Wyniki wyszukiwania - Biblioteka Nauki

1

Experimental investigation of dynamic instability of the turning process

100%

Kopač J. , Stoić A. , Lucić M.

Archives of Computational Materials Science and Surface Engineering

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2009

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tom 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

100%

Lucić M. , Stoić A. , Kopač J.

Journal of Achievements in Materials and Manufacturing Engineering

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2006

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tom 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

Implementation of cutting tool management system

100%

Svinjarević G. , Stoić A. , Kopač J.

Journal of Achievements in Materials and Manufacturing Engineering

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2007

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tom Vol. 23, nr 1

99-102

EN

Purpose: of this paper is to show the benefits of implementation of management of cutting tools in the company which specializes in metal cutting process, after which the production conditions alows new possibilities for improvement of the tool management. Design/methodology/approach: applied in this paper was identification current state and exploitation conditions of cutting tools on lathes and milling machines and organization of the departments and other services, which are directly involved in the cutting tools management system. Findings: of the controlled testings and analyses in every phase of tool management in departments and other services which are directly involved in the tool management system will help to reduce stock and costs. It is possible to identify which operator makes errors and is responsible for inappropriate use of cutting tool. Some disadvantages have been identified and a few suggestions for the improvement in the tool management system have been given. A result of research is easy to apply in company with developed informatic infrastructure and is mostly interesting for CNC workshops. Small companies and specialized low volume productions have to made additional effort to integrate in clusters. Practical implications: are reduction of cutting tool on stock, reduction of employee, quick access to the necessary cutting tools and data, simplicity in tool order and supply. The most important is possibility to monitor and to identify which cutting tools and employees are weakest parts of chain in tool management system. Management activity should be foreseeable in all its segments, which includes both the appropriate choice and use of cutting tools, and monitoring of unwanted phenomena during the cutting process and usage of these data for further purchase of tools. Originality value: in the paper is turnover methodology applied for determination of management efficacy and formation of employees from different departments in virtual tool management system.

4

Dynamic instability of the hard turning process

100%

Kopač J. , Stoić A. , Lucić M.

Journal of Achievements in Materials and Manufacturing Engineering

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2006

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tom 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.

5

Manufacturing of injection moulding tool with five axis milling machine

88%

Stoić A. , Kopač J. , Duspara M. , Micetic I. , Stoić M.

Journal of Achievements in Materials and Manufacturing Engineering

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2013

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tom Vol. 58, nr 1

38--46

EN

Purpose: The main intention of this paper is to show the advanced technology for production of the electrode for EDM that has a relatively complex geometry. Five axes CNC machining centre is used for production of an example ice scrapers since application of other type of machine requires a lot of auxiliary time and resources. Design/methodology/approach: Advanced manufacturing technology involves the application of various software tools and technologies, among them the tools and technology to automate the design, analysis, testing and manufacturing occupy a key position. Findings: The main outcomes are decrease of production time, better quality of surface and product geometry. Decrease of cutting time refers to decrease of number of used tools, preparation time is lower in comparison with conventional machines. Research limitations/implications: The practical part included the design of electrode in the CAD system, SolidWorks 2010, production of NC program for the operating unit Haidenhain iTNC 530 in CAM system ESPRIT 2010, and finally making the electrode on five axis machine center DMG DMU 40 Monoblock. Originality/value: Presented technology for a five-axis machining centre, ensures a great advantages in the process preparation while reduced set-up time, reduced number of required accessories and devices, reduced number of special tools is needed. This knowledge can support the development and design of technological processes

6

An investigation of machining efficiency of internal roller burnishing

88%

Stoić A. , Lacković I. , Kopač J. , Samardžić I. , Kozak D.

Journal of Achievements in Materials and Manufacturing Engineering

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2010

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tom Vol. 40, nr 2

188-194

EN

Purpose: of this paper is investigation of fine machining efficiency of 34CrMo4 steel with roller burnishing tools. Application of roller burnishing process as a clean and environmentally friendly machining process which can replace other pollution processes is of great interests. It is important to evaluate the influence of material properties (primary hardness) for smoothing efficiency and achieving of lower roughness and higher work piece hardness. Design/methodology/approach: Experimental tests of cutting outputs have been done on specimens prepared for final machining process to estimate the rate of roughness decrease, and diameter increase. Roughness measured data before and after roller burnishing process have been compared. Findings: It was found that surface roughness is significantly lower after roller burnishing. Roughness ratio (before/after process) and decrease factor was 4 what doesn’t satisfy expected results. Some roughness results after burnishing exceed upper limits. Research limitations/implications: Results and findings presented in this paper are qualitative and might be slightly different in other machining condition (e.g. higher hardness materials and higher roughness of row material). Practical implications: Smoothing process can be performed on standard machine tools without additional reconfiguration tasks. Process is very rapid. Process is very versatile for any workshop and can be conducted without coolant what is additional advantages for the environment and pollution free machining. Originality/value: Originality of the paper is in analysis of results and smoothing efficiency with Wilcoxon test.