May 2020

40 n LINEAR MOTION May 2020 www.drivesncontrols.com Servo-electric presses deliver forces up to 2MN and 80% energy savings T he Swiss powder-press manufacturer Osterwalder has been going for more than 130 years. Its machines are used to produce items ranging from automotive gears to metalworking tools such as drill bits. In the pressing process, a fine metal powder alloy is poured into a die and shaped under pressure. This“green body”– as the intermediate product is called – is then sintered to achieve the desired hardness, wear resistance and contour precision. About six years ago, Osterwalder brought a new type of drive technology to the powder press market. Direct Drive Technology (DDT), as it is known, comprises servo-electric motors and ballscrews, and has replaced the hydraulic drives that previously dominated this field. Thanks to DDT, the pressing process now offers much higher precision, because the measurement variables and adjustment criteria for electric displacement are easier to define and program than for hydraulic drives. In addition, ballscrews offer better stiffness than hydraulic cylinders, which can exhibit substantial displacement due to the compressibility of the fluid media. The workpieces produced by servo-electric powder presses are thus more homogeneous and their material properties can be adjusted with greater precision. Initially, Osterwalder used the DDT principle to achieve press forces of up to 160kN, and then up to 640kN. Having proven the principle, the next logical step was for the company to equip its larger presses with the new technology. However, at higher forces, conventional ballscrews reach their limits with regard to nominal service lives. For the smaller systems, Osterwalder had been using ballscrews fromNSK’s HTF series with its CA-SP Electric and CA-HM Electric servo-electric direct drives. These ballscrews allow fast traversing speeds as well as high precision and stiffness. They also allow large axial forces to be transferred, with minimal wear, even under high load and fast cycle conditions. A typical powder-press cycle time is 3s. Meanwhile, NSK had been developing a new series of ballscrews with higher dynamic load capacities in the same dimensions, thus capable of extending service lives. It achieved this by using proprietary materials that were not only capable of withstanding high loads, but thanks to a special heat treatment, could optimise the balance between hardness and toughness. The use of this TF (Tough Force) material ensures, among other things, that impurities in the raceway do not cause indentations or projections, but are instead smoothed out by repeated over-rolling. Laboratory tests showed that the TF technology could triple ballscrew lives, as well as achieving 30% higher dynamic load capacities than the HTF series, which already offered high values compared to rival ballscrews. Osterwalder decided to take advantage of the improved high- load ballscrew performance to produce its first servo-electric multi-level powder press capable of delivering a pressing force of 2MN. Called the OPP 2000, the newmulti-level press can be used to produce items such as engine components, parts for electric tools, and carbide rods. The energy consumption of the new presses is only about 20% that of hydraulic presses, depending on the part being pressed. Osterwalder says that this saving is a compelling argument because its customers typically operate up to 50 powder presses. Maintenance is also said to be much lower than for hydraulic presses and footprints are smaller. Another attraction is the ability to produce parts with improved accuracy, which reduces the amount of reworking needed, and cuts process and material costs. “We are able to achieve positioning accuracy of 1μm and travel through specified movement profiles,”says Michael Sollberger, Osterwalder’s product manager and construction team leader.“This significantly improves product quality and minimises the need for rework. “We can now realise the excellent dynamic movement control offered by a servo-electric drive in the higher power range, and meet the requirements of customers for the production of more complex geometries with a high degree of accuracy,”he adds. A Swiss manufacturer of powder-press machines has moved from using hydraulic drives on its larger machines to servo-electric drives. The resulting presses can deliver forces of up to 2MN, while using around 80% less energy than hydraulic versions, as well as producing more precise parts. Osterwalder’s 2MN powder presses incorporate several servo-electric direct drives that perform tasks previously handled by hydraulic cylinders