Efficiency of the laser texturing on the adhesion of the coated twist drills

The coating adhesion is an important property of cutting tools. High speed steel twist drills coated with TiN have proved that cutting speeds can be 2.5–4 times higher and feed velocity also can be 3–5 times higher than those speeds used when uncoated tools are utilized. However, a suitable adhesion is very important, because the coated tool with poor adhesion between the substrate and the coating presents a worse performance than the uncoated tool. The formation of hard and abrasives particles, resulting from the premature destruction of the coating, accelerates the wear of the surfaces which have sliding contact. A new technique to clean and texturing the surfaces using a laser beam, previous to the coating deposition was applied to a set of drills and its performance compared with another set of coated drills without texturing. In the texturing process, a laser of short pulses and high repetition rate generates a surface texturing due to the formation of small liquid drops of the material. After the solidification, nanostructures are formed which allow a better coating retention. The comparison between these two sets of drills was carried out in drilling tests of the ABNT 304 steel, in three different cutting speeds. The evaluation parameters were: the number of holes drilled by each drill, feed force, thrust moment and flank wear. The results showed a large increase of the tool life when texturing of the substrate was made.