1. UNIT - IV
ABRASIVE PROCESS AND BROACHING
Abrasive processes: grinding wheel – specifications and selection,
types of grinding process– cylindrical grinding, surface grinding,
centreless grinding and internal grinding- Typical applications –
concepts of surface integrity, broaching machines: broach
construction – push, pull, surface and continuous broaching
machines
2. ABRASIVE PROCESS
Grinding is mainly used for the following purposes:
To remove small amount of metal from the work pieces
and finish them to close tolerances
To obtain a better surface finish
Sharpening of cutting tools
3. GRINDING WHEEL
Grinding wheels are made up of small abrasive particles
held together by bonding materials.
Grinding wheel abrasives
Natural abrasives
Artificial abrasives
4. Natural Abrasives
These are produced by uncontrolled forces of nature. These are
obtained from mines.
Sandstone or solid quartz
Emery (50 to 60% crystalline Al2o3 + iron oxide)
Corundum (75 to 90% crystalline Al2o3 + Iron oxide)
diamond
5. Artificial Abrasives
These are manufactured under controlled conditions in
closed electric furnace in order to avoid the introduction of
impurities and to achieve the necessary temperature for the
chemical reaction to take place.
Aluminium oxide
Silicon carbide
Artificial diamond
Boron carbide
Cubic boron nitride
6. TYPES OF BOND
Bond is an adhesive substance which holds the abrasive
grains together to form the grinding wheel.
Bonds are classified into two types.
Organic
Non - organic
13. DESIGNATION OF GRINDING
WHEEL
The following elements are represented in a definite order
type of abrasives
Grain size or grit number
Grade of the wheel
Structure
Type of bond
Manufacture’s code
14.
15. SELECTION OF GRINDING
WHEEL
The selection of a proper grinding wheel very important
for getting the best results in grinding work.
The grinding wheel selection will depend the following
factors
Constant factors
Variable factors
26. TYPE OF GRINDING MACHINES
According to the type of operation
According to the quality of surface finish
According to the type of surface generated
27. Further classification
Rough grinders
Floor stand grinders
Bench grinders
Portable grinders
Abrasive belt grinders
Swing frame grinders
Precision grinders
Cylindrical grinders
Internal grinders
Surface grinders
Tool and cutter grinders
Special grinders
28. Rough grinders
Rough grinders are mainly used for removing large
amount of metal from the work piece. Therefore the
surface finish and the accuracy in dimension are not
high.
34. Precision grinders
Precision grinders are used to manufacture parts of
accurate dimensions and good surface finish. The work
piece and the grinding wheel are rigidly mounted but
they are adjustable according to the requirement of the
machining methods
35. Cylindrical grinders
There are four movements in a cylindrical centre type
grinding.
Rotation of cylindrical work piece about its axis
Rotation of the grinding wheel about its axis
Longitudinal feed movement of the work past the wheel
face
Movement of the wheel into the work perpendicular to
the axis of the work piece to give depth of cut
36.
37. Type of grinding operations are carried out
Transverse grinding
Plunge grinding
38.
39. Type of cylindrical grinding
Plain centre type cylindrical grinding machine
Centre type universal grinder
40.
41. Surface grinders
Surface grinding machines are used to produce and
finish flat and plane surfaces. By using special fixtures and
form dressing devices, angular and formed surfaces can
also be ground.
Horizontal spindle reciprocating table surface grinder
Horizontal spindle rotary table surface grinder
Vertical spindle reciprocating table surface grinder
Vertical spindle rotary table surface grinder
46. CENTRELESS GRINDERS
– Centreless grinding is performed on work pieces which
do not have centres, such as pistons, valves, rings, shafts
etc. centreless grinding can be done on both external
and internal cylindrical surfaces.
60. CUTTING FLUIDS IN GRINDING
It cools the workpiece
It acts as a lubricant and reduces friction between chips,
workpiece and grinding wheel.
It removes chips from the contact area
61. CONCEPTS OF SURFACE
INTEGRITY
Surface integrity is the surface condition of a workpiece
after completing by a particular manufacturing process. In
grinding process, the surface integrity of ground specimen is
analysed.
Classification of surface integrity
Traditional process
Non traditional process
Finishing treatment
62. BROACHING
Broaching is a process of machining a surface with a special
multipoint cutting tool called broach which has successively higher
cutting edges in a fixed path.
It is a faster and cheaper method of machining but the depth of
removed material is limited to 6mm or less.
Broaching the inside surface is called “internal or hole broaching”
and the outside surface is known as “surface broaching”.
63.
64. SPECIFICATION OF A
BROACHING MACHINE
Maximum length of stroke in mm.
Maximum force developed by the slide in tonnes.
Power rating of electric motor in H.P
Speed and feed ranges
Weight of the machine
Floor space required
65. ADVANTAGES OF BROACHING
Roughing , semi-finishing and finishing cuts are completed in one
pass of the broach.
Broaching can be used for either external or internal surface
finishing processes.
Semi skilled worker can perform a broaching operation
Broaching is mostly adopted for mass production.
66. LIMITATIONS
Initial cost of the broach tool is high when compared to other
tools
Broaching is not suitable for the removal of large amount of stock.
Almost all the work pieces will need the fixture for rigid support.
