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Lean Line

Photo | Gräbener Maschinentechnik
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Photo | Gräbener Maschinentechnik

The 2,500-ton press, converted for full automation, in the Gräbener prototyping center.
Photos: Gräbener Maschinentechnik

Components that are both thin and stable are in great demand in today’s automotive industry. That is why hydroforming is becoming increasingly popular for manufacturing closed, tube-like profiles and sheet metal parts. Gräbener Maschinentechnik is banking on Rexroth’s latest control technology.


Reduced CO2 emissions and lower fuel consumption: Nowadays, less is more in vehicle engineering. Especially when building bodies, the manufacturers are emphasizing lean. In mass production this has raised hydroforming to new popularity. Here a high-pressure liquid forms profiles, sheets and tubes so that their geometries correspond to the surrounding molds. New alloys, some of them extremely strong, can be used in this procedure to fabricate stronger and thinner frame and body parts. This reduces significantly the weights of these parts. Hydroforming is a concept that will promote lightweight engineering especially in the automotive industry.

This has triggered a rise in the call for new systems. Retrofitting modern controls makes preexisting hydroforming machines both productive and profitable. Suitable concepts are delivered by Gräbener Maschinentechnik GmbH & Co. KG. This manufacturer of hydroforming equipment and operator of its own prototyping center has adopted IndraMotion MLC by Rexroth, incorporating preconfigured regulators for the hydraulic system. Thus the complex process is significantly simplified and machine productivity rises. Thanks to these controls, both new and rebuilt machines are markedly more energy efficient.

Making new from old

Gräbener also uses this technology for its own machinery. Thanks to the October 2010 takeover of the hydroforming plant previously operated by Schuler AG, the firm has more than doubled its inventory of prototyping and short-run hydroforming machinery. Outdated controls in the machines thus acquired made a thorough overhaul necessary. “We, as a mechanical engineering company, expected a control concept that could be incorporated both quickly and efficiently and, at the same time, offered excellent functioning for complex processes,” explains sales manager Torsten Adam. As a machine user, the firm’s requirements for its own prototyping operations were quick prototype development and testing, great flexibility, and condition monitoring capacities.

IndraMotion MLC satisfies these requirements. Whereas two control units were previously used in hydroforming machines – a PLC and a subordinate NC axis control – the MLC now handles both functions. “Numerous hydraulic controllers are already preconfigured in the software. We only have to plug in the parameters,” Torsten Adam emphasizes. The developers use Indra-Works to sharply reduce the time and effort devoted to engineering. The Generic Application Template, a pre-defined program structure incorporating controls for machine procedures, simplified modularizing the software for the machines. Templates typical to specific users facilitate project launch and fault management.

Fast regulation

The MLC, a multi-axis controller, accelerates the complex hydraulic processes involved with hydroforming. The controls provide central regulation functions for all the hydraulic axes and makes use of the sercos communication system. That makes for quick and direct parameterization for all the axes.

The results are more than convincing. A rebuilt 2,500-ton hydroforming press – with a total of eight tool regulation axes and two pressure intensifiers – is operated using a closed-loop, digital controller. Each of the axes can be controlled in regard to position and pressure, and in dependency on a further axis.

Thoroughly efficient

Gräbener Maschinentechnik packs all the process sequencing programming into the Press Pro® 3. Visualization for the operator is included. The open interfaces and programming standards built into the MLC let users continuously refine their molding processes. Input and output of data relevant to the machinery, molds and processes are by way of intuitive GUIs.

Torsten Adam mentions a further favorable point. “We are not just a manufacturer, but a user at the same time. We are thoroughly aware of how important life cycle costs are in everyday operations.” That is why intelligent management for the hydraulic pumps makes for increased energy efficiency. The pumps can be parameterized to align with the process and thus always produce exactly the amount of energy needed at any given moment. Thanks to WinView, a Rexroth tool integrated into IndraWorks, the user can see the amount of wear at individual components and effect replacement before failure occurs. Long-term records simplify the analysis of sporadic faults and speed restarting following malfunctions. Thus Gräbener implements lean processes, all along the line.