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7/31/2019 Tool Matls and Fluids
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7/31/2019 Tool Matls and Fluids
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7/31/2019 Tool Matls and Fluids
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Tool Wear
1. Crater Wear
– Tool-chip interface
– Predominant at high speed
– Mitigated by efficient use of carbides
2. Flank wear – Tool-work piece interface
– Predominant at low speeds
7/31/2019 Tool Matls and Fluids
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Cutting Tool Materials
• High-speed steels
• Cast-cobalt alloys
• Carbides• Coated tools
• Ceramics
• Diamond
7/31/2019 Tool Matls and Fluids
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High-speed steels
• Molybdenum (M-series) – Contains up to 10% Molybdenum
– High abrasion resistance
–
Low distortion during heat treating – Low cost
– 95% of all high-speed steels are M-series
• Tungsten (T-series)
– Improved strength and hot hardness
– More expensive than M-series
7/31/2019 Tool Matls and Fluids
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Cast-cobalt alloys
• 38 to 53% cobalt
• High hardness
• Not as tough as high-speed
steels
• Used for deep continuous
roughing cuts
•High feed rates
7/31/2019 Tool Matls and Fluids
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Carbides
• Tungsten carbides (WC)
– Bonded together in a cobalt matrix
– Sintered
–6 to 16% cobalt
– Have largely replaced HSS tools
– Used for cutting steels and cast irons
7/31/2019 Tool Matls and Fluids
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Carbides
• Titanium carbides (TiC)
– Bonded in a Nickel-
molybdenum matrix
–
Higher wear resistancethan WC
– Not as tough as WC
– Used for cutting steels and
cast irons – Suitable for higher speeds
than WC
7/31/2019 Tool Matls and Fluids
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Coating materials
• Titanium-nitride
– Low friction and highhardness
• Titanium carbide
– Improves wear resistanceon WC
• Ceramics
•
Diamond – Increases tool life ten fold
compared to othercoatings
7/31/2019 Tool Matls and Fluids
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22.6: Alumina Based Ceramics
• Ceramic Tools
• Primarily made of aluminum oxide
• Introduced in the early 1950s
• After being cold pressed into insert shapes
under high pressure and sintered at high
temperature, they are known as “white
ceramics”.
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22.6 Alumina Based Ceramics
• Cermets (Black Ceramics)
• Consist of ceramic materials in a metallic matrix
• Typically: 70% Aluminum Oxide, 30% Titanium Carbide
• Not widely used due to high cost
Cermets tip
cutting blade.
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22.7: Cubic Born Nitride
• Cubic Boron Nitride• cBN: 2nd hardest material available
• Formerly known as Borazon
•
Polycrystalline cubic boron nitride is bonded to a carbidesubstrate by sintering under high pressure and temp.
• High thermal conductivity
• Excellent wear resistance
CBn coated cutting inserts
7/31/2019 Tool Matls and Fluids
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22.8: Silicon-Nitride-Based Ceramics
• Consist of silicon nitride, aluminum oxide, yttrium
oxide, and titanium carbide.
• Characteristics:
• Tough• Hot hardness
• Good thermal shock resistance
Sialon sink roll
bearing
7/31/2019 Tool Matls and Fluids
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22.9: Diamond
• Characteristics:
• Hardest material known today
• High wear resistance
• Low friction
• Maintains a sharp cutting edge
• Produces a very accurate cut and good surface finish.
• Most effective in light uninterrupted finishing cuts.
7/31/2019 Tool Matls and Fluids
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22.9: Diamond
• Synthetic diamonds are preferred because natural diamonds
have flaws which at times make them unpredictable.
Image of a
synthetic Russiandiamond
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22.9: Diamond
• Polycrystalline Diamond Tools
• Known as compacts
• May be used as dies for fine wire drawing
• Between .5 and 1 mm of diamond are bonded to acarbide substrate. (similar to cBN tools)
Image of acompact
7/31/2019 Tool Matls and Fluids
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22.10: Whisker-Reinforced Tool Materials
• Due to the high reactivity of silicon carbide with ferrrous
metals, SiC tools are unsuitable for machining irons and steels.
• Whisker-reinforced cutting tools include:
• silicon-nitride based tools with silicon-carbide whiskers
• Aluminum-oxide based tools reinforced with 25- 40 % silicon-
carbide whiskers
Image of whisker-
reinforced ceramics
7/31/2019 Tool Matls and Fluids
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22.11: Tool Costs and Reconditioning of
Tools
• Factors that affect tool cost:
• Material
• Size
• Shape
• Chip-breaker features
• Quality
7/31/2019 Tool Matls and Fluids
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Summary
Tools fail slowly with gradual wear or suddenly with fracture
Cutting fluids help reduce the effects of wear and temperaturefailure
The materials of the tool and the workpiece affect the tool shapeand life
Higher cutting speeds increase the operating temperature and
decrease tool life
It is necessary to calculate proper feed and speed to preventexcessive tool wear