Buying a Grinder: Latest Technological and Process Developments
Grinders have advanced in recent years with both technological and process improvements. Here is a rundown of some of those improvements.
Whereas previous posts have discussed grinding machine construction, the abrasive process and various industries’ applications of grinding technology, this post looks at recent developments in grinding processes and machine designs.
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-probe styli to access the tool surface. Worn cutters can be easily restored by using the gage to instruct the machine when to retract during the regrinding cycle.
Machine Design 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 in-feed 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 between 80,000 and 120,000 rpms 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.
Automatic Grinding Wheel Balancing
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.
Optimizing a camshaft lobe grinding cycle has traditionally been based less on science and more on educated guesswork and numerous test grinds. Now, computer thermal modeling software can predict areas where lobe burning is likely to occur, in order to determine the fastest possible work speed that won't thermally damage lobes and greatly reduce the number of requisite test grinds.
The double-disc grinding process is consolidating its position in automotive applications but is moving into other industries. Double-disc grinders are now easier to operate, and they have added capabilities for control flexibility, precision process control, faster changeovers, and grinding of nontraditional materials.
No other process can do what creep-feed grinding can do. Recent tests show even more can be gained by optimizing every element of a creep-feed system.