Proceedings of the 23 rd International Congress on Applications of Lasers and Electro-Optics 2004 2-D LASER FORMING COMPARATIVE STUDY ON ND:YAG OF TITANIUM ALLOY TI-6AL-4V Konrad Bartkowiak, S. P. Edwardson, G. Dearden, K. G. Watkins Laser Group, Dept. of Engineering, The University of Liverpool Liverpool, L69 3GH, UK Abstract Laser forming is an emerging technology which shows great potential for direct manufacture, prototyping and a means of alignment and distortion removal. An industry sector where its use is under consideration is aerospace, in particular for the forming of high strength aerospace alloys such as Ti-6Al-4V. This paper includes a multiple pass 2D laser forming comparative study on titanium alloy Ti-6Al-4V using two different types of Nd:YAG laser, pulsed (fibre delivered to an x-y stage) and CW (fibre delivered to a 6 axis robot). The use of Nd:YAG lasers for the laser forming of this material is being investigated as the need for absorptive coatings may be eliminated (costly and difficult to apply and remove). Key to the industrial acceptance of laser forming of this material is the development of cost-effective systems that avoid the detrimental diffusion of oxygen into the surface at elevated temperatures. To this end samples were processed in different atmospheres, in air and in argon (oxygen suppression), for the argon atmosphere two methods were investigated. The first employed a specially developed shroud delivery nozzle for the robot system. The second employed a controlled atmosphere chamber (<2ppm O 2 ). The cumulative bend angle at a number of processing conditions was recorded and a comparison made. The effects of laser forming on the material properties of the titanium alloy were also investigated; factors studied were the depth of transformed zones, total thickness of test coupons at various number of passes, microstructures formed and the microhardness of the heated section. Introduction The laser forming process (LF) has become viable for the shaping of metallic components, as a means of rapid prototyping and of adjusting and aligning. Laser forming is of significant value to industries that previously relied on expensive stamping dies and presses for prototype evaluations. Relevant industry sectors include aerospace, automotive, shipbuilding and microelectronics [1]. In contrast with conventional forming techniques, this method requires no mechanical contact and thus promotes the idea of ‘Virtual Tooling’. It also offers many of the advantages of process flexibility and automation associated with other laser manufacturing techniques, such as laser cutting and marking. The process employs a defocused laser beam to induce thermal stresses without melting in the surface of a workpiece in order to produce controlled distortion. These internal stresses induce plastic strains, bending or shortening the material, or result in a local elastic plastic buckling of the work piece depending on the mechanism active [2]. The range of metals and other materials that can be laser formed is considerable. As there is only localised heating involved, below the melting temperature, the bulk properties are not altered and good metallurgical properties are retained in the irradiated area. Materials of particular interest are specialist high strength alloys for the aerospace sector such as Ti6Al4V [3]. Key to the industrial acceptance of laser forming of this material is the development of cost-effective systems that avoid the detrimental diffusion of oxygen into the surface at elevated temperatures. To this end an investigation was conducted into the multi-pass 2D laser forming of Ti6Al4V sheet both in air and in an inert argon atmosphere. Two methods of oxygen suppression using argon were investigated and are detailed below. It has been reported in a number of studies that the use of absorptive coatings such as graphite, necessary for longer laser wavelengths such as 10.6µm (CO 2 ), are unreliable for the laser forming process [4]. They can degrade per pass, thus changing the absorption coefficient of a surface during processing, making prediction and control difficult. In addition, from a manufacturing point of view they can be costly and time consuming to apply and remove. Due to these factors the study presented in this paper was conducted on Nd:YAG (1.06µm) lasers without the use of absorptive coatings. It was hoped that this would further emphasise the potential manufacturing capabilities of the LF process and the study as a whole should provide an insight into how LF could be implemented for the manufacture of components from Ti6Al4V and other oxygen sensitive materials.