Viktor P. Astakhov

A METHODOLOGY FOR PRACTICAL CUTTING FORCE EVALUATION BASED ON THE ENERGY SPENT IN THE CUTTING SYSTEM

This paper presents a methodology for practical estimation of cutting force and cutting power. Based on a previously proposed definition, the power spent in metal cutting is the summation of four components: the power spent on the plastic deformation of the layer being removed by both major and minor cutting edges, the power spent on the tool-chip interface, the power spent on the tool-workpiece interface, and the power spent in the formation of new surfaces (cohesive energy). This paper provides a complete list of mathematical expressions needed for the calculation of each energy mode and demonstrates their utility for turning operation of two work materials: AISI bearing steel E52100 and aerospace aluminum alloy 2024 T6. The calculated cutting forces were in fairly good agreement with the experimental results. Energy partition in the cutting system and relative impact of the parameters of the machining regime are discussed. For the first time, a simple and practical method is available for the calculation of the total cutting power and the evaluation of the relative contributions of each individual component of the cutting system.

Chip structure classification based on mechanics of its formation

Abstract Understanding chip formation is the first step to good chip control, a necessity for automated machining. Such understanding results in the prediction of chip breakability for a wide range of machining conditions. This paper presents a generalized model of chip formation in metal cutting. The mechanical properties of the workpiece are of prime concern. A new classification of chip structure is proposed, according to which classification, seven different chip structures are distinguished, namely: the regular broken chip, the irregular broken chip, the continuous fragmentary chip, the continuous fragmentary chip with a wedge-shaped texture, the continuous chip, the continuous hump-back chip, and the fragmentary hump-back chip. Unlike the known classifications which often have a post-process nature, the proposed classification considers the chip structure, the chip stress and strains as the results of chip-formation dynamics. The methodology presented in this paper provides a new and viable means to predict chip breakability. The results of this study give clear ideas to the tool designer, technologist, or even to the foreman, as to what kind of chip-breaking should be used for a given set of machining conditions.

MACHINING RESIDUAL STRESSES IN AISI 316L STEEL AND THEIR CORRELATION WITH THE CUTTING PARAMETERS

It is well known that machining results in residual stresses in the workpiece. These stresses correlate very closely with the cutting tool geometrical parameters as well as with the machining regime. This paper studies the residual stress induced in turning of AISI 316L steel. Particular attention is paid to the influence of the cutting parameters, such as the cutting speed, feed and depth of cut. In the experiments, the residual stresses have been measured using the X-ray diffraction technique (at the surface of the workpiece and in depth). The effects of cutting conditions on residual stresses are analyzed in association with the experimentally determined cutting forces. The orthogonal components of the cutting force were measured using a piezoelectric dynamometer.

Geometry of Single-point Turning Tools and Drills

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Ecological Machining: Near-dry Machining

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Tools (Geometry and Material) and Tool Wear

This chapter points out major ways to reduce the ecological and health impacts of metal working fluids (MWFs). In the continuous quest for dry machining, only one process can offer a near-term solution for practical applications. This process uses a minimum quantity of lubrication and is referred to as “near-dry”. In near-dry machining (NDM), an air–oil mixture called an aerosol is fed onto the machining zone. Compared to dry machining, NDM substantially enhances cutting performance in terms of increasing tool life and improving the quality of the machined parts. This chapter presents a classification of NDM methods, discussing their advantages and drawbacks. Analyzing the available information on the performance of NDM, the chapter offers a physically attractive explanation of why NDM works. It considers the essential components of the whole NDM system, arguing that a 360° vision approach is the key to successful implementation of NDM.

Re-evaluation of the basic mechanics of orthogonal metal cutting: velocity diagram, virtual work equation and upper-bound theorem

This chapter presents the basic definitions and visualisations of the major components of the cutting tool geometry important in the consideration of the machining process. The types and properties of modern tool materials are considered as well, as a closely related topic, as these properties define to a great extent the limitations on tool geometry. The basic mechanisms of tool wear are discussed. Criteria and measures of tool life are also considered in terms of Taylor’s tool life models as well as in terms of modern tool life assessments for cutting tools used on computer numerical control (CNC) machines, manufacturing cells and production lines.

A novel approach to operating force evaluation in high strain rate metal-deforming technological processes

Abstract This paper re-evaluates the known velocity relationships expressed in the form of a velocity diagram in orthogonal metal cutting, arguing that the metal cutting process be considered as cyclic and consisting of three distinctive stages. The velocity diagrams for the second and third stages of a chip-formation cycle are discussed. The fundamentals of the mechanics of orthogonal cutting, which are the upper-bound theorem applied to orthogonal cutting and the real virtual work equation, are re-evaluated using the proposed velocity diagram and corrected relationships are proposed. To prove the theoretical results, the equation for displacements in the deformation zone is derived using the proposed velocity relationships. To prove that the displacements in the deformation zone follow the derived equation and that this zone consists of two unequal parts, a metallographical study of chip structures has been carried out. To estimate the variation of stress and strain in the deformation zone quantitatively, a microhardness scanning test was conducted. Because it is proved that the chip formation process is cyclic, its frequency is studied. It is shown that when the noise due to various inaccuracies in the machining system is eliminated from the system response and thus from the measuring signal, and when this signal is then properly processed, the amplitude of the peak at the frequency of chip formation is the largest in the corresponding autospectra.

An analytical evaluation of the cutting forces in self-piloting drilling using the model of shear zone with parallel boundaries. Part 1: Theory

Abstract One of the major problems that exist in verifying metal-forming force models is a significant scatter in the measurements of the actual process force(s). This is essentially true for any high-energy rate forming process, which involves high strain, high strain rate and high process temperature. Owing to the fact that any energy propagates in waves, this paper suggests that the interaction of the energy waves might affect the actual process force(s). A novel concept of interaction between the deformation and heat waves has been studied. The metal-cutting process was selected as a test process because it involves a combination of extremely high strain rates, large strains and high temperatures. The experimental results obtained from bar turning tests prove the proposed concept by revealing the existence of reinforcements and interferences as the result of interactions of the heat and deformation waves. The influence of the process parameters on this interaction is also studied.

Correlations amongst process parameters in metal cutting and their use for establishing the optimum cutting speed

The performance of a self-piloting tool is affected by its design and geometry parameters. These parameters constitute the tool-force system which directly defines quality of the machined holes, tool life and required power. This paper presents an analytical approach to describe the cutting forces in self-piloting drilling. The approach is useful at the level of tool and process design. The subject has been covered in two parts. Part one deals with the analysis of the cutting mechanics employing the shear-zone model with parallel boundaries. The analysis of the continuity condition results in better understanding of the traditional cutting models characteristics, such as the chip compression ratio and velocity diagram. Based on this analysis and using the thermomechanical model of the work-material resistance to cutting, a cutting-force model is proposed and has been verified experimentally.