Conventional acoustical sensors for detecting and monitoring small-tool wear and breakage are limited by their sensitivity and ability to overcome background, no-load noise. For example, drills of 0.12-in. diameter on a 15-kW spindle or 0.06-in. diameter on a 3.5-kW spindle are about as small as can be reliably monitored with conventional tool-monitoring systems.
An ultrasensitive WLM-3 power-measurement module developed by Nordmann Tool Monitoring, Hoffman Estates, Ill., is said to be 4 more sensitive than conventional units, making it possible to monitor drills as small as 0.07-in. diameter on a 15-kW spindle or 0.03-in. diameter on a 3.5-kW spindle. The WLM-3 module is used in conjunction with the company's SEH acoustic-measurement system, which employs a coolant or oil stream directed to the tool or its toolholder as a sound-wave conductor. A concentrated ultrasonic beam is transmitted over the coolant stream to the tool, and the time for the wave to reach the tool and return establishes a base cycle-time value. A sensitive acoustic-emission hydrophone measures vibration produced by the cutting process and tool breakage as transmitted over the coolant stream. During cutting, the cycle time of reflected sound waves from the tool are compared with the base value, and changes indicate the tool condition. For instance, a broken tool results in an increase in reflected-wave cycle time because the sound waves are reflected from machine parts more distant from the tool.
The system includes the company's SEM module, which provides a visual plot of the magnitude of acoustic emission over time indicating tool condition. The module can be interfaced with other sensors or other SEM modules for plant-wide tool monitoring.