High pressure molding

Illustration | design hoch drei GmbH & Co. KG
Marginal Column

The e-bike, e-automobile, e-motorcycle: They all need ceramic battery cases. With its high-efficiency isostatic presses, Dorst Technologies responds to this tremendous demand.

 

The first electromobiles – both fully electric and hybrid – are already on the road and their manufacturers are gearing up for mass production. The high-performance rechargeable battery assumes a key role in this development. To meet the demands of today’s and tomorrow’s cars, batteries will need to have higher capacities and be available in large numbers. Efficient manufacturing techniques are essential. One solution has been presented by Dorst Technologies GmbH & Co. KG, located in the Bavarian town of Kochel am See. This vendor of machinery and equipment used for manufacturing ceramics and sintered metals has developed a manufacturing cell to produce battery cases. The IPM 40/3 is modular in design, and can comprise up to three isostatic presses. The HNC100-3X motion controls made by Rexroth regulate the hydraulic regulation axes.

Identical results

The control electronics make sure that manufacturing satisfies the main requirement for the battery cases: absolute homogeneity within the material. Uniform pressure is essential here. To prepare for consolidation in an isostatic press, the powdered material is first placed in a mold. Then an emulsion of water and oil, at pressure of up to 2,000 bar, exerts force on the rubber envelope. “We selected a decentralized approach for the hydraulic functions and use at each module the NC functions built into the Rexroth HNC100-3X,” explains Günter Bergel, project manager at Dorst Technologies.

Each unit is equipped with motion control, which regulates the piloted and direct-drive diverter valves, with electric feedback for process-related movements. The digital control units are connected to the system PLC by way of a Profibus. That central PLC coordinates the three press modules and oversees automation and safety. The result is continuous molding and uniform densities in the cases.

Exerting pressure dynamically

When filling, when closing the mold, and when demolding the part, the main press axis with its 400 kilonewtons of clamping force is at work while the regulation electronics govern its positioning. “The hydraulics can move the upper piston, under full control, to any of several positions,” explains Günter Bergel. The second axis controls the pressure transformer for the emulsion. Pressure has to be raised as quickly as possible. “We profit from the dynamics of the valve and can develop 2,000 bar within a second,” Bergel emphasizes.

A central hydraulic power unit made by Rexroth supplies the three press modules, running at 300 bar operating pressure. Force is then applied in a closely controlled fashion in several steps. “The workpiece has to ‘breathe’ – a decisive factor in the dimensional accuracy and stability of the final cases,” Bergel notes.

During system development, Bosch Rexroth also helped with the programming of the NC functions. Complex tasks can now be quickly implemented with expanded, high-performance hydraulic regulators using NC commands tailored exactly to needs. Extensive cam functions and extended diagnostic options ensure movement that is both highly dynamic and precise. Parameterization and diagnosis of the press modules can be handled using either the system’s PLC or the Ethernet service interface, as desired. The Ethernet communications port now lets the user record the process data needed to document quality.

Flexible throughout

The modular concept for the manufacturing cell offers users an increase in freedom – in several respects. Users can begin with just a single press module and add others as required. It is also possible to quickly change the compositions of materials or work differing materials in parallel. “Recipe” management is integrated into the system controls so that production can be changed over with just a few commands. These are the best prerequisites for high-performance batteries produced in large numbers.