Tool Life Definition and Measurement of tool wear

Tool Life Definition

Tool life generally indicates the amount of satisfactory performance or service rendered by a fresh tool or a cutting point till it is declared failed.

Tool life is defined in two ways:

1. Actual machining time (period) by which a fresh cutting tool (or point) satisfactorilyworks after which it needs replacement or reconditioning. The modern tools hardly fail prematurely or abruptly by mechanical breakage or rapid plastic deformation. Those fail mostly by wearing process which systematically grows slowly with machining time. In that case, tool life means the span of actual machining time by which a fresh tool can work before attaining the specified limit of tool wear. Mostly tool life is decided by the machining time till flank wear, VB reaches 0.3 mm or crater wear, KT reaches 0.15 mm.

2. The length of time of satisfactory service or amount of acceptable output provided by a fresh tool prior to it is required to replace or recondition. Assessment of tool life Tool life is always assessed or expressed by span of machining time in minutes, whereas, in industries besides machining time in minutes some other means are also used to assess tool life, depending upon the situation, such as

  • no. of pieces of work machined
  • total volume of material removed
  • Total length of cut.

Measurement of tool wear

The various methods are:

i. By loss of tool material in volume or weight, in one life time – this method is crude and is generally applicable for critical tools like grinding wheels.

ii. by grooving and indentation method – in this approximate method wear depth is measured indirectly by the difference in length of the groove or the indentation outside and inside the worn area.

iii. using optical microscope fitted with micrometer – very common and effective method.

iv. using scanning electron microscope (SEM) – used generally, for detailed study; both qualitative and quantitative.

v. Talysurf, especially for shallow crater wear.

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