TWI Industrial Member Report Summary 1030/2013
By C L Earl and P A Hilton
Power beams have been utilised for many different types of surface modification. One of the more recent innovations is the generation of surface features using the Surfi-Sculpt® process, developed by TWI (Dance and Keller, 2002) using an electron beam (EB) to create arrays of customised features on the surface of a particular material. This effect has also been demonstrated using multi-mode laser beams on a wide range of metallic materials and non-metallic materials (Hilton et al, 2009) and using lower power, but brighter, diffraction limited solid-state laser beams. The latter produce smaller spot sizes, allowing the power densities required for the process to be provided by lower power lasers, thus reducing capital costs.
Fundamental to the Surfi-Sculpt® process is the ability to rapidly scan the electron or laser beam over the surface of the material to be treated. A convenient way to scan a laser beam is via a series of galvanometer driven orthogonal oscillating mirrors. In the work described here, a scanning system has been used to rapidly deflect a focused 1kW single mode laser beam over the substrate surface to displace material in a controlled manner. This results in a textured surface consisting of an array of protrusions above the original surface and a corresponding array of intrusions in the substrate. The beam can also be moved in a third, (z) axis, direction, by linearly moving a focusing lens within the mirror scanning system, thereby introducing a further experimental variable.
As usable laser power is increasing and scanning technology is evolving to accommodate these developments, the cost of using higher power laser systems is ever decreasing. This project has explored the potential of state of the art laser equipment to produce a greater range of Surfi-Sculpt® process features than possible in previous work carried out at lower laser powers. The project has also minimised feature production times, through utilising higher laser powers and programming of the scanner to process other features within an array, during the delay periods required for cooling of the samples. Investigating processing parameter relations and their influence on feature height has gained an understanding of preferential processing conditions. Through high speed imaging (HSI) and thermal analysis techniques, an additional goal of the project was to gain a greater understanding of the physical phenomena involved in the process, so that this knowledge can be applied to industry.
- Use DOE techniques to develop optimum Surfi-Sculpt® processing parameters for Ti-6Al-4V and stainless steel 304.
- Improve production rate through intelligent programming of the scanning software.
- Evaluate the capability of the scanning system to change the z-position of the beam focus during feature build.
- Extending the range of features produced by the laser Surfi-Sculpt® technique.
- Enhance understanding of the Surfi-Sculpt® process using high speed and thermal imaging.