Effects of hydraulic pressure on wrinkling and earing in micro hydro deep drawing of SUS304 circular cups

Abstract

Influences of hydraulic pressure on forming features in micro hydro deep drawing are different from those in normal drawing due to the small size of specimens. In this study, micro hydro deep drawing of SUS304 sheets was carried out in order to study the impacts of the hydraulic pressure on the quality of the drawn cup. Experimental results indicate that there is a critical hydraulic pressure range from 3 to 6 % of the blank's initial yield stress, where wrinkling and earing development trends change twice. The wrinkling and the earing of the drawn cup also reach their local extremes in the critical pressure range. The cup earing value moves in the opposite direction from the wrinkling value. Hydraulic pressure affects the wrinkling and the earing of the drawn cup through changes in the micro-frictional condition, the shape of the blank and its strain-stress state. Micro-finite element (FE) simulation which takes these factors as well as the material size effects into consideration showed similar results to the experimental ones, thus validating the experimental results and the suitability of the micro-simulation model for micro-forming FE simulation. The experimental and simulation results indicate that the critical hydraulic pressure based on the blank's initial yield stress can restrict the wrinkling and the earing of the drawn cup. Ultra-high pressure has the potential to avoid the cup wrinkling and earing. AbstractInfluences of hydraulic pressure on forming feature of cups are different in micro hydro deep drawing due to size effects. In this study, the micro hydro deep drawing of SUS304 sheets was conducted to study the impacts of the hydraulic pressure on drawn cups' quality. Experimental results indicate that there is a critical hydraulic pressure range from three to six percent of blank's initial yield stress, where wrinkling and earing developing trends change twice. The wrinkling and earing also reach their local extremums in the critical pressure range. The earing is strongly related to the wrinkling phenomenon. Friction plays an important role in micro hydro deep drawing and significantly affects the wrinkling and the earing of the drawn cup. Moreover, micro scale simulation with consideration of the size effects and friction change presents similar wrinkling development trend to that in the experiments, which proves the influence and importance of the size effects and friction change.

Effects of nano-particle lubrication on micro deep drawing of Mg-Li alloy

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Effects of TiO2 nanoparticle lubricant on micro deep drawing performance

“…The COF in micro forming is higher than that in the macro forming due to the tribological size effect, and the COF decreases when the punch velocity increases during the MDD process [11]. However, the forming with the higher velocity means the higher strain rate during the forming process, which needs more force to accelerate the deformed area to the higher forming velocity [29,30]. At the beginning of the forming process, the punch force is larger with the higher forming velocity because of the higher strain rate, then the contact area between the sample and die becomes larger as the MDD processing.…”

A state of the art review of hydroforming technology

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