Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - Ascent AM (Adding Simulation to the Corporate ENvironmenT for Additive Manufacturing)

Teaser

The achievement of the Clean Sky 2 (CS 2) objectives, concerning the reduction of CO2 and fuel burn by up to 30 % as well as the reduction of NOX by up to 40 %, is strongly associated with the availability of innova-tive technologies and adapted structural design. Additive...

Summary

The achievement of the Clean Sky 2 (CS 2) objectives, concerning the reduction of CO2 and fuel burn by up to 30 % as well as the reduction of NOX by up to 40 %, is strongly associated with the availability of innova-tive technologies and adapted structural design. Additive manufacturing (AM) is one of the key enablers and thus inalienable to reach these goals. First simple aero engine parts manufactured by AM processes, like laser beam melting (LBM) have successfully been introduced into mass pro-duction. To use all possible benefits of the technology like e. g. design freedom, cost efficiency and a reduced time to market, first time right pro-duction is essential. One major issue are the distortions after production. Employing manufacturing simulation to support process development is a promising approach to realize first time right production. Current simula-tion models however, fail to calculate distortions within an acceptable time frame and do not respect post-processes such as stress relief an-nealing. Thus, the goal of this project is to integrate a suitable simulation-based process chain into the tool landscape for AM process preparation that enables a prediction of distortions with high accuracy in reasonable time to generate benefit for AM users. The main focus lies on the metal-based layered manufacturing process of LBM as this is the most wide-spread approach to generating three-dimensional parts from powder ma-terial.
The following four objectives are set out for the proposed work:
Consideration of real life AM
Current simulation systems for the LBM process cover only the actual build-up process for simplified geometries. The proposed project aims to incorporate a creep model to enable the simulation of the stress relief an-nealing and a digital data chain for the pre-deformation of the input de-sign both with measured and simulated results in order to complete the process chain and to increase shape accuracy. Additionally, the simula-tion of industry relevant geometries as well as current and future devel-opments of LBM systems is realized.
Acceleration of simulation
With simulation results of small scale parts ranging in the order of days, the practical benefit of simulation is limited. The goal of this project is to use modelling techniques, adapted numerical methods as well as an effi-cient automation of data handling to decrease the duration of LBM simu-lations to be in the range or lower than the manufacturing time. With the implementation in an open source environment, all auxiliary processes can be tailored to the specific needs of the tool chain which increases the overall efficiency.
Increasing usability of AM
The LBM process itself is highly automated. However, certain downstream and upstream processes require a lot of manual work by an expert. There-fore, a digital data chain will be established in the simulation tool chain to support the worker in these processes. To increase usability of AM, the goal is that after the provided training sessions every participant is able to run the system without further expertise. The flexibility of open source programs will be used to automate all processes as far as possible. An exhaustive documentation is made available in addition to the source code itself, providing users with full insight and traceability.
Increase fidelity of predictions
The predictions of current simulation tools present valid tendencies of the actual warpage. However, in order to reach the goal of a first-time-right manufacturing, the quality of the results as well as the shape accuracy of the underlying mesh are required to increase. With the results being ac-curate enough to be used directly for the subsequent manufacturing, the way towards a simulation-based process chain is paved.

Work performed

The following results are achieved in the project AscentAM so far:
• A simulation tool for laser beam melting with the open source tool CalculiX is established. A sequential coupled thermomechanical model is implemented in to order to calculate the deformation and the induced residual stresses of a part after the build-up process.
• An optimization procedure is implemented which uses the results and iteratively pre-deform the geometry in order to find an optimal input geometry.
• A CAD-based data chain is developed with a maximal deviation of the FEM mesh on the range of the real layer height. The data chain includes a re-engineering of the CAD model with the pre-deformed mesh from the simulation.
• The calculation is accelerated by the development and implemen-tation of a LBM-specific direct solver and an adapted multi-rate method which takes advantage of the layer-wise partitioning of the part. In addition, the required time steps for the structural calcula-tion are reduced without loss of accuracy.
• A characteristic time scale is introduced in order to allow the trans-fer of the thermal history from a layer scale to a part scale.
• Heat management strategies are implemented to identify heat ac-cumulation during the build-up process and to adjust the energy input in those regions.
• The continuous verification and validation methodology is set up as a continuous integration process directly in gitlab.

Final results

A fast and accurate simulation tool for laser beam melting is established which takes into account the part-specific thermal history for the calcula-tion of the distortion and induced residual stresses of a part after the build-up process.
Support structures are indispensable for the manufacturing of complex parts. There are different types of support structures, most of them are fili-gree. The aim is to derive a fast and efficient consideration of those struc-tures in simulation in the further project. The focus will be on modelling of support structures, but also general filigree areas which belongs to the actual part will be regarded.
Creep experiments are conducted in order to generate viscoelasticity models for the simulation of stress relief annealing. As the proposed work also targets to determine whether creep is relevant for the build-up pro-cess itself, an analysis of relevant creep mechanisms is conducted. If ap-plicable, a combination of different models for the different process steps is employed.
This project possesses direct impact for the AM industry that enables e. g. shorter design cycles and less material waste. Additionally, the project will contribute to the establishment of AM as an alternative form of production to conventional casting and machining that provides advantages not only in the manufacturing of single parts, but also large-scale production. The direct impact of the project as well as the progression of additive manufac-turing in general contributes to the objectives set out in Clean Sky 2 pro-gramme for a more environmentally friendly air traffic and an increasing European competitiveness.

Website & more info

More info: https://www.iwb.mw.tum.de/ascentam/.