling the quality required for surface finishes. Unfortunately, surface roughness does not depend solely on the feed rate, the tool nose radius and cutting speed; the surface can also be deteriorated by excessive tool vibrations, the built-up edge, the friction of the cut surface against the tool point, and the embedding of the particles of the materials being machined. Hence, the forces, which can be considered as the sum of steady, harmonic and random forces, act on the cutting tool and contribute to the modification of the dynamic response of the tool, by affecting its stiffness and damping. These stiffness and damping variations are attributable to parameters that cannot be easily predicted in practice (regenerative process, penetration rate, friction, variation in rake angle, cutting speed, etc.). Furthermore, the effects of cutting parameters, which also contribute to the variation in the tool’s modal parameters, are more useful for controlling tool vibration. This study focuses on the collection and analysis of cutting-force, tool-vibration and tool-modal-parameter data generated by lathe dry turning of mild carbon steel samples at different speeds, feeds, depths of cut, tool nose radii, tool lengths and workpiece lengths. A full factorial experimental design (288 experiments) that takes into consideration the two-level interactions between the independent variables has been performed. This analysis investigated the effect of each cutting parameter on tool stiffness and damping, and yielded an empirical model for predicting the behavior of the tool stiffness variation.     

基于Labview的切削力监控系统

文章论述了利用Labview开发平台,实现切削力数据的采集、显示和存储,建立切削力测量数据库,实时监控切削力的状况,并通过大量数据的分析,推理反映出刀具磨损或破损及切削用量的合理性等的状态参数.     

钢材切割现状及Fast切割软件的应用

现代切割技术有别于传统手工切割技术．它是基于现代计算机信息技术．针对不同的切割下料设备。对传统切割技术加以改进提高，发展成为以优化套料技术、钣金展开技术和数据库管理技术为代表的计算机辅助切割生产和管理软件。以有效提高钢材综合利用率，提高切割效率和切割质量．加强切割生产管理。     

Fatigue failure of coated carbide tool and its influence on cutting performance in face milling SKD11 hardened steel

Failure patterns of coated carbide tool were investigated by high-speed face milling of the hardened steel SKD11. Tool failure surface morphology, cutting force and machined surface roughness were also analyzed to reveal the failure mechanisms. The results indicated that the dominant failure pattern of coated carbide tool was breakage. The primary mechanism of tool breakage was fatigue fracture. Under different cutting speeds, the distinctive morphologies of fatigue fracture were presented on the failure surfaces. At low cutting speeds, many fatigue sources were observed on the rake face. The distance between fatigue sources and tool nose was approximately two times of the depth of cut. With the increase of cutting speed, the fatigue striations and riven patterns were observed at the fracture surface. In addition, the fatigue steps and crack deflection were found under high cutting speeds. The main fracture mode was intergranular fracture at lower cutting speeds. However, it was transgranular fracture at higher cutting speeds. Furthermore, the irregular fracture surfaces at low cutting speeds and at high cutting speeds contribute to a larger cutting force increment compared with the medium cutting speeds. The increment of surface roughness in the initial and severe wear stages was lower than that in the steady wear stage, while the deviation of surface roughness was relatively large.     

数控等离子切割机切割件的变形控制

针对数控等离子切割机切割件产生变形的原因,对切割件的变形进行了分析.根据数控等离子切割机的特点,在加工过程中正确选择切割的起点、切割方向、切割顺序、切割速度等工艺,可以有效提高切割件的加工质量,同时对单边工件、细长件、异型件以及特殊件的变形控制进行了详细地阐述.     

Estimation of the specific cutting pressures for mechanistic cutting force models

This paper presents a new method for the estimation of specific cutting pressures for mechanistic cutting force models for the face milling process. Traditional methods for the estimation of specific cutting pressures require calibration tests using a single cutting insert on a workpiece which has no surface discontinuities. However, face milling operations in the industry are typically performed on workpieces that have workpiece surface discontinuities and using a large number of cutting inserts to enhance productivity. The performance of calibration tests to determine specific cutting pressures is usually very expensive. Hence, a new method to estimate specific cutting pressures directly from cutting force data collected during actual production is developed. The results obtained using the traditional and the new method are validated through simulations and experimental tests.