THE ANNALS OF DUNĂREA DE JOS UNIVERSITY OF GALAȚI [609566]

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THE ANNALS OF „DUNĂREA DE JOS” UNIVERSITY OF GALAȚI
FASCICLE V I, TECHNOLOGIES IN MACHINE BUILDING, ISSN 1221 – 4566, 201 8

A REVIEW ON SHEET METAL RUBBER -PAD FORMING

Cezarina Afteni1, Georgiana Costin1,
Ionel Iabob2, Viorel Păunoiu1, Teodor Virgil1

1Department of Manufacturing Engineering, “Dunărea de Jos” University of Galați, România
2Department of Mechanical Engineering, “Dunărea de Jos” University of Galați, România
[anonimizat]

ABSTRACT
In this study is present a systematic analysi s of already published works on the
field on sheet metal rubber -pad forming. This analysis consist s in a co mparative
aproach about different method used in metal forming processes. Durring last years
different te chnologies were developed and studied in researches. These studies were
analised and new aproaches and reserch directions were identified. Using different
materials for punches and dies the metal forming processes become more and more
competitive from cost point of view and also they are in trend with aerospace and
automotive industries which use the knowledge to improve their products and their
cost reduction/saving strategies. This overview of the actual status of the researches
developed in sheet metal r ubber -pad forming provide a basis for future work and
futures development projects.

KEYWORDS: rubber -pad, sheet metal forming, forming process, techniques .

1. INTRODUCTION

In the economical actual environment, automotive,
aerosp ace and defence industri es established their
objectives in order to improve the quality of their
products and the fiability, in the same time the cost
management strategies and projects are con sidered. In
order to achieve these targets all industries aims to
modernise their techn ologies by defining and
implementing different investment programs and also
by implementing research results.
Different materials are used in place of classic
material, for examples rubber -pad in place of metal
tools. Up grading the technologies it is use in order to
optimize the cycle time and production costs and also
to decrese their effect on the environment by minimise
their carbon emissions .
In these indust ries one of the most important
process is the metal sheet forming which have
influence on diffe rent aspects as process cycletime,
quality of the final products. This step is a decisive
step for all future production steps.
In recent years, numerous studies on the issue of
sheet metal rubber -pad forming have been developed.
This study presents a systematic analysis of the
current status of already published research on sheet
metal rubber -pad forming.

The forming process using rubber -pad is one of the
metal forming process used in automotive and
aerospace industries to manufacture small depth cups.
This process is used in prototype phase or to
manufacture small batches [1].
Rubber pad forming [2] highly improves the
formability of the blank because the contact surfaces
between the rigid die and the rubber pad is flexible.
The implementation of this process have the
advantage that using rubber -pad and high hydrostatic
pressure the forming process is more stable due to the
fact that this pressure it is applied in an uniform way
on the blank surface, this lead to small local thining
areas due to over -stress of the material and also to a
more favourable stress for the forming process [3].
The paper is organized as follows: section II
provides a literature review related to the rubber -pad
forming , there are presented the advantages and
disadvantages for this process . In section III are
presented the forming methods with rubber -pad
forming by specific processes. In sections IV is
developed a critical review of sheet metal ru bber-pad
forming , as reflected in published research up to date.
Finally, section V presents the study’s conclus ion and
future research directions.

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FASCICLE V I THE ANNALS OF “DUNĂREA DE JOS” UNIVERSITY OF GALAȚI
2. RUBBER -PAD FORMING PROCESS

Rubber -pad forming dates from the second half of
the nineteenth century when in 1872 Adolph
Delkescamp employed rubber pad for cutting and
shearing thin sheet s. Fred C. Cannon used rubber ov er
metal dies to eliminate scratching of the work piece
surface during forming in 1888 . In 1912, Leonard
Beauroth used a rubber bulging technique to form
metal barrels. Friedrich Hamptemeyer used rubber –
pads for formed the dental plates in 1922 [4].
Rubber -pad forming is a metal processing process
in which the sheet is pres sed between a die and a
rubber punch . The rubber and sheet metal are driven
under pressure into the die , forming the part.
To eliminate scratching of the sheet surface are
used the rubber -pads on metal die during forming
process . She have a general purpos e shape, like a
membrane, or can be machined in the shape of die or
punch.
The rubber -pad form ing is a deep drawing
technique, being ideally suited for the production of
small and medium -sized series. Because the d eep
drawing makes it possible to deform sh eet metal in
two directions, you get benefits in terms of function
integration, weight reduction, cleanability and such.
Besides the benefits obtained, the regular deep
drawing has also a disadvantage due to of is that
expensive tools consisting of an uppe r and lower mold
are needed.
In the forming process with rubber, the equipment
is composed from two dies. An elastic upper die,
usually made of rubber, wich is connected to a
hydraulic press and a rigid lower die, often called a
form block, provides the m old for the sheet metal to
be formed [5].
BlankF
DiePunchRubber pad

Figure 1. Schematic representation of rubber -pad
forming process [5]

Because the upper die can be used with separate lower
dies, the process is relatively cheap and flexible. Dies
do not wear as fast as in conventional processes such
as deep drawing. Howeve r, rubber die exert less
pressure in the same circumstances as rigid dies. The advantages of rubber pad forming process is:
i) the soft rubber not damage or scratch the sheet
metal ; ii) accurate and time consuming of die is not
necessary; iii) any of shape can be formed in one
process cycle; iv) uniform pressure to apply over the
surface of blank; v) tooling cost will be low; vi) that
require only one punch to manufacture of sheet metal.
However, the rubber pad formed process has
certain disadvantages such as: i) limit the number of
parts ; ii) require long time; iii) large force required; iv)
soft tool is deformed during the process; v) the soft
tool is wear also; vi) complex shape part formed
limited [6].

3. CLASIFICATION OF RUBBER -PAD
FORMING PROCESS

There are many processes such as Guerin process ,
Maslennikov ’s process, Marform process, Demarest
process, Verson -Whee lon process, Verson Hydroform
process and SAAB process which using rubber pad
forming. These various processes are being discussed
in brief in following section.
The Guerin process was named after Henry
Guerin, a head of the department of Dougl as Aircraft
California, the USA. The late 1930 s he discovered the
technique of using rubber as the half die instead of
metallic part . This process is commonly used to form
short runs of light metal parts . Using this process,
complicated components such as aircraft panels and
automobile panels are pro duced [7].
The Guer in process is considered to be one of the
oldest and most simplest rubber pad forming process.
Using this process can be shallow drawn aluminum
alloys, austenitic stainless steels and titanium alloys.
In this process, t he pressure produced is ordinarily
between 6.9 and 48 Mpa and the minimum pad
thickness is 30 percent bigger than the height of the
blank , and generally varies from 150 to 300 mm . The
rubber pad is made of soft elastomer (50 -75 Shore
hardness) [8]. In figure 2 is shown t he schematic
diagram of this process.

PunchBlankRubber pads

Figure 2. Guerin process [8]

In figure 3 is shown a nother ap plication of the
Guerin process. Here is used of rubber pad as low -cost
die for press brake forming. The pads are insulated at
the bottom of the die i n order to form sheet me tals of
various thicknesses to V -section and U -section.

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FASCICLE V I THE ANNALS OF “DUNĂREA DE JOS” UNIVERSITY OF GALAȚI
The defections of the pad due to the punch
penetration exerts forming pressure around the punch.
This rubber pad will assume the s hape of the punch at
the bottom of the stroke and the pad resumes its initial
shape when the pressure is released.
Punch
Blank Rubber

Figure 3. U -bending of sheet metals using rubber pad
forming process [8]

The Maslennikov’s process is a deep drawing
technique that uses annular rubber pad to draw very
deep cups [9].
In figure 4 is presented t he schematic of th is
process .
BlankRubber ringRubber container
DiePunch

Figur e 4. Schematic of Maslennikov’s process [9]

In paper [10], has been carried out an analytical
analysis and FE simulations of Maslennikov’s process
to investigate the process variables and deformatio n
mechanism. The authors are used a new friction model
for rubber/metal contact which allows the
determination of coefficient of friction as a function of
local contact conditions such as rou ghness, rubber
characteristics, and contact pressure . The results
obtained from analytical analysis are comparison with
the results obtained by FE simulations are carried out.
The Marform process (figure 5) was developed by
Glen L. Martin Company in the USA , is a refinement
of the Guerin process which features the addi tion of a
blankholder and a die cushion to make the process
suitable for deeper draws and to alleviate the
wrinkling problems common to the Guerin process
[11]. In this process, t he rubber pressure used ra nges
from 34 to 69 Mpa, and t he rubber pad used is similar
to the one used in the Guerin process [11].
Seal ring
PunchRubber padRubber container
Blank
Blank-holder

Figure 5. The Marform process [11] In this process, tooling includes a steel blankholder
supported by a hydraulic actuator equipped with a
valve controlling pressu re, compared to the Guerin
process.
In paper [12], has been carried out an analytical
analysis by finite element (FE) simulations to
investigate the effect of the key pr ocess parameters on
deep drawing of sheet met als using the Ma rform
technique. The authors are presented a new friction
model for rubber/metal contact which allows the
determination of coefficient of friction as a function of
local contact conditions such a s roughness, rubber
characteristics and contact pressure.
The Demarest process was developed particularly
to form axi -symatric shapes from cylindrical or
conical semi -finshed products . Cylindrical and conical
parts can also be formed by a modified rubber b ulging
punch [4].

(a)

(b)

(d)

(c)

Figur e 6. The Dem arest process ,
(a) blank; (b) rubber punch; (c) punch and die
assambly ; (d) completed workpiece [4]

The Verson -Wheelon process was developed
initially by the Douglas Aircraft Company in the US,
uses a comparatively lighter press with an inflatable
rubber bag . Special presses for this process are
developed and marketed by V erson Allsreel Press
Company in the US A.
The blanks are placed over simple male dies,
similar to those used in the Guerin process. This
process is designed to formed small parts but
sometimes also to formed large parts, using a rubber –
pad as a die , which is used in the aircraft industry . In
this process is used a 60-70 mm thick rubber pad.

PunchFlexible fluid cell
High pressure fluidCylindrical pressHydraulic inlet
BlackRubber pad

Figure 7. The Verson -Wheelon process ,
(a) released position, (b) forming position [11] (a) (b)

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FASCICLE V I THE ANNALS OF “DUNĂREA DE JOS” UNIVERSITY OF GALAȚI
The Verson Hydroform process it is different to the
other rubb er pad forming process es because she has is
the fact that the die cavity is not completely filled with
rubber but with hydraulic fluid. This cavity is termed
the pressure dome . In this process it is used a 60 -70
mm thick rubber diaphragm, t his is put betwe en the
fluid and the sheet metal . For this process is used a
special press, called a Hydroform press . In figure 8
shows the schematic details of this process.
BlankBlank-holderPunch
Rubber diaphragm
Hydraulic fluid
Pressure control gauge

Figur e 8. The Verson Hydroform process [11]

In paper [13], is presented a numerical simulation
of the rubber pad forming using a 2D axisymmetric
approach in LS -DYNA software package . The Verson
hydroforming process it was adopted for determinated
all th e simulation parameters needed for an accurate
finite element analysis of this process . For simulation
the author used a Inconel 625 and DX56D galvanized
sheet metal blanks with the support of four rubber
pads.
The SAAB process was developed in 1950 by th e
Swedish aerospace company . This process is
illustrated in figure 9, which uses a flexible diaphragm
punch which assumes the shape of the die .
Punch
Blank
DieVacuum valveRubber diaphragmHydraulic fluid

Figure 9. The SAAB process [11]

4. PARAMETERS ANALYSIS OF THE
RUBBER -PAD FORMING PROCESS

During the last years, a large number of
researchers analyzed the problems related to formed
process using the rubber pad.
In paper [14], the authors have analyze rubber -pad
forming process in a stamping of aluminum sheet
metal with soft punch . They have using the finite
element analysis for investigation the effect of some
key process parameters like hardness of rubber, type of rubber on the variation of the thickness, the
springback and damage of aluminum sheet metal.
These has been adopted during flexible forming
operation an elasto -plastic c onstitutive model with J2
yield criterion and mixed non-linear
isotropic/kinematic hardening coupled with Lemaitre's
ductile damage for the aluminum blank . A Mooney –
Rivlin theory is use d in the finite element simulation,
for to model the h yper-elastic behavior of rubber .
In the simulation of the rubber -pad forming
process is used an axisymmetric finite element model
in order to reduce th e CPU time, as shown in Figure
10. The rubber is c ontained in a retainer which will be
moved against a die with 5 mm depth by the punch in
order to form the blank of diameter 40 mm and
thickness of 1 mm.
Blank
DieRubberPunch

Figure 10. Schematic of rubber -pad forming [14]

Chen et al. were studied in [15] the wrinkling by
shrink flanging in rubber formi ng process with
orthogonal experimental design and simulation . This
paper is motivated by the need to advance the sheet
metal forming part/die design in aluminium aircraft
sheet applications. The autors has analyzed four effect
factors: die radius, the fl ange length, die fillet radius
and forming pressure and used as three alloy
materials: 2024 -O, 7075 -O, 2024 -T3.
A diagram of a shrink flange shows in figure 11.

Figure 11. Scheme of shrink flanging [15]
In figure 12 is shows the blank shape for shrink
flanging.
O

Figure 12. Blank shape [15]

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FASCICLE V I THE ANNALS OF “DUNĂREA DE JOS” UNIVERSITY OF GALAȚI
In [16] was carried out a finite element simulation
of the rubber -diaphragm forming process for an
aluminum alloy sheet aircraft component. Aluminum
alloy (AA) 2024 -O is widely used in various industrial
applications and especially in the manufacturing of
aircraft components. In your paper was studied AA
2024 -O material with 1.27 -mm (0.05 -in.) thickness.
The authors were studied the effects of the process and
material parameters such as friction and the ductile
fracture modeling . T hey were constructed an
elastoplastic constitutive models of an aluminum
alloy sheet with an anisotropic yield function and
ductile fracture criteria and a hyperelasticity model of
rubber materials that exhibit nonlinear stress‒strain
behavior under large deformation .
The process of rubber -diaphragm forming is
describes in figure 1 3.

Figure 1 3. Process of rubber -diaphragm forming [16]

In figure 1 4 shows the die for rubber -pad forming,
the shape of the blank sheet, and the final product.

Figure 1 4. (a) Die for rubber -diaphra gm forming;
(b) the shape of the blank sheet; (c) final aircraft
component [16]

Sun et al. have investigate in [17] the wrinkling of
the Ti -15-3 alloy sheet during the Fukui’s conical cup
forming test . Utilizing the foundational problems with
commonness in the simul ation of conical cup,
wrinkling behavior in the convex flange manufactured
by rubber forming was predicted. The authors was
employed the rubber forming, with a rubber pad
contained a rigid chamber, to stamp the Ti -15-3 alloy
sheet component. The component has a convex flange,
and the geometric of the flange is with convex radius
of 140 mm, bend angle of 90° an d circumferential
angle of 94°. The schematic diagram of the
experimental set -up is shown in figure 15.

PunchBlankRubber
Chamber

Figure 1 5. Schematic representation of exp erimental
set-up [17] In [18] the authors have investigated and explored
the rubber forming process of an aluminum alloy
aeronautic component with numerical simulation the
significant parameters associated with this p rocess ,
have been taken into account s everal effects,
depending on: stamping strategy, component
geometry and rubber pad characterization.
Thanks to extensive use of a finite element (FE)
packagehas been carried out the process analysis
useful for an app ropriate set -up of the process model.
The rubber pad forming process requires: a rubber
filled chamber, a blank and a form block, a punch.
This process finds useful applications as a sheet
shaping method as well as composite parts in the
aerospace industr y.
In fi gure 16 is schemati cally represented this
process.
PunchBlankRubber pad

Figure 1 6. Rubber Pad Forming (RPF) process
schematization: flexible rubber die (rubber pad) and
rigid tool (punch) [18]

Tandogan et Eyercioglu in [19] applied the finite
element method to investigat e the fracture, thinning
and effective stress distribution conventional forming
type is also analyzed to compare the formability of
sheet. They have used two types of shape for straight
rib and a part of components of aircraft wing, t hey
selected the alumi num sheet Al 1100 with 0.5 mm
thickness and polyurethane rubber with 60A and 80A
shore hardness as workpiece materials and flexible
material , respectively . In their paper, th ey used a
female dies are rigid and male dies for produced
flexible material and t he rubber pad forming was
carried out by means of Guerrin process.
In figure 1 7 is presented schematically the straight
rib die set was used in ex periments. To prevent the
flexible material flow to outside during pressing the
authors utilized the silicone rubber and styrene
butadiene rubber a die holder.

Container
Rubber
3D VIEW of partRib Geometry
PunchBlank

Figure 1 7. Schematic Representation of Straight Tib
Die Set [19]

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FASCICLE V I THE ANNALS OF “DUNĂREA DE JOS” UNIVERSITY OF GALAȚI
5. CONCLUSIONS

After browsing a large volume of papers published
in field on sheet metal rubber -pad forming (not all
included here, for reasons of space) one can draw the
following conclusions:
 The proposed approaches are extremely diverse
and in the same time each has particular
characteristics due to the kind of studied p rocess
and the scope of the used rubber p ad forming .

 Forming process is one of the important methods
that used in manufacturing field for typical and
complicated geometries.

 Rubber based forming process falls into the
flexible forming methods category.

 Rubber forming process is widely used in
producing many parts for automotive and
aerospace applications.

 Rubber pad forming is suitable process financially
and time consuming, because, it uses the half of
die as a rigid.

 Although the process is quite old but only during
last two decades, it ha s generated lot of enthusiasm
among intelligentsia and academic groups.

 The rubber pad forming process has been shown to
be capable of producing, from thin aluminum alloy
blank, shallow formed parts with a reduced metal
thinning.

 Guerin process has rema ined the most understood
technique.

 Using this kind of forming process can be shallow
drawn aluminum alloys, austenitic stainless steels
and titanium alloys.

 The process can be analysed using finite element
(FE) package useful for an appropriate set -up o f
the process model.

ACKNOWLEDGEMENT

This work was supported by the Romanian
Ministry of Research and Innovation, CCCDI –
UEFISCDI, project number PN -III-P1-1.2-PCCDI –
2017 -0446 / Intelligent manufacturing technologies
for advanced production of parts fro m automobiles
and aeronautics industries (TFI PMAIAA) – 82
PCCDI/2018, within PNCDI III.

REFERENCES

[1] M. Benisa, B. Babic, A. Grbovic, and Z. Stefanovic,
“Computer -aided modeling of the rubber -pad forming
process,” vol. 46, no. 5, pp. 503 –510, 2012.

[2] A. A. Abbas, M. A. Hussein, and M. M. Mohammad,
“Design Parameters Estimation and Design Sensitivity
Analysis in Manufacturing Process of Rubber Pad by Using
Finite Element Technique,” Int. J. Mech. Mecha tronics Eng. ,
vol. 18, no. 03, pp. 75 –85, 2018.

[3] B. N. S. Kut, “Numerical and experimental analysis of the
process of aviation drawpiece forming using rigid and rubber
punch with various proporties,” Arch. Metall. Mater. , vol.
60, no. 3, pp. 1923 –1928, 2015.

[4] M. M. Benisa, “Integrated process planning, die -design and
simulation in sheet metal rubber forming,” 2013.

[5] M. Benisa, “Numerical Simulation as a Tool for Optimizing
Tool Geometry for Rubber Pad Forming Process,” pp. 67 –
73, 2014.

[6] Z. M . R. Maziar Ramezani, Rubber -pad forming processes:
Technology and applications . Woodhead Publishing Ltd,
2012.

[7] S. Thiruvarudchelvan, “Elastomers in metal forming : A
review,” J. Mater. Process. Technol. , vol. 39, pp. 55 –82,
1993.

[8] A. Kumar, S. Kumar , D. R. Yadav, and I. I. T. Bhu,
“Review of Rubber Based Sheet Hydro -Forming Processes,”
Internatuinal All Indi a Manuf. Technol. Des. Res. Conf. , no.
Aimtdr, pp. 1 –5, 2014.

[9] M. Yamashita, T. Hattori, and N. Nishimura, “Numerical
simulation of she et metal drawing by Maslennikov’ s
technique,” J. Mater. Process. Technol. , vol. 187 –188, pp.
192–196, 2007.

[10] M. Ramezani and Z. M. Ripin, “A study on high r atio cup
drawing by Maslennikov’ s process,” pp. 503 –520, 2012.

[11] E. S. P. B. V, V. C. Venkatesh, and T. N. Goh, “A note on
mathematical models of cup drawing by the Guerin and
Marform processes,” J. Mech. Wor k. Technol. , vol. 13, pp.
273–278, 1986.

[12] M. Ramezani and Z. M. Ripin, “Analysis of deep drawing
of sheet metal using the Marform process,” no. October,
2018.

[13] H. S. Halkaci, “2D Finite Element Analysis of Rubber Pad
Forming Process 2D Finite Ele ment Analysis of Rubber Pad
Forming Process,” 2 ND Int. Conf. Sci. Ecol. Technol. 2D ,
no. January 2017, 2016.

[14] L. Belhassen, S. Koubaa, M. Wali, and F. Dammak,
“Numerical prediction of springback and ductile damage in
rubber -pad forming process of alu minum sheet metal,” Int. J.
Mech. Sci. , vol. 117, pp. 218 –226, 2016.

[15] L. Chen, H. Chen, Q. Wang, and Z. Li, “Studies on
wrinkling and control method in rubber forming using
aluminium sheet shrink flanging process,” Mater. Des. , vol.
65, pp. 505 –510, 2 015.

[16] J. Lee, H. Park, S. J. Kim, Y. N. Kwon, and D. Kim,
“Numerical investigation into plastic deformation and failure
in aluminum alloy sheet rubber -diaphragm forming,” Int. J.
Mech. Sci. , vol. 142 –143, no. November 2017, pp. 112 –120,
2018.

[17] Y. N. Sun, M. Wan, and X. D. Wu, “Wrinkling prediction
in rubber forming of Ti -15-3 alloy,” Trans. Nonferrous Met.
Soc. China (English Ed. , vol. 23, no. 10, pp. 3002 –3010,
2013.

[18] A. Del Prete, G. Papadia, and B. Manisi, “Computer Aided
Modelling of Rubb er Pad Forming Process,” Key Eng.
Mater. , vol. 473, pp. 637 –644, 2011.

[19] O. E. Mahmut Tandogan, “Experimental and Numerical
Investigation of Rubber Pad Forming Process,” Int. Adv.
Res. Eng. Congr. , pp. 47 –55, 2017.