1,721,108 research outputs found
Influence of the Minimum Chip Thickness on the Obtained Surface Roughness During Turning Operations
No full textAbstractConsiderable efforts have been put into analyzing the obtained surface roughness during turning operations. However, knowledge is still lacking on how to model the arithmetic mean surface roughness Ra through using a general model applicable for all workpiece materials and process parameters. Further, the influence of the minimum chip thickness on the obtained surface roughness needs to be clarified. This article presents a new model for predicting the Ra surface roughness during turning operations. The model is based on physical and empirical knowledge of the turning process and has been experimentally validated through turning Al-SiCp MMC, cast iron, conventional- and stainless steels, as well as Ti6Al4V. The obtained results show great potentials with an average error of 6.7% even though errors as large as 16.6% were obtained for some cases
A study on surface finish and electric signal of a PZT piezoelectric ceramic machined by abrasive water jet
Full text linkLAUREA MAGISTRALELe ceramiche piezoelettriche possono soddisfare i bisogni di molteplici applicazioni in numerosi campi, come ad esempio quello ottico, elettronico, meccanico e biomedico, grazie all’accoppiamento elettromeccanico dovuto all’effetto piezoelettrico e alle loro proprietà quali l’alta resistenza meccanica, alla corrosione, agli stress termici e l’inerzia chimica. Generalmente questo tipo di materiali è difficile da lavorare con tecnologie convenzionali e innovative come il laser, l’EDM o le microlavorazioni. La tecnologia water jet, al contrario, risulta promettente poiché presenta basse sollecitazioni meccaniche e termiche unitamente ad un’alta flessibilità e versatilità. Questo lavoro dimostrerà la capacità della tecnologia water jet di lavorare con successo una ceramica piezoelettrica chiamata zirconato titanato di piombo (PZT). Verrà investigata la finitura superficiale del taglio e analizzato il segnale elettrico acquisito direttamente dal pezzo in lavorazione nel tentativo di aumentare le conoscenze sul processo di taglio e sull’interazione getto-materiale.Piezoelectric ceramics can satisfy the needs of optical, electronic, mechanical and biomedical applications thanks to their properties such as electrical behaviour and electromagnetic response, high mechanical and corrosion resistance, high resistance to thermal stresses and chemical inertness. As these type of material are generally difficult to machine by conventional technologies, abrasive water jet is a promising technology compared to laser, EDM or micromachining thanks to the low forces involved in the cut, the absence of thermal stresses, high versatility and flexibility. The work will demonstrate the capability of water jet technology to successfully machine such materials, investigate the effect of process parameters on the surface finish of a thin sheet of a piezoelectric ceramic called lead zirconate titanate (PZT) and analyze the electric signal directly acquired from the workpiece during the cut in order to have a deeper understanding of the cutting process and jet-piece interaction
Analysis of Material Weakening in CFRP after a Drilling Operation
No full textAbstractDrilling Carbon Fibre Reinforced Plastics (CFRP) induces different material defects like delamination, burnt matrix material, rough bore channel surfaces, fibre pull-out and uncut fibres. Intensive research has been conducted to analyse the amount of defects caused, describing the surface and subsurface defects introduced by machining operations [1,2]. Additionally, the mechanical strength of rivet joints has been analysed intensively [3]. However, the mechanical performance of rivet joints includes many influencing factors as different materials prepared with various machining processes are being joined. The presented study introduces five newly developed test rigs to analyse the mechanical performance of single bores in relation to different drilling and loading conditions. The setups are designed to focus either on the mechanical strength of the bore channel or the drill entrance or exit. The developed test rigs expand the capability to describe the workpiece quality after a drilling operation. The test rigs facilitate an efficient quality evaluation of drilling processes as well as the development of adapted drilling tools
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Tool Life Time Extension with Nano-crystalline Diamond Coatings for Drilling Carbon-fibre Reinforced Plastics (CFRP)
No full textAbstractCarbon fibre reinforced plastics (CFRP) are delicate to machine as the material is highly abrasive and tends to show multiple workpiece damages like delamination, fibre pull out, uncut fibres and burnt matrix material. In result machining CFRP requires on the one hand tools which can withstand the massive wear, on the other hand geometrical highly adaptable tools to produce flawless workpieces. Diamond coated solid carbide tools can provide an excellent wear resistance in combination with a highly adaptable tool geometry. Nano-crystalline diamond coatings provide a good layer adhesion and can be applied to machining tools.This study focuses on required drilling tool characteristics for a large tool life time of diamond coated carbide tools. The workpiece material used is the M21/35%/370H5/AS4C-6K from Hexcel© which finds its main application in the aircraft industry. The machining tests are being conducted using a Mori Seiki NMV5000DCG at different feed rates and cutting velocities. Two different nano-crystalline diamond coatings are being evaluated regarding wear resistance depending on the drill geometry and tool diameter. The workpiece quality is measured using a microscope. It is shown that the tool geometry influences the wear resistance intensively. A change in wear resistance depending on the tool geometry is not unique for different diamond coatings. Finally, it is shown that cutting velocity and feed have only a small influence on tool life time
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Experimental investigation in turning as a basis for modelling chip formation, tool life and cutting fluid performance
No full textTool life is a parameter closely connected to the lubricating effect of a cutting fluid. Long tool life in turning corresponds to good lubrication and a process with good lubrication is preferred, since it normally results in lower tool wear and better surface quality. Cutting forces are mainly important for understanding the mechanism of the cutting process itself and to perform in this way data about the influence of the cutting fluids
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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