CuttingTool Materials

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Cutting-Tool Materials
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Inserts and Toolholders
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Complex geometrical tools
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CUTTING TOOL TECHNOLOGY

• Tool Materials are chosen to prevent failure,
  required to satisfy
• Toughness Impact forces on the tool in machining
  operations, vibration, during machining do not
  chip or fracture the tool.
• Hot hardness Hardness , strength and wear
  resistance of the tool are maintained at elevated
  temperatures.
• Wear resistance Acceptable tool life is obtained
  before the tool is replaced.
• Chemical stability No reactions between tool
  material and work part are allowed to prevent
  tool wear.

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Tool Materials
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Various Tool Materials in Chronological Order

• Tool Materials are usually divided into following
  general
• categories
• Carbon and medium-alloy steels (1880) Oldest
  tool material, rarely used in todays technology,
  poor hot hardness, need to be used in low cutting
  speed. Inexpensive, easily shaped and sharpened.
• High speed steels (1900) Good hot hardness,
  commercially one of the most important cutting
  tool material in use today. Good in complex
  geometries, less expensive, allows higher speed.
  Two basic types T-type Tungsten(tungsten and as
  alloying elements, chromium, vanadium, cobalt),
  M-type Molybdenum(tungsten and molybdenum,
  chromium, vanadium, cobalt)

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Various Tool Materials in Chronological
Order(continue..)

• Cast cobalt alloys Introduced in 1915,
  composites of cobalt, chronium and tungsten. They
  have better wear resistance than HSS, but not as
  good as cemented carbides. Toughness better than
  carbides, but not as good as high speed steels.
  Today not important. Capable heavy roughing cuts
  at speeds higher then HSS, feed higher then
  cemented carbides. Simple tool shape.
• Carbides(1930) (Cemented or sintered carbides)
  Hard tool material, divided into two categories
  Non-steel cutting grades which is used in
  machining aluminum, brass, copper, magnesium and
  titanium.Steel cutting grades. Both types show
  high compressive strength but low to moderate
  tensile stress, high hardness, good wear
  resistance, high thermal conductivity and hig
  modulus of elasticity. But toughness lower than
  HSS.

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Various Tool Materials in Chronological
Order(continue)

• Alumina based ceramicsCeramic tool materials
  introduced in the early 1950s. Usually consists
  of aluminum oxide and other oxides. Best for high
  speed turning of cast iron and steel. Also,
  applied to hardened steels if high cutting
  speed, low feed, low depth of cutand rigid work
  setup are employed. Results in good surface
  finish. Toughness is not good enough for
  roughing. Good hot hardness, high abrasion
  resistance.
• Coated tools (1960) Coating for cutting tools
  should have following characteristics (a)High
  hardness, (b)chemical stability, (c)low thermal
  conductivity, (d) good bonding, (e)little or no
  porosity. The coating may chip or peel due to
  dynamic force or thermal shock causing for
  premature tool failure.

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Various Tool Materials in Chronological Order
(continue)

• Cubic boron nitride Hardest next to diamond, but
  very expensive. It has good shock resistance and
  wear resistance. Good cutting edge strength.
  Prefered in small sized tools
• Silicon nitride Intendent for special
  aplications. Good thermal shock resistance. Not
  suitable for steel machining.
• Diamond Hardest tool material, used in high
  speed machining of non-ferrous metals and
  abrasive non-metals. Other metals are not
  practical, because of chemical affinity between
  metals and carbon. It has low friction, high wear
  resistance and used for good surface and accurate
  dimensions. Prefered in finishing cuts. It is
  brittle.

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Various Tool Materials in Chronological Order
(continue)

• Whisker-reinforced and nonocrystalline tool
  materials (new) Tool material that supplies high
  fracture toughness, resistance to thermal shock,
  good cutting edge strength and good hot hardness
  developed.

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General Characteristics of Cutting-Tool Materials
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General Properties of Tool Materials