Loading Path Design Research Articles

Loading Path Design for Grain Refinement in Hot Forming Process of Ti-6Al-2Zr-1Mo-1V Alloy

Loading Path Design for Grain Refinement in Hot Forming Process of Ti-6Al-2Zr-1Mo-1V Alloy

Topology optimisation of multiple robot links considering screw connections

AbstractThis paper presents a method for the lightweight design of robotic links subject to dynamic loads and requirements on the overall system stiffness. It includes (1) a decomposition scheme to enable separate component optimization and (2) an approach based on topology optimization for optimal load path design of screw connections. The approach reduces computing cost and mass of designs with screw connections.

Effect of alternative load path design method on preventing progressive collapse and reducing the rehabilitation cost using FEMA-P58

The alternative load path (ALP) method is an important modern design approach to prevent progressive collapse of buildings by redesigning adjacent structural elements to provide an alternative load path in case of partial collapse. This may lead to tangible changes in the mass and stiffness of the building, which means a change in the seismic behavior of the building. This shows the fact that choosing and designing an alternative load path is not an easy task. Studying the improvement in the seismic behavior of the building, whether direct or indirect, as a result of using the ALP, is the main objective of this paper. To achieve this goal, this study examined approximately 96 models, including the study of the possibility of progressive collapse occurring, whether there is or isn't an alternative path for the loads using non-linear static and dynamic analysis, as well as evaluating the study models using various seismic evaluation methods, where both the nonlinear static pushover analysis method and the FEMA-P58 method were used and compared. The study models are divided into two sections, with and without (ALP). The study models are also categorized by building height using heights of 6, 9, 12 and 15 floors. The models were also divided based on the locations of weak points in the original design that may be susceptible to damage and lead to progressive collapse, whether they are internal, side, or corner weak columns. The findings from the examined models indicate that the efficiency of (ALP) systems is more prominent in low and mid-height buildings compared to tall buildings. Additionally, the results demonstrate that the FEMA-P58 method yields similar predictions regarding building behavior as traditional seismic assessment methods like pushover analysis, but in a simplified manner that benefits non-engineers by providing clear insights into the financial and temporal aspects of different structural system solutions.

An Innovative Approach of Parameter Loading Path Design for Grain Refinement and Its Application in Ni80A Superalloy.

In order to obtain the desired mechanical properties of products, an innovative method of loading parameter designs for acquiring the desired grain refinement is proposed, and it has been applied in the compression process of Ni80A superalloy. The deformation mechanism maps derived from processing maps based on the Dynamic Materials Model (DMM) theory were constructed, since the critical indicator values corresponding to dynamic recrystallization (DRX) and dynamic recovery (DRV) mechanisms were determined. The processing-parameter domains with DRX mechanisms were separated from the deformation mechanism map, while such domains were chaotic and difficult to apply in innovative parameter loading path design. The speed-loading path derived from strain rate-loading path in a compression process was pursued. The grain refinement domains are discretized into a finite series of sub-domains with clear processing parameters, and the optimal strain rate of each sub-domain is determined by step-by-step finite element simulation. A 3D response surface of the innovative optimal loading path of strain rate was fitted by interpolating methods. Finally, the isothermal compression experiments for Ni80A superalloy were conducted, and the microstructure observations indicated that the desired grain refinement was achieved. This innovative method of parameter loading path design contributes to the microstructure adjustment of the alloys with DRX mechanism.

An empirical study on stress-based fail-safe topology optimization and multiple load path design

Explicitly considering fail-safety within design optimization is computationally very expensive, since every possible failure has to be considered. This requires solving one finite element model per failure and iteration. In topology optimization, one cannot identify potentially failing structural members at the beginning of the optimization. Hence, a generic failure shape is applied to every possible location inside the design domain. In the current paper, the maximum stress is considered as optimization objective to be minimized, since failure is typically driven by the occurring stresses and thus of more practical relevance than the compliance. Due to the local nature of stresses, it is presumed that the optimization is more sensitive to the choice of the failure shape than compliance-based optimization. Therefore, various failure shapes, sizes and different numbers of failure cases are investigated and compared on the basis of a general load-path-based evaluation scheme. Instead of explicitly considering fail-safety, redundant structures are obtained at much less computational cost by controlling the maximum length scale. A common and easy to implement maximum length scale approach is employed and fail-safe properties are determined and compared against the explicit fail-safe approach.

Investigation of Punch Shape and Loading Path Design in Hydro-Flanging Processes of Aluminum Alloy Tubes

Hydro-joining is composed of hydro-piercing, hole flanging and nut-inlaying processes. In this study, a new hydro-flanging process combining hydro-piercing and hydro-flanging is proposed. An internal pressured fluid is used as the supporting medium instead of a rigid die. Three kinds of punch head shapes are designed to explore the thickness distribution of the flanged tube and the fluid leakage effects between the punch head and the flanged tube in the hydro-flanging process. A finite element code DEFORM 3D is used to simulate the tube material deformation behavior and to investigate the formability of the hydro-flanging processes of aluminum alloy tubes. The effects of various forming parameters, such as punch shapes, internal pressure, die hole diameter, etc., on the hydro-flanged tube thickness distributions are discussed. Hydro-flanging experiments are also carried out. The die hole radius is designed to make the maximum internal forming pressure needed smaller than 70 MPa, so that a general hydraulic power unit can be used to implement the proposed hole flanging experiments. The flanged thickness distributions are compared with simulation results to verify the validity of the proposed models and the designed punch head shapes.

Movable Die and Loading Path Design in Tube Hydroforming of Irregular Bellows

Manufacturing of irregular bellows with small corner radii and sharp angles is a challenge in tube hydroforming processes. Design of movable dies with an appropriate loading path is an alternative solution to obtain products with required geometrical and dimensional specifications. In this paper, a tube hydroforming process using a novel movable die design is developed to decrease the internal pressure and the maximal thinning ratio in the formed product. Two kinds of feeding types are proposed to make the maximal thinning ratio in the formed bellows as small as possible. A finite element simulation software “DEFORM 3D” is used to analyze the plastic deformation of the tube within the die cavity using the proposed movable die design. Forming windows for sound products using different feeding types are also investigated. Finally, tube hydroforming experiments of irregular bellows are conducted and experimental thickness distributions of the products are compared with the simulation results to validate the analytical modeling with the proposed movable die concept.

Loading path design of thin-walled aluminum alloy T-shaped tube hydroforming process based on the control of limit pressure

Due to the influence of pressure control precision, the actual pressure in hydroforming process for the tube is usually greater than the design pressure, which causes the fracture of tube. The loading path of T-shaped tube hydroforming process was designed based on the control of limit pressure. First, the limit pressure of tube Pmax was obtained by improving the internal pressure until the tube cracked in the T-shaped tube hydroforming process without the feeding and a theoretical model for predicting instantaneous pressure is developed. Second, the tube bulge height Hmax and the maximum feeding Dmax were explored through manual operation of feeding and pressure in hydroforming machine, in which the overflow pressure is set to Pmax by using an overflow valve; finally, the loading path of internal pressure and feeding was designed using the ladder growth and linear growth in T-shaped tube hydroforming experiment in which the maximum pressure, the maximum feeding, and the overflow pressure (equal to internal pressure) were set to Pmax, Dmax, and Pmax, respectively. The results show that the obtained limit pressure Pmax can avoid the overpressure of the tube and restrain the fracture of the tube through the action of the overflow valve. Meanwhile, the accuracy of the prediction model to figure up Pmax was verified through experiments: the theoretical prediction value of the established model was consistent with the experimental true value. Compared with the T-shaped tube formed by linear loading path, the wall thickness of the formed T-shaped tube by ladder loading path is more evenly distributed without wrinkles and fractures and the height of the formed branch tube close to Hmax. At the same time, it is found that under the differential lubrication tube blank, the time of obtaining a suitable loading path is significantly reduced, and the collocation of ladder mode is simpler and more efficient.

Numerical and experimental studies on thin-walled aluminum alloy tube hydroforming using differential lubrication method

In this paper, it was analyzed that the friction forces that affected the material flow were influenced by the friction coefficient and the load path of internal pressure and feeding in T-shaped tube hydroforming process. Therefore, a novel differential lubrication method was proposed to adjust the material flow through changing the friction coefficient in the asymmetric zone in the T-shaped tube besides the loading path design method. The differential lubrication zones in T-shaped tube were divided, and a method called intermediate semiring differential lubrication was designed. The effects of differential lubrication and traditional uniform lubrication methods on the wrinkle, height of branch tube and wall thickness distribution of the T-tube were investigated under the same loading path of internal pressure and axial feeding. Meanwhile, the differential lubrication methods were also simulated under the different loading paths of the internal pressure and axial feeding. The differential lubrication experiments of T-shaped tubes hydroforming were carried out with fluorosilicone grease and PEFT film as lubrication medium. The simulation and experimental results showed that the differential lubrication method more effectively avoided wrinkles in the back zone of the main tube, increased the height of branch tube and weakened the thickening than the traditional uniform lubrication method. And it was a promising way to improve the formability of T-shaped tube hydroforming and reduced the over-reliance on the loading path.

Separation of dynamic recrystallization parameter domains from a chaotic system for Ti–6Al–4V alloy and its application in parameter loading path design

In order to acquire uniform and refined microstructures for Ti–6Al–4V alloy, the parameter loading path design plays a crucial role. Here, it is pursued to separate dynamic recrystallization parameter domains from a chaotic parameter system. A succession of isothermal compression tests in a temperature range of 1023–1323 K and strain rate range of 0.01–10 s−1 were performed to obtain the basic computation data. The processing maps were constructed, and the mapping relationships between microstructural mechanisms and power dissipation efficiency indicator (η) in such maps were identified by verification of microstructural observations. Then the inner relationships between processing parameters and microstructural mechanisms were mapped as a three-dimensional (3D) space, from which the grain refinement parameter domains with dynamic recrystallization mechanism were separated. But these domains were still chaotic, so finite element (FE) simulations were used to scatter and clear this system. The optimal parameter loading paths were determined. Five verification experiments with different varying strain rates were performed, and the grain refinement was more obvious than any constant strain rates. One of the optimization results shows that the original grains with average size of 200 μm are refined as 9.7 μm, while at a constant strain rate the original grains are refined as 22.3 μm.

Process and loading path design for hydraulic compound forming of rectangular tubes

Tubes with various cross-sectional shapes are widely used in automotive and bicycle manufacture for lightweight considerations. This study proposes a compound forming process for hydroforming a rectangular cross-sectional tube of aluminum alloys AA6061-O. The compound forming process is divided into crushing, hydroforming, and calibration. The finite element simulation software DEFORM was used to analyze the plastic deformation pattern of the tube during the compound forming processes and determine feasible loading paths that can generate a uniform thickness distribution, a lower internal pressure, and a smaller clamping force. The effects of varied internal pressures on the product shapes, thickness distributions, and forming loads are discussed. A self-designed hydroforming test machine with an internal pressure capacity of 30 MPa and axial feeding force of 40 tons was used to conduct hydroforming experiments. The experimental results of the product thickness distributions and dimensions were compared with simulation results, and the validity of the FE modeling is confirmed. Sound products with the required shape and dimensions can be obtained using the proposed hydraulic compound forming process with a low internal pressure of 8 MPa.

Feasibility Study of Complex Sheet Hydroforming Process: Experimental and Modelling

The application of finite element method (FEM) in the area of metal forming and material processing has significantly increased in the recent years. The presented study provides details of the development of a finite element modelling approach to form a part via sheet hydroforming (SHF) process. Both FEM analysis and experimental trials were introduced in this study to produce a complex shape component from Inconel 718 material. The FEM provides a robust feasibility study for forming this part in terms of blank design, load path and process design optimisation. The simulated hydroformed part was validated by performing experimental trials. The analysis demonstrated close correlation between the predicted FE model and the physical trial.

An adaptive loading path design method for tube hydroforming using fuzzy logic theory

The loading path is one of the most important design parameters for the success of a tube hydroforming process. Wrinkles, necking, and cracking may occur if the internal pressure and feeding are not correct. In this paper, we propose an adaptive loading path design method using fuzzy logic theory. The fuzzy logic controller is based on the properties of the tube hydroforming process, for asymmetric parts in particular. We investigated symmetric and asymmetric test cases to verify the proposed technique using the finite element method, and the results were consistent with our practical experiment.

Optimized design of tube hydroforming loading path using multi-objective differential evolution

Loading path design is one of the main factors that influence the quality of tube hydroforming processes. The conflicts between different quality indicators can be solved using multi-objective optimization evolutionary algorithms. In this paper, we propose a multi-objective optimization using differential evolution to obtain the optimum cooperation between the internal pressure and end feeding process. In the optimization process, several finite element simulations are performed to set up a least-squares support vector machine-based response surface model, which significantly improves the accuracy. We used a pre-bent hydroforming case study to demonstrate that this method is effective, accurate, and reliable.

Multi-Objective Optimization of Material Layout for Body-In-White using Design of Experiments

Vehicle mass reduction is a major area of research in the automobile industry. Various techniques like reduced part break up, section reduction, material alternatives and load path design are widely being researched across the world. This paper presents a new technique of identifying materials for the components of minimal part break-up Body-In-White (BIW) in the conceptual phase using design of experiments and multi-objective optimization. Prime focus was on the methodology to effectively consider the materials for the parts without compromising the structural performance of the target components. BIW structural load cases like bending and torsion stiffness were considered to evaluate the structural performance. Material list is used as the design variable and then sampled using design of experiments to undertake multi-objective optimization. As a result, optimal material distribution and mass savings have been achieved for the BIW parts. The optimized design performance is closer to the baseline design. The proposed methodology may be widely adopted by engineers to optimally distribute the materials for the BIW components at various stages of the vehicle design.

A Kriging-based non-probability interval optimization of loading path in T-shape tube hydroforming

In this study, the interval optimization method, in which the bounds of uncertain parameters are only required and knowing their probability distributions are not needed, is introduced to deal with limited information in T-shape tube hydroforming. The contact area between the counter punch and the tube is taken as the objective function and the protrusion height and maximum thinning ratio as constraints. To control the possibility degree of failure associated to each constraint, the reliability-based possibility degree of interval method is adopted to evaluate the reliability of T-shape tube hydroforming process. Before optimizing the process, the finite element model is validated against experimental results, and Taguchi method is employed to screen key factors from a number of potential factors. In addition, to improve computation efficiency, the Kriging model is adopted to construct the surrogate model, and the performance of the resulting surrogate model is validated using cross-validated method. Finally, the Kriging based on interval optimization method is applied for loading path design in T-shape tube hydroforming, and the results show that the robustness and reliability of the process can be guaranteed.

Multi-objective optimization of loading path design in multi-stage tube forming using MOGA

Pre-bending is a critical process required prior to hydroforming. The bending has an effect on the tube thickness and strain which will use up a portion of the formability of the as-received tube. To compensate for this loss of formability, a multi-objective optimization method was applied to improve the hydroforming process after pre-bending. A multi-objective genetic algorithm (MOGA) and Kriging surrogate model were used to optimize the loading path. The Kriging model was used to replace the finite element simulation in constraint handling. The optimal loading parameters in the hydroforming process were obtained for a tube that was previously bent 90°, and showed an improvement in reducing the corner radii of the part at the extrados and intrados of the bend (8.73 mm and 11.24 mm for the extrados and intrados of the bend, respectively). The corresponding corner fill expansion (CFE) was improved by 16.7% (or 1.79 mm) compared to the maximum expansion of 10.73 mm obtained experimentally.

A hybrid-constrained MOGA and local search method to optimize the load path for tube hydroforming

The production of a tubular hydroformed part often requires a combination of internal pressure and axial force at the tube ends to fully form the tube to its specified geometry. A successful hydroforming process requires not only achieving a part that conforms to the design specifications, but also ensures that the part has a reasonably uniform thickness distribution and is free of defects, such as wrinkles, severe thinning, or fractures. The load path design (pressure vs. end feed history) largely determines the robustness of the process and the quality of the finished parts. In this paper, a hybrid constrained optimization method was proposed to solve this type of multi-objective problem by coupling a multi-objective genetic algorithm and a local search. The load path design procedure was developed by considering five objectives: four formability objectives (i.e., to minimize the risk of wrinkling, global and local thinning, and fracture) and a geometric objective (to minimize the corner radius). A Kriging predictor was used to accelerate the computation of genetic operations and generate new feasible solutions. Finite element simulations of the hydroforming process were also used after each generation to accurately evaluate the objectives of the offspring, and solutions with rank 1 were retained throughout all generations. Once the Pareto solutions were obtained by multi-objective genetic algorithm, a local search was carried out in the regions of interest with the assistance of visualization. This optimization method was applied to the hydroforming of a straight tube to create a part with an expanded region with a square cross section; the optimum load path produced a very safe part with a corner radius of only 9.115 mm and a maximum thinning of only 23.9%.

Integration analysis of trimmable horizontal stabilizer actuators and technology evaluation

Commercial aircraft use a trimmable horizontal stabilizer to control the equilibrium of moments around the pitch axis independent of the elevator. The movement of the horizontal stabilizer is controlled by the trimmable horizontal stabilizer actuator (THSA). The limited testability of today’s systems is a huge disadvantage. To improve such systems, a variety of approaches are investigated, whose integration into the fuselage needs to be analysed. Considering the load transmission as well as their kinematics, this article deals with the integration analysis of novel THSA concepts with respect to the arrangement of load paths in the fuselage. Independent of the load path design (e.g. ball screw or hydraulic cylinder), THSA systems with two primary load paths are differentiated from those with one primary and one secondary load path. To evaluate innovative architectures, criteria are presented, which are the basis of multiobjective decision making. The procedure and the interpretation of results are shown in simplified examples of novel concepts.

Investigation of the effect of loading path and variation in material properties on robustness of the tube hydroforming process

In this paper, effect of loading path and variation in material properties on the robustness of the tube hydroforming process and final part requirements (i.e. thickness specifications) were studied experimentally and computationally. Small and simple tube hydroforming parts were used in the FE analysis to obtain some guidelines on the use of different loading path schemes. Developed guidelines, then, were applied experimentally on a production scale automotive structural frame part. Results emphasized the importance of the loading path design once more whereas variation of mechanical properties of incoming tubing within the experimented range was not found to be significantly effective on the final part specifications.