A novel anti-spatter technique for laser drilling: Applications to surface texturing

Laser drilling has been proposed as a method for texturing the surface of surgical implants in order to promote bone ingrowth and adhesion. The potential advantages of the laser technique are processing speed, design flexibility, surface durability, and the ability to texture a wide variety of materials. The main drawback of this method is the presence of dross or spatter, which is deposited around the periphery of the hole during the drilling process. This loosely adhered material must be completely removed from the implant prior to implantation. As the removal of spatter creates extra production costs, we investigated methods to reduce the deposition of spatter. Commercial anti-spatter coating were not acceptable due to FDA requirements on implants, so other techniques were investigated. A thin coating of a surfactant fluid developed by Castrol North America showed exceptional anti-spatter properties. In consultation with the manufacturer of the fluid, further improvements in the properties of this material for anti-spatter applications have been achieved. As part of the process to understand how this anti-spatter technique works, high speed photographs (104 frames/s) were taken of the drilling process in titanium alloy. These images showed that the dynamics of the ejection of molten material from the drill hole is changed significantly by the presence of the surfactant coating. The coating prevented wetting of molten metal onto the top surface of the part. Evaporation pressure is then able to blow the liquid metal out of the drill hole, causing the ejecta to become airborne, where it cools and solidifies before landing some distance from the drill site.