Grinding Journal - Fall 2007 - (Page 21)

Proper coolant delivery is especially critical when using CBN wheels. Success depends on nozzles and piping that achieve laminar flow and eliminate turbulence, matching coolant velocity to the wheel speed, providing enough coolant volume, and other factors. For example, in the system pictured here, the nozzle position adjusts automatically as the wheel gets smaller. Cuts deep grooves The main advantage of plated CBN wheels is the ability to generate deep radial grooves and slots with high depth to width ratios, features impossible to make with aluminum oxide or vitrified wheels. Using 5-axis CNC motion control, the wheels can produce shapes previously generated only by EDM. CBN plated wheels can also be stacked in a wheel set to produce multiple forms and enable the grinding of a variety of features at the same time. After the wheels wear, they can be re-plated up to ten times, but this requires a system to manage the wheel life and return failed wheels to the manufacturer for re-plating. Complex designs and flexible process A key consideration in making the decision to use plated wheels is the total amount of material being removed. The wheels have limitations regarding DOC, feed rates, and tool life. If it is necessary to grind a large volume of material – for example, a land base and cutting conditions. Because CBN works best with low to medium stock removal rates, cycle time is not ultra fast and the method is not well suited for heavy stock removal situations. Electroplated CBN: Complex forms Another method of CBN grinding uses a single layer of CBN grain bonded to a precision steel wheel core. The bonding method is usually nickel-plating. Wheel cores can be re-plated up to ten times, resulting in lower abrasive cost-per-part than experienced with vitrified wheels. Of course, plated CBN wheels can not be dressed resulting in a wheel that dulls with each cut and wheel failure is unpredictable. The accuracy of an electroplated CBN wheel form is at best +/-.0005 and can vary with wheel size and spindle runout. Electroplated wheels perform best in straight oil coolant which reduces the rubbing heat generated when grinding deep groove and slot features. However oil does not conduct heat as well as water-based coolants, necessitating larger filter system with temperature control. Oil also requires precautions against a flash fire during grinding with an active fire extinguisher system. 4. Electroplated CBN Part, Feature: Turbine blade, medium aero Machine: 5-axis CNC Wheel: 1"-wide, two-wheel plated CBN wheel set Wheel Speed: 12,000 SFM Roughing parameters: 0.012" DOC at 15 IPM Finish parameters: 0.002" DOC and 20 IPM Coolant: Oil base, 60 GPM, high pressure: 150-300 PSI Dressing: Not required Cycle time: 8 minutes Workholding: Robust Q Prime: 2 mm3/sec Plated CBN wheels are best used for grinding deep radial grooves and slots. Using 5-axis CNC, the wheels can produce shapes previously generated only by EDM. Grinding Journal 21

Table of Contents Feed for the Digital Edition of Grinding Journal - Fall 2007

Grinding Journal - Fall 2007 Contents From Virginia: Apparently no credit crunch for machine tools Why measure cutting tools Other perspectives on CNC tool measuring Productive grinding of superalloys SUPER service grinding BIG rolls Problem Solver

Grinding Journal - Fall 2007

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.