ASPECTS REGARDING THE GENERALIZATION OF THE TRIBOLOGICAL SYSTEM CONCEPT WITHIN THE METAL CUTTING PROCESSES

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1 THE INTERNATIONAL CONFERENCE OF THE CARPATHIAN EURO-REGION SPECIALISTS IN INDUSTRIAL SYSTEMS 7 th EDITION ASPECTS REGARDING THE GENERALIZATION OF THE TRIBOLOGICAL SYSTEM CONCEPT WITHIN THE METAL CUTTING PROCESSES Vlad Diciuc, PhD. Student, Lobonţiu, Mircea, PhD. prof., North University of Baia Mare, V. Babeş Street, 62A, Baia Mare, Romania Abstract: In the current paper complementary elements of the tribological cutting system are being elaborated as a substructure of the general theme of tribological systems.a short literature review of previous attempts to characterize the tribological cutting systemis presented, as well as a personal motivation for the generic approach of the tribosystem. A model is being proposed for better understanding of the elements and factors that influence the outcome of the cutting process. Key words: tribological system, metal cutting, energy 1. INTRODUCTION The systemic approach regarding various phenomena and processes has led to the introduction of the terms tribosystem, tribomechanical system, tribological system and to the definition of these terms through DIN Systemic approaches also exist in the scientific literature like [Crudu and Gramaticu, 1984], [Czichos, 1978], [Grzesik, 2000], [Rakic and Rakic, 2002], [Gekonde and Subramanian, 2002]. These researchers approached the systemic concepts at a certain level of detail, some of them even omitting to give a definition to the word or concept tribo-system like the author of the paper [Grzesik, 2000] who explains the tribo-system as a hard thin film against hot moving chip. To this matter the studies of [Friedrich and others, 1998] may also be added. Czichos in his work [Czichos, 1978] considers a system as a set of elements interconnected through structure and function. A systemic approach of cutting processes has at the base the principles of Ludwig von Bertalanffy who published the theory of general systems. According to this theory an entity should be resolved through its parts so that at the end the final result should consist of the result of the parts put together. This matter should be treated at a material level as well as at a conceptual one. The analysis of components belonging to an object, phenomenon or process that is to be studied allows a valuable itemization. The re-composition of the whole will indeed create the full image over the object/phenomenon/process also due to the known interactions between the parts. 2. LITERATURE REVIEW There have been attempts to characterize the metal cutting process from a system point of view, even with tribological implications i.e. the tribosystem. The first known researcher who dedicated a chapter of his book to this matter was Czichos H. [Czichos, 1978]. Others like Lobonţiu M., Rakic R., Alauddin M., Kajdas C.K. and Kopac J. followed.

2 None of the attempts made so far succeeded in offering an efficient and easy to use method for solving some practical issues. Some of the approaches known are limited in some context and they left out some leading factors that have a great influence on the outcome of the metal cutting process. [Czichos, 1978] describes the tribological system within a general frame and then he focuses on machine components and their applications. An interesting approach of the tribosystem concept is presented in the 6,020,072 patent registered on the 1 st of February Here the tribosystem is defined as consisting of 2 structural components in dry contact, each through a surface layer. This system is focused especially on aeronautical applications where friction may cause temperatures rising up to 1500 ºC. The authors stress out the ecological importance of lubricants and their replacement because of the toxic effects they have on the environment. This idea is underlined as well in [Stanford and Lister, 2005].. Fig. 1. Tribomechanical system for turning process [Rakic and Rakic, 2002] [Lobontiu, 1999] has defined the tribosystem as consisting of a fixed triboelement, a mobile triboelement, a material between the two triboelements and a working environment. The author stresses out that metal cutting is accompanied by tribological phenomena that take place at the tribocontact levels, tribocontacts that rise up during the cutting process from the interfaces (tool-chip, tool-workpiece). These complex tribological contacts can be structured from elementary contact elements standardized in STAS In [Nakayama, K. and Martin, J.M., 2006] the authors underline that the triboemissions involed in the friction and wear process are of crucial importance in solving tribological problems. The origins of chemical reactions in mechanical contacts are threefold depending on the reaction regions: inside the contact area (ICA), near or in the vicinity of the contact area (NCA) (especially in the gap between a sphere and a plan), and far outside the operating contact area (OCA). Each of the three region reactions has significant role depending on the tribosystem, the friction conditions and the time. Two or all three of the reaction regions can operate simultaneously or consecutively to cause chemical reactions, leading to effective or poor lubrication of the tribosystem. [Nakayama, K. and Martin, J.M., 2006]

3 Fig. 2. Factors influencing surface finish in end milling process [Alauddin and others, 1996] Fig. 3. General scheme of triboemission [Kajdas, 2005] In [Kopac and others, 2001] the authors take the tribosystem concept from [Czichos, 1978] and they add the energy approach to it. In this paper it is considered that friction and wear are 2 types of feedback from a tribological system and that they are greatly influenced by factors like cutting speed, cutting feed, rake angle, etc. Fig. 4. Cybernetic model of the general tribological system [Kopac and others, 2001]

4 3. SUGGESTED APPROACH The following tribological approach starts from considering all the factors involved in the cutting process of metals, their dependencies on one another and their influence on the resulting machined part and it is meant to arrange them in such a manner as to give it a general character suitable for all metal cutting processes. It is an approach aimed to provide a better picture when designing and planning metal cutting operations with consideration to surface quality, geometrical accuracy, energy usage and energy waste, wear and environmental issues. The elements involved in the cutting system and which, in my opinion could be regarded as inputs, are the machine, tool, work piece, environment and energy. The combination of the previously mentioned elements results in the tribological process of metal cutting, having as result or outputs the resulting piece and the chips. For a system to work it needs energy (electrical, mechanical, and thermal). Energy exchanges occur with consideration to time. For example electrical energy is converted by the machine into mechanical energy needed for the cutting process. This conversion leads to the heating of the machine components and thus to the release of thermal energy as well. Further on the process of chip forming also is thermal energy producer and it needs mechanical energy to take place and so on, yet these energy releases may also be considered losses. Losses of energy also occur at the transformation of energy due to the transformation mechanisms. It is important to stress out the specific factors of each element in the equation described in figure 5, factors that influence the resulting piece and its characteristics. For the machine these factors are represented by the machine characteristics i.e. spindle speed, maximum feed on each direction, type of transmission, etc., cutting data as well as the cutting strategy that is to be chosen for the cutting process. The outcome of the cutting process is also influenced by the tool factors such as tool geometry, coatings, tool s base material, tool type, tool deflection and run out. As for the work piece the type of material that is machined and its properties are the most important factors. The environment also plays a crucial role in the output of the cutting process as it was suggested by many researchers [Astakhov, 2007], [Klocke and Eisenblatter, 1997], [Rakic and Rakic, 2002], [Stanford and Lister, 2002], [Sales and others, 2002], etc. The worth-mentioning factors here are the cutting fluids, the atmosphere surrounding the working environment as well as the noise. As mentioned before, each of these factors may influence the characteristics of the cutting process outcome. The tribological interactions between these factors also have to be considered. For example the tool geometry has a great influence in the chip-forming process. So does the cutting data and cutting strategy. Due to the fact that the cutting process consists in 2 tribological phenomena i.e. friction and wear some of the elements in the equation shown in figure 5 (machine, tool) are influenced by these phenomena and in turn the phenomena of wear is influenced mostly by the work piece characteristics and by the environment. Of course that these influences are reflected on the outputs of the cutting process as well. The direct effects of tribology in the field of machining, effects like tool wear, machined surface quality are obvious. Secondary effects are important as well. It s a known fact that the tribological past of a product within its life-cycle has a tremendous influence on the product s reliability, resistance to corrosion and irradiation, fatigue and wear properties. Tribological problems may hinder the adoption of some machining processes or strategies like HSM (High Speed Machining). It is important to make a complete image of the machining process with all its elements and factors that lead to the quality of the product obtained.

5 Fig. 5. The generalized concept of tribological system

6 4. CONCLUSIONS a. The activity of modelling metal cutting processes from the tribosystem point of view is recommended because of the complexity of elements and factors involved in the process and because of their influence on the obtained results; b. The proposed model is meant to ease the understanding of all the elements involved in the cutting process and their factors that contribute to the output of the process; c. The preservation of energy during metal cutting processes as well as the optimization of these processes from the energetic point of view is a crucial problem with maximum priority towards solving. d. The suggested approach is, in the author s opinion, suited for a research grant project. As further work the authors will try to find out the best way to measure, express and optimize the energy quantities involved in the cutting process with respect to the tribological implications of the process, in order to obtain maximum efficiency and quality with as little energy spent/wasted as possible. 5. REFERENCES [1] ALAUDDIN, M., EL BARADIE, M.A. and HASHMI, M.S.J. Optimization of Surface Finish in End Milling Inconel 718. Journal of Materials Processing Technology, Vol. 56, 1996, p ; [2] ASTAKHOV, V.P. Cutting Fluids (Coolant) and their Application in Deep-Hole Machining ; [3] CRUDU, I., şi GRAMATICU, M. Asupra criteriilor de tribomodelare in conditii de uzura abraziva. In: Lucrarile Conferintei specialistilor in frecare, ungere si uzare TRIBOTEHNICA 84, Volumul IV, Institutul Politehnic Iasi, septembrie, 1984, p.49-55; [4] CZICHOS, H. Tribology a System Approach to the Science and Technology of Friction, Lubrication and Wear. Amsterdam Oxford New York, Elsevier Scientific Publishing Company, 1978; [5] FRIEDRICH, C., BERG, G., BROSZEIT, E. and BERGER, C. Fundamental Economical Aspects of Functional Coatings for Tribological Applications. Surface and Coatings Technology, Vol. 98, ianuarie, 1998, p ; [6] GEKONDE, H.O. and SUBRAMANIAN, S.V. Tribology of Tool-Chip Interface and Tool Wear Mechanism. Surface and Coatings Technology, Vol. 149, 15 ianuarie, 2002, p ; [7] GRZESIK, W. An integrated Approach to Evaluating the Tribo-Contact for Coated Cutting Inserts. Wear, Vol. 240, mai, 2000, p. 9-18; [8] KAJDAS, C.K. Importance of the Triboemission Process for Tribochemical Reaction. Tribology International, Vol. 38, 2005, p ; [9] KLOCKE, F. and EISENBLATTER, G. Dry Cutting. Annals of CIRP, Vol. 46, No.2, 1997, p ; [10] KOPAC, J., SOKOVIC, M. and DOLINSEK, S. Tribology of Coated Tools in Conventional and HSC Machining. Journal of Materials Processing Technology, Vol. 118, 2001, p ; [11] LOBONTIU, M. Tribosistemul scula melc abraziv-roata dintata cilindrica. Editura Universitatii de Nord Baia Mare, 1999; [12] NAKAYAMA, K. and MARTIN, J.M. Tribochemical Reactions at and in the Vicinity of a Sliding Contact. Wear, Vol. 261, 2006, p ; [13] RAKIC, R., and RAKIC, Z. The Influence of the Metal Working Fluids on Machine Tool Failures. Wear, Vol. 252, martie, 2002, p ; [14] SALES, W.F., GUMARAES, G., MACHADO, A.R. and EZUGWU, E.O. Cooling Ability of Cutting Fluids and Measurement of Chip-Tool Interface Temperatures. Industrial Lubrication and Tribology, Vol. 54, No. 2, 2002, p ; [15] STANFORD, M. and LISTER, P.M. Investigation into the Relationship between Tool-Wear and Cutting Environments when Milling an Austenitic Stainless Steel and En32 Low Carbon Steel. Industrial Lubrication and Tribology, Vol. 57, Issue 2, 2005, p ; [16] FREE PATENTS ONLINE ADDRESS FOR CORESPONDANCE ROMANIA Professor. Mircea LOBONŢIU, Ph.D., Vlad DICIUC, PhD Student North University of Baia Mare Dr. V. Babes St. 62A, RO Baia Mare mircea.lobontiu@ubm.ro, vlad.diciuc@ubm.ro