AbstractFE simulation was applied to study the material flow during infeed rotary swaging. The neutral plane according to the process parameters was investigated and compared with experimental results. A single forming stroke was analyzed precisely by using small time points of 10-4s. For analysis the essential steps between the first contact of wire and forging die and the last contact before the die opens again are represented. In that range the feed velocity is eliminated and the neutral plane can be observed as spatial velocity at nodes in the axial direction equal 0mm/s. During a single stroke the location, the geometry and the orientation of the neutral plane is changing

Hochrainer, Thomas

Hunkel, Martin

Ishkina, Svetlana

Kuhfuss, Bernd

Moumi, Eric

Struss, Adrian

Elsevier - Publisher Connector 

2D-simulation of Material Flow During Infeed Rotary Swaging Using Finite Element Method 

 Procedia Engineering  81 ( 2014 )  2342 – 2347 
1877-7058 © 2014 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.2014.10.331 
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Available online at www.sciencedirect.com
11th International Conference on Technology of Plasticity, ICTP 2014, 19-24 October 2014, 
Nagoya Congress Center, Nagoya, Japan 
2D-simulation of material flow during infeed rotary swaging using 
finite element method 
Eric Moumia,*, Svetlana Ishkinaa, Bernd Kuhfussa, Thomas Hochrainera, Adrian Strussa, 
Martin Hunkelb 
a bime Bremen Institut of mechanical engineering, University of Bremen, Bremen, Badgasteiner Strasse 1, 28359 Germany 
b IWT Stiftung Institut für Werkstofftechnik, Bremen, Badgasteiner Strasse 3, 28359 Germany  
Abstract 
FE simulation was applied to study the material flow during infeed rotary swaging. The neutral plane according to the process 
parameters was investigated and compared with experimental results. A single forming stroke was analyzed precisely by using 
small time points of 10-4s. For analysis the essential steps between the first contact of wire and forging die and the last contact 
before the die opens again are represented. In that range the feed velocity is eliminated and the neutral plane can be observed as 
spatial velocity at nodes in the axial direction equal 0 mm/s. During a single stroke the location, the geometry and the 
orientation of the neutral plane is changing. 
 
© 2014 The Authors. Published by Elsevier Ltd. 
Selection and peer-review under responsibility of Nagoya University and Toyohashi University of Technology. 
Keywords: Rotary swaging; Invremental forming; Material flow; Neutral plane; FEM 
1. Introduction 
Incremental forming processes have been studied in recent years in most cases using finite element method 
(FEM) (Brenneis et al., 2012; Ameli et al., 2007; Rong et al., 2006) due to its high precision. Specifically, finite 
element method is used in rotary swaging in order to study the strain and stress distributions in the workpiece 
* Corresponding author. Tel.: +49 421-21864825; fax: +49 421-2189864825. 
E-mail address: moumi@bime.de 
 
 
© 2014 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
2343 Eric Moumi et al. /  Procedia Engineering  81 ( 2014 )  2342 – 2347 
(Piela, 1997; Grossmann et al., 1996; Domblesky et al., 1995), how the axial feed velocity effects the strain field 
(Rong et al, 2006), the influence of friction and die angle on residual stresses (Ameli et al., 2007) and the 
temperature distribution during the process (Rong et al., 2007; Grossmann et al., 1996; Domblesky et al., 1995). 
In all above mentioned investigations the focus lies on the macro world in contrast to micro range, where the 
products are in at least two dimensions smaller than 1.0 mm, according to the CIRP-definition (Geiger et al., 2001). 
A project within the collaborative research center SFB 747 “Micro Cold Forming” investigates the manufacturing 
of metallic micro parts by rotary swaging. The main goal here is a better understanding of the process with focus on 
material behavior, accuracy and process performance using experimental analysis and simulation.  
Rotary swaging is an incremental cold forming process especially for rods and tubes. According to German 
standard DIN 8583 the rotary swaging belongs to the open die forging processes. The deformation of the work 
piece (1) takes place in the swaging head in small steps by a radial oscillating movement of the tools (2). Two main 
process variations can be distinguished (Fig. 1): the infeed and the plunge rotary swaging. They differ essentially 
by the direction of the feed motion. For the infeed rotary swaging process the workpiece is supplied axially in the 
swaging device and the reduction of the workpiece in the forming zone of the forming tools takes place over the 
whole feed length. In the plunge rotary swaging the workpiece is positioned and hold in the swaging head. An 
oscillating movement of the tools is superposed with a radial feed movement due to the axial movement of the 
wedges (3), so that a local reduction of the workpiece occurs according to the tool geometry (Kuhfuss et al., 2012). 
  
Fig. 1. Process variations of rotary swaging; (1) workpiece, (2) tool and  (3) wedge. 
In the first part of this contribution modelling of infeed swaging with FEM is presented. In the second part the 
set up for experiments, the conducted experiments and the different characterisation methods are described. Results 
and comparison are given in the third part. 
 
Nomenclature 
Į die angle 
d0 initial wire diameter 
d1 final diameter 
H stroke (radial tool displacement) 
R0 initial radius 
R1 final radius 
vf feed velocity 
μ friction coefficient 
2. Modeling 
The model for the simulation of infeed rotary swaging consists of two parts: the workpiece and the dies (Fig. 2). 
Due to the complexity of the process kinematics several authors recommend the use of three-dimensional 
2344   Eric Moumi et al. /  Procedia Engineering  81 ( 2014 )  2342 – 2347 
simulation (Ameli et al., 2007; Piela, 1997). However 3-dimensional simulations are excessively time consuming 
and material flows in radial and axial direction are predominant and may have a stronger influence on the neutral 
plane. Therefore it is assumed that a two-dimensional simulation is sufficient to confirm firstly the existence of the 
neutral plane and secondly to analyze the influence of processing parameters on the material flow in general and on 
the neutral plane in particular. 
 
Fig. 2. Axisymmetric 2D-model of infeed rotary swaging (a), Stress-strain curve of the workpiece material (b). 
The process is handled as an axis-symmetric problem under isothermal conditions. The model is build and 
simulated using ABAQUS Vers.6.12. Rotary swaging is a dynamic process so the presented numerical method is 
based on Abaqus/Explicit. The initial length of the sample is 100 mm. A quasi-steady-state is reached in process, 
for example for forming loads, when the calibrating zone is completely filled with material. Assuming volume 
constancy and using Eq. (1) the minimal sample length to be formed is calculated to 5 mm. Therefore the length to 
be formed is set to 10 mm. 
ܸ =  ߨ ܴଶ ܮ.   (1) 
In order to enhance the accuracy of simulations it is generally important to provide the interesting regions of the 
model with fine mesh. Thus smaller mesh than in the rest of the sample is generated for the 10 mm with 5168 
(323x16) elements. Following additional assumptions are made:  
- The tool is considered as a rigid body and thus not deformable.  
- An isotropic hardening is assumed for the workpiece material and it is characterized with the stress-strain 
curves in Fig. 2a. 
- The friction between tool and workpiece is constant at all tool zones. 
Other parameters for the simulation are summarized in Table 1. 
Table 1. Process parameters for FE-simulation of infeed rotary swaging. 
die angle 10° 
tool displacement (stroke) 0.1 mm 
stroke frequency 100 Hz 
length of the calibrating area 20 mm 
initial diameter  1.0 mm 
final diameter  0.5 mm 
friction coefficient 0.1; 0.5; 0.8 
material AISI304; EN AW-1050A 
3. Experiments 
Forming experiments are conducted with a set up consisting of the swaging head, in which the forming takes 
place, and a linear direct drive for feeding the workpiece. During the forming the workpiece is fed with a constant 
0
400
800
1200
0 0,2 0,4 0,6 0,8 1 1,2
St
re
ss
 (M
pa
)
Strain
AISI304 
AW-1050A 
        .      0.4      0.6       .        .0     .
(a)
(b)
2345 Eric Moumi et al. /  Procedia Engineering  81 ( 2014 )  2342 – 2347 
feed velocity and the diameter is reduced from 1.0 mm to 0.5 mm. The die angle is 10° and the calibrating zone 
measures 20 mm. Materials for experiments are wires from AISI304 and EN AW-1050A (Al99.5) with 1 mm 
initial diameter in annealed state.  
In order to vary the tribological conditions two states were investigated: in the 1st state lubricant is used on the 
workpiece and in the tools; in the 2nd state forming takes place without lubricant (dry condition). For these two 
tribological states the feed velocity is increased stepwise until a failure occurs in the process. Current process 
failures are breakage, wings formation, high surface roughness and strong deformation of the workpiece between 
feeding device and forming zone. 
The geometry of the samples after forming is investigated and the microstructure in longitudinal cross section is 
determined by optical microscopy. The Martens micro hardness distribution along the diameter is measured on a 
cross section using a Fischerscope H100C. 
4. Results and Discussion 
4.1. Analysis of the neutral plane 
In order to investigate the behaviour of the neutral plane with FE a single stroke is broken down in small steps 
by using constant time points of 10-4 s. The neutral plane is then investigated by finding the spatial velocity at 
nodes in the axial direction equal to 0 mm/s (Fig. 3). The case in Fig. 3a Pos. 1 represents the first contact between 
workpiece and tool during tools closing and Pos. 7 is the last contact where a neutral plane appears before the tools 
open and the next cycle begins. In Fig. 3b the scheme of two subsequent strokes is represented. The dots give an 
approximate indication of position 1 and 7. For the present example the other positions are located between the two 
points. All positions corresponding to the time points are located on the closing slope of the stroke. 
 
Fig. 3. Location of the neutral plane by FE-simulation for EN AW-1050A, μ = 0.5 and v f = 3 mm/s feed velocity. 
Fig. 3a shows also the location and the geometry of the first (Pos.1) and the following neutral planes. It can be 
seen that position, geometry and orientation change during a single stroke. These effects are observed for both 
materials aluminum and steel and for all investigated friction coefficients. In Fig. 4 the influence of the friction 
coefficient and the material are depicted. 
 
Fig. 4. Influence of the friction coefficient and the material on the location of the neutral plane for v f = 1 mm/s. 
Pos 1
2
3 4
5
6 7
0% 100%
Pos. 7
Pos. 1
(b)(a)
10 11
Pos 9
0% 100%
5 73 4
Pos 1 2
6
0% 100%
Pos 8
9 13
0% 100%
AW-1050A;  μ = 0.1 AISI304;  μ = 0.1AW-1050A;  μ = 0.8 
(a) (c)(b)
2346   Eric Moumi et al. /  Procedia Engineering  81 ( 2014 )  2342 – 2347 
With lower friction coefficients the first neutral plane is located closer to the calibrating zone. Additionally 
more movements of the neutral plane are detected with higher friction coefficients. For the same parameters the 
first neutral plane is in general closer to the initial diameter in steel than in aluminum (Fig. 4(a) and (c)). It was 
found experimentally that steel can be formed at a higher feed velocity than aluminum but when forming without 
lubricant the feed velocity for aluminum can be increased even though not to the level of steel (Fig. 5(c)). A 
decrease of the maximum feed velocity for dry forming is noticed for steel. The behavior of aluminum can be 
explained by the location of the neutral plane but additional phenomena have to be considered in the case of steel. 
In Fig. 5 (c) the maximum axial feed velocity that is achievable during forming with and without lubricant are 
given for aluminum and steel. When processing with higher velocities the previously mentioned failures occur. 
Axial feed velocity is also a parameter that strongly influences the neutral plane (Fig. 5(a) and (b)). 
 
Fig. 5. Influence of feed velocity on the neutral plane (a, b) and maximum feed velocities (experimental) (c). 
4.2. Analysis of plastic deformation 
The plastic deformation is analyzed in FE using equivalent strains. The strain equivalent along the diameter of 
the product is plotted in comparison with the measured Martens hardness (Fig. 6). Due to the strong deformation of 
the grains in the material after forming their size cannot be determined, therefore micro hardness measurements 
were made to enable a comparison as can be seen in Fig. 6(a) and (b). 
 
Fig. 6. Hardness (experimental) and strain distribution (FE) after forming of steel and microstructure in longitudinal cross section (a) before and 
(b) after forming.  
Pos 1
2
3 4
5
6 7
0% 100%
Pos 1
2
3 4
5
6 7
0% 100%
AW-1050A; μ = 0.5; v = 3 mm/s AW-1050A; μ = 0.5; v = 5 mm/s 
(a) (b)
(c)
(a)
(b)
2347 Eric Moumi et al. /  Procedia Engineering  81 ( 2014 )  2342 – 2347 
In Fig. 6 an increase of the equivalent strain from the middle to the surface of the product is given. In the areas 
with higher equivalent strains stronger work hardening should be expected. This is in some range the case when 
the hardening is characterized by the hardness. The hardness in a sample formed at vf = 1 mm/s and using lubricant 
correlates with the strain but decreases again before reaching the surface. The influence of the temperature and 
other hardening/softening mechanisms are neglected in the simulation. This might explained the partial 
discrepancy between the behavior of the strain and the hardness. 
Conclusions and outlooks 
The material flow during infeed rotary swaging of wire from d0 = 1.0 mm to d1 = 0.5 mm is studied. It is 
assumed that material flow takes place principally in axial and radial direction therefore a 2D model is developed 
for the FE simulation. Through an accurate examination of the closing movement of the forming tool and using 
adequate spatial velocity at nodes in the axial direction the neutral plane is studied. The behaviour of the neutral 
plane according to the friction coefficient and the material is investigated and compared with experimentally 
obtained results. Following conclusions are drawn: 
(1) The neutral plane can be detected by FE simulation very well. 
(2) The location and geometry of the neutral plane varies with the friction coefficient and the material. 
Moreover the position also changes within a single stroke. Hence it is time varying. 
(3) For the same setting of parameters the neutral plane in aluminum is generally closer to the final diameter 
than in steel and this is an explanation for the higher feed velocities that can be reached when forming steel. 
(4) The strain distribution is partially in agreement with the hardness distribution. 
With the presented model a close insight in the infeed rotary swaging is reached. Optimizations have to be made 
for the material model for example to take the strain induced martensite transformation into account that occurs 
during the forming of AISI304. Additionally the influence of the behavior of the neutral plane on the 
microstructure has to be investigated. 
Acknowledgements 
The authors gratefully acknowledge the financial support by Deutsche Forschungsgemeinschaft (DFG, German 
Research Foundation) for subprojects A4 "material displacement" and B2 “distribution-based simulation” within 
the Collaborative Research center SFB 747. 
References 
Ameli, A., Movahhedy, M., 2007. A parametric study on residual stresses and forging load in cold radial forging process. Int. J. Adv. Manuf. 
Tech., 33, 7-17. 
Brenneis, M., Groche, P., 2012. Smart components through rotary swaging. Key Engineering Materials Vols. 504-506 (2012), 723-728. 
Domblesky, J.P., Shivpuri, R., 1995. Development and validation of a finite-element model for multiple-pass radial forging. J. Mater. Process. 
Tech., 55, 432-441. 
Geiger, M. ,Kleiner, M., Eckstein, R., Tiesler, N., Engel, U., 2001. Microforming. Ann. CIRP, 50 (2), 445–462. 
Grossman, F., Piela, A., 1996. Metal flow in the deformation gap at primary swaging. J. Mater. Process. Tech., 56, 404-411. 
Kuhfuss, B., Moumi, E., Piwek, V., 2012. Effects of dry machining on process limits in micro rotary swaging. 7th ICOMM Northwestern 
University, Evaston, IL (USA), Nº23. 
Moon, H., Lee, M., Joun, M., 2007. An approximate efficient finite element approach to simulating a rotary forming process and its application 
to a wheel-bearing assembly. Finite Elem. Anal. Des., 44, 17-23. 
Perez, C.J.L., 2004. Upper bound analysis and FEM simulation of equal fillet radii angular pressing. Model. Simul. Mater. Sc., 12, 205-214. 
Piela, A., 1997. Analysis of the metal flow in swaging - Numerical modelling and experimental verification. Int. J. Mech. Sci., 39, 221-231. 
Rong, L., Nie, Z., Zuo, T., 2006. FEA modeling of effect of axial feeding velocity on strain field of rotary swaging process of pure magnesium.  
T. Nonferr. Metal. Soc, 16, 1015-1020. 
Rong, L., Nie, Z., Zuo, T., 2007. 3D finite element modeling of cogging-down rotary swaging of pure magnesium square billet - Revealing the 
effect of high-frequency pulse stroking. Mat. Sci. Eng. A-Struct, 464, 28-37. 


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2D-simulation of Material Flow During Infeed Rotary Swaging Using Finite Element Method

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