GRINDING AND DRILLING MACHINE CLASSIFICATION AND OPERATION

GRINDING MACHINE AND OPERATION

Abrasive grain+bond = Abrasive wheel

ABRASIVE GRAINS USED IN WHEELS ARE:-

• ALUMINIUM OXIDE 
• CERAMICS 
• SILICON CARBIDE 
• CUBIC BORON NITRIDE 
• DIAMOND

 Bonds hold the abrasive particles to the wheels. There are many bonds particles such as

• SILICATE 
• RESINOID 
• VERTIFIED 
• SHELLAC 
• RUBBER 
• OXY CHLORIDE 
• A ABRASIVE WHEEL

BASIC IDEA OF GRINDING:-
A grinder is a machine that performs machining by abrasive action of abrasive wheel which acts as cutting tool.The abrasive wheel has abrasive grains on it which removes small amount of material in form of small chips when wheel comes in contact of work piece. The material removal occurs as a result of shear deformation.

                              Fig:-grinding wheel action

Grinding is basically performed for finishing operation. It can attain high surface accuracy of 0.00002 mm. Mostly it is employed to remove material depth of 0.25 to 0.50 mm depth. But in some cases it can be employed to remove large material from work piece.
Coolant is also used during abrasive action as because large amount of heat is produced during abrasive action due to friction between abrasive wheel and work piece.

• The coolant helps to carry away heat from working region. 
• Carry away burr/machined particles. 
• Lubricates parts . 
• Lets have a look at a grinding machine.

Type of grinding machine:-

• Belt grinder 
• Bench grinder 
• Cylindrical grinder 
• Surface grinder 
• Jig grinder 
• Gear grinder 

1.. BELT GRINDER:-



Fig:-belt grinder

As it is abrasive machining process, it consists of a belt coated with abrasives. This coated abrasive belt is allowed to move over the surface of the work piece.
In actual belt grinders are used to provide surface finish. It removes very small amount of material from the work piece and provides dimensional accuracy.

APPLICATION:-

• Burr removal, stock removal from material. 
• Edge refining /shaping. 
• Polishing. 

2.. BENCH GRINDER:-



Fig:-bench grinder

It is basically mounted on the floor stand or workbench. These generally contain two abrasive wheel as shown in figure. Each abrasive wheel has abrasive grain of different sizes. Both roughing and finishing operation can be performed. They are generally used to shape the tools, their edges. For e.g. lathe tool bits etc.

3.. CYLINDRICAL GRINDERS:-

These are generally employed to obtain cylindrical objects of high surface finish and accuracy. There may or may not be multiple wheels. The work piece is allowed to rotate and grinding wheel makes contact with the work piece. The work piece is supported between tool and stationary wheel.

Apart from this grinder also performs action such as high precision gear manufacturing, acts as drill bit, finishing jigs and surface operation and finishing.

DRILLING MACHINE

A drilling machine a device that uses drill bit and is conventional machining process. Drilling is basically a process of making holes in work piece. The diameter varies from 0.025 mm to 1250 mm. It is a motor fitted device that has tool on the other end and is allowed to move (rotate) at required speed in order to create a new hole or to enlarge the existing hole.

OPERATION:-The process involves rotary tool bit which is pressed against solid work piece. The tool is sharp edged on the entrance side and on the exit side it has it is marked with burrs. The operation starts with supplying electric power to motor which allows it to rotate at high speed. This rotary motion is supplied to the spindle. As the spindle rotates, it intern rotates the tool at high speed. This rotary tool is pressed against the work piece and hence causes shear deformation of work piece.

The operation is mechanically sound as the material removal is accomplished by shear deformation of material layer by layer from inside of the hole, making the hole size increase layer by layer. Drilling machines are used for drilling, boring, countersinking, reaming, and tapping.

The various types of drilling machines available to us are:-

· Vertical drilling machine
· Horizontal drilling machine
· Multiple spindle drilling machine
· Gang drilling machine
· Center drilling machine
· Special purpose drilling machine.

1. VERTICAL DRILLING MACHINE:-

                     FIG:-VERTICAL DRILLING MACHINE

These are most widely used and it consists of vertical tool. The tool moves perpendicular to the work piece and used for mass production. Various tool like reamer, counter sink, drill bit is attached to the vertical spindle which is intern attached with motor as per operation required. As explained in working process, as motor rotates it rotates the spindle, which intern rotates the tool. This type of drilling also support automated operation in mass production process. Drill diameter of up to 12 mm can be easily achieved.

2. HORIZONTAL DRILLER:-

· The machine used for drilling large components like gas pipelines, or removing layer of rock from inside of ground. All this can be done with the help of horizontal driller.
· It is more complex process.

3. GANG DRILLING MACHINE:-

Its working and operation is similar to the vertical drilling machine. The major difference is that such machine has multiple spindle and each spindle carries a tool. Hence at same time such machine can drill number of holes whereas the vertical driller can machine only one hole. Such machine is very effective when we talk about mass production.
Automated production is feasible in such process.

4. MULTIPLE SPINDLE DRILLER:-

In such machine,for each tool there is single motor and multi spindle arrangement is there.
Two or three tools are assembled in one spindle. The advantage of such arrangement is, every tool can work separately at required speed and more than one hole is created at the same time. Such features enables to have automated operation. Used in mass production process.


Objective question on drilling:-

1) Tool used to cut a hole is called

a) Saw

b) Bit

c) Chisel

d) Hammer

2) How many types of drill press are there?

a) 2
b) 3
c) 4
d) 6

3) Drilling operation is done in order to :-

a) Machine the work piece,create hole.
b) Provide surface finish.
c) Both a and b
d) None of them


4) Drilling is a________process.

a) Conventional
b) Non conventional
c) Depends on operation
d) Both a and b


5) For mass production process which process is suitable?

a) Horizontal drilling
b) Vertical driller
c) Gang drilling
d) Multi spindle drilling
e) Both c and d.


6) Material deformation takes place by:-

a) Tensile stress
b) Shear deformation
c) Compressive action

d) Slipping phenomenon.