Along the development of the Formit project, several technical objectives have been achieved on different areas. Relevant advancements on manufacturing processes, tooling design and parts manufacturing have been obtained.
In order to manufacture the desired T shape stringers, several production processes have been developed. All the processes have achieved a maturity level enough to be used on the manufacturing of real parts with representative geometry. They are the following:
- Thermoplastic prepreg layup process
One of the Applus glide forming process characteristics is that is able to form a full thickness layup from flat to a final geometry in one step. A new stacking process has been developed to manufacture cohesive flat layups, involving cutting, positioning and spot welding on the key positions of the layup.
- Thermoplastic L shape stringer automated continuous forming process
The automated continuous forming process developed to form the L shape stringers of the project has been an adaptation of the previously existing Applus+ Glide forming technology, used for epoxy prepregs, to the much higher processing temperatures, around 400ºC, required for the thermoplastic material. Nearly all the elements involved on the forming (heating blankets, forming tool, forming effector, etc.) have been radically changed. Finally, a complete forming process has been defined, with a complete new set of parameters and tools, which is able to deliver good quality L shaped thermoplastic stringers.
- Thermoplastic T shape stringer assembly process
The technical solution adopted is very innovative. Self-heated tools have been implemented, allowing for a energy and cost efficient solution. A several stages process has been developed able to assembly complete T stringers of 1.2 meters with a representative geometry and good quality.
A total amount of 156 L shaped stringers have been manufactured. The first batch of 106 stringers were used to develop and improve the L shape forming bench, achieving an evolution on the surface quality and an improvement on the geometry reproduction of the part. The other 50 L stringers produced were used on the development of the assembly process. A total amount of 50 T shaped stringers were produced, achieving good quality parts with good compactation degree and geometry. A batch of parts was used for a test campaign performed by the Topic manager, who validated and accepted the T-stringer parts.
Regarding integration tools, the development carried out by Sertec started with conceptual designs based on the use of heating resistances as heat source, these resistances were placed in a vacuum and heating chamber below the machined surface of the table. This concept showed deformation problems for the poor thermal performance due to resistor placement inside a vacuum chamber. After that, the concept proposed for the integration tool switched to a solution where the resistors where embedded inside the top metallic plate to improve heat transmission. After some thermal simulation this concept was discarded due to the excessive technical difficulty to machine the long holes where the resistors where housed.
A new heating concept/system was proposed, based on the heat being generated by currents inside the table material (by means of the Joule effect), in order to minimize the thermal conduction and therefore improve the efficiency of the system. Among the possible solutions, induction was chosen. To test its feasibility, different thermal CAE analysis were carried on, and physical test demonstrator was built as a proof of concept. After having some promising results on the analysis and tests carried on, the development of a pre design for the final assembly tool was started and validated by simulation.
