CUTTING FORCE AND SURFACE ROUGHNESS IN CRYOGENIC MACHINING OF ELASTOMER

Proceedings of the 2nd
International Conference on Current Trends in Engineering and Management ICCTEM -2014
17 – 19, July 2014, Mysore, Karnataka, India
151
CUTTING FORCE AND SURFACE ROUGHNESS IN CRYOGENIC
MACHINING OF ELASTOMER
Rajesh Nayak1
, RavirajShetty2
1
(Assistant Professor, Mechanical, Manipal University, India)
2
(Professor, Mechanical, Manipal University, India)
ABSTRACT
Most products based on elastomers are produced by some kind of molding and curing process. This paper deals
with a new method of elastomer machining. A series of cutting experiments under different rake angle, cutting speed,
feed and constant depth of cut has been conducted on cutting force and surface roughness under ambient and cryogenic
condition. From experimental data it can be clearly seen that increase of cutting force become more significant with
higher cutting speeds for cryogenic cutting. Cryogenic machining showed remarkable reduction in surface roughness
compared ambient machining especially at high rake angle.
Keywords: Cryogenic Machining, Cutting Force, Elastomer, Surface Roughness.
1. INTRODUCTION
Elastomers have been used as an engineering material for nearly 180 years in various military equipment’s and
industries in applications such as liner layers of armored vehicles, tires, springs, shock isolators, noise and vibration
absorbers, seals, and electrical and thermal insulators. An elastomer can be defined as, “a macromolecular material,
which, at room temperature, is capable of recovering substantially in shape and size after removal of a deforming force
[1-3]. Most elastomer parts are manufactured using a molding rather than machining process, to manufacture elastomer
parts with complicated shapes, such as tire and footwear tread patterns, a set of molds must first be produced. However,
there are many disadvantages associated with molding elastomers including high cost, labor-intensive and time
consuming process of mold fabrication and the inflexibility of a mold to design changes. For these reasons, machining
offers an attractive alternative for manufacturing elastomer components.
Most elastomer parts are manufactured using a molding rather than machining process. In the molding process,
raw polymeric materials are mixed with other additives and then heated, melted, and pressed into a mold. Inside the
mold, the polymer material is subjected to a controlled temperature-pressure-time cycle. The material is cured,
vulcanized, and cooled to produce the desired properties and geometry. To manufacture elastomer parts with complicated
shapes, such as tire and footwear tread patterns, a set of molds must first be produced. However, there are many
disadvantages associated with molding elastomers including high cost, labor-intensive and time consuming process of
mold fabrication and the inflexibility of a mold to design changes. For these reasons, machining offers an attractive
alternative for manufacturing elastomer components, which would be especially useful for manufacturing low volume
custom or prototype parts and other applications requiring a complex shape and frequently modified designs. Potential
applications of elastomer machining include prototype tire and footwear tread patterns, custom seals for biomedical
applications, specialty vibration dampers, and scrap tire recycling equipment.
INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING
AND TECHNOLOGY (IJMET)
ISSN 0976 – 6340 (Print)
ISSN 0976 – 6359 (Online)
Volume 5, Issue 9, September (2014), pp. 151-156
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International Conference on Current Trends in Engineering and Management ICCTEM
This current work deals with cryogenic elastomer machining. A series of cutting experiments under different
rake angle, cutting speed, feed and constant depth of cut has been conducted on cutting force and surface roughness
under ambient and cryogenic condition. From experimental data it can be clearly seen that increase of cutting force
become more significant with higher cutting speeds for cryogenic cutting. Cryogenic machining showed remarkable
reduction in surface roughness compared ambient machining especially at high rake angle.
2. LITERATURE REVIEW
Very little research on elastomer machining has been conducted b
elastomers and the complexity of the machining process itself. Jin and Murakawa, [2] have carried out experiments with
variety of carbide end mills of various sizes and helix angles to mill grooves in three types
Norbornone rubber, and silicone rubber at various cutting speeds .They have reported that at high helix angle cutters and
high speeds yields smoother machined surfaces and lower forces.
Shih et al [3] investigated the machining of el
conditions and reported that proper selection of end mill geometries, process parameters, and fixture stiffness, clean
grooves can be machined in elastomers. It was also shown that cryogenic cooling
in achieving a smooth machined surface.
Strenkowski et al [4] carried out orthogonal rubber cutting experiments and examined the effects of various
machining parameters on chip morphology, machined surface roughness
significant effect on the types of chips generated during orthogonal cutting. Long and continuous ribbon
corresponding smooth machined surfaces were produced for high feed speed conditions and
Strenkowski et al [5] have developed wedge indentation models to investigate chip formation during incipient cutting
prior to material separation.
Shih et al [6] have done analysis on rubber workpiece to study its stiffness using A
design of the workpiece fixture was found to be a critical factor in achieving good surface finish in end milling of
elastomers because of the low elastic modulus.
Dhokia et al [7] have discovered the novel concept of cryogenic CNC
development of a process control system for cryogenic CNC machining.
3. EXPERIMENTAL SETUP
Nitrile Rubber (NBR) is commonly considered the workhorse of the industrial and automotive rubber products
industries. NBR is actually a complex family of unsaturated copolymers of acrylonitrile and butadiene. By selecting an
elastomer with the appropriate acrylonitrile content in balance with other properties, the rubber compounder can use
NBR in a wide variety of application areas
used in fuel and oil handling hose, seals and grommets, and water handling applications. With a temperature range of
40C to +125C, NBR materials can withstand all but the most se
specimens known as Nitrile rubber was used for this research. NBR is actually a complex family of unsaturated
copolymers of acrylonitrile and butadiene. Each rubber tube had an outside diameter of 60 m
mm.
The experiments were carried out in a PSG A141 lathe (2.2 KW) using the set up shown in Fig.1.
Fig.1. Cryogenic cutting condition
The Elastomers have a very low elastic modulus (1~10 MPa) as compared with 200 GPa for AISI 1020 steel.
Elastomers exhibit large elastic deformation before rupture. Based on previous end milling and orthogonal cutting tests, it
nference on Current Trends in Engineering and Management ICCTEM
152
le, cutting speed, feed and constant depth of cut has been conducted on cutting force and surface roughness
her cutting speeds for cryogenic cutting. Cryogenic machining showed remarkable
reduction in surface roughness compared ambient machining especially at high rake angle.
Very little research on elastomer machining has been conducted because of the complex material response of
variety of carbide end mills of various sizes and helix angles to mill grooves in three types of elastomers; H
high speeds yields smoother machined surfaces and lower forces.
Shih et al [3] investigated the machining of elastomers with sharp woodworking tools and under cryogenic
grooves can be machined in elastomers. It was also shown that cryogenic cooling of an elastomer workpiece is beneficial
machining parameters on chip morphology, machined surface roughness. Feed rate and rake angle were found to have a
significant effect on the types of chips generated during orthogonal cutting. Long and continuous ribbon
corresponding smooth machined surfaces were produced for high feed speed conditions and large rake angle tools.
Shih et al [6] have done analysis on rubber workpiece to study its stiffness using ANSYS. In this work, the
elastomers because of the low elastic modulus.
Dhokia et al [7] have discovered the novel concept of cryogenic CNC machining of elastomers and the
development of a process control system for cryogenic CNC machining.
ally a complex family of unsaturated copolymers of acrylonitrile and butadiene. By selecting an
NBR in a wide variety of application areas requiring oil, fuel, and chemical resistance. In the automotive area, NBR is
used in fuel and oil handling hose, seals and grommets, and water handling applications. With a temperature range of
40C to +125C, NBR materials can withstand all but the most severe automotive applications [2]. Elastomer work
copolymers of acrylonitrile and butadiene. Each rubber tube had an outside diameter of 60 mm and a wall thickness of 15
The experiments were carried out in a PSG A141 lathe (2.2 KW) using the set up shown in Fig.1.
Cryogenic cutting condition Fig.2. Fixture design
nference on Current Trends in Engineering and Management ICCTEM -2014
19, July 2014, Mysore, Karnataka, India
le, cutting speed, feed and constant depth of cut has been conducted on cutting force and surface roughness
her cutting speeds for cryogenic cutting. Cryogenic machining showed remarkable
ecause of the complex material response of
of elastomers; H-NBR,
astomers with sharp woodworking tools and under cryogenic
of an elastomer workpiece is beneficial
. Feed rate and rake angle were found to have a
significant effect on the types of chips generated during orthogonal cutting. Long and continuous ribbon-like chips and
large rake angle tools.
NSYS. In this work, the
machining of elastomers and the
ally a complex family of unsaturated copolymers of acrylonitrile and butadiene. By selecting an
requiring oil, fuel, and chemical resistance. In the automotive area, NBR is
used in fuel and oil handling hose, seals and grommets, and water handling applications. With a temperature range of –
vere automotive applications [2]. Elastomer work-piece
m and a wall thickness of 15

International Conference on Current Trends in Engineering and Management ICCTEM
has been shown that a stable fixture is necessary for producing a smooth surface finish for machined rubber [6]. To
achieve a stable condition for the elastomer workpiece, a mandrel was designed as shown in Fig.2.
The stretched workpiece provided adequate co
force was further increased by applying a vacuum through the series of small holes. The elastomer tube is fixed to a
mandrel with through screws for workpiece stability. The lathe chuck grabbed
of the flexible workpiece. The machining experiments were carried out using High Speed Steel (HSS) under ambient and
cryogenic conditions. In cryogenic condition, the rubber stiffness was increased by cooling the
nitrogen before conducting the turning tests. Based on previous studies [5, 6] the machining parameters were selected
with three factors and three levels per factor, as indicated in Table 1.
Table 1:
Levels Rake angle (degree)
1
2
3
The selected cutting tool for this study provided the variable experimental conditions. Therefore, HSS tools with
varying rake angles were used in experiments as shown in figure3.
The surface roughness of the machined workpieces were measured using Taylor Hobson manufactured
instrument Surtronic 3+ (112/1590).The length for which roughness test was carried out was 6mm.It had
range of 10µm, 100µm and 500µm.Resolution used to carry out the experiment was 0.5µm.The instrument had a
selectable cut off value of 0.25mm, 0.8mm and 2.50mm. Skid pick up stylus with diamond tip radius of 5µm was used to
measure the surface roughness. The fig.4 shows the photographic view of surface roughness measurement conducted.
.
Fig.3. HSS tools with varying rake angles
4. RESULTS AND DISCUSSIONS
4.1 Cutting Force
The rake angle is the most important geometric parameter for cutting tools, and its value affects the tool
performance dramatically. Fig.5 to Fig.10 shows the measured cutting force as a function of rake angle for vario
orthogonal cutting conditions. It is observed that the cutting forces are decreasing with increasing rake angle for similar
cutting conditions.
As shown in Figure larger cutting forces are produced during cryogenic cutting. This is due to a larger mod
of rubber at lower temperatures. In contrast, decreasing vertical forces were observed when cryogenically cutting rubber.
This is because the increased rigidity of rubber at lower temperatures leads to less workpiece material flow underneath
the tool clearance surface. In contrast, under ambient temperatures rubber is more flexible and easier to flow beneath the
tool during cutting, which would apply a larger force on the tool clearance surface in the positive vertical direction.
Lower vertical forces are beneficial in maintaining cutting stability and achieving a good machined surface finish
because the tool usually has a small included angle which results in a low tool rigidity
nference on Current Trends in Engineering and Management ICCTEM
153
been shown that a stable fixture is necessary for producing a smooth surface finish for machined rubber [6]. To
achieve a stable condition for the elastomer workpiece, a mandrel was designed as shown in Fig.2.
The stretched workpiece provided adequate contact force between the workpiece and the mandrel. The contact
mandrel with through screws for workpiece stability. The lathe chuck grabbed the mandrel in order to avoid deformation
cryogenic conditions. In cryogenic condition, the rubber stiffness was increased by cooling the work piece in liquid
with three factors and three levels per factor, as indicated in Table 1.
Table 1: Levels of variables used in the experiment
(A)
Rake angle (degree)
(B)
Cutting speed (m/min)
(C)
Feed (mm/rev)
10 68 0.11
30 109 0.18
50 150 0.25
ake angles were used in experiments as shown in figure3.
instrument Surtronic 3+ (112/1590).The length for which roughness test was carried out was 6mm.It had
roughness. The fig.4 shows the photographic view of surface roughness measurement conducted.
HSS tools with varying rake angles Fig.4. Photographic view of surtronic 3+
performance dramatically. Fig.5 to Fig.10 shows the measured cutting force as a function of rake angle for vario
As shown in Figure larger cutting forces are produced during cryogenic cutting. This is due to a larger mod
clearance surface. In contrast, under ambient temperatures rubber is more flexible and easier to flow beneath the
are beneficial in maintaining cutting stability and achieving a good machined surface finish
because the tool usually has a small included angle which results in a low tool rigidity
nference on Current Trends in Engineering and Management ICCTEM -2014
19, July 2014, Mysore, Karnataka, India
been shown that a stable fixture is necessary for producing a smooth surface finish for machined rubber [6]. To
ntact force between the workpiece and the mandrel. The contact
the mandrel in order to avoid deformation
work piece in liquid
Feed (mm/rev)
instrument Surtronic 3+ (112/1590).The length for which roughness test was carried out was 6mm.It had a selectable
roughness. The fig.4 shows the photographic view of surface roughness measurement conducted.
Photographic view of surtronic 3+
performance dramatically. Fig.5 to Fig.10 shows the measured cutting force as a function of rake angle for various
As shown in Figure larger cutting forces are produced during cryogenic cutting. This is due to a larger modulus
clearance surface. In contrast, under ambient temperatures rubber is more flexible and easier to flow beneath the
are beneficial in maintaining cutting stability and achieving a good machined surface finish

154
10 20 30 40 50
75
80
85
90
95
100
105
110
115
120
125
130CuttingForce(N)
Rake Angle (Deg)
Feed (0.11 mm/rev
Feed (0.18 mm/rev)
Feed (0.25 mm/rev)
10 20 30 40 50
90
100
110
120
130
140
150
160
170
180
190
CuttingForce(N)
Rake Angle (Deg)
Feed (0.11 mm/rev
Feed (0.18 mm/rev)
Feed (0.25 mm/rev)
Fig.5. Cutting force with rake angles under Fig.6. Cutting force with rake angles under
ambient condition at 68m/min cryogenic condition at 68m/min
10 20 30 40 50
85
90
95
100
105
110
115
120
125
130
135
140
145
150
CuttingForce(N)
Rake Angle (Deg)
Feed (0.11 mm/rev
Feed (0.18 mm/rev)
Feed (0.25 mm/rev)
10 20 30 40 50
95
100
105
110
115
120
125
130
135
140
CuttingForce(N)
Rake Angle (Deg)
Feed (0.11 mm/rev
Feed (0.18 mm/rev)
Feed (0.25 mm/rev)
10 20 30 40 50
60
65
70
75
80
85
90
95
100
105
110
115
120
CuttingForce(N)
Rake Angle (Deg)
Feed (0.11 mm/rev
Feed (0.18 mm/rev)
Feed (0.25 mm/rev)
10 20 30 40 50
70
75
80
85
90
95
100
105
110
115
120
125
130
CuttingForce(N)
Rake Angle (Deg)
Feed (0.11 mm/rev
Feed (0.18 mm/rev)
Feed (0.25 mm/rev)

155
4.2 Surface Roughness
The nature and extent of surface roughness in the longitudinal direction of the turned job depend mainly upon
the geometry of the cutting tool. The value of surface roughness increases sharply with the increase in feed and decreases
with increase in cutting speed. Built-up edge formation and vibration worsen the surface further.
10 20 30 40 50
3.00
3.05
3.10
3.15
3.20
3.25
3.30
3.35
3.40
3.45
3.50
3.55
SurfaceRoughness(µm)
Rake angle (Degree)
68m/min,0.11mm/rev
109m/min,0.11mm/rev
150m/min,0.11mm/rev
10 20 30 40 50
3.3
3.4
3.5
3.6
3.7
Rake angle (Degree)
68m/min,0.18mm/rev
109m/min,0.18mm/rev
150m/min,0.18mm/rev
Fig.11: Surface roughness with rake angles under Fig.12. Surface roughness with rake angles under
cryogenic condition at 0.11mm/rev cryogenic condition at 0.18mm/rev
10 20 30 40 50
3.60
3.65
3.70
3.75
3.80
3.85
3.90
3.95
4.00
4.05
4.10
4.15
Rake angle (Degree)
68m/min,0.25mm/rev
109m/min,0.25mm/rev
150m/min,0.25mm/rev
Fig.13. Surface roughness with rake angles under cryogenic condition at 0.25mm/rev
The results shown in Fig.11-13 indicate that surface roughness decreased substantially with the increase in rake
angle when machined under cryogenic environment. It is also noted that surface roughness decreased to some extent with
the increase in cutting speed, possibly due to smoothening of the nose profile by adhesion and diffusion types wear.
From the present experimental data it can be clearly seen that decrease of surface roughness become more
significant with higher cutting speeds for cryogenic cutting. This is due to a larger modulus of rubber and increased
rigidity of rubber at lower temperatures leading to less workpiece material flow underneath the tool clearance surface
which is very much beneficial in maintaining cutting stability and achieving a good machined surface finish. In contrast,
the rake angle of the tool plays an important role in generating a smooth machined surface. Tools with a large rake angle
produce a smooth surface with ribbon-like chips. Conversely, rough surfaces and discontinuous chips are generated with
tools with a small rake angle.
5. CONCLUSION
The use of cryogenic LN2 as cutting fluid along with dip method for machining of elastomer and comparing the
data with that of ambient machining the following conclusions can be made:-
• The cutting performance of cryogenic machining is better than that of ambient machining. Cryogenic dip
workpiece cooling provides the benefits mainly by substantially reducing the cutting temperature, which
improves the chip-tool interaction and maintains sharpness of the cutting edges.

156
• It can be clearly seen that cutting force component is decreasing with increase of rake angle. The cutting speed
and feed rate have a minor effect on cutting forces, although it can be observed that a larger feed rate
corresponds to larger cutting force.
• Cryogenic cooling by liquid nitrogen with different rake angle tools provided better surface finish and higher
dimensional accuracy as compared to ambient machining.
It was evident from the surface roughness vs. rake angle that cryogenic machining improves the surface finish of
the workpiece for any given combination of cutting speed, rake angle and feed.
REFERENCES
1. ASTM D1566-00, “Standard Terminology Relating to Rubber”, American Society for Testing of Materials, 2000.
2. Jin M and Murakawa M, “High-Speed Milling of Rubber (1st Report), Fundamental Experiments and
Considerations for Improvement of Work Accuracy,” Journal of the Japan Society for Precision Engineering,
Vol. 64, 6, Pp. 897-901, 1998.
3. Shih A.J, LewisM. A, LuoJ and Strenkowski,J. S, “End Milling of Elastomers, Fixture Design and Tool
Effectiveness for Material Removal,” ASME Journal of Manufacturing Science and Engineering, Vol. 126, Pp.
115-123, 2004.
4. Strenkowski J.S, Shih A.J, RodkwanS and LewisM.A, “Machining of Elastomers – Experimental and
Numerical Investigation”, 2003 NSF Design, Service and Manufacturing Grantees and Research Conference,
Birmingham, Alabama, 2003.
5. Strenkowski J.S, Yan J, Shih A. J and LuoJ, “Improving the Machinability of Elastomers with Induction
Heated Tools and Finite Element Cutting Models,” NSF Design, Service and Manufacturing Grantees and
Research Conference Proceedings, Scottsdale, AZ, 2005.
6. Shih A.J, LewisM. A, LuoJ and StrenkowskiJ. S, “Chip Morphology and Forces in End Milling of Elastomers,”
ASME Journal of Manufacturing Science and Engineering, Vol. 126, Pp. 124-130, 2004.
7. Dhokia V.G, Newman P.S. CrabtreeT and Ansell M. P, “A process control system for cryogenic CNC
elastomer machining,” Journal of Robotics and Computer-Integrated Manufacturing, Vol.27, Pp.779–784, 2011.
8. Rajesh N, Raviraj S, Sawan S, “Experimental and Finite element Analysis on Chip Formation Mechanism in
Machining of Elastomers”, Bonfring International Journal of Industrial Engineering and Management Science,
Vol. 2, pp. 10-13, 2012.

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