machining strategies

P V Petkov, S Scholz and S Dimov
Manufacturing Engineering Centre, Cardiff University, Queen's Buildings, The Parade, Newport Road, Cardiff, CF24 3AA, UK

Abstract

Laser milling with microsecond pulses is a thermal material removal process usually associated with detrimental effects such as heat affected zones (HAZ), a recast layer and debris. Process optimisation can lead to considerable reduction of the above mentioned negative effects. In this context, the research investigates the effects of tool path optimisation and material removal strategies on the resultant surface quality and edge definition. The conducted experimental study shows clearly that the applied milling strategies have a significant effect on the resulting surface topography and the edge definition. Also, the research demonstrates that by optimising the laser path and material removal strategies it is possible to reduce significantly the thermal load when milling micro features, and thus to minimise HAZ and other secondary effects.

C. Vincenta, G. Monteila, T. Barrièreb, J.C. Gelinb
a Laboratoire de Microanalyse des Surfaces, 25000 Besançon, France
b Institut FEMTO-ST, département mécanique appliquée, 25000 Besançon, France

Abstract

The aim of this work is to expose the machining of deterministic grooves by means of a laser Nd:YAG in a heterogeneous metallic material.

These grooves are defined by their cross section geometry and spatial distribution. For the cross section geometries, various profiles of the engraved lines are realised: hemispherical, rectangular, trapezoïdal and triangular. For the distribution or patterns of the grooves, they are classified in two categories: continuous lines and interrupted ones. The first pattern type allows the machining in the aeras where the crossing of the lines occurs to be studied. The second pattern type is dedicated to the measurement of the quality of the engraving process. The current dimensions of the grooves made on the metallic substrate are micrometric: typically up to 10 micrometers for the depth and up to 50
micrometers for the width.

In order to obtain the desired striation by laser machining, it is necessary to develop the adequate machining strategies. i.e., according to the slope of the surface to engrave on a horizontal plan, the direction of the laser beam has to use a varying slope: for a flat surface, the beam is machining vertically and for a tilted or vertical surface, the beam has various processing angles.

Moreover, this striation is engraved in a heterogeneous material, lamellar cast iron, leading to particular difficulties
arising during machining process. Accordingly to the material where the impact of the laser is located, graphite or
ferrous matrix, the engraved depth is different. However, an adjustment of the intensity of the current of lamp is carried out. It consists in comparing the machined depth with the required one after several laser machining passes.
Consequently, this adjustment allows us to obtain a correct machined average depth whatever the heterogeneity of
material is.

In addition the laser processing during the groove machining gives rise to burrs on the edges of the groove. The burrs elimination by fine grinding has been developed.