EXPERIMENTAL STUDY ON GRINDABILITY OF HSS WITH HYBRID ...icat-isaat.org/static/ISAAT-2017/pdf/CH01_Abrasive_Machining/R113… · , b [email protected] [email protected]

EXPERIMENTAL STUDY ON GRINDABILITY OF HSS WITH HYBRID ABRASIVE WHEEL

Manu Gee Mathen1,2, a *, S Gowri2,b and A. Xavier Kennedy 1,c 1Carborundum Universal Limited, India

2Department of Manufacturing Engineering,College of Engineering,Anna University, India

[email protected], b [email protected] , [email protected]

Keywords: Microcrystalline Alumina (MCA), Cubic Boron Nitride (CBN),Grinding Wheel wear

Abstract. The primary objective of modern day grinding is to increase productivity and to decrease

the time and energy consumption as well as the corresponding cost. Elongated dressing intervals and

enhanced part quality are the basic requirements of modern grinding and is achieved primarily

through new abrasive, developing better kinematic variation such as wheel work speed ratio etc. or by

grinding process parameters modification. This paper present the results from a cylindrical grinding

process conducted using a hybrid grinding wheel with microcrystalline alumina and varying volume

percentage of cubic boron nitride abrasives. The aim was to determine the effect of 6 % and 8 % by

mass of cubic boron nitride (CBN) abrasives along with microcrystalline alumina (MCA) abrasives.

The work includes experimental test on cylindrical grinding of High-speed steel (HSS) (62 HRC). A

wide range of test results were analyzed including grinding power using grind track, wheel wear,

material removal, G-ratio, Specific energy. It was found out that the addition of CBN abrasives along

with MCA abrasives has given a significant improvement in the wheel performance.

Introduction

Grinding can be considered as the one of oldest dated machining process which utilizes hard

abrasive particles for material removal. The uniqueness of grinding process when compared to other

machining process lies in cutting tool which is comprises abrasive grain which is responsible for the

cutting action and the bonding agent which will hold these abrasives as a solid mass. As each abrasive

grits potentially act like a microscopic cutting tool grinding is the process that could be used for

machining difficult to machine materials.

Rolling is a metal forming process in which the metal stocks are passed through a series of

rollers to reduce the thickness and make the thickness uniform. During rolling process the roller

undergo tremendous wear which requires reconditioning before it could be used for further rolling

process. Grinding process is used to recondition the work roller known as roll grinding process. Roll

grinding process which is a special form of cylindrical traverse grinding process in which the work

piece length is greater than two meters. During roll grinding process the grinding wheel is in contact

with the work piece for considerable amount of time which results in high wheel wear and the wheel

require frequent dressing for constant material removal. So an ideal grinding wheel for roll grinding

application needs to provide constant material removal rate as well as prolonged dressing period

which makes super abrasive grinding wheel to be more suitable for roll grinding application when

compared to conventional abrasive wheel. The major factor which hinders the use of super abrasive

wheel for roll grinding operations is the high cost of super abrasive grinding wheel when compared to

conventional abrasive grinding wheel.

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Proceedings of the 20th International Symposium on Advances in Abrasive Technology 3-6 December, Okinawa, Japan

So there is a scope for bridging the gap between the super abrasive grinding wheel and conventional

grinding wheel. The amount of research which was conducted in this region is minimal and huge

potential is still left untapped. [1] Fabricated a vitrified bonded grinding wheel with CBN abrasives

along the periphery was developed for roll grinding application. High G ratio and high surface quality

was obtained when compared to conventional abrasive wheel. A residual compressive stress was

imparted on the work piece which will in turn increase the roll life. [3] Evaluated the suitability of

microcrystalline alumina wheel in roll grinding application the results of the experiments showed that

the wheel is capable of long term grinding cycle with high material removal rate. Their cutting

abilities are positioned between the conventional alumina and CBN wheels. So in this paper an

attempt is made to combine the advantages of CBN and MCA abrasives by fabricating a hybrid

abrasive wheel.

Research objective

Roll grinding is a special type of cylindrical traverse grinding operation in which the grinding

wheel will be in contact with the work piece for a considerable amount of time with constant MRR

which could result in rapid wheel wear and frequent dressing cycle. This will result in both increases

in cycle time and decrease in productivity. So an attempt is made to find an economic and feasible

solution for roll grinding application by combining MCA and CBN into a single grinding wheel. It is

expected that the wheel will be having significantly better G-Ratio as well as high MRR which are

the key factors deciding the efficiency of grinding wheel in roll grinding application.

Methodology

The Taguchi method is very effective, because it is simple to carry on the experimental design

and this approach is very systematic to provide good quality results. In this study with the help of

Taguchi design of experiments an attempt was made to study the effect of varying mass percentage of

CBN abrasives in conventional grinding wheel and the effect of different process parameters on roll

grinding. The four factors used in this experiment are the depth of cut, number of pass, CBN

concentration and work piece speed.Three resinoid grinding wheels where fabricated having 0 % ,

4% and 6% CBN. The CBN abrasives in consideration of their high cost were added only along the

periphery of the grinding wheel which would be used for evaluation. Fig. 1 shows the fabricated

wheel.

Figure 1 Fabricated Grinding wheel

Rim Part

Core Part

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Advances in Abrasive Technology XX

Characterization of Nickel Coated CBN

In order to study the effect of Nickel coating on CBN abrasives the following test were

conducted. An Energy-dispersive X-ray spectroscopy was conducted on both uncoated and coated

abrasives to prove the presence of Nickel coating.

Microstructural analysis with Scanning Electron Microscope (SEM) . The SEM image of both

nickel coated and uncoated CBN was taken Fig. 2 (a),(b) shows the SEM image of uncoated CBN

abrasives whereas Fig 2. (c),(d) shows the SEM image of coated CBN abrasives. It was understood

from the SEM image that uncoated CBN abrasives where having irregular shape with angular edges.

Three kinds of surface texture were found in uncoated CBN abrasives. In coated abrasives the

particles was entirely coated with nickel and was having a dendritic structure. This dendritic structure

only is responsible for higher bonding strength of nickel coated CBN grains to resinoid bond.[5]

Figure 2 SEM image: (a,b) uncoated CBN, (c,d) Coated CBN

Elemental analysis with Energy Dispersive X- ray ( EDX) . The elemental composition of

both coated and uncoated CBN where analysed by the EDX. The EDX of coated CBN confirm the

presence of nickel. The EDS spectrum area chosen for analysis of uncoated CBN is shown in

Fig. 3 (a), and the graph showing elemental composition is shown in Fig. 3(b). The EDS spectrum

area chosen for analysis of coated CBN is shown in fig4(a),and the graph showing elemental

composition is shown in Fig. 4(b).

(a) (b)

(c) (d)

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Figure 3 (a) EDS spectrum of uncoated CBN shown in rectangle area (b) Elemental composition of

uncoated CBN grains.

Figure 4. (a) EDS spectrum of nickel coated CBN shown in rectangle area (b) Elemental composition

of Coated CBN grains

Experiment details

The Grinding experiments were conducted in Carborundum Universal LTD, Tiruvottiyur,

Chennai. Table 1 includes a presentation of the conditions in which experimental tests was

performed.

Table 1 General characteristics of grinding conditions

Process Traverse cylindrical grinding

Grinding machine CNC cylindical grinding machine from Micromatic Grinding Technologies

LTD

Dressing

parameters

Dresser - single-grain diamond dresser

Depth of cut 0.04 [mm], Traverse rate 200 [mm/min], No. of passes 8

Grinding

parameters

Wheel surface speed 35 [m/s], Feed rate 1500 [mm/min]

Coolant 80 [LPM]

Workpiece Cylindical rod made of HSS (60 [HRc] ) ,Lenght 140 [mm],ϕ 59.96[mm]

(a) (b)

(c) (b)

96


Grind Trak. Grind Trak is a portable diagnostic tool for in-process monitoring of the grinding

process. It enables the capture of various signals (currently, power and displacement) which serve as

a signature of the grinding process. These signals give an insight into the fundamental microscopic

interactions during the manufacturing processes, which in turn help to establish the cause and effect

relationship between the input, process and the outputs of the manufacturing process viewed as a

system. Frequently the signals and their observed variations by themselves are adequate to identify

opportunities for solving the process problems such as size holding, burn, chatter, etc.

[4]

Fig 2, shows the arrangement of LVDT to measure the infeed of wheel head during grinding

of a component and power cell to monitor the power drawn by spindle motor in cylindrical grinding

machine.

Figure 2 Layout showing the arrangement of sensors in a cylindrical grinding machine. [7]

Design of experiments. Design of experiments could be used to extract meaningful conclusion from

the measured response. Adequate experimental design requires competent process knowledge for

selection of the factors and their levels that could possibly significantly influence the response.[2].In

this research 9 sets of experiments are sorted based on Taguchi design of Experiments. The

experiment include four controllable process parameters with three levels which are mentioned in

table 2 and two constant parameters such as wheel speed and feed rate which are given in table 1.Nine

experiments were conducted with different combination of work speed, depth of cut, CBN

concentration and No. of Pass. With wheel speed and feed rate being maintained same throughout the

set of experiments. The parameters has been defined to obtain constant material removal rate from

work

Table 2 Factors and their Levels

Factors Levels

1 2 3

Depth of cut [μm] 8 10 12

No. of Pass 10 15 20

CBN concentration [%] 0 4 6

Work speed [RPM] 250 280 320

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Table 3 L9 Orthogonal array and Responses

Sl.

No.

Depth of

cut

No. of Pass CBN

concentration

Work speed Material

Removal

Rate

Grinding

ratio

[μm] [%] [RPM] [mm3/sec]

1 8 10 0 250 0.225942 0.0571

2 8 15 4 280 0.248194 0.0920

3 8 20 6 320 0.222185 0.0853

4 10 10 4 320 0.447511 0.121

5 10 15 6 250 0.296887 0.113

6 10 20 0 280 0.200036 0.070

7 12 10 6 280 0.554341 0.169

8 12 15 0 320 0.300651 0.112

9 12 20 4 250 0.19509 0.120

Results and discussion.

Taguchi analysis is carried out in Minitab software with material removal rate and G-ratio as

the responses .Material removal rate was selected as the response because in roll grinding application

the primary factory which decides the grinding wheel efficiency is material removal rate. The

objective of the project is also to maximize the material removal rate with minimum wheel wear

which in turn results in better G-ratio. The response table obtained for material removal and G-Ratio

is shown in Table 4 and 5 respectively.

From the table we are able to understand that number of pass have the maximum impact on

MRR during roll grinding. The main effects plot for signal to noise ratio is shown in the fig 3.

Table 4 Response Table for Signal to Noise Ratios-MRR

Condition – Larger is better.

Level Depth of

cut

No. of Pass CBN % Work Speed

1 -12.701 -8.343 -12.446 -12.555

2 -10.503 -11.030 -11.094 -10.402

3 -9.920 -13.746 -9.579 -10.163

Delta 2.777 5.403 2.866 2.392

Rank 3 1 2 4

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In main effect plot for SN ratio we are able to see MRR increase with increasing depth of cut

or stock. MRR decreases with increase in number of pass because as the grinding process goes on the

sharpness of the grits is reduced which will result in less material removal. [6] MRR shows an

increasing trend as the work speed increases due to higher cutting velocity achieved.

Figure 5 Main Effects plot for SN ratio- MRR

Table 5 Response Table for Signal to Noise Ratios-G Ratio.

Condition – Larger is better.

Level Depth of

cut

No.of Pass CBN % Work Speed

1 -19.54 -20.73 -22.33 -22.33

2 -19.55 -19.56 -20.13 -19.15

3 -20.97 -19.77 -17.61 -18.59

Delta 1.43 1.17 4.72 3.74

Rank 3 4 1 2

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From the Table 5 we are able to understand that CBN concentration in the grinding wheel

have maximum impact on G ratio for roll grinding. The main effect plot for signal to noise ratio is

shown in Fig. 4.

In the Main Effects plot for SN ratio we are able to see wheel with 6% CBN concentration will

have the maximum G-Ratio because the CBN abrasives are harder than conventional abrasives so it

will not wear off quickly which will in turn provide better G-Ratio.

Figure 6 Main Effects plot for SN ratio- G – Ratio

Validation of Taguchi analysis. The validation of the results obtained from Taguchi analysis was

done by conducting the cylindrical traverse grinding again with the optimum parameters obtained

from the Taguchi analysis. The results for the experiments are shown in the Table 6 and 7.

Table .6 Performance Evaluation of Grinding Wheels based on Taguchi Analysis.

Type Of Grinding

Wheel

Wheel wear MRR Grinding ratio

[mm] [mm3/sec]

0% CBN 0.04 4.419 0.08

4% CBN 0.035 5.515 0.12

6% CBN 0.03 6.606 0.17

100


The fig 7 shows the graphical representation of wheel wear and grinding ratio, it clearly

implies that the wheel wear gets reduced and grinding ratio has been increased when compared with

standard grinding wheel.

MRR

Figure 7 Comparison of MRR and grinding ratio between the wheels

The wheel with 6 % CBN concentration shows the best result with high material removal and

high G ratio. This is due to the fact that the CBN grains are harder than conventional grains, so CBN

grains penetrate more and results in higher material removal. The high G-Ratio for 6% CBN wheel is

due to high hardness as hardness is directly proportional to wear resistance.

Table 7. Performance Evaluation of Grinding Wheels based on Taguchi Analysis.

Type Of Grinding

Wheel

Power Q’ Specific Energy

[kW] [mm3/sec.mm] [kJ/mm

2]

0% CBN 1.0805 0.158 0.244

4% CBN 0.5518 0.197 0.100

6% CBN 0.6239 0.236 0.094

G R

ati

o

101


The Fig. 8 shows the graphical representation of Specific energy and grinding ratio, it clearly implies

that the specific energy gets reduced and grinding ratio has been increased when compared with

standard grinding wheel.

Figure 8 Comparison of Specific energy and Grinding ratio between the wheel.

From the results obtained we can find that wheel having 6% of CBN performs significantly

better than wheel with 0% CBN. There is significant increase in MRR and decrease in specific

energy. Specific energy can be considered as a measure of grinding efficiency. A low specific energy

implies low energy consumed to remove a given volume of material. The lower specific energy of 6%

CBN wheel corresponds to sharper condition of CBN grains during the course of grinding process

which results in shearing to be predominant rather than ploughing and rubbing.

Conclusions

In this study, the effect of CBN grains along with conventional abrasives was studied. The

conclusions drawn from the study are presented below.

The grinding wheel with CBN abrasives significantly performed better than that of standard

grinding wheel. With 6 % of CBN abrasives,50% improvement in MRR and 112%

improvement in G Ratio was obtained with respect to grinding wheel having 0% CBN

Number of pass during grinding operation and CBN concentration in the wheel has a

significant effect on the material removal rate during roll grinding.

CBN concentration and work speed are the significant parameters for the G Ratio during roll

grinding.

Grinding wheel with 6 % CBN had the lowest specific energy during the operation which in

turn reflects the higher grinding efficiency of the wheel.

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References

[1] Kris V Kumar and Biju Varghese U.S. Patent 20070099548A1 (2007)

[2] N.M ohanasundararaju, R.Sivasubramanian,N.Alagumurthi, Optimisation of work roll grinding

using Response Surface Methodology and evolutionary algoritham, Int. J. Manufacturing Research,

Vol. 3, No. 2, 2008.pp. 236-251.

[3] Miroslav NESLUŠAN, Jitka BAĎUROVÁ, Anna MIČIETOVÁ, Mária ČILIKOVÁ,

Performance of Norton Quantum Grinding Wheels, Precision Machining VIII, ISSN: 1662-9795,

Key Engineering Materials Vol. 686, pp 125-130.

[4] Vairamuthu R, Brij Mohan Bushan, R.Srikanth, N.Ramesh Babu Performance Enhancement of

Cylindrical Grinding Process with a Portable Diagnostic System, Procedia Manufacturing

Volume 5, 2016, Pages 1320–1336

[5] Yanghai Gui, Jianbo Zhao, Jingbo Chen, Yuanli Jiang, Preparation and Characterization of Ni

Spines Grown on the Surface of Cubic Boron Nitride Grains by Electroplating Method, Materials

2016,9,153

[6] Stephen Malkin, Changsheng Guo, Grinding Technology Theory and Application of Maching

with Abrasives Second Edition.

[7] Information on http://brij.scripts.mit.edu.

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EXPERIMENTAL STUDY ON GRINDABILITY OF HSS WITH HYBRID ...icat-isaat.org/static/ISAAT-2017/pdf/CH01_Abrasive_Machining/R113… · , b [email protected] [email protected]