Asymmetrical roll bending process study : dynamic finite element modeling and experiments

Roll bending is an efficient metal forming technique, where plates are bent to a desired curvature using forming rolls. This type of sheet forming process is one of the most widely used techniques for manufacturing axisymmetric hollow shapes. Moreover, this process is beginning to be taken into serious consideration by industries for producing large, thick parts such as the conically shaped crown of a Francis turbine runner or of a wind turbine tower. Because of the numerous processing parameters, reducing the bending force and improving the accuracy of the final shape are significant challenges in the roll bending process. Therefore, the primary aim of this research is to find the strategies for reducing forming forces and improving final part quality by employing numerical and experimental methods. In this thesis, a 3D dynamic Finite Element (FE) model of an asymmetrical roll bending process is developed using the Ansys/LS-Dyna software. The simulation results are then compared with experiments performed with instrumented parts and roll bending machine. The parameters that affect the accuracy of the final shape, the bending forces and the residual strain left in the formed plate have been investigated. Applying this 3D dynamic FE model in an industrial context may predict the forming forces or the accuracy of the final shape’s radius and thus will decrease the setup time before manufacturing. The forming forces can be reduced by heating the plate. In this research, the relationships between the heating plate temperature and the output parameters of roll bending process such as applied forces and final shape quality have been studied by performing FE simulation and analytical computations. These results yield to a better understanding of the mechanism of the process and provide an opportunity for the design of an efficient heating system to control the heat energy to be input in the plate during the roll bending process. This research also proposes a new, simple approach for reducing flat areas and forming forces. This approach includes moving the bottom roll slightly along the feeding direction and adjusting the bottom roll location. The FE results indicate that this new approach effectively minimizes the flat area extents and reduces also the forming forces

Design of parallel micromechanisms for knotting operation

Thesis (Master)--Izmir Institute of Technology, Mechanical Engineering, Izmir, 2009Includes bibliographical references (leaves: 61-63)Text in English; Abstract: Turkish and Englishix, 63 leavesThis thesis covers a study on the design of micromechanisms which are capable of imitating the knotting operation and their applications on carpet manufacturing.For this purpose, motion generation synthesis of a planar two degree-of-freedom serial manipulator is performed for a given path by using interpolation approximation. For a given four points, four design parameters are solved as a result of non-linear equations. Also, analysis of each stages of knotting operation is kinematically performed for the design of a cam-actuated mechanism which is designed as an alternative concept. Results of these analysis are used for the design of cam profiles those of which actuates the manipulators.After design stage of knotting micromechanisms, fully automated carpet loom design is introduced for a real-life experiment of designed mechanisms. Finally, assembly considerations of carpet loom and knotting mechanisms are given for carpet manufacturing purpose

Aeronautical engineering: A continuing bibliography with indexes (supplement 227)

This bibliography lists 418 reports, articles, and other documents introduced into the NASA scientific and technical information system in May, 1988

Aeronautical engineering: A continuing bibliography with indexes (supplement 214)

This bibliography lists 422 reports, articles and other documents introduced into the NASA scientific and technical information system in May, l987

Precision Machining

The work included in this book focuses on precision machining and grinding processes, including milling, laser machining and polishing on various materials for high-end applications. These processes are in the forefront of contemporary technology, with significant industrial applications. Their importance is also made clear by the important works that are included in the research that is presented in the book. Some important aspects of these processes are investigated, and process parameters are optimized. This is performed in the presented works with significant experimental and modelling work, incorporating modern tools of analysis and measurements

Multi cornered thin wall sections for crashworthiness and occupant protection

The desire to improve crashworthiness of a passenger vehicle for enhanced occupant safety has been a major challenge for decades. When a crash is unavoidable, it is the crash energy and the manner in which vehicle occupants experience the associated forces that will determine the extent of injury to those occupants. Axial collapse of the thin walled structures has been studied in detail over decades and the understanding was limited primarily to circular and square tubes. This research extended the knowledge beyond Square/Cylindrical shapes towards complex sections along with further exploratory works applicable to practical aspects. The hands on tools for designers to act as comparators for exercising flexibility in design decisions that are missing is addressed in this research study. Since axial crush mode is dominant in vehicle frontal crash and rear impact, dynamic and quasi-static, axial crush characterization has been developed with various cross-sections across different designs within the constrained packaging space. A new strategy has been proposed to improve energy absorption efficiency of thin-walled columns by designing extra stable corners in the cross-section. Several profiles of multi-corner thin-walled columns obtained through this strategy were presented and their crashworthiness capacities under axial crush loading were investigated analytically, experimentally, and numerically. Super Folding Element (SFE) concept was used in characterizing the collapse behaviour and parameters acting as comparators for designers were developed. The methodology was then utilized to develop a new 12-Edge section with better packaging at edge corners for robust collapse in asymmetric/inextensional mode with good corner angle and high energy absorption capacity. Thorough analysis of the results data from the crush tests both physical and numerical lead to an important conclusion that the maximation of edge corners with right packaging and favourable corner angles provided higher capacity to absorb the initial crash kinetic energy with good weight effectiveness. The 12-edge section’s dominance over the pack of other sections was widely analysed and established through the crush responses. A new methodology of design sensitivity analyses using DOE (design of experiments) based on Taguchi method was also proposed and performed to identify dominant characteristics. Analytical expressions for design parameters like Mean crushing force (Pm), Specific Energy Absorption(SEA), Solidity ratio(ϕ)and Collapse Efficiencies are derived while new design parameters of Weight effectiveness (WE), and structural effectiveness ( ) along with their application are proposed. The understanding and characterization developed at component and subsystem level fit well into the domain of upfront energy absorption motive and would not be complete if their ultimate responses are analysed at a full vehicle level in terms of their capacitance for crash energy absorption. The foundational dominance of 12-edge section at component level maturity and as applied to full automotive dynamic vehicle crash test resulted in achieving overall reduction in parameters reflecting Femur and chest injury of the occupants. Thus indicative of the potential of the multi-cornered sections for enhancement in crashworthiness of Automtive vehicles and reduction in occupant fatalities in severe crash events

Influences des paramètres du roulage à trois rouleaux asymétriques sur la qualité de la pièce formée

Le procédé de roulage à trois rouleaux asymétriques est un des processus les plus utilisés pour fabriquer des pièces cylindriques et coniques à partir de tôles planes. Les efforts engendrés, les contraintes résiduelles et la puissance nécessaire de roulage sont influencés par les paramètres du roulage et les propriétés du matériau (la contrainte élastique du matériau, l’épaisseur de la tôle, la largeur utile de roulage, le rayon de courbure et la conicité du tronc de cône). Afin de montrer ces influences, des analyses théoriques sur le roulage cylindrique et conique sont réalisées, sans tenir compte du frottement de la tôle avec les rouleaux. Le matériau de la tôle est considéré homogène, isotrope et a un comportement élastique parfaitement plastique. Les études analytiques ont démontré qu’une croissance de la contrainte élastique du matériau, de l’épaisseur, de la largeur utile, ou de la conicité du tronc de cône engendre des efforts de roulage, des contraintes résiduelles et une puissance de roulage plus importante. Par contre une croissance du rayon de courbure engendre des efforts de roulage, des contraintes résiduelles et une puissance de roulage moins importants. Ces résultats analytiques sont validés par des mesures expérimentales au laboratoire. Des vérifications géométriques sur les pièces finies ont montré que si la contrainte élastique du matériau, l’épaisseur, ou la conicité va en augmentant, la pièce roulée comporte moins des défauts géométriques. Il a était remarqué que lorsque la largeur utile, ou le diamètre est plus grande alors la pièce formée comporte plus des défauts géométriques. Pour maitriser davantage le procédé de roulage à trois rouleaux asymétriques, il reste à traiter les influences de la température et le nombre de passes sur la qualité du roulage et des pièces

Inverted Shell Foundation Performance In Soil

The use of shells in foundation structures over traditional forms has grown steadily since their inception in the early nineteen–fifties. Shell foundations outperform conventional flat footings and are reputable performers especially when heavy superstructural loads are to be transmitted to weak bearing soil. The geotechnical performance of shells in an elastic continuum concerns their bearing capacities and settlement behaviour, whose study has been trailing behind that of their structural performance. Bringing contact pressures closer to uniformity at the soil–shell structure interface is essential in developing a viable behavioural response under vertically concentric and monotonic loading conditions. This study encapsulates the development of new shell foundation geometries employing shell inversion under such loading conditions. Experimental investigation involves validation of the numerical phase in a comparative study following a two–dimensional analysis of shell models using commercially available geotechnical software with finite element analysis. New inverted triangular footings embedded in sand composed of ultra–high performance iShell Mix concrete using fiber–reinforced polymeric (FRP) microfibers are analyzed. A parametric analysis examines key sensitivity elements including shell angle and shell thickness in granular soil for both upright shells and their inverted counterpart. Linearly–elastic behaviour of concrete material is assumed while soil media is modeled under nonlinear elastic perfectly–plastic conditions following the Mohr–Coulomb yield criterion for loose, medium and dense sand states. Theoretical modeling was developed to generate inverted shell bearing capacity factors to predict ultimate bearing capacities of the shell footings. Simulation efforts scrutinized reveal comparable performance with bearing capacity increase of 3 – 5% for the inverted shells over upright shell models and notable improvements of 42 – 45% over conventional flat footings. The developed models investigated represent forefront configurations of superior performance signifying that shells in foundations be highly regarded and fully exploited whenever feasible