Maintaining tight tolerances is essential in the production of large, expensive parts that serve critical applications. For this reason, reducing the number of machine setups required to complete these low-volume, specialty parts has become a primary focus of the production strategies in many metalworking organizations. Reducing the number of machine setups also reduces the amount of work-in-progress that a shop must manage. In recent years, therefore, machine tools that incorporate multi-process capabilities have become widespread. Typically, however, the “multi-process” label is applied in reference to turning or machining centers.
With its recent introduction of the Maegerle MGC-Special line of high-performance grinding centers, United Grinding Technologies Inc. (Miamisburg, Ohio) now applies hybridization to the task of machining complex parts that require flexible grinding configurations. In addition to ordinary face grinding, for example, these machines also have the capability to grind bores, diameters and tapers.
Typical configurations for this line of machines are one vertical spindle with a second horizontal or two vertical spindles with a third horizontal. Besides grinding wheels, a 16-tool ATC magazine accepts turning, milling, boring and drilling tools, as well as a measuring probe. When the machine isn’t grinding, its 30 kW water-cooled, belt-driven, vertical spindle drives cutting tools at speeds ranging from 6,000 to 8,000 rpm. On machines equipped with three spindles, the second vertical spindle is a 15 kW direct-drive, water-cooled type designed for ID and OD grinding. Like the machine’s horizontal spindle, the second vertical spindle inclines automatically in 1-degree increments within a range of ± 30 degrees. These features give the machine substantial capabilities to perform both flat taper and steep taper grinding.
Designed first and foremost for precision grinding operations, the machine’s structure incorporates substantial rigidity that bolsters the accuracy of its additional machining functions. In addition to the changeable probe for measuring machined surfaces, a separate tool probing system is located at the right side of the machine table. All measurement data continually feeds back to the CNC for in-process verification and monitoring/control of machining. The machines may be equipped with either Fanuc 16i or Siemens Sinumerik 840D digital controls.
The MGC-Special incorporates a hydrostatic rotary NC table with brushless ring torque motor drive and Heidenhain direct measuring scales. The table speed is variable up to 80 rpm, and the table’s maximum load capacity is 10 tons. This line of machines offers X-axis travel ranging from 1,300 mm to 3,300 mm. Y-axis travel ranges up to 1,050 mm, and the machine’s three independent Y-axis spindle heads may be arranged in any orientation according to the user’s needs. Z-axis travel ranges up to 220 mm.
According to Larry Marchand, sales manager of aerospace applications for United Grinding, the hybrid machine addresses a variety of applications. “To manufacture turbine disks for aircraft engines and power turbines, several features must be machined with exacting tolerance relationships to each other,” says Mr. Marchand. “Face-flatness tolerance on these parts is 0.0002 inch, and perpendicularity to bore is 0.0005 inch. The MGC allows these features to be machined in the same setup.”
Some other current applications include machining parts such as aerospace castings and frames, large gears for power transmission systems and components for large engines and industrial machinery. “Some specific parts being run on this machine include piston rings for large ship diesel engines, frames for textile manufacturing machines and mold bases for large injection molds” says Mr. Marchand. “By combining grinding with boring, milling and turning, each of these customers has been able to improve quality and shorten cycle times.”