1:30pm - 1:45pm
Experimental investigations of a helical laser drilling process for pilot holes on complex surfaces
Institute of Machining Technology (ISF), Technical University Dortmund, Germany
Increasing requirements and a high degree of freedom in design increasingly demand the manufacturing of bore holes with small diameters and high length-to-diameter ratios on complex shaped surfaces. Injection nozzles, medical tools and implants, cooling holes or oil channels are just a few examples. Unlike mechanical drilling tools, the laser beam is not deflected on inclined or curved surfaces and can therefore be used to create pilot holes for a subsequent mechanical drilling process. In this paper, the generation of pilot holes on flat and inclined surfaces using a Nd:YAG laser is investigated. A helical laser drilling process is used to drill holes with a diameter of 1.5 mm in X2CrNiMo17-12-2 stainless steel. Hole depth, diameter, roundness, conicity and material influences are evaluated. Application tests with single-lip drilling tools prove the potential of the laser holes to serve as a drilling guide for the mechanical deep hole drilling process.
1:45pm - 2:00pm
Laser microdrilling of thin aluminium sheets for metal-composite adhesion promotion
1AIMEN, Spain; 2Rescoll, Société de Recherche, France
Thin (200 µm) aluminum sheets were drilled using a 1070 nm, CW fiber laser to improve hybrid metal-composite adhesion. The laser beam was guided by a BEO D35 laser cutting head. Micro holes of several diameters (40 – 220 µm) were generated with different spacing among them. The aluminum sheets were later coated with an adhesion promotion spray and thermoformed with a thin (200 µm) Carbon Fiber Reinforced Polymer (PA66) tape. InterLaminar Shear Strength (ILSS) and Single Lap Joint (SLJ) tests were performed on the following thermoformed samples: 1) Drilled, uncoated samples, 2) Non-drilled, coated samples, 3) Drilled, coated samples. The results show that a significant adhesion improvement for the drilled, coated aluminum samples is accomplished, reaching up to 100% higher apparent interlaminar shear strength than plain, coated samples. Finally, the pattern that provided the best ILSS values was replicated with a ns pulsed fiber laser, resulting in an equally strong bonding, while increasing productivity tenfold.
2:00pm - 2:15pm
Fluence dependence of the edge quality of microhole exits for percussion drilling with ultrashort laser pulses
IFSW, University of Stuttgart, Germany
For many applications, edge quality and shape accuracy of microholes are crucial. One assumption is that the fluence at the tip of the microhole during drilling is a key parameter for the quality of the microhole’s exit. It was therefore investigated experimentally how the fluence affects the edge quality. The experiments were performed in 0.5 mm thick steel using a Ti:Sapphire laser system operating at a wavelength of 800 nm, a pulse duration of 1 ps, and a repetition rate of 1 kHz. For the quantitative analysis of the edge quality, microscope images were evaluated using a machine learning approach. Two key figures, groove size and perimeter ratio, were defined that proved to be significant in characterizing the edge quality of exits. In the current talk it will be shown that the quality of exits of percussion-drilled microholes could be significantly improved if the fluence dependence is considered.
2:15pm - 2:30pm
High-speed offline and real-time monitoring and control for laser micro-drilling of large Ti sheets
TeknikerTekniker-Basque Research & Technology Alliance, Spain
High-throughput laser micro-drilling is a highly demanded technology for several applications, including making filters, creating surfaces with better aerodynamic performance, etc. However, it is usually found that the sensitivity of the laser process to small deviations is quite high. That is why, while parameterizing, it is convenient to have techniques that allow us to monitor and control the process to ensure reproducible results. For this, we have developed several methods that combine monitoring and control in real-time and offline. For real-time control and monitoring, we have used optical coherence tomography and captured the scattered laser radiation during the process by means of photodiodes. Regarding offline monitoring, a procedure using a high-speed camera and an algorithm for measuring the dimensions of the microholes provides us the quality characteristics and statistical information of complete micro-perforated Ti sheets. Both methods work as fast as the laser process, i.e., 300 holes per second.