The Interaction between the Sheet/Tool Surface Texture and the Friction/Galling Behaviour on Aluminium Deep Drawing Operations

Alaitz Zabala,Chris Childs,Iñigo Llavori,Andrea Aginagalde,Joseba Mendiguren,Lander Galdos,Eneko Saenz De Argandoña

doi:10.3390/met11060979

Abstract

The increasing demands for lightweight design in the transport industry have led to an extensive use of lightweight materials such as aluminium alloys. The forming of aluminium sheets however presents significant challenges due to the low formability and the increased susceptibility to galling. The use of tailored workpieces and controlled die roughness surfaces are common strategies to improve the tribological behaviour, whilst galling is still not well understood. This work is aimed at analysing the interplay between the sheet and tool surface roughness on the friction and galling performance. Different degrees of Electro Discharge Texturing (EDT) textures were generated in AA1050 material strips, and tooling presenting different polishing degrees were prepared. Strip drawing tests were carried out to model the tribological condition and results were corroborated through cup drawing tests. A new galling severity index (GSI) is presented for a quick and quantitative determination of both galling occurrence and severity. The present study underlines the key role of die topography and the potential of die surface functionalization for galling prevention.

Highlights

Today’s manufacturing industry has to cope with increasing demands for lightweight design, especially in the transport industry [1]
Different degrees of Electro Discharge Texturing (EDT) textures were analysed against different die surface topographies in order to test the influence of the EDT and die roughness degree on friction and galling performance
It can be observed that the non-textured surface presents a typically oriented surface topography corresponding to a mill finish (Str = 0.028); after the EDT texturing of the samples, an isotropic EDT texture is embossed on the surface (Str ~ 0.9)

Summary

Introduction

Today’s manufacturing industry has to cope with increasing demands for lightweight design, especially in the transport industry [1]. Galling is a severe adhesive wear mechanism, often seen in sheet metal stamping, which develops gradually as an adhesion of work material on the tool surface, which may change the tool geometry, increase the friction force, cause tearing, and lead to workpiece rejection [10]. Galling has a direct and negative influence on the surface quality of the products, and eventually, expensive tool maintenance is required in order to continue production. This has a dramatic impact on the forming processes, accounting for up to 71 % of the cost of die maintenance [11]

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