bluuebunny/crossref_metadata_2025 huggingface dataset:
An Investigation of Factors that Influence the Overall Magnitude of Cross-Sectional Distortions in Draw Bending
Authors: Welo Togeir , Widerøe Fredrik
Published: June 2013

European manufacturing companies are currently facing increased competition as a result of intensified globalization in the market and supply base. One strategy to meet this challenge is to develop and manufacture higher quality products at reduced cost. Metal forming is a typical manufacturing operation where improved technology can create advantages in the market place through higher value-added products. In the automotive industry, for example, improved shaping capabilities of profiles will improve product functionality, while reducing system cost due to reduction of part count and subsequent assembly operations such as welding. In addition, improved dimensional accuracy will provide benefits in terms of reduced quality costs and, sometimes, eliminating downstream processing steps such as calibration or machining. Rotary draw bending is typically used to manufacture profile-based shapes bent at tight radii with reasonable dimensional accuracy. The advantage of this process is low operational cost combined with relatively high flexibility, particularly with regard to bend angle. On the other hand, the disadvantage associated with the method is limited abilities to control local distortions of the cross section without taking special actions such as applying external stretching or complex tooling that ultimately would increase the investment and operational cost. The objective of the present paper is to identify the most important factors that influence cross-sectional distortions and quantify their impact on dimensional accuracy in draw bending, by performing a series of experiments in an industry-type draw bender. In order to accommodate different cross-sectional geometries, a flexible, modular tool concept was developed. AA6xxx aluminum alloy profile with different cross-sectional geometries (width, depth, thicknesses), single and multi-camber, were bent at different radii and bend angles, while measuring local distortions of the cross sections. The results have been presented in diagrams denoted flatness limit curves, showing the impact of various geometry (and material) parameters on local deformations of individual cross sectional members. The results show that the flange width (i.e. the free span between webs) is the main factor with regard to distortions, followed by wall thickness and bending radius and, finally, depth of the cross sections. Material parameters seem to have limited effect for the alloy tempers investigated. Attempts have been made to interpret the mechanisms associated with the development of local cross sectional distortions with the purpose of developing a practical design tool based on analytical calculations. The very first results show reasonably well agreement in the cases when local buckling of the internal compressive flange is less predominant.
Brass 70/30 and Incremental Sheet Forming Process
Authors: Fritzen Daniel , Daleffe Anderson , Castelan Jovani , Schaeffer Lirio
Published: June 2013

This work addresses through bibliographies and experiments the behavior of sheet brass 70/30 for Incremental Sheet Forming process - ISF, based on the parameters: wall angle (), step vertical (ΔZ) strategy and the way the tool. Experiments based on the method called Single Point Incremental Forming - SPIF. For execution of practical tests, we used the resources: software CAD / CAM, CNC machining center with three axles, matrix incremental, incremental forming tool and a device press sheets. Furthermore, measurement was made of the true deformation () and thickness (s1). Practical tests have shown that the spiral machining strategy yielded a greater wall angle, compared to the conventional strategy outline.
Prediction of Tensile Properties of Injection Moulding Flax Fibre Reinforced Polypropylene from Morphology Analysis
Authors: Lafranche Eric , Martins Carla Isabel , M. Oliveira Vania , Krawczak Patricia
Published: June 2013

The Young modulus and tensile strength of flax fibre reinforced polypropylene were determined and compared with the micromechanical models usually used in the case of short glass fibre reinforced composites. The fibre length and fibre diameter distributions of the injected reinforced of 2, 4, 8 and 22vol% compound were determined and used to the models in order to evaluate the expected properties of the composites. The mechanical properties were interpreted on the base of real fibre content, fibre orientation, fibre length and diameter distributions and morphology of the composites. The Kelly-Tyson’s model of the tensile strength prediction has been modified to take in consideration the fibre property variability due to the large distribution of fibre shape ratio induced by the process. Finally matrix modulus has been adjusted to take into account the change of crystallinity with fibre content.
Prediction of Surface Roughening and Necking Behavior for Metal Foils by Inhomogeneous FE Material Modeling
Authors: Furushima Tsuyoshi , Tsunezaki Hitomi , Nakayama Tomoko , Manabe Kenichi , Alexandrov Sergei
Published: June 2013

Micro metal forming with metal foils is one of the promising approaches to fabricate micro parts. In this study, a finite element (FE) model for metal foil considering material inhomogeneity due to different flow stresses for each crystal grain to predict free surface roughening and necking behavior is suggested. Material used is pure copper C1020-O, pure aluminum 1N30-O and pure titanium TR270C-O with thickness of 0.05mm. Material inhomogeniety parameter of variation in α value is determined by parameter fitting between uni-axial tensile test and FE analysis considering material inhomogeneity under uni-axial tensile state. Standard deviation σsd of variation in α value of 0.28 for C1020-O is obtained by parameter fitting process. In addition, free surface roughening behavior is observed by FE analysis considering material inhomogeneity and confocal laser microsope. As a result, the increase in surface roughness with uni-axial tensile deformation can be observed for both FE analysis and experiment. In addition, it is considered that the generation of concave parts in free surface roughening is due to grains with low flow stress by quantitative measurement of FE analysis and confocal laser microscope. Surface roughening behavior of FE analysis considering material inhomogeneity is in good agreement with that of experimental results. Thus, the validation of FE model considering material inhomogeniety for metal foils can be verified. Furthermore, the effect of material properties for metal foils such as grain size, material inhomogeneity parameters and strain hardening sensitivity on necking behavior is investigated. As a results, it is found that the ratio of surface roughening to thickness strongly affects necking behavior for metal foil. In particular, in case of large n-value, the concave part generated by surface roughening during plastic deformation would cause the onset of necking for metal foils. Therefore, it is found that the factor of surface roughening is very strong in micro metal forming with metal foils.
Structure-Properties Relationships in Processed Poly(ethylene terephthalate)
Authors: Viana Julio , Todorov Lyudmil
Published: June 2013

Abstract. Upon processing, polymeric products feature a complex microstructure. Besides evolving over the molded component, a through-the-thickness variation is also developed. This is the result of the thermo-mechanical environment (combined thermal and mechanical fields) applied during processing, which varies with the molding technique, the selected molding conditions and polymer properties (rheological, thermal, constitution). This complex microstructure makes rather intricate the establishment of structure-properties relationships in processed polymers. In fact, the basic identification of most relevant morphological parameters determining the behavior of the moldings is been revealed a difficult endeavor, further complicated by the multi-scale morphology presented by polymeric materials. This work follows an inductive approach for establishing the relationships between the structure and the properties (mechanical and barrier) of molded poly(ethylene terephthalate), PET. These relationships are investigated for specimens prepared by different methods, from “simple” to more “complex” stretching modes. Initially, PET specimens were prepared by stretching thin films at different high temperatures and strain rates, followed by quick cooling in a universal testing machine equipped with a thermal camera (uniaxial stretched specimens). More closely to processing, PET injection molded preforms were free blown without a mold with distinct conditions (free blown specimens). Finally, PET bottles were produced from the preforms also under different blown conditions. The morphology of all specimens was assessed by bi- and tri-refringence and DSC. The mechanical properties were evaluated by tensile tests at room temperature. Also, the oxygen transmission rate, OTR, was assessed for the PET bottles. For this low crystallinity and slowly crystallizable polymer, the initial modulus is mainly related to the amorphous phase (i.e., molecular mobility and orientation level). The yield stress appears to be determined by the degree of crystallinity and level of molecular orientation. In the case of free blown specimens (bi-axially stretched) the anisotropy of the initial modulus depends upon the induced anisotropy of the molecular orientation. OTR is influenced by the molecular orientation and the degree of crystallinity of the polymer. An attempt to interpret these types of relationships by molecular dynamics simulations is made.
Numerical and Experimental Study of Tube Hydroforming for Aerospace Applications
Authors: Mojarad Farimani Saeed , Champliaud Henri , Gholipour Javad , Savoie Jean , Wanjara Priti
Published: June 2013

In the tube hydroforming (THF) process, a pressurized fluid is used to expand a thin walled tube inside a closed die in order to fill the die cavity. THF has many advantages that render this process interesting for different industries such as automotive and aerospace. In this work, to investigate the effect of different process parameters, such as the friction condition, tube thickness and end-feeding on the final product, THF experiments were performed on stainless steel 321 (SS 321) tubes using a round-to-square die. Experimental loading paths were obtained via the data acquisition system of the hydroforming press, which is fully instrumented. An automated deformation measurement system, Argus®, was used to measure the strains on the hydroformed tubes. The THF process was simulated using Ls-Dyna software. The variation in the strain and thickness measured from the experiments were compared to the simulation results at critical sections. Comparison of the results from the finite element (FE) simulations and experiments showed good agreement, indicating that the approach can be used for predicting the final shape and thickness variations of the hydroformed parts for more complex shapes in aerospace applications.
An Experimental Study on the Friction Stir Processing Process of Aluminium Alloy
Authors: Weglowski Marek S.
Published: June 2013

The effect of rotational and travelling speeds and down force on the torque in Friction Stir Processing (FSP) process are presented. To find a dependence combining the spindle torque acting on the tool with the rotational speed, travelling speed and the down force, the artificial neural networks have been applied. Studies have shown that the increase in the rotational speed causes decrease in the torque while the increase in the travelling speed and down force causes the increase in the torque at the same time. The relationship between parameters of the process and the temperature of the tool, based on measurement head TermSTIR, were presented. Tests were conducted on casting aluminium alloy AlSi9Mg. Application of FSP process resulted in a decrease in the porosity in the modified material and microstructure refining
Press-Shaving Characteristics of Ultrahigh-Strength Steel Sheets
Authors: Murakawa Masao , Nakamura Kenta , Shionome Tomio , Komuro Fumitoshi , Muro Giichirou , Koga Nobuhio
Published: June 2013

The paper proposes new technologies able to improve the surface quality in the case of press-shaving applied to very high strength materials. Experimental researches were developed and the best combination of process conditions was identified.
Effect of Process Parameters on Surface Roughness in Hammer Peening and Deep Rolling
Authors: Steitz Manuel , Scheil Jan , Müller Clemens , Groche Peter
Published: June 2013

The challenges in die and mold making industry to increase productivity and reduce costs can be addressed by expanding the automation in the process chain. Conventionally the final surface quality is produced by manual polishing operations. This expensive time-consuming production step can be reduced significantly by using machine hammer peening (MHP) and deep rolling (DR). For both processes the emphasis of each process parameter on the resulting surface topographyis largely unknown. This gap of knowledge about significant and non-significant parameters needs to be closed in order to allow a fast process optimization and more economic use of both methods. Therefore this study focuses on figuring out the statistically secured effect of each process parameter on the attainable surface smoothing on cast iron and tool steel. Based on a fractional factorial test design the results of an experimental parameter study are presented and significant parameters are identified. Using a high-speed camera, it may also be proved why an inclination angle between the hammering direction and surface normal is advantageous with regard to the resulting surface quality. Finally, the results are discussed and advices for an industrial use of MHP and DR are given.
Deep Drawing of Ti6Al4V: Experiments and Modeling over a Wide Range of Strain Rates and Temperatures
Authors: Chartrel Benjamin , Massoni Elisabeth
Published: June 2013

A combined experimental-numerical approach using digital image correlation (DIC) and finite element simulation in order to get the temperature dependent mechanical behaviour is presented. Results from a series of experiments on a Ti6Al4V titanium alloy sheet are shown. Tensile tests were carried out on specimens along 3 different orientations in order to characterise the material anisotropy. The strain-rates are varied from 10-1 to 10-2 s-1 while observations are made at temperatures from 903 to 1003 K. The samples are heated by Joule effect, which allows to use the image correlation in order to obtain the deformation fields and thus the coefficients of Lankford [1]. Differences in the responses of this alloy are observed in terms of work hardening, strain rate and temperature sensitivities. The Norton-Hoff model and the Hill [2] criterion are used to effectively simulate the observed responses obtained from these experiments. An inverse analysis model using kriging meta-model [3] is applied to determine each parameter of the mechanical behaviour law. The model, with the constants determined from these experiments, is then used to predict the mechanical behaviour of Ti6Al4V. Thus, the model is implemented into the implicit finite element code Forge® to model forming of thin-walled structures. The predictions are found to be very close to the observations.
DPSS Nd:YAG Laser Precission Machining of Monocrystalline Sapphire
Authors: Wyszyński Dominik , Lipiec Piotr , Skoczypiec Sebastian
Published: June 2013

The paper presents some aspects concerning use of pulse laser source for precise machining of Al2O3 crystals for medical applications. The scheme of laser beam manipulation and the test stand has been presented. Application of the mathematical model enabled determination of values of basic sapphire machining parameters. Presented results gave rough information about dynamics of the process and were used for the test stand designing, development as well as determination of machining precision.
Air Jet Assisted Machining of Inconel 718 with Whisker Reinforced Ceramic Tool
Authors: Obikawa Toshiyuki , Funai Kazuhiro
Published: June 2013

Nickel alloy is widely applied to aero-engines, marine structures, chemical plants, etc. This alloy has superior mechanical and chemical properties, but is one of difficult-to-machine materials because of its superior properties. For this reason, various machining methods, such as cryogenic machining, hot machining, machining using high pressure coolant and rotary machining have been studied for increasing the cutting speed and cutting efficiency of this alloy. Recently, a new lubrication method called air jet assisted (AJA) machining was developed to extend tool life by 20-30% in finish-turning of Inconel 718 and Ti-6Al-4V. In this machining method air jet as well as coolant was applied to the cutting area. In this study, AJA machining was applied to high speed machining of Inconel 718 with a SiC whisker reinforced ceramic tool. The air jet was applied from an air nozzle at the tool flank face. Because the ceramic tool is likely to suffer from severe notch wear, the influence of AJA machining on flank and notch wear of the ceramic tool was investigated experimentally. As a result, it was found that as compared to conventional wet machining, AJA machining increased flank wear but reduced notch wear, which is usually critical to the tool life of the reinforced ceramic tool. The tool wear characteristics peculiar to AJA machining were effective for extending tool life in high speed machining of this alloy.
Metallurgical Aspects of Material Behaviour in Cutting of AISI 1045
Authors: Courbon Cédric , Mabrouki Tarek , Rech Joël , Mazuyer Denis , Perrard Fabien , D'Eramo Enrico
Published: June 2013

This contribution first aims at providing a more detailed analysis of the cutting mechanisms of a normalized carbon steel from a microscopic and metallurgical point of view. SEM and EBSD are used to highlight, in the main intensive deformation zones of the chip, a drastic grain refinement induced by a dynamic recrystallization process. The second part of this study intends to emphasize the consequences of the latter on the workmaterial behaviour. A rheological study based on dynamic compression tests is briefly presented and enables to understand their occurrence as well as their influence on the flow stress of the material. A "metallurgy based" constitutive equation is identified to reach a better description of the flow stress. Finally, this one is implemented in a Finite Element code (Abaqus/Explicit) to assess the potential of this method. It is shown that microstructural evolutions could be relatively well predicted especially when considering the level of recrystallization.
A Generic Methodology to Improve the Control of Forging Process Parameters
Authors: Allam Zakaria , Becker Eric , Baudouin Cyrille , Bigot Régis , Krumpipe Pierre
Published: June 2013

One of the common problems in forging processes is the lack of key process parameters control, as well as their identification. Certain controlled parameters exist, such as temperature or stroke length, which are usually identified and controlled through a systematic approach. Their selection depends particularly on the part to produce or on customer’s constraints, rather than a rational approach. In this paper, a methodology is proposed to select the key process parameters. There are some methodologies which already exist, such as the DMAIC, which are used to determine the control parameters and their influences on the desired specifications. However, this approach has certain drawbacks. For example, the key parameters are selected by experts, which makes each case study time consuming. The aim is to develop a generic methodology to improve the manufacturing process in the forging industry. The methodology is represented as a decision support system that connects product specifications (geometry, absence of defects…) or other forging specifications (tool wear, involved energy...) to the process parameters. The latter will be able to define the key parameters, their values and their appropriate way of control. These links will be setup using the empirical rules and physical laws.
Open Die Forging of Large Shafts with Defects – Physical and Numerical Modelling
Authors: Christiansen Peter , Hattel Jesper , Bay Nils , Alves Luis , Martins Paulo A.F.
Published: June 2013

The aim and scope of this paper is centered to analyze the influence of the geometry of V-shaped dies on the closure of internal centerline porosity defects in ingots during multistep open-die forging. The investigation is performed with small scale physical models made from lead using V-shaped dies with 90º and 120º and a reference pair of flat parallel platens. Holes drilled through the center of these preforms are produced to mimic centerline porosity in full scale cast ingots and intermediate rotation of the preforms replicate a multi-stage forging sequence under laboratory testing conditions. The presentation is supported by finite element modelling using an in-house developed computer program and the overall investigation shows that better results in closure of centerline defects are obtained with a V-shaped die with 120º die angle.
Utilizing Multiple Objectives for the Optimization of the Pultrusion Process Based on a Thermo-Chemical Simulation
Authors: Tutum Cem C. , Baran Ismet , Hattel Jesper
Published: June 2013

Pultrusion is one of the most effective manufacturing processes for producing composites with constant cross-sectional profiles. This obviously makes it more attractive for both researchers and practitioners to investigate the optimum process parameters, i.e. pulling speed, power and dimensions of the heating platens, length and width of the heating die, design of the resin injection chamber, etc., to provide better understanding of the process, consequently to improve the efficiency of the process as well the product quality. Numerous simulation approaches have been presented until now. However, optimization studies had been limited with either experimental cases or determining only one objective to improve one aspect of the performance of the process. This objective is either augmented by other process related criteria or subjected to constraints which might have had the same importance of being treated as objectives. In essence, these approaches convert a true multi-objective optimization problem (MOP) into a single-objective optimization problem (SOP). This transformation obviously results in only one optimum solution and it does not support the efforts to get more out of an optimization study, such as relations between variables and objectives or constraints. In this study, an MOP considering thermo-chemical aspects of the pultrusion process (e.g. cure degree, temperatures), in which the pulling speed is maximized and the heating power is minimized simultaneously (without defining any preference between them), has been formulated. An evolutionary multi-objective optimization (EMO) algorithm, non-dominated sorting genetic algorithm (NSGA-II [Deb et al., 2002]), has been used to solve this MOP in an ideal way where the outcome is the set of multiple solutions (i.e. Pareto-optimal solutions) and each solution is theoretically an optimal solution corresponding to a particular trade-off among objectives. Following the solution process, in other words obtaining the Pareto-optimal front, a further postprocessing study has been performed to unveil some common principles existing between the variables, the objectives and the constraints either along the whole front or in some portion of it. These relationships will reveal a design philosophy not only for the improvement of the process efficiency, but also a methodology to design a pultrusion die for different operating conditions.
Integrated Design and Numerical Simulation of Stiffened Panels Including Friction Stir Welding Effects
Authors: Paulo Rui Miguel Ferreira , Carlone Pierpaolo , Valente Robertt , Teixeira-Dias Filipe , Palazzo Gaetano S.
Published: June 2013

Stiffened panels are usually the basic structural building blocks of airplanes, vessels and other structures with high requirements of strength-to-weight ratio. They typically consist of a plate with equally spaced longitudinal stiffeners on one side, often with intermediate transverse stiffeners. Large aeronautical and naval parts are primarily designed based on their longitudinal compressive strength. The structural stability of such thin-walled structures, when subjected to compressive loads, is highly dependent on the buckling strength of the structure as a whole and of each structural member. In the present work, a number of modelling and numerical calculations, based on the Finite Element Method (FEM), is carried out in order to predict the ultimate load level when stiffened panels are subjected to compressive solicitations. The simulation models account not only for the elasto-plastic nonlinear behaviour, but also for the residual stresses, material properties modifications and geometrical distortions that arise from Friction Stir Welding (FSW) operations. To construct the model considering residual stresses, their distribution in FSW butt joints are obtained by means of a numerical-experimental procedure, namely the contour method, which allows for the evaluation of the normal residual stress distribution on a specimen section. FSW samples have been sectioned orthogonally to the welding line by wire electrical discharge machining (WEDM). Displacements of the relaxed surfaces are then recorded using a Coordinate Measuring Machine and processed in a MATLAB environment. Finally, the residual stress distribution is evaluated by means of an elastic FE model of the cut sample, using the measured and digitalized out-of-plane displacements as input nodal boundary conditions. With these considerations, the main goal of the present work will then be related to the evaluation of the effect of FSW operations, in the ultimate load of stiffened panels with complex cross-section shapes, by means of realist numerical simulation models.
Study of Formability of Sandwich Shells with Metal Foam Cores
Authors: Mata H. , Jorge R. Natal , dos Santos Abel , Parente Marco  P. L. , Valente Robertt , Fernandes A. A.
Published: June 2013

The main goal of this work is made a first approach to the study of formability of sandwich structures, composed by two aluminum sheets (skins), separated by an aluminum metal foam core, using bending tests. The bending tests performed on this work, can be described as a cylindrical punch, which apply a force at the middle span of the specimens, which were have three different lengths, 114 mm, 167.5 mm and 230 mm, in a specific die. The bending tests were used to evaluate the type of yielding of the global composite structure, by measuring the force / displacement values at a middle span. The type of yielding of the global structure has extremely importance in the study of formability of this type of composite, because it was composed by two different materials; each one presents a different mechanical behavior separately. The difference in mechanical behavior can be explained by the axisymmetric compressive stress states test and by the influence of the hydrostatic pressure in the yield stress of the porous material (aluminum foam) and has no influence on the yield stress of the homogeneous solid material (aluminum sheet). With this work, experimental information on the yielding of this composite structure was obtained, to be used in numerical models to study its formability.
Experimental Study on the Overall Spifability of AISI 304 Sheets under Different Bending Conditions
Authors: Centeno Báez Gabriel , Bagudanch Isabel , Garcia-Romeu Maria Luisa , Martínez-Donaire Andrés J. , Vallellano Carpoforo
Published: June 2013

In this paper the influence of the bending effect in the formability of AISI 304 metal sheets in incremental forming is analyzed. For this purpose, a series of single point incremental forming tests were carried out using a variety of tool diameters and step downs. The spifability (formability in single point incremental sheet forming) of the metal sheets was studied in the light of circle grid analysis by means of the 3D deformation digital measurement system ARGUS®. The results show the importance of the bending effect, induced by the tool radius, in the enhancement of formability in incremental forming compared to conventional forming processes.
Material Modeling and Numerical Analysis of the Heat Treatment in High Carbon Steels-Application to Ring Rolling
Authors: Kebriaei Reza , Vladimirov Ivaylo N. , Reese Stefanie
Published: June 2013

Numerical modeling of the heat treatment is developed over the past 30 years and connected to the industrial applications. This requires a good insight in the thermal, mechanical and metallurgical behavior of steels and the coupling effects among these physical phenomena. To describe these effects, a suitable material model is developed. Additionally, the thermo-mechanical behavior of multi-phase steel during the phase transformation is investigated. Furthermore, the material model is applied to describe the plastic behavior of the steel during the cooling process in process-integrated powder coating which is a new kind of ring-rolling process. It takes advantages of the high temperatures and high forces of the ring rolling process. This is not only to increase the ring's diameter, but also to integrate powder metallurgical multi-functional coatings within the same process. In order to increase the strength and wear properties of investigated steels, an appropriate heat treatment should be done. Therefore, the heat treatment after the rolling process is discussed which goes along with phase transformations. The paper is concluded by a detailed description of the process simulation and a comparison of its results with experimental data.
Towards Fracture Prediction in Single Point Incremental Forming
Authors: Guzmán Carlos Felipe , Habraken Anne Marie
Published: June 2013

The stress state in metal forming processes usually implies low values of triaxiality. It is well known that damage models based only on triaxiality fails to capture the damage behavior properly, and recent articles have stressed the effect of the Lode parameter in describing damage. Moreover, in some process like incremental forming, the through thickness shear could dominate the rupture mechanism making the description, using solely the triaxiality, inaccurate. In this paper, a preliminary study of the stress state is carried over a near-to-failure single point incremental forming (SPIF) formed cone, through finite elements simulations using a newly developed solid-shell element. The results provide a basis for further studies into damage development in SPIF.
Modelling of Damage in Blanking Processes
Authors: Del Prete Antonio , Papadia Gabriele , Primo Teresa , Mariano Emilia
Published: June 2013

Fracturing by ductile damage occurs quite naturally in metal forming process due to the development of microcracks associated with large straining or due to plastic instabilities associated with material behavior and boundary conditions. Metal forming processes generally introduce a certain amount of damage in the material being formed. Predictions of the damage formation and growth in a series of forming steps may assist in optimizing the individual operations and their order. This is particularly true for operations such as cutting and blanking, which rely on the nucleation of damage and cracks in order to separate material. In this work numerical simulation of the blanking process, using Deform 2D, taking in account the damage, has been performed. In order to evaluate the accuracy of the numerical solution, experimental test have been performed. Furthermore a numerical – experimental correlation has been carried out.
An Efficient Knowledge Based System for the Prediction of the Technical Feasibility of Sheet Metal Forming Processes
Authors: Steffes Lai Daniela , Turck Sven , Klimmek Christian , Clees Tanja
Published: June 2013

This paper presents an efficient knowledge based method using data mining and multilayer perceptrons (MLP) for the prediction of the technical feasibility of sheet metal forming processes. The stored forecast models can be applied to similar geometries and forming processes using the digital fingerprint to identify the most suitable MLP. Moreover, we establish an algorithm to detect extrapolation which is a priori applied to each new design in order to avoid probable high errors in the forecast model caused by extrapolation. We demonstrate the benefits of the method on a model problem specially designed to investigate a wide range of industrial relevant forming characteristics.
Transient Negative Strain Hardening during Severe Plastic Deformation of Al-30wt%Zn Alloys
Authors: Borodachenkova Marina , Grácio José , Barlat Frédéric , Picu Catalin R.
Published: June 2013

In this work we propose a new model (SOFTMAR) to describe the transient softening observed during severe plastic deformation of Al-30wt%Zn alloys. The model is divided in two main parts. The first one describes the softening process based on the evolution law of the mean free path of dislocations (L) with plastic strain . In the second part of the model emphazis is given to the relationship between the grain size and strain rate that in turn depends on diffusion-driven grain-boundary sliding.
Methodology to Straighten the End Parts of Long Workpieces
Authors: Belhadj Ahmed Abdelwahed , Baudouin Cyrille , Leleu Stéphane , Bigot Régis , Secordel Pascal
Published: June 2013

A workpiece is considered as “long” when one dimension is larger than the two others, for example, railways or guides of manufacturing machines. The customers’ requirements’ evolutions asks the question of workpieces end parts straightness. This paper deals with the means to measure and correct the straightness, a way to prevent flaws in adapting the process and it is especially focused on improving quality for the end parts of the long workpiece. At first, to get the right measure of the straightness, we take into account the fact that the workpiece is deformable; consequently, we assumed the hypothesis that the measured straightness is composed of the intrinsic straightness and the elastic one. Then an approach was developed in order to measure any straightness. Secondly, after getting the proof that the measures are reliable; the correction of the straightness has been studied. The method of semi-automated straightening has been developed in order to improve the productivity. Some experiments have been realized and the results have been compared to the theoretical ones. The conclusions will help to find ways to modify the process in order to prevent the flaws of straightness of long workpieces.
Experimental Setup to Validate Textile Material Models for Drape Simulation
Authors: Krieger Helga , Schnabel Andreas , Appel Lars , Gries Thomas
Published: June 2013

The simulation of the draping process of dry textiles allows one to predict the occurrence of folds and the local fibre orientations and fibre positions after draping. In this paper the experiments to determine the mechanical material properties of textile structures are discussed. The mechanical material parameters are used as input for the drape simulation on the macro-scale. The numeric material models can be validated by comparing the numeric results with the experimental draping results of a drapeability test with standardized geometries. The further developed drapeability test to validate the material models for textile structures will be presented.
Thermal Profiles and Fraction Solid of Aluminium 7075 at Different Cooling Rate Conditions
Authors: Ahmad Asnul Hadi , Naher Sumsun , Brabazon Dermot
Published: June 2013

In order to determine suitable processing conditions for semi-solid aluminium 7075 thermal analysis (TA) was performed in order to obtain the relationship between fraction solid and temperature. During experimental work, the alloy was heated to 750°C by induction furnace and solidified at various cooling rates. Cooling curves for the metal were recorded with two thermocouples, one at the centre of the melt volume and one beside the containing crucible wall. A specially designed chamber with kaowool blanket was used to achieve the slowest cooling rate. The faster cooling rate was achieved with the crucible in open atmosphere with a set air flow rate over the crucible. A Data Acquisition (DAQ) system controlled by LabVIEW software was used to record the temperature-time profiles. From these cooling curves, the phase change at any corresponding time and temperature was estimated. The temperature difference between centre and wall of crucible was used to determine dendritic coherency point (DCP). Results show that, the slowest cooling rate with the kaowool blanket was at 0.03°C/s. An intermediate cooling rate of 0.21°C/s was achieved by leaving the melt to cool without kaowool blanket or forced air flow, and the fastest cooling rate was 0.43°C/s. The change in cooling rate altered the temperatures at which phase changes occurred, including those for eutectic and solidus. It was found that for lower the cooling rates that the DCP occurred at lower temperatures. The DCP for the cooling rate of 0.03 °C/s was found to be 574°C (corresponding to 0.85 fraction solid) whereas the DCP for 0.43 °C/s was found to be 623°C (corresponding to 0.55 fraction solid).
Basic Experimental and Numerical Investigations on Chip Pressing
Authors: Grüner Martin , Merklein Marion
Published: June 2013

Aluminium alloys show a great potential for lightweight constructions due to their high strength and low density but the production of this material is very energy consuming. Also the recycling of aluminium alloys, e.g. chips from the milling process, shows different challenges. Beside contamination by cooling lubricant and oxidation of the surface of the chips the melting and rolling process for new semi finish products needs a high amount of energy. TEKKAYA shows a new approach for recycling of aluminium alloy chips by an extrusion process at elevated temperatures producing different kinds of profiles. A new idea is the production of components directly out of chips using severe plastic deformation for joining of the chips similar to the accumulative roll bonding process in sheet metal forming. In a first approach aluminium alloy chips out of a milling process were uniaxial compressed with different loads inside an axisymmetric tool installed in a universal testing machine. The compressed chip disks subsequently were tested with two experiments to gain information on their stability. First experiment is a disk compression test with the disk standing on its cylindrical surface, giving information on the stability perpendicular to the compression direction. Second experiment is a stacked disk compression test with three disks to investigate the stability parallel to compression direction. During all three tests force and displacement values are recorded by the universal testing machine. These data are also processed to calculate or identify input parameters for the numerical investigations. For numerical simulation ABAQUS in conjunction with the Drucker-Prager-Cap material model, which is often used for sintering processes, seems to be a good choice. By numerical simulation of the experiments and comparison with the experiments input parameters for the material model can be identified showing good accordance. This material model will be used in future numerical investigations of an extrusion process to identify tool geometries leading to high strains inside the material and by this to an increased stability of the parts.
Numerical Investigation of the Incremental Tube Forming Process
Authors: Becker Christoph , Isik Kerim , Bayraktar Ahmet , Chatti Sami , Hermes Matthias , Soyarslan Celal , Tekkaya A. Erman
Published: June 2013

As a response to the recent years’ growing demand for innovation in manufacturing processes towards lightweight design in several industrial sectors, a new process, called Incremental Tube Forming (ITF), and a corresponding machine layout have been developed. ITF is a process to manufacture bent tubes with varying cross-sections. During ITF a tube is clamped in a feeding device, which transports the tube through a spinning tool, where the diameter reduction takes place. This stage is followed by a superposed bending process without suppressing continuous feeding. This combination leads to various advantages such as improved tool life with reduced tool forces and improved product accuracy (e.g. springback behavior), as it is shown in various experimental works. This paper presents a complementary numerical treatment of the process using FEA. For this purpose, a 3D model is constructed using ABAQUS/Explicit, where the tube is modeled with conventional shell elements with uniformly reduced integration to avoid shear and membrane locking (S4R), whereas the spinning rolls are modeled as discrete rigid. With this model, the influences of process parameters, such as diameter reduction ratio and tool geometry, are investigated. This helps not only to gain a deeper understanding of the process but also to interpret already gathered experimental data with better precision and, thus establishing a basis for further improvement and optimization of this fairly new process.
Novel Experimental Set-Up to Investigate the Wear of Coatings for Sheet Metal Forming Tools
Authors: Sgarabotto Francesco , Ghiotti Andrea , Bruschi Stefania
Published: June 2013

The use of PVD and CVD coatings has increased significantly thanks to the improved tribological performances they offer in many metalforming processes. Nevertheless the proper coating selection for a specific forming operation is not well established yet, being mainly based on trails and error approaches. The use of FEM-supported analyses may represent an effective support in the optimization of process parameters, but the need of testing procedures and reliable models to describe the mechanical and tribological phenomena at the interface between the dies and the workpiece is still significant. The paper presents a novel experimental set-up for the evaluation of the wear resistance of dies coatings in sheet metal forming operations. A progressive stamping process was taken as reference case and analyzed by numerical analyses. Contact pressures, temperatures and tangential loads at the tools-blank interface were evaluated in each deformation step. TiAlN and CrN were selected as reference coatings and deposited via magnetron sputtering technique. The first part of the research was focused on the design of the novel set-up capable to carry out controlled wear tests in laboratory environment, performed with the parameters obtained from the numerical simulation. The results of such experiments were compared to the ones from standard laboratory tests and with industrial trials, though measurements of loads, of surface roughness evolution and by surface investigations trough Scanning Electron Microscope observations.
Microstructuring by a Combination of Micro Impact Extrusion and Shear Displacement Forming
Authors: Schubert Andreas , Jahn Stephan F. , Müller Benedikt
Published: June 2013

The Collaborative Research Centre SFB/TR 39 PT-PIESA is developing mass production technologies and process chains for the fabrication of aluminium piezo composites, which can be used as raw material for "smart sheet metal" [1]. Microstructuring by forming is a challenging task concerning material flow, tool and process design [2]. In this study, a hybrid forming process combined of micro impact extrusion and shear displacement is presented and discussed. The formed microstructure, depicted in figure 1, consists of ten parallel primary cavities with cross sections of 0.3×0.3 mm² and four larger secondary cavities which are surrounding the primary cavities. High demands are made concerning precision and reproducibility of the cavities' geometry according to the function of the cavities, which is to serve as collets for sensitive piezo rods. The microstructure has to be formed with one stroke of the stamp. Micro backward impact extrusion is chosen for structuring the primary cavities since it allows accurate forming without aligning die plate and stamp due to a flat die plate. Shear displacement forming, which is the selected process for the secondary cavities, requires a structured and aligned die plate but the forming forces are significantly lower than forming the same geometry with an extrusion process which in turn increases the accuracy. The investigations are focused on the characterization of samples formed with the hybrid process in comparison to structures which are formed solely by impact extrusion. Geometric parameters, material flow and process parameters were evaluated to assess the hybrid process. First experiments show promising results, whereas higher degrees of deformation could be reached at lower forming forces. Exemplary, sections for both processes are depicted in figure 2.
Microstructure and Mechanical Properties of Friction Stir Welded AA6060-T6 Tubes
Authors: D'Urso Gianluca , Longo Michela , Giardini Claudio
Published: June 2013

Friction stir welding (FSW) has received increasing attention in recent years thanks to its advantages over traditional welding processes, reducing distortion and eliminating solidification defects. Since melting does not take place and joining occurs below the melting temperature of the material, this welding process allows to obtain a weld characterized by very high quality with low heat input, minimal distortion, no filler material, and no fumes. FSW is also highly efficient and it is characterized by improved environmental performance if compared to traditional welding methods. For instance, FSW is particularly advantageous in the pipeline industry because this innovative welding process usually entails reduction in energy usage of up to 80% if compared to conventional fusion welding processes. Moreover, also alloys normally difficult to be welded can be considered with this technique. The objective of the present study is to establish and to study the weldability of aluminum tubes by means of FSW process. The study shows preliminary results on circumferential FSW of AA6060-T6 aluminum tubes and the influence of the welding process on weld quality. The experimental campaign was performed on tubes having a thickness equal to 5 mm and an external diameter equal to 80 mm. Tubes were welded by means of a four axes CNC machine tool. Particular care was paid to the fabrication of the inner support for the tube. The mandrel was designed in order to guarantee limited bending during the welding process. Some preliminary tests were carried out by varying the welding parameters, namely feed rate (f) and rotational speed (S). A tool having conical shoulder and cylindrical pin was used. The weld quality investigation was based on tensile tests, microhardness and macrostructure analysis of the joints.