Die-casting industry is currently undergoing a shift toward electric vehicles, and at the same time, it is facing challenges with entirely new part categories. German company Druckguss Service accepted this challenge and answered questions about future processes with DuoCast series of die-casting machines.
Druckguss Service Deutschland (DSD) GmbH is a globally oriented machinery manufacturing company headquartered in northern Germany. Core competence of company with more than 100 employees lies in construction of special machinery, especially die-casting machines. Currently, DSD GmbH is market leader in German-speaking area in the field of service and overhaul of die-casting machines. With development of DuoCast series, company is expanding its business areas and, in addition to machine overhaul and machine production, it has a production area of 11,000 square meters at Lübeck site.
Company will also mass-produce and debug die-casting machines in the future.

 

DuoCast Die Casting Machine Technology Overview
DuoCast die-casting machine technology is a new approach that can make die-casting production more cost-effective and sustainable. Principle is to clamp two sets of die-casting molds on one die-casting machine at the same time (Figure 1). Rated clamping force of die-casting machine can be used by user at interface of two molds. Patented "tandem arrangement" thus doubles throughput of castings compared to conventional horizontal cold chamber die-casting machines with comparable clamping forces. With innovative design of clamping unit, it is also possible to integrate die-casting unit into the entire system in a new way (Fig. 2).

 

DuoCast series is configured with a vertical casting unit located centrally between two clamping surfaces. On the one hand, this makes metal runner into mold cavity very short, and on the other hand, upper and lower plunger systems can be used to produce center runner castings for cut-off.
Tandem arrangement of two sets of die-casting molds in a clamping unit combined with a vertical casting unit is the best prerequisite for centralized casting of high-quality high-volume parts, such as shock towers, rotors and casings for electric vehicles, and even internal parts of transmissions. This makes complex processes such as three-plate molds and multi-cavity molds redundant.
Cycle time advantage
Essentially, upper and lower plungers of vertical casting unit enable cycle time savings during die casting cycle.
1. In order to inject liquid metal into pressure chamber, casting nozzle can be closed by lower plunger. In this way, filling process can be started when molding unit is open, and at the same time it can be adjusted so that pressure chamber is completely filled when clamping force is reached. By shifting charging process to empty cycle time, cycle time savings of up to 15% can be achieved, depending on cast product.
2. Compared with traditional horizontal cold chamber die-casting cycle, solidification time can be further reduced. In horizontal cold chamber die casting process, it is necessary to wait for die casting sprue to completely solidify, whereas in vertical casting cells with lower plungers, these residues have already separated from casting in die casting machine. This means that mold can be opened in advance and finished casting can be removed directly.
Overall, a 17% reduction in total cycle time can be achieved by pre-batching and early separation of die-cast sprues.
Results of foundry
To validate casting process, various experimental and casting test series were carried out at technology center in Lübeck. Taking example of two rotationally symmetrical automatic transmissions, technical advantages of DuoCast are particularly successfully demonstrated:
1. In original three-plate structure mold production process, gas pores first led to a high scrap rate in mechanical finishing process. Using DuoCast principle, this problem is almost eliminated. Due to vertical arrangement of injection chambers, 100% filling can always be achieved without melt accumulation during slow injection phase. Air may also be brought into melt during feeding process, rising and degassing due to different densities of air and metal melt, or remaining in low concentration in die-casting waste.
2. Another contribution of vertical principle to quality improvement lies in mold cavity closed by lower plunger. This way, even with simple systems, optimal vacuum results can be achieved without risk of premature introduction of melt into mold. Without special sealing at mold interface, a vacuum value of 300 mbar can even be achieved.
Sampled demonstration series is then fed into final customer's mechanical finishing process, resulting in 100% qualified parts (Figure 3), which are fed into next step of assembly process. In this way, scrap rate of traditional processes can be reduced by up to 30%.
Digital future

 

The almost entirely digital Duo-Cast series records process data of the entire die-casting cell and processes it further. Depending on requirements, defined evaluation process can be completed within cell or defined evaluation can be forwarded as a data stream to a networked factory. MQTT and OPC UA are established standards for secure communication in IIOT field. Automated analysis mechanisms extend all way to field level of machine, which minimizes dimensional congestion and further reduces downtime.
Research prospects
Specific capabilities of Duo-Cast machine are being expanded and improved through integration with two current research projects at TU Dresden.
1. Research and development focus of HyDrun project is to expand die-casting machine into a hybrid machine to achieve inline integration of complex engine-transmission hybrid components through a synchronized sequence of processes such as aluminum die-casting, stamping and surface modification, and thermoplastic injection molding. Production of components is achieved through special mold technology, new peripherals and specially controlled targeted process sequences in specially developed hybrid casting cells.
2. METEOR project uses DuoCast technology to lay foundation for development of a new energy-optimized production network that increases resource efficiency through targeted networking of process steps in manufacturing of lightweight structures and points way towards CO2-neutral production. Minimization of energy consumption and active utilization of introduced heat play a decisive role here. In addition, production network should be supported by modern methods, for example by actively integrating solar thermal cascades, and by explaining how resource-saving production can be achieved with current measures.

 

DuoCast machine and ongoing research projects will be housed at National Center for Verification of Lightweight Structures (LEIV) at Institute of Lightweight Structures and Plastics Technology at TU Dresden (Fig. 4), where testing can be carried out by relevant partners from industry and science to share facilities. Work to prepare machine and sub-projects for operation is planned to begin soon.