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Quality for AM

Freedom of design, customisation, materials efficiency, lighter components, these are but a few of the many advantages of additive manufacturing (AM) or 3D printing. To switch production successfully to AM, you need more than just a 3D printer. The cornerstones are the design, which often requires a completely different approach and mindset from the designer, and the final quality of the printed components. Quality assurance can only be completed when the process and the raw material are strictly controlled and monitored throughout the entire production process. Sirris invests continuously in their AM infrastructure and knowledge, by means of research projects to keep their AM expertise and services up to date or increase them.

Processing melt pool monitoring data for quality assessment

The development of Selective Laser Melting (SLM) additive manufacturing technology components, especially for the aviation industry, requires quality assessment throughout the production process. Within the Enable project, Sirris has been working on the use of in-situ monitoring systems for easier detection of print defects using non-destructive tests. A melt pool monitoring system and a camera to record production conditions have been added to our machines. However, the enormous quantity of data collected during the monitoring process makes it difficult to process the data and identify print defects. 

New development in processing of SLM melt pool monitoring data

The research objective is to control and process in-situ data in three steps: before, during and after the powder is molten using a laser. The images taken before and after exposure record critical information on the spreading of the powder layer and the quality of the printed layer. Both images are processed to detect anomalies. At the same time, the melt pool monitoring data was analysed using machine learning algorithms. A component was also manufactured to be used as a benchmark to check the accuracy of the proposed algorithms.

The anomalies were successfully predicted and a correlation was found between fault detection for the three analysed data types.

The end objective of this research was to decrease the use of non-destructive tests to detect print defects and to improve the localisation of these defects using a melt pool monitoring system. This type of research project enables Sirris to improve its expertise, in turn ensuring they can guide the industry even better towards gaining insight into additive manufacturing processes.

The Enable project is supported by the European Marie Curie innovative training networks (ITN) H2020-MSCA-ITN-2017 (N°764979).

Residual stress measurement to improve component quality

In additive manufacturing (3D printing), residual stress is introduced as a result of the rapid cooling of metal. The stress depends on the process parameters, the component design, metallurgic effects, etc. It can lead to distortions or cracking during the finishing phase, heat treatment or even in the use phase, and has a significant impact on the fatigue resistance of the metal.

In 2020, Sirris purchased a new X-ray diffraction system as part of the IAWATHA ERDF project. This equipment is used to measure internal stress in metal components using a non-destructive method. Selective material removal using electropolishing enables the measurement of stress depth profiles (from 20 µm to 1.5 mm). Measuring the depth profiles is a destructive test depending on the desired depth. This system is a powerful instrument for both quality assurance and research. Its ability to characterise local stress is key to improve processing conditions.

Unique in Belgium

The main advantage is the portability of the system, which is unique in Belgium. It offers on-site measurement of components of any size, not just test coupons or pieces cut from larger components. This is a major advantage when measuring large printed parts using technology such as wire arc additive manufacturing (WAAM) or laser metal deposition (LMD). For smaller parts with a complex shape, the equipment provides more flexibility, resulting in more options to measure stress in areas that are difficult to access. This new equipment has enabled Sirris to expand their service options further for Belgian industry. It will also provide important insight for the further development of modelling software for 3D printing.

Printing free-form components from hybrid materials using a cobot

Decreasing the material carbon footprint is a general concern and polymer-metal hybrid and polymer composite structures form an important part of this. Regardless of the field of application, the industry is looking for more efficient production methods, to decrease costs as a result of shorter lead times and to add complexity and functionality to standard components, which cannot be achieved using traditional production processes such as injection moulding. For some time, the Sirris experts have been studying options to ensure the manufacturing industry can produce cheaper, more sustainable and accessible hybrid structures. The Product Development Hub purchased a Stäubli Power Cobot for this purpose. In view of our experience in extrusion of exotic thermoplastics, Sirris plans to equip an arm with a pellet extruder, so we can create structures with the freedom of movement of a six-axis industrial robot.

There are many technical options, but our first priority was to add functionality via extrusion on an existing component and to connect to new components on an existing large-scale (metal or composite) substrate that could not be manufactured using overmoulding technology.

Experiments with material connections

A pellet extruder provides the extrusion procedure with more material flexibility. Sirris experts performed experiments with various materials to discover the limits of the procedure. They developed parameters for a few thermoplastics and elastomers and can quickly switch to another material. Lastly, they worked on free-form-printing applications to create hybrid components on composite and metal substrates. Creating strong connections between the substrate and a printed component results in various challenges. We research custom-made solutions, printing on non-flat surfaces and shapes. It is already possible to print very complex shapes on the inner and outer edges of components.

The most important fields of application for this technology are the automotive and aviation industries, where the use of composites is gaining ground. Making components cheaper, stronger and lighter contributes to increasing the efficiency of fuel consumption.