Volume 3, Number 4, December 2009
ISSN 1995-6665
Pages 312 - 321
JJMIE
Jordan Journal of Mechanical and Industrial Engineering
The Use of Rational Design in the Development of an Improved
Plug Tool for the Rotary Tube Widening Process
S. D. Al-Shobaki *, A. K. A. Al-Dahwi , R. H. Fouad
Department of Industrial Engineering, Hashemite University, Jordan
Abstract
To improve the performance of any metal forming process, a minimization in the process load parameters is needed. The
used die geometry significantly affects the process performance. Several die designs were developed to increase efficiency
and reduce defects. This paper investigates the effect of the widened plug profile on the tube widening process, and considers
the use of the Constancy of the Ratios of successive generalized Homogeneous Strain (CRHS) increments concept for
different die profiles. Five widening process parameters are considered: the axial plug load, the widening torque, the variation
in temperature, the widened tube thickness, and the widened tube quality. The investigation shows that an improvement in the
widening process parameters was achieved using (CRHS) plug design leading to a 25% increase in the maximum widening
ratio compared to other plug designs. This was achieved at relatively low tube ends temperature and an improved quality of
widened tube ends.
© 2009 Jordan Journal of Mechanical and Industrial Engineering. All rights reserved
Keywords: : Tool Design; Tube Widening Process; CRHS Concept; Widening Load Parameters; Temperature.
1. Introduction
*
Many deformation processes have been used as
manufacturing processes to widen the tubes ends [1] in
order to facilitate the requirements for overlapping joining
of tubes and pipes. The sealing condition in the joining
portions of the pipes networks may play an important
reason in their failure [[2], and calls for improving the
quality of the tube end to minimize that problem.
Different deformation process techniques have been
adopted to widen the tube ends with certain widening ratio.
A plug maybe inserted as a tool to widen the tube end.
This has given a limitation in the maximum achievable
widening ratio (the ratio of the final internal tube diameter
to the initial internal tube diameter). The process is critical
as the quality of the widened tube end depends on several
process parameters, such as the plug geometry and its axial
load and torque [3].
The use of hydrostatic pressure and a press with ballshaped tool were also considered in different studies for
tube widening [4]. However, these techniques required the
use of complex tooling and the amount of load and
consumed power were high.
Ball shaped and truncated conical plugs have also been
used in conjunction with the rotary forming process, in
which the formed elements are rotated during forming [5]
[6]. It was established that the rotary process gives high
quality products with good geometry shapes. This led to an
increase in the use of rotary forging and tube spinning in
producing flanges and elongated tubes [7] [8].
*
Corresponding author. sshobaki@hu.edu.jo.
The main aim of using different widening tools for tube
ends in rotary forming processes was to investigate their
effect on the process parameters. The ball shaped tool, for
instance, has been used to determine the maximum
widening ratio, which can be achieved with the increase in
ball diameter and tube thickness. Using these techniques, a
maximum widening ratio of 2.0 was achieved [5]. The
process axial load, specific widening pressure and its
defects have also been given. When the ball rests on bore,
a force is required to overcome friction and a sharp
increase in load is noticed.
It can be concluded from the previous research that the
widening tool shape with the tube rotary has a large effect
on the process parameters and calls for selecting a rational
tool design method to improve them. The concept of the
Constancy of the Ratios of successive generalized
Homogeneous Strain increments (CRHS) has been adopted
in many metal- forming processes, such as: tube
elongation [9], tube piercing [10], and the extrusion of
tubes and cans [11–12]. It has been concluded that the
designed tools using the CRHS concept give high products
quality while minimizing the load required in performing
the process. This is referred to as the reduction of the
redundant shear strain and consequently of the work
redundancy.
The ever-increasing demand for high quality product in
metal-forming processes necessitated the establishment of
working zone improved geometry by suggesting rational
methods of tool design. Nevertheless, the majority of these
methods can only deal with specific processes. The CRHS
concept showed a substantial reduction in the magnitude of
in-homogeneous deformation [13]. The incidence of
redundancy shearing strains was estimated and the
313
© 2009 Jordan Journal of Mechanical and Industrial Engineering. All rights reserved - Volume 3, Number 4 (ISSN 1995-6665)
correlation between force parameters and the work
redundancy of the system was made.
Furthermore, and to show the superiority of the curved
dies over the conventional conical dies for a wide range of
reductions and frictional conditions, Blazynski et al. [11]
reviewed many investigations which were based on slipline field, upper-bound and visioplasticity analytical
methods, to show the superiority of the curved dies over
the conventional conical dies for a wide range of
reductions and frictional conditions.
The CRHS concept is adopted in this study for the
plug, due to its successful application in other metal
forming processes and because it produces a curved profile
with different rates of deformation.
2. Theoretical Background
The axial plug load and the torque are the main two
force parameters that must be considered in any seamless
tube manufacturing, using a rotary forming process [10].
Therefore and in order to improve the performance of any
of these processes, these two parameters must be
minimized as much as possible.
As the plug tool is used to widen the tube end in the
rotary tube process, the forward movement of that plug
inside the tube leads to increasing the axial plug load to
overcome the friction, and dislocate the tube material size
which is required to achieve the designed widening ratio of
the tube end. This is also what is expected for the process
torque parameter. From that, the geometry of the widening
plug profile plays an important role in the magnitude of the
axial plug load and the torque as the variation of the plug
profile affects the contact area between the tube and the
plug and the total dislocation distant of the tube material
size under widening.
The CRHS concept, which has been applied to determine
the widening plug profile, relies on the consideration of the
homogeneous strain level (ε H ) in (n) equispaced transverse
sections of the pass and is defined by the following
equation [9]:
Z n / Z (n-1) = (Z 1 )S(n-1)
(1)
Where Z is defined by the physical dimensions of the
work piece. Thus ln(Z) = ε H . S is the rate of deformation
unrelated to time. The value of S determines the mode of
deformation, and so, S = 1 corresponds to a uniform rate of
flow (UCRHS), S > 1 corresponds to an accelerated rate
(ACRHS), and S < 1 corresponds to a decelerated rate
(DCRHS). Thus there are three sets of plug profiles that
can be designed for each value of tube widening ratio used
in this research.
Copper metal has been used as a model material to
determine the effect of the widening plug profile on the
process parameters. Thus is due to reasons of economy and
the limitation of laboratory facilities. It is important to note
that the basic requirement demanded of a model material is
that its mechanical behaviour should resemble, as closely
as possible, the prototype material required to be simulated
[14] [15]. This technique has solved many problems in
estimating the actual work parameters in metal-forming
processes.
3. Experimental Setup
To determine the effect of the widening plug profile on
the performance of the process, Copper tubes have been
used with different wall thickness of 2, 2.5, 3, and 3.5 mm
and with a constant internal diameter of 12 mm. Regarding
the widening plugs, different plug diameters of 18, 22, 24,
28, 30 and 32 mm have been used to give different
widening ratios; 1.50, 1.83, 2.00, 2.33, 2.50 and 2.67. It
has to be noted here that the plug profile shape is governed
by the constant (S), which determines the rate of
deformation for each diameter.
The designed plug profiles of three different rates of
deformation (S); 0.9, 1.0 and 1.1 were based on the CRHS
design concept. For practicality, a plug advance (The
length of the plug profile, Xp) of 12.5 mm has been used
[9] [10]. The respective changes in plug profiles and their
dimensions are shown in Figure 1 and Figure 2. Plugs
specifications are given in Table 1.
To run the experimental part of the research, an
automated drill machine with a dynamometer device
(Model No. BKM2000 – TeLC Co.) was used. Technical
modifications were made in order to facilitate the
measurement of the axial load and torque during the
widening process of the tube ends with different plug
profiles. At the same time, a temperature measurement
sensor (TeLC Co.) was used to measure the temperature
increase during the operation of widening the tubes end.
The process was carried out at a feed rate of 0.1 mm/rev.
and a spindle speed of 475 rpm. Oil was used as a
lubricant. The experimental process set up is shown in
Figure 3.
4. Experimental Results and Analysis
To show the effect of the widening plug profile type on
the process performance, several experiments were carried
out for the different plug dimensions shown in Table 1 and
the process parameters were measured to check the
widened portion of the tube and the quality of deformation.
The results will be considered in the next five sections.
4.1. Axial Plug Load
The values of this process parameter were obtained
using the load measurement Dynamometer. Figure 4
shows a plot of these results for different widening ratios,
tube thicknesses and plug profiles. It can be seen that the
axial plug load increases with the increase in the widening
ratio. This is due to the increase in the contact area
between the widening plug profile and the tube material.
Table 1 has shown that the surface area of the plug profile
is higher as the widening ratio and plug diameter increase.
Again, the axial plug load increases with the increase of
the tube thickness, since the displacement of the material
volume increases in unit time.
Figure 4 also shows that the ACRHS plugs give the
lowest values of axial plug load, while the DCRHS plugs
profile result in the highest. The reason of that can be
explained with reference to Figure 5, which shows the
mechanism of the tube metal flow during the widening
process using different plug profiles. It can be easily
noticed that the lowest metal flow displacement in the
deformation zone occurs using the ACRHS plug profile.
© 2009 Jordan Journal of Mechanical and Industrial Engineering. All rights reserved - Volume 3, Number 4 (ISSN 1995-6665)
314
Figure 1. CRHS – Concept design of widening plug profile (S is the rate of deformation).
Opposite to that, the metal flow displacement is highest
with the DCRHS plug profile.
The experiments have shown that using the ACRHS
plug profile and for the widening ratios of 2.50 and 2.67,
the shape of the widened tube end has become a round
flattened flange. This is due to the magnitude of the
inclination angle of the ACRHS plug profile, as it is
increased, at the rear portion, with the increase of the plug
diameter. As a result, this pushes the tube metal out of the
cylindrical part of the widening plug, as illustrated in
Figure 6.
4.2. Widening Torque
The variation of the widening process torque with the
different widening ratios, tube thicknesses and plug
profiles is given in Figure 7. As seen, the general
behaviour of the widening torque increases with the
increase of the widening ratio, which is similar to the
increases in the axial plug load. This is due to the increase
in both of the contact area between the widening plug
profile and the tube material, as the plug diameter
increases, and to the increase of the plug profile length, as
shown in Table 1. Also, the widening torque increases
with the increasing of the tube thickness and this is due to
315
© 2009 Jordan Journal of Mechanical and Industrial Engineering. All rights reserved - Volume 3, Number 4 (ISSN 1995-6665)
Figure 2. CRHS – Concept design of widening plug profile (S is the rate of deformation).
Table 1 Plug specifications.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
DCRHS
Deformation rate (s)
0.9
ACRHS
Plug type
1.1
UCRHS
Plug no.
1.0
Plug diameter
(mm)
18.0
22.0
24.0
28.0
30.0
32.0
18.0
22.0
24.0
28.0
30.0
32.0
18.0
22.0
24.0
28.0
30.0
32.0
Profile length
(mm)
15.442
16.161
16.597
17.321
17.749
18.178
15.090
15.799
16.227
16.940
17.367
17.793
14.992
15.698
16.119
16.827
17.250
17.675
Plug profile surface
area (mm)2
97.028
101.545
104.283
108.831
111.523
114.217
94.813
99.274
101.958
106.439
109.117
111.798
94.195
98.631
101.276
105.728
108.385
111.057
S p in d l e
C huck
P lu g
p r o fil e
Tu be
W id e n in g p l u g
P lu g h o ld er
D y n a m o m e te r
T em p eratu re
se n so r
Figure 3. Experimental process set up.
© 2009 Jordan Journal of Mechanical and Industrial Engineering. All rights reserved - Volume 3, Number 4 (ISSN 1995-6665)
Figure 4. Relation between axial plug load and widening ratio at different tube thicknesses.
Figure 5. Mechanism of tube metal flow for different plug profiles, (a) ACRHS (b) UCRHS (c) DCRSH.
316
317
© 2009 Jordan Journal of Mechanical and Industrial Engineering. All rights reserved - Volume 3, Number 4 (ISSN 1995-6665)
Figure 6. Round flatted flange at the tube ends: Top and side views.
Figure 7. Relation between widening process torque and widening ratio
the same reason of increasing in material volume
displaced in unit time.
It can be indicated again from Figure 6 that ACRHS
plugs give the lowest level of widening torque and the
DCRHS plugs give the highest due to the same reasons
mentioned in the analysis of the axial plug load.
4.3. Variation of Temperature
Analysis of the axial plug load and the widening torque
showed that ACRHS plugs give the lowest level of axial
plug load and torque. The reason for this was that the
widened tubes end experienced less metal flow
displacement in the deformation zone. To verify this
explanation, the temperature that results from the widening
process was measured using a temperature sensor, as
shown in the experimental setup in Figure 3.
Figure 8 shows the variation of temperature during the
widening process relative to the widening ratios, tube
thicknesses and plug profiles. As expected, the ACRHS
plugs profiles gives the least amount of temperature
increase compared to the other profiles.
© 2009 Jordan Journal of Mechanical and Industrial Engineering. All rights reserved - Volume 3, Number 4 (ISSN 1995-6665)
318
Figure 8. Temperature variation with the widening ratio for different tub thicknesses.
It has been known that one of the many factors that
lead to the temperature increase in the deformation
processes is the volume of the internal distortion that
occurs in the deformed material. It is important to note that
with large material displacement, which may be performed
in such deformation process, a high quantity of the internal
distortion will be deformed. This is the reason why the
ACRHS plug profiles give a small increase in temperature
during the process due to the small material displacement
achieved with those plug profiles.
4.4. Widened Tube Thickness
Figure 9 shows the variation in the final tube thickness
relative to the widening ratios, tube thicknesses and plug
profiles. Note that the increase of the widening ratios leads
to a high reduction in tube thicknesses. This is due to the
high tube material expansion i.e. high material stretching
or high incidents of strain and as a result of that high
reduction in the tube thicknesses.
As expected, the ACRHS plugs profile give less
reduction in the tubes thicknesses. This is again due to the
less tube material displacement or material expansion in
the deformation zone and as shown in Figure 5. This can
be clarified from the figure, where for the highest
widening ratios, the differences in tube thickness
variations relative to the type of the plug profiles are well
defined.
4.5. Widened Tube Quality
One of the most important requirements from any use
of deformation process is to gain high quality products.
This can be verified if the product has, for example, high
dimensional accuracy, precise shape, and minimum
internal and external defects. These three quality
considerations may be simulated in the case of the
widened tube ends using three parameters; the roundness
of the tube end, the uniformity of the tube end thickness
and the formation of tube tearing. Accounting for these
quality parameters can minimise the problem and failures
in pipes networks.
It has been found that the use of the concept of the
Constancy of the Ratios of successive generalized
Homogeneous Strain increments (CRHS) for the widening
plug profiles give a good effect on these parameters. This
can be seen in Figure 10, where all the plug profiles show
a perfect round tube ends in addition to a uniform
thickness for all tube thicknesses and widening tube ratios.
An exception to this case is the case of the ACRHS plug
profiles, where a round flattened flange resulted when
widening ratios of 2.50 and 2.67 were attempted.
Furthermore, no tearing defects occurred during the
process with the used widening ratios, even with those
widened tubes that have been deformed to a flattened
flange.
319
© 2009 Jordan Journal of Mechanical and Industrial Engineering. All rights reserved - Volume 3, Number 4 (ISSN 1995-6665)
Figure 9. Relation between final tube thickness and widening ratio.
Figure 10. Widened tube ends profile: Top and side view.
© 2009 Jordan Journal of Mechanical and Industrial Engineering. All rights reserved - Volume 3, Number 4 (ISSN 1995-6665)
5. Conclusions
The experimental results for the widening tubes end
process have shown that the process parameters are
completely affected by the geometry of the widened plug
profile. They have also shown that the use of the concept
of Constancy of Ratios of successive generalized
Homogeneous Strain increments (CRHS) has significantly
improved the performance of the process. It gives a
maximum widening ratio of 2.67 under all the conditions
selected for the process, which represents a 25% increase
in the widening ratio compared to other used techniques.
Adding to that, the produced widened tube ends are in high
dimensional precision and uniform thicknesses without
any tube wall tearing.
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