17-01-2013, 03:39 PM
CUTTING TOOL TECHNOLOGY
CUTTING TOOL TECHNOLOGY.pdf (Size: 886.03 KB / Downloads: 241)
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
Cemented Carbides
•Advantages (Cemented Carbide, Cermets & Coated Carbides)
–
High compressive strength and modulus
–
High room and hot hardness
–
Good wear resistance
–
High thermal conductivity
–
Lower in toughness that HSSs
•Grades
–
Nonsteels grade –WC-Co
–
Steel grades –add TiC and TaC due to the high solubility of WC into steels resulting in extensive crater wear
•Cemented Carbides –Mainly WC-Co
–
As grain size is increased, hardness decreases but TRS increases.
–
As the content of cobalt increase, TRS increases but hardness decreases.
–
For roughing or milling, high cobalt is desirable
–
For finishing, low cobalt is desirable.
Coated carbides
•Since 1970, they improve machinability.
•One or more layer of thinlayers of wear resistance CVD or PVD coating such as TiC, TiN, Al2O3, ZrN, CrC or Diamond.
•Coating thickness = 2.5 -13 μm (0.0001 to 0.0005 in)
•Applications: cast irons and steels in turning and milling operations
•Best applied at high speeds where dynamic force and thermal shock are minimal