Accelerating the adoption of laser powder bed fusion using digital integration

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Rita Bola, project manager at EWF, describes how digitally integrating the process steps of laser powder bed fusion will help accelerate its adoption in industry

Manufacturing, be that of either small or large parts, is ripe for the seismic change being brought about by Industry 4.0, which is already fast sweeping through all industries, regardless of their sector or geographical location.

A technology quickly coming of age that is set play an important role in this digital transformation of industry is additive manufacturing (AM), which like Industry 4.0 holds the potential to cause disruption across all sectors. In the not-so-distant future, printing structures on demand and on location with a range of diverse materials will become commonplace, providing unrivalled flexibility and a significant reduction in both cost and post-processing time.

But the fact is that there are still technological hurdles that need to be overcome which are hindering the expected increase in adoption of AM.

One AM technique facing such hurdles is laser powder bed fusion (PBF-LB), a process that has been available for over 20 years and which overall has fewer manufacturing constraints than traditional subtractive and formative manufacturing processes. However, it has still not lived up to its promise.

The reasons for this are many-fold: PBF-LB is slow and expensive, its overall efficiency is low, it has a limitation in the part size that can be manufactured, and it usually requires several iterations of builds to get up to the expected level of quality. This results in the need for a large amount of inspection and destructive testing.

Finding a solution to this conundrum will therefore create a fast track for the adoption of this promising and maturing technology.

Time to go digital

By digitally integrating all the steps of the PBF-LB process chain – the design, build and post-build processes – the partners of the ENCOMPASS project are tackling this problem. Together they are improving the efficiency and capability of the overall AM chain, and in doing this are contributing to Europe’s relevance in global leadership and innovation for the foreseeable future.

The project partners include some of the leading organisations in the field of AM, including the Manufacturing Technology Centre, Renishaw, Rolls-Royce, Altair and the University of Liverpool (UK); Fraunhofer ILT and ESI Group (Germany); ITP Aero (Spain); DePuy Synthes (Ireland); the European Welding Federation (Belgium) and Centro Ricerche Fiat (Italy).

Through their collective expertise these partners are concluding the developments on a software-based integrated design decision support (IDDS) system for PBF-LB and have provided a test case for its effectiveness.

Figure 1: Structure of the IDDS (Integrated Design Decision Support) System (Credit: ENCOMPASS project)

The IDDS system (see figure 1) provides integration at the digital level to enable synergies between the steps of the PBF-LB process chain. With it the partners aim to: provide a user support interface within a CAD environment; provide digital tools for simulating and optimising melt strategies; provide digital tools for simulating post-build material and quality processes; apply monitoring solutions for key variables of the post process; and develop a framework for the optimisation of PBF-LB products and process design.

The developed system is being tested with Rolls-Royce and IPT Aero to prove its positive impact in reducing the amount of materials and energy used to produce titanium parts for the aerospace sector. In addition, the automotive tooling and medical sectors are also set to benefit from the results of the ENCOMPASS project.

Big challenges

Before the new IDDS system could be developed, the ENCOMPASS partners had to identify the hurdles that had to be overcome. These were many-fold, and ranged from issues concerning the existing decision support and geometric design tools for PBF-LB, to the complex requirements for component simulation and post-processing.

While there are a number of tools for conventional manufacturing process chains when designing a part for PBF-LB, or AM in general, there are very limited tools available to enable the checking of a particular geometry for manufacturability.

There are also many AM process decision selector tools available1, which aim to help identify the most appropriate AM process to develop a particular component based on direct inputs from the user – component characteristics such as material, size, tolerance, surface finish etc – but these also have significant limitations.

The ENCOMPASS project has resulted in the development of a software-based integrated design decision support (IDDS) system for laser powder bed fusion (Credit: ENCOMPASS project)

In addition, current geometric design tools on the market exploit the design freedom of AM – such as lattice structure and topology optimisation software – enabling geometrically complex and lightweight components (‘design for performance’), however they don’t include AM-specific manufacturing constraints, let alone PBF-LB-specific constraints. These tools do not take into account post-processing – specifically access for support removal, access for inspection, and consideration of orientation and support for surface finishing.

Lastly, while component simulation can be used to inform decision making at the design stage, design rules based on physical predictions of distortion during the build have not yet been developed, due to the computational challenges and specialist software required.

Bigger goals

In addressing these numerous challenges, the ENCOMPASS project sort to do the following: enable an average 42 per cent reduction in time from ‘design to piece’, an average 27 per cent increase in overall process chain productivity, and an associated decrease in cost of production by 26 per cent – estimated using methodology from the EU project AMAZE2.

This would be made possible by achieving a 43 per cent average reduction in design time, a 51 per cent average reduction in quality control time, and a 46 per cent average reduction in post-processing time.

Designed to accomplish just that, the fully digital IDDS system developed within ENCOMPASS has four distinct elements (as shown in figure 2): Component design, process design, process chain design, and optimised component & process design.

Figure 2: ENCOMPASS Representation Scheme Workflow (Credit: ENCOMPASS project)

The system, based on a newly developed extensible architecture, considers the whole PBF-LB process chain and integrates in an optimal way with the design workflow. It considers the context of topology optimisation (and concept design more generally), the generation of geometric CAD models, and orientation dependence of the design rules. It links to the whole process chain design rule database (including knowledge of the PBF-LB process, post-processing and inspection) and enables current product, process and process chain design.

The extensible architecture developed by the partners includes an extended data format for data exchange, as well as a CAD-based user interface, with suggestions of product and process redesigns. The extended data format covers the whole process chain, including post-processing and quality control, building on previous standards and ensuring compatibility. A knowledge repository based on functional workflows supported by the new data format, including the whole process chain, is also being developed.

Conclusion

The IDDS system being developed within the ENCOMPASS project, which will conclude in February 2020, will provide a new and effective approach to the fast adoption of powder bed fusion. It will empower developers of AM processes to capture their process data in a structured way, as well as add to the design rules of AM and thus accelerate the maturity of the process. While the system is initially aimed at PBF-LB, the techniques will in the future be further developed by the consortium to cover other processes.

A sample piece developed using the ENCOMPASS IDDS system (Credit: ENCOMPASS project)

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