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EFFECT OF REDUCING TOOL WEAR BY CRYOGENIC PROCESS

Dr.I.Satyanarayana

Principal and Professor of Mechanical Engineering, Sri Indu Institute of Engineering and Technology,

Sheriguda(V), Ibrahimpatnam(M), Ranga Reddy district, Hyderabad – 501 510, Telangana State

Abstract - The main objective of this research is to find the optimum working condition to

reduce tool wear rate in HSS drill bit. Cryogenic treatment on HSS drill bit has shown changes in its

properties like increased hardness; increase in wear resistance which results in increase in tool life. The

high speed steel (HSS S400) is used as a cutting tool, since it has good quality and reliability in cheaper

rate when compared to other cutting tools. So it is very important to increase the ability of the tool further

for its reliability. So the best way is to increase the hardness (HRBC). For the improvement of hardness

and wear resistance, various heat and cold treatment process are used. One such effective and currently

used process is cryogenic treatment. Cryogenic treatment of high speed steel is one of the developments

in manufacturing field. It offers much better wear resistant and hardness for the high speed steel. The

conventional cryogenic treatment (CCT) process involves cooling down the samples to (-180°C) for

certain period(18 Hours), for soaking and constantly heated up to the room temperature in 6 hrs. By using

this conventional method the material get its default hardness. To overcome this drawback the deep

cryogenic treatment,(DCT) is used to subject the steel tool placed in a specially constructed tank to

temperature around 77k (-196°c) for a 12 hours using liquid nitrogen as the refrigerant.

Key Words – Cryogenic process. High speed steel, Hardness, Deep cryogenic treatment

I. INTRODUCTION

Deep cryogenic Treatment system is the methodology of ultra low temperature‖ processing of material to

enhance their metallurgical properties. The process involves reducing and raising the temperature.

Thermal control is achieved by continuously monitoring inputs and regulating the flow of liquid nitrogen

into the chamber and alternating the heat. Precise program control takes the cycle through three phases

of descend, soak, and ascend with no fear of thermal shock. Single point cutting tool is the most used

tool of machining industry. Single point cutting tool is used in different machines gives different rate of

accuracies and surface finish of final work piece. When Single point cutting tool is used in Computer

/numeric Controlled machines the precision of cut and surface finish are almost the expected. But when

Single point cutting tool are used in general Lathe machines the precision and surface finish are not good

enough. But since CNC machines are costing more than general purpose lathe, in small scale industries

where costing is one of the factor there normal lathe are only used. Turning operation is the most basic

operation used to decrease the diameter of work piece fixed on rotating spindle while the Single point

cutting tool held stationary on tool mounting. When Single point cutting tool is used in lathe there are

different problems faced by the Single point cutting tool. There are three zones created in the total

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system. Primary deformation zone where major of the plastic deformation takes place. Secondary

deformation zone between chip and tool interface results in secondary plastic deformation because of

friction between chip and tool. Tertiary deformation zone between tool and the work piece due to

frictional rubbing. Heat generated because of friction in rubbing is distributed between the three zones

majorly taken by secondary zone that is the chips. Heat generated makes the work piece softer resulting

in little decrement in cutting force but this heat also affects in deformation of cutting surface of Single

point cutting tool.

High speed steel (HSS) is a form of tool steel. HSS bits are much more resistant to heat. They can be used

to drill metal, hardwood, and most other materials at greater cutting speeds than carbon steel bits.HSS

tools are so named because they were developed to cut at higher speeds. Developed around 1900 H S S is

the most highly alloyed tool steels. The tungsten (T series) was developed first and typically contains 12 -

18% tungsten, plus about 4% chromium and 1 - 5% vanadium. Most grades contain about 0.5%

molybdenum and most grades contain 4- 12% cobalt. Cryogenic treatment on HSS will result in the

conversion of retained austenite into martensite. This results in increase in hardness of HSS drill bit due

to increase in density of dislocation and gaps.

II. LITERATURE REVIEW

The commonly used cutting tool material in conventional machine tools is high speed steel. As the

technology has been more rapidly advancing, cutting tool materials such as cemented carbides and

ceramics are needed to machine many difficult to machine materials at higher cutting speeds, and metal

removal rates (MRR) with performance reliability [2]. In recent years, increased interest in the effects of

low temperature on tool and die materials, particularly HSS tools has been Tested. Over the past few

years, there has been an increase in the application of cryogenic treatment to different types of materials.

Research has shown that cryogenically treated tool increases Tool life, and in most cases provides

additional qualities to the Tool, such as stress relieving, hardness, toughness, etc. In the research area of

cutting tool, which includes High speed steel (HSS) [2]. Mohan Lal et al. [3] studied the improvement in

wear resistance, and the significance of treatment parameters, in different tool and die materials. It has

been found that cryogenic treatment imparts nearly 110% improvement in cutting tool life. Cohen et al.

[6] proved that the power consumption of cryogenically treated (HSS) tools is less, when compared to the

untreated (HSS) tools. Cryogenic treatment of tool steels is a proven the technology to increase the wear

resistance, and extend intervals between component replacements for blades, machining mills, etc., and

hence improves surface quality of the different machined parts. Correct mechanical configuration,

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Combining optimized lubrication, and cryogenic treatment of wearing parts results in the maximum

performance of lubricated components, and can significantly extend the component life. A fundamental

distinction among different CT processes is given, by the parameters of the cooling warming cycle, and

especially on the minimum temperature reached during the cycle. These are categorized as [1] 1. Shallow

Cryogenic Treatment or Subzero Treatment: the samples are placed in a freezer at -80 °C and then they

are exposed to room temperature. 2. Deep Cryogenic Treatment: the samples are slowly cooled to -196

°C, held-down for many hours and gradually warmed to room temperature. Cryo-treatment is a

supplementary process to conventional heat treatment, that involves deep freezing of materials at

cryogenic temperatures (-190 °C) to enhance the mechanical and physical properties. The execution of

CT on cutting tool materials increases wear resistance, hardness, dimensional stability, but at the same

time, reduces tool consumption and down time for the machine tool set up, thus leading to cost

reductions. The dry cryogenic process is precision controlled and the materials to be treated are not

directly exposed to any cryogenic liquids. Overall, all the treated materials retain their size and shape.

Cryogenically treated materials with some occasional heat treatment generally improve hardness,

toughness, stability, corrosion resistance and reduced friction, cryogenic treatment has been successfully

applied to die and HSS ferrous [4]. temperature controller regulates the flow of LIN in the chamber and

stop further cooling. The LIN gets converted and leaves the system as nitrogen gas.[6].

III. MAIN COMPONENTS AND SPECIFICATIONS

Table.1.0. Experimental Specifications

Sr. No. Parameter Experimental conditions/ M/C tool and equipment specifications

1 Machine tool High-power rigid lathe machine, 6.5-feet bed, 3-phase 2 HP motor

2 Cutting tools Untreated addition makes, HSS T-42, S-400 (UT) 1/2”x 4”single point

turning tool.

Cryogenically treated, HSS T-42, S-400 (CT) 1/2"x 4”

Single point turning tool.

Chemical composition; C-1.430, Cr-3.920, Mo-3.560,

W-8.56, V-2.900, Co-9.45.

3 Tool

Geometry

Back rake angle: 08°, side rake angle: 10°, end flank angle: 05°, side flank

angle: 05°, end cutting edge angle: 15°, side cutting edge angle: 15°, nose

radius: 0.5 mm

4 Work

Material

Mild steel, AISI/SAE-1020, Diameter 36 mm, same for both the tools

Chemical composition; C-0.190, S-0.40, P-0.38, Si-

0.140, Mn-0.43.

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5 Cutting

Speed

58 m/min (constant for both the tools)

6 Feed rate 0.5 mm/rev

7 Depth of cut 0.8 mm

8 Spindle speed

rpm

187

IV. ANALYSIS OF EXISTING AND MODIFIED SINGLE POINT CUTTING TOOL

(a) (b)

Figure1: (a) HSS Single point cutting tool 11⁰ Rake angle, (b) HSS Single point cutting tool 12⁰ Rake angle

V. EXPERIMENTAL TESTING AND RESULTS

The experimental work was carried out in the workshop. The turning operation was carried out on the

work specimen using cryogenically treated and untreated HSS tools. The surface roughness of work

specimen, hardness, and flank wear of cutting tools were predicted. Micrographs of the UT and CT HSS

tools were also obtained. Both the cutting tool blanks (UT and CT HSS) are commercially available,

made by Miranda Tools Ltd. So, the tool blanks, namely, T42-S-400 (UT) and T42-S-500 (CT), were

purchased from the market. The tools were prepared as per desired tool geometry.

MACHINING TIME CALCULATION

Cutting time,t = L / (f. N) Where L= length of the shaft (mm), f =feed rate (mm/rev) ,N =spindle speed

(rpm )

t = L / (f. N) = 550/ (0.5*187) = 5.88 min

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Figure2: Turning operation

METALLOGRAPHIC EXAMINATION

SEM was carried for both cryogenically treated and untreated HSS samples to study the micro structural

changes.

(a) (b)

Figure3: a & b cryogenic treated single point cutting tool microstructure

Results Of Sem Analysis For Untreated Hss Samples

(b) (d)

Figure4: c & d untreated single point cutting tool microstructure

FLANK WEAR TEST

In the present work, the tool samples were subjected to turning operation in a high speed lathe

(6.5-feet bed) with a maximum spindle speed of 187 RPM..As soon as lathe was started, stop

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watch was switched on to note down the machining time.At the end of each run, flank wear was

measured in a tool maker’s microscope.

Table 2: flank wear

Sl. No. Time (min) Flank wear (mm)

Rake angle

11

Untreated

Rake angle

11

treated

Rake angle

12

Untreated

Rake angle

12

treated

1 11.76 0.205 0.130 0.190 0.111

2 23.52 0.220 0.146 0.198 0.135

3 35.28 0.236 0.175 0.210 0.156

4 47.04 0.258 0.184 0.228 0.179

Time (mins)

Figure5: flank wear for 11° modified HSS tool

0

0.05

0.1

0.15

0.2

0.25

0.3

11.76 23.52 35.28 47.04

Rake angle 11untreated

Rake angle 11treated

Flank

wear

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Figure 6: flank wear for 12 treated and untreated Tool

From the graph it was observed that cryogenically treated HSS tools showed slightly higher value

of tool life.

Table 3: hardnes s test

S.No Tool Condition Hardness (HRB)

1 Untreated Tool 49.5

2 Treated Tool 53

VI. CONCLUSIONS

The cryogenic treatment process must be performed according to predefined temperature

protocols, to ensure the maximum effectiveness; the cryogenic process should be carried out in a

dedicated programmable cryogenic system. Cryogenic treatment can increase the cutting forces which can

be reducing by use of secondary liquid nitrogen. The experimental investigation clearly explains that the

different tool condition of the single point cutting tool. By this investigation cryogenic treated single point

cutting HSS tool performance is better than the untreated single point HSS tool. After cryogenic

0

0.05

0.1

0.15

0.2

0.25

0.3

11.76 23.52 35.28 47.04

Rake angle 12untreated

Rake angle 12treated

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treatment, the performance of cryogenically treated tool had been significantly enhanced. From the

micrographs shown in Figures and it can be seen that the microstructure of HSS gets more refined and the

particles are uniformly distributed after the cryogenic treatment.

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