25-07-2012, 03:13 PM
CUTTING TOOL TECHNOLOGY
CUTTING TOOL TECHNOLOGY.ppt (Size: 1.39 MB / Downloads: 53)
Three Modes of Tool Failure
Fracture failure
Cutting force becomes excessive and/or dynamic, leading to brittle fracture
Temperature failure
Cutting temperature is too high for the tool material
Gradual wear
Gradual wearing of the cutting tool
Preferred Mode: Gradual Wear
Fracture and temperature failures are premature failures
Gradual wear is preferred because it leads to the longest possible use of the tool
Gradual wear occurs at two locations on a tool:
Crater wear – occurs on top rake face
Flank wear – occurs on flank (side of tool)
Taylor Tool Life Equation
where v = cutting speed; T = tool life; and n and C are parameters that depend on feed, depth of cut, work material, tooling material, and the tool life criterion used
n is the slope of the plot
C is the intercept on the speed axis at one minute tool life
Tool Materials
Tool failure modes identify the important properties that a tool material should possess:
Toughness ‑ to avoid fracture failure
Hot hardness ‑ ability to retain hardness at high temperatures
Wear resistance ‑ hardness is the most important property to resist abrasive wear
High Speed Steel Composition
Typical alloying ingredients:
Tungsten and/or Molybdenum
Chromium and Vanadium
Carbon, of course
Cobalt in some grades
Synthetic Diamonds
Sintered polycrystalline diamond (SPD) - fabricated by sintering very fine‑grained diamond crystals under high temperatures and pressures into desired shape with little or no binder
Usually applied as coating (0.5 mm thick) on WC-Co insert
Applications: high speed machining of nonferrous metals and abrasive nonmetals such as fiberglass, graphite, and wood
Not for steel cutting