Grinding Wheel-Grinding Process: Grinding is the conventional finish machining operation used for producing a good surface finish on the components.
The abrasive particles present on the surface of a grinding wheel will be acting as a single point cutting tools for removing the material from the workpiece.
The cubical or rectangular shape of the abrasive particles used in the grinding wheel will produce an approximate cross-section of the chip as triangular.
As the machining continuous, the abrasive particles are wearing out slowly so that the blunt abrasive particles will be started rubbing onto the workpiece producing rubbing forces.
These rubbing forces will pull out the blunt abrasive particles so that the fresh and new abrasive particles present behind will come in contact with the workpiece and started removing the material from the workpiece called as self-sharpening of the grinding wheel.
Out of all the conventional machining methods, the grinding is the one which requires the highest specific cutting energy.
This is because of
- Random orientation of the abrasive particles i.e. during the manufacturing of a grinding wheel by using powder metallurgical process, the abrasive particles are oriented randomly.
- Therefore, only one-third of the abrasive particles are acting as a single point cutting tool and remaining are simply rubbing onto the workpiece without doing any machining.
Hence, rubbing energy losses are higher which increases the specific cutting energy.
- Lower penetrating Arc ploughing action i.e.even though the abrasive particles have the capability to penetrate more into the workpiece but the presence of the bonding material besides the abrasive particle is not allowing the abrasive particle to penetrate more into the workpiece.
hence, the size of the chip produced is reduced and it reduces the material removal rate.
The machining ratio for the earlier machining operations is very high. hence, this value is neglected but, machining ratio in grinding operation is called a grinding ratio.
If the abrasive particles present on the periphery or circumference of a grinding wheel and if it is used for removing the material from the workpiece called as plunge grinding.
If the particles present on the face of a grinding wheel and if it is used for performing the machining operation then it is called a surface grinding operation.
Time/cut = L/fN
fm– Table feed in mm/min
f- Table feed in mm/rev
Out of all the conventional machining methods, the grinding operation is used at very high cutting velocity and broaching is done at the lowest cutting velocity.
V is equal to 18000 to 3000 metre per minute.
For Grinding Operation:
V= 18000 to 30000 m/min
For Broaching Operation:
V = 0.1 to 0.5 m/min
I will tell you how to remember the specification of the grinding wheel. It is simple for me to remember and it will be simple for you if you just follow the below diagram. The grinding wheel will be specified by using a standard 5 parameter code.
These parameters will be remembered as follows.
If you see the image, It has an Alphabet, Number, Alphabet, Number, Alphabet in the sense, the first parameter starts by an Alphabet which is (A, B, C, D) and you can understand the rest easily.
Just look at the below diagram.
The 1st Parameter is the Type of Abrasives and as an indicator, it must be an alphabet.i.e.
1st Specification-Type of Abrasives:
“Type of abrasives” indicates the material used for manufacturing of abrasive particles.
- B4C- Poor performance in machining.
- Diamond is very costly.
hence Aluminium Oxide(Al2O3)) and Silicon Carbide(SIC) are most commonly used abrasive particles in the grinding wheel.
- Aluminum Oxide is soft and tougher than silicon carbide whereas
- Silicon Carbide is hard and brittle than aluminum oxide.
Selection of type of abrasive is based on the mechanical properties of workpiece material i.e. for grinding of soft and ductile workpieces, the aluminum oxide will be used and for grinding of hard and brittle workpieces, silicon carbide will be used.
2nd Specification-Grain Size:
Grain Size or Grit Size
10-24 –> Coarse Grains
30-60–> Medium Grains
220-600–>Very Fine Grains
The formula for determining the Grain Size is
x indicates Grain size and
GSN indicates Grain Size Number.
As the grain size of abrasive particles is increasing or the grain size number is reducing, then the material removal rate is increased first and then decreasing.
Selection of grain size of the abrasive particle is based on surface finish requirements on the workpiece i.e. for
- Rough grinding operation, course or medium grain size is selected and for
- Finish grinding operation, fine or very fine grain size will be selected.
The grade of grinding wheel indicates the hardness of the grinding wheel.
A-H–> Soft Grade
Even though everything is the same, the grade of grinding wheel can be changed by changing the pressure applied in the compacting stage of powder metallurgical process used for manufacturing of grinding wheel i.e. by applying large amounts of pressure, hard wheels can be obtained and by the small amount of pressure, soft wheels can be obtained.
The grade of grinding wheel will be selected based on the mechanical properties of the workpiece material.
During the grinding of hard workpieces, the forces induced are very high. Therefore, tool wear is high and abrasive particles will become blunt very fast i.e. within 2 to 3 minutes, the blunt abrasive particles will start rubbing onto the workpiece producing rubbing forces.
These rubbing forces are not sufficient to pull out the blind abrasive particles if the grinding wheel is hard.
Hence, the grinding wheel is simply rubbing onto the workpiece before performing the machining called as glazing or blunting of grinding wheel.
To remove this glazing of grinding wheel, the dressing is to be done.
The dressing is a turning operation used for removing a layer of material from the surface of a grinding wheel using a diamond cutting tool. The conditions are as follows.
1. This dressing operation will take 10 to 15 minutes I.e. if hot wheels are used for grinding of hard workpieces, for every 2 to 3 minutes of grinding operation it is required to spend 10 to 15 minutes of dressing time. hence, it is not recommended.
2. If soft wheels are used for grinding of hard workpieces, whatever rubbing forces produced by the blunt abrasive particles is more than sufficient to pull off the particles.
Hence a self-sharpening of grinding wheel will be taking place.
3. Soft wheels are not used for grinding of soft workpieces because it is not economical.
0-7 indicates Dense Structure and
8-16 indicates Open structure.
The structure of the grinding wheel can be changed by changing the percentage of abrasive particles present in the grinding wheel.
The structure is selected based on mechanical properties of workpiece material and surface finish requirements on the workpiece.
During grinding of a soft workpiece and rough grinding operation, the size of the ship produced is larger.
If a dense structure is used because of the presence of a smaller gap between the Abrasive particles, the large size chips may get clogged in between the abrasive particles and it is not allowing the next abrasive particle to participate in machining operation and this is called loading of grain grinding wheel.
If an open structure is used for this, because of a large gap between abrasive particles there is no clogging will be taking place.
During grinding of a hard workpiece, because of forces induced are higher and to withstand for this process, the abrasive particles must be very close. hence, the dense structure is used.
Rough grinding of soft workpiece: 12-16
Finish grinding of soft workpiece:7,8,9.
Rough grinding of hard workpiece:6,7,8.
Finish grinding of hard workpiece:<5.
The bond indicates the bonding material used for producing a bond between the abrasive particles.
1.Vitrified: It is the most commonly used bonding material in grinding wheels because it produces higher bonding strength with temperature withstanding capability and high thermal conductivity.
2.Shellac or rubber:
It is used as a bonding material for producing flexible grinding wheels called buffing wheels.
This is the detailed explanation of Grinding Process and Grinding wheel along with its specifications.
If this article is helpful to you, Let it be Shared…
Read: Surface Grinding Machine: Definition, Types of Grinding Process, Function of Parts, Working