bluuebunny/crossref_metadata_2025 huggingface dataset:
Wall Thickness Distribution during a Combined Tube Spinning and Bending Process
Authors: Becker Chrstioph , Tekkaya A. Erman
Published: July 2015

During a tube bending process the wall thickness distribution plays an important role concerning the process limits. Especially the wall thinning at the extrados of the tube is crucial. The wall thickness in a combined tube bending and tube spinning process will be analyzed. Therefore, possible stages of complexity are presented to show the possibilities of such a process combination. Based on this the interactions between the bending and spinning process on the wall thickness distribution will be discussed. Finally, a diagram will show how to adjust the wall thickness at the extrados of the tube only by adapting the tube spinning process.
Forming Limit Diagram Predictions Using a Self-Consistent Crystal Plasticity Model: A Parametric Study
Authors: Jeong Youngung , Pham Minh Son , Iadicola Mark , Creuziger Adam
Published: July 2015

A numerical model to predict forming limit diagrams (FLD) for polycrystalline metal sheets is presented. In it, the Marciniak-Kuczynski (MK) approach is incorporated into the framework of the viscoplastic self-consistent (VPSC) crystal plasticity model. The current model, dubbed the VPSC-FLD, can run simulations along individual loading paths in parallel, which can make use of a CPU-cluster to enhance the computational speed. The main objective of the current work is to provide a detailed sensitivity report based on the VPSC-FLD. First of all, the influence of the initial inhomogeneity, f , as defined in the MK approach, is illustrated. Secondly, FLDs resulting from various sizes of the statistical population for the crystallographic texture are examined. Lastly, the computation time spent for various sizes of the statistical population is given.
Room Temperature Forming of AA7075 Aluminum Alloys: W-Temper Process
Authors: Sáenz de Argandoña Eneko , Galdos Lander , Ortubay Rafael , Mendiguren Joseba , Agirretxe Xabier
Published: July 2015

As important light-weight structure material, aluminum alloys have been widely used in automotive and aerospace industries. In the last years, the manufacturing of parts with high strength and good dimensional accuracy has become the main objective in industrial applications. Within the available aluminum alloys, the 7xxx series has attract the interest of the industrial designers due to the high yield strength and ultimate tensile strength they present. However, the formability of these alloys in as-received industrial condition is very poor at room temperature and various studies are being carried out to develop efficient warm and hot forming processes to form them industrially using heated tools. In the present paper, the W-Temper forming is studied as an alternative to the warm and hot forming processes. Heat treatment temperatures and critical times are presented and an industrial B-Pillar is formed to validate the new process. In the last chapter, the final mechanical properties of the part are reported, before and after a virtual e-coat process where the W-Temper forming is compared with a hot stamping process.
Physical Simulation of Pipes Production Cycle for Lean Alloyed Pipeline Steel X80
Authors: Naumov Anton A. , Bezobrazov Yuriy A. , Chernikov Evgenii V.
Published: July 2015

Lean alloyed pipeline steel X80 with experimental chemical composition was taken for the present research. Rolling schedules for researched steel were developed for continuous mill 2000 by means of numerical simulation using HSMM, AusEvol+ and AusEvol Pro software. Developed schedules were analyzed in order to choose several of them, which guarantee the required final mechanical properties. The chosen schedules were realized on Gleeble-3800 system by tension-compression tests for experimental chemical composition. Mechanical testing of received samples was made. After that physical simulation of strip flattening, forming, expanding and coating using Gleeble-3800 system was produced and mechanical testing of received samples was made to compare results with samples after rolling simulation and with requirements submitted to pipeline steel X80.
Experimental Investigations on the Relation of the Lubricant’s Flash Point and Quality of the Piston Made from Aluminium Alloy for its Application in Internal Combustion Engines
Authors: Petrov Michael A. , Basyuk Timophey S. , Petrov Pavel A. , Petrov Alexander N.
Published: July 2015

In the current paper there was made an attempt to develop an experimental method of physical (lubricant’s flash point Tfp) and subjective (forgings’ quality) parameters coupling for hot isothermal-like forging operation. The quality forgings could be manufactured both by high and low lubricant’s flash point. The increase of Tfp value in exothermal reaction follows to the increase of the released heat amount by the lubricant, because it needs more initial activation energy transmitted from the external source to initialize transformation of the material from one aggregate state into another (from liquid or solid into gaseous or sol-like). This can prevent the temperature decrease on the punch due to strong convective heat transfer with the environment through the building of the isolation temperature shield on the punch contact surface at the beginning of the punch stroke. On the other hand it can cause the defect building on the forgings like penetrations, which could not be eliminated during cleaning operation before mechanical treatment due to chemical interactions of the dissolved active agents, or unfilled sections.
Flow Localization Modelling in Ti Alloys and Ti Matrix Composites
Authors: Halici Dilek , Poletti Cecilia
Published: July 2015

Titanium-based alloys are commonly applied to aerospace, medicine and energy due mainly to their high specific mechanical properties and high corrosion resistance. Reinforcement with particles further improves their specific strength and stiffness. In previous studies, the hot formability of both unreinforced Ti6Al6V2Sn alloy, and reinforced with 12%vol of TiC particles was analyzed by hot compression tests carried out by means of Gleeble device and metallography. It was observed that the hot workability of these materials is limited at given forming conditions by non-desirable shear bands, voids, as well as micro- and macro cracks, especially in the composite. In this work, damage during hot deformation is predicted by damage models coupled to FEM. Therefore, the flow localization parameter α described by thermal and microstructural softening and the strain rate sensitivity are computed and implemented in DEFORMTM 2D to describe the localization of the plastic flow. The results show intense flow localization as a combination of low dynamic restoration (given by small m values) and temperature gradient. The damage analysis combined with the Cockcroft and Latham continuum cumulative stress model.
Experimental Investigations and Automatic Numerical Optimization of a Bulk Metal Forming Process to Avoid Forging Folds
Authors: Behrens Bernd-Arno , Bouguecha Sonda Moakhar , Vucetic Milan , Bouguecha Anas , Kazhai Mohammad
Published: July 2015

The detection of process failures in earlier design stages is essential for preventing high additional costs and a loss of time. Here, the finite element analysis (FEA) is an inherent part of the process design.
This work represents numerical and experimental investigations, which were carried out in order to identify factors that influence the fold formation in an upsetting process of hollow parts, i.e. different forging velocities, different materials or the friction. The experimental results were compared with the numerical simulations. Based on these investigations, an automatic optimization model was created, which is the focus of this work. It allows varying and optimizing the experimentally determined process parameters, influencing the fold formation, automatically with the aim to produce a workpiece free of folds. For this purpose the commercial Software-System Forge (Transvalor) was used.
The results of this work provide basic information for the development of complex processes.
It can be shown that the automatic numerical optimization is an indispensable tool for the process design. It helps determining optimal process parameters individually and avoiding extensive trial and error investigations and hence a loss of time and costs.
Numerical Prediction of Internal Stresses due to Weaving
Authors: Vidal-Salle Emmanuelle , Florimond Charlotte , Boisse Philippe
Published: July 2015

The increasing use of finite element simulation in the field of composite material forming involved in the past few years a large amount of research on the constitutive modelling of textile material at the mesoscopic scale (i.e. the scale of individual fiber tow). Up to now, the community interest was focused on a consistent shape prediction. Moreover, the large amount of contacts between yarns imposed the use of dynamic explicit approaches for numerical efficiency reasons. Recent advances in contact algorithms make now possible the use of implicit schemes. The present paper shows how a constitutive equation written and implemented in the dynamic explicit scheme with ABAQUS/Explicit is adapted to implicit one (i.e. ABAQUS/Standard), for large displacement analyses.Validation and perspectives are illustrated on a weaving operation.
Bias Extension Test for In-Plane Shear Properties during Forming - Use at High Temperature and Limits of the Test
Authors: Boisse Philippe , Wang Peng , Hamila Nahiene , Lemeur Kevin , Rusanov Anton , Guzman E. , Ferretti Manuel , D'Agostino Marco , Madeo Angela
Published: July 2015

The results of in-plane shear tests performed on 5-hardness satin woven carbon/PPS thermoplastic prepregs are described. The experimental analyses are based on bias-extension tests performed in an environmental chamber. The results are given for different temperatures on both side of the melting point. This range of temperature is those of the part during a thermoforming process. In another hand it is shown that second-gradient energy terms allow for an effective prediction of the onset of internal shear boundary layers which are transition zones between two different shear deformation modes. The existence of these boundary layers cannot be described by a simple first-gradient model.
Investigation of the Residual Stress State in an Epoxy Based Specimen
Authors: Baran Ismet , Jakobsen Johnny , Andreasen Jens H. , Akkerman Remko
Published: July 2015

Process induced residual stresses may play an important role under service loading conditions for fiber reinforced composite. They may initiate premature cracks and alter the internal stress level. Therefore, the developed numerical models have to be validated with the experimental observations. In the present work, the formation of the residual stresses/strains are captured from experimental measurements and numerical models. An epoxy/steel based sample configuration is considered which creates an in-plane biaxial stress state during curing of the resin. A hole drilling process with a diameter of 5 mm is subsequently applied to the specimen and the released strains after drilling are measured using the Digital Image Correlation (DIC) technique. The material characterization of the utilized epoxy material is obtained from the experimental tests such as differential scanning calorimetry (DSC) for the curing behavior, dynamic mechanical analysis (DMA) for the elastic modulus evolution during the process and a thermo-mechanical analysis (TMA) for the coefficient of thermal expansion (CTE) and curing shrinkage. A numerical process model is also developed by taking the constitutive material models, i.e. cure kinetics, elastic modulus, CTE, chemical shrinkage, etc. together with the drilling process using the finite element method. The measured and predicted in-plane residual strain states are compared for the epoxy/metal biaxial stress specimen.
Inter-Ply Friction Effect on the Forming Result of Multi-Layered Composite
Authors: Allaoui Samir , Hivet Gilles , Cellard Christophe
Published: July 2015

During forming, defects can occur and have to be taken into account because they can significantly affect the mechanical performance of the part. This experimental study shows the type and number of defects is a function of the punch geometry, the process parameters, the orientation of the fabric with respect to the punch and the inter-ply friction. Inter-ply friction has a huge effect on the quality of the preform when inter-ply sliding occurs. This inter-ply Friction leads to several overhanging yarn shocks that generate high tangential forces, which inhibit the relative sliding of plies.
Shear Characterization of a Thermoplastic Cross-Ply Prepreg
Authors: Dangora Lisa M. , Sherwood James A. , Parker Jason C. , Mitchell Cynthia J.
Published: July 2015

This paper presents the investigation of a thermoplastic cross-ply sheet for use in manufacturing small arms protective helmets. The material system contains four unidirectional layers oriented in a [0°/90°/0°/90°] configuration. This advanced composite is wholly thermoplastic, consisting of ultrahigh molecular weight polyethylene (UHMWPE) fibers within a polyurethane matrix. Due to the polymeric nature of the constituent materials, the mechanical behavior of the composite system will have a dependence on forming temperature. The shear characterization of the prepreg and the investigation of the factors influencing the representative shear stiffness including sample geometry, strain rate, conditioning and temperature are discussed.
Locking and Enrichment Strategies
Authors: Wolthuizen D.J. , Akkerman R.
Published: July 2015

A short overview of different locking mechanisms is presented, in which the more recent locking phenomenon tension locking is placed. Tension locking is found during composite forming simulations and occurs when the element edges are unaligned with the fiber directions. Discontinuities in composite forming simulations show similarities with other weak discontinuities such as material interfaces and shear bands found during shear localization. Two enrichment strategies are explored to resolve tension locking in linear triangular elements.
A Parametric Study on Compression Molding of Reference Parts with Integrated Features Using Carbon Composite Production Waste
Authors: Abdul Rasheed Mohammed Iqbal , Rietman Bert , Visser Hendrikus Antonius , Akkerman Remko
Published: July 2015

Compression molding of near net-shaped rib-stiffened plates has been performed for a parametric investigation on the filling behavior of chopped woven flake reinforcements. The experimental investigation showed that different aspect ratios of ribs can be filled completely within the tested maximum ratio of flake size to rib opening width of 6.25 and a maximum consolidation pressure of 15 bar. However, defects such as voids, non-impregnated regions and fiber matrix separation may arise depending on the combination of parameters and a mechanical jamming effect caused by the woven architecture of the flakes. A tendency for a limiting consolidation pressure is observed based on the fiber matrix separation. The ability to re-use thermoplastic prepreg cutting waste has been demonstrated.
Warm Forming and Paint Bake Response of AW-7xxx Sheet in Various Tempers
Authors: Kumar Manoj , Ross Nigel
Published: July 2015

In this paper, we have investigated AW-7921 in various tempers - specifically under aged T4P1-and T4P2-tempers, naturally aged T4 and peak-aged T6-tempers - for their warm formability at 230°C and paint baking response through one step and five step paint baking treatments. It was found that warm formability depends on dynamic recovery and dissolution of precipitates. However, the response to paint baking was dependent on the stability of the precipitates against coarsening. Of the tempers investigated the T4-temper exhibited the best combination of formability and paint baking response. This study also indicated that we can achieve much better performance in the warm forming processing chain by optimization of the temper and paint baking heat treatment procedure.
Towards a Fracture Energy Based Approach for Wear Prediction of WC-Co Tools in Industrial Cold Heading Process
Authors: Debras Colin , Dubois André , Dubar Mirentxu , Dubar L.
Published: July 2015

Tools sustainability and reliability is a key axis for economic competitiveness of companies in the field of cold heading of steels. This durability is currently limited by the damage occurring at the contact surfaces.The main objective of this study is to propose an energy based approach to understand the mechanisms of deterioration of the WC-Co carbide tools.Firstly a finite element simulation of an industrial cold heading process is run in order to identify the contact condition at the tool workpiece interface. Main results are the stress, strain and temperature distributions in the near surface of the tools. A particular attention is paid to the location of critical areas that may limit the tool life.Jointly, characterizations of the morphology of the worn surfaces are performed. SEM observations added to EDS and roughness measurements are done from midlife to end of life of industrial tools. Friction tests are performed with the Upsetting-Sliding Test involving contactors extracted from real worn tools to identify friction coefficients in order to provide the evolution of the friction coefficient according to the wear state of the tools. Finally, the correlation between the numerical analysis and the experimental measurement is discussed to attest to the relevance of the energy fracture based model to explain the deterioration of the tribological conditions.
Evaluation of Tooth Surface Micro-Finishing on Gear Noise
Authors: Jolivet Simon , Mezghani Sabeur , Isselin Jérôme , Giraudeau Alain , El Mansori Mohamed , Zahouani Hassan
Published: July 2015

For automotive gear manufacturers, reducing gear noise while maintaining the gear load-carrying capacity as well as the wear resistance has become more and more important. Macro- and micro-geometrical defects have long been studied in order to explain the vibratory behavior of gears. However, the contribution of the micro-scale roughness of the flanks, essential in the gear contact mechanics, has not yet been fully understood.This paper addresses this issue where gears were manufactured with two industrial finishing processes (grinding and power-honing) while having the same macro-scale characteristics. Tridimensional topographical features of teeth surface were hence measured using a three-dimensional white light interferometer. As manufactured surface topographies are highly complex, irregular, and multiscale, all the teeth surfaces were characterized in the entire wavelength band using a multiscale method based on wavelets transform. Vibration performances of the gears were then tested on a single-stage low powertrain. Results demonstrate the influence of micro-roughness scales on vibrations amplitude.
Feasibility Analysis of Lubrication through Magneto-Rheological Fluids in Sheet Metal Forming Processes
Authors: Medea Francesco , Ghiotti Andrea , Bruschi Stefania
Published: July 2015

Magneto-rheological fluids represent one of the most recent technologies introduced in many industrial applications to design fast and reliable electro-mechanical devices. Such fluids, which consist of a dispersion of metallic particles in a fluid carrier, may drastically change their rheological properties when subjected to external magnetic fields with short response times and low power consumption. Up to date, the most common applications of MR fluids regard the integration in mechatronics applications mainly in civil and mechanical fields, where they are often used as active lubricants in rotary components such as bearings. However, no investigations can be found in literature on their tribological performances when applied in metal forming processes.The paper aims at investigating the tribological behaviour of magneto-rheological fluids when applied as lubricants in sheet metal forming processes. To this aim, a new experimental apparatus has been developed to test the friction coefficient at the interface between the tools and the metal sheet when different magnetic fields are applied. The stamping of AA alloys was taken as reference case to select the process parameters in terms of contact pressure, magnetic field and sliding speed.
Validation of Cellular Automata Model of Dynamic Recrystallization
Authors: Sitko Mateusz , Madej Łukasz , Pietrzyk Maciej
Published: July 2015

Development and validation of the micro scale cellular automata (CA) model of dynamic recrystallization (DRX) were the main goals of the present paper. Major assumptions of the developed CA DRX model, which is based on the Digital Material Representation (DMR) concept, are described. Parameters like neighborhood type, state and internal variables of the proposed model and their influence on final results are presented and discussed. Particular attention was put on description of the developed transition rules used to replicate mechanisms leading to dynamic recrystallization. Finally, obtained results in the form of flow stress curves are compared with the experimental predictions.
Experimental Investigation of Heat-Treated Aluminum Profiles
Authors: Merklein Marion , Graser Matthias , Lechner Michael
Published: July 2015

Tailor Heat Treated Profiles (THTP) are profiles that exhibit local different mechanical properties optimized for a subsequent forming operation. The property distribution is realized by short term heat treatment before a forming operation. Based on the interaction of soft and hard areas the material flow can be improved and the formability can be enhanced. Prerequisite for a successful application of the technology is a comprehensive material characterization. Therefore, within this paper the influence of short term heat treatment on the mechanical properties of profiles will be presented. In particular, different heating technologies based on heat conduction and laser radiation are compared. Based on the results, a process window will be derived. All investigations were performed using the precipitation hardenable aluminum alloy EN AW 6060.
Young’s Modulus Determination: Influence of Microplasticity and Pseudo-Elasticity on Metal Forming
Authors: Balland Pascale , Tabourot Laurent , Bizet Laurent , Sene Ndéye Awa , Depres Christophe , Balan Tudor , Manach Pierre Yves
Published: July 2015

This paper shows that non-linearity of mechanical behaviour of metal in the elastic regime has an influence on the forming process. Discrete Dislocation Dynamics simulations show that pure elastic behaviour is altered when reversible dislocation displacements occur even in the very beginning of the elastic stage. The influence of such a non-linearity has an impact on the results of numerical simulations of industrial forming of very thin metal sheets of copper.
Evaluation of Bendability of Hot-Rolled S960 Grade Steel Using Optical Strain Measurements and FE-Modelling
Authors: Arola Anna Maija , Kaijalainen Antti , Kesti Vili
Published: July 2015

Bending is an important forming process for ultra-high strength steel (UHSS) because it is cost-effective, fast and in many cases it can be used to replace welding in a part manufacturing processes. One major challenge in air bending of UHSS is to predict the limits for bendability since the traditional methods for failure prediction, such as forming limit diagram (FLD), cannot generally be applied to bending process. In this paper, 3D FE-modelling coupled with a CDM-damage model is used to simulate the air bending process and to determine the bendability limits for a hot-rolled 960MPa grade. Damage parameters for the CDM-model are determined by using optical strain measurements and inverse modelling of the tensile test. Three point bending tests with optical strain measuring were carried out to determine the deformation field of the outer bend in different bending angles and the results of the bending simulation are compared with the strain measurements of the bending tests. The damage model is then calibrated using the experimental results of the bending tests to adjust the crack occurrence in the simulation. A good agreement was found between simulations and experimental measurements.
Investigation of Tribological Properties of AlMg4,5Mn0,7 in a Warm Forming Process Using the Barrel Compression Test
Authors: Müller Benedikt , Jahn Stephan F. , Fang Ru , Schubert Andreas
Published: July 2015

Within the German Collaborative Research Center 39 PT-PIESA the forming of micro cavities into aluminum sheets is one challenging task. During this forming process high forces and stresses occur which lead to a high tool wear. Hence, the actually applied cold forming process should be replaced by a warm forming process. This paper shows the tribological investigations for the warm forming process. Within the experiments the barrel compression test is used to determine the friction conditions by varying the size of the cylindrically shaped samples of AlMg4,5Mn0,7, the forming degree and the lubrication condition (dry, graphite, forming oil). The flat punches were made from hardened steel 1.3343. The friction factor was calculated, and surface roughness was evaluated by 3D-laser microscopy. The experiments show that the friction factor increases, especially at forming degrees below 1 and for small specimen size, compared to cold forming processes. In addition to that, an influence of the lubrication condition onto the surface roughness was observed. For experiments conducted with graphite, the surface roughness is significantly higher than for samples, which were formed dryly or with forming oil.
Analyzing the Electrical Pulses Occurring during EDM of Non-Conductive Si3N4 Ceramics
Authors: Ojha Nirdesh , Zeller Florian , Mueller Claas , Reinecke Holger
Published: July 2015

With the help of an Assisting Electrode (AE), non-conductive ceramics can be machined using Electrical Discharge Machining (EDM) process. The AE helps start the EDM process and the intrinsic conductive layer (ICL) ensures that the electrical contact between the workpiece and the generator is maintained. However, the understanding of EDM process of non-conductive ceramics is limited due to the typical characteristic of the process: the geometric dimension of the discharge region is limited to few micrometers and the duration of the dielectric discharge is in the range of few microseconds making it difficult to directly observe the spark and the associated crater formation phenomenon. Analyzing the electrical signals during the EDM process could provide an insight of the process. This paper presents a study on analyzing the electric pulses occurring during the EDM process of a conductive workpiece (copper) and a non-conductive workpiece (Si3N4 ceramics). Typical pulses occurring during the EDM of a metal and a non-conductive ceramics are identified with the signal recorded at a sampling rate of 2.5 GS/s. Sampling rate of 25 MS/s is used to monitor the pulses occurring while machining a hole with depth of 1 mm. The pulses during EDM of non-conductive materials are significantly different than those during EDM of metals. Four most outstanding differences have been identified in terms of the ringing behavior of the voltage signal, the recharge time required to reach the set value of open voltage, the presence of the reverse current and the value of the peak current detected in case of Si3N4. The pulses monitored with lower sampling frequency was characterized and discriminated into sparks, arcs and short circuits. The percentage of the discriminated pulses for varying machining depth of the test structure has been presented.
Selective Laser Melting on Aluminum Foam Surface and Mechanical Properties of Fabricated Aluminum Foam with Nonporous Surface Layer
Authors: Matsumoto Ryo , Kanatani Shigehiro , Utsunomiya Hiroshi
Published: July 2015

To fabricate aluminum foam having nonporous surface layer (sandwich structure), the selective laser melting (SLM) was applied to fill surface pores of a commercial closed-cell type aluminum foam with aluminum. A commercially pure aluminum powder was continuously melted and solidified by irradiating with a pulsed Nd:YAG laser with a maximum average power of 50 W. As a result, the aluminum foam having nonporous surface layer (SLM surface layer) was successfully fabricated. The compressive deformation behavior of the fabricated aluminum foam having the SLM surface layers was investigated with uniaxial compression test. The plateau stress of the aluminum foam having the SLM surface layers was improved by approximately 20%, compared with that of the aluminum foam without the SLM surface layers.
Energetic Consideration of the Spark Erosion Using Different Process Energy Sources and Pulse-Unit-Gap Conditions
Authors: Schulze Hans Peter
Published: July 2015

The energetic calculations of pulse energies are only very rough approximations in many publications, because some boundary conditions are not known or are not considered. In the paper is shown that problems resulting from the choice of process energy source and the supply-gap conditions. Approximations that were still considered for long pulse durations, for example, can for micro and nanoEDM no longer be accepted. The smaller the pulse energy, it can also not allow for the simulation of a linear rising enthalpy may be used. The shifts between the measured current and voltage must not be neglected. Practical tests to have shown, that the peak of the energy input is shifted in time and the maximum is lower by about 70%. The parasitic capacitances of the connection pulse unit - working gap and electrode arrangement results in the largest errors in the power calculation. It follows that the connection conditions of industrial plants may not be changed or should be recalculated.
New Criterion for Prediction of the Wrinkle Formation in Deep Drawing Process
Authors: Liewald Mathias , Han Fei , Radonjic Ranko
Published: July 2015

Wrinkling is one of the primary failure modes in deep drawing of sheet metal parts. Previous studies showed that the second principle stress can be a measure for the initiation and growth of wrinkles. The wrinkling analysis is usually made with using conical cup geometries. Recent experiments and numerical simulation results at the Institute for Metal Forming Technology (IFU) showed that the wrinkling analysis using simple conical cup geometries is not suitable for description of complex wrinkling conditions for real deep drawing processes. In the presented experimental results, fender shaped geometry was chosen as an example. During deep drawing of this geometry, different wrinkling formulation mechanisms were observed. Regarding these wrinkling mechanisms, a new wrinkling limit curve can be determined. By use of this new wrinkling limit curve, it is possible to detect the occurrence of wrinkles in each area of the formed sheet metal part until the wrinkle is finally formed.
Mechanical Testing of Additive Manufactured Metal Parts
Authors: Merklein Marion , Plettke Raoul , Junker Daniel , Schaub Adam , Ahuja Bhrigu
Published: July 2015

The quality of additive manufactured parts however depends pretty much on the workers experience to control porosity, layer linkage and surface roughness. To analyze the robustness of the Laser Beam Melting (LBM) process a Round Robin test was made in which specimens from four institutes from different countries were tested and compared. For the tests each institute built a set of specimens out of stainless steel 1.4540. The aim of this work is to analyze the influence of the process parameters on the mechanical properties. The results show that there is a high potential for additive manufacturing but also a lot of further research is necessary to optimize this technology.
Optimization of the Wire Electrical Discharge Machining Process Using Grey Relational Analysis and Taguchi Method
Authors: Dodun Oana , Merticaru Vasile , Slatineanu Laurenţiu , Coteaţă Margareta
Published: July 2015

The wire electrical discharge machining is a machining method able to allow detaching parts from plates type workpieces as a consequence of electrical discharges developed between workpiece and wire tool electrode found in a motion along its axis; there is also a work motion along the contour to be obtained. There are many factors able to exert influence on the sizes of parameters of technological interest. On the other hand, there are various methods that can be used in order to establish the optimal combination of the input factors, so that obtaining of machining best results is possible. When there are many process output factors, a problem of multiobjective optimization could be formulated. The Grey relational analysis method and the Taguchi method could be applied in order to optimize the wire electrical discharge machining process, when various criteria having distinct significances are considered. An experimental research was designed and developed in order to optimize the wire electrical discharge cutting of parts made of an alloyed steel, by considering six input factors: test piece thickness, pulse on time, pulse off time, wire axial tensile, current intensity and travelling wire electrode speed. As output parameters, one took into consideration surface roughness, wire tool electrode massic wear, cutting speed along the contour to be obtained. 16 experiments were developed in accordance with the requirements specific to a Taguchi table L16. The results of experiments were processed by means of Grey relational analysis method and Taguchi method.
Micro Electrical Discharge Machining of Tungsten Carbide with Ultra-Short Pulse
Authors: Kroening Oliver , Herzig Mathias , Hackert-Oschätzchen Matthias , Kühn Ralf , Zeidler Henning , Schubert Andreas
Published: July 2015

Micro EDM (Electrical Discharge Machining) is a known nonconventional process for the machining of hard to cut materials. Due to its ablating nature based on melting and evaporation through heat induced by electrical discharges, it can function independently of the hardness, toughness or brittleness of the workpiece. Thus micro EDM is a possible process to fulfill the requirements of higher precision and high quality in carbide metal machining. Thereby the surface and the roughness of machined carbide metals depend on the discharge energy used. For machining carbide metals with high surface quality pulse generators with ultra-short discharges are required.
This paper presents the development of a two-staged pulse generator with the ability to provide ultra-short pulses by using a two-staged pulse. The current and voltage signals of the discharges were recorded and their characteristics were analyzed.
Effect of Pass Number, Rotational and Traverse Speed on Particle Distribution and Microstructure of AZ31/SiC Composite Produced by Friction Stir Processing
Authors: Jabbari A.H. , Sedighi Mohammad , Vallant Rudolf , Huetter Andreas , Sommitsch Christof
Published: July 2015

In this paper, Friction Stir Processing (FSP) is used to produce a homogenous AZ31/SiC Metal Matrix Composite (MMC). The product could be used in industries such as aerospace, which needs materials with a high strength to weight ratio. AZ31B magnesium alloy plates and about 5 vol % SiC powder are selected as matrix and reinforcement particles, respectively. The effect of the number of FSP passes, the rotational and traverse speed on the particle distribution and the matrix microstructure of MMC are investigated. Optical microscopy is used to observe both particle distribution and matrix microstructure. The results show that a perfect particle distribution with no defect can be achieved at very low rotational and transverse speeds which are 300 rpm and 15mm/min. Moreover, the number of passes significantly improves the particle distribution. The mean grain size decreases from 9.5 μm to 1.95μm for a 4-pass MMC.
Numerical Prediction Model of Temperature Effect on DP1000 Steel Damage during Warm Formability
Authors: Keita Oumer , Dubos Pierre Antoine , Chottin Jerôme , Hug Eric
Published: July 2015

In this work experimental tensile tests were performed on a DP1000 steel at different temperature levels in the range (293-600) K. This experimental database was used for the identification of a Johnson-Cook constitutive model taking into account temperature effects. A critical void area fraction and a corresponding critical equivalent plastic strain were also identified from each temperature using a metallographic analysis previously described. This critical equivalent plastic strain was considered as a fracture criterion instead of the traditional fracture strain of the Johnson-Cook model and a corresponding damage parameter was determined in these specific conditions. Finally numerical simulations were carried out to analyze the influence of the temperature on the macroscopic critical fracture during a forming operation by bending.
Effect of Additive Manufactured Metallic Structures on Laser-Based Thermal Joining of Thermoplastic Metal Hybrids
Authors: Amend Philipp , Hentschel Oliver , Scheitler Chritian , Gorunov Andrey Igorevich , Schmidt Michael
Published: July 2015

In future, the use of tailored multi material parts consisting of thermoplastics and metals will increase especially in the field of automotive applications based on the pursuit of lightweight design. This provides completely new demands on automated manufacturing because dissimilar materials have to be joined reliably. A promising approach is the thermal joining by laser radiation which enables a non-contact, automated and reproducible production of thermoplastic metal hybrids. Thereby, laser radiation heats the metal and through heat conduction the thermoplastic melts and wets the metal surface. The surface topography of the metallic joining partner plays an important role for the strength of the hybrid joint. In this paper, a novel approach for the fast and flexible fabrication of part-adapted surface structures by means of laser cladding with powder injection is investigated. The aim of the performed experiments is to find out how the geometry and arrangement of additive manufactured line-like metallic structures affect the strength of the dissimilar joint. Therefore, the height and width of the structures are varied. The structure geometries are investigated by microscopy of cross-sections and laser-scanning microscope measurements. As substrate and powder material stainless steel is used. Finally, the metallic samples are joined with polyamide 12 by means of laser radiation and mechanically analyzed by tensile shear tests.
Hybrid Processing of AZ91 Magnesium Alloy/Nano-Al2O3 Composites
Authors: Yadav Surya Deo , Bhingole Pramod P. , Chaudhari Gajanan P. , Nath Sameer K. , Sommitsch Christof
Published: July 2015

In the present work mechanical and wear behaviour of AZ91 magnesium alloy based composites, reinforced with nanoAl2O3 particles is studied. The composites with different amount of alumina particles are fabricated by a hybrid processing approach. The hybrid processing involved alumina particles dispersion in molten AZ91 alloy by mechanical stirring assisted with ultrasonic processing. Dry sliding wear tests are performed using a pin on disc apparatus against hardened steel at loads ranging from 4.9 N to 14.7 N. The microstructural investigation revealed that, a refined microstructure is obtained because of the heterogeneous nucleation induced by ultrasonic processing and nanoAl2O3 dispersion. Hardness, yield strength and maximum compressive stress of the nanocomposites are found to be superior to that of the matrix alloy. The resistance against wear is increased due to incorporation of reinforced nanoAl2O3particles. The wear rate of nanocomposite is decreased with increasing the amount of the reinforcement. The identified wear mechanisms are abrasion and oxidation.
Surface Modification of Pure Magnesium and Magnesium Alloy AZ91 by Friction Stir Processing
Authors: Hütter Andreas , Huemer Wilfried , Ramskogler Claudia , Warchomicka Fernando Gustavo , Lachehab Aymen , Vallant Rudolf , Sommitsch Christof
Published: July 2015

In recent years an interest in magnesium and magnesium alloys not only for the automotive industry but also for medical applications was increasing due to the low density and good specific strength. Magnesium alloys show good castability but lower ductility and strength than wrought materials. For this reason, refinement of grains and homogenous distribution of intermetallic phases are needed to improve formability and mechanical properties. On the other hand, the degradation of the material by corrosion is influenced by the grain size and phase distribution. This work investigates the microstructure evolution of pure Mg and magnesium alloy AZ91 by friction stir processing (FSP) technique. FSP experiments are carried out by constant force, optimizing the rotation and feed rate to obtain a homogenous microstructure, free of defects stir zone, good surface finishing and stable conditions during the process. The results show that the grain size is affected by the spindle speed. Increasing the number of passes reduces also the size of the grains and the intermetallic phases in the AZ91 alloy. The overlapping of passes between overlapping ratio 0.5 to 1 determines an uniform depth of the stir zone over a larger surface area.Hardness measurements are performed to evaluate the influence of FSP parameters on the mechanical properties. The degradation rate of the studied FSP Mg alloys is determined by hydrogen evolution in corrosion immersion tests, which depend strongly on the phase distribution and grain size.
The Use of a New Viscous Process in Constitutive Models of Polymers
Authors: Sweeney John , Spencer Paul E.
Published: July 2015

In constitutive models of polymers, there has been a long history of the use of strain-rate dependent viscous processes, such as the Eyring and Argon models. These are combined with elastic elements to generate viscoplastic models that exhibit typical phenomena such as rate dependent yield, creep and stress relaxation. The Eyring process is one of the most frequently used such mechanisms. It has two significant drawbacks: it implies a temperature dependence of mechanical behaviour that is in an opposite sense to that observed; and it predicts a strain rate dependence of yield stress that is less complex than that observed, leading to the requirement for two or more Eyring processes. In recent years, new ideas for amorphous polymers have been developed that lead to an alternative plastic mechanism that addresses these concerns. In this paper a constitutive model that incorporates this mechanism is developed, and its effectiveness in modelling macroscopic mechanical behaviour of polymers is explored with respect to published data.
Effect of Surface State of Die on Flow Rate of Steamed Bamboo Powder in Thermal Flow Test Using Capillary Rheometer
Authors: Kajikawa Shohei , Sakagami Riku , Iizuka Takashi
Published: July 2015

Thermal flow tests were performed on steamed bamboo powder using capillaries that were processed under different conditions in order to investigate the effect of the die surface state on the fluidity of the woody powder. The capillaries were processed by wire-cut electric discharge machining, reaming or drilling, and the arithmetic average roughness (Ra) varied from 0.5 to 2.5 μm. The bamboo powder was first steamed at 200 °C for 20 min, and its particle size was then controlled using different mesh screens. The thermal flow temperature was set at 200 °C. The results indicated that the flow behavior improved with increasing particle size. For the capillaries processed by WEDM, the flow rate for samples with particle sizes of 75~150 and 150~300 μm decreased with increasing Ra. On the other hand, when reaming or drilling was used to process the capillaries, the flow rate was almost independent of Ra, regardless of the particle size.
Integrated FEM-DBEM Simulation of Crack Propagation in AA2024-T3 FSW Butt Joints Considering Manufacturing Effects
Authors: Sonne Mads Rostgaard , Carlone Pierpaolo , Citarella Roberto , Hattel Jesper Henri
Published: July 2015

This paper deals with a numerical and experimental investigation on the influence of residual stresses on fatigue crack growth in AA2024-T3 friction stir welded butt joints. An integrated FEM-DBEM procedure for the simulation of crack propagation is proposed and discussed. A numerical FEM model of the welding process of precipitation hardenable AA2024-T3 aluminum alloy is employed to infer the process induced residual stress field. The reliability of the FEM simulations with respect to the induced residual stresses is assessed comparing numerical outcomes with experimental data obtained by means of the contour method. The computed stress field is transferred to a DBEM environment and superimposed to the stress field produced by a remote fatigue traction load applied on a friction stir welded cracked specimen. Numerical results are compared with experimental data showing good agreement and highlighting the predictive capability of the proposed method. Furthermore, the influence of the residual stress distribution on crack growth is evidenced.
Effect of Equivalent Stress-Strain Relation and Differential Hardening on Accuracy of Forming Limit Analyses
Authors: Hakoyama Tomoyuki , Kuwabara Toshihiko
Published: July 2015

Multiaxial tube expansion tests (MTETs) were performed to measure the multiaxial plastic deformation behavior of a cold rolled interstitial-free (IF) steel sheet for a range of strain from initial yield to fracture. The testing machine is capable of applying arbitrary principal stress or strain paths to tubular specimens using an electrical, closed-loop servo-control system for an axial force and an internal pressure. Tubular specimens with an inner diameter of 44.6 mm were fabricated from a cold rolled IF steel sheet with a thickness of 0.7 mm by roller bending and laser welding. Many linear stress paths in the first quadrant of stress space were applied to the tubular specimens to measure the forming limit strains and forming limit stresses of the as-received sheet sample, in addition to the contours of plastic work and the directions of the plastic strain rates. It was found that the shapes of the measured work contours changed with increasing plastic work. The observed differential hardening behavior was approximated by changing the material parameters and the exponent of the Yld2000-2d yield function (Barlat et al, 2003) as functions of the reference plastic strain. The hydraulic bulge tests were also conducted to measure the forming limit strain and forming limit stress for equibiaxial tension and to determine the equivalent stress-equivalent plastic strain relation for a larger strain range. The forming limit curve and forming limit stress curve were calculated using the Marciniak-Kuczyński-type approach. The calculated results were in fair agreement with the measurement.
Effect of the Process Parameters on the Geometrical Defects of Ti-6Al-4V Hot Rolled Sheets Laser Beam Welded
Authors: Boccarusso Luca , Arleo Giuseppe , Astarita Antonello , Bernardo Franco , de Fazio Piero , Durante Massimo , Giudice Giuseppe , Minutolo Fabrizio Memola Capece , Sepe Raffaele , Squillace Antonino
Published: July 2015

Ti-6Al-4V is an alloy that is increasingly used in aeronautics due to its high mechanical properties coupled with the lightness. An effective technology used to manufacture titanium components with a reduced buy to fly ratio is the laser beam welding. Previous studies showed that the key factor that rules the mechanical properties and the fatigue life of the joint is its morphology. The aim of this paper was to investigate the influence of the main process parameters, such as welding speed and laser power, on the geometrical features of the joint, in terms of undercut, underfill, reinforcement and so on. 3.0 mm thick Ti-6Al-4V rolled sheets were welded in butt joint configuration by using a Nd-YAG laser source. The joint performances were studied in terms of weld morphology, microstructure and Vickers microhardness. Then, defects such as underfill and reinforcement, controlling the whole weld morphology, were observed, and the relationship between the occurrence, the entity of these defects and the process parameters was studied.