Investigation on Flow Stress Level of Spherical Preforms Generated by Laser Melting

Abstract

A laser-based micro upsetting process is presented which takes advantage of scaling effects in order to optimize the conventional multistage upsetting process. Due to the fact that the surface tension exceeds the gravitation force with increasing miniaturization, in the microrange, an accumulation of molten material forms a nearly perfect sphere. This material accumulation can be finally formed in a secondary process step. In former investigations, it has been shown that the laser-based free form heading process improves the upset ratio up to 250 instead of 2.3 commonly achieved by conventional multistage upsetting processes.

In this article, the second stage of the upsetting process is examined by investigating the deformation behavior of laser free formed austenitic chromium-nickel steel (1.4301) with a rod diameter of 0.5 mm and head diameters ranging from 1.1 mm to 2.1 mm, using a pneumatic forming machine. The experiments show that the maximum achievable true strain is much higher compared to a conventional multistage upsetting process. Furthermore, the flow stress level of material preforms is compared with values gained in cylinder compression tests.

Keywords:

• Formability
• Laser melting
• Micro
• Micro preform
• Microforming
• Size effect
• Upsetting