Formation of Built-Up Layer on the Tool in Turning Operation of Magnesium Alloys

Nikola Tomac ,Knut Sørby ,Sandro Doboviček

doi:10.17559/tv-20151027130036

Abstract

The present work highlights some factors which affect formation of a protective built-up layer (BUL) on the rake face of the cutting tool when cutting magnesium alloys. This work suggests that BUL can positively affect tool life, surface roughness, cutting speed and tool forces. The BUL is formed in cutting magnesium alloys with the PCD tool inserts at cutting speed range from 500 to 2500 m/min and at the carbide tool inserts at lower cutting speed range around 550 m/min. It has been found that deposit layers primarily have similar chemical composition as MnAl inclusions which are incorporated in the structure of the examined AZ91 magnesium alloys.

Highlights

It is well known that a protective built-up layer (BUL) is formed on the face surface and/or flank face of the cutting tool when cutting "free machining alloys"
It has been found that deposit layers primarily have similar chemical composition as MnAl inclusions which are incorporated in the structure of the examined AZ91 magnesium alloys
These inclusions, which are favourable for the BUL generation, are formed when additives, commonly called free machining additives, such as sulphur, selenium, tellurium, lead and bismuth are added to the work material

Summary

INTRODUCTION

It is well known that a protective built-up layer (BUL) is formed on the face surface and/or flank face of the cutting tool when cutting "free machining alloys". A number of machining tests have demonstrated that this layer formation can allow the use of higher cutting speed, produce longer tool life, improve surface finish, reduce tool forces and power consumption. All these machining characteristics may result in a reduction of the machining cost by increasing productivity or eliminating finish machining operations. The net effect of the low melting phase is to produce thinner and smaller chips, a smaller chip-tool contact area, lowering tool forces, reducing tool wear, and improving the surface finish It was noted, that low melting inclusions are only effective in the presence of the primary MnS inclusions [3]. It is suggested that based on high resolution transmission electron microscopy and the knowledge of cutting process, dynamic recrystallization took place in the formation of the built-up layer [8]

EXPERIMENTAL PROCEDURES

RESULTS AND DISCUSSION

CONCLUSION