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Procedia Engineering 81 ( 2014 ) 2379 – 2384
Available online at www.sciencedirect.com
1877-7058 © 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/3.0/).
Selection and peer-review under responsibility of the Department of Materials Science and Engineering, Nagoya University
doi: 10.1016/j.proeng.2014.10.337
ScienceDirect
11th International Conference on Technology of Plasticity, ICTP 2014, 19-24 October 2014,
Nagoya Congress Center, Nagoya, Japan
Friction-spinning – Interesting approach to manufacture of
complex sheet metal parts and tubes
Benjamin Lossen*, Werner Homberg
University of Paderborn, Warburger Strasse 100, Paderborn 33098, Germany
Abstract
Friction-spinning is an innovative incremental forming process that permits the defined a djustment of material properties in a
particularly precise manner. The process is characterised by the use of process elements from both metal spinning and friction
welding. As the workpieces are being processed, friction sub-processes are employed to achieve self-induced heat generation.
Compared with conventional spinning processes, this in-process heat treatment permits the extension of existing forming limits
and allows more complex geometries to be achieved, together with defined, favourable part properties. The process thus holds a
high potential for the manufacture of functionally graded workpieces, such as complex hollow parts made from tubes and sheets.
In order to achieve functional gradation, i.e. to influence the material properties (strength or grain size) in a defined manner, it is
essential to be able to set specific temperature profiles. It would be possible to influence these profiles by selecting appropriate
process parameters like the feed rate, relative motion and the coefficient of friction. The process characteristics of friction-
spinning make it eminently suited to tube processing. A further approach to the manufacture of parts with functionally graded
areas is the use of sheet metal blanks as another semi-finished product. The paper will present the corresponding results of basic
research into the manufacture of sheet metal parts with the aid of friction-spinning. Here, the influence of significant process
parameters, forming strategies and tool systems on both the course and the outcome of the friction-spinning process will be
shown. In addition, the differences and correlations that exist between tube and sheet processing will be described and
discussed on the basis of parts made of tubes and sheets. These parts are manufactured by the friction-spinning process
employing different process strategies and tool setups.
© 2014 The Authors. Published by Elsevier Ltd.
Selection and peer-r eview under responsibility of Nagoya University and Toyohashi University of Technology.
Keywords: Friction-spinning; Sheet; Tube; Tool system; Incremental forming; Process design
* Corresponding author. Tel.: +49-5251-60-5341; fax: +49-5251-60-5342
E-mail address: bl@luf.upb.de
© 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/3.0/).
Selection and peer-review under responsibility of the Department of Materials Science and Engineering, Nagoya University
2380 Benjamin Lossen and Werner Homberg / Procedia Engineering 81 ( 2014 ) 2379 – 2384
1. Introduction
The requirement for a high performance, coupled with ecological concerns, such as for reduced material and
energy consumption, calls for innovative lightweight products and hence for effic ient manufacturing
technologies (Kleiner et al., 2004). Promising lightweight structures include hollow components like those
employed in the transportation sector and in general engineering (Finckenstein and Dierig, 1990). In conventional
spinning processes, the forming limit of the workpiece is restricted due to the work-hardening effect that occurs
during the process. An effective approach to counteracting and achieving these complex structures is the use of
incremental forming processes combined with an extension of the forming limits through the use of heat
treatment (Neugebauer et al., 2006 and Awiszus et al., 2005). Normally, this heat treatment is realized by burner
systems, intermediate heating or the use of lasers (Bergs et al., 2005). All these approaches increase the costs
associated with energy, investment and maintenance. Another approach is to use friction processes for the heat
generation, which means that the process can then be referred to as friction-spinning. This combines elements of
friction welding and a metal spinning process to achieve a localized warm-forming operation through the process-
integrated friction. By selecting appropriate process parameters, defined temperature profiles can be set in the
workpiece. As a consequence, it becomes possible to manufacture multifunctional components such as complex
hollow parts made of tubes, profiles or sheet metal blanks with locally varying mechanical properties that satisfy
the demands of lightweight design. The aim of the ongoing investigations is to extend the forming limits and
achieve load-adapted workpieces with locally graded properties in aluminum, steel and stainless steel. The
promising results from tube forming, such as the defined influence on the grain structure (Homberg and Lossen,
2013), hardness, residual stresses (Homberg and Hornjak, 2011), surface roughness (Homberg et al., 2012) and the
high degree of deformation that is feasible for forming a wide range of new geometries (etc.) (Hornjak, 2013),
constitutes the motivation for transferring the knowledge to sheet metal forming. The basic process principle of
friction-spinning for a sheet metal component is shown in Fig. 1.
Fig. 1. Friction-spinning – principle behind the sheet metal forming process.
The sheet metal blank (Fig. 1 – a) is clamped with the aid of a tailstock, thus permitting the torque to be
transferred. Once the blank has been brought to rotate, the friction-tool feed is activated, and the fixed tool comes
into contact with the blank. Due to the friction induced by the relative motion, the temperature increases
significantly (Fig. 1 – b). Consequently, the plasticity of the material is increased, thereby permitting high-degree
forming operations (Fig. 1 – c). Additionally, tools can be used to support the forming process and/or the
temperature generation/control (Homberg and Hornjak, 2011). With regard to the temperature, this can either be
controlled in a defined manner over the entire process or be set according to the requirements by varying the
rotation speed or the friction ratio, for example. Here, the friction ratio can be influenced due to the usage of
different tool types and their relative motion between the sheet. It is possible to set a maximum dynamic friction
with a stationary tool. Further with a rotating tool a minimal rolling friction can be realized. At the LUF, current
research work is focusing on the development of friction-spinning tools and tool systems for the manufacture of
complexly structured workpieces from tubes and sheets. This paper builds on the results obtained for tube forming,
High-Temperature-
Zone
b)
Tailstock
k
Process Parameters:
- Rotation speed
- Material pairings
- Feed rates
-Axial forces
-Surface
q
ualities
- Wear resistance
- Heat capacity
- Forming path
- Lubricant
Forming Tool/
Roller
c)
FA
n
Too l
Material
FR
μR
R
FA
n
Workpiece Material
W
ǻT
FR
F
F
Sheet
Spinning Mandrel
a)
2381
Benjamin Lossen and Werner Homberg / Procedia Engineering 81 ( 2014 ) 2379 – 2384
e.g. a high D/s and D1/D0 ratio for flange processing (Homberg and Lossen, 2013). These high D/s ratios make for
a smooth transfer to sheet forming. A fundamental process investigation is conducted in a bid to achieve the
maximum wall thickness reduction in cup forming through multi-pass forming strategies. In addition, the results of
the influence of hardness and grain structure on the cup forming process are investigated and described.
2. Investigation of friction-spinning in sheet metal forming
Basically, the conventional spinning process is characterized by complex tool path geometries and the use of
additional equipment e.g. a counterholder to form a cup, as is illustrated in Fig. 2 – 1a. This kind of process allows
a maximum spinning ratio of 2.5 during the 1st pass on the basis of investigations of linear, quadratic, and involute
tool paths (Kawai et al., 2002; Hayama et al., 1970). Hayama et al. (1970) clarified the typical non-constant wall
thickness distribution of the conventional spinning process, which is due to the high tensile st rain and can be
influenced by the tool path geometry. A similar approach using a multi-roller head from Kawai et al. (2002) makes
it possible to increase the spinning ratio to 3.3 using a single roller pass. An overview of the options for designing
a spinning process is provided by Music et al. 2010. A considerable effort is required to form cup geometries with
a height of 35 mm from an initial sheet metal blank in aluminum alloy 6082 (diameter of 120mm and a wall
thickness of 5 mm) using a spinning mandrel with a diameter of 66 mm, and this can involve generating a complex
tool path in synchronization with the counterholder. If an additional wall thickness reduction in the cup side wall is
required, it is nece ssar y to u se mult i- pass st rategies (cf. Fig. 2 – 1b). A further approach to sheet metal forming is
the friction-spinning process. This constitutes a good alternative on account of the linear tool path strategies and
the low forming forces by contrast to conventional spinning. The sheet forming investigation shows the results for
maximum wall thickness reduction, wall thickness distribution and the hardness and grain structure influence with
less complex tool and tool path designs by comparison with conventional spinning processes. Also, the possibility
of generating a gradation by adjusting the influence of the hardness or defined grain structure in cup forming is to
be verified. The basic process principle behind the friction-spinning process is shown in Fig. 2.2(a-d).
Fig. 2. Cup forming principle with a one-pass and two-pass forming strategy in conventional spinning and friction-spinning.
Here, a linear tool pass with a universal friction tool is used for the 1st pass. The process starts by bringing the
sheet metal blank to rotate. The friction tool makes contact with the outer edge of the sheet due to a linear axial
tool movement (Fig. 2.2 – a). The friction generated by the relative motion and the contact with the stationary tool
causes the temperature in the forming zone to increase significantly. Once the required temperature level and the
requisite material ductility are attained, the feed rate can be set to a higher level to form a conical intermediate
geometry (Fig. 2.2 – b). The cup is formed by an ongoing linear radial tool movement, illust rated in Fig. 2.2 - c. A
further adjustment of the resulting wall thickness sn on the side wall of the cup can be achieved by setting an
adequate gap between the mandrel and the tool directly in the 1st pass. The process strategy can be extended with a
2nd forming pass and is shown in Fig. 2.2-d. The 2nd pass involves a further overrun forming step following the first
1st Pass
2a)
)
F
a
n
n
Sheet
S
s0
2nd Pass
2d)
n
n
n
n
F
r
d
M
2b)
n
n
b)
F
r
Tool
2c)
n
n
F
r
sn
Į
n
n
n
n
n
n
n
n
n
n
d
M
sn
Friction-
Spinning
Conventional
Spinning
n
n
s0
Counterholder
Mandrel
M
1a) 1b)
Tool Path
Tool Path
Spinning
roller
Tailstock
n
n
Metal Spinning Flow turning
2382 Benjamin Lossen and Werner Homberg / Procedia Engineering 81 ( 2014 ) 2379 – 2384
radial tool movement to form the cup geometr y (Fig. 2.2). In the 2nd pass, it is possible to select the desired friction
ratio. This can be varied between the minimum friction ratio (rotating tool) and the maximum friction ratio
(stationary tool) and has a significant influence on the microstructure and hardness (cf. Chapter 2.1 and 2.2).
)XUWKHUWKHWRRODQJOHĮLQ)LJ 2.2 is set to 45° due to experimental investigations which have shown that an angle
of 45° constitutes a good compromise between the forming forces and the material flow (Homberg et al., 2012;
Hornjak 2013). In special cases a tool with 0° and 90° degrees can be used for manufacturing by means of an axial
upsetting forming operation to produce a pulley, for example.
2.1. Wall thickness reduction and grain structure influence
This chapter deals with the manufacture of tall cups with thin wall thicknesses without a complex tool path
strategy or the use of multi-pass strategy to avoid the problem of local thinning in the cup side wall. The
correspond ing investigation starts with the analysis of the maximum possible wall thickness reduction due to
different parameters (rotation speed/feed rate) and forming strategies 1st and 2nd pass described above (cf. Fig. 2.2).
The spinning ratio is about 1.8 in this investigation, and the resulting D/s ratio is nearly 4 without the additional
and customary roller overruns or counterholder (Music et al., 2010). Furthermore, the process forces do not exceed
3 kN and are thus insignificant by comparison to conventional spinning. In Fig. 3, two typical thickness
distributions are illustrated along the cup side wall with the minimal wall thickness for one and two-pass strategies.
The minimum wall thickness of 78.5 % (ijs = -1.5) compared to the initial wall thickness was observed in the
bottom radius region using a single-stage strategy, as shown in Fig. 3 (a). Using this strategy, an increase in the
thickness at the end of the cup sidewall was observed as a general trend. At this point, the wall thickness reduction
is 62.2 % (ijs = -1).
Fig. 3. Grain structure influence and maximum wall thickness reduction of cup forming process with one and two-pass forming strategy.
The reduction in the wall thickness at the beginning results from the engagement of the residual material with
the tool. The resulting tensile strain due to the radial movement from the tool in combination with the friction and
material ductility generates longitudinal stretching in this area (15 mm) of the cup. This effect results in thinning
near the bottom and will decrease if less sheet material is in contact with the tool. Ultimately, the aforementioned
section of the cup marks the limited area in which the maximum reduction can be achieved with a one-pass
forming strategy. In contrast to the one-pass strategy, the 2nd pass (b) shows the opposite trend. Here, the maximum
reduction is at the end of the cup and amounts to 75 % (ijs = -1.4). Hence, the minimal wall thickness reduction is
in the bottom region and is nearly 65 % (ijs = -1.05). The maximum reduction in the 2nd pass is limited due to the
constant increase in the temperature in the mandrel and sheet due to the longer manufacturing time and the
prevailing friction. All in all, the maximum wall thickness reduction was achieved with a one-pass strategy and
produces taller cups (115 mm) than a two-pass strategy (95 mm). Basically, a significant constant wall thickness
profile can be observed with two-pass forming strategies. The influence on the grain structure of the workpiece
with the one-pass strategy is illustrated in Fig. 3 (A and 1). The friction-spinning process generated grain
refinement due to the high shear loads and the high temperature of this thermo-mechanical process (Homberg and
Lossen, 2013). The initial grain structure of the AA-6082 material used has a grain size of approx. 100 – 150 μm
and is oriented in the direction of rolling (cf. Fig. 3 – A). By contrast, the grain structure in area 1 is significantly
influenced and is adjusted in a range of 5 – 15 μm. It is the same grain refinement effect as in tube processing and
is dependent on the time for which the temperature load acts and the degree of deformation. Further investigations
Material : AW-6082
Diameter Ø : d
0
=120 mm
Wall thickness : s
0
=5 mm
Mandrel-Ø : d
M
=66mm
Rotation speed : n = 400 rpm
Axial feed rate : f
a
= 0,5 mm/s
Radial feed rate: f
r
= 2 mm/s
Tool angle : Į=45°
200μm
A
-2,0
-1,5
-1,0
-0,5
0,0
0 20406080100120
Strain in thickness
direction ij
s
(
)
Distance from the bottom [mm]
A1
b
a
100μm
1
1
st
pass; min. wall thickness
a
2
nd
pass; min. wall thickness
b
2383
Benjamin Lossen and Werner Homberg / Procedia Engineering 81 ( 2014 ) 2379 – 2384
will be conducted in future studies into the defined influencing of the grain structure so as to generate an
approximately ultra-fine grain structure with multi-axial forming strategies taken from tube processing (Homberg
and Lossen, 2013).
2.2. Analyses of the hardness adjustment
A further focus of investigation is a define influencing and adjustment of hardness in the manufactured
workpieces. Previous hardness investigations conducted for the tube forming of aluminum alloy 6082 show that a
defined and locally restricted influence of the workpiece properties is readily possible (Homberg and Hornjak,
2011; Hornjak, 2013). Fig. 4 shows the resulting hardness distributions of the specimens referred to above. The
initial hardness of the material depends to a significant extent on the process characteristics of the friction-spinning
process. The high temperature and the high degree of deformation give rise to grain refinement (cf. chapter 2.1)
that also has an influence on the hardness reduction of the formed material.
Fig. 4. Process strategy influence on the hardness distribution.
The hardness distribution of the 1st pass (a), with the maximum wall thickness reduct ion, involves an increase in
the hardness from 50 HV5 to 70 HV5, starting at the bottom of the cup. If a two-pass strategy (b) is used, the
hardness distribution remains more consistently at a level of 55 HV5 from the beginning, ending near the end of
the cup. This effect of a hardness increase at the end of the specimens always occurs, since it is caused by the
temperature drop at the end of the forming process. This is because of the reduced amount of forming material
which is in contact with the tool and the lack of material resistance for generating the required temperature. Here,
the effects of a warm rolling process result, leading to an increase in the hardness. The adjustability of the hardness
in sheet forming is shown in Fig. 5. This illustrates three forming strategies (a - c) which have the same parameters
and give rise to the same wall thickness reduction in this forming process. The process strategies are varied, with a
one or two-pass strategy and with a maximum or minimum friction ratio.
Fig. 5. Possibility of hardness adjustment with an aluminum alloy 6082.
Fig. 5 – b shows the hardness distribution for a one-pass strategy with an end wall thickness of 2.5 mm. The 1st
pass investigations show a hardness adjustment in a range of 10 HV5 with a parameter variation of only the
rotation speed (n) and the feed rate (fa/fr). If a significant hardness influence is desired, the two-pass strategy has to
be applied. Fig. 5 – a/c shows the maximum hardness adjustment range using the two-pass strategy. The 2nd pass
can be applied with a minimum or maximum friction ratio. Fig. 5 – a illustrates the 2nd pass with the minimu m
0
20
40
60
80
100
0 20406080100120
Hardness [HV5]
Distance from the cu
p
bottom
[
mm
]
Material : AW-6082
Diameter : d
0
=120mm
Wall thickness : s
0
=5 mm
Mandrel-Ø : d
M
=66mm
Rotation speed : n = 400 rpm
Axial feed rate : f
a
= 0,5 mm/s
Radial feed rate: f
r
= 2 mm/s
Tool angle : Į=45°
2
nd
p
ass; min. wall thickness
1
st
pass; min. wall thickness
ba
Initial hardness:120 HV5
a
b
40
50
60
70
80
90
100
0 1020304050
Hardness [HV3]
Distance from the cup bottom [mm]
Material : AW-6082
Diameter : d
0
=120mm
Wall thickness : s
0
=5 mm
Cup Wall thickness : s
n
=2,5mm
Mandrel-Ø : d
M
=66mm
Rotation speed : n = 900 rpm
Axial/radial feed rate : f
a
/f
r
= 1 mm/s
Tool angle : Į=45°
2
nd
pass; second stage: min. friction ratio
a
2
nd
pass; second stage: max. friction ratio
c
1
st
pass
b
a
b
c
Initial hardness: 120 HV3
2384 Benjamin Lossen and Werner Homberg / Procedia Engineering 81 ( 2014 ) 2379 – 2384
friction ratio. This st rategy results in the maximum hardness att ained, which is about 20 HV3 higher than the
single stage. The other two-pass strategy with the maximum friction ratio generates the lowest, but constant
hardness distribution. The minimum hardness results in the range of 60 HV3 and is on average 15 HV3 lower than
for the single-stage forming process. Finally, the hardness in the cup forming process can be adjusted within a
range of 35 HV3.
3. Conclusion
The friction-spinning process is an interesting approach which holds a high potential for the production of new
and complex geometries with functionally graded properties in the tube and sheet forming of aluminium alloys.
The possibility of extending the forming limits of conventional metal spinning processes through in-process heat
generation is examined, mak ing it possible to achieve a cup forming process with a high wall thickness reduction
in one or two forming steps. This paper describes a maximum reduction to approximately 80 % of the initial wall
thickness. Additionally, the thickness of the cup side wall can be adjusted through the infeed of the tool to the
mandrel. Further, this paper shows that it is possible to achieve a defined adjustment of the hardness distribution
through parameter variation and special process strategies in sheet metal for min g. Also, it has been po ss ib le to
verify the basic influence on the grain structure in sheet metal forming which characterizes the friction-spinning
process. To conclude, friction-spinning is an innovative forming technology that expands the existing forming
limits and holds a high potential for the efficient manufacture of the lightweight structures of tomorrow made from
tube and sheets.
Acknowledgements
The authors from the subproject A7 centre of the collaborative research Transregio 30 would like to thank the
German Research Foundation (DFG) for supporting this project.
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