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[December 06, 2012]
CNC Puts Precision into Gear Production [Manufacturing Engineering]
(Manufacturing Engineering Via Acquire Media NewsEdge) A high-performance 11-axis CNC system from NUM Corp. (Naperville, ID provides complex control for the Grono 250 gear honing machine from Sicmat SpA for posthardening fine-finishing. The Grono 250 uses an innovative honing wheel with external teeth and an application-specific CNC program to provide accuracy in gear shaving that eliminates the need for shaving and grinding stages.
Until recently, Sicmat specialized in machines that used shaving technology to obtain the necessary finish to medium and high-quality gears for the automotive industry. Shaving generally was performed before the workpiece was case hardened by heat treating. Any heatinduced deformation had to be corrected by grinding or honing. Sicmat's objective was to develop a high-power honing machine that would help gear manufacturers accelerate production throughput by reducing the number of process stages.
Until now, gear-honing automation has used highly specialized machine tools, comprising circular ring-type assemblies with teeth cut in their internal face. These tools are expensive and time-consuming to set up. Sicmat believed that by using a honing wheel with external teeth, the accuracy of the process could be improved to such an extent that it could replace gear shaving in many applications with the advantages of lower tooling costs and simpler setup.
Needing high mechanical rigidity for accurate and repeatable results, Sicmat chose to base its new honing machine on the proven mechanical platform of its Raso TP 250 gear-shaving machine, a platform with exceptional stiffness and resistance to vibration. Also, the physical layout provides excellent accessibility for operation and maintenance, and features vertical workpiece positioning to simplify integration with other production line automation.
The NUM Flexium CNC was selected and provides eight motion axes control, plus another three on an associated robotic loader. The motors of all 11 axes are driven by NUMDrive C servodrives, and the overall system is equipped with two NUM MDLL 3050 regulated power supplies. Each power supply is rated at 50-kW continuous and uses regenerative braking to maximize efficiency. The main machining axes are operated by direct-drive motors, while the honing wheel and workpiece axes are driven by high-torque motors synchronized and controlled by NUM application-specific software.
Every stage of the honing process on the Grono 250 is automated. In normal use, the case-hardened workpiece is removed from the production line conveyor by a robotic handler/ clamp unit which identifies the type of gear by checking its outside diameter before transferring it to an integral pre-process measurement station. The workpiece is synchronized with a secondary gear, then driven into mesh and rotated through a complete revolution. During this time, the displacement between the two axes is measured continuously to ascertain how much stock material needs to be removed from the workpiece, and these data are fed to the NUM Flexium CNC.
After measurement, a robotic handler transfers the workpiece to the honing stage, where it is initially indexed before being run up to speed and synchronized with the abrasivetoothed honing wheel. The honing wheel is then driven progressively into mesh with the workpiece. The two axes operate in a unique master-slave configuration that has zero delay of the slave which required NUM to create a second master for the workpiece motor. Controlling the speeds of both these axes precisely and fractionally-varying one relative to the other - facilitates fine adjustment of the honing process. As soon as the honing process is complete, the workpiece is disengaged from the honing wheel, spun to remove coolant, and then transferred back to the production line by the robotic handler.
Grono 250 machines are capable of spindle speeds of 7000 rpm. A 10,000-rpm spindle speed is being developed for even tighter process control. The Grono 250 was introduced at IMTS. Sicmat is represented in the US and Canada by Star SU LLC (Hoffman Estates, IL).
For more information on NUM Corp., go to www.num.com, or phone 630-505-7722; on Star SU LLC/Sicmat, go to www.star-su.com, or phone 847-649-1450.
(c) 2012 Society of Manufacturing Engineers (publishers)
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