Mechanical Technology February 2015

⎪ Local manufacturing and beneficiation ⎪

PE’s new state-of-the-art servo press

During a visit to Port Elizabeth late last year, Peter Middleton visited Precision Press, a new G.U.D Holdings facility, where Flip Gunter, PE plant manager, was commissioning the company’s new Schuler 630 t servo press, part of a R70- million investment that Gunter says could “change metal pressing in the automotive sector”.

A lmost all presses currently in use in South Africa are mechanical presses that use electrical motors and flywheels, with the pressing stroke being driven by a crank mechanism,” Gunter explains. Simply put, a servo press is a press driven by servo motors. The torque pro- duced by the motors is converted via ball screws and sliders into linear pressure, which forms steel components from flat sheet. This new servo press uses two electric servo motors that provide some 15 000 Nm of torque – way more than we had before,” he continues. While the lack of a flywheel, clutch and brake combination reduces the number of wear parts and associated maintenance, Gunter says that the real advantage lies in the ability to “vary the stroke speed for higher cycle times and better optimised part pressing”. He elaborates: “The limitation of the

slide mechanism on a conventional fly- wheel press is that it is set to run at a fixed speed. This directly driven servo press can be programmed for the slide to run

Flip Gunter, Precision Press’ PE plant manager, demonstrates the HMI for the plc-based controller, which receives constant feed- back signals though load cells and encoders embedded into both the press and the dies.

at any speed. When pressing a part, the upper forming die first moves down until it is in contact with the metal sheet in the lower die. From this point of contact with the material, the press should, ideally, slow down to a speed that optimises the cold drawing process. “Then, once the part is pressed and the load is removed, the speed of the press can again be increased. This is, basically, the key advantage of this modern press. A set of die tools that can run at 10 strokes per minute on a conventional press, can run at 20 or more strokes per minute, simply by ac-

celerating and decelerating the stroke at appropriate times. Actual pressing work is only being done for 15 to 20 % of the stroke. The remaining stroke movement is for automation and clearance operations for the advancement of the part to the next pressing position. The servo motors, therefore, allow the automation side to run at high speed without impacting the pressing operations,” he tells MechTech . This speed control feature also allows older dies to be used, because the actual pressing speeds can be reduced to make the die last longer, while the net cycle times are significantly reduced. The position and speeds of the slides are very tightly controlled via a plc-based controller, which receives constant feed- back signals though load cells and encod- ers embedded into both the press and the dies. “Each die can be fitted with up to 32 sensors to monitor and control the process and to protect the tooling. The slide motion curve for each part being formed can be individually programmed to the speeds and forces required, and these settings will automatically be set when the die for a new part is inserted,” Gunter continues. “Another important role of the control system and sensors is the part transfer process, because you need to know that a part has been suc- cessfully picked up and properly placed in the subsequent die cavity.” Describing how the machine oper- ates, he points to a sheet metal coil on the left-hand side of the machine. This press can accommodate a 7.0 t coil with a width of up to 800 mm − enough for 7 000 1.0 kg components. An automatic decoiler takes the material from the coil

Precision Press’ new Schuler 630 t servo press in Port Elizabeth is part of a R70-million investment by parent company G.U.D Holdings in the local automotive industry.

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Mechanical Technology — February 2015