Main technical issue
The rail industry is a strong industrial sector that generates a great income for the economies where components are manufactured, and the increase of the competitiveness a key aspect to maintain the market share of the companies. In general, machining of low rigidity big size structural parts with the required precision is a real challenge. In the railway industry, these components are joined by welding processes, also involving many intermediate machining processes to obtain some geometric features and the final shape of the component. The process chain drives to intermediate distorted geometries and pieces prone to deformation. So, the referencing and set up of these components for the machining operations become a problem due to the distortions associated to previous processes. The main objective of this experiment is the integration of efficient and fast measurement systems as a part of the fixture in order to improve the setup of the workpiece, adapting the tool path to the deformed geometry. The tolerance required in the machined features is ±0.1 mm.
Proposed technical solution
In order to solve the problems and limitations currently observed in the railway manufacturing industry, the solution selected deals with the integration of a laser scanning sensor to check the real deformed geometry of the workpiece and adapt the tool path to the measured geometry. The integration of different subsystems in the fixture has been done to achieve the required functionality, involving the following element: • Integration of a movement system to control the position of the 2D laser scanning sensors in the fixture; • Software to control the fixture, to capture the distorted workpiece geometry and to treat the data for the definition of the adapted tool path; • Communication with the CNC of the machine tool to send the adapted tool path. Additionally, vacuum support elements have been included to increase the workpiece stiffness in order to avoid vibration and deformation problems during machining.
Main advantages of the solution
Currently, in the industrial application of the experiment, the measurement is done by a slow process with touch probe systems that allow the definition of the workpiece position. This probing process currently represents up to 60% of the manufacturing time for the selected operation, the rest being for the loading/ unloading the workpiece and the machining itself. The use of efficient and fast set up processes is an important issue that could improve the performance of the manufacturing processes mainly by reducing the process time. The developed intelligent clamping unit aims at substituting the current set up process with a reduction up to just 25% of the manufacturing time. The use of a laser scanning sensor allows the use of a large amount of data, obtaining a better and more precise characterization of the workpiece. The system allows keeping the workpiece below the required tolerance, and also avoid problems that normally arise in the curved areas of the workpiece. Finally, the use of vaccum clamping elements allow an improvement of the workpiece stiffness. In this situation, the machining speed can be increased by 20%, so the machining time is also reduced.