A large variety of modern components and products such as fuel injectors and spinning nozzles require holes drilled to very high standards as fare as roundness, diameter and aspect ratio are concerned. Laser-beam helical drilling has shown great promise to produce such high quality micro holes. In helical drilling, the laser beam is rotated relative to the work piece. In this case, the rotational movement is produced using a Dove prism, mounted in a high speed, hollow shaft motor. The goal is to investigate the main influencing factors on quality and productivity, such as pulse energy (fluence), helical diameter and conicity of the rotating beam. For this a ns-pulsed laser source with a wavelength of 532 nm is used. Different kind of holes are drilled in stainless steel and analyzed with a microscope afterwards. Modifications of the wedge prism position in front of the hollow shaft motor have an immediate effect on the helical diameter and thus on the hole diameter. However, the pulse energy is also influencing the diameter. It is possible to control the taper ratio of the drilled hole if the deflection mirror is moved parallel to the rotational axis.
di Christian Fornaroli, Jens Holtkamp, Arnold Gillner