AWARD Winning Diploma Thesis. - Academic Club Lightweight construction (ACL) AWARD
Written by Sabine Müller, Student at TU Dresden faculty of Mechanical science and engineering.
Industrial sponsor of the thesis: Composite Cluster Singapore Pte Ltd.
Development of an ultrasonic welding head for a robotised deposition of thermoplastic tapes
The deposition of thermoplastic tapes has been an established process in the aviation industry for some years, but this is still associated with high production costs. In addition, a separate consolidation step is necessary to manufacture the structure. The research carried out by the company Boikon had a system for depositing and consolidating with ultrasound as a result. Nevertheless a separate consolidation is still necessary. In order to pursue the idea of innovation, the process is to be optimized to such an extent that the consolidation step can take place simultaneously with the filing.
The aim of the diploma thesis was to define the the lay-up of the carbon fiber reinforced thermoplastic tape with the help of a robot that simultaneously consolidates the tape with ultrasound. The stinted consolidation process should reduce the process time. This is to achieve a higher depositing capacity and process speed which result in a better profitableness. For this purpose it was necessary to design and validate a suitable tape laying head.
Approach and experimental design
• Conceptual design and development of the tape laying head
• Construction of an integrated force sensor (force measurement by resistance change)
• Selection of relevant parameters, creation of a screening design to determine the parameter significances as well as the process window
◦ Production of test specimens in accordance with DIN 1465
- Performing a tensile shear test to determine the weld strength ◦ Supplementary optical evaluation of the near surface and cross-sectional area ◦ Establishment of a rating matrix
The tensile strengths obtained in the tensile shear test are in the range from 11 to 19 MPa. The highest achieved strength corresponds to 50% of the basic material strength of PA6. In addition, an optical image analysis and micrograph analysis was carried out. The results of the optical analysis coincide with the findings of the mechanical test. High connection strength can be achieved by setting a high ultrasonic frequency and welding force. Based on the results, the process window could be defined with the most suitable parameter combination (see Fig. 2).
With this parameter combination, the welding of a continuous seam with a length of 300 mm was carried out. The result in Fig. 3 shows a satisfactory surface area of the deposited and welded tapes.
Within the scope of the diploma thesis, a new type of tape laying head was developed, which consolidates the tape directly with the storage with an integrated ultrasound head. Despite the compact design and the integrated sensor system for welding force measurement, the head has a low weight. In the future it is advisable to integrate a tape conveyor and a cutting system as well as to make the tape laying head stiffer (stiffer) in order to allow higher welding forces. On the basis of a software-based experimental plan, parameter significances and the process window could be determined. The bonding strength achieved in the tests corresponds to 50% of the pure matrix material and is thus classified as high. Furthermore, the process was successfully tested by continuous welding tests. For future tests, it is recommended to test different fiber matrix combinations, as well as to vary tape thickness and width.
Reference for the price won:http://hightech-saxony.de/acl/acl-nachwuchspreis/