Experimental Investigation on Micro Deep Drawing of Stainless Steel Foils with Different Microstructural Characteristics

Jingwei Zhao,Qingxue Huang,Tao Wang,Fanghui Jia,Zhengyi Jiang,Cunlong Zhou,Zhou Li

doi:10.1186/s10033-021-00556-5

Abstract

In the present work, austenitic stainless steel (ASS) 304 foils with a thickness of 50 µm were first annealed at temperatures ranging from 700 to 1100 ℃ for 1 h to obtain different microstructural characteristics. Then the effects of microstructural characteristics on the formability of ASS 304 foils and the quality of drawn cups using micro deep drawing (MDD) were studied, and the mechanism involved was discussed. The results show that the as-received ASS 304 foil has a poor formability and cannot be used to form a cup using MDD. Serious wrinkling problem occurs on the drawn cup, and the height profile distribution on the mouth and the symmetry of the drawn cup is quite non-uniform when the annealing temperature is 700 ℃. At annealing temperatures of 900 and 950 ℃, the drawn cups are both characterized with very few wrinkles, and the distribution of height profile, symmetry and mouth thickness are uniform on the mouths of the drawn cups. The wrinkling becomes increasingly significant with a further increase of annealing temperature from 950 to 1100 ℃. The optimal annealing temperatures obtained in this study are 900 and 950 ℃ for reducing the generation of wrinkling, and therefore improving the quality of drawn cups. With non-optimized microstructure, the distribution of the compressive stress in the circumferential direction of the drawn foils becomes inhomogeneous, which is thought to be the cause of the occurrence of localized deformation till wrinkling during MDD.

Highlights

Driven by ongoing miniaturization in diverse areas including medical devices, precision equipment, communication devices, micro-electromechanical systems and micro fluidics systems, the demands for micro metallic parts have been tremendously increased [1,2,3,4]
3.1 Microstructure The optical microscope (OM) microstructure of the annealed austenitic stainless steel (ASS) 304 foils in the thickness direction is shown in Figure 3a–f, which correspond to the specimens A700, A850, A900, A950, A1000 and A1100, respectively
The major conclusions derived from the present work are as follows: 1) Recrystallization of ASS 304 takes place with the increase of annealing temperature, but the microstructure cannot be fully recrystallized when the annealing temperature is lower than 950 °C

Summary

Introduction

Driven by ongoing miniaturization in diverse areas including medical devices, precision equipment, communication devices, micro-electromechanical systems and micro fluidics systems, the demands for micro metallic parts have been tremendously increased [1,2,3,4]. As a fundamental microforming process, micro deep drawing (MDD) has extensive applications in the forming of hollow, thin walled and cup-like micro metallic parts. Due to the common problem of size effects existed in the forming of metals in microscale, research on MDD becomes more comprehensive as compared to those on the conventional deep drawing. A large number of studies have been conducted to identify the size effects in MDD of metals with the purpose of manufacturing high quality micro parts and promoting the development of MDD technology [5,6,7]. Micro cups produced with ASSs are extensively used in medical and electronic devices, and the research on MDD of ASSs has been increasing tremendously for years. Chen et al [9] conducted experimental

Objectives

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Results

Conclusion