An application of ultrasonic vibration to the deep drawing process

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Abstract

An experimental apparatus with the blank-holder or die plate vibrated in a radial mode was constructed in order to make the apparatus compact. The application of 20 and 28 kHz oscillation increases the LDR from 2.68 to 3.01, from 2.58 to 2.94 and from 2.38 to 2.77 respectively, in the case of cold rolled steel for deep drawing, cold rolled steel and 304 stainless steel. greater accuracy and deeper cups can be formed by stopping the oscillation after the maximum punch load rather than applying the oscillation throughout the deep drawing process. The radial vibration induces the axial vibration in the blank-holder or die plate and the axial vibration contributes strongly to the rise in the limiting drawing ratio (LDR) rather than the radial one. When one of the blank-holder and die plates is vibrated, the vibration in anti-phase is induced in the other. This means that both the blank-holder and the die plate should be simultaneously vibrated in anti-phase. Seasoning cracks of drawn cups can be avoided when the vibration is applied to the deep drawing process of 304 stainless steel sheets.

Introduction

At present, there are various methods for applying vibration to the deep drawing process 1, 2, 3, 4, 5. For example, the drawing ratio can be increased by about 25% [1]. However, even without vibration, the limiting drawing ratio (LDR) of more than 3.0 is obtained with forced-feed lubrication. This means that a greater increase in LDR is needed for this novel technique to be put into service. However, the theoretical value for LDR is 2.7 (e, the base of the natural logarithms), when deep drawing by ideal tools without friction. Ultrasonic oscillation has also been applied to machining and drawing processes. Judging from these, both a reduction in friction and that in deformation resistance (called the Blaha effect) makes the LDR higher.

In this paper, a design and adjusting process and experimental results are discussed for a vibratory deep drawing apparatus manufactured by way of trial, followed by some proposals with regard to the design of the apparatus.

Section snippets

Design of vibratory tools

An axisymmetric deep drawing process is adopted. The diameter of the punch and die hole is 26.9 and 28.6 mm, respectively and the radius of each corner is 4.0 mm. The forming speed is set to 1.3–11.7 mm s−1. Blanks for deep drawing are SPCC (cold rolled steel), SPCE (cold rolled steel for deep drawing) and SUS304 (304 stainless steel) with a thickness of 0.5 mm. Teflon sheets 0.1 mm in thickness are used for lubrication on both faces of the blank. An apparatus generating ultrasonic oscillation

Abnormal vibration

The radial amplitude of the resonator at the outer circumference is measured by an eddy current potentiometer. An preliminary experiment with sixteen transducers fixed at the circumference of the blank-holder, which has a nominal resonance frequency of 28kHz, showed that the transducer oscillated alternately and that the flexural vibration with some 200Hz appeared when increasing the amplitude. After detaching the transducers from the resonator and measuring the resonance frequency of the

Limiting drawing ratio

When the sheet is deep-drawn with the condition that the diameter of the sheet is kept constant and the blank-holding pressure is changed, the flange wrinkle appears with the pressure low and breakage appears with the pressure high. When the diameter is also changed, two limiting lines are drawn, which are called flange wrinkle generating line and breakage generating line. The intercourse of these lines is defined as the limiting drawing ratio (LDR). According to Fig. 5, the wrinkle generating

Conclusions

Adeep drawing apparatus with vibratory tools was newly designed and fabricated in order to make it compact. After considering the ways of applying vibration which have been tried to date, the blank-holder and die were vibrated in the radial direction.

(1) LDR can be increased from 2.58 to 2.94 for SPCC, from 2.68 to 3.01 for SPCE (for deep drawing) and from 2.38 to 2.77 for 304 stainless steel.

(2) It is not necessary that the ultrasonic oscillation be applied throughout the drawing process and is

Acknowledgements

This research was supported in part by Ministry of Education and Tokyo Institute of Technology. Resonators and tools were fabricated and supplied by Fujitsu and Hitachi and Transducers were contributed by NGK. The authors are grateful for these supports.

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