Numerical simulation of hydro forming at elevated temperatures with granular material used as medium compared to the real part geometry

Abstract

Modern automotive bodies are made of high and ultra high strength steel up to 90 mass percent of the body in white. These steels do not only possess a high light weight potential but also increase crash performance of the passenger cabin. The described benefits are facing the problems of forming these steels. With a low formability at room temperature and high flow stresses the complexity of parts out of these materials is limited. In a warm forming process with temperatures up to 600 °C the formability could be increased and the process forces could be decreased. Especially high complex parts are produced by hydroforming a technology allowing undercuts and uniform strain distributions in the part. For temperatures up to 600 °C there is a need of an appropriate medium for hydroforming. Fluids normally used at room temperature are only temperature stable up to about 350 °C and tend like gases to leakage. Using a granular material like small ceramic beads allow high temperatures and reduce the risk of leakage. The Drucker-PragerCap material model allows to describe this medium for the numerical simulation. The accuracy of the numerical simulation with the gained material model is compared with different experiments in which the parameters were identified and a real part geometry of a cup formed with granular material as medium.

A critical review on special forming processes and associated research for lightweight components based on sheet and tube materials

“…Figure 22. Experimental tool for hydroforming using granular material as a medium at elevated temperatures [37]. the results showing that specimens formed with VPF have less wall-thinning and consequently have a more uniform wall thickness distribution compared with those formed with polyurethane and steel (see Figure 17).…”

“…Merklein et al [37,38] used ceramic beads as a forming medium and designed and assembled an experimental apparatus (see Figure 22) to conduct the process at elevated temperatures. The apparatus can make SGMF parts at temperatures of up to 600°C, when the lightweight materials such as high-and ultra-high-strength steel or titanium are suitable for forming.…”

Investigation on granular medium forming formability of TA1 titanium alloy cylinder-shaped parts

“…In order to explore the flow and deformation characteristics of granular medium in the forming process, domestic and foreign scholars have used a variety of measurement methods, including axial static pressure transmission formability test, direct shear test and so on [5,16] , however, these methods are unable to reflect the dynamic flow properties of the material during the compression deformation process, and its applicability is not good for the GMF process. The tri-axial compression test, which is a relatively mature geotechnical test method, is suitable for measuring the dynamic compression deformation characteristics of granular materials under the condition of triaxial compressive stress.…”

“…The GMF process, which uses granules as a pressure-transfer medium in order to form a workpiece, is a newly proposed flexible die-forming technique [5][6][7][8][9] . Because the application of this process can fully exploit recent advances in the formability of lightweight materials at elevated temperatures, as well as overcome the limitations that the heat-resistant oil used in warm hydroforming operations can withstand temperatures of no more than 350•C [10][11][12] and that the inert gas used at higher temperatures in hot pneumatic bulging processes usually causes leakage problems [13,14] , the GMF process has recently attracted considerable attention by several researchers [15][16][17][18] .…”

Investigation of a New Method for Sheet Deep Drawing Based on the Pressure of Magnetic Medium

“…This method is not only suitable for the forming for multi variety, large quantities and complex shape parts, but also solves some forming problems of low plastic sheet. However, because of the limit of its own characteristics, the forming method based on the hydraulic pressure inevitably exists sealing problems, 7) the poor effect of force transmission 8) and need to increase subsequent cleaning process 9) etc. series of problems.…”