bluuebunny/crossref_metadata_2025 huggingface dataset:
Two Fabrication Schematics of Silicon Micro Perforated Panel Based on MEMS Technology
Authors: Wu Shao Hua , Zhao Zhan , Guo Li Jun , Du Li Dong , Xiao Li , Fang Zhen , Zhao Jun Juan , Xuan Yun Dong
Published: February 2012

Two kinds of fabrication schematics of micro perforated panel (MPP) based on MEMS technology is expatiated in the article. MPP has been widely used to reduce noise, and theory reveals that better ability of sound absorption of the MPP will be getting by means of reducing the diameters and increasing the dense of the perforators properly. Small error of the dimension will decline the sound absorption seriously on such a scale. MEMS technology is applied to fabricate the micro perforated panel which is hard to be realized utilize machine. The parameters are calculated based on the theory of Maa D-Y to obtain a kind of wide band, high sound absorption structure. The computer simulation is also conducted to forecast the capability of the MPP and the experiment result shows the accordance with the simulations.
Design of Ethernet Interface Based on FPGA and W5300
Authors: Li Sheng Kun , Wang Xue Song
Published: February 2012

In order to give consideration to the speed and distance of data transmission, we design and put forward a design of ethernet interface based on FPGA and W5300, in which we achieve the high-speed ethernet connectivity between equipment and terminal device. UDP unicast mode is adopted in ethernet interface, and high-quality transmission medium is used to ensure the reliability of transmission link. It is proved that, the interface, with characteristics of relatively high-speed and long-distance, is relatively reliable and almost no package lost.
Detecting DNA Using a Single Graphene Pore by Molecular Dynamics Simulations
Authors: Si Wei , Sha Jing Jie , Liu Lei , Li Jia Peng , Wei Xiao Long , Chen Yun Fei
Published: February 2012

DNA charged negatively could be transported through a solid nanopore by the force of an electrical field. Recently, the nice properties of graphene attract a lot of researchers. In this paper, A single graphene membrane was punched to form a nanopore and a ds-DNA was driven to pass through the pore by all-atom molecular dynamics simulations. The single graphene membrane was demonstrated useful in DNA sequencing. It suggested that the velocity of DNA translocating through a single graphene pore could be controlled by adjusting the appropriate voltage and the diameter of the nanopore.
MEMS Grating with Interdigitated-Comb Structure
Authors: Zhang Heng , Yao Jun , Tao Feng Gang , Zhuang Xu Ye
Published: February 2012

Grating as an important spectral component can be applied to spectral analysis, filtering, dispersion compensation, sensing and so on. Their advantages are compactness, potentially high actuation speed and the ability to deflect light at large angles. In this paper, a MEMS interdigitated-comb grating actuated by a comb-drive actuator is presented. An experiment is performed to demonstrate how the proposed grating works with an applied voltage. At 85V, the displacement of comb-drive actuator can achieve 2.1μm; accordingly the gap between the interdigitated-comb gratings varies by 2.1μm. The mechanical and the optical sensing properties of the MEMS grating are both analyzed in this paper. This grating can be widely used in optical sensor and to detect the micro-displacement.
Stretch Blow Moulding of Mineral Filled PET
Authors: Billon Noelle , Haudin Jean Marc , Vallot Camille , Babin Charles
Published: February 2012

Injection Stretch Blow mouldng is a two step processing that was designed and optimized mainly using unfilled PET resins. This study focuses on stretch blow moulding of a PET filled with a few percent of sub micronic mineral fillers. Based on DSC, DMA, tensile tests as well as blowing on prototype machine main effects of fillers are analysed. It is demonstrated that fillers increases crystallization kinetics resulting in a reduction of the processing range. Difference in strain hardening induced by fillers makes it necessary to adjust blowing temperature. However main effect occurs during heating phase. Temperature within the perform is much less homogeneous than in PET making thermal gradient totally different if heating protocole is kept unchanged. Once heating is controlled to reach to equivalent thermal gradients as for PET blowing is possible and rather equivalent to that of pure PET.
Measurement & Modelling of Slip during Plug-Assisted Thermoforming
Authors: Martin Peter , Choo Hui Leng , O'Connor Ciaran P.J.
Published: February 2012

Plugs are a common feature of most deep-draw thermoforming processes and are used to ensure that the wall thickness distribution in the final product is controlled and balanced. Through contact with a moving mechanical plug, the heated sheet is locally captured and protected from excessive deformation and thinning. Previous work has clearly demonstrated that slip plays a critical role during this process and that its magnitude is determined by frictional properties that are strongly dependent on temperature. Work to discover the appropriate friction relationships has been very limited to date and this has greatly hampered the progress towards effective thermoforming process simulations. In this paper the magnitude of slip that occurs during the plugging stage of the thermoforming process was experimentally investigated. Preform shapes were created by pushing a specially designed plug into a heated sheet and then freezing it at the end of the plug displacement. A variety of processing parameters such as the plug and sheet materials, the temperature and plug displacement were evaluated. The results show that large variations in slip occur when different combinations of plug and sheet materials are employed and these are most affected by the contact temperature. A finite element based simulation of the plugging process is currently being constructed and it will be used to investigate different friction relationships and compare their performance with the experimental behaviour.
Mechanical Behavior of Highly-Flexible Elastomeric Composites with Knitted-Fabric Reinforcement
Authors: Bekisli Burak , Pancrace Johann , Nied Herman F.
Published: February 2012

This paper examines critical issues associated with the fabrication and forming of highly-flexible polymeric composites, reinforced with knitted-fabric structures. Knitted-fabric reinforcements have not generally been preferred over more traditional woven reinforcements in high-performance composites, mainly because of their lower stiffness/strength performance when embedded in a rigid, thermosetting matrix material. However, with their unique formability, knitted fabrics promise great potential in applications where large deformation of the structure is desirable; such as energy/impact absorption and forming applications. One very attractive feature of knitted composite materials, is the large displacements that the underlying knitted fabric can potentially undergo before exhibiting a significant increase in stiffness. The unusual extensional behavior of knit fabric is attributed to the fact that the fibers are more-or-less free to slide over each other before the yarns become highly oriented, eventually “locking” in a packed formation. When the loops become highly elongated, the knit fabric achieves its maximum resistance to in-plane deformation, and exhibits a stiffness closely related to the elastic stiffness of the straightened fiber/yarn bundles. The unique formability of knitted fabrics is mainly due to this yarn movement. The highly “stretchable” behavior of knitted textile reinforcement materials can be used to great advantage in thermoforming composite structures. In order to fully utilize the exceptional stretch properties of the knitted-fabric, the matrix material should be able to deform at least as much as the fabric, and the knitted yarn movements need to be restricted by the matrix as little as possible. In this study, a multi-level finite element procedure was developed to analyze and control the deformation characteristics of plain weft knit reinforced composites. A database of mechanical properties for various knit geometries was obtained. Using these results, it is shown that carefully “tailored” knit fabric reinforcement can be used to improve mechanical performance and facilitate polymer forming processes, such as thermoforming. In this study, elastomeric materials such as polyurea and thermoplastic elastomer (TPE) were used to fabricate composites with knitted-fabric. Two different types of arrangements were experimentally studied: knitted fabric embedded in the elastomer and a sandwich of knitted fabric between elastomeric skins. It is shown that by fully utilizing the high stretchability of the knitted fabric reinforcements, attractive material properties can be obtained especially for energy/impact absorption and forming applications. The improvement of thermoforming process stability with the use of carefully tailored knitted fabric reinforcements is also presented.
Methodology to Produce Locally Heat-Treated EN AW-5182 Aluminum Alloy Sheet Metal Parts
Authors: Sulzberger Andreas Magnus , Merklein Marion , Staufner Wolfgang , Wortberg Daniel
Published: February 2012

Compared to steel, aluminum has a reduced formability. The consequence is that the drawability of aluminum needs to be extended. This can be achieved by a material recovery that takes place near the zones in which a material failure is initiated during deep drawing. In the considered process, first the aluminum component will be preformed to a specific stress state. In the second step, it will be partial heat treated, before the component is getting finished. Based on the selective intermediate introduction of heat, the material flow of the pre-drawn part is influenced in such a manner that the most highly stressed zones are subjected to further reduction in sheet thickness. This is possible by sacrificing material out of zones near the crack. These areas are referred to below as “sacrificial zones”. They depend on the position of the critical region as a result of the material pre-strain. In these regions, the temperature can be varied. This paper focuses on the development of a methodology to determine a layout of intermediate heat treatment of preformed aluminum sheet metal components. In order to determine such a layout, a principal part must be designed on which the methodology can be reviewed.
Wire-EDM of ZTA-TiC Composites with Variable Content of Electrically Conductive Phase
Authors: Landfried Richard , Kern Frank , Burger Wolfgang , Leonhardt Wolfgang , Gadow Rainer
Published: February 2012

Electrical Discharge Machining (EDM) enables an economical production of high performance ceramics with high hardness and toughness in complex shapes and fine structures. Recent research work identified ZTA-TiC composites as one of the most promising ED machinable materials with high strength for injection molds, which significantly reduce abrasive wear. In order to improve the surface finish and processing time of ED-machined ceramics zirconia toughened alumina composites with addition of 20-30 vol.-% titanium carbide as electrically conductive phase were developed. Processing was performed by hot pressing at 50 MPa and 1525°C. Mechanical and electrical properties were investigated. The influence of TiC volume fraction on the surface quality after wire-EDM and the maximum possible sample feed rate was analyzed. The variation of TiC content moderately influences toughness and bending strength while electrical resistivity and indentation modulus strongly depend on the volume fraction of TiC. A competitive feed rate of 2.45 mm/min for samples with a height of 13 mm was obtained. Further improvement of the surface quality can be achieved by increasing the amount of the electrically conductive phase. Additional machining steps proved feasible to decrease significantly the surface roughness and corrugation depth without inducing any defects in bulk material.
Study on Single-Pulse Discharges under Special Flushing Conditions
Authors: Munz Markus , Sternkopf David , Haas Rüdiger
Published: February 2012

Investigations on the special flushing conditions with an electrical discharge drilling machine were done to analyze single discharges. While flushing speeds in electrical discharge drilling are quiet higher as in electrical discharge sinking, the craters are influenced by the strong flushing. The topography of the craters in terms of depth, length and volume were analyzed. Crater depth and crater length are increasing with higher flushing speeds. Under a dielectric flushing the removed material on the tool electrode is less than on the workpiece. If the volume flow is high enough, the whole plasma channel is pushed in the direction of the flow. A computational fluid dynamics analysis was done to simulate the flow speeds in the narrow gap. Flow speeds above 500 m/s were simulated in the gap.
Fully Coupled Numerical Simulation of Electromagnetic Forming
Authors: Doley Jyoti Kumar , Kore Sachin D.
Published: February 2012

Electromagnetic forming (EMF) is a typical high speed forming process using the energy density of a pulsed magnetic field to form work pieces made of metals with high electrical conductivity like aluminum. In view of new lightweight constructions, special forming processes like EMF gain importance for the associated materials. In this paper modeling of electromagnetic sheet metal forming process is carried out by using commercial finite element software LS-DYNA®. A fully coupled numerical simulation method has been incorporated to study the interaction of the electromagnetic field and the structural deformation via transient analysis. Studies on the effect of first current pulse in electromagnetic forming are reported in the paper.
Effects of the Laser Beam Interaction with the Workpiece Material
Authors: Coteaţă Margareta , Slătineanu Laurenţiu , Grigoraş (Beşliu) Irina , Pop Nicolae
Published: February 2012

The laser beam machining uses the effects generated at the impact of the workpiece surface with a laser beam that has adequate energetically and spatial - temporal characteristics. It is known that, as result of the laser beam impact with the workpiece material, local chemical and physical effects are signalized. In order to study such effects and simultaneously the technological possibilities of laser beam equipment, some experimental researches were developed on an Ytterbium fiber laser equipment of 300 W. Movements of the laser spot along established trajectories were ensured, changing the sizes of the machining parameters. The influence exerted by the machining parameters and by the materials characteristics on the material removal from the test piece was highlighted. The surface layer modifications were also studied.
Roll Forming Set-Up Influence in the Forming Forces and Profile Quality
Authors: Sáenz de Argandoña Eneko , Larrañaga Jon , Legarda Aritz , Galdos Lander
Published: February 2012

The roll forming process is a very interesting process for the production of profile shaped parts because of its high production rate, low investment and efficient use of the material. However, as in most of the manufacturing processes, the set up of the machine is very important for the quality of the profiles to be manufactured being the traditionally used trial and error method high time and scrap consuming. Within the set up, one of the most important variables to be defined is the right gap or distance between the upper and the lower roll at each station. This gap can lead to, or avoid, the appearance of geometrical errors such as differences in springback effect or longitudinal bow of the final profile. Furthermore, to find the correct gap between the rolls,a traditional tedious and costly work must be made based on a trial and error methodology. Different sensor based methodologies have already been implemented successfully in other forming processes. The present work aims at evaluating if force and torque measurements are a viable solution to decrease the roll forming process set-up time. This way, the effect of the gap for three different materials, a DC01, DP600 and MS1200 steel, has been analyzed. For this purpose, force and torque measurement together with final geometry measurements have been made at different gap configurations. A correlation between the profile quality and the process variables has been carried out in order to identify the influence of the gap at the setting up of the machine.
Investigation on Surface Integrity of STAVAX ESR AISI 420 Martensitic Stainless Steel by Cryogenically Treated Steel Balls with Low Plastic Burnishing Tool
Authors: Thamizhmanii Sivapraksam , Rajendran K. , Rasool Mohideen , Hassan Sulaiman
Published: February 2012

Low plasticity burnishing (LPB) is a new method of surface improvement, which raises the burnishing to the next level of sophistication. LPB can provide deep compression for improved surface characteristics. The study focuses on the surface roughness, micro-hardness and surface integrity aspects on soft AISI 420 STAVAX ESR martensitic stainless steel AISI 420 material. This material is pronounced as difficult to cut materials like titanium, Inconel 718 etc. The investigation of surface integrity was done on this materials in terms of operating parameters like sliding speed, feed rate and depth of penetration (DOP) identifying the predominant factors among the selected parameters. The steel balls used were cryogenically treated at sub zero temperature of -176 degrees. Sub-surface micro-hardness study were also done to asses the depth of compression altered zone, surface roughness and surface hardness. The process can be applied to critical components effectively as the LPB process has cycle time advantages and also low investment cost. This can be also realized by introducing on high speed machines. This process was studied by using cryogenically treated different ball diameters at various operating parameters. This also improved on concentricity of work material. More the depth of compression produced low surface roughness at low sliding speed, feed rate with larger ball diameter. The DOP also helps to improve on surface and sub-surface hardness and close roundness. There are limitations on DOP beyond which the surface deteriorated.
Effect of Convex Sheared Punch Geometry on Cutting Force of Ultra-High-Strength Steel
Authors: Kutuniva Kari , Karjalainen Jussi A. , Mäntyjärvi Kari
Published: February 2012

Extremely high strength of the ultra-high-strength steels leads to increased load factors on the tooling machines and punching tools. This experimental study examines how much convex punch geometry affects cutting forces when punching ultra-high-strength steels. Tools used in punching tests were four different convex sheared rooftop punches and one conventional flat end punch, to which rooftop punches were compared to. The material in punching tests was ultra-high-strength steel Ruukki Optim 960 QC, with a thickness of 4 mm. The test material in punching tests was sheared with rooftop punches and a flat end punch and occurred cutting forces were measured. The qualities of punched holes were evaluated visually and the roundness measurements were also performed. The results show that the cutting forces of Optim 960 QC can be reduced radically with optimal convex punch geometry. With using 14-degree shear angle of the punch end, the cutting forces reduced up to 57 % compared to forces of the conventional flat end tool. However, largest tested shear angles caused several negative effects on the cutting quality of the holes and therefore they are not suitable in all applications. Punching tests proved that the cutting clearance had no appreciable effect on cutting forces when punching ultra-high-strength steel. Instead there was a noticeable effect on the quality of the punched hole, especially when large shear angles were used.
Design of Lightweight Composite Structures: A Parameter Free Structural Optimization Approach
Authors: Fischer Michael , Masching Helmut , Firl Matthias , Bletzinger Kai Uwe
Published: February 2012

This contribution presents computational concepts and algorithmic techniques for simulation and gradient-based optimization of geometrically nonlinear and large-scale finite element models of composite structures. Several industrial application examples illustrate the methods, show the applicability to large problems, and prove the high parallel efficiency.
Experimental Characterization and Modeling of Bending Properties of Woven Fibrous Preforms
Authors: Syerko Elena , Comas-Cardona Sebastien , Binetruy Christophe
Published: February 2012

The properties of final composite parts depend on properties of dry preforms often being formed over doubly-curved shapes. In this case the fibrous preforms exhibit intricate large deformations, including shear, tension, and bending modes. Although the bending stiffness of fibrous materials is small, in shaping of preforms, when wrinkling occurs, its influence is important, not negligible and responsible for the wrinkles shape. Because of the structural and mechanical peculiarities, the experimental determination of bending properties of fibrous materials is rather complex, and there is no unique generally adopted test. A set of cantilever tests was chosen to be carried out in this study, in the form of sequence of different loading cases for one material that permits to reveal the eventual non-linear and non-elastic behavior of the material in bending. The tests were realized for glass fabrics with different types of weaving patterns and different areal weights. The effect of these parameters on the bending response is studied. The analysis of the data on bending of fabrics and bending of yarns, extracted from fabrics with the preserved undulated shape, is performed as well. The regions of the deformed specimens characterized by the largest scatter of experimental data are identified and analyzed. Besides, the analytical model based on corrugated plates theory, taking into account the undulated architecture of fabrics, is employed to characterize its bending properties, and to make a future comparison with the test results.
Analyze of the Contact Behaviour between Two Layers of Dry Glass Plain Weave Fabric
Authors: Allaoui Samir , Hivet Gilles , Ouagne Pierre
Published: February 2012

The market demand for thicker complex shaped structural composite parts is increasing. Processes of the Liquid Composite Moulding (LCM) family, such as Resin Transfer Moulding (RTM) are considered to manufacture such parts. The first stage of the RTM process concerns the preforming of the part. During the preforming of multi-layered reinforcements, friction between the plies occurs and needs to be characterize and then to be taken into account for the forming simulation. An experimental device designed to analyze the ply/ply, ply/tool and yarn/yarn frictions has been built. Tests carried out on a glass plain weave highlight specific contact behaviour for dry reinforcement fabric in comparison to non-technical textiles. This behaviour exhibits a substantial variation of the contact tangential loads which is directly related to shocks between the yarns. It demonstrated that period and amplitude of the friction response is directly related to the relative positioning of the samples but also to fabric meso-strucrure. In addition, the sample relative orientation has a significant influence on the friction response. The meso-architecture is responsible for the high variations of the friction coefficient as a function of the ply orientations for different fabrics. In addition, the friction response appears to be very sensitive to tests parameters like the relative positioning, orientation of the samples and the cycling. A honing effect classically observed in dry fabric testing has also been pointed out through cyclic experiments. It can be attributed to both fibre material abrasion and fibre reorganisation inside the yarn.
Lightweight Construction by Means of Profiles
Authors: Chatti Sami , Pietzka Daniel , Ben Khalifa Nooman , Jäger Andreas , Selvaggio Alessandro , Tekkaya A. Erman
Published: February 2012

This paper shows some product and process developments at the Institute of Forming Technology and Lightweight Construction of the TU Dortmund University supporting the lightweight construction. It presents the manufacturing of lightweight profiles by hot extrusion and their benefits as well as their design, material, and manufacturing potential for lightweight construction. Examples of process extensions in hot extrusion like curved profile extrusion, twisted profile extrusion and manufacturing of functional graded profiles and profiles with variable cross-sections during extrusion are shown. These procedures allow a flexible change of the profile geometry or contour in longitudinal axis and, therefore, support the shape lightweight construction. Other extensions like composite profile extrusion and energy efficient extrusion of profiles from scrap materials like chips support the material lightweight construction. The manufacturing and use of these profiles allow the realisation of diverse lightweight construction principles and promise to become a pillar of lightweight construction in future.
Modelling of Strain Hardening Behaviour of Sheet Metals for Stochastic Simulations
Authors: Quetting Florian , Hora Pavel , Roll Karl
Published: February 2012

In current forming simulations, Ghosh or Hockett-Sherby extrapolation functions are used to model strain hardening effects of sheet metals. When it comes to stochastic simulations, the respective parameters have to be recalculated according to the scattering of the mechanical material properties like yield or tensile strength. As present stochastic samplings for deep drawing simulations only consider yield strength and tensile strength, it is non-trivial securing the extrapolated area of strain hardening curves due to lack of data beyond uniform strain. It is current practice to improve the description of the flow curve beyond uniform elongation point by using the maximum force criterion, which takes into account the gradient of the yield curve at the last known point. The corresponding system of equations has to be solved numerically. We propose a method for adjusting parameters of the Ghosh or Hockett-Sherby extrapolation functions, which overcomes the need of numerical calculations and keeps flow curve information from the extrapolated interval, even if the stochastic sampling doesn’t incorporate any data regarding that area.
2D Meshless Solution of Elastoplastic with Damage Problem
Authors: Sendi Zohra , Labergère Carl , Saanouni Khemais , Salah Hedi Belhadj
Published: February 2012

The Finite Element Method (FEM) is today the most widely used in numerical simulation of forming processes, due essentially to the continuous improvement of the FEM over the years and the simplicity of its implementation. However, this method has some limitations such as the distortion of elements under large inelastic deformation and the influence of the mesh on the results in several applications. The simulation of metal forming process with large plastic strain is a classical example where the successive remeshing is often the proposed solution in this case. But the remeshing raises the problems of precision and computing time. In this context and in order to avoid the remeshing process, a Meshless method is experimented in the solving of an elastoplastic problem coupled to the isotropic ductile damage. An Element Free Galerkin (EFG) method based on Moving Least Square (MLS) concept is considered in this proposal. A two-dimensional Mechanical problem was studied and solved by a Dynamic-Explicit resolution scheme where the material behaviour is based on an isotropic hardening fully coupled to ductile damage model. In a first step a parametric study is conducted in order to find the most influent parameters on the accuracy of the results. The effect of the number of nodes, of support nodes, of quadrature points, the effect of the time-step and the support domain size are analysed and optimal values are found. In a second step, the meshless results are compared with those of the finite element method and some concluding remarks relative to the accuracy and the computing time are given.
Analysis of Plastic Flow during Friction Stir Spot Welding Using Finite Element Modelling
Authors: Gao Zeng , Krumphals Friedrich , Sherstnev Pavel , Enzinger Norbert , Niu Ji Tai , Sommitsch Christof
Published: February 2012

Friction stir spot welding (FSSW) as a variant of the linear friction stir welding is implemented in automotive industry as a partial replacement of resistance spot welding for aluminium. FSSW as a solid state joining technology, primarily takes advantage of severe thermoplastic deformation, to achieve the joining between two parts, which can be from the same material or even dissimilar. In this paper, the coupled thermo-mechanical viscoplastic finite element formulation is presented based on the character of FSSW. The model was calibrated by comparing temperature history obtained from the simulation with experimental data and subsequently used to investigate the effective strain distribution in the weld zone as well as the material flow and the shape of the stir zone.
Constitutive Equations for Finite Element Simulation
Authors: Bruni Carlo , El Mehtedi Mohamad
Published: February 2012

The necessity to simulate extrusion processes requires the knowledge of the material in terms of the constitutive equations. The present investigation deals with the development of a methodology based on the multivariable regression analysis in order to predict the flow behaviour of a ZEK200 Mg alloy in the interval of temperature varying between 150 and 450°C. The proposed models relate the flow curve levels with temperature, strain rate and deformation with the variables selected using the statistical method. It has been found that the proposed methodology allows the modeling of the flow behaviour of the Mg alloy under investigation from the beginning of the plastic deformation down to the softening phase taking into account the peak value. In addition, it is comparable, in terms of the temperature intervals considered in the modeling, with the Sellars and Tegart-based models.
Numerical Approach for the Evaluation of Seam Welding Criteria in Extrusion Processes
Authors: Schwane Martin , Kloppenborg Thomas , Reeb Andreas , Ben Khalifa Nooman , Brosius Alexander , Weidenmann Kay André , Tekkaya A. Erman
Published: February 2012

The accurate simulation and the optimization of extrusion processes can be a helpful technique to ensure producibility of complex aluminum profiles, for example for the automobile industry. Currently, the die designing is based on expert’s knowledge and cost-intensive prototyping. The paper deals with numerical investigations based on finite element simulations as well as experimental investigations of an industrial extrusion process. A newly developed method for longitudinal seam weld prediction is applied to analyze the position of the longitudinal welding line and the welding quality.
Velocity Gradients and the Evolution of Material Properties in a Narrow Layer near Surfaces of High Friction in Metal Forming Processes
Authors: Alexandrov Sergei , Jeng Yeau Ren
Published: February 2012

Theoretical solutions for several rigid plastic models used to describe plastic flow in metal forming processes are singular in the vicinity of maximum friction surfaces. In particular, velocity gradients and the equivalent strain rate approach infinity near such surfaces. Such singular behavior can be excluded from consideration by choosing another friction law or material model. However, a different approach is proposed in the present paper. The starting point of this approach is that many experiments show that velocity gradients are very high in the vicinity of surfaces of high friction and that a narrow material layer is formed near such surfaces whose properties are very different from the properties in the bulk. Taking into account that the equivalent strain rate has a significant effect on the evolution of material properties, this experimental fact suggests that a theory based on the singular plastic solutions can be developed to describe the formation of the aforementioned material layer. In the present paper such a theory is proposed to describe the evolution of grain size. It is assumed that, in addition to the equivalent strain rate, the material spin has an effect of the evolution of grain size. It is then shown that the solutions for the material spin are singular as well. The interrelation between the present theory and strain gradient theories of plasticity is discussed. It is shown that it is necessary to account for the strain rate gradient to propose a more adequate theory to deal with the material flow near surfaces of high friction. Some experimental results on the formation of the narrow layer of ultra-fine grains in the vicinity of the fraction surface in extrusion are presented. An illustrative example to relate these experimental results and the new theory is given.
Tribological Performances of Two White Lubricants in Hot Steel Forging
Authors: Dubois André , Dubar Mirentxu , Dubar Laurent , Tlili Brahim
Published: February 2012

The tasks of a lubricant used in the hot forging of steel is to reduce friction, cool down tool surfaces, and limit tool surfaces pollution by wear debris and oxides scales transferred from work piece surfaces. The most widely used lubricants in hot forging are dispersions of graphite particles in water or in oil. The graphite is involved to reduce friction. The liquid is used, first, to carry the graphite solid particles to the tool surfaces and, second, to reduce tool surface temperature. But graphite and vapours resulting from the lubricant deposition on hot surfaces lead to dirty workspaces. Some new lubricants are then developed in order to reduce friction in a cleaner way. When they are graphite free, those new lubricants are called “white lubricants”. The aim of the present work is to test two different white lubricants. The first one is a mineral salt; the second one is an organic salt. Lubricant performances are classified using the Warm and Hot Upsetting Sliding Test (WHUST). This friction bench simulates tests with contact pressure, sliding velocity, contactor and specimen temperatures similar to industrial ones. Before performing friction tests, work piece are heated up to 1200°C, contactors are heated up to 200°C, and lubricants are sprayed on contactor surfaces. Then the contactor slides against the specimen with a constant penetration, leaving a residual deformed track on its surface. Direct WHUST results are tangential and normal loads measured on contactor, surface roughness and chemical compositions on specimen and contactor surfaces. “Wear markers” are derived from those direct results, and provide useful information on the ability of the tested lubricants to reduce friction and protect tool surfaces. In the present study, tests are performed with different sliding speed and different contact pressure. The two white lubricants are compared to a generic graphite in water dispersion. Results show the tested white lubricants lead to coefficient of friction in the same range of the graphite lubricant one, but white lubricants lose their ability to reduce friction as soon as the sliding lengths becomes greater to 10 mm, where graphite lubricants can undergo sliding length greater than 30 mm.
Optimization of Pre-Stressed Press Frames
Authors: Strano Matteo , Monno Michele , Rossi Andrea
Published: February 2012

Pre-stressing is a technique often used in presses, and it is obtained either by wire or tape winding or by bolted rods. Pre-stressing is always performed by combining two materials: one which is tougher and used as the pre-stressing medium and one which is less resistant and used as the pre-compressed casing. Pre-stressing can be applied for several reasons: for reducing the cost of manufacturing and assembling the press frames in case of very large tonnage presses, for reducing the deflections and elongations of the frames during pressing operation, for improving the fatigue resistance of the press components, etc. In this paper a simple analytical model of loads, stresses and deformations will be proposed for pre-stressed columns. The results of the model will be validated and compared to the results of realistic FEM simulations of the behavior of the press frame in operation. The equations of the analytical models will be then used as the constraints of a global optimization algorithm, implemented with Matlab. The results clearly show that, only if the press frame structure is monolithic, it is possible to obtain a solution which is truly optimal by pre-stressing, i.e. by combination of a more expensive and high performance material with a relatively “poor” material. This conclusion seems to be robust with respect to potential noise or uncertainty issues, which in this case are mainly related to the coefficient of the objective functions.
Texture Based Finite Element Simulation of a Two-Step Can Forming Process
Authors: Glavas Vedran , Böhlke Thomas , Daniel Dominique , Leppin Christian
Published: February 2012

Aluminum sheets used for beverage cans show a significant anisotropic plastic material behavior in sheet metal forming operations. In a deep drawing process of cups this anisotropy leads to a non-uniform height, i.e., an earing profile. The prediction of this earing profiles is important for the optimization of the forming process. In most cases the earing behavior cannot be predicted precisely based on phenomenological material models. In the presented work a micromechanical, texture-based model is used to simulate the first two steps (cupping and redrawing) of a can forming process. The predictions of the earing profile after each step are compared to experimental data. The mechanical modeling is done with a large strain elastic visco-plastic crystal plasticity material model with Norton type flow rule for each crystal. The response of the polycrystal is approximated by a Taylor type homogenization scheme. The simulations are carried out in the framework of the finite element method. The shape of the earing profile from the finite element simulation is compared to experimental profiles.
Identification of the Plastic Behaviour in the Post-Necking Regime Using a Three Dimensional Reconstruction Technique
Authors: Rossi Marco , Fabrice Pierron
Published: February 2012

Nowadays a wide number of constitutive models are available to describe the plastic behaviour of metals at large deformations including anisotropy, strain rate effect, kinematic hardening etc. Often the main limitation to the practical applicability of a model resides in the difficulty of experimentally identifying the constitutive parameters. At large deformations the identification can become very complicated because of the occurrence of instabilities, e.g. localized necking or buckling, which create a complex three-dimensional stress and strain state inside the specimen. In these cases, the identification problem is usually tackled by Finite Element Model Updating where a numerical model of the test is built up and the parameters are iteratively varied to achieve the best agreement with the experiments. Recently it has been demonstrated that the Virtual Fields Method (VFM) can be successfully adopted to solve the identification problem using three dimensional displacement data [Rossi and Pierron, Identification of plastic constitutive parameters at large deformations from three dimensional displacement fields, Comp. Mech., 2011]. This paper presents the first experimental validation of this approach. It deals with the identification of plastic constitutive parameters at large strains looking at the post-necking behaviour of a notched specimen. The experiment consisted in a tensile test performed on a notched specimen obtained from a 3 mm thick sheet of 316L stainless steel. An experimental procedure has been developed to reconstruct the volume deformation history of the specimen during the test. A set of four cameras, two for each side of the specimen, has been used to measure the displacement field on the two faces at the same time using Digital Image Stereo-Correlation. The adopted spatial resolution is good enough to describe the out-of-plane movement which takes place at the surface after the occurrence of necking. Starting from the surface measurements, the volume displacement field inside the specimen has been reconstructed using a non-linear volume interpolation. The procedure as well as the reliability of the reconstruction process is described in the paper. Finally, the three dimensional displacement field is used to identify the parameters of a plastic constitutive model using the VFM. The anisotropy of the sheet metal is also taken into account. The main outcome of the paper is to illustrate that it is possible to retrieve the three dimensional deformation history of a specimen in the post-necking region using surface measurements and that these data can be quantitatively used to identify the constitutive model.
Investigation of Vibration Assisted Friction Stir Welding
Authors: Montazerolghaem Hamid , Badrossamay Mohsen , Fadaei Tehrani Alireza
Published: February 2012

Friction Stir Welding (FSW) is a relatively new solid state joining method that can be used to achieve very good weld quality. This technique is energy efficient, environment friendly, and versatile. The FSW process utilizes a rotating tool in which includes a pin and shoulder to perform the welding process. FSW applications in high strength alloys, such as stainless steel remain limited due to large welding force and consequent tool wear. It has been shown that applying the ultrasonic vibration on some processes such as turning and drilling the resultant forces are decreased and process condition is improved. In this paper the influence of applying vibration on FSW is investigated in simulating tools. For FSW modeling a proper transfer function of axial force has been proposed. The resultant axial force of conventional FSW and Vibration Assisted FSW (VAFSW) are compared in frequency and time domain state spaces. A good correlation between FSW simulation and experiments is observed. For further investigation of VAFSW the response surface of design of experiment (DOE) method is utilized. The influence of changing VAFSW process parameters is investigated. The simulation results indicate that vibration helps to decrease the welding force. Using DOE method the effects of implemented frequency and vibration speed amplitude in FSW are found.
Bending Testing Rig Development through CAE Tools Application
Authors: Del Prete Antonio , Papadia Gabriele , Primo Teresa
Published: February 2012

Bending can be considered one of easier sheet metal forming processes. In fact, it represents one of the basic variants of applied deformations to metal blanks. However, the numerous research contributions dedicated to sheet metal bending that have been published over the past decade and the constant stream of announcements by R&D departments of machine constructors are strong indications that not all research challenges related to sheet metal bending have been done. This paper reports the developed activity carried out to design a bending testing rig characterized by: a working horizontal axis, a maximum bending length equal to 200 mm, a maximum applicable force equal to 80 kN. A partitioned blankholder has also been designed to allow bending operations on tailored blanks. Moreover, a Graphical User Interface hollows to set up the process parameters and the acquisition of testing data (Temperature and/or Force as function of the process time or punch stroke). CAE tools application had a strategic role to develop the best layout and to find the optimum solutions for the process variables tuning. CAE techniques have allowed to investigate and verify different layout solutions both for the bending process and the structural components of the tooling.
Optimizing Roll Forming Processes with the Aid of a New Numerical Algorithm
Authors: Abrass Ahmad , Kessler Thomas , Groche Peter
Published: February 2012

For the manufacturing of large quantities of profile-shaped products, the roll forming process represents one of the most effective metal forming technologies. During this process, the sheet metal will be formed into a desired cross-sectional profile using successive pairs of forming rolls. This process is well known as a very complex process in industry because of the multiplicity of the process and design parameters. For that reason, the optimization of roll forming processes using numerical methods like the finite element method is very complex and time-consuming. In this paper, a numerical method will be introduced to accelerate the simulation and to optimize the roll forming process. The newly developed algorithm will be illustrated and validated by analyzing the roll forming process. The details of the FE-model and the numerical algorithm will be described. Furthermore, the results of the numerical simulation with and without the application of the numerical algorithms will be compared. Finally, the process will be optimized using the newly developed method.
Preliminary Studies on the Determination of FLD for Single Point Incremental Sheet Metal Forming
Authors: Tisza Miklos , Kovács Péter Zoltán , Lukács Zsolt
Published: February 2012

Development of new technologies and processes for small batch and prototype production of sheet metal components has a very important role in the recent years. The reason is the quick and efficient response to the market demands. For this reasons new manufacturing concepts have to be developed in order to enable a fast and reliable production of complex components and parts without investing in special forming machines. The need for flexible forming processes has been accelerated during the last 15 years, and by these developments the technology reaches new extensions. Incremental sheet metal forming (ISMF) may be regarded as one of the promising developments for these purposes. A comprehensive research work is in progress at the University of Miskolc (Hungary) to study the effect of important process parameters with particular emphasis on the shape and dimensional accuracy of the products and particularly on the formability limitations of the process. In this paper, some results concerning the determination of forming limit diagrams for single point incremental sheet metal forming will be described.