On Extrusion Forging and Extrusion Rolling of Thin Metal Sheets

Abstract

Sheet metal surfaces with pin-fin features have potential fluid and thermal applications. Extrusion forging process and extrusion rolling process can be used to create such surface features on sheet metals.

Extrusion forging process is a metal forming process that combines extrusion and forging into one operation. In extrusion forging, the pin-fin surface feature is created by compressing the work-piece using a punch with designed cavities. Experiments and numerical analysis were conducted to investigate the effects of tooling geometries, material properties, work-piece thickness, thickness reduction ratio and friction on the deformation behavior of sheet metals. It was found that increasing fillet radius of the orifice results in decrease in compressive force and boss height. As the negative draft angle increases, the compressive force and boss height decrease. Higher yield strength and higher friction lead to higher compressive force. The boss height is not significantly affected by the friction between the tooling and the work-piece.

Due to limitation in force capacity, it may not be feasible to apply extrusion forging technique to generate surface features on large surface area. As such, the extrusion rolling process is proposed. In extrusion rolling, the pin-fin feature is created by compressing the strip using a pair of rolls. The upper roll is manufactured with surface cavities. Finite element method are employed to investigate the effects of rolling speed, thickness reduction ratio, roll diameter and front tension force on the deformation behavior of metal strip. It was found that the rolling speed has little influence on the roll force and boss height. The front tension force has little effect on the average pressure and boss height. Increase the roll diameter results in in roll force increase.

This research investigated the effect of parameters on the deformation behavior during the extrusion forging and extrusion rolling processes. The research generated the knowledge needed for design and manufacture of micro/meso surface features on thin metal sheet. Moreover, this thesis presents a novel bulk forming process on metal sheets, which can have significant impacts in industrial practice.