Challenging the God of Winds – Making “One Shot” Possible with Simulation, 3D Printing and Casting
The example chosen in this study is an Ebay access door located at the nose fuselage which is used by operators for airplane inspection and maintenance. The Ebay access door turned out to be an interesting case study in many ways as the team faced some tricky engineering challenges: The door is too big to be feasible using DMLS (about 800 mm x 500 mm x 250 mm), it is made of AS7G06 aluminum which is not yet qualified in aeronautics using DMLS, and it possesses a very thin skin with very tight dimensional and geometrical tolerances.
Named EOLE after the Greek god of winds, the study describes the investment casting applied on an aircraft access door. The manufacturing process is based on investment casting from a 3D printed resin pattern. The EOLE study was led by SOGECLAIR aerospace and was done in collaboration with CTIF, Ventana, and voxeljet. voxeljet is a leading manufacturer of 3D printing systems for industrial applications that specializes in Powder-Binder-Jetting of plastic and sand.
The major technical problem addressed in this project was casting an aircraft access door (class 2F part) in “one shot” and nearly net shape integrating a thin skin with organic stiffeners. With the aim to demonstrate that this is possible, the engineers involved in this study followed a systematic roadmap ensuring that all project requirements are met. The optimization study lasted about two months, involving eight topology optimization runs and four mechanical stress checks to achieve a satisfying design.
Among the many challenges the engineers faced in this project, two were of utmost importance. For casting, the skin thickness had to be set at the minimum feasible wall thickness. This is important because the outer surface of the door, considered a part of the fuselage, has to fulfill very tight dimensional and geometrical tolerances. Another tricky point on the access door was the connection between the skin and the stiffeners. In order to handle this, SOGECLAIR aerospace sketched some ideas which were used for a CAD model and the subsequent process simulation.
At the beginning of the study, topology optimization was used in the concept phase of the design process to optimize the material layout within a given design space, which was one of the main constraints. In a subsequent FE analysis, the engineers investigated the optimized design.
The ensuing casting simulation, in particular solid fraction, enabled the engineers to improve the design of the part and to minimize the presence of defects (shrinkage, cracks, etc.).
Filling and solidification simulations were run in order to accurately predict the position and size of certain defects such as incomplete filling areas or air bubbles. Then, feasibility samples were made for representative areas of the aircraft access door, especially the trickier ones. On the basis of these samples, SOGECLAIR aerospace finally manufactured the access door at real scale, and 3D printed it in PMMA resin using the binder jetting technology. According to this procedure, the resin was first soaked into barbotine and coated with a shell composed of several layers of sand to build the mold. Next, the mold was heated and the resin could be eliminated. Finally, the access door was casted and heat treated after removal from the mold. The result was an optimized access door, which aside from the correct dimension, fulfilled all the important requirements of this project.