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Chatter has always been a detrimental problem restricting the improvement of surface quality and processing efficiency in machining processes. Chatter detection is an essential approach to prevent these harmful effects, which aims to identify chatter occurrence at the early stage. Energy entropic methods explain chatter from randomness perspective of energy distribution and are often applied to detect chatter in machining processes. However, the energy of the milling system at the chatter frequency increase slowly at the onset of chatter, which lead to that energy entropy is sometimes challenging to identify weak chatter. In this paper, a new method based on combination of wavelet packet energy entropy and energy ratio is proposed to monitor chatter. By detecting the energy ratio of chatter frequency band, it is feasible to set a threshold to represent the different milling states and can accurately detect weak chatter. The proposed approach is assessed by using preliminary numerical simulation and several milling experiments, and the results demonstrate that the proposed method can effectively detect chatter. [ABSTRACT FROM AUTHOR]

Geometric error measurement is crucial for error compensation and machining accuracy of CNC machine tools. However, traditional double-ball bar (DBB) method cannot be used for full-scale measurement of geometric errors due to the constant length of bars. In this paper, a full-scale measurement of geometric errors for CNC machine tools with high efficiency is carried out based on the double ball bar with a ball joint (J-DBB) method. Firstly, the principle of J-DBB is introduced. The J-DBB can be used for a full-scale measurement thanks to its freely measuring radius. Then, the equations of geometric errors which include squareness error, straightness error, roll error, pitch error, and yaw error of the axes are theoretically analyzed. In the end, we compared the theoretical trajectories of circular interpolation with the actual ones. The geometric errors between theoretical trajectories and actual ones can be measured and shown by J-DBB method. The results revealed that the J-DBB can be applied to conduct the full-scale measurement of geometric errors in CNC machine tools. Besides, the measurement range of geometric errors is extended from a two-dimensional circle to a three-dimensional sphere with a radius of 0.259L to 2L. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Cross-sectional deformation of the double-ridged rectangular tube inevitably occurs in the rotary draw bending process. It has serious effect on the characteristic of microwave transmission and restricts the quality and performance of tube. Different mandrels play different roles in the bending process, so the rigid and polyvinyl chloride (PVC) mandrels are applied in the E-typed and H-typed rotary draw bending of double-ridged rectangular tube to study their influence on the cross-sectional deformation. Based on the platform of ABAQUS/Explicit, the three-dimensional finite element models for E-typed and H-typed rotary draw bending of H96 brass double-ridged rectangular tube with rigid and PVC mandrels have been established and validated by experiment. Results show that whether in the E-typed or H-typed bending, the PVC mandrel has better inhibitory effect on the cross-sectional long-side deformation δ , short-side deformation δ , and spacing deformation between the bottom of ridge grooves δ of the tube. And the PVC mandrel can be more helpful to reduce the width deformation of ridge grooves of the tube in H-typed bending. The rigid mandrel can restrain the width expansion deformation of outer ridge groove of the tube more effectively in E-typed bending. However, whether using the rigid or PVC mandrel, the width shrinkage deformation of inner ridge groove of the tube in E-typed bending is less affected by the type of mandrels. And the width of two ridge grooves on sidewalls of the tube in H-typed bending also has the obvious shrinkage deformation. [ABSTRACT FROM AUTHOR]

The deformation inhomogeneity of transitional region plays a great role in both the macro and micro forming qualities in the local loading forming. In this work, the dependence of deformation inhomogeneity of transitional region on the die parameters in the local loading forming of Ti-alloy rib-web component was studied based on finite element (FE) simulation. To evaluate the deformation inhomogeneity, an area-weighted strain inhomogeneity index was employed, which is calculated through the user subroutine of FE software (DEFORM-2D). It is found that there exist two kinds of strain concentration areas contributing to the deformation inhomogeneity of transitional region. One kind is the almost symmetric strain concentration area at the non-partitioned ribs, which is essentially related to the filling of rib. Another kind is the slant strain concentration area at the partitioned rib, which is caused by the multi-step loading during local loading forming. Besides, the effects of die parameters on the deformation inhomogeneity of transitional region were studied by the combination of orthogonal experiment design and FE simulation. The results suggest that the draft angle of the right rib is the most significant factor for both the deformation inhomogeneities of the partitioned rib region and whole transitional region. And, these two deformation inhomogeneities both decrease with the draft angle of the right rib decreasing. Furthermore, the relationship between die parameters and deformation inhomogeneity of transitional region is developed using the response surface methodology (RSM). Based on the RSM model, the die parameters were optimized to improve the deformation homogeneity of transitional region. The results will provide basis for the design of die parameters to improving the deformation and microstructure homogeneities in the isothermal local loading forming of Ti-alloy rib-web component. [ABSTRACT FROM AUTHOR]

Cross-sectional deformation is one of the critical factors that affect the forming accuracy of double-ridged rectangular tube (DRRT) in E-typed rotary draw bending (RDB). In the forming process, springback is inevitable and it has a direct impact on the cross-sectional deformation. Based on ABAQUS platform, three-dimensional finite element (3D-FE) models for bending and springback of H96 brass DRRT in E-typed RDB were established. With the models, the impact of springback on the cross-sectional deformation was studied. Results show that after springback, the deformation of cross-sectional height and two ridge grooves spacing increase in cores-support zone while decrease in no-cores-support zone. The impact of springback on width deformation is not significant. The maximum values of cross-sectional height deformation and two ridge grooves spacing deformation from 0° to 30° become larger after springback, while the change rules of these two from 30° to 90° are reversed. What's more, the maximum value of width deformation from 0° to 60° becomes larger after springback while that of outer ridge groove width deformation becomes smaller, and these two from 60° to 90° both have the reversed change rules as well. [ABSTRACT FROM AUTHOR]

Rolling-spinning of titanium alloy tubes is an advanced plastic forming technology that has been developed due to the urgent need for light-weight, high-precision, and high-reliability components in high-tech fields, such as aviation and aerospace. However, due to the complexity of the rolling-spinning process and the sensitivity of titanium alloy to temperature and strain rate, it is easy to crack, which severely restricts the improvement of the forming quality and forming limit of components. In this study, the critical deformation of Ti-6Al-2Zr-1Mo-1V was obtained by a hot compression test under various temperatures and strain rates. The damage threshold was obtained through FE simulation for the hot compression process under these temperatures and strain rates. The relationship among damage threshold, temperature, and strain rate was established by introducing the Zener-Hollomon factor. A thermal damage model for Ti-6Al-2Zr-1Mo-1V was established by combining the Oyane ductile fracture criterion with the relationship among damage threshold, temperature, and strain rate. By coupling this thermal damage model into the FE model for rolling-spinning of a Ti-6Al-2Zr-1Mo-1V tube, the damage prediction for the process was realized. The results show that the stress triaxiality at the top and bottom ends of the rolling zone is positive, the accumulation of damage is fast, and the strain rate is large in the zone. Thus, these ends are the zones most prone to damage in rolling process. The stress triaxiality at the local inner surface area of the spinning region is positive, the accumulation of damage is fast, and the strain rate is large in the zone. Therefore, the inner surface of the spinning region is the zone most prone to damage. [ABSTRACT FROM AUTHOR]

In-depth understanding and quantification of the forming characteristics of the taper-rolling process are crucial for process design and parameters determination in order for producing a desired precise helical blade from a metal strip. To this end, a quantitative study is carried out on this process through finite element (FE) simulation and experiment. For the FE simulation, a 3D model is established by handling problems observed in experiments about strip bite, sideways movement, and interference with the rolls and then is calibrated in numerically dynamic effect and validated by experiment. The results show that the plastic hoop and thickness strain components exhibit linearly increasing distributions from the inner to outer rim of the blade, which is a result of the hyperbolic-curve distributed roll gap. Thus, small radial strain that coordinates the deformation in hoop and thickness directions varies from positive to negative across the blade width. As a result, less spread and smaller bending radius have been achieved on the blade than that on the in-plane bent ring under the same conditions. Screw diameter increases with increasing initial position of the strip ( H), initial roll gap ( S ) and rolls offset ( S ), and screw pitch increases with increasing S and S but is uncertain with increasing H, the rules of which are quantified. The reason is attributed to the change of roll gap and thus the change of strain distribution with varying H, S , and S . Then, three forming defects (turning-I, turning-II, and wrinkling) are defined and correspondingly the stable condition is determined as 0.9 <= a / b <= 1.6 and t / t ≥ 0.3. Thus, a formable window of H, S , and S for sound formation is determined, within which the forming limit defined as the achievable minimum relative bending radius R / b is quantified by simulation and validated by experiment. [ABSTRACT FROM AUTHOR]

The under-filling defect is prone to occur in the forging of large-scale titanium alloy rib-web components (LTRC). A rigorous preform design with accurate volume distribution is required for a desirable LTRC. The unequal thickness billet (UTB) design divides the preform into multiple regions of varying thickness and can not only adjust the volume distribution effectively but also control forming defects with low cost and high efficiency. The purpose of this paper is to attain LTRC without any under-filling defects using the UTB methodology. Firstly, cross sections are extracted from a desirable LTRC so as to create the initial UTB according to the calculated neutral layer of material flow between ribs. Then a finite element (FE) model is established, using the Deform-3D software for the isothermal closed-die forging to study the material flow and die cavity filling. Finally, three schemes to modify the initial UTB are proposed for those areas where there is under-filling: (I) increase the number of regions in affected areas, (II) adjust the size parameters of the regions around affected areas, and (III) increase the thickness of the regions in affected areas. In conclusion, it is found that scheme I and scheme II are based on the constancy of volume principle and can be adopted if the distribution of the ribs on those affected areas is quite simple. However, scheme I increases the complexity of the UTB, so scheme II is preferred. Alternatively, if the distribution of ribs on those regions is more complicated, scheme III can be adopted. Although the volume of the UTB is increased slightly, all ribs can be completely filled, allowing the most accurate LTRC to be produced. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Incremental in-plane bending (IIB) is a new and advanced flexible manufacturing technology for small-lot production of strip with various bending radii. The strip of sheet metal is bent incrementally by a beating inclined punch. The bending radius is strongly affected by mechanical properties of the material, geometry of the strip, and processing parameters. It is difficult to predict the bending radius due to the complex synergistic effects of the controlling parameters. How to predict the bending radius accurately has therefore become a key point to be urgently solved in the development of this advanced forming technology. In this paper, a model based on a back propagation neural network (BPNN) is introduced to reveal the relationship of bending radius with angle of die α, indentation s, pitch p, and width of strip w. Out of 14 different BPNN architectures trained, the 4-9-9-1 BPNN with two hidden layers having nine neurons trained with the Levenberg-Marquardt algorithm (trainlm) is found to be the optimum network model, and the prediction error is less than 2 % on average. Otherwise, a 1-9-9-4 reverse BPNN is developed to build the processing window for a given bending radius. Meanwhile, taking section moment of inertia I as a quantitative index of forming stability, α, p, s, w are optimized as design variables in order to make objective functions of I maximized simultaneously. Finally, to verify its predictive capability, the present approach is applied to a case study, and the optimal combination of parameters for stable forming during IIB is obtained. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The extruded large-scale thick-walled pipes made from Inconel 625 alloy are widely used in many fields such as in the oil and chemical industry, thermal power generation, nuclear power plant, aerospace, and defense industry. However, the nonuniform distribution of grain size along the thickness and length directions of the extruded pipe always appears, which has a great influence on the mechanical property and uniformity of the pipe. The inhomogeneous distribution of the exit temperature in the entire extrusion process is the decisive factor leading to the grain nonuniformity of the extruded pipe. Therefore, it is necessary but difficult to reveal the evolution of the exit temperature under some key extrusion parameters in order to effectively control the exit temperature uniformity. In this paper, a thermomechanical coupled finite element (TMC-FE) model, which can precisely predict the hot deformation behavior of the extrusion process for large-scale thick-walled Inconel 625 pipe, has been firstly developed based on the DEFORM-2D platform. And then, the influence of key extrusion parameters, namely extrusion speed ( V), initial billet temperature ( T), extrusion ratio ( λ), and friction ( μ), on the exit temperature was revealed by comprehensive simulations. In addition, using the standard deviation of exit temperature (SD) as the measure indicator of the exit temperature uniformity, we also disclosed the influence of the key process parameters on the exit temperature uniformity in detail. The results show that with the increase of V, T, and μ, the uniformity of exit temperature in the entire process firstly becomes better and then gets worse. The larger λ can result in a more uniform exit temperature. In consideration of the obtained results, within the feasible window of the key extrusion parameters defined in this paper, the conditions of T = 1,100-1,150 °C, V = 125-150 mm/s, μ = 0.015-0.02, and a larger extrusion ratio ( λ) are suggested for the extrusion of large-scale thick-walled Inconel 625 pipe in order to get more uniform exit temperature. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Based on the ABAQUS/Explicit, a three-dimensional elastic-plastic finite element model of the H96 brass double-ridged rectangular tube (DRRT) during H-typed rotary draw bending (RDB) was established and its reliability was validated by an experiment. With the model, distribution characteristic of cross-sectional deformation and effects of clearance and friction coefficient between tube and dies and core number on it were studied. The results show that the maximum cross-sectional height distortion ratio appears at the bending angle 60°. And the maximum cross-sectional width distortion ratio between side walls, as well as side walls of the ridge grooves, appears at the bending angle 80° and 60°, respectively. In addition, retracting mandrel has a great effect on the cross-sectional height distortion, but its influence on the cross-sectional width distortion can be ignored. And the maximum cross-sectional distortion ratio initially increases with increasing of clearance between tube and mandrel c and friction coefficient μ between tube and bending die, and then decreases with their increase, and initially decreases with the increase of core number N, and then increases with increasing of N. Moreover, the reasonable value of N is taken as 4. [ABSTRACT FROM AUTHOR]

The heat rotary draw bending of large-diameter thin-walled (LDTW) commercial pure titanium (CP-Ti) tube is a highly nonlinear thermo-mechanical coupled physical process. Developing a reliable finite element (FE) model for this process is an effective way to investigate the heat loading and the complex bending behaviors. In this study, considering the characteristics of multi-die constraints and local heating, a thermo-mechanical 3D-FE model was established for preheating and heat bending of LDTW CP-Ti tube in terms of both accuracy and efficiency. First, using the static implicit algorithm, a preheating model was developed to predict the temperature distribution of bending tools. In this model, the key issues such as the full-sized geometry modelling, thermal interaction definition, and automatic heating control were solved to increase the simulation accuracy and efficiency. Then, introducing the predictions of preheating model and using the dynamic explicit algorithm, a thermo-mechanical coupled 3D-FE model was established for the heat bending simulation via the geometry modelling simplification, temperature definition of bending tools, realization of non-uniform temperature distribution, etc. Considering the temperature history of bending tools and wall thickness changing of bent tube, the reliability of preheating model and heat bending model was verified by several experiments. The results showed that the maximum relative errors of both predicted temperature and wall thickness changing degree were less than 9 %. Based on the reliable models, the effects of preheating temperature on the temperature distribution of bending tools and wall thickness changing of tube were numerically evaluated. The established model provides the scientific basis for the prediction and control of bending qualities of the heat RDB process, and the modeling method is also of general significance to the other heat-aided forming process. [ABSTRACT FROM AUTHOR]

Radial-axial ring rolling process is an irreplaceable metal forming technology for manufacturing various seamless rings. However, during the process, there exists complex interaction of deformations in the radial and axial directions of the ring, so the coordinate deformation between radial and axial directions has crucial influences on the quality of the rolled ring. In this paper, a reliable FE model based on in-process control for the radial-axial ring rolling process has been established under the ABAQUS/Explicit platform. In this model, the motions of the rolls are real-time controlled based on in-process measurement. Then, taking the ratio of axial to radial feed amount as the key parameter, we explored the effects of the coordinate deformation between radial and axial directions on the radial-axial rolling of sleeve-type rings by FE simulations. It is found that the rational diameter growth rates become fewer for making the sleeve-type ring roundness stay well as the ratio of axial to radial feed amount decreases. The ratio of axial to radial feed amount has slight effects on the precision of the ring diameter when the diameter growth rate is large. With the ratio of axial to radial feed amount increasing, the deformation of the sleeve-type ring becomes more nonuniform, while the temperature distribution becomes more uniform. [ABSTRACT FROM AUTHOR]

Cross-sectional distortion is one of the main defects severely restricting the improvement of the forming limit in the rotary draw bending of double-ridged rectangular tube. So, how to rapidly and efficiently predict the forming limit (minimum bending radius R with allowed cross-sectional distortion) and improve it has become an urgent problem to be solved for the development of rotary draw bending of double-ridged rectangular tube. Based on ABAQUS/Explicit, finite element model of rotary draw bending for double-ridged rectangular H96 brass tube has been established and verified by experiment. Using the model combined with the virtual orthogonal experiment, the significance analysis of influence of processing parameters on cross-sectional distortion was carried out. And based on the technique of orthogonal regression analysis, a prediction model of the forming limit with allowed cross-sectional distortion was built. The results show that: (1) processing parameters significantly influencing cross-sectional distortion are tube-mandrel clearance Δ c, tube-bending die friction coefficient μ, bending radius R, and core number N. (2) Effect laws of significant parameters on R were obtained: R gradually decreases with increasing of μ; when the value of Δ c is smaller than 0.37 mm, R slightly decreases with increasing of Δ c; and when the value of Δ c is larger than 0.37 mm, R sharply increases with increasing of Δ c. (3) The 3D forming limit diagrams and the minimum bending radii in different processing conditions were obtained, which can provide a crucial guide for selecting of processing parameters in RDB of the double-ridged rectangular tube. [ABSTRACT FROM AUTHOR]

The rotary draw bending of double-ridged rectangular tube is a complex nonlinear physical process with multifactors coupling effects. Processing parameters, especially clearances and friction coefficients between tube and various dies, have a significant effect on the forming quality of the double-ridged rectangular tube in rotary draw bending. If the values of these processing parameters are inappropriate, some defects including cross-sectional deformation, wall thinning, and wall thickening easily occur in the bending process of double-ridged rectangular tube. So optimization of these processing parameters is of great importance to control these defects. Based on the grey relational analysis method combined with the orthogonal experimental design and finite element simulation, a grey relational analysis model was established for the rotary draw bending process of double-ridged rectangular H96 brass tube. With the model, optimization of clearances and friction coefficients between tube and various dies was implemented with consideration of interactive effects of the above defects. The results show that (1) the main factors influencing cross-sectional deformation, wall thickening, and wall thinning are tube-mandrel clearance Δ c, tube-bending die clearance Δ c, and tube-mandrel clearance Δ c, respectively. (2) The optimal values of clearances Δ c, Δ c, Δ c, and Δ c and friction coefficients μ, μ, μ, and μ of tube-mandrel, tube-pressure die, tube-wiper die, and tube-bending die are 0.15, 0.2, 0.2, 0.2, 0.02, 0.3, 0.06 and 0.17 mm, respectively. Furthermore, the verification for the optimal values of these processing parameters was carried out, and the double-ridged rectangular H96 bent tube obtained by using the optimal values of these processing parameters has the minimum values of cross-sectional deformation, wall thinning, and wall thickening and can satisfy the national aviation industry standards. [ABSTRACT FROM AUTHOR]

The weld profiles, weld width, weld positions, and mechanical property changes in the weld and heat-affected zones (HAZ) are the most important parameters that influence the potential formability of the welded tube. To investigate the effect of weld characteristics on the forming behaviors of the welded tube, finite element models which consider the geometric profile and mechanical properties of the weld and HAZ are employed. The results show that (1) the mechanical constitutive relation of the weld region determined by the microhardness empirical formula obviously decreases the tangent strain, thickness strain, and cross-sectional deformation ΔD in the weld and HAZ as compared with that determined by the improved rule of mixtures, which is contrary to the hoop strain, and the predicted results determined by the improved rule of mixtures are much closer to the experimental ones; (2) different weld and HAZ widths determined by the microhardness profile and metallographic section have a little effect on the tangent strain, thickness strain, and ΔD distribution; (3) the implementation of weld profile and material properties decreases the wall variation of the weld region as the weld line locates on the outside and inside. On the contrary, both the weld profile and weld material properties increase the maximum ΔD. The sectorial weld profile has a stronger effect on the wall variation and maximum ΔD than the hourglass profile; and (4) the same weld and HAZ volume have a stronger effect on wall thinning and Δ D. [ABSTRACT FROM AUTHOR]

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 x (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. [ABSTRACT FROM AUTHOR]

Friction plays an important role in bulk metal-forming process. Especially, it has an important influence on metal flow in the local loading process. In the present study, the influence of friction on the metal flow in local loading forming process of rib-web component was analyzed by using analytical method, numerical simulation, and experiment. Constant shear friction model was employed in the analytical analysis and numerical simulation. Two kinds of local loading experiment were carried out, which differ in the shape of billet. The results in the present study indicated that (a) in local loading state, increasing friction is beneficial to reduce or avoid the occurrence of shearing deformation behavior; (b) the metal flowing into rib cavity would increase if friction factor increases; (c) as the width of local loading increases or thickness difference of variable-thickness region decreases, the friction effect will reduce. [ABSTRACT FROM AUTHOR]

To predict and control wall thickness distribution of thin-walled rectangular 3A21 aluminum alloy tube, the experiments of rotary draw bending process under multi-dies constraints are conducted. It is found that the thickness changing rates in middle bent zone are large, and the maximum values are obtained nearby the tube ridges. The effects of core die, pressure die, mandrel die, and bend die on thickness changing rate are significant. And the thinning rate increases with increase of core number, bend velocity, clearance between tube–pressure die interface and mandrel extension, but it decreases with increase of bend radius and boost velocity of pressure die. The thickening rate increases with increase of core number, boost velocity of pressure die and clearance between tube–wiper die interface, but it decreases with increase of bend radius and bend velocity. [ABSTRACT FROM AUTHOR]

Determining appropriate process parameters is key to obtain qualified TA18 (Ti-3Al-2.5V, ASTM Gr. 9) titanium alloy tubes with medium strength by numerically controlled (NC) bending at low cost. This paper focuses on the variations in wall thickness and cross-section under various operating parameters and mandrel parameters for the NC bending of TA18 tubes. We put forward a method for quickly determining the range of the axial mandrel feed. The method is based on the principle of an equivalent mandrel supporting radius for a given bending radius but employing some mandrels with varying diameters and the principle of an equivalent mandrel supporting angle for various bending radii but employing the same diameter mandrel. The finite element analysis and the experimental verification results show that the bending speed should be less than 0.5 rad/s and the pressure die velocity should be approximately equal to or slightly higher than the bending speed, and that the method for determining the range of the axial mandrel feed is feasible. Considering the effects of an equivalent mandrel supporting radius and equivalent mandrel supporting angle, the mandrel diameter and axial feed should be chosen in a compatible range. [ABSTRACT FROM AUTHOR]

The significant cross-sectional distortion is one of the major problems in the bending of thin-walled rectangular waveguide tube. The cross-sectional distortion, which contains the flange distortion and the web distortion, depends on the stress components distribution. In this paper, the cross-sectional distortion characteristics are investigated using a three-dimensional finite element (FE) model. Results show that: the maximum flange distortion locates at the symmetric line; meanwhile, the maximum web distortion locates at the extrados ridge of the tube. The deformation zone of the tube can be divided into three sub-zones considering the loads and deformation, viz., the clamp die affect zone, the middle zone, and the mandrel/cores affect zone. Then the underlying relations between the cross-sectional distortion and the stress components are obtained. It is found that the flange distortion has a close relation with the circumferential stress. At the same time, the web distortion is relevant to both the tangential and the circumferential stress. The above relations are verified by FE models with different cores number. Moreover, some guidelines are introduced to help reduce the cross-sectional distortion. [ABSTRACT FROM AUTHOR]

Large-scale TA15 (Ti-6Al-2Zr-1Mo-1V) titanium alloy bulkhead is a key lightweight load-bearing structure part in an aircraft, which has a large plane view and has a complex shape with high ribs and thin webs. In its forging process, the forming defects, such as folding and under-filling are prone to occurrence. The near-net shape forming with saving force of this large-scale complex component can be realized with proper preform design combining local loading condition. By analyzing isothermal local loading process characteristic of large-scale bulkhead, it indicates that the simple unequal-thickness billet is suitable for small lot manufacture of large-scale TA15 titanium alloy bulkhead. Considering the geometry and forming characteristics, such as large dimension, complex shape, mass data, etc., a design method of unequal-thickness billet using analytical analysis and numerical simulation is proposed. The preform for a large-scale TA15 titanium alloy bulkhead is designed by the proposed method. The basic three-dimensional shape of billet is determined by the analytical models based on local loading features, and the basic billet is modified according to numerical simulation result and considering the local loading forming characteristic, and then the preform without resulting in folding and under-filling can be obtained after two modifications. [ABSTRACT FROM AUTHOR]

Exploration of microstructure evolution is of significance for manufacturing the large ring with high performance and high reliability in hot ring rolling. In the study, the microstructure evolution model and the rate-/temperature-/microstructure-dependent constitutive model of titanium alloy are implemented in ABAQUS/Explicit through the user material subroutine VUMAT. The developed subroutine is validated by single-element models and isothermal upsetting experiments of Ti-6Al-4V cylinder. The subroutine is imbedded into a coupled thermomechanical three-dimensional finite element (3D-FE) model for hot rolling of Ti-6Al-4V large ring. The evolution characteristics of β phase volume fraction and grain size of Ti-6Al-4V during the process are revealed, and the final microstructures of the large ring under different processing conditions are explored. The results obtained show that (1) microstructure evolution follows the trend with the process progressing: the fine grain zone transfers from the surface layer (SL) to the middle layer (ML) of the ring; the poor β zone extends from the outside of the SL to the end-plane of the ML, and the rich β zone always locates at the SL. (2) decreasing the rotational velocity of the driver roll n, or increasing the feed rate of the idle roll v or the initial temperature of the ring T contributes to more uniform distributions of β phase and its grain size, but results in the increase of the β phase volume fraction and grain size. [ABSTRACT FROM AUTHOR]

To understand the reason of defects and the basic mechanics involved in the welded tube numerical control bending process, it is important to study the effects of the weld and processing parameters on the strain distributions of the tube. The grid method that combines with vision-based surface strain measurement system GMASystem is used to research the strain distributions of the bent tube experimentally. The results show that the weld has a limited effect on the strain evolution as the weld is not located in the region of locally highest strains. As the weld line locates on the outside, the maximum tangent and thickness strain decrease by 0.94 and 8.78 %, while the maximum hoop strain increases by 22.15 % as compared with that the weld line locates on the middle. As the weld line locates on the outside and inside, the thickness strain decreases obviously in the weld region. The variation of thickness strain is little with smaller mandrel extension length, and the maximum thickness strain increases by 21.38 % as the extension length changes from 6 to 10 mm. The thickness strain decreases with larger push assistant level. The maximum thickness strain increases with larger bending angle. [ABSTRACT FROM AUTHOR]

Using the unequal-thickness billet, a good cavity fill can be obtained in the local loading process of the large-scale complex component with high ribs and thin webs. However, the folding/lap defect is prone to occur in variable-thickness region of billet (VTRB) in the forming process. In this paper, the finite element method is adopted to study the deformation behavior of VTRB in local loading process. The evolution and reasons for the folding under the different transition patterns (stepping pattern, rounding pattern, beveling pattern, etc.) and the different located positions (die partitioning boundary, web region, rib cavity, etc.) of VTRB are analyzed systemically. The results of the present study may provide a basis for determination of the transition pattern and transition condition of VTRB for large-scale unequal-thickness billet. [ABSTRACT FROM AUTHOR]

The friction at die-workpiece interface is an important parameter in metal forming processes, which affects the metal flow, cavity fill, surface quality, etc. The friction in the forming process is influenced by material properties and forming conditions. The friction in forming process of TA15 (Ti-6Al-2Zr-1Mo-1V) titanium alloy under high temperatures (isothermal forming) and low strain rates is studied here by ring compression test. The friction calibration curves are elaborated by means of finite element method. The research on the calibration curves and friction factor at the loading speed v = 0.1-1.0 mm/s and the conventional forging temperature (950°C) and near-beta forging temperature (970°C) is carried out. The influence of loading speed on friction calibration curves is similar to the influence on friction factor m: at the low ( m about 0.7) friction condition, the influence of loading speed can be ignored, however the influence is notable in the midst magnitude (about 0.2-0.5). The temperature variation from 950°C to 970°C has little influence on friction calibration curves, but has notable influence on m under lubricated condition. [ABSTRACT FROM AUTHOR]

The clearances between tube and various dies have a significant and complicated influence on the onset of wrinkling during the rotary draw bending process. To study the effect of clearance on wrinkling, a 3D finite element (FE) model of the process for thin-walled rectangular aluminum alloy tube has been built using the explicit code ABAQUS/Explicit and validated by comparing the experiment. Then, simulation and analysis of the process have been carried out based on the model. The influence laws of clearances between tube and various dies on wrinkling have been studied and the reasonable combination of clearances obtained using the combination method of 3D FE simulation and orthogonal experimental design. The results show that with the increase of tube mandrel clearance, Δcm, and tube bending die clearance, Δcb, the wrinkling wave number decreases rapidly, whereas the wrinkling wave height increases sharply. The effects of tube wiper die clearance, Δcw, and tube pressure die clearance, Δcp, on wrinkling are not significant. The reasonable combination of clearances is Δcm = 0.15 mm, Δcb = 0 mm, Δcw = 0 mm, and Δcp = 0 mm. These achievements are helpful to the design and optimization of the process. [ABSTRACT FROM AUTHOR]