Wall Thickness Distribution Research Articles

Numerical analysis on the elastic deformation of the tools in sheet metal forming processes

The forming tools are commonly assumed as rigid in the finite element simulation of sheet metal forming processes. This assumption allows to simplify the numerical model and, subsequently, reduce the required computational cost. Nevertheless, the elastic deformation of the tools can influence considerably the material flow, specifically the distribution of the blank-holder pressure over the flange area. This study presents the finite element analysis of the reverse deep drawing of a cylindrical cup, where the forming tools are modelled either as rigid or as deformable bodies. Additionally, the numerical results are compared with the experimental ones, in order to assess the accuracy of the proposed finite element model. Considering the elastic deformation of the tools, the numerical results are in better agreement with the experimental measurements, namely the cup wall thickness distribution. On the other hand, the computational time of the simulation increases significantly in comparison with the classical approach (rigid tools).

Therapeutic potential of adipose stem cell-derived conditioned medium against pulmonary hypertension and lung fibrosis.

Pulmonary hypertension (PH) and pulmonary fibrosis (PF) are life threatening cardiopulmonary diseases. Existing pharmacological interventions have failed to improve clinical outcomes or reduce disease-associated mortality. Emerging evidence suggests that stem cells offer an effective treatment approach against various pathological conditions. It has been proposed that their beneficial actions may be mediated via secretion of paracrine factors. Herein, we evaluated the therapeutic potential of conditioned media (CM) from adipose stem cells (ASCs) against experimental models of PH and PF. Monocrotaline (MCT) or bleomycin (Bleo) was injected into male Sprague-Dawley rats to induce PH or PF respectively. A subset of MCT and Bleo animals were treated with ASCs or CM. Echocardiographic and haemodynamic measurements were performed at the end of the study. Lung and heart tissues were harvested for RNA, protein and histological measurements. CM treatment attenuated MCT-induced PH by improving pulmonary blood flow and inhibiting cardiac remodelling. Further, histological studies revealed that right ventricular fibrosis, pulmonary vessel wall thickness and pericyte distribution were significantly decreased by CM administration. Likewise, CM therapy arrested the progression of PF in the Bleo model by reducing collagen deposition. Elevated expression of markers associated with tissue remodelling and inflammation were significantly reduced in both PF and PH lungs. Similar results were obtained with ASCs administration. Our study indicates that CM treatment is as effective as ASCs in treating PH and PF. These beneficial effects of CM may provide an innovative approach to treat cardiopulmonary disorders.

Springback and compensation of bending for hydroforming of advanced high-strength steel welded tubes

Bending springback plays an important role in hydroforming of curved hollow components, and the effect will be more apparent with the increase of the strength of the material. In order to predict and eliminate the effect of springback on hydroforming process, springback of DP590 welded tube was investigated in computer numerical control (CNC) bending process using theoretical analysis, numerical simulation, and experimental methods. The effects of the bending angles, the diameter-thickness ratio d/t, and the relative bending radius R/d on springback are studied, and the influence factor of the weld position is considered. The theoretical and experimental results show that the springback of the DP590 welded tube with 65 mm in diameter and 2.6 mm in thickness varies within the range from 4.0 to 4.9 % and the amount of springback is influenced by the tube diameter and thickness. The springback reduces from 7.0 to 3.5 % when the diameter-thickness ratio is increasing from 10 to 40. On the contrary, the springback increases from 3.7 to 7.2 % when the relative bending radius is increasing from 1.2 to 4.0. The effect of weld position on springback is very little, but it has a negative effect on defects of hydroforming and wall thickness distribution. It is liable to crack when hydroforming if the weld locates on the outside or neutral layer of the bend. Finally, springback rules and weld effect are applied to form a control arm. A sound part had been successfully manufactured to avoid flash and crack defects considering the appropriate springback compensation and weld position.

Consistency of Strain Fields and Thickness Distributions in Thermoforming Experiments Through Stereo DIC

This paper proposes a methodology to determine wall thickness distributions in thermoformed products derived from in-situ surface strain measurements obtained with stereo digital image correlation (DIC), under the assumption of material incompressibility. Wall thickness equations are derived for the Green-Lagrange, Hencky, Biot, logarithmic Euler-Almansi and Euler-Almansi strain definitions and validated with an analytic example. The equations are then used to calculate the wall thickness from digital image correlations with both a commercial software (VIC-3D, version 2012) and an academic software (MatchID3D). Obviously, the choice of the strain definition in the correlation software should not influence the resulting wall thickness values. The comparison reveals that the wall thickness values prove to be identical, regardless of the strain definition that was used, and manual measurements show the validity of the DIC based results. It was also found that, when using VIC-3D version 2009, an earlier release in the software series of Correlated Solutions, all but the Green-Lagrange strain definition bring forth unrealistic minimum principal strain values, resulting in different values for the wall thickness.

Surface Structure and Acidity Properties of Mesoporous Silica SBA-15 Modified with Aluminum and Titanium: First-Principles Calculations

Ordered mesoporous silica materials are considered promising supports for the development of novel hydroprocessing catalysts. Specifically, the mesoporous silica SBA-15 exceeds because of high specific surface area, wall thickness, and pore size distribution, features that make this material more stable at environments at which hydroprocessing reactions take place. However, the SBA-15 lacks strong Bronsted acid sites and this fact still hinders its widespread commercial use. In this work we report density functional theory analyses of the structure and acidity properties of the SBA-15 surface. Periodic boundary models are used and the temperature dependence of the silanol surface density is taken into account. Surface modification by isomorphic substitutions with aluminum and titanium is investigated. It is found that aluminum substitution favors creation of bridging hydroxyl groups. However, surface modifications with aluminum and titanium also create local structural distortions inducing H-bond interact...

12 mm Thick Circular Blanks of Al-killed AISI 1020 Steel -Applied for Cylindrical Cup Manufacturing by Multistage Deep Drawing with Simultaneous Ironing

In this paper a new modified processing route has been proposed for producing long cylindrical cups from 12 mm thick circular blanks of AISI 1020 steel (Aluminium (Al) -killed). In this route, flat blanks were made to preformed shape by stamping operation, followed by multistage deep drawing processes(without blank-holder and with inter-stage stress relief annealing) to increase cup depth. Wall ironing was also purposefully included in each draw step to reduce wall thickness and earing tendency on cup edges. Thus, evolution of wall thickness distribution, Drawability and Ironability, punch force history, and strain distribution profiles on outer cup surfaces were obtained as the effects of interaction between processes, tools and material. The overall draw stages showed: LDR 2.06; overall draw reduction >50% with a drawing efficiency ~72%; LIR 3.55; overall ironing reduction >70% with an ironing efficiency ~68%, which were achieved in the experimental works.

Nylon 6,6/Polyaniline Based Sheath Nanofibers for High-Performance Supercapacitors

Nylon 6,6/PANI nanofibers using electrospun nylon 6,6 nanofibers as a template are synthesized by the in situ polymerization of different aniline concentrations for the preparation of all-polymer based core-sheath nanofibers with high electrochemical and mechanical properties, such as lightness and flexibility. These nylon 6,6/PANI based sheath nanofibers are used as electrode materials for supercapacitors. The electrochemical performance is examined by cyclic voltammetry (CV), galvanostatic charge/discharge tests and electrochemical impedance spectroscopy (EIS). The galvanostatic charge/discharge test reveals the highest specific capacitance of 665Fg−1 at a current density of 1Ag−1. This electrode also shows remarkable rate charge/discharge capability and high cyclic stability (62% after 1000 cycles). In addition, the high energy density of the nylon 6,6/PANI composite electrode can reach 91Whkg−1 at a power density of 500Wkg−1. The superior electrochemical properties of the core-sheath nylon 6,6/PANI nanofibers are attributed to their core-sheath structure, thin wall thickness and uniform wall distribution, which can improve the performance of electroactive PANI during the charge/discharge process. The good electrochemical performances highlight the potential of the nylon 6,6/PANI electrode as an electrode material for high-performance supercapacitors.

Electromagnetic pulse-assisted incremental drawing of aluminum cylindrical cup

Based on the needs of low plasticity materials and large height diameter ratio parts forming, a new forming approach named electromagnetic pulse-assisted incremental drawing (EMPAID) has been proposed in this study. The radial magnetic force produced by circular auxiliary coils on and underneath a flange pushes sheet metal in the radial direction. The axial magnetic force generated by drawing coil in the bottom of the punch pushes the sheet metal into the die cavity. The magnetic force produced by the corner coil provides a through-thickness pressure on the sheet metal around the die corner, which prevents wrinkling. The forming process and principle of the new method are analyzed in this study. To investigate the effects of the auxiliary and corner coils, which are added to stamping tools to improve the wall-thickness distribution, the stress state, and the forming quality, two different cases are compared and analyzed in simulation and experimentally. The result indicates that the radial magnetic force generated by the auxiliary coil could reduce the radial tensile stress, which mitigates the crack of the workpiece. Using this new forming method, the limit drawing height can be increased to 2.16 times of that in the conventional drawing.

Experimental Studies on Flexible Forming of Sheet Metals Assisted by Magnetic Force Transfer Medium

To improve the thickness uniformity and increase the forming limit of sheets to enhance their overall quality, a magnetorheological fluid (MRF) was injected into the punch cavity to act as the force transfer medium and fulfill the function of flexible pressing during the sheet bulging process. The rheological properties of the MRF were changed under the influence of a magnetic field produced by loading different currents, which allowed variation of stress states and deformation modes in the 0.75-mm-thick 304 stainless steel sheets. With increasing current (up to 3.5 A), the sheet-forming limit increased by 16.13% at most, and the fracture morphology experienced a certain change. Additionally, both the bulge height and the wall thickness distribution had obvious changes with a punch stroke of 10 mm. According to the experimental analysis, the MRF can be used successfully as a pressure-carrying medium in the sheet forming process.

Numerical Analysis of a Skew Rolling Process for Producing a Stepped Hollow Shaft Made of Titanium Alloy Ti6Al4V

Abstract The paper describes a rolling process for a hollow Ti6Al4V alloy shaft used in driving systems of light trucks. The shaft is formed by skew rolling using three tapered rolls. The principle of this forming process was discussed stressing its universality due to the potential of applying it for forming various products by one set of rolls. The numerical analysis results (product shape progression in rolling, wall thickness distribution, effective strain, temperature and variations in loads and torques) confirm that the proposed technique can be used for producing hollow long shafts.

Fabrication of curved generatrix workpiece of TA15 titanium alloy by variable thickness tube spinning and flaring process

This study combined the tube spinning and flaring process to provide a novel method for forming curved generatrix workpiece with uniform thickness. Through 3D elastic–plastic finite element simulation based on the software ABAQUS/Explicit, the deformation characteristics of tube flaring were analyzed, and the formation mechanism of compressive buckling of the transition zone and rupture of tube end were explained reasonably. The tube flaring experiment shows that the thickness and mechanical properties of the as-flared workpiece became quite homogenous after tube flaring by pre-changing the wall thickness distribution of the tubular preform through tube spinning, exhibiting the special advantage of the combined process for forming curved generatrix tubular workpieces.

New processing research on sheet metal bidirectional pressure forming using a magnetorheological fluid

In order to break through the technical bottlenecks of the traditional power transmission medium which existing in the sheet forming process, this paper firstly proposes a method of the sheet metal bidirectional pressure forming using a magnetorheological fluid (MRF), then the experimental device and the key structure are developed. Taking the 304 stainless steel sheet as an example, the results of the sheet metal forming under different current intensity conditions are compared. When the current intensity is increased from 0 to 4 A, the increase of the sheet forming limit reaches to 18.03 %. The maximum thinning rate of the wall thickness decreases from 28 to 22.6 %, but the forming height has an increasing trend when the punch down stroke is 15 mm. The sheets’ wall thickness distribution and deformation uniformity are improved by the loading force transmission and the viscosity shear of the MRF under the gradual increased magnetic field. In conclusion, with the maturity of the process theory, it is expected to open up a new way for the study of the sheet flexible medium pressure molding process.

A New Strategy for Manufacturing Tailored Blanks by a Flexible Rolling Process

Applying bulk forming processes on sheet metals enables the manufacturing of functional components with local wall thickness distributions. Using tailored blanks improves the forming of the functional components and increases the material efficiency. One process for manufacturing tailored blanks with defined sheet thickness distributions is a flexible rolling process. However, this process requires a complex process strategy. Additionally, tailored blanks out of high-strength steels from this process have failed in subsequent forming. Thus, a new rolling concept with a defined shaping of the material into a die cavity has been developed. This new concept requires the development of a new process strategy. In this paper, the general qualification and first results of the new concept are presented.

Effect of the Degree of Ovality of the Finishing-Stand Passes in a Reeling Mill on the Accuracy Characteristics and Deformation of the Pipe

A study is made of the effect of the degree of ovality of the passes in the finishing stands of an FQM mill on the accuracy and deformation characteristics of the rolled product with the use of a system of 384-mm passes. The transverse distribution of wall-thickness at the outlet of the deformation zone in the fourth and fifth stands is determined for different degrees of ovality of the finishing-stand passes. Relations are obtained to calculate the degree to which the mandrel is enveloped by the metal, the increase in the thickness of the semifinished product, and its spreading for different pass ovalities in the finishing stands of the FQM mill. It is established that it is best to regulate pass ovality in the leader stand in order to significantly improve the accuracy of the rolled pipe’s geometric dimensions.

Analysis of the Effect of Process Parameters on Part Wall Thickness Variation in Conventional Metal Spinning of Cr-Mn Austenitic Stainless Steels

Metal spinning is one of a number of flexible sheet forming processes which is a cost effective option for the production of parts with a very high strength to weight ratio. Although the wall thickness of the formed part in conventional spinning is generally considered to be nearly constant, a non uniform distribution of wall thickness is in fact observed. In this study, the wall thickness variation of a formed part made of Cr-Mn austenitic stainless steel was analysed. The thickness variation was measured using an optical 3D scanning method and the influence of mandrel speed, feed ratio and tool path profile (convex, concave and linear) on wall thickness variation was studied. A three-level full factorial design of the experiment and ANOVA (Analysis of Variance) were used. The results show that the maximal variation in wall thickness is observed in approximately half of the part wall height (thinning) and on the open end of the part (thickening). Feed ratio and roller path profile are statistically significant factors governing wall thickness variation. There was no obvious effect from the variation in mandrel speed on the thickness distribution.

Simulation on the Effect of Bottle Wall Thickness Distribution using Blow Moulding Technique

The aims of this study are to assess the deformation behavior of a polymeric material during a blow moulding process. Transient computations of two dimensional model of a PP bottle were performed using ANSYS Polyflow computer code to predict the wall thickness distribution at four different parison's diameter; 8mm, 10mm, 18mm, and 20mm. Effects on the final wall thickness diameter and time step are studied. The simulated data shows that the inflation performance degrades with increasing parison diameter. It is concluded that the blow moulding process using 10mm parison successfully meet the product processing requirements. Factors that contribute to the variation in deformation behaviour of the plastic during the manufacturing process are discussed.

The Forming Process of the Sharply Curved Offsets by the Pushing Method

The scheme of device for the thin-walled sharply curved offset parts forming by pushing the tube-shaped workpiece through the die channel is presented. The numerical simulation of the bending process by pushing the tube-shaped workpiece is performed using ANSYS-LS/DYNA program complex. The wall thickness distribution law along the generatrix of curved workpiece is determined. The influence of curvature radius of the curved offset part on thinning deformation during bending process is defined. The experimental determination of the AISI 304 stainless steel tube-shaped workpiece thickness changes is performed. Application of the developed device for the sharply curved offset parts manufacturing according to DIN/ISO standards is demonstrated.

Material Distribution Optimization for the Shell Aircraft Composite Structure

AbstractOne of the main goal in aircraft structures designing isweight decreasing and stiffness increasing. Composite structures recently became popular in aircraft because of their mechanical properties and wide range of optimization possibilities.Weight distribution and lay-up are keys to creating lightweight stiff strictures. In this paperwe discuss optimization of specific structure that undergoes the non-uniform air pressure at the different flight conditions and reduce a level of noise caused by the airflowinduced vibrations at the constrained weight of the part. Initial model was created with CAD tool Siemens NX, finite element analysis and post processing were performed with COMSOL Multiphysicsr and MATLABr. Numerical solutions of the Reynolds averaged Navier-Stokes (RANS) equations supplemented by k-w turbulence model provide the spatial distributions of air pressure applied to the shell surface. At the formulation of optimization problem the global strain energy calculated within the optimized shell was assumed as the objective. Wall thickness has been changed using parametric approach by an initiation of auxiliary sphere with varied radius and coordinates of the center, which were the design variables. To avoid a local stress concentration, wall thickness increment was defined as smooth function on the shell surface dependent of auxiliary sphere position and size. Our study consists of multiple steps: CAD/CAE transformation of the model, determining wind pressure for different flow angles, optimizing wall thickness distribution for specific flow angles, designing a lay-up for optimal material distribution. The studied structure was improved in terms of maximum and average strain energy at the constrained expense ofweight growth. Developed methods and tools can be applied to wide range of shell-like structures made of multilayered quasi-isotropic laminates.

A numerical study of multi-pass design based on Bezier curve in conventional spinning of spherical components

Bezier curve has been widely used as the roller path in conventional spinning. In this paper, Finite Element model with parameterized 2-pass conventional spinning tool paths based on quadratic Bezier curve is developed to explore the influence on the wall thickness reduction of spherical components. The results show that the first path has significant effect on wall thickness distribution and the selection of parameter values in tool path is crucial for thickness distribution.

The effect of wall thickness distribution on mechanical reliability and strength in unidirectional porous ceramics

Macroporous ceramics exhibit an intrinsic strength variability caused by the random distribution of defects in their structure. However, the precise role of microstructural features, other than pore volume, on reliability is still unknown. Here, we analyze the applicability of the Weibull analysis to unidirectional macroporous yttria-stabilized-zirconia (YSZ) prepared by ice-templating. First, we performed crush tests on samples with controlled microstructural features with the loading direction parallel to the porosity. The compressive strength data were fitted using two different fitting techniques, ordinary least squares and Bayesian Markov Chain Monte Carlo, to evaluate whether Weibull statistics are an adequate descriptor of the strength distribution. The statistical descriptors indicated that the strength data are well described by the Weibull statistical approach, for both fitting methods used. Furthermore, we assess the effect of different microstructural features (volume, size, densification of the walls, and morphology) on Weibull modulus and strength. We found that the key microstructural parameter controlling reliability is wall thickness. In contrast, pore volume is the main parameter controlling the strength. The highest Weibull modulus () and mean strength (198.2 MPa) were obtained for the samples with the smallest and narrowest wall thickness distribution (3.1 m) and lower pore volume (54.5%).