Yantai, China
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Zhang C.,Shandong University | Zhang C.,Conglin Aluminum Co. | Zhao G.,Shandong University | Guan Y.,Shandong University | And 3 more authors.
International Journal of Advanced Manufacturing Technology | Year: 2015

In this paper, the “trial-and-repair” process of the extrusion die is transferred from the workshop to the computer for a complex hollow aluminum profile used in high-speed trains. Firstly, a finite element (FE) model of the extrusion process is established with the arbitrary Lagrangian–Eulerian code HyperXtrude. To balance the material flow velocity in the die cavity, more than ten baffle plates are used and distributed in the welding chamber. Then, taking the exit velocity uniformity as the evaluating criterion, the initial extrusion die is modified by adjusting the shapes, the layout, and the heights of the baffle plates. Through a series of modifications, the velocity difference in the cross-section of the extrudate decreases significantly from 102.3 mm/s with the initial die to 26.6 mm/s with the final one. The local twisted or bent deformation of the extrudate is well controlled with the optimal die. Finally, a real extrusion die is manufactured and a practical profile is extruded. The difference in the rib thickness of the profile between the experimental measurements and desired dimensions is 0.12 mm, which satisfies the practical requirements. Moreover, the microstructures in the profile and its ribs are examined, and no heat defects are observed in the profile. Therefore, the virtual tryout of the extrusion die in this work are well verified, and the design rules of extrusion dies could provide theoretical guidance for practical repairs of complex extrusion dies in workshop. © 2014, Springer-Verlag London.


Zhao G.,Shandong University | Chen H.,Shandong University | Chen H.,Inner Mongolia Electrical Power Research Institute | Zhang C.,Shandong University | And 3 more authors.
International Journal of Advanced Manufacturing Technology | Year: 2014

The extrusion die plays a crucial role in the quality control of aluminum alloy profile production. But in practice, the design of extrusion die is mainly dependent on the experience and intuition of die designers; thus, many times of modifications and experiments should be undergone until an acceptable product is gained. In this paper, the extrusion process of a large wallboard aluminum alloy profile used for high-speed train was simulated by means of HyperXtrude software, and the flow behavior of material and deformation mechanism in the die cavity were investigated. With the simulation results of the initial die design scheme, a nonuniform velocity distribution in cross-section of the extrudate was observed. For optimizing the die design scheme, two optimal schemes (adoption of double-step welding chamber and introduction of baffle plate) were proposed. Through optimization, the velocity differences in the extrudate for optimal schemes are decreased from 39.9 to 12.2 and 10.8 mm/s, respectively. Thus, the uniformity of velocity distribution was improved in optimal schemes. The extrusion die design methods for large wallboard profiles were summarized and proposed, including the design methods of baffle plate and double-step welding chamber. Through trial production, a sound wallboard aluminum profile with good geometric shape and high dimensional accuracy was gained. Additionally, the mechanical properties of the extrudate were examined by means of experimental method. It is found that the test results stratified the practical engineering requirements. © 2014 Springer-Verlag London.


Zhang C.,Shandong University | Zhang C.,Conglin Aluminum Co. | Ding J.,Shandong University | Dong Y.,Shandong University | And 3 more authors.
International Journal of Mechanical Sciences | Year: 2015

In this work, a two-stage inverse analysis technique is proposed to identify the friction coefficients during hot compression test of aluminum alloy 6N01 (AA6N01) and its material parameters in the strain-compensated Arrhenius-type constitutive model. Firstly, the minimal shape error between the measured and simulated specimen is set as the optimization objective. Based on the material parameters obtained by a traditional linear fitting method, the friction coefficient under each forming condition is obtained by the first-stage inverse analysis method. Secondly, on the basis of the obtained friction coefficients and taking the minimal error between the experimental and predicted forces as the optimization objective, 16 unified material parameters in the constitutive model are identified by the second-stage inverse analysis method. Then above two stages are combined together to realize loop calculation: the first-stage inverse analysis provides friction coefficients for the identification of material parameters while the second-stage updates new material parameters for identifying better friction coefficients. When the average error (Er (friction)) between friction coefficients obtained at the current and last loop is less than 5%, the whole identification process comes to the end and the optimized friction coefficients and material parameters are obtained. Results show that the maximum shape error is only 2.48%, which indicates that the obtained friction coefficients can reflect the practical lubrication conditions between the tooling head and specimens. Additionally, at low strain rates (0.01, 0.1 and 1 s-1), the predicted forces have a good agreement with experimental ones. While at high strain rate (10 s-1), some discrepancy exists between the predicted and experimental results and the maximum error arrives at 8.58%. But the global predicted error is only 4.2%, which verifies that the proposed model and obtained material parameters can describe well the rheological behavior of AA6N01 at elevated temperatures. By comparing the predicted forces obtained by the inverse analysis and traditional linear fitting method, it is found that the predicted forces by the inverse analysis are more close to experimental data. Therefore, it can be concluded that more accurate material parameters can be obtained and provided for the numerical simulation of the extrusion process of AA6N01 using the two-stage inverse analysis technique proposed in this paper. © 2015 Elsevier Ltd. All rights reserved.


Lu X.,Shandong University | Zhang C.,Shandong University | Zhang C.,Conglin Aluminum Co. | Zhao G.,Shandong University | And 3 more authors.
Materials and Design | Year: 2016

Aluminum alloy profiles have been widely used in many fields and are attracting more and more attention now. However, for the hollow profiles, longitudinal welding lines occur inevitably and appear on the extruded profiles. Currently, most research in the literatures focuses on the two-dimensional extrusion welding process, which could not reflect the real formation process of a welding line and there are not effective method to evaluate the welding quality during extrusion process. The first part of this work reviews the-state-of-the-art of the extrusion welding in the current literatures. In the second part, a novel method is proposed to evaluate the welding quality during a three-dimensional extrusion process. This method extends the application of the current welding criterion from a two-dimensional extrusion process to a three-dimensional one. By simulating the transient extrusion process of an aluminum tube with Forge-3D, the proposed method is used to evaluate the welding quality of the extrusion process. Based on the method, the effects of extrusion speed and welding chamber on welding quality are investigated quantitatively. With the increasing extrusion speed or decreasing height of welding chamber, the welding quality is getting worse, which is identical to the experimental observations in other publications. © 2015 Elsevier Ltd.


Dong Y.,Shandong University | Zhang C.,Shandong University | Zhang C.,Conglin Aluminum Co. | Zhao G.,Shandong University | And 3 more authors.
Materials and Design | Year: 2016

A deep understanding of hot deformation behavior of a material plays a crucial role in determining process parameters and designing extrusion dies during the extrusion process of the aluminum alloy profiles. Firstly, with the stress-strain data obtained by hot compression tests of AA6N01, the material parameters in the Arrhenius constitutive model with strain compensation were identified, the processing maps were established according to dynamic material model (DMM), and favorite processing parameters of this alloy were accordingly determined. Then, the identified material parameters and processing parameters were applied to simulate the extrusion process of a complex cross-section profile used in manufacturing high-speed train body. To reduce the severe twist deformation in the cross-section of the profile, different die correction schemes (adding baffle plates, adjusting bearing lengths) were taken to improve material flow uniformity in the cross-section of the profile. Through a series of die modifications, the velocity uniformity was improved greatly. With the modified extrusion die, the complex cross-section AA6N01 profile was finally extruded with desired size and geometry. The good agreement between numerical results and experimental observations verified the constitutive model, process parameters and numerical model built in this work. © 2015 Elsevier Ltd.


Zhang C.,Shandong University | Yang S.,Shandong University | Wang C.,Shandong University | Zhao G.,Shandong University | And 2 more authors.
International Journal of Advanced Manufacturing Technology | Year: 2016

Aluminum profile extrusion involves complex thermal, tribological, and mechanical interactions; thus, material flow and thermal behavior during extrusion process are very complicated. In this work, the material flow and thermal behavior of a 7 × × × aluminum alloy profile during an entire extrusion cycle are investigated numerically and experimentally. Hot compression tests are firstly carried out, and inverse analysis method is used to identify the material parameters of AA7N01 in Arrhenius constitutive model. The calculated global error is only 6.2 % between the predicted and experimental force–displacement curves, which verifies that the proposed model and obtained material parameters can describe well the rheological behavior of this alloy at elevated temperatures. Then a thermo-mechanical finite element model based on DEFROM-3D is built, and the transient extrusion process of the profile is simulated. By numerically analyzing the nose-end shape of the extruded profile, the evolution curves of exit temperature and of extrusion load, material flow and thermal behavior during extrusion process are investigated, respectively. Practical extrusion experiments verify the numerical model and results. Additional microstructure examination with electron backscatter diffraction (EBSD) technique also shows fine grains with the uniform grain size of about 9 μm on different locations of the extruded profile. Therefore, the material constitutive model and numerical model of extrusion process built in this work are capable enough to provide theoretical guidance in optimizing process parameters and designing extrusion dies. © 2016 Springer-Verlag London

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