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Innovative Re-Design and Validation of Complex Airframe Structural Components Formed by Additive Manufacturing for Weight and Cost Reduction

Periodic Reporting for period 2 - AddMan (Innovative Re-Design and Validation of Complex Airframe Structural Components Formed by Additive Manufacturing for Weight and Cost Reduction)

Reporting period: 2018-07-01 to 2020-04-30

Additive manufacturing (AM) is widely acknowledged as an enabler for revolutionising the manufacturing landscape as it can be used to produce industrial parts that are both lighter in weight, cheaper to manufacture, and with complex geometries that are difficult or impossible to realise with conventional methods. The overall aim of AddMan was, therefore, to redesign and manufacture a door component by AM for reduced weight and costs while meeting the prevailing stress and fatigue requirements and regulations.

The AddMan project has been a success as it has accomplished this major market opportunity through:

• Testing and characterisation of AM manufactured parts to determine the effect of geometry, microstructure, surface roughness and residual stresses on material behaviour to enable optimisation of fatigue performance by five different cost effective surface post processing methods.
• Extension of existing Topology Optimisation (TO) techniques for AM specific material characteristics and complex geometries for optimal performance and structural strength.
• Development of Computer Aided Engineering (CAE) methods for metal AM including connection to TO and flexible parametric CAD models to enable holistic product optimisation.
• Demonstration of the applicability of the developed methods and tools, and the gained knowledge by designing and manufacturing a door component made of Ti6Al4V.
P1 Management, dissemination and exploitation set up the necessary processes and plans for the project management, dissemination and exploitation at the start of the project. The website and social media channels were launched. The project has published 6 peer-reviewed papers, 4 conference papers, 3 posters, 5 other reports and given 14 conference presentations and other talks.

WP2 Material properties and post processing performed extensive testing and characterisation of mechanical properties on several different sample geometries to determine effect of geometry, build orientation, microstructure, surface roughness and residual stresses on material behaviour. The testing comprised both as-build and post processed AM specimens. The post processes evaluated were laser polishing, linishing (abrasive finishing), centrifugal finishing, shot peening and laser shock peening. Centrifugal finishing was identified as potentially the most appropriate post-processing method for the demonstrator due to its achieved roughness reduction and ability to access complex geometries.

Topological optimisation (TO) was developed and extended in certain essential ways in WP3 Topology optimisation and structural strength to fully utilise it for AM. First, the communication between Catia software and the general purpose finite element analysis (FEA) software Trinitas was accomplished. Then, a procedure was developed to optimise the AM build orientation considering anisotropic elastic material properties. Two additional design variables were added in order to control the orientation of the material. Uncertain distribution of Young’s modulus in an isotropic material has been derived and implemented in Matlab. Further, both stress and high-cycle fatigue were implemented as constraints in TO. The fatigue damage was integrated for a general loading history including non-proportional loading and avoiding the use of a cycle-counting algorithm.

The WP4 Design for additive manufacturing work was initiated with an in-depth examination of the key process variables through the AM entire process chain (pre-, in- and post) to understand demands for metal AM design and describe the manufacturing flow from concept to end-use part. The WP4 team went through over 1500 different publications in the area of DfAM, design automation, optimisation and relevance of AM to develop an automated process. Then, a further automated framework, connecting TO, CAD and CAE tools with flexible parametric CAD models to allow for a faster product development process, has been proposed. The framework was implemented in different design concepts to show the potential and evaluate manufacturability, costs and performance of the demonstrator as well as enable multi-objective optimisation for cost and weight. A comprehensive guideline with information regarding design, material, manufacturing, and post processing was created at the end.

The practical benefits from WP2, WP3 and WP4 were tested on a real-life door component in WP5 Demonstrator, concepts for weight reduction, Figure 1. Three innovative concepts were developed with different design strategies in mind with the aim to describe different ways of working when designing components manufactured by AM. Then, one concept was down-selected based on weight and performance requirements for the manufacturing. From WP2, Centrifugal High Energy Finishing was selected as the finishing process. A bespoke 3D printed fixture for finish machining was designed to meet required tolerances and surface textures. Inspection results of the demonstrator show tolerances of 0.1mm were achieved, well within the tolerances specified in the drawing. From a structural perspective, the finite element analysis showed that the maximum stresses for all the load conditions were below the limits.
AddMan has advanced TO methods and tools for AM by developing extensions addressing anisotropic material behaviour, build process orientations, graded materials, stress constraints, uncertainty in material properties, residual stresses, fatigue life damage parameters and redundancy requirements for structural safety. AddMan has developed a Knowledge Based Engineering tool for structural AM components to reuse existing knowledge and automate repetitive tasks. The KBE tool is based on a Master Model (MM) approach to reduce gap between TO, CAD, computer simulations, manufacturing and post-processing. The MM enables automatic export of models for different purposes in the design process and has been used in the Multidisciplinary Optimisation framework to evaluate manufacturability, costs and performance as well as enable multi-objective optimisation for cost and weight reduction. Besides this, five different post processing methods were evaluated and optimised to achieve right surface quality and mechanical properties, and make a step closer to serial AM. Finally, AddMan has validated and demonstrated the project results by designing and manufacturing an airframe titanium door component meeting the weight target and the performance requirements. The demonstrator will become a test case on the next generation of cargo doors and aircraft structures under Clean Sky 2.

The work in AddMan has showed a reduction of support material with about 44% without a significant increase of the weight. ‘Buy-to-Fly ratio’ is lower compared to subtractive machining of the fitting from the billet as the ‘Buy-to-Fly’ ratio of the manufactured demonstrator is close to 1. Weight saving of the demonstrator will reduce the fuel consumption over the service life of aircraft as the weight of the demonstrator is 1.52 kg which is lesser than the target of 1.8kg. Reduced manufacturing lead time will also reduce the costs, the build time of the bracket with EBM is 68.4 hrs, i.e. 3 days. By using polymer AM fixture for the finish machining, the lead time for manufacturing of custom tooling (jigs/fixtures) needed for subtractive machining is further reduced.
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