Process design in flashless forging of rib web-shaped plane-strain components by the finite element method
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ELSEVIER
Journal of Materials Processing Technology 47 (1995) 291 309
Journal of
Materials
Processing
Technology
Process design in flashless forging of rib/web-shaped
plane-strain components by the finite element method
B.S. K a n g * , J.H. Lee, B.M. K i m , J.C. C h o i
"Pusan National University, Research Institute ~2/ Mechanical Technology, Pusan 609-735, South Korea
(Received July 5, 1993)
Industrial Summary
In this work preforming operations in the forging of rib/web-shaped plane-strain components are designed by the rigid-plastic finite element method to obtain flashless products, the
height-to-width ratios of rib the geometry used for the analysis and design being 1.0, 2.0 and 3.0.
The two design criteria of flashless geometrical filling and an even distribution of effective strain
in the final products are investigated in controlling the preform configuration and establishing
a systematic procedure of process design. One preforming operation is designed for flashless
forging with a sound distribution of effective strains at ratios of 1.0 and 2.0. The case of a ratio of
3.0 also needs one preform to satisfy flashless geometrical filling, but has high effective strain,
a further preforming operation needing to be added to avoid the high value of effective strain:
thus the case of a ratio of 3.0 is designed as two preforming operations. The resulting preform
configurations in plane-strain forging are compared with those of axisymmetric forging of
rib/web components. It is noted that the flashless forging of plane-strain rib/web components
requires a unique preforming operation to make the metal flow slower at the central part.
1. Introduction
Closed-die forging is one of the most important metal forming processes in
industry, a billet of simple cross-section, round or square, being deformed plastically
in closed-die forging by applying compressive force through two or more dies to
obtain a more complex desired shape.
In the conventional closed-die forging process, the formation of flash restricts
the lateral flow of material and thus facilitates the filling of the die cavity, the
excess material of the flash being trimmed upon the completion of the forging
*Corresponding author.
0924-0136/95/$09.50 ~C~ 1995 Elsevier Science S.A. All rights reserved
SSDI 0 9 2 4 - 0 1 3 6 ( 9 5 ) 0 1 3 3 0 - 4
292
B.S. Kang et al. / Journal ~[" Materials Processing Technology 47 (1995) 291-309
process. There is normally about 50% of the material lost as scrap in the form of
flash and scale losses, and the trimming process requires additional machining
cost [1-3].
Process design in die forging involves many areas, such as the determination of
required processes, die design, preform design and the selection of the process
conditions. Recent development in the field of forgings has had the objectives of
reducing costs by minimizing scrap losses and expensive secondary operations such as
machining, reducing preforming steps and improving forging tolerances. Forging
difficulties in the closed-die situation may not be related to the occurrence of fracture
but rather to a poor grain-flow pattern and lack of die filling. Thus, one of the most
important aspects of the closed-die forging process is the design of preforms to achieve
adequate metal distribution without any defects [4,5].
Computer-aided approaches have been proposed for preform and die design,
research on this subject having been carried out in several countries [6-15]. CAD
systems have been developed for preform and die designs of rib/web type forgings
using empirically established design rules [6 9].
Recently, some useful results have been published in which the finite-element
method was applied to preform design in metal forming processes. Rebelo and
co-workers [10] have proposed a new approach, called the backward tracing scheme,
using the capabilities of the finite element method, and tested it for preform design in
shell nosing. The concept of the approach is to trace the loading path of a forming
process backwards from a given final configuration. It has been applied to preform
design in various metal forming processes, such as plane-strain rolling [11], ring
rolling [12], the forging of a disk [13], the forging of an airfoil section blade [14] and
axisymmetric H-shaped cross-sections [ 15].
In this study, the closed-die forging of H-shaped plane-strain components with
different rib height-to-width ratios is investigated and designed, the main objective of
the design being to obtain preforms that satisfy the design criterion of flashless
geometrical filling with sound distribution of effective strain in the final products. This
study also attempts to establish systematic procedures for accomplishing the objectives of the preform design.
2. Problem description and design procedure
The problem explored in the present work is the design of preforms for
H-shaped plane-strain closed-die forging without flash using the finite-element
method. An example of preform design for steel finish forgings of various H-shapes is
shown in Fig. 1 [1]. Conventional closed-die forging of this type is designed to
produce proper filling of the die with formation of flash. The main goal of the present
study, however, is to find preforms which do not form any flash when H-shaped
finisher dies are used. Flashless forging is a type of impression-die forging in which the
dies are designed not to include a flash area, the pattern of metal flow being very
complex, and depending on the design of the preforms. Thus, the most important
aspect of the flashless closed-die forging process is the design of preforms to achieve
B.S. Kang et al./Journal of Materials Processing Technology 47 (1995) 291 309
F//~//"/~
" V//,~///3
I
293
U pse t s tock
I
Pre form
None
Finish
h=b
h= 2b
h=5b
Fig. 1. Preformssuggested by Lange et al. [1] for the H-shaped closed-die forging.
adequate metal distribution without any defects. The preform design in this study has
wide applicability, since H-shapes are one of the most common cross-sectional shapes
of structural components. The dies shown in Fig. 2(a)~c) are called finisher dies I, I!
and III, respectively, according to their rib height-to-width ratios (H/B).
A finisher die is used for the forging of the final H-shaped forging products. The choice
of parting line is based on grain-flow and die manufacturing problems [2]. The computational results depend on forging parameters such as interface friction, forging speed and
material properties. The following computational conditions are Used: friction factor at
the die-workpiece interface, m = 0.1; frictional stress = mk, where k is the shear strength;
forging speed, 0.2; work-hardening material, 6-/Yo = (1 + g/0.319)°34, where 6" is the
effective stress, Yo is the initial yield strength and ~, is the effective strain.
As mentioned earlier, many design procedures for the preform design in axisymmettic closed-die forging have been used in practical cases for forged rib/web-type
components free from forging defects such as cracks, laps, shuts or folds. Systematic
procedures are also needed in a numerical approach for the preform design under the
plane-strain condition. In this study, the design procedure to find the preforms to
achieve flashless closed-die forging is developed for H-shaped plane-strain components, the procedure consisting of the following steps (see Fig. 3).
Step 1. Obtain information on material flow from the loading simulation of the
initial stock of rectangular cross-section with a finisher die.
Step 2. Design a test preform in the light of the information obtained in Step 1, and
carry out loading simulation.
Step 3. Design a modified preform using the information obtained in Step 2.
Step 4. Check the preform by loading simulation to see whether or not it satisfies
the final design conditions such as die filling and effective strain distribution. If the
294
B.S. Kang et al./Journal of Materials Processing Technology 47 (1995) 291 309
PARTING
LINE
,
5.0 ~
t!5
,
1
LOWER DIE
(a)
B=I,0
.~
~
3,5 "I
5.o +
f
,
\
(b)
B~0.75
(c)
Fig. 2. Dimensions and configurations
of finisher dies: (a) finisher die
IIH/B = 1.0); (b) finisher die II
(H/B = 2.0); and (c) finisher die Ill
(H/B = 3.0).
preform satisfies the final design conditions, the process stops here: otherwise a possible preform shape is o b t a i n e d , then going back to Step 3.
The r i g i d - p l a s t i c finite-element m e t h o d is used for the analysis and design in the
study. F o r s y m m e t r y reasons, only one q u a r t e r of the deformed region is considered in
the numerical simulation.
B.S. Kang et al./ Journal of Materials Processing Technology 47 (1995) 291 309
I
295
FINAL PRODUCT I
SIMULATION OF INITIAL STOCK
AND DESIGN TEST PREFORM
l SIMULATION OF TEST PREFORM I
I-¢~-PREFORM DESIGN
1LOADING SIMULATION
[ 1MPROVE
I
PREFORM
uo
l
Fig. 3. Schematic flow chart of the design procedure.
3. Rigid-plastic finite element formulation
The theory and the procedure of the rigid-plastic finite element method, which
latter has proven to be one of the most effective method in simulation of metal forming
process available at the present time [10, 16, 17], can be found in the literature
[18, 19]. The first-order variation of the functional for rigid plastic material model,
based on the extremum principles and the incompressibility penalty function, can be
written as
V
V
S~
where 8 = ~ / 2 ( a l j a ' i y / 2 , ~ = ~ / ~ (~.ij~ij)l..2, ~. = ~ii, and a~j, iij, ~, v and K are the
deviatoric stress tensor, the strain rate tensor, the surface traction tensor, the velocity
tensor and the penalty constant with a large positive value, respectively. Eq. (1) is
discretized according to the standard procedure of the finite-element method and
becomes a set of non-linear equations with the nodal velocities as the unknowns,
which can be solved iteratively using the Newton Raphson method. The stiffness
equations obtained finally are
KAu,+I = F,
(2)
where K = K(u,) is the stiffness matrix, related to the nodal velocities, u,, obtained
from the nth iteration and F is the equivalent nodal force vector. After solving Eq. (2)
with respect to Au, + 1, the assumed velocity field is updated by u, + :¢Au, + 1, where the
deceleration coefficient, ~, is taken as 0.0 -Guntil the ratio IiAull/[I ull becomes less then a small preset-value and the calculated
nodal point force error norm reaches a pre-assigned value.
296
B.S. Kang et al./ Journal o[Materials Processing Technology 47 (1995) 291 309
4. Simulation by the finite-element method
4.1. Preliminaries
For developing design procedures, it would be helpful to obtain some knowledge on
the metal flow involved in H-shaped plane-strain closed-die forging. Thus, to obtain
qualitative information on the pattern of metal flow, two simulations were performed
as preliminaries, one being the simulation of the finish forging of the rectangular
stock, and the other the simulation of the finish forging of the test preforms. The
volume of the rectangular stock and test preforms is taken to be the same as that of the
finisher die I cavity. First, a solid rectangular bar is chosen as an initial stock, and
tested preliminarily to investigate the material flow with the finisher die I (H/B = 1.0).
Dimensions and mesh system of the initial stock are given in Table 1, whilst Fig. 4
shows the initial mesh (left) and the deformed grid (right).
The grid distortion of the solid rectangular bar shows that flash already occurs
before the workpiece fills the die completely. Even if an initial stock of lesser width is
used, the deformation trend will be similar to the result in Fig. 4, since the stock is
upset with friction below the web of the die, hence one or more preforms are needed to
accomplish flashless forging. For complete filling in the finisher die without any flash,
it is necessary to make the side flow slower. Thus, the two test preforms shown in Fig.
5 were selected for forging with finisher die 1. Dimensions and mesh systems of the test
preforms (preforms TP-1 and II) are given in Table 1.
The two test preforms are designed to check the metal flow involved in the rib and
in the flash formation. These are not, however, practical in industry. From the
simulation using these test preforms a preforming operation it may be decided
whether the preforming operation should be a lateral indentation or a up-down
pressing operation. The initial mesh (left) and grid distortion (right) of test preforms
TP-I and II are shown in Fig. 6 and Fig. 7, respectively.
Table 1
Dimensions and mesh systems
Workpiece
type
Finisher
die
Dimensions
Mesh systems
Height
H
Initial
stock
TP-I
TP-II
I
2.04
I
I
I
II
Ill
1.0
1.75
1.22
1.05
0.96
(Alternative)
H/B = 3.0
Ill
2.49
H / B - 1.0
H/B = 2.0
H/B = 3.0
No. of elements No. of nodes
Width
H1
W
W1
3.00
3.07
3.00
2.80
5.00
6.00
6.50
2.50
4.20
204
234
180
192
220
242
246
208
221
253
276
299
315
352
B.S. Kang et al./Journal of Materials Processing Technology 47 (1995) 291 309
FINISHER
-8.0-7.0
297
DIE I
6.0-5.0-4.0-&0-2.0-10
0.0 1.0
20
30
40
50
6.0
70
8.0
WlDTH
Fig. 4. Grid distortion and flash formation of a solid rectangular bar for
PREFORM T P - I
H/B = 1.0.
PREFORM T P - I I
Fig. 5. Configurations of test preforms: (a) preform TP-I: (b) preform TP-11.
o
F I N I S H E R DIE I
~
4
~o,4
o
c4
q
-
o
d
-80-7.0
50-50
40-3.0-Z0-1.0
0.0
1.0
20
30
4.0
5.0
60
70
8.0
NDIH
Fig. 6. Grid distortion and flash formation of test preform TP-I for H / B
cavity).
-
1.0 (the dark area is unfilled
The result of the simulation with preform TP-II in Fig. 7 shows that the material
almost fills the finisher die I, whilst the simulation with preform TP-I in Fig. 6 shows
a considerable unfilled cavity (darkened area). Thus it is proposed that a lateral
indentation be applied to a rectangular stock as a preforming operation.
4.2. Prqfbrm design
Some parts can be forged in a single set of dies, whilst others, due to shape
complexity and material flow limitations, must be shaped in multi sets of dies. The
298
B.S. Kang et al.,./Journal of Materials Processing Technology 47 (1995) 291 309
o
o
,B
o
u~
~o
~o
FINISHER
DIE
1
o
d
-8.o-7.o-6.o-5.o-4.0-,5.o-2.o-1.0
o,o 1.o
2.0
3.o
4.0
5.0
60
70
8.0
~DIH
Fig. 7. Grid distortion and flash formation of test preform TP-I1 for H/B = 1.0 (the dark area is unfilled
cavity).
purpose of a preforming operation is to distribute the volume of the parts such that
material flow in the finisher dies will be sound. The initial stocks for forging of
H-shaped plane-strain component are rectangular workpieces and the volume of the
stocks is the same as those of the finish forgings given in Fig. 2. Dimensions and mesh
systems of rectangular workpieces are listed in Table 1. Preform designs in the
flashless forging of three H-shaped geometries are carried out for rib height-to-width
ratios (H/B) of 1.0, 2.0 and 3.0, and the shapes and dimensions of blocker dies I, II and
III for indentation are shown in Fig. 8 blocker dies I, II and III being used for
H/B = 1.0, 2.0 and 3.0, respectively.
The lateral indentation of rectangular stocks using the blocker dies in Fig. 8 can
achieve similar effects to those of preforms TP-I and TP-II. The three blocker dies, I,
II and IIl for lateral indentation are designed to have different indentation angles. As
restraining the vertical material flow at the center of the web and indenting the lateral
part of the workpiece, it is expected that the rib is formed first without a cavity and
that the lateral part around the parting line deforms slowly. Thus, the flashless forging
of rib/web components can be achieved.
(1) H/B = 1.0. The test preform T P - I I in Fig. 7 shows sound die filling even though
a small cavity is formed in the rib. Thus, complete die filling may be obtained with
slight modification of the preform. Pre-form HT-I is made at about 40% with lateral
indentation and the shape of the blocker die I are determined through preliminary test
simulations under several trial simulations at various conditions, such as different
stock size, depth of indentation and shape of blocker die. Fig. 9 shows the preforming
operation of preform HT-I and the finishing operation with the finisher die I.
The preform of HT-I satisfies the final design condition of flashless forging since the
workpiece fills the die completely without any flash when the finisher die I is applied
to yield the final product. The useful preform is of saddle-like shape derived from
lateral indentation.
(2) H/B = 2.0. The preform design for the case of H/B = 2.0 is carried out by
considering the simulation result of a test preform and the case H/B = 1.0. Preform
H T - I I is made from a solid rectangular stock having the same volume as the final
product. Blocker die II is used to obtain the preform of H T - I I which has 58% case of
H/B = 1.0, deeper lateral indentation is required. The slope angle of blocker die II is
B.S. Kang et al / Journal o[Materials Processing Technology 47 (1995) 291 309
©
¢,i
L__
e~
1
o
,;.d
"o
c
I
o
,q
©
&
¢-
.c
t~
z6
299
300
B.S. Kang et al./Journal of Materials Processing Technology 47 (1995) 291 309
o
~6
o
o
q
BLOCKER D I E I
o
0
I
I
I
I
I
I
I
I
8.0-7.0-B.O-5.O-4.0-5.O-2.0-1.0
I
I
1
I
I
I
I
I
0.0
1,0
2.0
5.0
4.0
5.0
6.D
7,0
8,D
WIDTH
o
o
o
d
I
-8,0-7.0
I
60
I
I
I
I
I
5.0-4.0-5.0-2.0-%0
I
~
I
I
I
40
.5.0
I
1.0
I
20
I
I
I
I
I
5.0
4.0
5.0
6.0
7.0
8,0
WIDTH
F I N I S H E R DIE I
-80-7,0-6.0-50
I
0.0
I
I
2.0-1.0
I
I
I
I
0.0
1.0
2D
.50
I
40
I
5.0
I
60
I
7.0
13.0
WIDTH
c~
o
,.5
ei
o
o°'
l
I
-8.0 -7.0 -5.0
I
I
~
5.0 - 4 . 0 - 5 . 0 - 2 0
I
I
-1.0
I
I
0.0
1.0
[
I
I
I
I
I
20
50
4.0
50
6.0
7.0
80
WIDTH
Fig. 9. Simulation of the entire forging process using designed blocker die 1 and preform HT-I (H/B = 1.0).
designed to have greater than that for the blocker die 1, and also the width of the stock
becomes greater than the case for H/B = 1.0. The resulting preform shape allows
smooth filling in the rib of finisher die II. Fig. 10 shows loading simulations of the
initial stock with the blocker die II and finisher die II. It is seen that preform HT-II
satisfies the design condition of flashless forging successfully when finisher die II is
used.
(3) H/B = 3.0. It is obvious that the deep and narrow rib cavity of the finisher die is
difficult to be filled without flash as the ratio of rib height-to-width becomes large,
which means that the preform design requires more careful consideration according
to the increase of the rib height-to-width ratio. The same procedures as for the two
case of H/B = 1.0 and 2.0, are followed to obtain a reasonable preform shape for the
case of H/B = 3.0. The preform is made from a solid rectangular stock having
a greater width than for the case of H/B = 2.0 and the same volume of the final
product. Preform HT-III, which is shown in Fig. 11, is obtained at 62% reduction in
B,S. Kang et al./ Journal o[ Materials Processing Technology 47 (1995) 291-309
q
.¢
BLOCKER
DIE
301
H
,6
o
o
i1..111
o
d
[
:,:~,,,,~iiiiiiii i i
I
I
I
I
I
-8,0-7.0--8.0--5.0--4.0-3.0--Z0-I.0
0.0
1.0
20
3.0
40
50
60
7.0
8.0
o
WIDTH
c~
,6
_
q
~
I
I
-80-70-6,0
I
I
I
I
5.0
4.13
3.0
2O
I
I
1.00.D
I
10
I
2.O
I
I
I
I
I
30
4.0
5O
60
7O
g.O
o
NDTH
o
o
,d
o
el
o
6
I
I
I
I
I
I
I
--~IO --~'0 --~I0 --5"0 --~IO --~IO --2"0 ~I "0
¢i
I
0.0
I
I
I
I
I
I
I
I,0
2,0
~,0
4.0
~,0
6,0
7,0
I
I
I
I
I
I
~,0
WIDTH
N
o
d
I
I
I
I
I
I
I
I
I
WIDTH
Fig. 10. Simulation of the entire forging process using designed blocker die II and preform HT-II
(H/B =
2.0).
width of the stock by open-die forging with blocker die III, the preforming and
finishing operations being illustrated in Fig. 11.
The final stage of the simulation shows no flash and no cavity. Thus it can be
concluded that preform HT-III is acceptable for flashless forging. It should be noted
also that the amount of indentation, initial stock size and blockerdie shape are critical
to prevent flash.
(4) Comments on the design procedure. Preforms HT-I, lI and III are obtained by
open-die forging with blocker dies I, II, and III, respectively. The shapes of the blocker
dies are determined to give the workpiece a smooth flow to provide final forgings
without flash and defects such as laps and folds. Valuable information for designing
the preform shape is derived from a number of preliminary simulations. Figs. 12 and
13 show the distributions of the effective strain of each preform and final product. The
302
B.S. Kang et al./Journal of Materials Processing Technology 47 (1995) 291 309
BLOCKERDIEIII ]
x'x~iiiiiiii~iiill
ii!i i i i
I
I
]
I
I
I
I
I
I
I
I
I
I
I
I
-8.0-7.0-6.0-5.0-4.0-3.0-2.0-1,0 0.0 1,0 2.0 3.0 4.0 5.0 6.0 7.0 8.0
~:°~ 1
~o°
o
do
°
WIDTH
I I I I I I I I I I I I I I I
-8.0 7.0-6.0-5.0-40-3.0-2.0-1.0 0.0 1.0 2.0 3.0 4.0 6.0 6.0 7.0 8.0
° ° ' ~ ~" I o
N
t
I
O
I
,
I
I
6
I
WIDTH
O
I
I
I
I
I
I
~
I
I
o -8.0 -7.0 -6.0 -50 -4.0 -3.0-2.0 -1.0 0.0 1.0 2.0 3,0 4.0 5.0 6.0 7.0 8.0
,.d
WIDTH
o.4
o
o
el
o
d
I I I I I I I ~ I I I I I ~ 1
80-7.0-6.0 5.0-40-3,0-2,0-t,0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8,0
WIDTH
Fig. 11. Simulation of the entire forging process using designed blocker die II1 and preform HT-III
(H/B = 3.0).
maximum effective strain becomes large as the rib height-to-width ratio increases.
Especially in the case of H / B = 3.0 the degree of distortion becoming severe.
Fig. 14 shows load~tisplacement curves during loading simulation. The curves in
Fig. 14(a) represent forging load according to the die stroke when applying the blocker
dies to the rectangular stock, whilst the curves in Fig. 14(b) show the cases when
applying the finisher dies to the designed preforms. The sharp increase of die load at
the closure of dies, shown in Fig. 14(b), is typical of the closed-die forging process. The
load is normalized by dividing it by the initial yield strength of the workpiece. The
final loads during the finish operation become greater with the increase of the rib
height-to-width ratio.
B.S. Kang et al./ Journal o[ Materials Processing Technology 47 (1995) 291 309
-L.._
303
"YL
-8.0-7.0-6.0-5.0-4.0-3.0-2.0-1.0
O0
I.O
2.0
3.0
4.0
5.0
6.0
7.0
8.0
0.0 1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
I
I
I
3,0
4.0
50
60
70
o
rZ
I-
-8.0-7.0-6.0-5.0-4.0-30-2.0-1.0
WlOTH
o
M
I
I
~
~
I
8.0-7,0-6.0-5.0-40-3.0-2.0-1,00.O
1.0
2.0
8.0
W~DTH
Fig. 12. Distributions of total effective strains within the preforms.
4.3. Alternative design.for the case of H/B = 3.0
The previous simulation checks only the design condition of complete die filling,
which condition can be accomplished with one preform for each case. It is important
to minimize the n u m b e r of preforming operation, but such a design would be useless if
any defect is found in the final product.
Here is investigated the effective strain distribution in the final product. Sound
products require relatively even distribution of effective strain. The m a x i m u m value of
effective strain in the final product is limited to 4.5. F r o m Fig. 13, can be seen that the
two cases of H/B = 1.0 and 2.0 pass this criterion, even if the final product of the case
of H/B = 2.0 has a small spot near to the parting line with a higher value of effective
strain than 4.5. The case of H/B = 3.0, however, has a m a x i m u m effective strain of 6.5
near to the parting line, which is a much greater value than the limitation, more even
distribution of effective strain being required in the case of H/B = 3.0.
304
B.S. Kang et al./Journal o[ Materiah" Processing Technology 47 (1995) 291 309
0.5
o
0.0 1.0
-8.0-7.0-6.0-5.0-4.0-3.0-2+0-1.0
2.0
5.0
4.0
2.0
30
4.0
5.0
60
7.0
8.0
WIDTH
o
Q
l
tr/+ :,°
i
-8.0-7+0-6.0-5.0-4.0
3.0-2.0-1.0
0.0
1.0
5.0
I
l
6.0
7.0
8.0
WIDTH
o
<6
o
,6
~o
o 4
u~
so
cq
H/B=3.0
s.o
4.0
+o
~
I
-8.0-70-6.0-5.0
,o+o
[
4.0-3.0-2.0-1.0
0.0 1.0
2.0
3.0
4.0
5.0
I
I
6.0
7.0
WIDTH
3.0
2.5
8.0
Fig. 13. Distributions of total effective
strains wihin the final forgings.
70
-~- BLOCKER
BLOCKER
~-
DIE I
DIE H
60
2~
"~- FINISHER
-~- FINISHER
-~- FINISHER
DIE I
BIB I1
DIE lll
r
5O
~
c3
2.0
o
o
40
z°
30
o
20
1.5
Z
(~ 1.0
kL
0.5
10
--J
2O
DIE STROKE
(a)
40
60
80
DIE STROKE(N)
1O0
(b)
Fig. 14. Variations of forging loads: (a) blocker dies applied to solid stocks; (b) finisher dies applied to
designed preforms.
305
B.S. Kang et a/./ Journal of Materials Processing Teclmo/ogy 47 (1995) 291 309
Thus, one more preforming operation is needed to avoid severe distortion in the
final product. For this purpose, blocker dies IV and III are used to make preform
HT-IV and preform HT-V, as shown in Fig. 15. The configurations of blocker dies IV
and III are shown in Fig. 8(d) and (c) respectively, and the dimensions of the initial
stock and mesh system are given also in Table 1. Fig. 15 shows the preforming
operations to produce preform HT-IV and preform HT-V, and the finishing operation
with finisher die III.
The flashless filling in the final product is achieved, which is one of the design
conditions. The even distribution of effective strain in the final product should be
investigated during the two preforming operations and the finishing operation.
Fig. 16 shows the distributions of the effective strain of the two preforms and of the
BLOCKERDIE IV
-8.0-7.0-6,0-5.0
4.0
3.0
2.O
1.0
O.O
1.0
2,0
3.0
4O
5.(1
6.O
7O
8.O
WID1H
o
'5
~
70 04
R DIE III
~/~
~o
I
8.O-7.0
I
I
F
I
I
I
80-50-40-,5.0-20-1.0
I
I
I
1.0
2.0
5.0
I
1
I
I
40
50
60
70
80
WIDTH
o
0
I
O0
4
90
o
o
c5
I
I
I
I
r
t
I
-8.0-7.0-8.0-5.O-4.0-,50-2.0-1.O
~
o
o
.e
!
o
,6
I
I
I
I
I
I
I
0.0
1.0
2.0
5.0
4.0
5.0
6.0
I
7.0
8.0
•DTH
o
N
o
d
I
8.O
70-80
J
I
50
I
t
4O-50-2.0
I
I
I
I
I
I
I
f
I
I
1.O
0.0
1.0
2.0
5O
40
5.0
6.0
70
80
WIDTH
Fig. 15. Simulation of the entire forging process using designed blocker dies and preforms (H/B
alternative design).
=
3.0:
306
B.S. Kang et al./ Journal o[Materials Processing Technology 47 (1995) 291 309
o
o
o
o
o
M
-
o
o
d
o
-8.0
70-6.o-50-4.0-3.0-2.0-1.0
0.0
1.0
2.o
30
4.0
5,0
6.0
70
8.0
NDm
o
o
o
.n
o
EFORM HT
d
-8.0
~
I
70
6.0
I
I
I
I
I
5.0-40-3.0-20-1.0
I
I
O,0 1.0
I
I
I
I
I
I
2.0
3.0
40
5.0
6.0
7.0
80
20
30
40
50
6.0
7.0
80
WIDTH
80
70-60
50
40
30
2.0
10
00
1.0
WIDTH
Fig. 16. Distributions of total effective strains within the preforms and the final forging (H/B = 3.0:
alternative design).
final product, from which it is seen that the effective strain decreases considerably and
is distributed more evenly than in the previous design using one preform. The
maximum die load at the final stage is far less than in the previous design. Thus, it is
concluded that the alternative design is much better than the previous design.
5. Comparison with the case of axisymmetric flashless forging
It is useful in preform design to compare the shapes of the preforms designed in this
study with the shapes of preforms suggested by other researchers. Fig. 17 [16] shows
the preform shapes and the corresponding process for three axisymmetric
H-shaped cross-sectional finisher dies. The study referred to [16] also aimed to design
preforms which would produce flashless products in axisymmetric cases.
B.S. Kang et al. / Journal ~?["Materials Processing Technolog~y 47 (1995) 291 309
,13o 1341275
4.]71
307
2.87
PREFORM
FINISH
H/B=I.0
H/B=2.0
I-I/B=3.0
Fig. 17. Preforms designed for H-shaped axisymmetric flashless closed-die forging [15].
It is shown that one preform is required for H/B = 1.0 and two for H/B = 2.0 and
3.0 to obtain flashless forging products in axisymmetric cases, whilst, in this study one
preform is required for H/B = 1.0 and 2.0 and two preforms for H/B = 3.0. Lateral
indentation in this study as a preforming operation is different in comparison with
axisymmetric flashless forging. In axisymmetric forging, axial indentation of a circular
cylindrical stock is considered as a preforming operation. In the present work,
however, horizontal indentation is used for a preforming operation. The main reason
for this difference is the characteristics of the material flow. The movement of material
along the horizontal plane of symmetric plane is faster in the plane-strain forging than
in the axisymmetric forging,
6. Summary and concluding remarks
This study places an emphasis on establishing systematic procedures for preform
design in the flashless closed-die forging of plane-strain H-shaped components. Three
different rib height-to-width ratios of H/B = 1.0, 2.0 and 3.0 are investigated. Design
procedures are developed for the flashless forging of a typical two-dimensional
plane-strain component. The preforms are derived from qualitative considerations,
and the results of preliminary simulations and a number of systematic loading
simulations. Two design criteria of flashless geometrical filling and even distribution
308
B.S. Kang eta/./Journal of Materials Processing Technology 47 (1995) 291 309
I
I
J
.
.
.
.
.
J24!
I
--+--_
I
I
H/B~t.O
H/B=Z.O
BIB=3.0
Fig. 18. Preformsdesigned for flashless closed-dieforging of H-shaped plane-strain components.
of effective strain in the final products are investigated in controlling the preform
configuration. The preforms and the final forgings obtained are summarized in
Fig. 18.
One preforming operation is designed for flashless forging at the ratios o f H / B = 1.0
and 2.0. The case of H/B = 3.0 also needs one preform to satisfy flashless geometrical
filling, but it does not pass the criterion of even distribution of effective strain, thus
another preforming operation is added to avoid a high value of effective strain in the
final product, the case for a ratio of 3.0 therefore being designed as two preforming
operations. Another important conclusion compared with the axisymmetric flashless
forging is that the plane-strain forging without flash, horizontal indentation is an
effective method of obtaining the preform. In this investigation, the design criteria are
related to geometrical filling of the workpiece and even distribution of effective strain
in the final products. Design optimization remains a problem, but the results of
simulations such as of effective-strain distributions and forging loads involved in the
preforming and finishing operations, are useful information for the preform design of
similarly shaped components.
Acknowledgement
The authors would like to thank the Korean National Science Foundation for
financial support.
B.S. Kang et al./ Journal ~![ Materials Processing Technology 47 (1995) 291 309
309
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