Fabrication of micro channels for titanium PEMFC bipolar plates by multistage forming process

Although the multi-stage incremental sheet forming strategy is beneficial for manufacturing complex geometrical shapes via objective transitional stages, the forming limit and geometric accuracy are highly dependent on intermediate shapes, which need further improvement. Therefore, a novel forming strategy by combining the multi-stage sheet forming with ultrasonic-assisted vibration (UV) was proposed in the present work. This paper investigates the effect of ultrasonic vibrations on forming forces, thickness distribution, and stress–strain distribution through experimental tests and finite element (FE) simulations. Initially, a series of tests were conducted to determine the forming limit for three proposed strategies based on parameters including depth, initial diameter, and angle, both with and without the assistance of UV. Afterward, the FE model was established in ABAQUS/Explicit based on the optimal strategy by adopting the modified crystal plasticity constitutive model. The results indicated that, after superimposing the ultrasonic vibration, forming forces were effectively reduced and plastic deformation was greatly improved due to the increased equivalent plastic strain. Meanwhile, the application of the UV field efficiently reduces the high-stress zones and significantly decreases the stress value. Finally, it was discovered that by imposing UV at the appropriate forming stages, formability and thickness distribution can be successfully improved. The present investigation is beneficial to well understand the affecting mechanism of UV in completing the multi-stage sheet forming technique and obtaining the enhanced sheet formability. 

Deformation characteristics and formability enhancement during ultrasonic-assisted multi-stage incremental sheet forming

Novel hydromechanical reverse drawing method for thin-walled aluminum alloy sheet forming

An appropriate machining sequence can benefit the deformation control of structural parts. However, the existing machining sequence optimization methods can only take single-sided parts into consideration, which is not sufficient to the deformation control of the double-sided parts. To this end, this paper proposes a double-sided collaborative optimization method of machining sequence for deformation control of structural parts. Off-line numerical analysis and on-line deformation monitoring are combined in the proposed method, i.e., the relative residual stiffness of the workpiece in different machining sequence is obtained by off-line numerical analysis, and the residual stress distribution is reflected by on-line deformation monitoring data, respectively. Then, a fuzzy comprehensive evaluation model aiming to decrease the overall deformation is established to realize the collaborative optimization of machining sequence. The machining efficiency is also considered in this model by optimizing the number of alternate flip-over, where the machining features of the part with two sides are machined alternatively according to the optimized sequence. The experiment shows that the proposed collaborative optimization method of machining sequence can decrease the machining deformation of double-sided parts effectively.

A collaborative optimization method of machining sequence for deformation control of double-sided structural parts

An inverse strategy to determine constitutive parameters of tubular materials for hydroforming processes

https://vbn.aau.dk/ws/files/295103829/1_s2.0_S1000936118300372_main.pdf

Chun Zhang

Papers

Design of an innovative multi-stage forming process for a complex aeronautical thin-walled part with very small radii