Discontinuous coatings on cutting tools

To increase the life of cutting tools, it is proposed to form wear-resistant discontinuous coatings on their surface. In order to ensure cohesive strength of coating, coating crack spacing is taken as the size of discrete portion. It has been shown that under contact loading conditions, such coatings prevent contact fracture thanks to reduction of residual stresses. __________ Translated from Problemy Prochnosti, No. 1, pp. 138–143, January–February, 2007. Report on International Conference “Dynamics, Strength, and Life of Machines and Structures” (1–4 November 2005, Kiev, Ukraine).     

The economics of multi-cutting and deformation region tools

Conventional economic analyses of metal cutting processes enable the machining condition to be identified which correspond to such criteria as minimum cost, maximum production rate and maximum profit. Such analyses have been applied extensively to single point cutting processes such as turning and to a lesser degree to multi-point cutting processes such as milling. However, there are other more complex processes that employ cutting tools, where a number of cutting and deformation edges act simultaneously to remove material. The conditions are not necessarily the same at each edge. Examples of such processes are broaching, subland drilling and deep drilling, all of which have primary and secondary machining regions. In this paper the economics of deep drilling are presented and it is shown that the wear at the secondary region (i.e. the pads which burnish the hole surface) affects the economics of the primary region (the cutting edge) in a manner which had not been previously appreciated. A minimum cost analysis is presented which shows the cost-feed-speed surface is not a continuous smooth curve as is the case for conventional tools, but consists of a series of steps or discontinuities joined by curves. Thus, a minimum cost can be determined between consecutive discontinuities which may be considered with production rate in order to decide the optimum machining conditions. The presence of discontinuities can also result in relatively large variations in cost for small changes in machining conditions.     

Intelligent design of cutting tools using smart material

Shaving metal from a workpiece to produce desired geometric shape is carried out in turning machine tool. Attenuating a micro level vibration of a cutting tool using smart materials can save old machines and enhance flexibility in designing new generations of machine tools. The finite element method is employed to investigate structural stiffness, damping, and switching methodology using smart material in tool error attenuation. In this work, a dynamic force model is deployed to investigate the effectiveness of using such technique in toolpost dynamic control. Effects of short and open circuit conditions on tool critical frequencies for different structural stiffness ratios are assessed. In the transient solution for tool tip displacement, the pulse width modulation (PWM) technique is implemented for smart material activation to compensate for the radial disturbing cutting forces. A Fuzzy Algorithm is developed to control actuator voltage level enhancing improved dynamic performance. The influence of minimum number of PWM cycles in each disturbing force cycle is investigated in controlling the tool error growth. A methodology is developed to utilize toolpost static force–displacement diagram to obtain required activation voltage to shrink error under different dynamic operating conditions. Time delay of applied voltage during error attenuation is evaluated at different frequencies.     

Tool life criterion of single point tools when cutting with NC machine tools

Owing to expense effects, the operation of NC machine tools requires safely calculable technological data. The tool life criteria must form the basis of these, the connection of which with the technological data for given tool-workpiece material coupling can be determined simply, at low cost and quickly, even by the employer of the machine. The study deals with the calculation of tool life of semi-rough turning. The tool life criterion is the depth of crater. Its changes are calculated for length and cross-turning. The analytical method valid for cross-turning offers a direct possibility for the continuous plotting of the Taylor curve, for determination of its constants. The procedure after the solution of still unclarified questions offers a possibility for a decrease in the order of cost and time requirements of tool life tests     

On chip formation in cutting metallic materials using tools with a large negative rake

It has been noted that the chip formation mechanism in metal cutting with edge tools with a large negative rake angle γ is not fully understood. Methods for assessment of some chip formation characteristics are put forward and examples are given of how they are implemented during the comparison between calculated and experimental values for the case of cutting lead workpieces using tools with a rake angle γ ranging from zero to −60°.     

Instrument for measuring the radius of round-off of the cutting edges of cutting tools and hard alloy plates

Translated from Izmeritel'naya Tekhnika, No. 6, pp. 20–21, June, 1990.     

Fracture of cutting tools due to the formation of untempered martensite

Three case studies are presented in which untempered martensite produced during forming or use caused premature failure or failures in unexpected regions. The sources of formation of untempered martensite observed were: laser cutting of circular saws, friction originated from poor fixation of blades, and uncontrolled thermal cycling in the vicinity of a weld. Due to its very high hardness, untempered martensite favors the appearance of microcracks that develop into premature catastrophic failures.     

Modelling the orthogonal machining process using coated carbide cutting tools

In this paper finite element methods were used to determine the influence of various coated and uncoated tungsten carbide cutting tools on the machining of a nickel-based super alloy Inconel 718. Disposable coated and uncoated carbide inserts were used both experimentally and as FEA models to study how the stress distribution within different coatings and carbide grades compared to each other, under a range of cutting conditions. Simulation of an orthogonal metal cutting process was performed using FORGE2, an elasto-visco plastic FEA code. All FE models were assumed to be plane strain. The results include the stress and temperature distributions through the primary shear zone, the chip/tool contact region and the coating/substrate boundaries. The tool wear and stress results from the FE modelling agree favourably with those obtained from experimental work.     

Boundary element analysis of the thermal behaviour in thin-coated cutting tools

Temperature measurement and prediction have been a major focus of machining for several decades, but now these problems become more complex due to the wider use of advanced cutting tool coatings. In all literature items cited the boundary element method (BEM) were used to find the distribution of temperature inside the uncoated tool body or along the tool–chip interface in the machining processes. The BEM-based approach proposed in this paper overcomes this limit and the temperature distribution in thin coated layers is well studied. In this study, a general strategy based on a nonlinear transformation technique is introduced and applied to evaluate the nearly singular integrals occurring in two dimensional (2D) thin-coated structures. For the test problems studied, very promising results are obtained when the thickness to length ratio is in the orders of 1.0E?6 to 1.0E?10, which is sufficient for modeling most thin-coated structures in the micro- or nano-sclaes.     

Tribology of cutting by tools equipped with cBN-based PSHM

Mechanisms of the contact interaction between the cutting tool equipped with cBN-based PSHM and the material machined in the cutting zone have been considered. The influence of the thermobaric conditions of loading on the tool (cutting temperature and contact stresses) on the mechanisms has been discussed.     

Application of moiré technique in the stress analysis of cutting tools

Knowledge of the stress field in cutting tools is necessary for their strength evaluation. However, the experimental analysis of stresses in cutting tools during machining poses a number of problems in view of the steep stress gradient present. Photo-elasticity and the 'built-up tool' methods are the common techniques used for this purpose. In the present paper results on the stresses in cutting tools obtained during actual machining through the successful application of the transmitted moiré technique, are presented. In these experiments transparent epoxy tools carrying moiré gratings were used to machine commercial lead alloy at low speeds. The tool rake angle was varied. The effectiveness of moiré method, basically a displacement analysis technique, in providing useful data on tool stresses comparable with the other direct stress analysis techniques such as photo-elasticity is also discussed in the paper.     

Finite element analysis of bending occurring while cutting with high speed steel lathe cutting tools

The bending which occurs on a cutting tool during machining on a lathe affects tool life, surface roughness and dimension correctness. In this research, the bending which has been calculated by Castigliano theorem has been compared with the bending obtained by finite element method. Under the constant cutting conditions, material Ç1060 has been machined with high speed steel (HSS) lathe cutting tools having 60°, 75° and 90° of cutting edge angle. It was determined by using ANSYS finite elements program that the bending of the cutting tool generated by the forces, which varied between 1360 N and 1325 N and occurred during cutting, varied between 0.039958 and 0.04373 mm. According to the results, it has been observed that the bending that was calculated by Castigliano theorem and that varied between 0.03542 and 0.034505 mm was almost the same with the bending determined by finite elements method. In other words, it was seen that the calculated values approach to the analysed results up to 0.4% .     

Carbon nanotube reinforced metal binder for diamond cutting tools

The potential of carbon nanotube reinforcement of metallic binders for the improvement of quality and efficiency of diamond cutting wheels is studied. The effect of multi-walled carbon nanotube (MWCNT) reinforcement on the mechanical properties i.e. hardness, Young modulus, strength and deformation behavior of copper and iron based binder for diamond cutting wheels is investigated experimentally and numerically. Computational micromechanical studies were carried out to clarify the mechanisms of the MWCNT material strengthening. It is demonstrated that the adding of MWCNTs leads to the decrease of grain size of the structural constituents of the binder, what in turn leads to the improved simultaneously hardness, Young modulus, plastic extension, bending strength and performances of the metallic binders. Comparing service properties of diamond end-cutting drill bits with and without MWCNT one observed the drastic increase of the cutting speed as a result of MWCNT reinforcement.     

The formation of diamond-hardmetal granules for the use in rock cutting tools

The paper describes a process of formation of diamond-hardmetal granules based on synthetic diamond grains and sintering the granules subject to the condition of minimized strength degradation of diamond. Requirements have been defined for the composition and structure of hardmetals that are used in the granules in order to ensure a reliable diamond retention. A trial application of a composite material based on diamond-hardmetal granules onto steel inserts for rock cutting tools by the intensive electric sintering method has been accomplished.     

Manufacture and properties of ceramic cutting tools: a review

Abstract

The past 15 years have seen major advances in the development of ceramic tool materials to give high cutting speeds and long tool lifetimes. These developments require rigid machine tools and high-power motors, and a change in the way the tool tips are used. The main areas of application of these new tool materials are in the aerospace industries and, to a somewhat lesser extent, in cast iron production. There is an ever increasing number of grades (and tradenames) available, and in this paper the background and development of the materials are described. Briefly, the materials may be classified as alumina or silicon nitride based; these base compositions, with alloying additions, form two main families of materials. The manufacturing routes are discussed as these influence both the grain size and the porosity of the finished material, and both these properties affect the behaviour of the materials in use. Finally, the wear of these tools is examined in the light of present understanding of the microstructures.

MST/713