Biography:

In the past Dongkai Xu has collaborated on articles with Shengfa Zhu and Rui Xu. One of their most recent publications is Topology optimization of die weight reduction for high-strength sheet metal stamping. Which was published in journal International Journal of Mechanical Sciences.

More information about Dongkai Xu research including statistics on their citations can be found on their Copernicus Academic profile page.

Dongkai Xu's Articles: (5)

Topology optimization of die weight reduction for high-strength sheet metal stamping

AbstractHigh-strength steels have been increasingly used for vehicle body structures to improve fuel efficiency and vehicle safety. In order to maintain the stiffness and forming conditions under higher forming loads, stamping dies have to be designed with larger dimensions and thicker structures which may result in heavier die weight. Targeting to save the die weight/cost and keep the required stiffness, a topology optimization method is proposed based on Solid Isotropic Microstructure with Penalty (SIMP) to reduce the weight of key die components. During optimization, multiple loading conditions at different forming positions are considered to assure the maximum deflection at the above mentioned positions within the limit values. Besides, the interaction behaviors between die components are also taken into account to reflect the real contact evolution. A step-bottomed cup is designed to testify the proposed method. Through topology optimization, the weight of blank holder is reduced by 28.1%. Based on the optimization result, the blank holder is redesigned and machined, stamping test results indicate that defect-free stamping parts are formed with same blank holder forces, and the thickness difference between the original and newly stamped parts along a cross section is less than 0.06 mm, i.e. 4.29% of the initial blank thickness. This verifies that the proposed approach can effectively reduce die weight and maintain the derived forming performance of stamped part.

Flange forming at an arbitrary tube location through upsetting with a controllable deformation zone

AbstractInstability is the most common challenge faced in the production of tubular flanged parts, which is usually limited by dimensional parameters, such as the slenderness ratio of height to thickness and the ratio of initial tube thickness to final flange thickness. To extend the formability limit in a single step, an alternative forming method called upsetting with a controllable deformation zone (U-CDZ) is proposed in this paper. In the proposed method, the workpiece is pushed from the holding cavity of a die into the forming cavity. Under an appropriate counter force, a stabilized deformation zone is established, which eliminates the limitation of the initial slenderness ratio in the conventional upsetting method. Detailed analyses of the forming qualities and forming load were performed. Due to the employment of the location zone, the tube flange could be formed at an arbitrary location (at the end of tube or away from the ends) without defects. The feasibility of the U-CDZ method was validated through finite element modelling and metal experiments on aluminium.

Technical paperAnalytical prediction of stepped feature generation in multi-pass single point incremental forming

AbstractSingle point incremental forming (SPIF) is a new sheet metal forming process characterized by higher formability, product independent tooling and greater process flexibility. The inability of conventional single pass SPIF to form vertical walls without failure is overcome by forming multiple intermediate shapes before forming the final component, i.e., multi-pass single point incremental forming (MSPIF). A major issue with MSPIF is significant geometric inaccuracy of the formed component, due to the generation of stepped features on the base. This work proposes analytical formulations that are shown to accurately and quantitatively predict the stepped feature formation in MSPIF. Additionally, a relationship is derived among the material constants used in these analytical equations, the yield stress and thickness of the blank material, such that the computational effort required for the calibration of these constants can be minimized. Finally, the physical effects of yield stress and sheet thickness on the rigid body translation are further discussed.

A Comparative Study on Process Potentials for Frictional Stir- and Electric Hot-assisted Incremental Sheet Forming☆

AbstractIncremental sheet forming (ISF), as an advanced forming technique, has received increasing interest from both academia and industry due to its improved formability, greater process flexibility and reduced energy consumption in its life cycle. However, with the growing application of lightweight alloys with very limited material elongation, conventional ISF inevitably encounters challenges in processing these alloys at room temperature, especially in forming magnesium and titanium alloys. Therefore, heat-assisted ISF techniques have been proposed to further enhance material formability at elevated temperatures. In this work, two heat-assisted ISF approaches, frictional stir- and electric hot- assisted ISF, have been employed to process the hard-to-form materials in terms of the flexibility and local dynamic heating. The temperature evolution and corresponding forming force at different feed rates of these two techniques, is investigated in detail to build up a processing window. In addition, process capabilities are compared by forming different geometrical shapes of magnesium alloy AZ31B of 1.4 mm sheet thickness. The investigation results show the pros and cons of frictional stir- and electric hot- assisted ISF. Frictional stir-assisted ISF is more efficient than electric hot-assisted ISF under current experimental results. However, electric hot-assisted ISF has faster heating rate which makes this technique less dependent on the component geometry.

Research LettersA preliminary study on the fatigue behavior of sheet metal parts formed with accumulative-double-sided incremental forming

AbstractAccumulative-double-sided incremental forming (ADSIF) is a newly developed die-less sheet metal forming process, which can form complex freeform sheet metal parts without using any part-shape-specific tooling. This preliminary study investigates the fatigue life of parts formed with ADSIF, on a AA2024-T3 sheet material. It is shown that the material formed with ADSIF has a longer fatigue life than the virgin material. Micrographs of the fracture surface obtained using a scanning electron microscope (SEM) is used to examine the mechanism of failure after the fatigue test. The areas of future work on fatigue life of parts formed with incremental forming are also discussed.

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