Automotive and Aerospace Industries

Cutting Tool Types and Observation and Inspection Using a Digital Microscope

The pursuit of higher strength, greater accuracy, and lighter weight has led to increasing demand for workpieces in difficult-to-cut shapes made from hard-to-cut materials, such as cemented carbide, hard brittle materials, and quenched stainless steel. Hard-to-cut materials put a large strain on cutting tools, so particular attention is required to monitor wear and chips (defects) on the edges of cutting tools. This section introduces types of cutting tools along with examples of observing and analysing them using our digital microscope.

What is Cutting?
Typical Cutting Methods and Cutting Tools
Typical Tool Materials and Features
Throwaway Tips
Examples of Observation and Inspection of Cutting Tools Using a Digital Microscope

What is Cutting?

Cutting refers to processing that cuts metal and other materials using tools such as blades.
Another metal processing method, called grinding, scrapes surfaces using a grindstone.

Principle of cutting

A cutting tool continuously chips the target material and generates chips.
In the ideal scenario, chips are generated in a continuous and smooth manner.

A: Uncut chip

B: Chip

C: Workpiece

D: Tool

E: Rake angle

F: Rake surface

G: Relief surface

H: Relief angle

Cutting conditions

The cutting speed, feed speed, and cut amount are all important factors for proper cutting.

Cutting speed = Distance cut per minute (m/min)

Cutting speed (m/min) refers to the distance that a tool cuts per minute.
The faster the cutting speed, the higher the productivity, but the shorter the service life of the tool.

A: Workpiece

B: Distance cut per minute

The faster the cutting speed,
the higher the productivity,
*but*
the shorter the service life of the tool.

Feed speed = Distance to travel per revolution (mm/rev)

The feed speed (mm/rev) refers to the distance that a tool travels per revolution.
As the feed speed increases, productivity increases but so does the roughness of the cut surface.

A: One revolution

B: Workpiece

C: Distance travelled per revolution

As the feed speed increases,
productivity increases
*but*
so does the roughness of the cut surface.

Cut amount = Distance to cut into the workpiece

The cut amount refers to the distance that a tool cuts into the workpiece.
The greater the cut amount, the higher the productivity, but the ideal cut amount is determined by the type and material of the tool.

The greater the cut amount,
the higher the productivity,
*but*
the ideal cut amount is determined by the type and material of the tool.

Typical Cutting Methods and Cutting Tools

This section describes typical cutting methods, their characteristics, and the cutting tools that are used.

Turning

Generally, this method cuts cylindrical or discoidal workpieces into round shapes by turning them.

Drilling

Tools rotate to make holes in surfaces of workpieces.

Boring

Tools rotate and machine the inside of drilled holes with high accuracy.

Broaching

Broaches (tools to finish holes) cut workpieces by moving linearly. Broaching can perform a whole process (through to finishing) with one machine, and it’s easy to estimate the service life of tools. These factors make broaching attractive to the automotive industry where mass production is necessary.

Gear cutting

Gears are cut with a rotating cutter.

Milling

Milling removes material by turning a tool called a milling cutter. Milling machines are used to shave surfaces and make grooves. There are generally 2 types: face milling cutters for surface machining, and end mills for grooving.

Typical Tool Materials and Features

This section describes the materials and features of typical cutting tools.

High-speed steel

Metals, including tungsten, chromium, vanadium, and molybdenum, alloyed with an iron base

AdvantageExcellent toughness
DisadvantagesLower heat and wear resistance

Target materials: Carbon and alloy steel

Cemented carbide

Alloys of titanium carbide and tantalum carbide that are added to tungsten carbide powder and then sintered using cobalt.

AdvantagesExcellent balance of toughness, high hardness, and wear resistance

Target materials: Carbon steel, alloy steel, stainless steel, and other cutting resistant materials

Ceramic

Hard materials, including aluminium oxide, titanium carbide, and silicon nitride, that are sintered.

AdvantagesExcellent heat and wear resistance
DisadvantagesPoor toughness and chip easily

Target materials: Cast iron, heat-resistant alloys, quenched steel, and tool steel

Diamond

Moulded material made from diamond monocrystal (the hardest material)

AdvantagesExcellent heat and wear resistance, and suitable for mirror face cutting
DisadvantagesPoor toughness and chips easily

Target materials: Non-ferrous metals including aluminium

Sintered diamond

Polycrystalline body made by adding cobalt to fine diamond powder and sintering.

AdvantagesExcellent heat and wear resistance, and higher toughness than diamond
DisadvantageHard to make sharp edges

Target materials: Non-ferrous metals, cemented carbide, ceramics

Cermet

Nickel and other materials are added to titanium carbide and titanium nitride and then sintered.

AdvantagesA type of cemented carbide. Excellent wear and corrosion resistance compared with normal cemented carbide. It is often used for finishing steel.

Target materials: Carbon and alloy steel