With the automotive industry putting emphasis on lightweighting and sustainability for several decades, there has been continuous growth in the use of aluminum. This is due to the material’s light weight, excellent mechanical properties, corrosion resistance, and processing possibilities. In response to this demand from the automotive market, Hydro has been working to increase the use of post-consumer scrap in its high quality aluminum products. One recent such investment occurred at the aluminum recycling plant in Rackwitz, Germany, where the company officially opened the new HyForge casting line in September 2023. The €40 million investment increased the recycling of post-consumer scrap and enables the production of small diameter forging stock with high surface quality for the automotive industry.
Background
Founded in 1925, the Hydro Rackwitz casthouse has decades of experience in the recycling of aluminum. The site handles around 85,000 tonnes of scrap per year, including 20,000 tonnes of post-consumer scrap from the automotive, building and construction, and general engineering industries. The use of recycled scrap enables the plant to cut emissions and deliver products with a very low carbon footprint.
“Rackwitz is an integral wheel in Hydro’s recycling growth strategy, serving as a specialty casthouse, focusing mostly on automotive products,” said Marijn Rietveld, director of Innovation & Strategic Partnerships at Norsk Hydro. “The location in Rackwitz enables us to serve the region’s automotive industry hub as more customers pursue their aim to decarbonize. It also provides good access to post-consumer scrap, providing significant customer value and contributing to the circular economy.”
The majority of the production is in the form of billet for the extrusion industry. In the extrusion ingot production area, Rackwitz has two melting furnaces, three casting furnaces, a vertical casting machine (with seven diameters, including 152 mm, 178 mm, 203 mm, 228 mm, 254 mm, 305 mm, and 382 mm), a continuous homogenizer, a batch homogenizer, ultrasonic testing, saw and packaging station. Extrusion billet is available in 6060, 6061, 6082, and 6005 alloys for building and construction, transport, industry, and automotive applications.
With the expansion in 2023, the facility added a new casting line for the production of HyForge forging stock. Rackwitz now has the capacity to produce 95,000 tonnes of extrusion ingot and 25,000 of forging stock per year.
The Rackwitz casthouse is certified to the ISO 9001, 14001, 45001, and 50001 standards for its management, occupational safety, environmental controls, and energy efficiency. In addition, the site received the Aluminium Stewardship Initiative (ASI) Performance Standard in recognition of its sustainable production and procurement. It also recently obtained IATF 16949 certification for supply chain management.
HyForge Technology
Car manufacturers are increasingly using closed die forging to manufacture aluminum wheel suspension parts. Forged aluminum parts can reach 400 MPa, which provides a combination of lightweight design, high strength, durability, and fatigue resistance properties. These components also play a significant role in improving the required noise, vibration, and harshness properties of the vehicle.
“The European forging market is divided into steel and aluminum solutions,” said Rietveld. “With ongoing demand for lightweighting electric vehicles, aluminum solutions can offer as much as 30–40% weight reduction over a steel solution. Newer platforms often are designed with an aluminum forged component. Forged components can be found as chassis parts, such as steering knuckles, but we also see applications such as brackets for the e-drive. These are new applications that arise from battery electric vehicle (BEV) development.”
Forging stock generally has a smaller diameter than traditional aluminum billet and requires a superior surface quality. As a result, producing forging stock tends to have a relatively high production cost due to the multi-step process involved. Generally, after casting, the billet has to be further processed to remove the outer skin in order to remove the inverse segregation zone. This typically has been achieved by either extruding or scalping the material to provide a better surface, which added both processing time and cost to production.
In order to address this challenge, Hydro developed its HyForge forging stock, which is manufactured in a single step. The stock is produced using advanced casting technologies that significantly reduce the inverse segregation zone, making it possible to skip the additional processing steps and forge the ingot directly into high-quality automotive components.
Hydro produces this HyForge stock using two casting methods. The low pressure casting (LPC) technology, developed by Hydro Aluminium and Hycast and implemented at the Husnes smelter in Norway in 2021, is a form of gas cushion (GC) billet casting technology that performs the casting process under vacuum, nearly eliminating the inverse segregation zone. The second method is the HPI ForgeMaster® technology, which is a horizontal casting method that was recently started up in Rackwitz. The LPC technology in Husnes is utilized for the production of larger diameter forging stock, while the HPI technology is being used to produce smaller diameters.
Hydro is now expanding HyForge production into the U.S., with the installation of a US$85 million casting line at its plant in Henderson, KY. The company has not yet stated which HyForge casting technology will be implemented, but the project will add 28,000 tonnes of aluminum forging stock for the U.S. automotive market. The new line will become operational in 2026.
New Rackwitz Casting Line
The construction of the Rackwitz HyForge line took just over 14 months. The project included the construction of several new buildings, including the furnaces and casting building, as well as an additional scrap yard and indoor finished goods storage to ensure excellent surface quality when the stock is delivered to the customer. In addition, Hydro revised and optimized the internal logistics throughout the entire plant to ensure efficient material flow.
“The benefit of the Rackwitz HyForge project was that we could leverage the knowledge we had gained from our market entry with primary HyForge ingot at our Husnes primary production plant in Western Norway,” said Rietveld. “Our understanding of the market trends and needs supported the decision-making process, as well as the fact that we wanted to build on the strong experience of specialty and automotive products in Rackwitz.”
The scope of the new casting line includes a state-of-the-art twin-chamber melting furnace, two casting furnaces, a horizontal casting machine, an ultrasonic testing line, a peeling machine, a chips treatment line, and a packing line. “For the HyForge product, we need to fulfill highest metal and surface quality standards and therefore have selected benchmark suppliers leading in their individual fields of technology,” said Rietveld. “The major elements were certainly the furnaces supplied by Jasper, as well as the casting machine from HPI.”
The dedicated twin-chamber melting furnace from Jasper enables the plant to efficiently melt a high amount of contaminated post-consumer scrap, as well as production scrap from customers and chips generated during the peeling process. The material is charged onto the dry hearth of the scrap chamber via a rotatable, fully automated charging machine supplied by RIA. The dry hearth is long enough to achieve the resting times required to reach full gasification of any organic contaminants on the scrap, as well as preheating the material before it enters the liquid sump. Hot metal from the main chamber is circulated through the scrap chamber using an electromagnetic pump, which also feeds the peeling chips into the furnace. This enables the furnace to increase energy recovery and metal yield.
“Although we are consuming a lot of post-consumer scrap with organic contaminations on it, we have the ideal and dedicated technology available to handle this,” noted Rietveld. “The special melting furnace uses the organic contaminants, such as paint, lacquer, or oil on the scrap as secondary fuel. The fumes generated in the furnace are cleaned in a state-of-the-art baghouse filter plant and the air that is released to the environment via the chimney is well within the strictest and latest limits and standards.”
Around 80–120 tons of molten aluminum is transferred from the twin-chamber melting furnace to one of the two casting furnaces, each of which has a capacity of 25 tons (Figure 1). During this transfer, the liquid aluminum is processed through a Hycast SIR degasser to ensure high melt quality. The two casting furnaces operate together as a pair. While one casting furnace supplies metal to the casting machine, the other one is being filled, alloyed, and settled, so that it will be ready to take over casting when the first one is empty. This allows for continuous operation of the casting line, while also enabling throughput to be flexibly adjusted and synchronized with the demand of metal at the casting machine. All three furnaces are equipped with regenerative burners and Jasper control systems, both of which are designed to keep energy consumption and emissions from the furnaces as low as possible.
While horizontal casting used to be characterized by numerous demanding manual activities, the new HPI ForgeMaster line installed in Rackwitz is designed to bring the process of horizontal casting of forging stock into the new millennium. Innovations include the reduction of manual activities, increased automation that supports various casting activities without the need for operator support, and safety improvement for personnel.
Once the starting conditions are met, the interface notifies the operator that casting can commence, and they initiate the process. The furnace is tilted to the desired level in the casting trough and the dams for filling are automatically opened and closed, while the system checks that proper temperatures have been attained (initiating a flushing routine, in the event the metal is too cold). The ForgeMaster system optimizes solidification conditions and ensures a more uniform distribution of material properties (due to improved microstructural isotropy), resulting in a minimal border zone and limiting losses due to peeling. The casting line is able to produce forging stock in diameters from 42 mm to 110 mm with high surface quality.
In addition, the HPI casting line is designed to simplify the maintenance of the molds, eliminating the tedious task of replacing the graphite pins with pressing and drilling holes. In the new line, the mold is heated and replaced as a simple wear part. All these combined factors contribute to enhancing the cost-effectiveness of the ForgeMaster process route.
The entire HyForge production line is controlled via Hydro’s in-house automation system, which communicates with all of the individual technology and equipment elements, including full automation between the casting and packaging areas. Combined with the optimized logistics in the plant, which minimize the total distances driven by vehicles and avoid critical crossings of external and internal traffic, automation greatly improves the safety of the operation. “Our absolute top priority in Hydro is safety and this counts for both traffic risk minimization, as well as automating critical process steps, especially when they are close to liquid metal or other potential sources of risk,” explained Rietveld.
The HyForge line has a nameplate capacity of 25,000 tons of forging stock per year, which will supply customers with smaller diameter aluminum billet that can be forged directly into high quality automotive components and other products. As European automakers are increasingly focused on the reuse and recycling of end-of-life scrap, the forging stock produced contains a high share of scrap with only a small percentage of primary aluminum being used. “Importantly, the scrap used will to a large extent be post-consumer scrap from various aluminum applications at the end of their life,” said Rietveld “The HyForge line in Rackwitz is also delivering on the ambition to recycle more locally sourced scrap to ensure market leading sustainability performance. We are targeting an average 50% post-consumer share of scrap over time and can deliver material with a CO2 footprint below 4.0 kg CO2e/kg AL.”
Conclusion
The Rackwitz HyForge line is currently ramping up capacity, which will be gradually built up over a year from the September 2023 production start. According to Rietveld the facility and the HyForge technology tick all the right boxes when it comes to the automotive industry’s high-quality standards and increasing focus on sustainability. This includes offering low-carbon aluminum with high post-consumer scrap content to decarbonize the automotive industry, the ability to support the lightweighting of a new generation of electric cars, and the ability to offer the best value-for-money proposition on the market.
In addition, the investment in Rackwitz is a key contribution to Hydro’s overall ambition to grow its recycling business, including the goal of doubling the use of post-consumer aluminum scrap by 2025. The company reached its 2025 target of 520–670 tonnes at end of 2023, which Rackwitz played a part in. Looking ahead, Hydro aims to further increase post-consumer scrap usage with the goal of reaching 850–1,200 tonnes by 2030.
Editor’s Note: This article first appeared in the June 2024 issue of Light Metal Age. To receive the current issue, please subscribe.