Research On Experiment And Numerical Simulation Of Multi-point Forming With Discrete Blank-holder

Sheet metal stamping are used to form skin parts of automotive and aircraft in industrial production with the advantages of high dimensional accuracy, stable product quality, short processing time, high production efficiency and easy automation. In the process of stamping forming, there are easily to cause wrinkling in blank flange part due to the instability of sheet metal. Normally, it can effectively suppress wrinkling by setting the blank holder device. However, material flow is not uniform as the part has a complex shape and large deformation because of the different depth in different position. Under the action of blank-holder device, metal flow is restricted which results in a decrease or increase of metal so that wrinkles or cracking defects arise.Blank multi-point forming with discrete blank-holder combines rigid blank-holder forming with discretizing idea, which can realize flexible forming by coordinated movement of discrete blank-holder block through the suitable bank holder force with hydraulic or mechanical way instead of rigid blank-holder device. Bring to the new way of blank flexible forming, wrinkles or cracking defects of part decrease and stress, strain, and thickness distribution are uniform by setting different blank-holder blocks according to the position and adjusting the corresponding blank holder force.The main research contents and conclusions are summarized as follows:1. Discrete blank-holder process and experimental researchPut forward the design idea and the basic principle of multi-point forming with discrete blank-holder process. The forming process has been studied systematically. Point out the advantage of the forming technology. Taken the multi-point of spherical parts as example, a series of discrete blank-holder forming experiments are conducted with the single variable method. Results show that optimal forming parts are formed with no corner blank-holder, the more blank-holder blocks, the smaller blocks, the smaller gap and the optimized blank holder groove.2. Building finite element model of discrete blank-holder formingDiscuss the constitutive relation of elastic-plastic material, and mainly introduce the yield rule, material flow rule and hardening rule. The basic equations of plastic deformation and the principle of virtual work of the large deflection plate dynamic finite element analysis are studied. On the basis of the finite element theory, the paper introduces the modeling process of multi-point forming with discrete blank-holder, including the construction of geometric model and material model, defining boundary conditions and contact, dividing mesh and so on, which provide guidance for the numerical simulation of discrete blank-holder forming.3. Comparative analysis between rigid with discrete blank-holder formingTaken the spherical part as example, the finite element model of rigid blank-holder and discrete blank-holder are established. Through the comparative analysis of stress, strain, thickness, material flow and fracture of two forming modes of, multi-point forming with discrete blank-holder is verified the superiority way. The results showed that the part with discrete blank-holder has a reasonable material flow control, uniform stress and strain distribution, so the forming quality is good due to the flexible forming in blank holder region.4. Effect of blank-holder block parameters on discrete blank-holder formingDifferent finite element models are established, and the influence of block size, quantity and angle blank-holder on the forming results are systematically studied. Research results show that smaller the block length is, more uniform the stress distribution is and the length of forming part is closer to the theory depth; With the increase of the blank-holder block number, the wrinkling be suppressed and the stress distribution is more uniform; Distribution of stress and strain are more uniform and the forming depth is greater when forming without angle blank-holder.5. Effect of force-energy parameters on with discrete blank-holder formingTaken the spherical part as example, the size of the blank holder force, blank-holder force distribution and the friction coefficient are analyzed in many factors. Research shows that: The forming part has a uniform stress and thickness distribution when the blank-holder force is 10MPa; After optimization of blank holder force distribution, the maximum stress forming part significantly reduced so that stress and strain distribution is more uniform; With the increase of the friction coefficient range from 0 to 0.3, stress distribution range decreases, hence the equivalent strain and thickness distribution is more uniform.