Influencia de los efectos residuales en el springback

|the influence of residual stress distribution on the springback parameters in the case of cylindrical drawn parts

Neculai NANU, Gheorghe BRABIE, IMT Centre of Research, Bacau University, Marasesti Street, Bacau, Romania|nicu.nanu@ub.ro, g-brabie@ub.ro

Abstract: In the case of deep drawing process, the springback is an important phenomenon that leads to the modification of the part shape and dimensions after the tools removing. For this reason, in order toobtain a drawn part with a good accuracy of the shape and dimensions, this phenomenon must be controlled. The main cause of the springback phenomenon is represented by the residual stress distribution on the sheet thickness of the drawn part. Hence, in order to control the springback, the residual stress distribution on sheet thickness must be known and controlled. In this paper an analysis was madeconcerning the influence of the residual stress distribution on the springback intensity in the case of cylindrical drawn parts made from steel sheet.

Key words: deep drawing, residual stresses, springback.

1. INTRODUCTION

The springback phenomenon leads to the modification of the dimensional and shape parameters of the drawn parts after the tools removing. In order to obtain anaccurate drawn part, the minimisation of the springback effects must be performed. The researches performed in order to minimise the springback have been focused on reduction or compensation of their effects. The reduction of the springback effects suppose the knowledge of it causes and the influence factors that affects it intensity. The researches performed concerning the generating causes of thespringback shows that the main cause of this phenomenon is the uneven distribution of residual stresses in thickness of the deformed part generated before tools removing [1], [2], [3]. Hence, in order to control the springback effects, the residual stress distribution in the sheet thickness must be controlled. In the case of deep drawing processes, the material is subjected to a complex loading, thestresses varying on the part region and in the sheet thickness [4], [5], [6]. In order to compensate the springback, the study was focused on the optimisation of the process parameters in order to minimisation of the springback effects. The compensation is based on such algorithms that use the results from experiment, finite element simulation and different models of calculation.
This aim of thispaper is to study the influence of residual stress distribution on the springback intensity in the case of cylindrical drawn parts.

2. GEOMETRY OF PART AND MATERIAL

The determination of residual stress distribution was performed on cylindrical drawn parts made from steel sheets. The blank diameter was equal to 200 mm; the sheet thickness was equal to 0.75 mm. The part geometry is shown infig.1 and the material properties in table 1.

Fig. 1 Geometry of cylindrical drawn part

Table 1. Material properties

|Material properties |Measuring unit |Value |
|Young’s modulus |[MPa] |144120 |
|Yield strength |[MPa] |156 |
|Strength coefficient |[MPa] |531|
|Uniform elongation |% |21.42 |
|Total elongation |% |38.84 |
|Anisotropy |r0 |- |1.25 |
|coefficients | | | |
| |r45 | |1.90 |
| |r90...