Understanding CNC wheel dressing machines

© Destina | Adobe Stock

In the grinding industry, CNC superabrasive wheel dressing machines are gaining widespread adoption. Traditionally, wheel dressing was performed manually, requiring skill and precision. However, CNC technology offers a more efficient and precise alternative.

A quick note on truing vs. dressing: While truing restores a grinding wheel’s geometry, dressing maintains its cutting ability. In practice, however, the two processes often happen simultaneously. Whenever a worn diamond or CBN wheel is removed for dressing, it undergoes truing and dressing. Eventually, the wheel’s shape becomes uneven due to wear, while grinding debris and swarf accumulate, clogging the surface and preventing worn diamond crystals from shedding. As a result, what’s commonly referred to as the dressing process is both truing and dressing.

The market offers two types of CNC dressing machines: semi-automatic and fully automatic. Semi-automatic machines are typically used for single-wheel dressing and require an operator to be present during the process. Fully automatic machines feature additional CNC axes, allowing for complete automation without manual intervention. These machines are capable of dressing entire wheel packs – multiple wheels mounted on a single arbor, commonly used in tool grinding.

The dressing wheel is made from conventional abrasives, typically aluminum oxide (white) or silicon carbide (green). During the dressing process, both wheels rotate against each other at different peripheral speeds.

The wear ratio between a diamond grinding wheel and the dressing wheel is influenced by several factors, including linear and rotary speeds, abrasive type, and bond material. In general, the wear ratio between the dressing wheel and the superabrasive wheel ranges from 10:1 to 100:1, meaning the dressing wheel wears 10x to 100x faster than the superabrasive wheel. However, this wear is inconsistent and difficult to predict with precision. Ensuring accuracy in fully automatic machines requires continuous compensation. This is achieved through automatic gap detection using an acoustic emission (AE) sensor to detect contact between the wheels. This detection process must be performed after every dressing pass to maintain optimal performance.

CNC programming for a fully automated dressing process requires pre-measuring the wheels before dressing. Then, the operator must input the desired final shapes into the control system. Most automatic multi-axis machines can precisely dress angles and radii, achieving seamless intersections between the two.

An essential step in the automatic dressing process is the final preparation of the bond. During dressing, the bond is eroded to allow worn diamond crystals to detach, but the process also leaves the wheel’s surface closed, limiting its grinding efficiency. To restore optimal performance, new, sharp crystals must protrude from the surface – a process known as opening or sharpening. CNC dressing machines can achieve this by adjusting the rotary speed parameters of both wheels after dressing.

Finally, these machines require a continuous supply of coolant oil to ensure optimal performance. Due to the high volume of conventional abrasive grits produced during the dressing process, paper filtration systems are typically used to maintain clean and efficient oil filtration.

MyGrinding Inc.
https://www.mygrinding.com