Machinery's Handbook, 31st Edition
Microcutting Tools 1167 50 m m flank/nose wear on carbide tools, or chipping dimensions relative to cutting tool grain size, or peeling of tool coating, etc. A variety of techniques have been suggested for tool monitoring; the direct techniques measure the tool conditions (e.g., flank wear, crater wear) while the indirect techniques measure the consequence of tool wear (e.g., burr size, change of microhole diameter). Table 3. Microtool Wear and Monitoring Techniques Measurement Metrology Equipment / Sensor
Tool wear Tool edge conditions Wear particles Particle radioactivity
Microscope
Spectrophotometer, scintillator
Direct
Tool-workpiece junction resistance Workpiece features (hole diameter, slot depth…)
Voltmeter Microscope Interferometer
Dynamometer Strain gage, ampere meter Acoustic emission transducer Microphone
Cutting force, torque, power
Sound emitted from tool-workpiece friction
Accelerometer Displacement sensor
Vibration
Indirect
Thermocouple Pyrometer
Temperature
Profilometer, interferometer, optical profiler… Microscope, interferometer, optical profiler…
Surface roughness Burr dimension
The importance of tool life monitoring and tool life prediction is presented in the section MACHINING ECONOMETRICS starting on page 1196. The following material expands from that and covers relevant information for tool life of microtools. The general Taylor equation that relates tool life and machining parameters also applies in micromachining: (1) where V = surface cutting speed (m/min, ft/min) f = tool feed (mm/rev, in/rev) or chip load (mm/tooth, in/tooth) d = depth of cut (mm, inch) T = tool life (min) g, a, b, c = constants When thermal damage mechanism dominates then a >> b , c in Equation (1). The term a dominates mathematically and the effects of feed and depth of cut are insignificant com pared to speed. The general Taylor equation can be rewritten as: (2) If n = 1/ a , then this equation is the same as that in the Econometrics section: (3) When tool chipping occurs then both terms b , c >> a , therefore the feed and depth of cut are more important than surface speed. The general tool life reduces to V f d T g a b c = V T f d g a b c = VT f d g n b c = c C n = m
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