bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Investigation of Dry and Lubricated Sheet Metal Forming Processes
Authors: Merklein Marion , Affronti Emanuela , Steiner Jennifer
Published: July 2015

The current global development towards efficient and sustainable usage of resources as well as a stronger environmental awareness motivates lubrication abandonment in metal forming. Dry forming processes accomplish besides a green production technology also a shortage in production steps and time. However, the change of the tribological conditions influences the material flow during the forming operations and has therefore to be taken into account for the design of complex sheet metal forming operations. The aim of this study is a comparison of dry and lubricated processes by numerical as well as experimental investigations. To ensure reliable results a test setup is necessary which provides a discrete control of the process parameters. Furthermore, an analysis of the local material flow by an optical strain measurement system during the whole test procedure should be possible. These requirements are well fulfilled by the so called Nakajima test, which is typically used for the characterisation of the formability of sheet metals. The influence of varying friction coefficients on the material behaviour is discussed based on the numerical model built up in the Finite Element Software LS-Dyna. The numerical results show a good conformity with the experimental outcomes by identifying the strain localisation. Based on the gained knowledge of the investigations an increase of process understanding for dry forming operations will be derived.
Effects of Thermal Parameters on the Mechanical Characteristics of Ti6Al4V Sheets Deformed at Elevated Temperatures
Authors: Valoppi Beatrice , Bruschi Stefania , Ghiotti Andrea
Published: July 2015

Over these last decades, titanium and its alloys have been largely used for many applications in different sectors such as aerospace, military and biomedical ones. Many studies have investigated the behaviour of the most broadly used alloy, the Ti6Al4V, under hot forging and superplastic forming conditions, whereas almost no records can be found about the Ti6Al4V sheet behaviour at elevated temperature and moderate strain rate (i.e. above 0.1 s-1).
The research starts analysing the influence of the thermal cycle parameters of on the Ti6Al4V mechanical properties and microstructural characteristics by means of micro-hardness measurements and Optical Microscopy (OM) analysis. Different soaking times, cooling rates and heating technologies, namely furnace and induction, were considered and their effects investigated.
Based on these results, uniaxial tensile tests were carried out at different temperatures, ranging from room temperature up to 900°C, and strain rates of 0.1 and 1s-1, adopting the thermal parameters and heating means previously investigated. The Ti6Al4V sensitivity to the rolling direction was highlighted, calculating the average normal anisotropy as a function of the testing parameters. The samples fracture areas were then measured in order to calculate the strain at fracture as a function of the temperature and strain rate, while the fracture morphology was investigated through Scanning Electron Microscopy (SEM). OM and SEM analyses were also used to investigate the deformed samples microstructure. Finally, the samples micro-hardness, as a measure of the post-forming characteristics, was measured in order to evaluate its sensitivity to the temperature and strain rate.
Dry Rotary Swaging - Tube Forming
Authors: Herrmann Marius , Kuhfuss Bernd , Schenck Christian
Published: July 2015

Rotary swaging is an incremental cold forming process for tubes and rods. The established processes use lubricants based on mineral oil. The functions of the lubricant are the reduction of friction, wear and tool load, furthermore it cools the tools and flushes the working zone. But the use of lubricant increases the cost due to additional process steps and lubricant is diverted with the work piece during the process. Thus from economic and ecological points of view it is worthwhile to eliminate the use of lubricant. Therefore it is necessary to realize the functions of the lubricant in another way. For example by means of coating and micro-structuring of the tools the friction and wear can be influenced. In this study dry rotary swaging is tested with conventional tools and machine settings. The analysis of the recorded process parameters and the formed geometry of the workpiece reveal the potential of dry rotary swaging, but also the difficulties that arise. Dry rotary swaging needs a modification of the process and system parameters as well as an adjustment of the tools.
A New Method of Producing Bend Angle by Applying Sheet Forging to V-Bending Process
Authors: Aso Takayuki , Iizuka Takashi , Ota Tomoyuki
Published: July 2015

In actual manufacturing, some empirical method such as the bottoming technique is generally used in order to adjust the bend angles of products. In this study, a new method for controlling the bend angle in the V-bending process was attempted by applying sheet metal forging. In the experiments, three punches with lumps at the punch tip were used. These lumps were pushed into a bent section at the final stage of bending and were able to stretch the inside plane of the bent section. In both cases examined (using punches with one or two lumps at the tip), the bend angle decreased with an increase in punch displacement. This result shows new possibilities for controlling the bend angle by introducing plastic deformation to the bent section.
Evaluation of Friction at High Strain Rate using the Split Hopkinson Bar
Authors: Forcellese Archimede , Mancini Edoardo , Sasso Marco , Simoncini Michela
Published: July 2015

The present work aims at studying the influence of strain rate on the frictional behaviour of AA7075 aluminium alloy in the O-annealed temper state. To this purpose, ring compression tests were performed both under quasi-static and dynamic loading conditions. The high strain rate tests were carried out by means of the Split Hopkinson Tension-Compression Bar in the direct version. In both cases, hollow cylindrical samples, characterised by an initial outer diameter to inner diameter to height ratio of 6:3:2, were tested under dry condition and by lubricating with molybdenum disulphide grease. The different frictional behaviour exhibited by AA7075-O under quasi-static and dynamic loading conditions can be attributed to the strain rate effect both on the plastic flow behaviour of the deformed material, and on the thickness of the lubricant film.
Improving Accuracy in Aluminum Incremental Sheet Forming of Complex Geometries Using Iterative Learning Control
Authors: Fiorentino Antonio , Ceretti Elisabetta , Feriti Gian Carlo , Giardini Claudio
Published: July 2015

Incremental Sheet Forming is a flexible process characterized by low costs and higher process times with respect to traditional forming technologies. It is therefore suitable for prototypes, small series or custom mass productions. Its flexibility derives from the use of a hemispherical punch that is moved by a CNC machine and gradually deforms the sheet in presence, or not, of a counter die. As a consequence, the sheet clamping is reduced and the part accuracy is lower than traditional sheet forming process as stamping. Therefore, the improvement of the part accuracy in Incremental Sheet Forming is a relevant research topic and solutions for error reduction are required for improving the process quality.The present paper describes the use of an Iterative Learning Control (ILC) algorithm for compensating the ISF part geometrical error. In particular, it iteratively corrects the part geometry on the basis of the error map obtained as the difference between formed and target part geometries. The ILC uses the target geometry to form a first trial part, it measures the obtained geometry and estimates the geometrical error map. Then the error map is used to modify the target geometry and another part is formed. This procedure gets iterated until the desired geometrical tolerance is achieved.The correction algorithm was experimentally tested in forming both axisymmetric and not axisymmetric parts using aluminum sheets. Results showed that in few iteration steps it was possible to significantly improve the part accuracy and to achieve geometrical tolerances comparable with the traditional sheet forming processes.
Predicting Tube Ovalization in Cold Bending: An Analytical Approach
Authors: Welo Togeir , Paulsen Frode
Published: July 2015

Ovalization (or flattening) of tubes in cold bending operations causes dimensional inaccuracy that may lead to loss of fit-up and function of the formed product. The particular distortion mechanism is governed by radial bending stress components forcing the extremities of the tube section towards the neutral layer of the cross-section. Thus, the magnitude of distortions is limited by the instantaneous stiffness of the tube section upon plastic bending. In order to proactively consider tube ovalization in the product design process, it is necessary to develop a practical methodology that takes into account the impact of governing parameters such as material, tool and section geometries. In the present work, an analytical model of the ovalization problem has been developed using the deformation theory of plasticity. The results show that the diameter of the tube is the most important parameter with respect to tube ovalization, while the thickness of the tube section and the bending radius are of the same relative importance. The developed model indicates that strain hardening is the most important material parameter, whereas tube ovalization is nearly unaffected by the initial yield stress. The present model shows good correlation with a number of experiments.
Assessing 3 and 5 Degrees of Freedom Toolpath Strategy Influence on Single Point Incremental Forming
Authors: de Farias João B. Sá , Bastos Ricardo P. , Ferreira Jorge A. , de Sousa Ricardo J. Alves
Published: July 2015

Single Point Incremental Forming (SPIF) is a promising manufacturing technology concerning the production of customized products, low batches or prototyping of ready-to-use parts, given its easy implementation and absence of dedicated tooling. The range of application is wide, covering many materials and virtually unlimited geometries. Indeed, nowadays’ boundaries of the process are more related to the machines limitations than to the process itself. The SPIFA machine [1] developed at the University of Aveiro allies high payload capacity to flexibility driven by a kinematics based on a Stewart Platform. In this work, it will discussed the effects of employing five degrees of freedom toolpaths to produce aluminium and high strength steel parts.
Uncertainty Management of Cutting Forces Parameters and its Effects on Machining Stability
Authors: Rivière Lorphèvre Edouard , Letot Christophe , Ducobu François , Filippi Enrico
Published: July 2015

Virtual manufacturing is a field of research which numerically simulate all the manufacturing processes seen by a mechanical part during its production (for example casting, forging, machining, heat treatment,…). Its use is rising on various industries to reduce production costs and improve quality of manufactured parts. One of the most challenging component of the whole simulation chain is the simulation of machining operations due to some of its specificities (need of material law at high strain, strain rates and temperature, heterogeneities of machined material, influence of residual stresses,…).In order to circumvent these difficulties, macroscopic models of machining process have been developed in order to compute more global information (cutting forces, stability of the process, tolerance or roughness for example). For this approach, the cutting forces computation is done by using simple analytical law based on mechanistic approach. The parameters of the models have no clear physical meaning (or at least cannot be linked to intrinsic properties of the material to be machined) and are therefore considered constants for a given set of simulations.The aim of this paper is to take into account the uncertainty on the variability of the cutting force signal during machining operation used as input for mechanistic model identification. The variability of the response during a test on fixed conditions (cutting tool, machined material and cutting parameters) is taken into account to develop a model where parameters of the model can evolve during a given operation.The proposed model is then used as an input of a milling operation simulation in order to study its influence on machining stability as compared to a classical approach.
Study of an Industrial FEM Tool for Line Boring Process of Cylinder Blocks
Authors: Tabibian Shadan , Lorong Philippe
Published: July 2015

The aim of this study is to realize a simple simulation tool, in order to predict the form defect of cylinder block bore liners in the moment of rough boring process. Geometrical defect prediction is critical for Process Engineering in order to optimize all machining sequences in the production line, to grantee the finale product, according to the norms defined by the Design Engineering. In revenge, Process Engineering can suggest a new product design according to geometrical defect predictions. Simulation can significantly reduce the time of Process-Product parameters adjustment (pre-project).In this study a simple static FEM model, based on the cylinder block geometry, is proposed to predict the form defect of the bore liners in the moment of process. The cutting tool is supposed as a rigid part in this model. The clamping condition and meshing information are applied on the part in the initial state. Calculation of cutting force components is performed through the Kienzle cutting law and applied on the bore liners by means of a Python script. The Python script runs the calculation automatically by means of ABQUS software. Another Python script is in charge of simulation results post-processing. The interface of this tool is an Excel sheet which allows us to inter the process parameters and automatically run the FEM calculation. Out-put excel file contains the form defect of each bore according to 3 levels of bore (top, middle and the bottom) and different angular position.The simulation results put forward that the clamping condition plays an import role in the bore distortion. Consequently, optimizing the clamping pressure and its localization is critical, before cutting parameters adjustment, in line boring process. Experimental validation is performed in parallel with the simulation. The first correlation between experimentation and simulation results shows that the first influent factor which disturbs the correlation is the initial form defect of rough part due to the casting process. Integration of casting form defect in the simulation is crucial and should be taken into account in the next studied.
Economical Comparison of Cryogenic vs. Traditional Turning of Ti-6Al-4V: A Case Study
Authors: Tirelli Stefano , Chiappini Elio , Strano Matteo , Monno Michele , Semeraro Quirico
Published: July 2015

Due to their poor machinability, titanium alloys need to be worked at low cutting speeds to prevent a fast tool failure caused by the very high temperatures that are reached at the tool-chip interface. As demonstrated by previous works by the authors, an improvement of productivity for Titanium alloys can be obtained by adopting cryogenic cooling during the machining operations.The present work shows the features of a toolholder specifically designed for cryogenic adduction in turning operations, following Hong’s design guidelines. The paper compares tool life results between traditional and cryogenic rough turning by adopting Grade 5 titanium as the working material. Rough turning is economically more relevant to the machining industry, especially in the aerospace field where generally a large quantity of rough material has to be removed due to the very high buy-to-fly ratio of aerospace components. A full factorial experimental plan was performed basing on typical rough turning parameters. Machining outputs such as forces, roughness, temperatures, friction coefficients were calculated in order to define statistical differences between cryogenic cooling method using the special toolholder and traditional oil water emulsion cooling system.Furthermore, thanks to tool life results the Taylor’s law for cryogenic and traditional cases was calculated and an hypothetical production scenario for Ti6Al4V parts was analysed. An analytical model to calculate production costs and time was built for both cooling methods. A 4-turrets turning centre was considered and cooling methods and costs per hour of machine tool were taken into account in a cost model. The results show that the benefits in terms of tool life offered by liquid nitrogen cooling allows to improve productivity by adopting higher optimal cutting parameters. This improvement, coupled to an increase of tool life, is very significant and allows not only to reduce time of production but also to cover the major costs of liquid nitrogen and have a slight reduction of machining total costs.
Application of Optimal Control Problem for Surface Roughness Improvement in Milling
Authors: Skrypka Kateryna , Bosetti Paolo
Published: July 2015

This paper presents an improvement of the approach for increasing automation level of CNC machines by using a supervising controller that, for a given toolpath, tool geometry, and workpiece material, calculates the optimal sequence of controls. The developed system, based on three steps: process simulation, solution of the optimal control problem (OCP), and state reconstruction with state learning, is improved while reformulating the OCP by taking into account the surface roughness.
Dynamic Recrystallization Observed at the Tool/Chip Interface in Machining
Authors: Senecaut Yannick , Watremez Michel , Brocail Julien , Fouilland-Paillé Laurence , Dubar Laurent
Published: July 2015

In numerical approaches for high speed machining, the rheological behavior of machined materials is usually described by a Johnson Cook law. However, studies have shown that dynamic recrystallization phenomena appear during machining in the tool/chip interface. The Johnson Cook constitutive law does not include such phenomena. Thus, specific rheological models based on metallurgy are introduced to consider these dynamic recrystallization phenomena. Two empirical models proposed by Kim et al. (2003) and Lurdos (2008) are investigated in machining modeling.
A two-dimensional finite element model of orthogonal cutting, using an Arbitrary Lagrangian-Eulerian (ALE) formulation, is developed with the Abaqus/explicit software. Specific rheological models are implemented in the calculation code thanks to a subroutine. This finite element model can then predict chip formation, interfacial temperatures, chip-tool contact length, cutting forces and chip thickness with also and especially the recrystallized area.
New specific experiments on an orthogonal cutting test bench are conducted on AISI 1045 steel specimens with an uncoated carbide tool. Many tests are performed and results are focused on total chip thicknesses and recrystallized chip thicknesses.
Finally, compared to numerical results got with a Johnson Cook law, numerical results obtained using specific rheological models to take into account dynamic recrystallization phenomena are very close to experimental results. This work shows also the influence of rheological behavior laws on predicted results in the modeling of high speed modeling.
The Use of FEA in the Simulation of a Metal Cutting Operations in the Presence of Random Uncertainty
Authors: Franchi Rodolfo , Del Prete Antonio , Primo Teresa
Published: July 2015

Forces and temperatures in specific orthogonal cutting conditions and calculated by finite element analysis, have been evaluated taking into account the uncertainty of some process conditions. A traditional deterministic approach, in machining simulations, is not able to explain the uncertain physical variations related to material characteristics (yield and tensile strenght, hardness, etc.) and tool/chip/workpiece interface conditions (friction and tool wear). During machining operations many different sources of non-controllable process variations usually display their effect leading to a degree of uncertainty in the final parts quality. Statistical tools and methods are increasingly being used in combination with FE numerical simulation, in order to take in account of the variability of the process. Then, if one of the purposes of process design is to study and model robustness or reliability of a given process in aleatory conditions, a CAE study might become a feasible way to do it. Today, the evaluation of the performances of a metal cutting process is possible using several commercial FEA packages. These software tools automatically allow the preventive evaluation of the robustness of technological decisions. In this work the authors, by means the integration between stochastic simulation tools and machining FE codes, have evaluated the process sensitivity to a random variation of uncontrollable parameters or conditions. Furthermore, a specific experimental and numerical activity has been performed in order to better understand the technical capabilities in terms of process simulation in stochastic conditions.
Strain-Path Effects on the Formability Behavior of Interstitial-Free Steel
Authors: Ferreira Jetson Lemos , Tepedino José Osvaldo Amaral , Wolff Marco Antonio , Moreira Luciano Pessanha
Published: July 2015

In this work, the formability behavior of Interstitial-Free (IF) steel sheet, grade DC07 with 0.65 mm of nominal thickness, was evaluated by means of both linear and bi-linear strain-paths to define the Forming Limit Curve (FLC) at the onset of necking according to ASTM E22182 standard. In the first strain-path, flat-bottomed punch with 200 mm diameter and 10 mm corner die radius was adopted together with counter-blanks of an IF steel sheet grade DC07 with 0.80 mm nominal thickness in order to yield two equal amounts of plastic work under uniaxial tension and under equibiaxial stretching strain-paths. Afterwards, Nakajima’s 100 mm hemispherical punch stretching procedure and bulge tests were adopted to determine the FLC of both as-received and strained DC07 blanks with the help of an automated digital image correlation system to define the linear and bi-linear limit strains. Increasing the straining level (5 and 10%) of the first strain-path in uniaxial tension improved the limit strains of the DC07 steel sheet between the plane-strain intercept (FLC0) and the biaxial stretching region of the FLC. On the other hand, blanks which were firstly pre-strained in equibiaxial stretching mode (4.8 and 9%) provided better formability in the FLC drawing region and reduced limit strains in plane-strain and biaxial stretching regions.
Microstructure Induced Wear Mechanisms of PVD-Coated Carbide Tools during Dry Drilling of Newly Produced ADI
Authors: Meena Anil , El Mansori Mohamed
Published: July 2015

Near-net shape austempered ductile iron (ADI) castings can be considered as a significant economic advantage to the increasing industrial demand for cost and weight efficient materials. However, due to microstructure induced inherent properties, ADI is considered as hard to machine material. The present paper thus investigates the interaction between the microstructural characteristics of ADI and wear mechanisms of PVD-coated carbide tools. The inherent properties of ADI materials are the function of its microstructural characteristics (retained austenite volume content and its carbon content, ferritic cell size, etc.) which can be controlled by the austempering parameters. Experimental studies of dry drilling of different ADI materials with the PVD-coated carbide tools were carried out at a cutting speed of 60 m/min and at a feed of 0.15 mm/rev. The wear mechanisms of the cutting tools were studied by using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analysis techniques. The obtain results revealed the evolution of crater wear as the main wear mode. In addition, it provides the key findings aims to correlating the machining characteristics of ADI with its microstructure and production conditions.
Virtual Process Design for Cold Formed Components
Authors: Schratter Sonja , Keckes Jozef , Winter Gerald , Buchmayr Bruno
Published: July 2015

Finite element models optimizing cold forged products have to incorporate the complete manufacturing pathway. Virtual process design as a method based on a multistep operation approach can describe interacting phenomena. Thus, inheritance effects like residual stress and damage evolution can be tracked throughout the processing chain. Besides the influence of the deformation direction (Bauschinger Effect) on material flow can be predicted. Using intermediate step optimization may also extend geometrical limits. Furthermore it may increase life time and improve material efficiency for a given component. The exploitation of these coupling effects may also form a basis for further product and process innovations.
Efficient Updated-Lagrangian Simulations in Forming Processes
Authors: Canales Diego , Leygue Adrien , Chinesta Francisco , Cueto Elías , Feulvarch Eric , Bergheau Jean Michel , Vincent Yannick , Boitout Frederic
Published: July 2015

A new efficient updated-Lagrangian strategy for numerical simulations of material forming processes is presented in this work. The basic ingredients are the in-plane-out-of-plane PGD-based decomposition and the use of a robust numerical integration technique (the Stabilized Conforming Nodal Integration). This strategy is of general purpose, although it is especially well suited for plateshape geometries. This paper is devoted to show the feasibility of the technique through some simple numerical examples.
Numerical Damage and Failure Modelling of Lightweight Alloys during Metal Forming Processes
Authors: Horr Amir M.
Published: July 2015

There have been many efforts to investigate and develop a numerical damage and failure models during metal forming process of lightweight alloys. Due to the difficulties experienced during experimental determination of the incurred damage during forming of lightweight alloys, many researchers have sought to predict the damage, failure and forming limit curves using numerical simulations. Conventional finite element analysis of metal forming processes for lightweight parts which have been subjected to a nonlinear strain history often breaks down due to numerical difficulties. Many scientific research works have attempted to use different mathematical methods to model the damage progression and failure of alloying material under large deformation. The damage initiation, progression and also failure of alloys are a result of accumulated damage under plastic deformation [1-3]. These models (single and multi-damage parameters) are generally based on energy and constitutive equations to simulate the fracture and failure processes in metal alloys. However, these methods have serious short comes in predicting the damage and failure in metal forming process with strain rate effects. In the present study, following the in-depth study of damage initiation and progression in lightweight alloys, a frame work has been setup to develop a numerical model for damage accumulation during forming process. Based on the existing damage theory, a mathematical extension for damage initiation and also damage accumulation under wide range of stress triaxiality (including near pure shear) has been developed. An experimental program has also been carried out using samples made from lightweight alloys. One of the main contributions of this paper is to show the advantages of using plasticity-based modified damage models to investigate the damage accumulation in cast aluminium alloys.
Recent Developments in LS-DYNA to close the Virtual Process Chain for Forming, Press Hardening and Welding
Authors: Klöppel Thomas , Erhart Andrea , Haufe André , Loose Tobias
Published: July 2015

Forming, press hardening and welding are a well-established production processes in manufacturing industry, but predicting the finished geometry and the final material properties of the processed parts is still a major issue. In particular, deformations caused by welding are often neglected in the virtual process chain, although they have to be compensated for in order to fulfill the requirements on shape tolerance. This presentation will give an overview on novel features of LS-DYNA implemented particularly for welding simulations.To begin with, new keywords will be presented that allow applying the heat generated by the weld torch. LS-DYNA offers a very convenient way to define the well-known Goldak heat source, but it is also possible to define arbitrarily shaped torch geometries.In order to obtain a predictive model for welding simulations, specific material models have been devised in LS-DYNA. The properties of filler material in weld seams are accounted for by a ghost material approach. Material is initialized as ghost material and is activated, i.e. it is given base material properties, when the temperature reaches the melting point. This approach has been implemented for a relatively simple thermo-elasto-plastic material formulation *MAT_CWM as well as for the more complex material law *MAT_UHS_STEEL. The latter has initially been implemented for press hardening simulations and is able to predict the microstructure of steel alloys including phase transformations and the resulting mechanical properties.In this contribution, details of the material formulations and novel features are presented. Examples will demonstrate how these features can be applied to multistage processes including several forming and welding stages.
Virtual Joining Factory – Integration of Microstructure Evolution in the Manufacturing Process Chain Simulation
Authors: Beyer Ulrike , Neubauer Ingo , Kreyca Johannes , Kozeschnik Ernst
Published: July 2015

Over the past years engineering has established itself in many areas of production technology on the basis of simulation methods. Efficient tools and software applications for the development and planning of products, machines and systems have been developed which allow virtual analyses especially for critical areas, e.g. micro structural analysis’s, forming processes or joining applications. However, these are often isolated solutions which only cover one particular aspect and are not complete calculation tools. This is often caused by data transfer between simulation programs. There are hardly any automatic links between software tools which often come from different providers. Often data formats have to be converted first and then transferred manually. Therefore, interdependencies can only be taken into consideration to a small extent and with a high expenditure of resources. This affects the quality of numerical results and hence the development and optimization process. Consequently, the necessity of a process chain simulation which covers all production steps similar to a virtual factory becomes obvious. This automatic simulation should make it possible to consider the numerical results from micro structure calculation to the manufacturing of the composite tools successively and thus contribute to having a nearly fault-free perfected process for the real factory.
Using Data Sampling and Inverse Optimization for the Reduction of the Experimental Effort in the Characterization of Hot Working Behaviour for a Case Hardening Steel
Authors: Kraemer Alexander , Lohmar Johannes , Bambach Markus , Hirt Gerhard
Published: July 2015

For the full characterization of the hot working behaviour of a given material a large number of laboratory experiments have to be performed. The experiments themselves are time consuming and the required specimen material can be quite expensive. With the increasing versatility of the testing machines, like dilatometry with easily variable temperatures, overthinking the classical approaches for materials characterization becomes expedient.In this paper a new technique for the reduction of the experimental effort is presented at the example of a 25MoCrS4 case hardening steel. To analyse the potential for the reduction of the experimental effort the classical approach of a full experimental test matrix is chosen. Here 55 flow curves with temperatures between 700 and 1200°C and strain rates from 0.01 to 100/s are experimentally determined. Then a semi-empirical model for strain hardening and dynamic recrystallization is fitted using an automated routine for parameter determination, taking all available flow curves into account. Subsequently, the number of flow curves used to fit the model parameters is gradually reduced. The model accuracy obtained with the reduced experimental data is compared to the initial fit. The natural decrease in accuracy with the use of less data compared to the gain due to the reduction of experimental effort is analysed. In addition optimal distribution of the sampling points in the experimental matrix for a reduced number of experiments is discussed. It is shown that less than a quarter of the full matrix is sufficient to reach accuracies comparable to using the full matrix. Using the vertices and symmetrical distribution of the data within the full experimental matrix allows a drastic reduction of experimental effort while maintaining the initial accuracy. The results suggest that it might be possible to reduce the costs and effort for material characterization by 50-80%.
Determination of Thermal Boundary Conditions for Modeling the Hot Roll Bonding Process
Authors: Melzner Alina , Hirt Gerhard
Published: July 2015

Innovative product characteristics can be realized by hot roll bonding of two or more layers of different materials. To optimize the roll bonding process, an approach to align the strength differences in both materials by a temperature difference between the layers has been proposed. Therefore, the temperature distribution has to be investigated by finite element (FE) simulations. In these simulations the heat transfer coefficient (HTC) between the two aluminum layers is of great importance. With this coefficient the temperature transfer between the two layers can be determined in order to estimate the temperature field and the material strength difference in the layers.In hot roll bonding there are two ranges for the HTC depending on whether bond formation takes place or not. This effect can be used to determine at which pressures bond formation starts. To evaluate the HTC for this application and to determine its value ranges, a simple setup has been developed. This setup allows conducting experiments under defined temperature and pressure conditions. The resulting force-time measurements were used as input values for inverse FE-simulations, with the goal to gather the HTC by inverse modelling the temperature distributions of the specimens. First results show that the range of the pressure dependent HTCs leads up to 21 kW/(m²K) in the unbonded range. In the range where bonding occurred between the specimens, values over 150 kW/(m²K) were estimated. The data for the HTC was implemented in roll bonding simulations as an interaction property. A comparison between the simulated temperature curve and a measured temperature curve during roll bonding showed a good agreement between the temperature values.
Application of a Non-Invasive Form Finding Algorithm to the Ring Compression Test with Varying Friction Coefficients
Authors: Landkammer Philipp , Steinmann Paul
Published: July 2015

It is a great challenge in the development of functional components to determine the optimal blank design (material configuration) of a workpiece according to a specific forming process, while knowing the desired target geometry (spatial configuration). A new iterative non-invasive algorithm, which is purely based on geometrical considerations, is developed to solve inverse form finding problems. The update-step is performed by mapping the nodal spatial difference vector, between the computed spatial coordinates and the desired spatial target coordinates, with a smoothed deformation gradient to the discretized material configuration. The iterative optimization approach can be easily coupled non-invasively via subroutines to arbitrary finite element codes such that the pre-processing, the solving and the post-processing can be performed by the habitual simulation software. This is exemplary demonstrated by an interacting between Matlab (update procedure for inverse form finding) and MSC.MarcMentat (metal forming simulation). The algorithm succeeds for a parameter study of a ring compression test within nearly linear convergence rates, despite highly deformed elements and tangential contact with varying friction parameters.
Multi-Objective Optimization of the Hydroforming Process Considering Different Plastic Yield Criteria
Authors: Piglionico Vito , Piccininni Antonio , Palumbo Gianfranco , Tricarico Luigi
Published: July 2015

The present work aims at determining the optimal working conditions for the manufacturing of the AA6061-T6 Al alloy by the hydroforming process. As case study a stepped geometry was used. A numerical model was created using the commercial explicit Finite Element code LS-DYNA. The plastic behaviour of the investigated alloy was modelled implementing experimental data (flow stress curves, Lankford coefficients and Forming Limit Curves) and using two different yield criteria: an anisotropic one (Barlat ‘89) and the conventional isotropic one (Von Mises). Finite Element models were tuned using experimental data from warm hydroforming tests: comparing both the sheet thinning and the die cavity filling, quite different friction conditions had to be supposed for obtaining a good fitting with both the yield criteria.Finite Element models were finally used for evaluating the working range of the hydroforming process: results from a CCD simulation plan were imported within an integration platform (modeFRONTIER) to evaluate the optimal hydroforming conditions based on a multi-objective genetic algorithm optimization. Quite different results in terms of optimization and working range were obtained when adopting different yield criteria.
Study of the Metallurgy of a Dissimilar Ti-6Al-4V – Stainless Steel Linear Fiction Welded Joints
Authors: Impero Filomena , Scherillo Fabio , Astarita Antonello , Beamish Kathryn A. , Curioni Michele , Squillace Antonino , Zhou Xiao Rong
Published: July 2015

This paper deals with the investigation of the metallurgy of a dissimilar Ti-6Al-4V-stainless steel joint linear friction welded. In particular two different stainless steel were considered: AISI 304 and AISI 316. These two alloys differs in the Molybdemun content. Metallographic observations, EDS analysis and Vickers Microhardness measurements were carried out, particular attention was focused on the study of the intermetallic compounds and on the microstructures of the different zones produced by the process. As usual for solid state welding processes, three different zones can be identified: the parent material, the heat affected zone (HAZ) and the thermo-mechanical affected zone (TMAZ), furthermore a very thin joining line, rich of intermetallic compounds, was also observed. In this zone diffusive phenomena also occurred resulting in a variation of the alpha phase content on the titanium side.In the TMAZ, the bimodal microstructure of the parent material was deformed and the presence of elongated alpha grains with broken beta-phase particles was established. Moreover it was observed that in the weld region, exposure to supertransus temperatures (995°C) combined with hot-deformation working and rapid cooling after joining induced the recrystallization of a martensitic beta grain structure. Concerning the joint between Ti-6Al-4V and AISI 316 some cracks were observed within the weld line, this due to the presence of brittle intermetallics compounds in this zone. The formation of these intermetallics was promoted by the presence of Molybdenum.
Friction Stir Lap Joining of Blanks under Different Conditions
Authors: Bruni Carlo , D'Orazio Alessio , El Mehtedi Mohamad
Published: July 2015

The present investigation aims at studying the effect of the tool geometry and of rotational velocity of the tool, at different welding velocities, on the tensile shear strength of the friction stir welded joints realised with blanks of different thicknesses. The proposed trial and error methodology was based on experiments, numerical simulations and microstructure observations.It was observed that, at the lowest rotational velocity, the slender tool determines tensile shear strength values lower than those obtained with the thick tool in particular at the highest welding velocity investigated. The numerical simulation evidenced a wider stirred zone for the thick tool when compared with that realised with the slender tool at the lowest rotational velocity. Microstructure observations evidenced that the increase in the welding velocity determines reduced stirred zones and an homogenisation of material particularly relevant for the slender tool.
Experimental Comparison of the MIG and Friction Stir Welding Processes for AA 6005 Aluminium Alloy
Authors: Caruso Serafino , Campanella Davide , Candamano Sebastiano , Varrese Claudia , Crea Fortunato , Filice Luigino , Umbrello Domenico
Published: July 2015

In this study, the mechanical properties of welded joints of AA 6005 aluminum alloy obtained with friction stir welding (FSW) and conventional metal inert gas welding (MIG) are studied. FSW welds were carried out on a semi-automatic milling machine. The performance of FSW and MIG welded joints were identified using tensile and bending impact tests, as far as the environmental aspects are also included in the discussion. The joints obtained with FSW and MIG processes were also investigated in their microstructure. The results indicate that, the microstructure of the friction stir weld is different from that of MIG welded joint. The weld nugget consists of small grains in FSW than those found in MIG weld. Taking into consideration the process conditions and requirements, FSW and MIG processes were also compared with each other to understand the advantages and disadvantages of the processes for welding applications of studied Al alloy. Better tensile and bending strength were obtained with FSW welded joints.
Heat Transfer and Crystallization Modeling during Compression Molding of Thermoplastic Composite Parts
Authors: Faraj Jalal , Pignon Baptiste , Bailleul Jean Luc , Boyard Nicolas , Delaunay Didier , Orange Gilles
Published: July 2015

We present in this paper, the coupling of heat transfer to the crystallization of composite in a closed mold. The composite is based on thermoplastic resin (low viscosity PA 66) with glass fiber (50% volume fraction). In order to realize this coupling, an accurate characterizationof thermo physical properties in process conditions, especially in the molten and solid state is needed. In addition, theidentification of the parameters of crystallization kinetics is required. Therefore, we present the methods that were used to study the thermo physical properties as the thermal conductivity, heat capacity and the specific volume. Moreover, the kinetic of crystallization was estimated over a large temperature range by using Flash DSC and classical DSC. In order to validate the measurements, the whole process was modeled by finite elements. The model includes the resolution of the strong coupling between the heat transfer and crystallization. Finally, the experimental and numerical results were compared.
Detailed Heat Transfer Modelling & Optimization of a Forced-Convection Kiln Using CFD Methods
Authors: Maier Hermann , Berger Walter , Breyner Robert
Published: July 2015

The efficiency of many industrial processes is strongly governed by the 3D-flow conditions in the fluid domain. An important step in the production of special wires is the patenting in forced convection kilns. An unfavourable deviation in the distribution of key parameters (e.g. velocity and temperature) can be found in the material properties of the product later.The usage of CFD methods (Computational Fluid Dynamics) is an alternative capable approach to analyse the 3D-heat transfer process in the kiln in detail with less effort & costs. In the current improvement study a detailed CFD-modelling of two different forced convection kilns was done for a typical load case. Considering the detailed kiln geometries and important heat transport phenomena the initial situation in the heat transfer zone was analysed for each kiln.In a second step an improvement concept was developed by increasing the heat transfer into the wire as well as smoothing the flow distribution in the heating zone of the kiln. After revamping of the kilns a number of different improvements could be realized. Despite of the plant’s higher flexibility at different load cases a significant improvement of the wire’s product quality could be found. With respect to important key parameters the deviation of material properties could be reduced to >90%. In a next step a solid-fluid-coupling will be done in the CFD-approach which allows examining the developing temperature profile of each wire line in the kiln.
Determination of Heat Transfer Coefficients for Different Initial Tool Temperatures and Closed Loop Controlled Constant Contact Pressures
Authors: Mendiguren Joseba , Ortubay Rafael , Agirretxe Xabier , Martín José Miguel , Galdos Lander , Sáenz de Argandoña Eneko
Published: July 2015

The boron steel quenching requirement on hot forming manufacturing processes allows the industry to create tailored parts to improve their mechanical functionality. During the cooling, the microstructure of the material changes depending on the imposed cooling rate. However, an accurate prediction of the cooling ratios is needed in order to correctly design the process. In this work the interfacial heat transfer coefficient (HTC) has been determined at different contact conditions, varying the initial die temperature. Experimental tests have been realized in a SCHMIDT micro servo-press, which is able to compensate the thermal contraction of the blank and tools to precisely keep constant the contact pressure. Temperature evolution of the tools and the blank has been monitored with nine thermocouples. For the determination of the heat transfer coefficient (HTC) an analytical-numerical method has been used leading to a fast and reliable calculation method able to determine the HTC value for each process time. This methodology allows relating the HTC to the blank temperature, difference on temperature on the interface to improve the tailor tempering of boron alloys simulation.
Influence of Layer Number on Mechanical Property of Steel Hollow Sphere Sheet Sandwich Construction
Authors: Yoshida Yoshinori , Noritake Takafumi
Published: July 2015

Two sheets of steel hollow sphere sheet (TEC SHEET) are laminated and its mechanical property is investigated by means of stab proof test. The construction is sandwiched by a pair of pure aluminum plates with two kinds of bonding methods. Three point bending test and compression test are conducted for the construction. As the results, stab proof strength is advanced more than that of a single layer sheet. In the bending test, bending load increases with increase of the layer in the sandwich construction. Bending mechanism is investigated and the influence of bonding method on breakage condition of the sandwiches. Compression test for the sandwich construction and foam metal filling construction is conducted and the difference of the energy consumption behavior is investigated.