Effect Of Different Machining Parameters On Machinability Of Different Materials

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Effect Of Different Machining Parameters

On Machinability Of Different Materials

SANJAY KUMAR 1, S.P. TEWARI2, JYOTI PRAKASH3 M.Tech1., Professor2, Research Scholar3

Mechanical Engineering Dept.,

Institute of Technology, Banaras Hindu University, Varanasi-221005,India

Abstract

It is important to view machining, as well as all manufacturing operations, as a system consisting of the workpiece, the tool and the machine. Machinability is the relative susceptibility of a material to the machining process. The ease with which a metal can be machined is one of the principle factors affecting a product's utility, quality cost. The usefulness of a means to predict machinability is obvious. Depending on the application, machinability may be seen in terms of tool wear rate, total power consumption, attainable surface finish or several other benchmarks. In this study ,the effects of variable machining parameters on machinability were investigated.

Key words : Machinibility, Machining parameters, Surface finish

1. Introduction

A customer study reveals that 60% of all components need some machining operation. One explanation for this is the inability to produce geometries as transverse holes, undercuts and treads during the pressing operation. Another explanation is the reported general trend towards design of complex parts that call for machining [1]. Powder metals are generally considered to have poor machinability in comparison with wrought or cast metal [2]. Influence of additive on the mechanical properties reveals that nearly all additives decrease the mechanical properties. If decreased mechanical properties can be accepted the effect of sulphur, selenium and tellurium increases, going from sulphur to selenium and tellurium [ 3]. There is a large effect from MnS addition . Explanation for the effect is reduced strain in the shear plane. Measurement of the acting forces (passive, feed and main force during a cutting operation reveals decrease in forces with MnS addition [4]. Machinability can be difficult to predict because machining has so many variables. In most cases, the strength and toughness of a material are the primary factors. Strong, tough materials are usually more difficult to machine simply because greater force is required to cut them. Other important factors include the chemical composition, thermal conductivity and microstructure of the material, the cutting tool geometry, and the machining process parameters. Sometimes, especially for non-metals, the ancillary factors are most important. For example, soft materials like plastics can be difficult to machine because of their poor thermal conductivity.[5]

2. Machining Parameters

Feed

The feed of a cutting tool in a lathe work is the tool advances for each revolution of the work. Feed is expressed in millimetre per revolution. Increased feed reduces cutting time.

Depth of cut

The depth of cut is the perpendicular distance measured from the machined surface to the uncut surface of the work piece. In a lathe, the depth of cut is expressed as follows;

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Machining Time

If s is the feed of the job per revolution expressed in mm per revolution, l the length of the job in mm, r.p.m. of the work is n, then time taken to revolve the job through l/s revolution for a complete cut will be;

T= l÷(s×n) min. ---(2)

Cutting Speed Cutting speed (v) of the tool is the speed at which the metal is removed by the tool from work piece.[6] V= π_{dn/1000 m/ min --- (3)}

Machinability can be based on the measure of how long a tool lasts. This can be useful when comparing materials that have similar properties and power consumptions, but one is more abrasive and thus decreases the tool life. The major downfall with this approach is that tool life is dependent on more than just the material is it machining; other factors include cutting tool material, cutting tool geometry, machine condition, cutting tool clamping, cutting speed, feed, and depth of cut. Also, the machinability for one tool type cannot be compared to another tool type (i.e. HSS tool to a carbide tool). Tool life can be expressed by the relation V_{= constant=c (Taylor Equation)} Where V = cutting speed in m/min. T= tool life in min. b,c are constants. For High speed steel cutting tool, b=0.1 and c=50 3. Experimental Analysis Material : Brass, Mid steel, Cast Iron TABLE FOR CALIBRATION OF DYNAMOMETER S NO. LOAD (Kg) Dynamometer reading(Div.) 1. 0 0

2. 11 15

3 16 22

4. 21 29

5. 26 35

6. 31 42

7. 36 49

8. 42 60

9. 47 66

10. 52 73

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In orthogonal turning operation, vertical force should be used which is measured with the help of dynamometer adjusted below the cantilevered tool( in the direction of force), so power consumed can be evaluated by following formula;

P= F×V --- (4) Where, F= cutting force in the direction of cutting.

V = cutting speed = DN m/min

For Mild Steel

(When feed, R.P.M. of the work piece are taken as constant and depth of cut is varying). Diameter of rod before machining = 24mm

Turned length of rod=6cm Machining time =10.4 min. Least count of vernier calliper=.02

Diameter of rod after turning operation =22.8mm

Cutting speed(r.p.m.) Feed Depth of cut(mm) Dynamometer reading(div.)

646 .227’’ 0.2 12

From Calibration chart, 12 div≈8.8 kg Cutting Speed = V= π_{× ×}

=π_×₂₄_{× 10}_×₆₄₆ =48.7 m/min

Cutting Force = 8.8 kg × 9.8 m/sec2 = 86.24 N

Power Consumed= F×V

= 86.24×48.7 =4199.8 Nm/ min. =69.9Nm/sec= 69.9 w

For Cast Iron:

( when feed,R.P.M. of the workpiece are taken as constant and depth of cut is varying). Diameter of rod before turning operation=24mm

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Machining time =10.4 min.

646 .227’’ 0.2 16

V= π_{× ×}

=π_×₂₄_{× 10}_×₆₄₆ =48.7 m/min

From Calibration chart, 16 div≈11.73 kg

Cutting Force= 11.73 kg × 9.8 m/sec2 = 114.95 N Power Consumed= F×V

= 114.95×48.7 = 5598.25Nm/ min. = 93.30/sec= 93.30 w

For Brass:

(When feed, R.P.M. of the workpiece are taken as constant and depth of cut is varying).

Diameter of rod before turning operation=24mm Turned length of rod=6cm

Machining time =10.4 min.

Feed= .227’’ taken from table on lathe=5.76 mm

646 .227’’ 0.2 14

V= π_{× ×}

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From Calibration chart, 14 div≈10.26 kg Cutting Force = 10.26kg × 9.8 m/sec2=105.7 N Power Consumed= F×V

= 105.7×48.7 = 5147.59Nm/ min. = 85.79Nm/sec=85.79 w

OBSERVATION TABLE:

For Brass

S No. Depth of cut Cutting speed

Feed(mm/rev) Dynamometer reading(div.)

Load(kg) Cutting force(N)

1 0.2 646 5.76 12 8.8 86.24

2 0.4 646 5.76 12.6 9.24 90.55

3 0.6 646 5.76 13.0 9.53 93.40

Cutting forces Vs depth of cut:

X- axis: depth of cut (mm) Y –axis: power consumption(w) Power Consumption Vs Depth Of Cut:

114 115 116 117 118 119 120 121

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S No. depth of cut(mm) Power consumption(w)

1 0.2 69.99

2 0.4 73.49

3 0.6 75.80

X- axis: depth of cut (mm) Y –axis: power consumption (w)

For Cast Iron

1 0.2 646 5.76 14 10.22 100.15

2 0.4 646 5.76 14.4 10.51 102.99

3 0.6 646 5.76 15.2 11.09 108.68

0 20 40 60 80 100 120

0 0.5 1 1.5 2 2.5 3 3.5

Series1

Series2

0 20 40 60 80 100 120

0 0.5 1 1.5 2 2.5 3 3.5

Series1

Series2

0 20 40 60 80 100 120

0 0.5 1 1.5 2 2.5 3 3.5

Series1

Series2

0 20 40 60 80 100 120

0 0.5 1 1.5 2 2.5 3 3.5

92 93 94 95 96 97 98

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X- axis: depth of cut (mm) Y –axis: cutting force (N)

POWER CONSUMPTION Vs DEPTH OF CUT:

1 0.2 81.28

2 0.4 83.59

3 0.6 88.21

X- axis: depth of cut (mm) Y –axis: power consumption (w)

114 115 116 117 118 119 120 121

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

0 20 40 60 80 100 120

0 0.5 1 1.5 2 2.5 3 3.5

Series1 Series2 0 20 40 60 80 100 120

0 0.5 1 1.5 2 2.5 3 3.5

Series1 Series2 0 20 40 60 80 100 120

0 0.5 1 1.5 2 2.5 3 3.5

Series1 Series2 0 20 40 60 80 100 120

0 0.5 1 1.5 2 2.5 3 3.5

92 93 94 95 96 97 98

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Series1 92 93 94 95 96 97 98

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Series1 92 93 94 95 96 97 98

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For Mild Steel

S No. Depth of cut

Cutting speed

1 0.2 646 5.76 16 11.68 114.46

2 0.4 646 5.76 16.4 11.97 117.30

3 0.6 646 5.76 16.8 12.26 120.15

X- axis : depth of cut (mm) Y –axis: cutting force (N)

POWER CONSUMPTION Vs DEPTH OF CUT

1 0.2 92.90

2 0.4 95.20

3 0.6 97.52

114 115 116 117 118 119 120 121

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

114 115 116 117 118 119 120 121

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X- axis: depth of cut (mm) Y –axis: power consumption(w)

(When depths of cut, R.P.M. of the workpiece are taken as constant and feed is varying). Readings of feed taken: .798’’=.202mm

.709’’=0.180mm .672’’=0.1706mm Depth of cut (taken as constant)= 0.4mm

For Cast Iron

Feed(mm) Dynamometer reading(div.)

Power (w)

1 0.4 646 0.170 10.0 7.3 71.86 58.30

2 0.4 646 0.180 10.5 7.7 75.46 61.24

3 0.4 646 0.202 10.5 7.7 75.46 61.24

0 20 40 60 80 100 120

0 0.5 1 1.5 2 2.5 3 3.5

Series1 Series2 0 20 40 60 80 100 120

0 0.5 1 1.5 2 2.5 3 3.5

Series1 Series2 0 20 40 60 80 100 120

0 0.5 1 1.5 2 2.5 3 3.5

Series1 Series2 0 20 40 60 80 100 120

0 0.5 1 1.5 2 2.5 3 3.5

92 93 94 95 96 97 98

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Series1 92 93 94 95 96 97 98

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Series1 92 93 94 95 96 97 98

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Series1 92 93 94 95 96 97 98

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For Mild Steel

(When depth of cut, R.P.M. of the work-piece are taken as constant and feed is varying). S

No.

Depth of cut

Cutting speed

Feed(mm) Dynamometer reading(div.)

Power (w)

1 0.4 646 0.170 17 12.46 122.10 99.10

2 0.4 646 0.180 17.3 12.68 124.32 100.9

3 0.4 646 0.202 17.4 12.76 125.05 101.49

71.5 72 72.5 73 73.5 74 74.5 75 75.5 76 76.5

0.16 0.17 0.18 0.19 0.2 0.21

C

UT

T

IN

G

F

O

RC

E

FEED

110 110.5 111 111.5 112 112.5 113 113.5 114

0.16 0.17 0.18 0.19 0.2 0.21

p

ow

e

r

N

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4. RESULT AND DISCUSSIONS

In this experimental analysis for the relative machinability of mild steel, brass and cast iron under varying feed and depth of cut, Cutting forces are measured with the help of dynamometer while keeping the cutting speed as a constant throughout the operation and hence power consumed is also calculated. It is found out that among the three materials, mild steel requires largest cutting force, and Brass requires lowest cutting force, range of cutting forces required for the cast iron comes in between the brass and mild steel. These results have been plotted in graphs between cutting forces Vs depth of cut, power consumption Vs depth of cut (when feed remains constant),and cutting force, power Vs feed ( when depth of cut is taken as constant).Chips of brass was found smaller than cast iron and because of brittleness of cast iron, hard chips of cast iron becomes the cause for tool wear, such as flank wear, crater wear. On the basis of cutting forces, power consumption measurement under the variation of depth of cut and feed respectively, form and size of the chips obtained during the operation , It is obtained that machinability of brass is better than cast iron and mild steel . mild steel has least machinability than cast iron because of higher cutting force, higher power consumption and long and continuous form of chips formed in the machining operation.

98.5 99 99.5 100 100.5 101 101.5 102

0.165 0.17 0.175 0.18 0.185 0.19 0.195 0.2 0.205

P

O

W

E

R

(W

)

FEED

110 110.5 111 111.5 112 112.5 113 113.5 114

0.16 0.17 0.18 0.19 0.2 0.21

A

x

is

T

it

le

Axis Title

Series1

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5. REFERENCES

[1] K.H. Roll, Powder Metallurgy at the Turn of the new century, 1987 Annual Powder Metallurgy Conference Proceedings, Metal Powder Industries Federation.

[2] J.S. Agapiou and M.F. DeVries, Machinability of Powder Metallurgy Materials, Int. J. Powder Metal., Powder Technol., Vol 34 (No. 1), 1988

[3] U.Engström: Machinability of Sintered Steels, Powder Metallurgy, Vol 26, No 3 1983, p. 137-144. [4] Hoganas Handbook for Sintered Components, Machining guidelines.

[5] R.K. Jain, Production Technology,16th edition, Khanna publishers,2004,P 1180-1182.