26.1 Introduction

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Millions of products are manufactured daily by a variety of processes. A basic method to form bulk metal

into a desired final shape is through the process of metal cutting, also referred to as machining. Metal

cutting is essentially the removal of excess material from a workpiece by moving a working tool over the

26-1

© 2005 by Taylor & Francis Group, LLC

surface of the workpiece at a certain depth, speed, and feed rate. Conventional machining operations are

turning, milling, and drilling.

Despite the high level of technology built into every aspect of modern metal cutting operations, the

phenomenon of tool wear still hampers the reliability and complete automation of machining processes.

Tool wear is the loss of material on the edge of the cutting tool. Although tool wear can be minimized, it

cannot be eliminated. Unfortunately, excessive or even a small quantity of tool wear may cause a defect in

a machined component, and therefore it is always necessary to be aware of the extent of the current tool

wear before machining can commence. Economic losses due to tool wear occur as a result of the

scrapping of expensive parts and the nonoptimal use of tool inserts. A conservative approach is often

taken, and the insert is recycled long before it should have been. Furthermore, secondary damage due to

tool wear can be extreme and even catastrophic. For this reason, many approaches to tool condition

monitoring (TCM) have been proposed through the years. There exist sensorless and sensor-based TCM

approaches. Sensorless approaches are generally tool-life equations and not monitoring methods. Thus,

sensorless approaches attempt to determine the optimal tool life under certain machining conditions.

These are often extended versions of the famous Taylor equation, which is described by

vTn ¼ C ð26:1Þ

where v is the cutting speed, T is the tool life, and n and C are constants that must be determined

experimentally for a given tool and workpiece combination.

This chapter is focused on sensor-based TCM, and specifically those methods that are based on

vibration related properties such as force, acceleration, and acoustic emission (AE). These sensor types

are known to be most effective for TCM. Furthermore, discussions will be focused on the application of

TCM in turning operations, though reference will be made to other machining operations as well. Besides

vibration-based approaches, other sensor based TCM methods are:

* Use of noncontact capacitive sensors

* Vision systems

* Measurement of the motor current

* Surface roughness monitoring

* Ultrasonic monitoring

* Temperature monitoring

* Laser scatter methods

* Audible emission monitoring

The reader is also referred to other excellent overviews of sensor-assisted TCM, published by Dan and

Mathew (1990), Byrne et al. (1995), Scheffer and Heyns (2001a), and Dimla (2000). A TCM database was

also published by the CIRP, supervised by Teti (1995), which includes more than 500 research papers

focusing only on TCM.

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