Tool Life (T): Definition & Key Influencing Factors

Tool life (T) is defined as the total cutting time (in minutes) until a tool reaches a specified wear criterion. In production, tool life is commonly defined as the time required to reach normal flank wear of VB = 0.3 mm.

Other definitions of tool life include:

• Reliability life: The number of workpieces completed to quality standards under specified cutting conditions.

• Dimensional accuracy life (automated production): The number of workpieces produced while maintaining required dimensional accuracy.

• Fatigue life: The number of impact cycles a tool withstands before failure.

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Factors Affecting Tool Life

1. Cutting Speed (vₐ)

Increasing cutting speed (vₐ) raises cutting temperature and accelerates wear, thereby reducing tool life (T). When the wear criterion is set to VB = 0.3 mm, the relationship between cutting speed and tool life can be expressed as:

vc⋅Tm=Cvc​⋅Tm=C

Where:

• m = exponent indicating the influence of vₐ on T (determined through cutting experiments)

• C = constant (depends on workpiece material, tool material, and other conditions)

Typical m values (when turning carbon steel and gray cast iron):

Practical example:

Using an indexable carbide turning tool to machine 45 steel:

• When vₐ = 100 m/min → T = 60 minutes

• When vₐ = 150 m/min → T = 12 minutes

*Increasing cutting speed by 0.5× (50%) reduces tool life to 1/5 of its original value.*
Conclusion: Cutting speed has a very significant effect on tool life.

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2. Feed Rate (f) & Depth of Cut (aₚ)

Increasing feed rate (f) or depth of cut (aₚ) both reduce tool life, but to different degrees:

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3. Tool Geometry

Key geometric parameters affecting tool life include:

• Rake angle (γₒ)

• Lead angle (κᵣ) (also called entering angle)

• End cutting edge angle (κ’ᵣ) (also called clearance angle)

• Nose radius (rₑ)

Rake angle (γₒ):

• Increasing γₒ reduces cutting temperature and extends tool life

• However, too large a rake angle reduces tool strength and heat dissipation, shortening tool life

• There is an optimal rake angle for each set of machining conditions, determined through production experience and cutting experiments

Lead angle (κᵣ), end cutting edge angle (κ’ᵣ), and nose radius (rₑ):

• Decreasing κᵣ and κ’ᵣ increases tool strength and reduces cutting temperature

• Increasing rₑ also improves tool strength and reduces cutting temperature

• All three changes help extend tool life

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4. Workpiece Material

Higher strength, hardness, and toughness of the workpiece material lead to:

• Higher cutting temperatures

• Shorter tool life

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5. Tool Material

Tool material is a major factor influencing tool life:

Effective ways to extend tool life:

• Use coated tools

• Select high-performance tool materials (e.g., carbide, ceramic, CBN, PCD)

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