Uzwil (Canton of St. Gallen), Linz – She is a typical hidden champion: Bühler AG from Uzwil in the Swiss canton of St. Gallen. Every second car produced worldwide is fitted with lightweight die-cast parts manufactured using Buhler technology. Now, in a development cooperation with the Linz Center of Mechatronics GmbH (LCM), the pump life of the Carat die casting machine has been significantly extended. This is achieved with an optimized pressure curve in the hydraulic system during the machining cycles. Higher efficiency and productivity are quite desirable side effects of the system update. As “Smart Pump Management”, this has been installed in all new machines since April 2018. Older machines can be retrofitted within four hours.
Increasing availability while reducing maintenance costs is a constant target in the automotive industry. “In order to further increase the reliability and service life of our die casting machines, we have examined the entire hydraulic system in search of potential optimization potential,” explains Roland Herde, development engineer at Bühler. The main reason for finding a new home is thanks to the cooperation with LCM. Step by step, the Linz hydraulic experts analyzed and simulated the relevant processes and the documented failures. During this three-month project phase, the LCM developers finally found a concrete starting point for a process improvement. “We suspected at a very early stage that the high pressure rise rates, especially for the hydraulic pumps, are an enormous burden,” explains Bernd Winkler, Business Area Manager Drives at LCM.
Therapy against impending film rupture
Ultimate certainty was finally provided by data logging and tests on the test stand specially set up at LCM. “If one considers that the pressure jumps from five to 200 bar within 50 milliseconds, this is an enormous burden for all hydraulic components,” explains Winkler. At these pressure rates, even a crack of the lubricating film or even cavitation – and thus an extremely high stress on the pump mechanism – can not be ruled out. “Our goal was therefore to reduce the switching rates without increasing the cycle times for production,” explains Andreas Plöckinger. The LCM development engineer and team leader “Hydraulic Drives” started with his team in November 2016 the second project phase with preliminary tests at the LCM. For this purpose, a test stand for the Carat hydraulic system was set up in the in-house laboratory in order to develop the ideal system configuration for the control with five different valve variants. This was of course accompanied by detailed measurements.
The dress rehearsal in Uzwil is followed by a trial by fire in practice
“In a comparatively short time, we were able to use proportional pressure control valves and a specially developed control software to set up and reduce the hydraulic pressure slightly more dosed, thus reducing the load on the entire hydraulic components,” explains Plöckinger. The first dress rehearsal for the development finally took place in February 2017 at the hydraulic test facility at the Buhler plant in Uzwil. The fire test passed the update developed by LCM in the practical text of an industrial customer of Bühler, who manufactures highly complex lightweight components for the automotive industry. “We integrated ourselves there with three Carat pilot machines, which were equipped with our system, directly into the ongoing production process. With this we controlled the pumps directly via our black box – an industrial PLC – and also carried out the measurements including evaluations accordingly. It was clear to us from the outset that our system had to run smoothly in production, “says Plöckinger, recalling the successful and exciting test.
Quality leap in series and for retrofitting
Based on the findings gained from measurements and data logging, it was already possible to work on the serialization of the system. Following the selection of suitable control hardware and corresponding tests, the integration of the LCM code into the Bühler software and the verification of the entire system at the Bühler test bench, the most important milestone took place in autumn 2017. “After successfully commissioning a pilot plant from a customer for many years in October 2017, there was nothing to stand in the way of mass production,” emphasizes Buhler development engineer Roland Herde. “One of the first optimized serial conversions was made together with LCM at the Albert Handtmann metal casting plant in Biberach / Riss. Handtmann is a long-standing customer and places great emphasis on energy efficiency and a long service life. ”
Since April 2018, all newly produced Carat models are now equipped as standard with “smart pump management”. “In order to benefit all our customers from the leap in quality of this hardware and software update, we also offer a cost-effective upgrade of all Carat die casting machines produced from 2007,” says Herde. The installation of the “Smart Pump Management System” with integrated proportional valve technology, electrical connection cables and a smart software package, which ensures the optimized pressure curve in the hydraulic system, only takes three to four hours.