29-11-2012, 04:21 PM
CUTTING TOOL TECHNOLOGY
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Introduction
•Machining is accomplished by cutting tools.
•Cutting tools undergo high force and temperature and temperature gradient.
•Tool life
•Two aspects of design
–Tool Materials
–Tool Geometry
•Cutting fluids
Tool life
•Three modes of failure
–Premature Failure
•Fracture failure -Cutting force becomes excessive and/or dynamic, leading to brittle fracture
•Thermal failure -Cutting temperature is too high for the tool material
–Gradual Wear
•Gradual failure
•Tool wear: Gradual failure
–Flank wear -flank (side of tool)
–Crater wear -top rake face
–Notch wear
–Nose radius wear
Possible Wear Mechanisms
•Abrasion–Flank and Crater wear
–Hard Inclusions abrading Cutting tools
–Hot Hardness Ratio
•Erosion
•Attrition
•Adhesion
–Compatibility chart
•Diffusion/Dissolution–Crater wear
–Chemical solubility
–Diamond dissolves into iron.
–Oxide coating resists crater wear.
• Plastic deformation
Tool Materials
•Plain Carbon and Low Alloy Steels
–Before High Speed Steels
–Due to a high carbon content, heat treated to Rc=60
–Poor hot hardness
•High-speed steels (HSSs)
–tungsten type (T-grade)–12-20% of W
–molybdenum type (M-grade)-6% W and 5% Mo
–Other elements: Tungsten and/or Molybdenum, Chromium and Vanadium, Carbon, Cobalt in some grades
–Typical composition: Grade T1: 18% W, 4% Cr, 1% V, and 0.9% C