Digitization in Plant Engineering Digital Twin Supports Predictive Maintenance

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Magnesium alloys are processed in melting furnaces, where extreme heat and large temperature fluctuations prevail. If the so-called crucible fails, the entire casting cell comes to a halt. Rauch Furnace Technology has drastically reduced this risk by using a digital twin to monitor the crucible condition in detail.

What connects hydropower and foundry technology? They are traditional industries where large forces are at work. They are also considered conservative and often underestimated when it comes to topics like digital transformation. However, this is unjust, as seen in the example of Verbund, the operator of large Austrian hydropower plants, which has been digitally securing the operational readiness of its facilities for years.

For this purpose, real sensors supply the condition monitoring of critical components with current load data. Virtual sensors at critical points also allow for the evaluation of the occurring load and assessment of wear. When defined threshold values that indicate a failure are reached, technicians can take care of maintenance or replacement without delay.

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Digital Twins Have Several Origins

The presentation of the Verbund project at the Cadfem Conference in Linz in 2019 so inspired Florian Sipek, a physicist working for the Austrian specialist in melting technology Rauch-FT, that he applied the "lessons learned" to his own solutions. It is important to consider that melting furnaces are quite complex: when metals are melted, recycled, and alloyed, temperatures reach up to 2,000 degrees Celsius (3632 °F), gas flows reach speeds of up to 1,000 km/h (approx. 621 mph), and load changes are the norm.

Greater reliability of the melting systems is of great importance to operators. If a system suddenly stops, not only is there a risk of damage to the furnace but also significant production delays or outages. In the worst case, there is a risk to employee safety.

Thus, the idea was born to use digital twins to significantly reduce such risks by making problems visible early on. Additionally, Rauch-FT aims to provide customers with valuable insights during ongoing operations, meaning they can be alerted to maintenance or cleaning needs.

Data and Simulation Knowledge Perfectly Orchestrated

In foundry technology, there were previously no comparable approaches. Rauch-FT, like its inspirer Verbund, tackled the challenge with Itficient and Cadfem: Itficient was responsible for data management, business model, and IT architecture, while Cadfem focused on simulation—from flow to various transient and nonlinear structural mechanical applications and sensitivity studies to system simulations including condition assessment. Thus, Rauch-FT was well-prepared for the digital twin.

On the one hand, many systems and components are already being simulated. This mostly involved fluid mechanics, with the range extending from transient cooling and heating processes to operations in dosing or flow pumps and even chemical reactions. On the other hand, a large data pool is already available via remote maintenance alongside a powerful IT infrastructure. The evaluation of this data provided valuable insights into the operation of the furnaces.

How Long Does the Crucible Last?

The ideal component for the first practical implementation is the crucible. The welded steel construction is highly stressed: "2,000 degrees Celsius (3632 °F) hot exhaust gas outside, corrosive shielding gas, and hydrostatic pressure from up to 4 tons of molten metal inside," explains Florian Sipek. "Additionally, there are extreme temperature gradients, the radiant power of the flame, and high speeds with inhomogeneously distributed radiation energy." If the crucible fails, the system comes to a halt.

Maintenance is usually based on experience, which can work—in an ideal world. However, as soon as irregularities occur in the processes or handling, failure and consequential damage threaten. "That's exactly when the added value of predictive maintenance becomes apparent," Florian Sipek summarizes.

Influences of Segregation

The approach to digital condition monitoring of the crucible is based on a combination of real measurements and virtual sensors. Due to the segregation occurring in the melt (settling of certain chemical compounds), a "sump" forms at the crucible bottom. This locally changes the flow conditions and the material parameters of thermal conductivity and heat capacity, disrupting heat transport from the furnace chamber to the melt at the crucible bottom. Combined with the inhomogeneous temperature distribution on the outer wall, high stresses are generated in the crucible.

The sump quantity is therefore an important parameter for a correct assessment of the real-time stress on the crucible, and thus also for the reliability of predictive maintenance. Due to the environmental conditions in the crucible and furnace, the use of real sensors for temperature measurement is hardly possible. Thus, Cadfem's concept included virtual sensors for the simulations. Together with a sump quantity calculated from the temperatures and the process parameters, this allows local stress on the crucible to be inferred from just a few measurement points and input variables.

For predicting the remaining service life of the crucible, precise modeling of the temperature distribution in the furnace chamber through flow simulation (Computational Fluid Dynamics, CFD) and stresses at the weld seams (structural mechanics, FEM) is essential. On the CFD side, a combustion simulation of the burner and furnace chamber is conducted for accurate prediction of the flame temperature, thermal radiation, and momentum input. Based on the CFD results, a temperature field and stress analysis are performed, with the melt as a variable heat sink to model the melting of inserted ingots.

IT Integration and Digital Twin

The digital twin must reflect the individual conditions at the end customer—in the processes being modeled as well as in the used IT infrastructure. Therefore, a concept for IT integration is an important building block in the implementation. This involves processing sensor data, operating the digital twin, and addressing security and network issues. Itficient was able to build on a data pool and an IoT platform. The necessary microservices—receipt of sensor and machine data, calculation of virtual sensors, models and processes, data storage and analysis, as well as visualization of results—were integrated in such a way that IT resources were utilized optimally, no IT silos were created, and Rauch-FT retained full control over all processes, allowing it to further develop the system independently.

A powerful digital twin encompasses two essential aspects: accurate simulations and a reliable IT infrastructure. The project becomes successful when both aspects interlock. This has also been achieved at Rauch-FT because Cadfem and Itficient, two partners with extensive experience in their respective fields, were involved. At the same time, they maintain close communication with one another, being both organizationally connected as part of the Cadfem Group.

The third partner is Rauch-FT, supported by its pilot customer Georg Fischer Casting Solutions, who achieves greater occupational safety for employees with the digitally monitored melting furnace. In-depth product knowledge, openness to new ideas, extensive communication, a clear vision of what is to be achieved, and the involvement of all company areas in the project were the keys to success. Existing competencies were integrated, some tasks were carried out cooperatively, while others were outsourced as pure services—always in the spirit of complete knowledge transfer.

Scale Up Acquired Digital Twin Capabilities

Because the crucible was only the starting point—Rauch-FT wants to scale up the acquired capabilities for planning, building, and managing a digital twin and, in the future, provide all relevant components such as dosing pumps, heating systems, or circulation pumps and entire systems with digital solutions for predictive maintenance.

This vision does not end with our own products. A typical die-casting cell consists not only of the melting furnace but also of other components from various manufacturers. Whether it's robots, presses, heating/cooling devices, or the die-casting machine itself—in the foundry, almost every component has potential for the digital twin.

*Alexander Kunz is an editor at Cadfem Germany, Florian Sipek is Head of the R&D Department at Rauch Furnace Technology GmbH.

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