| 51. |
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Agglomeration, clusters and entrepreneurship : Studies in regional economic development
- 2014
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Samlingsverk (redaktörskap) (övrigt vetenskapligt/konstnärligt)abstract
- Regional economic development has experienced considerable dynamism over recent years. Perhaps the most notable cases were the rise of China and India to emergent country status by the turn of the millennium. With time now for hindsight, this book identifies some of the key forces behind these development successes, namely agglomeration, clusters and entrepreneurship.
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| 52. |
- Aghaee, Nam, et al.
(författare)
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Communication and Collaboration Gaps among PhD Students and ICT as a Way Forward : Results from a Study in Sweden
- 2015
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Ingår i: Proceedings of E-Learn. - : Association for the Advancement of Computing in Education. ; , s. 237-244
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Konferensbidrag (refereegranskat)abstract
- The low completion rate and slow progress in PhD education have been highlighted in many studies. However, the interaction problems and communication gaps that PhD students encounter make this attempt even more challenging. The aim of this study is to investigate the peer interaction problems and ICT based solutions from PhD students’ perspectives. The data collection method was an online questionnaire and in-depth interviews were used to follow up. The target group for the survey was the PhD students in Computer Science at Stockholm University. The total number of respondents for the survey was 53 PhD students and eleven randomly selected PhD students for the interviews. The results reflected a lack of peer interaction as an important issue in the perspective of the students. Based on this, the study showed several ICT solutions that have the potential to reduce the interaction problems and thereby improve PhD students’ collaborative learning and research quality.
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| 53. |
- Aghaee, Naghmeh, et al.
(författare)
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Interaction Gaps in PhD Education and ICT as a Way Forward: Results from a Study in Sweden
- 2016
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Ingår i: International Review of Research in Open and Distance Learning. - : Athabasca University Press. - 1492-3831. ; 17:3, s. 360-383
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Tidskriftsartikel (refereegranskat)abstract
- Many research studies have highlighted the low completion rate and slow progress in PhD education. Universities strive to improve throughput and quality in their PhD education programs. In this study, the perceived problems of PhD education are investigated from PhD students' points of view, and how an Information and Communication Technology Support System (ICTSS) may alleviate these problems. Data were collected through an online open questionnaire sent to the PhD students at the Department of (the institution's name has been removed during the double-blind review) with a 59% response rate. The results revealed a number of problems in the PhD education and highlighted how online technology can support PhD education and facilitate interaction and communication, affect the PhD students' satisfaction, and have positive impacts on PhD students' stress. A system was prototyped, in order to facilitate different types of online interaction through accessing a set of online and structured resources and specific communication channels. Although the number of informants was not large, the result of the study provided some rudimentary ideas that refer to interaction problems and how an online ICTSS may facilitate PhD education by providing distance and collaborative learning, and PhD students' self-managed communication.
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| 54. |
- Agic, Adnan, 1967-
(författare)
-
Analysis of entry phase in intermittent machining
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Cutting forces and vibrations are essential parameters in the assessment of a cutting process. As the energy consumption in the machining process is directly affected by the magnitude of the cutting forces it is of vital importance to design cutting edges and select process conditions that will maintain high tool performance through reduced energy consumption. The vibrations are often the cause of poor results in terms of accuracy, low reliability due to sudden failures and bad environmental conditions caused by noise. The goal of this work is to find out how the cutting edge and cutting conditions affect the entry conditions of the machining operation. This is done utilizing experimental methods and appropriate theoretical approaches applied to the cutting forces and vibrations. The research was carried out through three main studies beginning with a force build-up analysis of the cutting edge entry into the workpiece in intermittent turning. This was followed by a second study, concentrated on modelling of the entry phase which has been explored through experiments and theory developed in the first study. The third part was focused on the influence of the radial depth of cut upon the entry of cutting edge into the workpiece in a face milling application. The methodology for the identification of unfavourable cutting conditions is also explained herein. Important insights into the force build-up process help addressing the correlation between the cutting geometries and the rise time of the cutting force. The influence of the nose radius for a given cutting tool and workpiece configuration during the initial entry is revealed. The critical angle i.e. the position of the face milling cutter that results in unfavourable entry conditions has been explained emphasizing the importance of the selection of cutting conditions. Finally, the theoretical methods utilized for the evaluation of the role of cutting edge geometry within entry phase dynamics has been explored. This has revealed the trends that are of interest for selection of cutting conditions and cutting edge design.
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| 55. |
- Agic, Adnan, 1967-, et al.
(författare)
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Dynamic effects on cutting forces with highly positive versus highly negative cutting edge geometries
- 2019
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Ingår i: International Journal on Interactive Design and Manufacturing. - : Springer Science and Business Media LLC. - 1955-2513 .- 1955-2505. ; 13:2, s. 557-565
-
Tidskriftsartikel (refereegranskat)abstract
- Understanding the influence of the cutting edge geometry on the development of cutting forces during the milling process is of high importance in order to predict the mechanical loads on the cutting edge as well as the dynamic behavior on the milling tool. The work conducted in this study involves the force development over the entire engagement of a flute in milling, from peak force during the entry phase until the exit phase. The results show a significant difference in the behavior of the cutting process for a highly positive versus a highly negative cutting edge geometry. The negative edge geometry gives rise to larger force magnitudes and very similar developments of the tangential and radial cutting force. The positive cutting edge geometry produces considerably different developments of the tangential and radial cutting force. In case of positive cutting edge geometry, the radial cutting force increases while the uncut chip thickness decreases directly after the entry phase; reaching the peak value after a certain delay. The radial force fluctuation is significantly higher for the positive cutting edge geometry. The understanding of such behavior is important for modelling of the milling process, the design of the cutting edge and the interactive design of digital applications for the selection of the cutting parameters.
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| 56. |
- Agic, Adnan, 1967-
(författare)
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Edge Geometry Effects on Entry Phase by Forces and Vibrations
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Intermittent machining is in general strongly related to the large impacts in the entry phase and related vibrations. The influence of the impact forces and vibrations on the cutting process is dependent on workpiece material, structural properties of the tool-workpiece system, cutting edge geometries and cutting parameters. Cutting forces adopt generally a periodic behaviour that gives rise to forced vibrations. In addition, self-induced vibrations may arise because of lowrigidity and insufficient damping in the tool-workpiece system at specific cutting parameters. The ability of the cutting tool to carry the loads during the entry phase and minimize the vibrations is often the key parameter for an effective machining operation.This research work is based on the experiments, analytical studies and modelling. It was carried out through six main studies beginning with a force build-up analysis of the cutting edge entry into the workpiece in intermittent turning. This was followed by a second study, concentrated on modelling of the entry phase which has partly been explored through experiments and theory developed in the first study.The third part was focused on the influence of the radial depth of cut upon the entry of the cutting edge into the workpiece in a face milling application. The methodology for the identification of unfavourable radial depth of cut is also addressed herein. Next, effects of the cutting edge on the vibrations in an end milling application were investigated. This study was related to a contouring operation with the maximum chip thickness in the entry phase when machining steel, ISO P material.The results of this work provide some general recommendations when milling this type of workpiece material. After that, the focus was set on the dynamic cutting forces in milling. The force developments over a tooth engagement in milling showed to be strongly dependent on the cutting edge geometry. A significant difference between highly positive versus highly negative geometry was found.The implication of this phenomena on the stress state in the cutting edge and some practical issues were analysed. Finally, the role of the helix angle on the dynamic response of a workpiece was investigated. The modelling technique using force simulation and computation of the dynamic response by means of modal analysis was presented. Extensive experimental work was conducted to compare the modelling and experimentally obtained results. The modelling results showed a similar trend as the experimental results. The influence of helix angle on the cutting forces and the dynamic response was explained in detail.The research conducted in this work contributes to the deeper understanding of the influence of the cutting edge geometry and the cutting parameters on the force build up process during the entry phase. The presented studies investigate the force magnitudes, force rates and dynamic behaviour of the tools and workpieces when machining at the challenging entry conditions. The methodologies applied are focused on the physical quantities as forces and vibrations rather than the experimental studies that evaluate tool life. The methods and results of the research work are of great interest for the design of the cutting tools and optimization of the cutting processes.
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| 57. |
- Agic, Adnan, 1967-, et al.
(författare)
-
Experimental analysis of cutting edge effects on vibrations in end milling
- 2019
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Ingår i: CIRP - Journal of Manufacturing Science and Technology. - : Elsevier BV. - 1755-5817 .- 1878-0016. ; 24, s. 66-74
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Tidskriftsartikel (refereegranskat)abstract
- The ability to minimize vibrations in milling by the selection of cutting edge geometry and appropriate cutting conditions is an important asset in the optimization of the cutting process. This paper presents a measurement method and a signal processing technique to characterize and quantify the magnitude of the vibrations in an end milling application. Developed methods are then used to investigate the effects of various cutting edge geometries on vibrations in end milling. The experiments are carried out with five cutting edge geometries that are frequently used in machining industry for a wide range of milling applications. The results show that a modest protection chamfer combined with a relatively high rake angle has, for the most of cutting conditions, a reducing effect on vibration magnitudes. Furthermore, dynamics of a highly positive versus a highly negative cutting geometry is explored in time domain and its dependency on cutting conditions is presented. The results give concrete indications about the most optimal cutting edge geometry and cutting conditions in terms of dynamic behavior of the tool.
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| 58. |
- Agic, Adnan, 1967-, et al.
(författare)
-
Influence of cutting edge geometry on force build-up process in intermittent turning
- 2016
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Ingår i: Procedia CIRP. - : Elsevier BV. - 2212-8271. ; 46, s. 364-367
-
Tidskriftsartikel (refereegranskat)abstract
- In the intermittent turning and milling processes, during the entry phase the cutting edges are subjected to high impact loads that can give rise to dynamical and strength issues which in general cause tool life reduction. In this study the effect of geometrical features of the cutting tool on the force generation during the entry phase is investigated. Cutting forces are measured by a stiff dynamometer at a high sampling frequency. In addition, the chip load area is analyzed and related to the measured cutting force. The results show that micro-geometrical features, in particular the protection chamfer, significantly affect the force generation during the entry phase.
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| 59. |
- Agic, Adnan, et al.
(författare)
-
Influence of radial depth of cut on dynamics of face milling application
- 2016
-
Ingår i: The 7th International Swedish Production Symposium, SPS16, Conference Proceedings. - Lund : Swedish Production Academy. ; , s. 1-9
-
Konferensbidrag (refereegranskat)abstract
- The choice of milling cutter geometry and appropriate cutting data for certain milling application is of vital importance for successful machining results. Unfavourable selection of cutting conditions might give rise to high load impacts that cause severe cutting edge damage. The radial depth of cut in combination with milling cutter geometry might under some circumstances give unfavourable entry conditions in terms of cutting forces and vibration amplitudes. This phenomenon originates from the geometrical features that affect the rise time of the cutting edge engagement into work piece at different radial depths of cut. As the radial depth of cut is often an important parameter, particularly when machining difficult to cut materials, it is important to explore the driving mechanism behind vibrations generation. In this study, acceleration of the work piece is measured for different radial depths of cut and cutting edge geometries. The influence of the radial depth of cut on the dynamical behaviour is evaluated in time and frequency domains. The results for different radial depths of cut and cutting geometries are quantified using root mean square value of acceleration. The outcome of this research study can be used both for the better cutting data recommendations and improved tool design.
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| 60. |
- Agic, Adnan, 1967-, et al.
(författare)
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Influence of radial depth of cut on entry conditions and dynamics in face milling application
- 2017
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Ingår i: Journal of Superhard Materials. - New York : Allerton Press. - 1063-4576 .- 1934-9408. ; 39:4, s. 259-270
-
Tidskriftsartikel (refereegranskat)abstract
- The choice of milling cutter geometry and appropriate cutting data for certain milling application is of vital importance for successful machining results. Unfavorable selection of cutting conditions might give rise to high load impacts that cause severe cutting edge damage. Under some circumstances the radial depth of cut in combination with milling cutter geometry might give unfavorable entry conditions in terms of cutting forces and vibration amplitudes. This phenomenon is originated from the geometrical features that affect the rise time of the cutting edge engagement into workpiece at different radial depths of cut. As the radial depth of cut is often an important parameter, particularly when machining difficult-to-cut materials, it is important to explore the driving mechanism behind vibrations generation. In this study, acceleration of the workpiece is measured for different radial depths of cut and cutting edge geometries. The influence of the radial depth of cut on the dynamical behavior is evaluated in time and frequency domains. The results for different radial depths of cut and cutting geometries are quantified using the root mean square value of acceleration. The outcome of this research study can be used both for the better cutting data recommendations and improved tool design.
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