Weld Pool Shaping and Microstructural Control Using Novel Computer Generated Holographic Optic Laser Welding of Steel and Stainless Steel

Abstract

This work considers the use of Holographic Optical Elements (HOEs) to shape the weld beam and control the microstructure of the weld bead. The beam profiles investigated are a standard Gaussian and an Offset Rugby Post produced by a HOE. Autogenous welds have been produced on plain carbon steel with the introduction of a nickel alloy filler powder, using different energy densities. Cross sections of the welds have been analysed in terms of the weld profile, weld pool shape, HAZ and the extent of the deposit/substrate mixing. Electron BackScatter Diffraction (EBSD) coupled with Energy Dispersive X-ray Spectroscopy (EDS) has been used to study the microstructures developed. The results have shown that by utilising HOE’s the weld pool shape can be modified so that a squarer profile can be obtained. The grain structure within the weld pool can be controlled such that a finer more equiaxed grain structure can be developed when compared with the coarse columnar grains seen with a Gaussian beam with a marked difference in the microstructures in the HAZ.

The use of holographic optical elements (HOE's) to investigate the use of a flat irradiance profile in the control of heat absorption in wire-fed laser cladding

“…HOE's have previously been used to investigate laser welding and powder-bed laser cladding (Kell et al 2011;Higginson et al 2010;Kell 2007;Higginson et al 2012), experimenting with complex, asymmetrical beam profiles for thermal control. This research has included placing additional heat concentrations in different parts of the beam, as well as the addition of thermal ramps for pre-and post-heating.…”

Selective laser melting using holographic beam manipulation: influence of polypropylene molecular weight

“…The two kinds of beams are illustrated in Figure 1. The Gaussian beam has the majority of the energy at the centre, with a rapid decrease towards the beam edges, which will generate a non-uniform heat distribution on the work piece (Higginson et al, 2010). Moreover, since the Gaussian beam has a round shape when projected on the working plane, during a normal scan the exposure time for the central region is longer than that for the edge.…”

“…By using HOE, a user defined temperature profile on the work-piece can be generated. The thermal profile of Gaussian and HOE reconstructed beams (including square uniform beam and 'Rugby Post' beam with high energy intensity at the edges) has been compared during laser metal deposition and it is stated that the different temperature profile generates a driven force in the molten pool to control the material flow (Gibson et al, 2009;Higginson et al, 2010). However, all HOE tests were reported in metal processing and no applications were found in other laser processing fields such as polymer additive manufacturing.…”

Using wire shaping techniques and holographic optics to optimize deposition characteristics in wire-based laser cladding

“…In this work, experimental studies of laser deposition using shaped wire are presented. Holographic optical elements (HOEs) [13] have previously been used to control the laser beam thermal distribution in laser welding [14], powder-bed laser cladding [15] and laser cladding with pre-placed circular section wire [16], showing the ability to control the shape and fluid flow within a melt pool. Building on previous wire work, the use of wire shaping seeks to further develop the process by optimizing the wire shape to give uniform heat transfer from wire to substrate across the width of the heat affected zone, HOEs were used to give a uniform laser profile.…”