In this work are presented the physical model, experimental conditions and researches concerning the lobe process. For this purpose it was created a physical experimental system composed of the deformation die, the hydraulic press and the data acquisition system – resistive force transducer, the electronic tensometer Spider 8, and the computer. The experiments are focused on the establishing of the force variation during the deformation process

Dinel TANASE

Nicolae CANANAU

Ovidiu DIMA

The Annals of “Dunarea de Jos” University of Galati Fascicle IX Metallurgy and Materials Science

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FO N D ATĂ
19 76
 
 
THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI. 
FASCICLE IX. METALLURGY AND MATERIALS SCIENCE 
N0. 3 – 2011, ISSN 1453 – 083X 
 
 
 
 
EXPERIMENTAL RESEARCHES ON THE LOBE  
DEFORMATION PROCESS 
 
Ovidiu DIMA, Nicolae CANANAU,  
Dinel TANASE 
Dunărea de Jos University of Galati 
email: ncananau@ugal.ro 
 
ABSTRACT 
 
In this work are presented the physical model, experimental conditions and 
researches concerning the lobe process. For this purpose it was created a physical 
experimental system composed of the deformation die, the hydraulic press and the data 
acquisition system – resistive force transducer, the electronic tensometer Spider 8, and the 
computer. The experiments are focused on the establishing of the force variation during the 
deformation process.   
 
KEYWORDS: physical model, lobe, deformation, force 
 
1. Introduction 
 
The force at the lobe deformation process is, 
generally, calculated with the empirical mathematical 
expressions. One of these is shown above [1]:    
 SpkF ⋅⋅=            (1) 
In this relation k is coefficient whose values are 
rendered in Table 1, p – the pressure applied on the 
material and S is the plan surface of the lobe (Table 2). 
 
Table 1. Values of the coefficient k 
 
Advised values of coefficient k 
t ≤ 1 mm t = 1 – 1.5 mm 
0.7 – 0.8 1.0 – 1.6 
 
Table 2. Values of the pressure, p 
 
Pressure p [daN/mm2], for: 
Light steel Brass  Aluminum  
30 – 40 20 – 25 10 – 20 
 
For evaluation of the deformation force we can 
consider the maximum values of the deformation degree. 
Thus at the final moment of the deformation process 
we have the maximum strain in the superior section of the 
lobe (Fig.1). 
The effective dimensions of the stamped lobe are: D 
of 24 mm, d of 18 mm, h of 5 mm, R of 2 mm, r of 1 mm. 
In this section, the strain has the maximum value εmax 
that may be calculated in function of the local decreasing 
of the thickness [2]. 
Between the strain and real stress there is a 
correlation defined by the hardening equation. 
 
 
 
 
 
 
 
 
 
Fig. 1. Scheme of the stamped lobe 
 
For example: 
 nεσσσ ⋅+= 10                           (2) 
Where 0σ  is the yield stress in the actual 
deformation conditions, 1σ -constant, and n  is the 
hardening coefficient. 
Thus for maximum value of the strain it results the 
maximum value of the stress, respectively: 
 nmax10max εσσσ ⋅+=             (3) 
Using the equation (3) we can write: 
 ( )nSF max10max εσσ ⋅+⋅=             (4) 
In this equation, S is the effective value of the cross area 
in the superior section of the part, respectively: 
 
 eftlS ⋅=                             (5) 
where l ( )bdl ⋅= π  is the length of lobe bottom and tef 
is the effective value of the thickness in this section. 
In the practical calculus, we can use a relation: 
 rSkF σ⋅⋅= 01max                             (6) 
crack sensible section 
d 
h r 
D 
t R 
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FO N D ATĂ
19 76
 
 
THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI. 
FASCICLE IX. METALLURGY AND MATERIALS SCIENCE 
N0. 3 – 2011, ISSN 1453 – 083X 
 
 
In this relation, S0 is the initial area of the superior 
section (for thickness t0), rσ  is the ultimate tensile stress 
and k1 is a coefficient with values approach unit. 
 
2. Experimental conditions 
 
The aim of this work is to establish in the 
experimental way the variation of the force at the lobe 
stamping process. 
The laboratory conditions of the lobe stamping are 
the following: 
- The samples are cut from steel strip for sever 
drawing deep, with 0.6 mm thickness, 
- the lobe die showed in the figure 2, 
- force resistive transducer, 
- the data acquisition system, 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Fig. 2. The experimental lobe die: 
1-hydraulic press, 2-lobe die, 3-resistive force 
transducer. 
 
 
 
 
 
 
 
 
 
 
 
 
 
Fig. 3. General view of the experimental system. 
 
3. Experimental results 
 
The experimental program had the following 
objectives: 
- establishing the force variation; 
- visualizing the microstructure aspect; 
- estimation of crack sensible section. 
The dimensions of samples were: the length of 80 
mm and the width of 30 mm. In each sample were 
stamped two lobes. 
For example, in the Figure 4 is shows one stamped 
sample.  
 
 
 
 
 
 
 
 
 
 
For establishing the sensible crack section, we 
prepared a micrographic prove and we analyzed the 
variation of the thickness. 
In the section A, the thickness of the sample 
presents a visible decreasing (Fig. 5). 
 
A
 
 
Fig. 5. Aspect of stamped sample section 
(×50, Nital attack 5). 
 
The decreasing of the thickness in the critical 
section is of approximately 80%. Moreover, in this zone 
the structural hardening of the material has a great 
intensity. 
In Figure 6 is shows the variation of the 
microstructure in the sensible crack section. Because the 
level of the deformation degree is great, the 
microstructure is strongly influenced. 
 
 
 
3 
1 
2 
Fig.4. Example of stamped sample. 
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FO N D ATĂ
19 76
 
 
THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI. 
FASCICLE IX. METALLURGY AND MATERIALS SCIENCE 
N0. 3 – 2011, ISSN 1453 – 083X 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
The crystalline grains are much deformed. 
Consequently, local hardening intensity is great and the 
probability that cracks appear in this zone is very great. 
The variation of the force during of the lobe 
stamping process is shown in Figure 7. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Fig. 5. Variation of force during stamping process. 
 
The force rapidly increases up to the maximum 
value of 11190N, then it maintains at this value when the 
change of the movement sense.  
The stress, in the sensible crack section, may be 
calculated in the function of the maximum value of the 
force using the above relation: 
 
td
F
⋅⋅
=
π
σ max                              (7) 
In the present conditions we have the level of the 
tensile strain in the critical section  
 
=σ 329.97 N/mm2 
that is 97.05 % of the conventional tensile stress σr of the 
material. 
Considering the hardening coefficient by the plastic 
deformation, the real maximum stress, corresponding of 
the maximum deformation degree, is equal to 566.6 
N/mm2. 
Thus the effective maximum stress at the lobe 
stamping process is 58.23% from the real maximum 
tensile stress of the material. Consequently, in the 
practical data conditions cracks not will appear. 
The technological coefficient of the lobe stamping 
process, in the given case, is calculated as the ratio 
between the length of the unfolded form of the 
deformation zone and L and the diameter D of the same 
zone.  
 
D
LC =                                            (8) 
We have 
 
 drRL +⎥⎦
⎤
⎢⎣
⎡ ++= 2)(
2
2 π               (9) 
respectively, 
 
 
D
drR
D
C +⎥⎦
⎤
⎢⎣
⎡ ++= 2)(
2
2 π
             (10) 
 
In the data conditions we have C=1.309.  
The cumulated deformation degree may be 
calculated as the logarithmic form, respectively: 
 269.0ln ==
D
Lε  
It results a great value of the cumulated deformation 
degree. The local deformation degree can be with 20-25% 
greater than the cumulated deformation degree. 
This result confirms that the material has a good 
reserve for plastic deformation and the risk that cracks 
appear decrease. 
 
4. Conclusions 
 
The lobe stamping is a deformation process based on 
the local elongation of the material without its traction 
from the neighbor zone. Consequently, the elongation, at 
lobe stamping, takes place in the base of the thickness. 
Along of the lobe profile the dimension increases and the 
thickness decrease. In the point where the increasing of 
dimension, in the length direction, is greater, the 
decreasing intensity of the thickness is smaller. 
This fact must be known in order to forestall the 
crack appearance.  
In this context, it may be established the critical 
value of the deformation degree. The level of the 
deformation intensity, in the practical conditions, is 
defined by the deformation coefficient C, or the 
logarithmic strain. 
 
 
Force 
[N] 
2000 
4000 
6000 
8000 
10000 
12000 
0 
0 1 2 3 4 5 Time, [s] 
Fig. 6. Aspect of crystalline grains in 
critical section, (×250, Nital attack 5).
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FO N D ATĂ
19 76
 
 
THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI. 
FASCICLE IX. METALLURGY AND MATERIALS SCIENCE 
N0. 3 – 2011, ISSN 1453 – 083X 
 
 
The experiments systematized in this paper show the 
variation of the force during of the lobe deformation 
process, the variation of the thickness, specially, in the 
critical zone and the variation of the microstructure of the 
material. 
In the critical section of the deformed zone the 
crystalline grains are deformed very much.  
The experimental results and the calculated values of 
the maximum real stress and the maximum deformation 
degree show that it is unlikely that cracks should occur. 
References 
 
[1]. Teodorescu, M. a.o. – Elemente de proiectare a stantelor si 
matritelor, EDP, Bucuresti, 1977. 
[2]. Roamnovski, V.P. - Stantarea si matritarea la rece, Ed. Tehn., 
Bucuresti, 1970. 
[3]. Lazarescu, I., Stetiu G. – Proiectarea stantelor si matritelor, EDP, 
Bucuresti, 1973. 
[4]. Merchant, E.M. - Mechanics of the metal cutting process, Journal 
of applied physics, MC Shaw, 2004. 
[5]. Jaspers, S. - Material behavior in conditions similar to metal 
cutting: flow stress in the primary zone, Journal of Material Processing 
Technology, vol.122, Issues 2-3, March 2002, p.322-330. 
[6]. *** - ASM, Metals Handbook, vol.4, Forming, Ohio, SUA, 1969.
 
 
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Experimental Researches on the Lobe Deformation Process

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Experimental Researches on the Lobe Deformation Process

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