TWI Industrial Member Report Summary 919/2009
By P A Hilton, B G I Dance and L Nguyen
TWI has invented and patented a power beam process called Surfi-Sculpt®. The technique enables controlled surface features to be produced on a range of substrates such as metals, polymers and ceramics (Dance and Keller, 2002). Such surface features were first demonstrated using electron beams (EBs), employing electromagnetic coils to first focus the beam and then deflect this focused beam over the material surface in a rapid and controlled manner. The material melted by the beam moves, in part, due to the surface tension generated by a temperature gradient created across the molten material surface. How the material moves and ultimately the shape of the features produced, can be determined by precisely controlling the beam path and speed over the surface. The process is generally deployed to manufacture simultaneously several hundred features which may be identical or different. A wide variety of feature shapes have been made in order to meet different functional requirements (Dance and Buxton 2007). In particular, this scale of surface feature offers performance benefits for a number of applications including orthopaedic implants, composite to metal joining, heat exchangers and to aid in the application of ultra-thick coatings. A key characteristic of the Surfi-Sculpt process is that the beam makes multiple returns to the same point and multiple swipes to sequentially build individual surface features. These characteristics differentiate it from conventional surface texturing processes. The patented Surfi-Sculpt process is being commercialised by TWI.
This work describes a laser variant of the Surfi-Sculpt process that uses optical power to melt and displace material, thereby creating the surface feature. In order to perform this work, two recent developments in laser materials processing have been utilised. High brightness fibre delivered laser beams, using both fibre and disc lasers as the source of the laser light have been used. Because of their high beam qualities, these lasers have the advantage that their beams can be focused to small spots of high power density, whilst still using a long focal length beam focusing lens. This large distance between the focusing lens and the focused spot is a necessity for the laser Surfi-Sculpt process, because the rapid manipulation of the laser beam required is achieved by orthogonally mounted and galvanometer driven beam scanning mirrors. These are arranged in a similar configuration to those used in a laser marking system. Recent developments in this field, in the area of remote laser welding for body-in-white applications in the automotive sector, have produced a new generation of laser beam scanning systems capable of operating with several kilowatts of laser beam power, without causing aberration to the beam. For the applications reported here, this is significant, in that high beam quality is particularly attractive for processing with the type of scanning systems described above. In the work reported here, both disc and fibre lasers have been used at relatively modest laser powers of less than 2kW, in conjunction with two different and commercially available laser beam scanning systems, both developed primarily with laser welding applications in the automotive industry in mind.
- Demonstrate production of Surfi-Sculpt process features using laser beams.
- Compare the results achieved with Surfi-Sculpt process features produced using EBs.