Axisymmetric Drawing of Parts from Brass Sheets with Regulated Thinning

Abstract

This paper describes the results of a study that looked at the effect of the dimensions and mechanical properties of L63 brass alloy sheets on the drawing forces and the dimentions of axisymmetrically drawn tubs. Specifically for tubs made of L63 brass, the paper presents a number of different options in terms of the actual process and the pre-hardening parameters for sheet metal. Computer modelling was performed based on the results of pilot passes conducted on a two-high mill 350×450 operated by Kolchugino Non-Ferrous Metal Working Plant. For this, 380×380 mm square 1.5–1.7 mm thick sheets with accumulated strain were driven through the mill, and the workpieces were turned around before the second pass. Due to varying properties of annealed sheets, the yield strength doubled rising from 145 to 280 MPa, whereas the plasticity dropped. The simulation study helped determine that as pre-deformed material becomes 10 % harder, it tends to form more evenly in the Tub stamping operation with L63 brass material used. At the same time, the thinning effect in critical areas decreases. Due to this process solution, the workpiece thickness could be decreased from 1.7 to 1.6 mm. The reduced thinning of the round part is combined with a slight thickening of the flange edge. The paper also decribes a drawing option which could help save half of the required operations due to a 5 mm bigger diameter of the workpiece (leading to an only 3% increase in the surface area of the workpiece). Due to the use of pre-hardened sheet metal, one can avoid big cross-sectional thickness variations in axisymmetrically drawn parts. To implement this process, one is advised to use a single-action press of the P2228A type designed for 630 kN.