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In situ manufactured carbon-thermoplast curved stiffened panel

Periodic Reporting for period 2 - INSCAPE (In situ manufactured carbon-thermoplast curved stiffened panel)

Reporting period: 2017-07-01 to 2018-05-31

Objectives of the project
INSCAPE’s main objective is to enhance the automated thermoplastic fiber placement process and machine to manufacture an in situ consolidated (AFPisc) double-curved structure including in situ joining of stiffener and skin laminate.
This production strategy is a fundamental change compared to the state of technology, where composite structures typically build within process chains. AFPisc is integrating the major steps of material deposition and consolidation and represents a technology today named as 3D printing or more precisely described as additive manufacturing.
Technical objectives and achievements (...):
• Development of the AFPisc process to meet aerospace requirements, including joining for reduced assembly efforts. (Partially achieved except full aerospace quality grade).
• Weight reduction by 20% of final structure compared to state of the art joined panels. (No testing on subcomponent level was performed within the project, therefore reduction is a theoretical consideration).
• INSCAPE aims for an overall reduction of manufacturing time of 50% compared to todays mutli step processing chains. (Ony in best case scenarios achievable, where AFP can be used at its best performance).
• Reduction of additional downstream quality assurance procedures. (Offline manufacturing data evaluation demonstrated, further data qualification needs to be done in future).
Scientific objectives:
• Parameter study on mechanical and physical properties of in situ placed laminates (laminate in-plane properties) and of in situ joined structures (inter-plane properties of joint) - (Intensive test campaign was performed on PEEK-CF tapes).
• Feasibility to integrate lightning protection layer into fiber placement process (Could not be demonstrated).
Ecological objectives:
• Reduction of manufacturing scrap by 15% compared to standard thermoset prepreg part production. (Could be demonstrated).
• No need for vacuum bagging and other consumables like backing papers, no frozen material logistic required. (Could be demonstraded).
• Energy efficient low carbon dioxid processing. (Performed LCA has shown up to 50% improvement at relevant impact indicators for AFPisc).
• Reduction of number of tools required to manufacture a stiffened panel assembly. (Could be demonstrated by additive manufacturing approach on male mould).
• Enabling new high performance recyclable thermoplastic polymers with excellent FST properties for future aerospace part production. (PEEK as well as PEKK based tapes are theoretically recycable, but available amount of waste material prevents efficient recycling today.)
• The in situ joining process enables a one material design approach for future aerospace parts. (Could be demonstrated.)
Summarizing INSCAPE develops a new manufacturing approach for future lightweight structures used in aerospace application with the impact of more ecological friendly material, production and improved recyclability after end of use, higher productivity due to an automated manufacturing setup with high reproducibility and flexibility and therefore shall strengthen the future production of aerospace structures in highly developed societies with the ambition of high ecological and social standards.
The technological base of the project is an AFP machine capable for in situ consolidation installed in 2012 at TUM and supplied by AFPT GmbH
INSCAPE implements the demands of the aerospace industry with additional requirements in terms of quality, productivity, flexibility and intensive use of full 3D placement as well as the integration of subcomponents like thermoformed stiffeners and spars.
Project activities:
• Developments on machine hardware
• Design work related to the demonstration hardware
• Material and Process development, process demonstration as well as material performance characterization
These activities correlate with the project partners experience whereby the AFPT GmbH is focused on machine hardware development and machine code generation, FACC AG as composite component supplier to the large aircraft manufactures, concentrate on demonstrator and tool design. The scientific partners put emphasis on the material and process development topics.
Operation on 3D curved panels as well as improved performance and improved contour accurate layup required a higher complexity compared to the existing single tow head design. Two development trajectories were driven: A new head design for new hardware and a technology prove by modification of the existing hardware.
The component design was performed within CATIA Composite Design for laminate definition, but transfer to an offline machine programming environment is limited. There’s no consistency between CAD and CAM. Individual approaches were required to enable the demonstrator manufacturing. An adapted version of CGTech VERICUT software is used for 3D offline programming the skin placement code.
Even the main manufacturing stream of INSCAPE is based on AFPisc processing, two alternative routes had to be prepared by TUM for stringer manufacturing. The interaction of both processing routes were proved within the manufacturing and demonstration activities.
The demonstrator manufacturing has revealed major influences of the solid aluminium tool. Big difference in heat transfer properties between mould and carbon fiber laminate (stiffener profiles) requires specific control strategies for the AFPisc process. Typically controlled by a closed loop control, no predictive actions can be performed. But this is a requirement for the in situ joining process. Therefore hard coding of machine parameters linked to position information had to introduced for advanced demonstrator manufacturing.

PEEK and PEKK based CF tapes were investigated for their processability. Fiber and resin distribution as well as homogenity and resin flow behaviour are critical characteristics for AFPisc.
Project partner INEGI performed an intensive material characterization program, based on panels produced with the demonstrator manufacturing setup. The mechanical performance could not fulfill the high expecations for aerospace use. Insufficent interface creation, indicated by porosities, are assumed to be a major reason. The optimization of the tape material for use in the AFPisc process is one recommendation. The optimziation of processing parameters are the second topic to close the gap to an aerospace quality level.
The aim of the applied project is to develop an advanced additive manufacturing process beyond the state of the art which enables light-weight design at proper mechanical performance under ecological friendly conditions.
The main challenges are:
• In situ placement of customized blanks with the TP-AFP head; the thermoplastic tapes are laid and consolidated in one step (in situ) before hot forming instead of applying a cost and energy intensive consolidation process
• In situ joining of the stiffened structure; the skin layers are directly (in situ) placed on the stiffener flanges. No further joining between the parts is needed.
• Improve process performance in terms of material through put, process robustness and laminate quality also in terms of multi tow operation
A new way of future lightweight composite manufacturing shall be developed and demonstrated.