Wall Thickness Distribution Research Articles

Parameter Prediction of Stretch-Blow Molding Process of PET Using Neural Networks

This study presents a parameter selection strategy developed for the Stretch-Blow Molding (SBM) process to minimize the weight of preforms used. The method is based on a predictive model developed using Neural Networks. The temperature distribution model of the preform was predicted using a 3-layer NN model with supervised backpropagation learning. In addition, the model was used to predict the uniform air pressure applied inside the preform, taking into account the relationship between the internal air pressure and the volume of the preform. Parameters were validated using in situ tests and measurements performed on several weights and lengths of a 0.330 Liter Polyethylene Terephthalate (PET) bottles. Tests showed that the model adequately predicts both the blowing kinematics, mainly zone temperatures and blowing and stretching pressures along the walls of the bottle while maintaining the bottle strength and top load requirements. In the second step, the model was combined to automatically compute the lowest preform weight that can be used for a particular 330 ml bottle design providing a uniform wall thickness distribution.

Multilayer and Fiber Metal Laminate Materials Hydro-Bulging

Advanced materials such as aluminum alloys and composites offer great potential for weight reduction applications in automotive and aerospace vehicles construction. In order to investigate the feasibility of using such materials in the form of laminates, sheet bulging with single-layer aluminum and the aluminum/Composite laminate with the carbon cloth as the middle layer is investigated under uniform liquid pressure conditions. The aluminum sheet stress-strain, wall thickness distribution, carbon fiber radius stress-strain distribution and the effect of die entrance radius etc. are discussed and compared in details. FE results validate that the numerical method can predict the same fracture regions for bulging-blank as observed in experimental tests. Furthermore, the study validates that multi-layer sheet hydro-bulging process with composite fiber as a middle layer is not feasible to form laminates due to rupture of composite fibers near edge regions. Further study is needed to improve the methodology.

بهبود سفتی ماشین فرز با استفاده از بهینهسازی آرایش تقویتکنندههای داخلی و توزیع ضخامت دیواره ستون

Machine tool static deflection due to the machining forces and thus the displacement of tool tip is the most important factor in reducing the dimensional accuracy of workpiece. Also, overlap of the operation frequency range with the machine natural frequencies causes an undesirable resonance phenomenon. Since the operating frequency range is lower than the first natural frequency, increasing the first natural frequency of milling machine and reducing the displacement of tool tip is a desirable modification that can be achieved by optimizing the wall thickness distribution and the internal stiffeners layout of column. This paper suggests a new method for the optimization of stiffeners layout for plate/ shell structures. In each step of optimization, by establishing a loop of relationship between MATLAB and ABAQUS software and based on the sensitivity analysis, the most effective stiffeners on optimizing the objective function are added to design space. After optimizing the wall thickness distribution of the column using the ABAQUS software size optimization module, the suggested method is used to optimize the internal stiffeners layout. Ultimately, without increasing the column weight, the maximum displacement of machine tool is reduced by 6.9% and the first natural frequency is improved by 16.5%.

Simulation of thermoforming processes with directed air‐flow

AbstractThermoforming is a manufacturing process suitable for mass‐production of simply shaped plastic products. One of the main limitations of the common process is the resulting inhomogeneous wall thickness distribution. The authors show experimentally that it is possible to positively influence the wall thickness distribution by using directed air‐flow. In order to numerically reproduce the process, a simulation model is set up. The simulation results clearly show how the temperature distribution during deformation can be influenced.

Hydraulic bulging process with axial feedings and strain field of U-shaped metal bellows

Based on the traditional hydraulic bulging process, an improved hydraulic bulging process with axial feeding in the bulging process was proposed. The finite element simulation and experiment of bellows formed by the traditional and improved hydraulic bulging processes were conducted. The grid strain measurement system analysis results of strain and wall thickness distribution of the metal bellows, obtained from simulation and experiment, show that the maximum thinning rates of the wall thickness under the traditional and improved processes were 15% and 10%, respectively. And the wall thickness distribution of the metal bellows formed with improved process was more uniform. The strain values from the root to crown of the waveform increased gradually. However, the strain values were smaller than those of traditional process due to the axial feeding of the improved process in bulging process.

Experimental investigation of new blank holder approach for incremental forming method

In this study, a new method is developed to reduce the variation of the wall thickness in incremental sheet forming method used in prototype production of sheet metal parts. Unlike the traditional incremental forming method, this new method defined as “rolling blank holder incremental forming method” is aimed primarily at the force optimization of the blank holder. In this context, 27 different experimental runs were carried out with 1 mm thick DC01 sheet metal. According to the experimental results, when 2 bar pressure was applied to the pneumatic clamps that supply the clamping force, 4.5% improvement of the minimum wall thickness was observed. Clearly, a better wall thickness distribution can be obtained when this new method is used, compared to the conventional incremental forming method.

The effect of conventional metal spinning parameters on the spun-part wall thickness variation

Conventional metal spinning technology is based on the sequential shaping of a circular sheet over a mandrel through the action of a roller that produces localised pressure to produce a hollow axisymmetric product. The wall thickness of the formed part in this process is, in general, considered to be nearly constant, but in fact, a non-uniform distribution of wall thickness is observed. The wall thickness variation is a major defect found in produced parts that can cause part failure and therefore the spinning process must be properly optimized. This paper deals with the analysis of the chosen conventional metal spinning parameters (tool path profile, mandrel speed and the tool feed rate) on the wall thickness variation of cylindrical shaped spun-parts made of DC01 low carbon steel, while a three-level full factorial design of experiment method (DoE) and ANOVA (Analysis of Variance) were used. The experimental results revealed that tool path profile and the tool feed affects the wall thickness variation in a significant way. The effect of the mandrel speed was not clearly observed.

Wall thickness distribution of Cu–Al bimetallic tube based on free bending process

In this study, we focused on bimetallic tube comprising copper and aluminum (Cu–Al) and proposed a theoretical model of its wall thickness distribution by the free bending technology. Compared to the single metal tube, the minimum thickness of the copper tube is smaller than the minimum thickness of the copper layer in the Cu–Al bimetallic tube, whereas the minimum thickness of the aluminum tube is greater than that of the Cu–Al bimetallic tube under different bending radii; the maximum wall thickness of the copper tube is larger than that of the copper layer in the Cu–Al bimetallic tube, whereas the maximum wall thickness of the aluminum tube is smaller than that of the aluminum layer in the Cu–Al bimetallic tube. Further, the reliability of the proposed theoretical model was verified by finite element simulation and experiments. Both of these results showed that the wall thickness distribution of the bimetallic layer of the metal tube tends to be more uniform. The offset rule of the strain neutral layer of Cu–Al bimetallic tube in the free bending process was also revealed. Moreover, the difference between the U–R curve of the Cu–Al bimetallic tube and the single metal tube was also investigated, and the results indicated that the U–R curve of the Cu–Al bimetallic tube is roughly located between the U–R curves of copper and aluminum.

Image-Based Computational Evaluation of the Effects of Atrial Wall Thickness and Fibrosis on Re-entrant Drivers for Atrial Fibrillation.

Introduction: Catheter ablation (CA) is a common treatment for atrial fibrillation (AF), but the knowledge of optimal ablation sites, and hence clinical outcomes, are suboptimal. Increasing evidence suggest that ablation strategies based on patient-specific substrates information, such as distributions of fibrosis and atrial wall thickness (AWT), may be used to improve therapy. We hypothesized that competing influences of large AWT gradients and fibrotic patches on conductive properties of atrial tissue can determine locations of re-entrant drivers (RDs) sustaining AF.Methods: Two sets of models were used: (1) a simple model of 3D atrial tissue slab with a step change in AWT and a synthetic fibrosis patch, and (2) 3D models based on patient-specific right atrial (RA) and left atrial (LA) geometries. The latter were obtained from four healthy volunteers and two AF patients, respectively, using magnetic resonance imaging (MRI). A synthetic fibrotic patch was added in the RA and fibrosis distributions in the LA were obtained from gadolinium-enhanced MRI of the same patients. In all models, 3D geometry was combined with the Fenton-Karma atrial cell model to simulate RDs.Results: In the slab, RDs drifted toward, and then along the AWT step. However, with additional fibrosis, the RDs were localized in regions between the step and fibrosis. In the RA, RDs drifted toward and anchored to a large AWT gradient between the crista terminalis (CT) region and the surrounding atrial wall. Without such a gradient, RDs drifted toward the superior vena cava (SVC) or the tricuspid valve (TSV). With additional fibrosis, RDs initiated away from the CT anchored to the fibrotic patch, whereas RDs initiated close to the CT region remained localized between the two structures. In the LA, AWT was more uniform and RDs drifted toward the pulmonary veins (PVs). However, with additional fibrotic patches, RDs either anchored to them or multiplied.Conclusion: In the RA, RD locations are determined by both fibrosis and AWT gradients at the CT region. In the LA, they are determined by fibrosis due to the absence of large AWT gradients. These results elucidate mechanisms behind the stabilization of RDs sustaining AF and can help guide ablation therapy.

Thermal Analyses of Active-Cooled Strut in RBCC Engine

Fuel-injection strut is an efficient way to increase the depth of fuel penetration and strengthen the mixing process of hot gas in supersonic combustor. With a validated numerical model, this article analyzed the effects of leading edge's radius, wall thickness and mass flow distribution on cooling efficiency of fuel-injection strut and proposed an optimizing strategy for active-cooled strut. Results showed that the larger radius of leading edge not only decreased the heat flux on the leading edge, but also has a negative effect on the aerodynamic performance of strut; and a thinner wall could enhance the cooling efficiency and uniformize the temperature distribution of the wedge; furthermore, the flow distribution of inlet coolant had a significant impact on the heat transfer and flow processes, an optimized way of flow distribution was obtained by comparing three different ways of distribution.

Influence of blank thickness fluctuation on flange state and final thickness distribution in the power spinning of thin-walled head

The initial blank exists unavoidable thickness fluctuation. In the spinning process of head parts, this fluctuation affects the flange state and final wall thickness distribution of the parts, which seriously deteriorates the forming quality. To research the blank thickness fluctuation on flange and spun head thickness distribution, three-dimensional (3D) finite element (FE) models considering blank fluctuation for the spinning process of 2219 aluminum head parts were established. The blank fluctuation was characterized using the Latin hypercube sampling method (LHS), and three fluctuation ranges and three fluctuation types were adopted (type 1, the average blank wall thickness is approximately equal to 1.0 mm, 1.0 mm is defined as the ideal standard blank thickness (ST); type 2, the average blank wall thickness is bigger than ST; type 3, the average blank wall thickness is smaller than ST). Then, flange fluctuations and the variations of wall thickness deviation were analyzed. The results showed that the maximum flange fluctuation appears within the 20% spinning process; the maximum flange fluctuation of type 1 is larger than those of type 2 and type 3. In the top zone of the spun head, the maximum wall thickness deviation of type 3 is the largest. While in the middle and edge zones, the maximum wall thickness deviation of type 2 is the largest. Simultaneously, a greater initial blank fluctuation leads to the bigger thickness frequency deviation. The research provides an in-depth understanding of the effects of blank wall thickness fluctuation on the forming quality in the head spinning process, and thus lays a basis for choosing the blank.

Deep drawing of press hardening steels

Press hardening of low alloy steel sheets is an efficient way of manufacturing high strength automotive components relevant for passenger safety in case of a crash. The press hardening process combines the advantages of good formability at elevated temperatures as well as high strength and good form accuracy after quenching in the closed die. Since cooling during forming and subsequent quenching has a significant influence on the mechanical behaviour of a steel sheet, a strongly coupled thermo-mechanical model has been developed for the simulation software ABAQUS. Accurate simulation results require the knowledge of temperature dependent thermal and mechanical material properties as well as occurring interactions between the sheet and the die. They were determined in a series of experiments and provide the input for the numerical model. During the quenching step in the closed die, the high strength of the component is achieved by a martensite phase transformation. This transformation is strongly influenced by the deformation in the heavily bent areas as well as the temperature evolution of the sheet. Accurate results for the shape of the final components and for the properties within the operating service time can only be obtained if the numerical model accounts for the microstructure formation including the TRIP (Transformation Induced Plasticity) effect. This is accomplished by means of a user subroutine. Consequently, the model allows to analyse the forming and cooling process in the closed die in detail throughout the entire process cycle. Concluding, the final geometry, the wall thickness distribution of the component and the press forces during forming are used as parameters to compare the simulation results with forming experiments and to validate the chosen material model.

Research on Quick Superplastic Forming Technology of Industrial Aluminum Alloys for Rail Traffic

Quick superplastic forming is a new technology, which combines hot drawing preforming and superplastic forming. It makes full use of the high speed of hot drawing and good formability of superplasticity. For aluminum alloy complex components, the difficulties of stamping and low speed of superplasticity be perfect solved. In this work, the best forming process of side wall outer panel of metro vehicle was determined by forming experiment using quick superplastic forming technology. The high-speed rail edge skin with a very small fillet shape (R≤4 mm) and the large-size subway door frame part (h≈80 mm) formed by straight wall deep drawing were manufactured, using industrial aluminum alloy sheet with thickness of 4 mm. Meanwhile, the formed parts show the advantages of high dimensional accuracy and uniform wall thickness distribution, and the mechanical properties of formed parts can completely meet the requirements as well, which demonstrates the desirable efficiency, low cost and feasibility of this new technology.

Creep of closed-cell aluminum foams: Effects of imperfections and predictive modeling

The influence of five different types of morphological imperfection – curved cell wall, corrugation, cell shape irregularity, missing cell walls and non-uniform distribution of cell wall thickness – on steady state creep of closed-cell aluminum foams is systematically studied under uniaxial compressive loading. A refined theoretical model is developed to predict the steady state creep rate of idealized tetrakaidecahedral (TKD) closed-cell foams. Based upon the TKD model, finite element modeling is also carried out. The presence of imperfections usually leads to significant increase in steady state creep rate. The creep rate increases linearly with the degree of cell shape irregularity and the curvature of curved cell walls, while increases as a power law function of the area fraction of missing cell walls and the dispersion degree of non-uniform distributed cell wall thickness. The combined effect of three different random defects—cell shape irregularity, missing cell walls and non-uniform distribution of cell wall thickness—causes more drastic increase in creep rate than any single or dual imperfections. Interactions among the three are small and can be neglected. Finally, an empirical formula of steady state creep rate is proposed to give a good prediction for closed-cell foams with random imperfections.

Fabrication of metallic bipolar plate for proton exchange membrane fuel cells by using polymer powder medium based flexible forming

Flexible forming process-polymer powder medium based flexible forming (PPFF) is presented in this research. The metallic bipolar plate (BPP) for a proton exchange membrane (PEM) fuel cell, with a micro-scale flow channel on its surface, is formed using rigid die forming and PPFF process, respectively. Pure copper C1100 (with a thickness of 0.1 mm), annealed at 450 °C for 1 h in vacuum condition, is selected as blank material. The forming experiments are carried out at room temperature in dry friction condition. By comparing the limit forming depth, fracture topography, section wall thickness distribution and surface forming quality of micro-scale flow channels between rigid die forming and PPFF process, it reveals that PPFF process could be developed as a feasible technique to fabricate the bipolar plates of PEM fuel cells. The PPFF process has the following advantages: greater forming depth, more uniform wall thickness distribution, and low cost of the die.

Automatic image processing morphometric method for the analysis of tracheid double wall thickness tested on juvenile Picea omorika trees exposed to static bending

We present and test an automatic image processing morphometric method for the analysis of tracheid double wall thickness. Measurements of various anatomical characteristics of wood cells are of great importance in research of wood structure, either for the evaluation of environmental influences or for estimation of wood quality. We present and test an automatic image processing morphometric method for the analysis of tracheid double wall thickness. A new algorithm of image analysis was developed. It uses morphological processing of structural elements with the different orientations from distance maps to analyze tracheid double wall thickness distribution separately for radial walls, tangential walls, and cell corners. For testing the performance of the method, we used confocal laser scanning microscopy images of stem cross-sections of juvenile Picea omorika trees exposed to long-term static bending. As a response to mechanical stress, conifers form compression wood (CW), which occurs in a range of gradations from near normal wood (NW) to severe CW. However, visual detection of compression wood severity, more precisely the determination of mild CW, is difficult. One of the anatomic features that characterize CW is increased wall thickness. After testing proposed automatic image processing morphometric method for the analysis of tracheid double wall thickness separately for radial walls, tangential walls and cell corners, combined with statistical analysis, we could suggest it as a tool for estimation of compression wood severity, or for estimation and gradation of changes in tracheid cell wall thickness as a response to environmental influences during growth and developmental process.

Improvement in formability and geometrical accuracy of incrementally formed AA1050 sheets by microstructure and texture reformation through preheating, and their FEA and experimental validation

The work involves finite element analysis (FEA) and experimental investigation of formability and geometrical accuracy prevailing in single point incremental forming (SPIF) process. Preheating at different temperatures was performed in order to reform microstructures (grain size) and texture (spatial grain orientation distribution) of AA1050 sheet. Preheating led to removal and rearrangements of defects in the crystal structure in comparison with the distorted structures present in cold-worked commercial aluminum sheets. Preheating at higher temperatures resulted in coarser grains with preferential texture and increased area fraction of homogenously oriented grains. Numerical simulation of SPIF process has been done to predict the effect of preheating on von Mises stresses, forming load, wall thickness distribution and geometrical accuracy of formed parts. For the purpose, Johnson–Cook models’ parameters were evaluated by mechanical characterization of the samples with varying microstructural and texture arrangements resulted due to variations in preheating temperatures. FEA of the process revealed that preheating of the sheets resulted in reduced forming load, uniform wall thickness distribution and improved geometrical accuracy. The results were further validated by experiments and compared to the original samples with fine and randomly orientated grains.

Interaction of Mannitol and Sucrose with Gellan Gum in Freeze-Dried Gel Systems

The effect of sucrose and mannitol addition to low-acyl (LA) gellan gum gels at both the molecular and macroscopic levels prior to, and after freeze-drying has been investigated. It has been shown that the gel network order as well as the mechanical properties are changed with the solute content, especially in the case of sucrose. The freeze-dried gel structure, containing either mannitol or sucrose, was studied, reporting for the first time the interaction of mannitol with the gellan gum gel. The generated freeze-dried gel network was evaluated in terms of porosity, pore size and wall thickness distributions. The solute physical state was correlated the water activity trend as a function of the solute content. Since mannitol is crystalline, the water activity decreases, in contrast with the amorphous sucrose. The rehydration mechanism was investigated and associated with the solute release from the structure. Specifically, the material properties (surface and bulk) as well as the role of the dissolution medium over time were assessed. It was found that the rehydration for both the gellan/sucrose and gellan/mannitol systems was highly influenced by the additive content, as an increase in water uptake was measured up to 10 wt%. A further increase in solute led to a considerable drop in the rehydration rate and extent due to the change in the freeze-dried structure, with smaller pores and with higher wall thickness values.

Earlywood and Latewood Features of Pinus sylvestris in Semiarid Natural Zones of South Siberia

Chronologies of the anatomical and integral parameters of the Scots pine (Pinus sylvestris L.) earlywood and latewood were investigated for two sites in the Minusinsk depression with different soil moisture conditions. Patterns of statistical characteristics and climatic responses of the chronologies were identified. Differences between sites were revealed in the cell diameter and wall thickness distributions. These differences are indicators of adapting pine wood structure to the moisture deficit.

Simulation on Effect of Preform Diameter in Injection Stretch Blow Molding

Polyethylene terephthalate (PET) is the most common material of resin for manufacturing plastic bottle by injection stretch blow molding due to its excellent properties. As various issues of health and environmental hazards due to the PET use have risen, PET bottle manufacture may be improved by minimizing the wall thickness to reduce the PET use. One of the critical qualifications of the manufacturing process which lead to the wall thickness distribution is the initial preform diameter. In this project, we used the ANSYS Polyflow with aim to evaluate the wall thickness distribution of PET bottle for different diameter of initial preform. As a result, only 4 mm preform diameter presented wall thickness below than 1 mm. On the other hand, at least 6 mm preform diameter can permit the wall thickness 1.3 mm i.e. at the shoulder area.