Large-scale Rib-web Component Research Articles

A non-sequential isothermal local-loading forming process for large-scale rib-web components

In order to solve the problem of deformation and warpage of large-scale rib-web components by the local-loading method, we propose a new non-sequential isothermal local-loading (NSILL) forming method. First, we design the forming die and then establish a finite element (FE) model of the new NSILL forming method. The reliability of the FE model is evaluated by comparing the load-time curve and warping effect. We introduce the bending angle and extension length of the billet to comprehensively evaluate its formability. Our research found that the larger top die length, the larger the bending angle and the smaller the metal extension length. In addition, we compare these two indexes of three typical loading sequences of NSILL forming, and find that sequential loading from left to right can improve bending angle, meanwhile loading successively from both sides to the middle can reduce metal extension. We therefore propose a multiple-region control non-sequential local-loading forming method. This novel method can achieve better deformation compatibility for forming LSRW components with bending angle changed from 155.11° to 179.81° and metal extension length decreased from 89.55 mm to 0 mm, and the maximum forming load was reduced with a reduction rate of 19.24%.

Robust optimization of the billet for isothermal local loading transitional region of a Ti-alloy rib-web component based on dual-response surface method

Billet optimization can greatly improve the forming quality of the transitional region in the isothermal local loading forming (ILLF) of large-scale Ti-alloy rib-web components. However, the final quality of the transitional region may be deteriorated by uncontrollable factors, such as the manufacturing tolerance of the preforming billet, fluctuation of the stroke length, and friction factor. Thus, a dual-response surface method (RSM)-based robust optimization of the billet was proposed to address the uncontrollable factors in transitional region of the ILLF. Given that the die underfilling and folding defect are two key factors that influence the forming quality of the transitional region, minimizing the mean and standard deviation of the die underfilling rate and avoiding folding defect were defined as the objective function and constraint condition in robust optimization. Then, the cross array design was constructed, a dual-RSM model was established for the mean and standard deviation of the die underfilling rate by considering the size parameters of the billet and uncontrollable factors. Subsequently, an optimum solution was derived to achieve the robust optimization of the billet. A case study on robust optimization was conducted. Good results were attained for improving the die filling and avoiding folding defect, suggesting that the robust optimization of the billet in the transitional region of the ILLF was efficient and reliable.

Improving the deformation homogeneity of the transitional region in local loading forming of Ti-alloy rib-web component by optimizing unequal-thickness billet

Isothermal local loading forming (ILLF) provides a new way to form large-scale Ti-alloy rib-web components (LTRC). However, the material undergoes complex inhomogeneous deformation in transitional region, which influences the forming quality of the component. The purpose of this paper is to improve the deformation homogeneity of the transitional region in ILLF by optimizing unequal thickness billet (UTB), which can adjust the initial volume distribution and control material flow with low cost and high efficiency. Based on the finite element (FE) simulation, the strain distribution of the transitional region in ILLF was investigated. It is found that the strain concentration at the root of formed rib in the first-loading region is more intense than that in the whole loading forming. Besides, the most strain concentration occurs at the root of partitioning rib on the side of first-loading region, which was not observed in the whole loading forming. The material transferred into the first-loading region during the second-loading step, and subsequent rib shift is the fundamental reasons for the strain concentration. The initial volume distribution of UTB has a significant effect on the strain concentration. In order to optimize the UTB, the average strain of strain concentration zone was correlated with geometric parameters of UTB by using response surface method (RSM). Based on the RSM model, the optimized UTB was achieved. The FE simulation of optimized UTB shows that the transferred material, rib shift, average strain, and maximum effective strain were all effectively decreased compared with equal thickness billet outcomes. The present RSM-based optimization method of UTB is proven to be a promising strategy to improve the deformation homogeneity of the transitional region in ILLF.

Formation mechanism, prediction and control of the forming defects in transitional region during local loading forming of Ti-alloy rib-web component

Abstract Predicting and controlling the forming defects in transitional region are two key problems needed to be solved in the isothermal local loading forming of Ti-alloy rib-web component. To this end, the authors have conducted systematic works, which are reviewed here. First, according to the structural features of large-scale rib-web component, the finite element (FE) model of transitional region was established and validated by physical experiment. Then, the material flow and deformation inhomogeneity of transitional region are quantitatively studied by the FE model. In addition, the formation mechanisms of forming defects were revealed. Subsequently, an adaptive folding index was proposed to measure the severity of folding defect, based on which a quick prediction model of the folding defect was developed. Finally, the forming limit considering the forming defects in transitional region was determined by the stepwise searching method combined with the defect prediction model.

Improving the process forming limit considering forming defects in the transitional region in local loading forming of Ti-alloy rib-web components

The isothermal local loading forming technology provides a feasible way to form Ti-alloy large-scale rib-web components in aerospace and aviation fields. However, the local loading process forming limit is restricted by forming defects in the transitional region. In this work, the feasibility of controlling forming defects and improving the process forming limit by adjusting die parameters is explored through finite element (FE) simulation. It is found that the common cavum and folding defects in the transitional region are significantly influenced by the fillet radii of left rib and middle rib, respectively. The cavum and folding defects can be effectively controlled by increasing the fillet radii of left rib and middle rib, respectively. The process forming limits considering forming defects in the transitional region are determined by the stepwise searching method under various die parameters. Moreover, the relationship between the process forming limit and die parameters is developed through the response surface methodology (RSM). The developed RSM models suggest that increasing the fillet radii of left and middle ribs is effective to improve the process forming limit during local loading forming of rib-web components. The results will provide technical basis for the design of die parameters and the reduction amount, which is of great importance to control forming defects and improve the process forming limit in local loading forming of Ti-alloy large-scale rib-web components.

Forming limit of local loading forming of Ti-alloy large-scale rib-web components considering defects in the transitional region

The forming quality in the transitional region largely determines the formability of local loading forming of the large-scale rib-web component. Thus, it is very critical to determine the forming limit considering defects in the transitional region during local loading forming. In this paper, the stepwise searching method based on Kriging metamodels of defect indexes is adopted to determine the above forming limit. First, the finite element (FE) simulation of the transitional region during local loading forming and the evaluation indexes for folding and cavum defects are introduced. Then, the Kriging metamodels of defect indexes are developed based on quantities of FE simulation results under various geometry parameters. During Kriging metamodeling, in order to guarantee the accuracy of the metamodel in the global design space and interesting region simultaneously, the space-filling maximin Latin hypercube designs (maximin LHDs) and sequential sampling approach are employed to design sample points. After metamodeling, extra random samples designed within the whole space are simulated to validate the developed Kriging metamodels. At last, the method of determining the forming limit considering defects in the transitional region is presented and applied to two specific transitional region models. It is realized through stepwise searching based on Kriging metamodels of defect indexes. The application results show that the proposed method is an effective and reliable method to determine the forming limit considering defects in the transitional region. It would provide an important guideline in the processing design of local loading forming of titanium alloy large-scale rib-web components.

Fast analysis on metal flow in isothermal local loading process for multi-rib component using slab method

Based on the local loading characteristics and the slab method (SM) models describing the meal flow of T-shaped component under local loading condition, an algorithm for fast analyzing metal flow and cavity fill in local loading process of titanium alloy multi-rib component has been proposed. The key technologies of fast analysis based on SM were explored, such as the description of geometric parameters, definition of calculating area, treatment of dynamic boundary condition, and so on. Based on the above key technologies, an analysis system for local loading process of multi-rib component was developed, and its reliability was verified by finite element simulation. Comparing with the finite element simulation, the computational time by the developed system has been greatly reduced. The reasonable parameter range and initial shape of billet for isothermal local loading process of large-scale rib-web component can be quickly determined by using the developed system, and then the times of three-dimensional finite element simulation can be reduced in the process optimization.

Quick prediction of the folding defect in transitional region during isothermal local loading forming of titanium alloy large-scale rib-web component based on folding index

Forming quality of transitional region determines the performance of titanium alloy large-scale rib-web component under isothermal local loading forming. As folding defect is the most sensitive defect in transitional region, its prediction is very critical to the precision shape forming in isothermal local loading forming. In this paper, a quick prediction model for the folding defect in transitional region was established to replace the traditional defect prediction method by time-consuming FE simulation. First of all, the FE model of local eigen model of transitional region during local loading forming of large-scale rib-web component was established and validated by physical experiment. Then, an adaptive folding index was proposed to measure the possibility and severity of folding defect based on the mechanism that there exists a local increase of strain rate when a folding tends to appear. Availability of the adaptive folding index was checked by large numbers of uniform experiments designed by the space-filling Maximin Latin hypercube designs (maximin LHDs). Furthermore, a judging criterion for folding defect based on the folding index was developed and validated by random samples. Subsequently, the folding index was correlated with the geometrical characteristic parameters of transitional region model by RSM model, through which the folding index can be predicted quickly without the time-consuming FE simulation. Finally, a quick prediction model was established for folding defect judgment under various geometrical parameters by combination of the RSM model for folding index and proposed judging criterion. Prediction results are quite consistent with the results of FE simulation and experiment. The folding prediction model can greatly facilitate the design space exploration and engineering design thereby providing guideline to the precision shape forming. Besides, the adaptive folding index and corresponding judging criteria for folding defect put forward in this work have reference significance to the study on folding defect in other forging processes.

Forming defects control in transitional region during isothermal local loading of Ti-alloy rib-web component

The forming quality of transitional region plays a key role in the performance of titanium alloy large-scale rib-web component under isothermal local loading forming. In this work, a local eigen model of transitional region in the local loading forming of large-scale rib-web component is extracted so as to catch the detail-forming characteristics of transitional region with low computation time in simulation and experiment cost. Then, based on the local eigen model, the mechanism of forming defects in transitional region and their dependence on processing parameters are studied by the combination of physical experiment and verified finite element (FE) simulation. It is found that the second loading step can be divided into two forming stages according to the material flow pattern: (1) the transverse flow stage and (2) the stable forming stage. In the transverse flow stage, there exists long-range transverse flow of web material and excessive transverse flow would lead to the formation of folding and cavum defects. Moreover, the severities of defects are well correlated with the quantity of material transferred into the first-loading region in this stage. For a certain reduction amount, decreasing spacer block thickness and increasing friction both can decrease the quantity of transferred material and then suppress the development of folding and cavum defects, while the deformation temperature and loading speed have little effect on the quantity of transferred material and defects. In the end, an effective way is put forward to suppress and prevent the defects in transitional region during the local loading forming of titanium alloy large-scale rib-web component.

Quantitative analysis of the material flow in transitional region during isothermal local loading forming of Ti-alloy rib-web component

The material flow in transitional region plays an important role in the forming quality of transitional region in the isothermal local loading forming of titanium alloy large-scale rib-web component. To study the material flow in transitional region, the finite element (FE) model of transitional region was established based on DEFORM-2D software and validated by physical experiment. Then, a quick and easy method, which can measure the area of different local regions of forged part in DEFORM-2D via user subroutine, was proposed to achieve the quantitative analysis of material flow mechanism. This technique can also be used in the analysis of other forming process, such as the calculation of fill ratio in forging process. The material flow pattern of transitional region during local loading forming was analyzed step by step and compared with integral forming. The results show that the material flow of transitional region during local loading process can be divided into six stages according to the material flow pattern and load-time curve. Twice transverse material flow with opposite directions occurred in the first and second loading steps sequentially, which does not exist in the integral forming. Four characteristic values evaluating the transverse flow of material, which are associated with the formation of defects and their severities, are defined and quantitatively measured at various processing conditions. It is found that decreasing the spacer block thickness and increasing friction both can decrease the four characteristic values, thus weaken the transverse material flow, which are helpful to improve the forming quality in transitional region. However, the transverse flow of material is little affected by the loading speed.

Prediction of Folding Defect in Transitional Region during Local Loading Forming of Titanium Alloy Large-scale Rib-web Component

A prediction model for the folding defect in transitional region during local loading forming of titanium alloy large-scale rib-web component was developed by the combination of finite element simulation, space-filling Maximin Latin hypercube designs method and back-propagation neural network. The FE model of local eigen model of transitional region during local loading forming of large-scale rib-web component was established based on DEFORM-2D and validated by physical experiment. The Maximin Latin hypercube designs method was applied to design uniform experimental schemes with geometrical conditions and reduction amounts as experimental variables. After simulations of the designed experiments, the back-propagation neural network was used to synthesize the data sets (results of folding defect). Finally, a prediction model was established for folding defect judgment in transitional region under various geometrical conditions and reduction amounts during local loading forming of large-scale rib-web components. The predicted results are quite consistent with the results obtained from FE simulation and experiment.

Metal flow characteristics of local loading forming process for rib-web component with unequal-thickness billet

To explore the metal flow and filling law of large-scale rib-web component local loading forming process is important for fast design of unequal-thickness billet (UTB), parameter optimization and process control of the rib-web component local loading forming process. T-shaped component forming under UTB can reflect the forming characteristics in the large-scale rib-web component forming process. In the forming process by using UTB, the width of local loading changes dynamically, the thickness difference of billet changes notably, and the boundary conditions are very complex. By introducing new assumptions, variables and boundary conditions, a mathematical model for local loading pattern caused by UTB is established by using slab method (SM). Based on the virtualizing experimental data observed by finite element method (FEM), a predicted model for the dynamic width of local loading is established by using polynomial regression and partial least squares (PLS) regression. Comparing with FEM results indicates that the relative differences are less than about 10 % for predicted model of local loading width. Comparing with FEM and physical modeling experimental results indicates that the relative differences are less than about 15 % for SM model. The metal flow, cavity fill, and increased width of local loading under local loading condition are studied by using the mathematical models and numerical simulation, and the results indicate that: the metal flow and deformation pattern under local loading are determined by the thickness of billet and the width of local loading; the increased width of local loading is determined by initial geometric parameters, and the forming parameters such as materials (Ti-6Al-4 V and Ti-6Al-2Zr-1Mo-1 V), loading speed (0.1–1.0 mm/s), temperature (950–970 °C), etc. have little influence on it; the value of xk (position of neutral layer) under local loading pattern caused by geometric parameters of billet is less than that caused by geometric parameters of die at initial forming stage.

Effects of Parameters on Inhomogeneous Deformation and Damage in Isothermal Local Loading Forming of Ti-Alloy Component

Isothermal local loading (ILL) forming technology provides a new way to form largescale rib-web (LSRW) components of Ti-alloy, widely used in the aero-space fields as key load-bearing structures. However, the metal undergoes complex plastic inhomogeneous deformation and microstructural evolution, this will lead to macroscopical forming defects and further damage due to multi-process parameters and local loading method, making the process and forming quality hard to control. Using numerical simulation, combined with experiment, influences of various process parameters on forming process, inhomogeneous deformation and damage have been explored for ILL of LSRW components, such as the types of die-forging mode, frictional conditions, and local loading parameters (partitioning of the loading zone, constraint conditions, and loading pass). Then the reasonable forming conditions for LSRW components of Ti-alloy to be studied are proposed. The practical forming experiment of TA15 LSRW component was achieved successfully and the forging with good forming quality, excellent microstructure, and comprehensive mechanical properties was obtained, which indicates the reliability and practical value of results obtained in this article.

Effect of deformation inhomogeneity on the microstructure and mechanical properties of large-scale rib–web component of titanium alloy under local loading forming

In the present paper, the effect of deformation inhomogeneity on the microstructure and mechanical properties of large-scale rib–web component of TA15 titanium alloy under near-β local loading forming was investigated. It is found that four different microstructures can be produced under near-β local loading forming with the variation of deformation degree and thermal processing path: (primary α phases + clustered lamellar α phases + transformed β matrix) produced by small deformation; (primary α phases + disordered lamellar α phases + aggregated transformed β matrix) produced by large deformation in the first-loading step; (primary α phases + partly globularized second α phases + transformed β matrix) produced by moderate deformation in the second-loading step; (primary α phases + fully globularized second α phases + aggregated transformed β matrix) produced by large deformation in the second-loading step. With the increase of strain, the volume fraction of primary α phases increases, while the grain size increases first and then decreases. The comprehensive mechanical properties under local loading are close to that under integral loading.

Analysis of local loading forming for titanium-alloy T-shaped components using slab method

A large-scale rib-web component may be considered as a combination of many T-shaped components which can reflect forming characteristics of large-scale rib-web components by local loading. So exploring the material flow and filling law of the T-shaped components local loading forming is important for parameter optimization and process control of local loading forming processes of rib-web components. With the help of reasonable assumptions and simplifications, the slab method (SM) is used to analyze the isothermal forming process of titanium-alloy T-shaped components under local loading in this paper. The process of local loading forming and the characteristics of material deformation are analyzed, and two deformation patterns under local loading are found by using the physical experiment. Mathematical models of loading force, rib height (depth of cavity filling) and the position of neutral layer in loading process are established by using the slab method. Calculation-program for models is developed under MATLAB environment, and then the loading force, rib height and position of neutral layer are predicted. The comparison of the SM results with the experimental and FEM results indicates that the models established based on the slab method are reliable. The reasonable parameters determined by using the mathematical models, such as the width of punch, the thickness of billet, the reduction amount etc., may provide a basis for analysis of local loading forming for large-scale rib-web components.