Wyniki wyszukiwania - Biblioteka Nauki

1

Modelling of fracture wear in vitrified cBN grinding wheels

100%

Jackson M. J.

Journal of Achievements in Materials and Manufacturing Engineering

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2007

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tom Vol. 24, nr 1

230-236

EN

Purpose: The paper describes modelling of fracture wear in vitrified cBN grinding wheels. Design/methodology/approach: The approach used in the paper is based on using finite elements to model fracture wear processes in vitrified cBN grinding wheels. The approach used models fracture wear processes and ignores abrasive wear of the abrasive grains. Findings: The findings show that during grinding the grain is subjected to forces that create fracture initiation zones in the sharp abrasive grains where tensile and compressive stresses dominate in certain parts of the abrasive grains. Research limitations/implications: The findings show that further research is required that prevents the formation of crack initiation zones and considers the effects of wear flats on the magnitude of stresses in the abrasive grains. Practical implications: The results imply that abrasive fracture wear is the dominant wear mechanism when grinding with sharp vitrified cBN grinding wheels. Originality /value: The originality of this paper is reflected in the fact that this is the first time that fracture wear has been modelled in sharp vitrified cBN grinding wheels. The results presented in this paper will illuminate the need for accurate modelling of the wear of vitrified superabrasive grinding wheels.

2

Numerical analysis of small recessed silicon carbide grinding wheels

100%

Jackson M. J.

Journal of Achievements in Materials and Manufacturing Engineering

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2010

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tom Vol. 43, nr 1

27-37

EN

Purpose: Silicon carbide grinding wheels are tools used in manufacturing industry to form precision components and continue to be used to increase production rates due to their ability to remove high volumes of material at high speeds. There is a demand to increase the speed of rotation of the grinding wheel in order to achieve high removal rates. The increase in speed creates a situation where the grinding machine and the operator are subjected to a possible catastrophic failure of the wheel due to the stresses generated in the coarse brittle structure of the vitrified grinding wheel. The study focused on building and analyzing computer models of grinding wheels with recessed features spinning at different rotational speeds. By employing a computational approach, it was possible to determine the maximum principal stresses in the wheel together with the location of the stresses. The geometry of vitrified wheels considered included a plain-sided rotating wheel and a recessed rotating wheel. Design/methodology/approach: The paper shows how stresses and factors of safety are calculated in order to predict the bursting speeds of small recessed SiC grinding wheels. The main methods used include finite element analysis and mechanical testing of abrasive materials. The approach of the paper is to integrate the use of numerical analysis techniques and experimental techniques to predict the safe operating conditions of SiC abrasive products. Findings: Calculations were conducted to determine maximum stress in parallel-sided and recessed cup wheels. Relevant factors of safety and bursting speed were also calculated and compared with experimental data. The paper proves the usefulness and applicability of a method developed for taking account of stress concentrations at the recess of small cup-shaped silicon carbide grinding wheels. Research limitations/implications: The paper is limited to analyzing small recessed SiC grinding wheels. Further work should focus on large recessed wheels and wheels made with different abrasive grains and bonding materials. The type of porosity distribution should also be investigated. Practical implications: The paper shows how numerical methods are used to design safe operating conditions for brittle grinding wheels. The methods used show that numerical techniques are suitable for calculating the measures of safety that are an important consideration when designing high speed rotating grinding wheels that can be devastating if allowed to fail in service. Originality/value: The originality in the paper is revealed owing to the fact that fracture mechanics principles are applied to the prediction of failure of rotating grinding wheels. The paper is of practical importance to mechanical designers who are responsible for the safe design of grinding wheels.

3

Micromachining electrical grade steel using pulsed Nd-YAG lasers

63%

Jackson M. J. , Robinson G. M.

Journal of Achievements in Materials and Manufacturing Engineering

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2007

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tom Vol. 20, nr 1-2

451-454

EN

Purpose: Multi-wavelength capability allows diode pumped, solid state (D.P.S.S.) lasers to perform operations such as micro machining in a variety of materials such as ceramics, metals and polymers. Results from this study reveal how traditional plasma-controlling gases have a detrimental effect on the surface morphology of machined components. The paper explains how the machining of thin plates of silicon steel can benefit the rapid production of electrical components such as transformer cores and dynamo pole pieces. Design/methodology/approach: A series of experiments was performed to investigate how shielding gas environment and gas pressure affect the ability to cut and machine silicon steel. The experiments were designed to show the differences between the use of various assist gases that shield the machining zone. Findings: The results of the work indicate that oxygen shielding gases allow silicon steel to be machined at a faster rate than using helium, argon and air. However, the surface roughness produced is highly dependent on assist gas used and the pressure at which it is delivered. Research limitations/implications: The results presented imply that assist gases perform a variety of functions and further research is required to understand how the assist gases improve machinability when machining different workpiece materials. Practical implications: The practical implications of this research indicate that a significant amount of research effort is required to optimize the type of assist gas used in laser micromachining of engineering materials. Originality/value: The paper reveals how assist gases interact with both laser and the surface of workpiece materials. It is practical value to microengineers and micromachinists working in the field of micro and nanomanufacturing.

4

Machining strain hardening metals using nanostructured thin film end mills

51%

Jackson M. J. , Robinson G. M. , Morell J. S.

Journal of Achievements in Materials and Manufacturing Engineering

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2007

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tom Vol. 21, nr 1

79-82

EN

Purpose: This paper discusses improvements associated with the tool life of cutting tools used to machine alloy steels. To achieve this in an efficient manner, experiments on a variety of tool coatings are conducted on AISI M42 tool steel (58-63 HRC). Design/methodology/approach: In order to assess the impact of different tool coatings on machining process, initial experiments simulate current machining operations; this provides a benchmark standard for tool life and surface finish. Findings: The findings in the paper show that TiAlCrN and TiAlCrYN coated WC-Co cutting tools perform better than uncoated and TiN coated cutting tools. Research limitations/implications: The implications of the paper tend to indicate that dry machining of M42 tool steels can be optimized using coated cutting tools. The limitations of the paper include machining at specific cutting speeds and the employment of a short-time tool wear method. Practical implications: The practical implications of the paper show that dry machinig of hardened tool steels can be achieved under specific circumstances. Further research is needed to explain how the wear mechanism changes under various machining conditions. Originality/value: The paper presents original information on the characteristics of dry machining of tool steels under specific machining operations. The paper is of interest to manufacturing engineers.

5

Machining M42 tool steel using nanostructured coated cutting tools

51%

Jackson M. J. , Robinson G. M. , Morell J. S.

Journal of Achievements in Materials and Manufacturing Engineering

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2007

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tom Vol. 23, nr 1

83-86

EN

Purpose: This paper discusses improvements associated with the life of cutting tools used to machine M42 tool steel. To achieve this in an efficient way, experiments on a variety of tool coatings are conducted on AISI M42 tool steel (58-63 HRC). Design/methodology/approach: In order to assess the impact of different tool coatings on the machining process, initial experiments simulate existing machining operations; this provides a standard for tool life and surface finish. Findings: The findings in the paper show that TiAlCrYN coated WC-Co cutting tools perform better than uncoated cutting tools. Research limitations/implications: The implications of the paper tend to indicate that machining M42 tool steels without lubricant can be optimized using coated cutting tools. The limitations of the paper include machining at one specific cutting speed and the employment of a short-time tool wear method. Practical implications: The practical implications of the paper show that dry machining of hardened tool steels can be achieved under certain circumstances. Further research is needed to explain how the wear mechanism changes with varying machining conditions. Originality/value: The paper presents original information on the characteristics of dry machining of M42 tool steel under specific machining operations. The paper is of interest to manufacturing engineers and materials scientists.

6

Manufacture of nanocrystalline metals by machining processes

51%

Jackson M. J. , Robinson G. M. , Whitfield M. D.

Journal of Achievements in Materials and Manufacturing Engineering

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2007

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tom Vol. 20, nr 1-2

27-30

EN

Purpose: The paper shows how extremely high-speed micromachining can be used as a method for manufacturing nanocrystalline feedstock from machining chips. The feedstock can be used in processes such as cold spraying that improve the surface characteristics of engineering components. Design/methodology/approach: The design and methodology relies on the construction and the correct operation of a micromachining operation that produces functional feedstock material that is produced from machining chips at spindle speeds in excess of half-a-million revolutions per minute. The approach provides an economical way of producing metal nanocrystals. Findings: The findings of the research show that intense plastic shearing of metals produces nanosized crystals in the range 30 nm to 150 nm. The crystals produced can be used to create superior funtional coatings on engineering components. Research limitations/implications: The research conducted implies that a cost effective and environmentallybenign process can produce metal nanocrystals. The limitations of the research are currently restricted to cold spraying of funtional surfaces. Practical implications: The practical implications of the research show that high-speed micromachining can be used as a method of producing nanocrystalline feedstock that can be used in a variety of secondary manufacturing processes in addition to cold spraying. Originality/value: The paper demonstrates the originality of using well-established machining processes for producing nanocrystalline metals. The paper describes how machining at extremely high speeds can be achieved to produce material that can be used to strengthen and harden engineering components.

7

Reactive oxygen species as signals for adaptation in healthy and diseased skeletal muscle

38%

Jackson M. J. , McArdle F. , Close G. , Vasilaki A. , Jesus P. , Pye D. , McArdle A.

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2006

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tom 53

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nr Supplement 1