טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentRaz Danny
SubjectHydroforming Deep Drowing with Differential Temperature
DepartmentDepartment of Mechanical Engineering
Supervisor Professor Emeritus Jehuda Tirosh
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Abstract

In this research we suggest a basic improvement for deep drawing process. It is based on the possibility to use a moderately high fluid pressure to assisted the drawing when pushing hydrostatically at the rim of the blank. In addition to this we accompany this operation with temperature gradient along the blank. It is done  such that high temperature is prescribed at the rim and gradually diminishes to nearly ambient temperature at the lip. It was found experimentally that this combined effect (temperature gradient with fluid rim pressure) enhances the limit drawing ratio (LDR) of the deep drawing.

In conventional deep drawing of cups the LDR reaches 2.2 , whereas a theoretical LDR is bounded by e=2.71. The main reason for this deviation is seemingly due to the interfacial friction between the blank and the dies.

Using fluid pressure in hydro-mechanical deep drawing process reduces friction significantly, thus enabling the LDR to be increased. Several fluid pressure assisted deep drawing processes have been developed in order to extend the forming limitations. Each one of the processes has unique features compared with the others.

In our research it has been shown that sheet metal could be deep drawn more 'easily'  under differential heating (to produce temperature gradient) than the standard isothermal forming process. It was done by cooling the punch area while heating the blank in areas where the die and blank are in contact.

An analytical model has been conducted by the upper bound approach. The model takes into consideration the effects of the fluid pressure and the frictional shear traction acting on the product. The model also includes the effects of the die curvature and the blank thickness. The Analytical upper bound formulation has used  Johnson-Cook constitutive material (which includes strain hardening and strain rate sensitive and non linear temperature).   Ultimately, the resulting equations where solved numerically.

Experiments where conducted with Aluminum blanks at various radii and operated with fluid rim pressure (at about 600 bar) using:

1. Room temperature.

2. Differential heating.

Differential temperature of 500 was achieved by heating the blank to 800 C  and using cold water to circulate in the punch to get its temperature and the blank-lip temperature down to   300 C.

Both experiments and the associated analysis show improvements in LDR  by requiring  less punch force and less rim pressure when the temperature gradient was activated, as compared to otherwise.