Wyniki wyszukiwania - BazTech

1

Turning conditions of Ck 45 steel with alternate hardness zones

Stoic A., Kopac J., Ergic T., Duspar M.

Journal of Achievements in Materials and Manufacturing Engineering

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2009

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Vol. 34, nr 1

87-94

EN

Purpose: of this paper is investigation of dynamic impacts on cutting edge during machining of locally hardened steel. Alteration of hardness on a single work piece is a source of impact on tool, which could lead to breakage of cutting tool and work piece surface damage in turning. Influence of material properties (primary hardness) is important when work piece is hardened locally by induction and part of material is soft annealed. Design/methodology/approach: Experimental tests of cutting outputs have been done on specimens after induction hardening to evaluate the rate of variation of cutting forces, surface roughness and chip formation because of hardness alteration. Measured data of main cutting force were analyzed in frequency and time domain. Findings: It was found that chip formation condition, chip thickness and chip shape depends on cutting forces alteration in transition areas in the range of 10 to 15%. Much higher alteration of force signal is recorded when machining is performed with low depth of cutting value as a result of backlash in system. The most important value of cutting force correlates with depth of cutting, and roughness correlates oppositely to the hardness. Research limitations/implications: Results and findings presented in this paper are qualitative and might be slightly different in other cutting condition (e.g. other heat treatable steels or other hardening techniques or other single cutting point processes). There is evident force value alteration in the transition (hard to soft state) zone. Practical implications: Surface roughness is a consequence of both cutting impacts and of tool/work piece loading condition. Originality/value: Originality of the paper is in analysis for stability of turning to heat treatable steel influenced with alternating work piece hardness. It was recorded edge loading shock overcome from hard to soft machining. It was recorded and analyzed self-exited vibration. A new type of chips: horseshoe-type was found.

2

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.

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.

4

Wpływ głębokości skrawania na stan naprężeń w pile taśmowej bez końca

Wojnarowski J., Kaczmarczyk J.

Zeszyty Naukowe Katedry Mechaniki Stosowanej / Politechnika Śląska

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2005

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z. 29

505-510

PL

W pracy przedstawiono analizę stereomechaniczną ostrzy piły w ustalonym procesie cięcia przy zmiennej głębokości skrawania. Obliczenia numeryczne przeprowadzono przy użyciu metody elementów skonczonych wykorzystując system komputerowy MSC/Patran z modułem liczącym MSC/Nastran. W procesie modelowania uwzględniono nieliniowości geometryczne wynikające z faktu styku (kontaktu) powierzchni skrawającej modelu wycinka piły z modelem wycinka materiału obrabianego. Wybrane wyniki obliczeń zestawiono: na rysunkach, graficznie na wykresie i w postaci barwnej mapy naprężen Hertza.

EN

In the paper, the stereomechanic analysis of cutting edges of a band saw in established cutting process with variable depth of machining was presented. The numerical calculations were carried out with the finite element method using the computer system MSC/Patran with the computational module MSC/Nastran. In modelling process, the geometrical nonlinearities coming from the fact of a contact of cutting surface of the band saw sector model with the machining material sector model were taken into consideration. The selected results of numerical calculations were put together: in figures, graphically in a diagram and in the form of a colourful map of Hertz's stresses.