tool matls and fluids

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



Cutting Tool Materials

• High-speed steels

• Cast-cobalt alloys

• Carbides• Coated tools

• Ceramics

• Diamond

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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



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



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

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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



Coating materials

• Titanium-nitride

– Low friction and highhardness

• Titanium carbide

– Improves wear resistanceon WC

• Ceramics

•

Diamond – Increases tool life ten fold

compared to othercoatings



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”.



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.



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



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



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.



22.9: Diamond

• Synthetic diamonds are preferred because natural diamonds

have flaws which at times make them unpredictable.

Image of a

synthetic Russiandiamond



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



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



22.11: Tool Costs and Reconditioning of

Tools

• Factors that affect tool cost:

• Material

• Size

• Shape

• Chip-breaker features

• Quality



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

tool matls and fluids

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