The aviation market is rebounding post-COVID, driving the demand for lightweight materials to reduce fuel consumption and CO2 emissions. However, machining Carbon Fiber-Reinforced Plastic (CFRP) is challenging and costly. Microdrilling (⪅1 mm diameter) for acoustic linings, consisting of CFRP skins in a sandwich structure, is widely requested. Laser drilling offers advantages such as smaller hole diameters and wear-free machining. To scale up laser microdrilling, process efficiency and heat control are crucial. This study conducted a thermal evaluation using a short pulse laser and thermal camera. The temperature curves were evaluated taking into account results obtained from studies based on a layout using design of experiments.
The global demand for air travel and air transport is expected to increase again in the next couple of years and so the environmental protection will also increasingly come into focus again. In the aviation sector, this means not only saving fuel and reducing emissions but also reducing the noise pollution caused by aircrafts. A typical method for noise reduction is the use of acoustic liners for sound insulation. Among different designs, acoustic liners can consist of sandwich panels, with one perforated, micro-drilled skin layer, a honeycomb structure and a closed rear layer. Wherever the operating conditions allow, the skin layers are made of carbon fiber reinforced plastics (CFRP), due to weight reasons. Compared to conventional drilling methods for CFRP, laser drilling offers unique benefits such as significantly smaller achievable bore diameters, wear free cutting and flexibility in bore diameter. However, for a large-scale application of laser micro drilling, the process efficiency must be increased and a process control is necessary to avoid damage due to excessive heat input. In this investigation, a process control method based on thermography is presented and evaluated. The control mechanism uses the temperature course in the drilling area to decide whether the process can be terminated in order to avoid time losses and unnecessary heat input. This method was found to be very reliable, however, the synchronization between temperature recording and laser irradiation and the data interpretation need further improvement.
An adequate use of finite resources is one of the greatest challenges of our times. To address this, lightweight concepts based on continuously fiber reinforced composites (FRC) are already being adapted for the transportation industry, especially within the automotive and the aerospace sectors. In order to broaden the use of lightweight composite structures and components, suitable processing, monitoring and control techniques are required for a variety of materials, constituting a prerequisite for economic, flexible and automated high volume production. In this regard, photonic technologies can provide valuable solutions. In this presentation, the latest developments within the field of FRC laser machining are summarized. For the processing of large structures such as resin transfer molding parts, combinations of galvo scanners with robots or axis systems are of particular interest. For this purpose, both high brightness cw fiber lasers and pulsed systems are used. Within the repair chain for valuable FRC parts, pulsed UV and NIR lasers are used for the precise removal of fiber layers in order to generate a defined scarfing. For both applications, disintegration of the fiber matrix interconnection due to thermal impact has to be avoided. Thermoplastic composites are becoming increasingly important for many industrial applications. In contrast to thermoset systems, welding techniques are particularly applicable. In this context, laser welding is not limited to the joining of transparent-absorbing-combinations, as it is required for conventional laser transmission welding processes but can be extended to the welding of structural parts consisting of high-performance carbon fiber reinforcements.
In the aviation industry, a major market for carbon fibre reinforced plastics (CFRP), <40.000 drilling operations are performed throughout the assembly process of a small aircraft. Additionally, the drive to minimize costs and time are prevalent in the manufacturing process. The quality requirements in the aviation industry are set to a high level and drilling tools have to be changed frequently, causing considerable costs in terms of tooling and time losses. Laser processing offers benefits such as flexible, and wear free cutting, which contributes to the optimization of processing costs. In this investigation a laser machine, process control, processing strategies and handling equipment adapted to high precision macro drilling and low cycle times were presented. The setup included a novel short pulsed high power laser source by TRUMPF Laser GmbH emitting at λ = 1030 nm integrated in a 5-axis machine. The lab-state laser source provides pulses at tp = 20 ns, at a maximum pulse energy of Ep = 100 mJ and a maximum average power of Pavg = 1.5 kW, while maintaining a very good beam quality, allowing small focus diameters. Due to a large variety of parameters that have an influence on the process, a test plan based on design of experiments was applied to identify ideal parameter fields. Parameters optimized towards high ablation rates and orthogonal kerf angles were identified. The results revealed a promising industrial processing option for high quality macro boreholes.
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