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1

Experimental investigation of dynamic instability of the turning process

Kopač J., Stoić A., Lucić M.

Archives of Computational Materials Science and Surface Engineering

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2009

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Vol. 1, nr 2

84-91

EN

Purpose: Purpose of this paper is consideration of dynamic instability in turning process. There are several sources which lead to instability in turning process (cyclic variation of depth of cutting, inadequate rigidity of machine tool, high passive force component Fp, small tool nose radius and small tool/workpiece contact length, non-uniform stress distribution over contact length). In hard turning, when depth of cutting and feed have low values, lead edge angle and passive force Fp are strongly depend on real time value of depth of cutting. Design/methodology/approach: Experimental tests and numerical modeling of tool/workpiece contact line have been done to evaluate the rate of cutting instability while using and comparing different process monitoring sensors, and acquisition techniques. This data can be used for prediction and compensation of machining errors. Findings: It was found that high chip thickness alteration occurs because of cutting depth vary for a value of some 60 %. Even higher alteration of Fp force signal is recorded when machine tool has inadequate stiffness. Research limitations/implications: Results and findings presented in this paper are qualitative and might be slightly different in other cutting condition (e.g. if wiper inserts are used). Also there are no experiences with coated workpieces or with workpiece material with low deformation energy. Practical implications: Assuming that a hard turning is a semi finishing or finishing process, surface finish is of big relevance. Surface roughness is a consequence of both cutting instability and of tool/workpiece loading condition. Results of test indicates an optimal cutting depth for final pass when minimum surface roughness can be achieved what can be valuable for cutting regime determination. Furthermore, more effective use of the machine tool performances might be achieved. Originality/value: Originality of the paper is in analysis of sources of turning instability (variable depth of cutting combined with lead edge angle and tool nose radius) which lead primary to condition where Fp sensing data does not fit to the normal distribution and secondary to cyclic push-offs of the edge.

2

Investigation of aluminum single lap adhesively bonded joints

Lucić M., Stoić A., Kopač J.

Journal of Achievements in Materials and Manufacturing Engineering

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2006

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Vol. 15, nr 1-2

79--87

EN

Purpose: The purpose of research was to find an optimum overlap length ensuring the settled bearing performance of adhesive bonded joint. At the optimum overlap length it is possible to reach a maximum load bearing capacity using a minimum quantity of applied adhesive. Design/methodology/approach: In accordance with experimental test results, an optimum overlap length was achieved. In numerical analysis, the proposed material model (MISO) fits well in simulations. Findings: Mechanical properties of adhesive which are often public unknown have very strong influence on reliability of material models used in numerical analysis. Therefore, it was crucial decision of research to made an adhesive specimen for tensile testing. Research limitations/implications: At the overlap lengths above critical (optimal) ones, the usage of a MISO material model in FEA is not acceptable any more. In further work is of great interest to verify simulation with other materials model approaches. Practical implications: Maximal strength of joint might be reached if optimal overlap length of joint is applied, nevertheless if less adherend material is consumed. Originality/value: Originality is in true stress/strain diagram of adhesive which is based on experimental testing of adhesive specimen. Material model in numerical analysis is based on true stress/strain diagram.

3

Dynamic instability of the hard turning process

Kopač J., Stoić A., Lucić M.

Journal of Achievements in Materials and Manufacturing Engineering

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2006

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Vol. 17, nr 1-2

373--376

EN

Purpose: Purpose of this paper is consideration of dynamic behavior of the hard turning process. There are several indicators which could confirm assumption of turning instability (depth of cutting, high ratio of forces Fc/Fp, small tool nose radius, and non-uniform stress distribution over tool/workpiece contact). Lead edge angle and passive force Fp are strongly depend on depth of cutting in hard turning what additionally increase instability. Design/methodology/approach: Numerical calculation and experimental tests have been done to evaluate the rate of cutting instability while using and comparing different process monitoring sensors, and acquisition techniques based on PC platform. Findings: It was found that high chip thickness alteration occur because of cutting depth vary for a value of some 60% and even more if Fp force signal is analyzing when machine tool has inadequate stiffness. Research limitations/implications: Results and findings presented in this paper are qualitative and might be slightly different in other cutting condition (e.g. if wiper inserts are used). Also there are no experiences with coated workpieces or with workpiece material with low deformation energy. Practical implications: Assuming that a hard turning is a semi finishing or finishing process, surface finish is of big relevance. Surface roughness is a consequence of both cutting instability and of tool/workpiece loading condition. Results of test indicates an optimal cutting depth for final pass when minimum surface roughness can be achieved what can be valuable for cutting regime determination. Furthermore, more effective use of the machine tool performances might be achieved. Originality/value: Originality of the paper is in analysis of sources of turning instability (variable depth of cutting combined with side edge angle and tool nose radius) which lead primary to condition where Fp sensing data does not fit to the normal distribution and secondary to cyclic push-offs of the edge.