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International Journal of Mechanical Engineering and Technology (IJMET)

Volume 8, Issue 7, July 2017, pp. 1906–1915, Article ID: IJMET_08_07_212

Available online at http://iaeme.com/Home/issue/IJMET?Volume=8&Issue=7

ISSN Print: 0976-6340 and ISSN Online: 0976-6359

© IAEME Publication Scopus Indexed

EXPERIMENTAL STUDY OF EFFECTS OF

ANNEALING PROCESS ON MACHINABILTY

AND TOOL LIFE OF DRILL BIT FOR 20MNCR5

STEEL

Dr. Lakhwinder Pal Singh

Assistant Professor, Industrial and Production Engineering,

Dr. B.R. Ambedkar National Institute of Technology Jalandhar, Punjab, India.

Guravtar Singh Mann

Assistant professor, School of Mechanical Engineering,

Lovely professional university, Jalandhar, Punjab, India.

ABSTRACT

One of the most important grade of steel, low carbon steel has been immensely

used in automobile industry as shafts and gears and to manufacture them, they need to

be normalized after forging. In present research, machinability of 20MnCr5 have

been improved and effect of various process parameters of normalizing such as time,

normalizing temperature and iso-annealing temperature on machinabilty has been

studied. The settings of the process parameters were determined by using Taguchi’s

experimental design method. Orthogonal arrays of Taguchi, the signal-to-noise (S/N)

ratio and the analysis of variance (ANOVA) were employed to find optimal process

parameter levels and to analyze effect of these parameters on hardness of component.

Confirmation test with the optimal levels of machining parameters have been carried

out in order to illustrate the effectiveness of the Taguchi optimization method. The

conclusion drawn were that at soaking time of 25 min, normalizing furnace

temperature of 930-940oC and iso-annealing temperature of 635-645oC resulted in

drastic increase in number of parts produced before further tool sharpening.

Key words: 20Mncr5, hardness, Taguchi, optimization methods, Anova.

Cite this Article: Dr. Lakhwinder Pal Singh and Guravtar Singh Mann Experimental

Study of Effects of Annealing Process on Machinabilty and Tool Life of Drill Bit for

20MNCR5 Steel. International Journal of Mechanical Engineering and Technology,

8(7), 2017, pp. 1906–1915.

http://iaeme.com/Home/issue/IJMET?Volume=8&Issue=7

Experimental Study of Effects of Annealing Process on Machinabilty and Tool Life of Drill Bit for

20MNCR5 Steel


1. INTRODUCTION

20MnCr5 is a low carbon steel contributing to many engineering applications such as

automobile industry components through for example like gears and shafts [2] Mechanical

properties such as softening the metal, change the grain size, modifying the microstructure of

the material and reliving the stress set up in the material the process heat treatment is carried

out first by heating the metal and then cooling it in water, oil or brine water. One of the heat

treatment process which is widely used post forging process is Normalizing process which is

a softening process in which iron base alloys are heated 40 to 50°C above the upper-critical

limit for both hypo and hyper eutectoid steels and held there for a specified period and

followed by cooling in still air up to room temperature. The resulting structure is usually fine

pearlite with an excess of ferrite or cementite [1, 2].

Inefficiencies during this process can lead to reduce the tool life to minimum. Such a

experience have been recently faced by one of the medium scale industry. Where, drilling

operation has been carried out on a low carbon steel 20Mncr5 spider cross. During this

process not a single hole has been drilled in to the material. The main reason for the concern

is failure of drill bit in core area but was able to cross case portion. Moreover, parameters

such as feed speed for the drill bit have been varied but no positive response observed. As a

result rise in tooling cost has been observed. Hence, there is a need to investigate the drill

material and parameters. That would help the industry in improving the production rate and

tool life beside reduced material wastage.

The organization of the rest of the paper is as follows: Section 2 reviews previous work

related to the 20MnCr5 steel, tool wear and also on optimization by Taguchi methods. Section

3 discusses the procedure adopted for the experiments which were done to get the desired

results post normalization process. Section 4 discusses the results section 5 presents the

conclusion and future work.

1.1. Related Work

Kohli [3] performed induction hardening is a form of heat treatment furthermore they have

investigated the effects of various process parameters of induction hardening like feed rate,

dwell time and current during rolled, hardened tempered and normalized condition to reveal

their impact on depth of hardening of the material of medium carbon steel (EN8D) in rolled

condition using one variable at a time approach. The optimal set of process parameters has

also been predicted to maximize depth of hardening during normalized condition of the

material. Wang et. al. [4] investigated the effect of case hardening treatment on the structure

and properties of low carbon steel automobile gears. Furthermore, comparative study of the

following gears viz. grade of EN353, SAE8620 and 20MNCR5 has been performed. Micro

structure study, testing of hardness gradient of automobile gears has also been studied.

Rentsch [5] discussed for high performance applications, shafts and gears made of 20MnCr5.

He studied material properties, process perturbations and asymmetries in shape and operation

setups for the distortion of parts, often released by heat treatment. Athreya [6] performed

optimization of lathe facing operation by using Taguchi method. It is considered parameters

such as feed, depth of cut and speed. Mondal et. al. [7] presented the prediction and

evaluation of laser clad profile formed by means of CO2 laser applying Taguchi method and

the artificial neural network (ANN).

Initial investigation is performed on the drill bit as low production of a work piece has

been observed during machining. At this early stage of investigation some experiments were

performed on the normalizing treatment of 20MnCr5 material. The parameters such as

Soaking Time, Normalising Furnace Temperature and Iso-Annealing Furnace Temperature

Dr. Lakhwinder Pal Singh and Guravtar Singh


were varied. Due to variation in parameters microstructure for the material has been

modified. During the initials trials hardness observed within the range 160-210 BHN and 190-

260BHN. Moreover course grains were also found on the surface of material for initial trails.

Microstructure under soacking and over soacking was not uniformly distribution of ferrite and

pearlite.

With the above limitations, the objective of this paper is to study the influence of

annealing process on machinability of 20MnCr5 a low carbon steel by varying heat treatment

parameters such as Soaking time, Normalising furnace temperature, Iso-annealing furnace

temperature and to increase tool life of a drill bit by reducing hardness of the material and to

optimize heat treatment parameters to increase tool life.

1.3 Method of Optimizing

1.3.1. Taguchi Experiment: Design and Analysis

Essentially, traditional experimental design procedures are too complicated and not easy to

use. A large number of experimental works have to be carried out when the number of process

parameters increases. To solve this problem, the Taguchi method uses a special design of

orthogonal arrays to study the entire parameter space with only a small number of

experiments [8]. Taguchi methods [9] have been widely utilized in engineering analysis and

consist of a plan of experiments with the objective of acquiring data in a controlled way, in

order to obtain information about the behaviour of a given process

The greatest advantage of this method is the saving of effort in conducting experiments;

saving experimental time, reducing the cost, and discovering significant factors quickly.

Taguchi’s robust design method is a powerful tool for the design of a high-quality system. In

addition to the S/N ratio, a statistical analysis of variance (ANOVA) can be employed to

indicate the impact of process parameters on hardness values. The steps applied for Taguchi

optimization in this study are as follows.

• Select noise and control factors

• Select Taguchi orthogonal array

• Conduct Experiments

• Hardness measurement

• Analyze results; (Signal-to-noise ratio)

• Predict optimum performance

• Confirmation experiment

2. EXPERIMENTAL PROCEDURE

2.1. Plan of Experiments

Taguchi methods which combine the experiment design theory and the quality loss function

concept have been used in developing robust designs of products and processes and in solving

some taxing problems of manufacturing [10]. The degrees of freedom for three parameters in

each of three levels were calculated as follows [11]. Parameters for annealing is shown in

table 1


20MNCR5 Steel


Table 1 Process parameters for annealing of 20mncr5

Category Parameters Level1 Level2 Level3

A Soaking time 15 min 20 min 25 min

B Normalizing furnace

temperature 900-925οC 925-932οC 932-950οC

C Iso annealing furnace

temperature 615-625οC 625-635οC

Cooling at room temp. in

air

Degree of Freedom (DOF) = number of levels -1 (1) For each factor, DOF equal to: For

(A); DOF = 3 – 1 = 2 For (B); DOF = 3 – 1 = 2 For (C); DOF = 3 – 1 = 2

In this paper nine experiments were conducted at different parameters. For this Taguchi

L9 orthogonal array is used, which has nine rows corresponding to the number of tests, with

three columns at three levels. L9 OA has eight DOF, in which 6 were assigned to three factors

(each one 2 DOF) and 2 DOF was assigned to the error.

Table 2 Taguchi L9 array for Hardness of 20MnCr5

Experiment No. Soaking time

A

Normalizing

furnace

temp B

Iso annealing furnaceC

1 1 1 1

2 1 2 2

3 1 3 3

4 2 1 2

5 2 2 3

6 2 3 1

7 3 1 3

8 3 2 1

9 3 3 2

For the purpose of observing the degree of influence of the process parameters in

normalizing process, three factors, each at three levels, are taken into account, as shown in

Tables II. The hardness values corresponding to each experiment were shown in Table IV.

3. EXPERIMENTAL PROCEDURE AND DETAIL

3.1. Material :

As an objective of this present study is to improve the machine ability of low carbon steel

component of 20MnCr5. Composition of elements has been determined by using

spectroscopy. Table shows the observed composition of elements.

Table 3 Elements of 20MnCr5

Elements C Si Mn P S Ni Cr Moo

Observed

value 0.18 0.34 1.27 0.026 0.022 - 1.08 -



ii. Specimen: for the above discussed material is shown in the figure 1. Specimen is known as

spider cross, which is widely used in differential mechanism.

Figure 1 Spider cross

3.2. Experiment Procedure

Specimen is manufactured by using forging which is followed by normalizing in the SQF

(Sealed Quenched Furnace) by setting above said parameters. Then hardness is measured

using brinell hardness tester. Finally, drilling operation is performed using radial drilling

machine. Next section discusses the results obtained from the experimentation and

optimizing parameters.

4. RESULT AND ANALYSIS

4.1. Analysis of S/N Ratio

Taguchi method stresses the importance of studying the response variation using the signal –

to – noise (S/N) ratio, resulting in minimization of quality characteristic variation due to

uncontrollable parameter. The hardness was considered as the quality characteristic with the

concept of "the larger-the-better". The S/N ratio used for this type response is given by [12].

The S/N ratio for the larger-the-better is: S/N = -10*log (mean square deviation).

S/N= -10log10 =(1/n∑1/y2 ) ( 1)

Where n is the number of measurements in a trial/row, in this case, n=1 and y is the

measured value in a run/row. The S/N ratio values are calculated by taking into consideration

Eqn. 1, the hardness values measured from the experiments and their corresponding S/N ratio

values are listed in Table No IV. The hardness response table for the soaking time,

normalizing furnace temperature and iso annealing furnace temperature was created in the

integrated manner and the results are given in Table 4


20MNCR5 Steel


Table 4 Table for S/N Ratio at Various Hardness Levels

EXP

.No

Soaking time

(A)

Normalizing

Furnace

temperature

(B)

Iso annealing

Furnace

temperature (C)

Trail( T1

) Trail(T2)

S/N

Ratio

1 15 900-925οC 615-625οC 160

BHN

210BHN 14.2

2 15 925-932οC 625-635οC 160

BHN

210BHN 14.2

3 15 932-950οC Cooling at room

temp. in air

190BHN 260BHN 3.03

4 20 900-925οC 625-635οC 145BHN 185BHN 15.2


temp. in air

190BHN 260BHN 3.03

6 20 932-950οC 615-625οC 160

BHN

210BHN 14.2


temp. in air

200BHN 290BHN 44.9

8 25 925-932οC 615-625οC 185BHN 230BHN 43.27

9 25 932-950οC 625-635οC 185BHN 230BHN 43.27

Regardless of the category of the performance characteristics, a greater S/N value

corresponds to a better performance. Therefore, the optimal level of the machining parameters

is the level with the greatest S/N value. Based on the analysis of the S/N ratio, the optimal

machining performance for the hardness was obtained at soaking time =20min normalizing

furnace temperature =900-925οC and iso annealing temperature=625-635οC .Fig 2 shows the

shows that how S/N ratios behaves with normalizing temperature, iso annealing temperature

and annealing temperature. Most effecting factor is time and minor effecting factor on the

hardness is normalizing temperature.

Table 4.1 S/N ration values for hardness by factor level

Level Time( A) Normalizing

temp(B) Annealing temp(C)

1 10.47 24.78 23.89

2 32.43 20.16 24.22

3 34.92 20.16 16.98

Delta 24.45 4.62 7.24

Rank 1 3 2

Most effecting factor is time and minor effecting factor on the hardness is normalizing

temperature.

Fig. 2 shows that how S/N ratios behave with normalizing temperature, iso-annealing

temperature and annealing temperature. In which importance of time and temperature for the

process has shown as hardness changes with change in these parameters at 20 minutes time

and for temperature from 900-925οC and Iso-annealing temperature from 625-635οC and

hence related these parameters with S/N ratio of 15.2.



Figure 2 Effect of process parameters on hardness.

4.2. Analysis of Variance (ANOVA)

ANOVA is a statistically based, objective decision-making tool for detecting any differences

in the average performance of groups of items tested. ANOVA helps in formally testing the

significance of all main factors and their interactions by comparing the mean square against

an estimate of the experimental errors at specific confidence levels. First, the total sum of

squared deviations SST from the total mean S/N ratio nm can be calculated as [12].

(2)

Where n is the number of experiments in the orthogonal array and ηi is the mean S/N ratio

for the ith experiment. Statistically, there is a tool called an F test, named after Fisher [9], to

see which design parameters have a significant effect on the quality characteristic. In the

analysis, the F-ratio is a ratio of the mean square error to the residual error, and is traditionally

used to determine the significance of a factor.

Table 4.2 ANOVA table for hardness of 20MnCr5

Treatments (p) 1(block r) 2 (block r) sum Mean

1 160 210 Y1= 370 185

2 160 210 Y2 =370 185

3 190 260 Y3 =450 225

4 145 185 Y4 =330 165

5 190 260 Y5 =450 225

6 160 210 Y6 =370 185

7 200 290 Y7 =490 245

8 185 230 Y8 =415 207.5

9 185 230 Y9 =415 207.5

941.0928.5912.5

24

22

20

63062025

252015

24

22

20

normalising temp.(c)

Mea

n

Isoannealing temp

Soaking time

Main Effects Plot for S/N ratioData Means


20MNCR5 Steel


Table 5 ANOVA in Relation to Calculation of F-Test

Source of variation D.O.F Sum of square Mean square F-test

Treatment p-1 568525 MSTR=71065.

62

MSE =1725

41.9 Error p(r-1) 15525

Total rp-1 584050

So null hypothesis be rejected and the treatment 4 is most effective and having best result

Figure 3 3D scatter plot for input parameters like hardness, normalizing temperature and iso-

annealing temperature

This 3D scatter plot depicts hoe input parameters like hardness, normalizing temperature

and iso-annealing temperature affects the correspondingly S/N ratios.

4.3. Confirmation Test

The experimental confirmation test is the final step in verifying the results drawn based on

Taguchi’s design approach. The optimal conditions are set for the significant factors (the

insignificant factors are set at economic levels) and a selected number of experiments are run

under specified cutting conditions. The average of the results from the confirmation

experiment is compared with the predicted average based on the parameters and levels tested.

The confirmation experiment is a crucial step and is highly recommended by Taguchi to

verify the experimental results [12] In this study, a confirmation experiment was conducted

by utilizing the levels of the optimal process parameters since the predicted error, that is

difference between observed value (db), the additive model is adequate.

Table 4.2 Optimum Level for Hardness

Time( A) Normalizing temp(B) Annealing temp(C)

25 min 930-940οC 635-645οC

4.4. Analysis of Results

In view of confirmation experiment, it is clear that the results obtained by optimum setting

parameters is soaking time, normalizing furnace temperature and iso-annealing furnace

temperature gives the hardness 150 BHN so we recommend to the company that the following

set of parameters should be implemented (table 4.3)

940

9300

15

30

9200

45

200400 910

600

S/N ratio

normalising temp.(c)

Isoannealing temp

165.0

185.0

207.5

225.0

hardness(BHN)

Mean of

3D Scatterplot of S/N ratio vs normalising temp vs Isoannealing tem



From the above results, it is apparent that these normalizing factors contribute more in

hardness and helps to increase machining of the component .The effect of factors that

contribute little could not be neglected. However, the effectiveness of these results can be

improved by conducting more number of experiments with increased number of levels for

each variable, so that its range can be widened .The results revel that these three parameters

are significant contributors of variation in hardness of 20MnCr5 steel and hence very

important role during the machining of the components manufactured during production.

Confirmation experiments were conducted at optimum parameter settings and observed

hardness was compared with predicted hardness .The predicted and observed hardness values

are close to each other .Hence, the additive model is adequate and optimum conditions are

considered confirmed. The best factor combination is recommended for implementation .The

results can be summarized as given in the table 4.4.

Table 4.4 shows the optimum conditions

Soaking time (A) Normalizing furnance

temperature(B)

Iso annealing

furnace

temperature (C)

Hardness

23 min 930-940οC 635-645οC 150BHN

5. CONCLUSION

The following conclusions have been made from the dissertation work:

• The process parameters such as soaking time (A), normalizing furnace temperature (B)

and also annealing temperature (C) effects the hardness of component which ranges from

145-230 BHN post normalizing process of 20mncr5 steel.

• The best combination of parameters to get the desired hardness by the customer for

machining as the range was found 145- 185 BHN which showed that desired hardness can

be achieved at 20 minute soaking time and with normalizing furnace temperature and iso

annealing furnace temperature 900-925o and 625-635o C respectively at which maximum

production of 415 pieces of component were drilled.

• The analysis of the confirmation experiment has shown that the taguchi parameter design

showed optimal range of hardness from 150- 155 BHN, post normalizing process in which

parameters are soaking time 25 minute normalizing furnace temperature as 930-940o and

iso annealing temperature 635-645o C.

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