MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II Chapter 5 TOOL WEAR AND TOOL LIFE Prof. Dr. S. Engin KILIÇ 4/26/2017 MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II

MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II Content Tool Wear and Life Machinability Economics of Metal Cutting Operations Optimization Criteria Choice of Cutting Conditions Unit Production Time Unit Production Cost Photos from internet sites. 4/26/2017 MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II

Tool Life - Definitions A tool that no longer performs the desired function is said to have reached the end of its useful life. Criterion to mark the end point for the tool’s life is not necessarily to correspond to a state that the tool is unable to cut the workpiece, but that it is merely unsatisfactory for the purpose. Such tools which have consumed their lives may be Resharpened (if applicable) and used again Used on less restrictive operations Disposed off Add picture here! 4/26/2017 MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II

MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II Tool Wear Failure of the tool to perform a desired function may be due to Catastrophic failure Fracture Temperature Gradual (progressive) failure Forms of wear Crater wear Flank wear Workpiece Tool Flank Rake Chip Crater wear 4/26/2017 MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II

MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II Tool Wear Mechanisms 4/26/2017 MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II

MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II Tool Wear (f) (g) Taylor tool life equation: 4/26/2017 MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II

MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II Tool Wear (2) 250 200 150 100 50 0.8 0.7 0.6 0.5 0.4 0.2 0.1 0.3 C D B Rapid breakdown Uniform wear rate Initial Width of flank wear land VB, mm VB Cutting time, s 4/26/2017 MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II

MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II Tool Wear (3) KT KB KM A + re Crater Rake Section A-A Zone C B N VN VC b b/4 VB VBmax Wear notch 4/26/2017 MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II

MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II Tool Life Criteria A tool-life criterion is defined as a predetermined threshold value of a tool-wear measure or the occurrence of a phenomenon. For HSS or Ceramic Tools Catastrophic failure, or VB = 0.3 mm (uniformly worn flank in zone B) or VBmax = 0.6 mm (irregularly worn flank) VB = 0.75 mm (HSS – finish) VBmax = 1.5 mm (HSS – rough) ISO Double check! Schey’s recommendation 4/26/2017 MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II

MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II Tool Life Criteria (2) For Sintered Carbide Tools: VB = 0.3 mm (uniformly worn flank in zone B), or VBmax = 0.6 mm (irregularly worn flank), or KT = 0.06 + 0.3f mm (f : feed) VB = 0.4 mm (uniformly worn flank in zone B), or VBmax = 0.6 mm (irregularly worn flank) ISO Schey’s recommendation 4/26/2017 MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II

MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II Tool Life Tool life is defined as the cutting time required to reach a tool-life criterion. Most important factor affecting tool life (for a given work material-tool combination) is the cutting speed. 4/26/2017 MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II

Taylor’s Tool Life Model Frederick W. Taylor (1856-1915) 4/26/2017 MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II

MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II Taylor’s Equation vTn = C v : cutting speed [m/s] T: tool life [min] C: Constant [m/s] (cutting speed for 1 min. tool life) Typical values of n are 0.1 HSS 0.25 Cemented Carbides 0.3 Coated Carbides 0.4 Ceramics For an approximate value of C: take recommended value and multiply it by 1.75 (HSS) or 3.5 (Carbides). Kennametal: Revise the definitions 4/26/2017 MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II

Extended Taylor’s Equation For HSS: 0.1 < 0.17 < 0.25 4/26/2017 MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II

MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II Machinability Machinability is defined as the relative ease and economy with which a material (usually a metal) can be machined using appropriate tooling and cutting conditions. There are various criteria to evaluate machinability: Tool life Forces and power Surface finish Ease of chip disposal 4/26/2017 MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II

Material Properties Affecting Machinability Ductility Strain hardening ability Strength Bonding tendency between tool and workpiece Thermal conductivity Melting temperature Abrassive particle content of workpiece Existence of second-phase particles (lead, sulphur, phosphorus, etc.) which are soft or softened at high temperatures (favors machinability!) 4/26/2017 MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II