EXPERIMENT NO 8: GRINDING

SUBMITTED BY : vikas tirki

ROLL NUMBER: 13790

DATE OF SUBMISSION:9/07/2015

OBJECTIVE To study the effects of grinding variables on grinding forces, specific energy

and surface finish.

EXPERIMENTS The experimental set-up consists of HMT horizontal surface grinding machine

with reciprocating table, Quartz – 3 – component dynamometer with built – in

charge amplifiers for measuring the three orthogonal component of forces.

The dynamometer consists of four 3 – component Piezoelectric force sensor

fitted under high pre load between a base plate and a cover plate. The force

components are measured in terms of voltage across Piezoelectric sensor. A four –

range miniature change amplifier is fitted in the dynamometer for each of the 3

component. Therefore, the output signal at the dynamometer is of low impidence.

The integrated cable is connected to the control unit type 5233A. The control unit can

select the four measuring ranges in two groups (Fx and FY resp. Fz).

The control unit is easy to operate and contains power pack, keyboard with

status displays together with a connector for single input. The output voltages are

proportional to the forces occurring.

The number of active grains on the wheel surface can be measured by observing

the active surface of the wheel under a stereo-microscope. Illumination of the surface

at a glancing angle will provide considerable help in identifying the active cutting

grains. The active grains will have glazed appearance because of metal deposit. A

magnification factor of X50 will be sufficient for the purpose.

Surface roughness is measured with the help of a portable surface roughness

measuring instrument.

BACKGROUND Chip thickness t in surface grinding (Fig. 2.3) can be evaluated from the

equation.

4v d

tVCr D

Where C is the no. of active grains per unit area of wheel surface and

'

1.5b

rt

The specific energy (energy required to remove a unit volume of materials) u

can be evaluated from the equation.

BASIC POINTS

Wheel specification: A46J5VCJ

t = Chip thickness

l = Chip length

D = Wheel diameter

d = Wheel depth of cut

V = Wheel speed

v = Work speed

b = Width of grinding path

b′ = Chip width

Fig. 2.3 Chip produced in horizontal surface grinding (a) Schematic

view of the process, (b) Idealized chip and (c) Actual chip.

Where A= Aluminum oxide(Abrasive grain)

46=grain size

J=wheel grade ‘soft’

5=grain spacing

V=Vitrified (Wheel bond)

Wheel wear:

The three mechanisms of grinding Wheel wear are as follows:

1. Grain fracture : in which a portion of the grain breaks off during cutting.

2. Attrious wear : in which the grains become dull during cutting.

3. Bond fracture : in which the grains are pulled out of the bonding material.

1

Wheel dressing:

The most common form of dressing is performed using a DIAMOND-TIPPED

TOOL.Using a DIAMOND-TIP TOOL, the operator removes material from the

wheel’s surface.

Wheel balancing:

Out-of-wheel cause excess vibration , which leads to chatter marks.

Detecting wheel balance:

1. A simple method for detecting wheel imbalance is to take a wheel that has been

mounted on a mandrel and set it between two equal points, such as the balancing

stand. If the wheel stays at rest, even if it is rotated to a new position, it is said to

be in static balance.

If the wheel is then pushed along the stand, and it rotates smoothly, stopping only

when it losses momentum, the wheel is said to be in dynamic balance.If the

wheel is out of balance, it will rock back and forth before coming to rest with its

heaviest side down.

2. A current and more practical method of balancing uses movable weights that

attach to the outer flange. These weights are placed next to each other, opposite

the wheel’s heavy side, and are slowly moved apart until balance is achieved.

Sample calculation

wheel rpm =1500 wheel speed=1329.84m/min

Width of work piece =11mm

Diameter of wheel = 28.22 cm

Limiting value of depth of cut =0.002mm

Formula to be used for chip thickness

4v d

tVCr D

Work speed(V)=5 m/min

Depth of cut=6mm

Number of active grains per unit area(C)=800000 grains/m^2

5.1*800000*84.1329

2.282/006.0*5*4t

t =7.60*10^(-6) m = 7.60*10^(-3)mm

Other calculation:

S. No. Table

speed (v),

m/min

Depth of

cut (d),

mm

Tangential

force (Ft),

kgf

Normal

force (Fq),

kgf

Specific

energy (u),

J/mm3

Chip

thickness (t),

mm

1 5 0.006 214.29 953.06122 8457.44

7.60*10^(-3)

2 5 0.010 213.78 1157.1428 5062.38

8.64*10^(-3)

3 5 0.014 212.76 1325.5102 3598.74

9.40*10^(-3)

4 5 0.020 211.73 1470 2506.92

1.03*10^(-2)

5 10 0.006 209.18 1711.2244 4124.33

1.07*10^(-2)

6 10 0.010 208.16 1808.4693 2464.65

1.22*10^(-2)

7 10 0.014 207.65 2026.7346 1757.26

1.33*10^(-2)

8 10 0.020 207.65 2229.3877 1757.26

1.45*10^(-2)

9 15 0.006 208.16 2484.6938 2740.23

1.32*10^(-2)

10 15 0.010 214.29 3234.6938 1692.56

1.49*10^(-2)

11 15 0.014 226.02 3702.0408 1275.15

1.63*10^(-2)

12 15 0.020 229.59 3776.7346 906.70

1.78*10^(-2)

13 20 0.006 229.59 3865.3061 2266.75

1.52*10^(-2)

14 20 0.010 247.96 4156.0204 1468.87

1.73*10^(-2)

15 20 0.014 248.98 4173.4693 1053.51

1.88*10^(-2)

16 20 0.020 249.49 4208.6734 738.97

2.05*10^(-2)

Discussion and Observation and Conclusion:

With the constant speed of work table, the tangential force increase with the

increase in depth of cut. So, more force is required.

With the constant depth of cut tangential force increases with the increase in

speed. So there is large change in momentum

With the constant speed of work table normal force increases with the increase in

depth of contact.

With the constant depth of cut normal force increases with the increase in speed

of work table.

Specific energy decreases with the increase in chip thickness.

Specific energy decreases with the increase in depth of cut with constant work

table speed.

Normal force is much higher than the tangential force.