Double-ended face grinding affords companies a further viable market and a potential for innovative developments. In order to expand its established super-finish product range and to open new market segments, German based Supfina Grieshaber developed a new series of machines presented under the name Planet V.
The machine is employed for the surface finishing of flat components that are 3 to 250 mm in diameter and up to 100 mm thick. They are machined with conventional or super-abrasive grinding disks and ground flat on both sides in a single pass. In this process, an accuracy of 2-3 micrometers and a roughness depth of less than 2 micrometers are achieved.
A machine with grinding disks with a diameter of up to 762 mm requires a sturdy design to absorb the high grinding forces and to prevent vibrations. “We built the machine frame as a welded structure which is lined with concrete to reduce vibrations,” explains designer Joachim Schulte. Interesting here is the division of the machine frame in two. The top half is carried on three points and can be shifted in three axes to set the grinding disk at an angle. This tilt is measured and enables a speedy machine setup at a high rate of repeatability.
The dressing system works on both sides simultaneously and is completely integrated into the machine. It features CNC axis which enables the exact shaping of the grinding disk sides. To ensure the required accuracy, the work pieces are measured by an integrated measurement system with an accuracy of 0,1 micrometer.
Drives and control from a single source
The new double-sided grinding machine has a total of four controlled axes and two grinding spindles. The drives of the grinding disk accelerate the spindles up to 3000 RPM and develop a torque of 248 Newton meters during this process.
Such a highly developed drive technology also requires tremendous power. The Simodrive 611D drive system is used in conjunction with 1FT6 servomotors, which were selected in particular because of their extremely high concentricity, which is especially important during grinding.
The control for the machine is also from Siemens. The electronic backbone of the Planet V series is a Sinumerik 840D which is designed in accordance with the required standard Solutions for Powertrains in the automotive industry. A Windows XP computer functions as an operator interface; with its standard architecture it enables a trouble-free connection to existing system environments. Joachim Zech, head of design, explains: “We have decided in favour of Siemens as an automation partner because of good experience with the Sinumerik 840D control in the past. The openness of this control is significant for our machine as well as its integrated safety concept.”
Functions for perfect grinding
The control itself possesses everything necessary for a highly productive grinding machine such as travel with no contouring error and the integration of internal measurement systems. In addition there is the safety system of the Sinumerik 840D, Safety Integrated, which contains functions such as safe standstill safe acceleration, safe position and safety reduced spindle speed. These are properties that are indispensable to ensure the safety of the operator and the machine, particularly when grinding with large grinding disks.
“It was not difficult to integrate the external measurement systems used for the in-process and post-process measurement of the work pieces and grinding disks monitoring,” reports Zech. He also praises the openness of the control which allows the system for measurement and compensation of the grinding disk tilt to be fully integrated.
The entire machine control is based on an open concept which also incorporates the communication with prior and later processes. For example, handling systems can be coordinated with the machine sequences via Profibus DP. All in all, Siemens has created an excellently-attuned solution. The 500% increase in productivity documents the benefits for a machine builder when designers and control specialists form an interdisciplinary team.
For more information contact Keshin Govender, Siemens Southern Africa, +27 (0)11 652 2412, [email protected], www.siemens.co.za
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