Before starting discussion on “Different types of chips” lets see Mechanism of chips formation in machining.
What is Machining Process
Simple definition is “Machining is a semi finishing or finishing process essentially done to convert work piece in to desire shape and size.”
Under machining process excess material from the work piece is removed in the form of chips.
The form of chips is an important index of machining because it directly or indirectly indicates :-
- Nature and Behavior of material under machining process
- Amount of energy require to remove material (specific energy requirement)
- Nature and degree of interaction at the chip-tool interfaces.
The chips are depend on :-
- Work material or nature of work piece
- Geometry and material of cutting tool (Nature of tool)
- Level of cutting velocity and feed rate
- Machining environment or cutting fluid
- Dimension of tool
- Friction between tool and work piece
Types of chips :-
Different types of chips of various size ,shape ,color etc are formed during machining process and this all depend on:-
- Types of cut, i.e., Continuous (boring, turning etc) or intermittent cut (milling)
- Workpiece material (ductile or brittle etc.)
- Geometry of cutting tool(rake, cutting angles etc.)
- Cutting velocity feed rate (Low , medium , High )
- Cutting fluid
Basic major types of Chips are:-
Continuous Types Chips:-
- According to its name, continuous chips are formed by continuous plastic deformation of metal without fracture in front of the cutting edge of the tool and are formed by the smooth flow of the chip up the tool face.
- Ductile material like aluminium , mild steel , copper,are considered to be best for continuous type chips.
- this type of chips provide good surface finish
Require condition to form continuous type chips:-
- Material should be ductile in nature
- Rake angle and cutting speed should be high
- Friction should be minimum
- Deft of cut should be small
- Use of efficient cutting lubricants
- Tool material should have low-coefficient of friction
Without BUE (Built up Edge):-
|Rake angle||High and positive|
|Cutting fluid||Both cooling and lubricating|
Continuous chip with built up edge:-
- This type of chip is similar to continuous chip, only difference is that it has a build up edge at the face of tool and also it not so smooth.
- At high temperature and pressure chips material get stick to the cutting edge and tool face near the nose it is called BUE.
- As the cutting goes continuous built up edge increases and change the geometry of tool.
- This chip is obtain by machining on ductile material under high temperature and extreme pressure .
- Built up edge can be decreased by using a tool that has a lower chemical affinity towards the work piece material.
With BUE (Built up Edge):-
|Feed rate||Medium or Large|
|Cutting fluid||Inadequate or absents|
Discontinuous or segmental chips:-
- According to name this chips are breakup in to small segment and these chips are convenient to collect handle and dispose off.
- These type of chips are forms while machining the brittle material.
- This chips are formed when friction between tool and work piece is high and cutting speed is low with small rake angle.
Require condition for forming this type of chips:-
- Brittle material
- Low cutting speed
- Large chip thickness
- Small rake angle
Of irregular size and shape:-
|Work piece material||Brittle like grey cast iron|
Of irregular size and shape:-
|Work piece material||Ductile but hard and work hardenable|
|Took rake angle||Negative|
Comparison of Continuous chips, Continuous chips with built edge, Discontinuous chips:
|Sr. No.||Work piece material||Rake angle||Depth of cut||Cutting speed|
|Continuous chips with built edge||Ductile||Low/Medium||Medium||Medium|
|Discontinuous Chips||Brittle, Ductile but hard||Medium||High||Low|