The Maximum Drawing Ratio in Hydroforming Processes

Abstract

The concept of Maximum Drawing Ratio (MDR), supplementary to the well-known Limit Drawing Ratio (LDR), is defined, examined, and illustrated by experiments. In essence the MDR is reached when the two basic failure modes, namely: rupture (due to tensile instability) and wrinkling (due to buckling instability) are delayed till they occur simultaneously. Thus the process is beneficially utilized for higher drawing ratio by postponing earlier interception of either one of the above failures alone. The ability to suppress (up to a certain extent) the appearance of these failure modes depends heavily on the fluid-pressure path which controls the hydroforming process. The effect of the material properties, like the strain hardening exponent, the normal anisotropy of the blank, etc., as well as the geometrical properties (i.e., the thickness of the blank, the radius of curvature at the lip, etc.) on the MDR, are considered here in some detail. The nature of the solutions by which MDR is reached is discussed.

Hydroforming highlights: sheet hydroforming and tube hydroforming

“…Yossifon and Tirosh [47][48][49] proposed the concept of maximum drawing ratio (MDR). It was confirmed that the liquid pressure in the die cavity is very important for preventing the instability of the sheet.…”

Study on hydromechanical deep drawing with uniform pressure onto the blank

“…With respect to different goals, various methods are proposed, such as hydrodynamic deep drawing [3], the aquadraw process [4], the hydromechanical deep drawing (HDD) [5], the hydroform process [6], the radial pressure deep drawing with hydraulic counter [7] and the reverse hydrorim deep drawing [8] and so on. In the above methods, the boundary conditions are quite complicated which makes it difficult to carry out numerical simulations, and many experiments have to be made to find the optimum process parameters [9].…”

The effect of the key process parameters in the innovative hydroforming on the formed parts

“…However, still many black boxes exist in the sheet hydroforming, especially for the quality of the formed parts there is no definitive rules to determine according to the certain process parameters [4,5]. This paper investigated the innovative hydromechanical deep drawing with uniform pressure onto the blank, which has a very clear boundary condition for the pressure in the die cavity that makes it much easier to simulate than in the other HDD processes [6].…”