Reducing energy costs in die casting with bivalent furnace
The energy consumption of melting and holding furnaces is high. At the same time, the price often fluctuates significantly over the course of the day. A bivalent furnace should now switch dynamically between gas and electricity without interrupting the production process. Depending on which energy source is more cost-effective. The oven is being developed by the Fraunhofer Institute for Manufacturing Engineering and Automation together with partners.
Pressure die casting is one of the most efficient moulding processes. Hundreds of thousands of castings can be produced quickly with just one mould. But like so many industrial processes, this production method is extremely energy-intensive, with crucible furnaces leading the charge in terms of considerable energy consumption. Such furnaces are used to melt metal ingots which are then pressed into a metallic mold at high pressure and speed. The total energy consumption of German light-metal foundries is accordingly high; it was recorded at 4.4 terawatt hours by the German Federal Statistical Office in 2019. The concept of making the production process energy-flexible creates the possibility of balancing out fluctuations in the electricity grid and thus reduce their production costs.
Bivalent furnace technology is the key to energy-flexible operation. „Furnaces are typically operated using only one energy source — either fuels such as gas and oil or alternatively electricity. Bivalent crucible furnaces, however, can switch dynamically between electricity and gas during operation. This technology has not been available until now,” explains Alexander Mages, a researcher at Fraunhofer IPA in Stuttgart. “It means that we can use different energy sources to cover the energy requirements of crucible furnaces in any operating state.”
Designing energy consumption flexibly
Due to the high energy consumption of melting and holding furnaces, the price of the energy source used represents a significant cost factor in the production of castings. The price also fluctuates significantly within a day. Reasons for this are, for example, that the electricity grid is utilized to varying degrees or that the energy from renewable resources is volatile.
Together with its partners Hindenlang GmbH, Bark Magnesium GmbH and the Institute for Energy Efficiency in Production (EEP) at the University of Stuttgart, the Fraunhofer Institute for Manufacturing Engineering and Automation IPA is developing a bivalent furnace that enables dynamic switching between the energy sources gas and electricity. In this way, energy-flexible operation can be realized and energy can be used when it is cost-effective.
The research team had modelled various heating concepts, optimized plant designs through thermal simulations and implemented the bivalent design into a crucible furnace. The crucible furnace forms part of a plant center including punches, presses and CNC machines at Bark Magnesium GmbH’s die-casting foundry. Tested successfully in April 2023, it was commissioned in May to melt magnesium ingots.
Uninterrupted production processesGiven that the melt has to be kept at a constant operating temperature, the researchers’ aim was to use energy flexibly, at ideal electricity prices, without having to interrupt the production process due to a changeover. This means that the bivalent furnace can be switched to gas operation when the electricity price is particularly high — for example, due to the regular increase of electricity consumption in the mornings or evenings. When prices are low, on the other hand, the system switches to electricity operation. “An energy-flexible demand for electricity can contribute significantly to reorienting our electricity system toward renewable energy generation. Industrial companies account for 44 percent of our total electricity consumption,” says Mages.
Operators can switch manually between electricity and gas using the furnace control system or the furnace switches automatically via a signal issued by the hall network. Likewise, the hall network connection provides the option of switching after receiving a signal from the electricity supplier. “By switching the energy source, the process start time does not have to be postponed to when electricity prices are low, nor do shifts have to be adapted to accommodate break times. These are common measures to achieve flexibility in terms of energy,” the researcher points out, explaining another advantage of the bivalent furnace.
The furnace was developed as part of the Kopernicus project SynErgie II, funded by the German Federal Ministry of Education and Research (BMBF). An application has already been submitted for the follow-up project, SynErgie III, which aims to optimize the furnace, including its heating and network design. Using thermal measuring elements, the project partners are determining parameters such as temperature distribution in the furnace to draw conclusions about energy efficiency. They are also testing whether the furnace can be operated with hydrogen. “It’s almost as if we are conducting research on a live object,” describes Mages.