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
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.
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.
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.