NOV 2018

Techspex provides metalworkers free research and analysis tools to help them find the right machine for their job.

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T O D A Y ' S G R I N D I N G T E C H N O L O G Y 8 switch to a different spindle by using a turret and precision Hirth coupling to auto index 0 to 180 degrees, thereby enabling an ID spindle to grind internal features. Another spindle might then be used to finish-grind the part face. In-Process Gaging for Closed-Loop Grinding Closed- loop, in-process gaging is an option for measuring diameters and other features such as length during the machining cycle. For cylindrical grinding, electronic probes or gage heads may be mounted on the table, on slides or in the indexing turret to access the part being measured. In-process gaging of multiple diameters or dimensions can be accomplished using multiple gage heads or multiple slides, all using the same gage readout. By using a precision ring gage of a known size, gage fingers can detect the precise workpiece diameter, then touch the top and bottom of the part diameter to feed results to the control system to command the machine to stop or to continue grinding until the exact diameter size is achieved. For tool and cutting grinders, closed-loop gaging is quite remarkable because of the complicated geometry of most cutting tools. Grinding flutes and complex surfaces, such as the helixes on cutting tools that can vary widely by design, requires equally sophisticated, odd-shaped touch probes styli to access the tool surface. Worn cutters can easily be restored by using the gage to instruct the machine when to retract during the regrinding cycle. Latest Developments Advancements in grinder design are producing high-precision, high-output, exceptionally fast grinders. The operation is becoming more automated, and the skill level of the experienced grinding operator is being embedded in the CNC control so that almost any machine operator can produce consistent, accurate parts. Backlash-free, direct-drive linear motors are replacing ballscrews. Linear drives enable the machine to move exceptionally quickly, perform precise contouring and provide vibration damping in all infeed axes, thus resulting in better grinding performance, better surface finish and greater precision. Likewise, there is a move toward faster, integral spindle drive motors with high- frequency air bearings capable of running at between 80,000 and 120,000 rpm while maintaining a constant torque curve throughout the speed range. Elsewhere in machine design, direct-drive motors are replacing drive belts to gain better machine control, higher speed and better precision. Auto-balancing of the grinding wheel while the spindle is running is another notable development. It uses a sensor that disperses weight to balance the wheel automatically to adjust for uneven distribution of wheel mass. Grinding wheels can sometimes become unbalanced because oil or coolant becomes trapped in portions of the wheel, whereas a balanced grinding wheel provides higher cutting rates, reduced cycle times and finer surface finishes. Control units on today's grinders have more options and more automatic functions to assist the operator. For example, auto dressing with compensation enables the machine to go right back into the cut after dressing. CNC units with touchscreen capability and teach functions enable the operator to skip typing in data manually. Applications Common automotive applications for OD and ID grinding include brake cylinders, brake pistons, hydraulic steering pistons, selector shafts, spline and gear shafts, connecting

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