The German team "upgraded" the processing of aviation titanium alloy plates with

Recently, researchers from Helmholtz Zentrum Hereon Institute for Mechanics of Materials in Germany announced that they had completed an experiment on laser peening technology. The experiment was mainly to study the potential of this technology in the processing of aerospace titanium alloy plates. It is reported that the research will generate quantitative data to develop process planning algorithms, thereby significantly improving the automation of laser peening.

(Photo source: Helmholtz Zentrum Hereon Institute for Mechanics of Materials, Germany)

Laser shot peening has advantages in creating some aircraft parts with curves (such as wing front, tail and fuselage structure). In many normal service aircraft, these parts are usually made of light and high-strength titanium alloy Ti-6Al-4V. However, this kind of alloy is not easy to be "tamed" - you will experience obvious "rebound" when trying to shape this kind of alloy parts (such as using traditional hot stamping or incremental sheet metal forming process). This springback is a geometric change that occurs when the forming components are released from the load and constraint of the forming process, which is particularly difficult in the aerospace industry. The final parts are usually scrapped because they do not meet the strict tolerance requirements.

Siva Teja Sala, a doctoral student in the Department of Laser Material Processing and Structure Evaluation of Helmholtz Zentrum Hereon Institute of Material Mechanics, pointed out that: "This is not ideal for large-scale production, so aviation manufacturers are currently looking for a flexible and cost-effective calibration process to control these tolerances, and laser jet forming is very suitable for this application. It is very flexible, requiring only limited fixtures or clamping systems (no huge machines) As a whole, it only needs a pulse laser and a robot that can process parts. Compared with the traditional molding process, it has a high degree of automation and low energy consumption. "

Therefore, Sala and his colleagues began to study laser jet forming within the framework of the "PEENCOR" project, which aims to correct the inevitable deviation in the production of bent titanium aircraft parts. By developing an automatic laser shot peening process, this project measures these complex deviations and corrects them according to the specified tolerances, so as to reduce the scrap of parts and improve the overall productivity.

Precision controlled micro explosion
The experiment was carried out by Helmholtz Zentrum Hereon Institute of Material Mechanics in Germany in cooperation with Formtech, Zentrum f ü r Angelwandte Luftfahrtforschung (ZAL) and L ü neburg Institute of Product and Process Innovation, University of Leuphana. ZAL has the largest commercial laser shock strengthening equipment in Europe - capable of processing 5 meters in a few minutes × 1m × Parts weighing 1 m and 180 kg.

In the experiment, the research team hopes to conduct a comprehensive qualitative evaluation on the process parameters of laser jet forming of titanium alloys and their effects on material bending. They used pulsed laser to irradiate the surface of the titanium alloy part sample, which was covered with a protective steel foil to generate plasma, causing a small explosion on the surface. The researchers use the layered water flow on the surface of the material to limit the explosion and generate pressure waves that penetrate into the material to further bend the material. Finally, they can control the bending degree of titanium alloy plates by adjusting the laser parameters.

The laser system used in the experiment is a Nd: YAG 1064 nm laser customized and designed by Quantel Company, which can generate 5J pulses with a frequency of 10Hz, a duration of 10-20 ns, a uniform beam profile and a cross section of 1 × 1mm2. As a result, they found that laser power density is one of the most critical factors affecting the bending deformation of plates. In this setting, the laser intensity is equivalent to 25GW/cm2, and the researchers plan to further increase the power to 10J pulses.

The research team also considered whether this technology would encounter the same batch production problems as the ultrafast laser texture processing application. Sala explained: "At present, a 20 × It takes about one minute to process a 20 mm square, so it will take more time to process a 1 m2 component. In terms of texture processing applications, ultrafast lasers have recently achieved the improvement of average power and the maturation of multi beam transmission systems to achieve faster parallel processing. "

In the future, researchers may use multiple lasers or lasers guided by scanning technology. It is reported that compared with the current settings, this will affect the interaction between the pulse and the surface.

Industrial applications face severe challenges
According to Sala, the biggest challenge to carry out this work for the aerospace industry is its strict requirements. Because no surface defect can appear on any part, it is particularly important to control the key process. In this process, it is necessary to protect the steel foil and achieve a very good surface finish based on this. In the absence of steel foil protection, the researchers observed that 1.5 μ M, which increases the risk of part failure under fatigue load.

In addition, different from the residual stress when the protective foil is not used, the residual stress left in the material after laser peening penetrates relatively deeper along the thickness of the material when the protective foil is used, which means that they will perform better than the plates treated without the protective foil.

Although the application of laser peening on an industrial scale is still in its early stage, its application has attracted the attention of many industrial sectors, including maritime and aerospace sectors.

Sala cited LSP Technologies as one of the commercial companies that have made good progress in these areas. The company has been experimenting with different applications, such as correcting the deformation of gear shafts, extending the life of jet engine blades, and even processing aluminum plates on naval combat ships. The company even cooperated with Airbus and other companies to develop a portable laser jet system for maintenance of areas that are difficult to reach on the aircraft.

He added: "Although large industry participants such as Airbus and Lufthansa Technologies are currently testing this technology, they may want to keep it confidential before obtaining consistent and reliable results certified by relevant departments, so we cannot know their test results in the short term."

On the other hand, although laser jet forming does show great prospects for industry, it does pose a certain challenge in terms of its applicability, because the process needs to be customized for each application case. In the future, traditional process optimization strategies may be replaced by the most advanced artificial intelligence or machine learning methods to achieve maximum automation.

In general, Sala believes that although laser peening cannot completely replace the traditional forming technology, it does show a bright prospect as an accurate correction process and has huge economic potential.

Source: OFweek