Journal of Materials Processing Technology

ELSEVIER J. Mater. Process. Technol. 45 (1994) 709-714

Application of physical modeling, FEM and knowledge-based process planning program to forging process design

J. S. Lee, S. S. Hong, S. H. Lee, N. C. Cho and N. H. Kim

Agency for Defense Development, Taejon 305-f~0, Korea

In order to develop the forging process for a cup-shaped product, three methods for process modeling and design have been applied. As an experimental approach, physical modeling with plasticine has been performed. A commercial FEM code DEFORM and a knowledge-based process planning program have also been used as computational methods. Partial forging technique has been proposed to forge a large forging with a capacity-limited machine and verified with the above process modeling and design methods. It has been found that the proposed forging process is feasible in the medelings. The actual forging of this product has been successfully performed proving that these approaches are reliable in developing the forging processes with efficiency and low cost.

1. INTRODUCTION

Forging processes have primarily been developed costly by empirical guidelines or trial and error. However, the manufacturing cost and time can be reduced by adopting computational and experimental modeling and design approaches to the process design when the results of these methods are reliable.

In this work, forging process for a cup-shaped product shown in Fig.1 has been developed using three modeling and design approaches. As an experimental approach, physical modeling with plasficine has been performed. A commercial FEM code DEFORM and a knowledge-based process planning program have also been used as computational methods.

Because the dimensions of the cup- shaped product exceed the capacity of available forging equipment, 35 ton counterblow hammer (energy capacity 350 kJ) in the present work, partial forging

• . ~841.2 1

O~

Fig. 1. A cup-shaped forging product.

technique has been proposed. The developed process has been verified with the above modeling and design methods before the actual forging has been performed.

0924-0136/94/S07.00 © 1994 - Elsevier Science B.V. All rights reserved. S SD I 0924-0136(94)00264-9

710

2. FORGING PROCESS DESIGN

If the required forging load is greater than the available one, the multi-stage forging should be used. Presently, the forging process for the cup-shaped product made of AISI 4130 steel is designed to forge the central region of the product first and then radially the remaining part of it to its final dimensions. This technique employs an empirical equation for the estimation of the forging load suggested by Schey [1] as the following.

L = CzA (1)

where L is the forging load, a is the average flow stress of the material and A is the projected area of the forging including flash. C is the shape complexity factor ranging from 3 to 12 depending on the shape of the forging.

However, the above equation can not be used directly for the hammer forging processes because the hammer is energy- restricted machine, that is, the forging capacity of a hammer is not represented by its maximum load but by its energy. In order to apply this equation to the hammer forging processes, the maximum energy of the hammer should have some equivalence to the forging load of the load-restricted machine such as the hydraulic press.

There is another empirical equation, Eq. (2), which relates to the forging capacity between these two types of the forging equipments [2].

L (in mem'c ton) = 0.4 E (in k g . m) (2)

where E is the hammer energy. From this equation, it can be known that the forging capacity of 350 kJ hammer is equivalent to

that of 140 IVIN hydraulic press. Restricting the forging load in Eq. (1) to

140 MN and assigning the shape complexity factor to 3.5 which corresponds to a simply shaped forging without flash, the forgible projected area is calculated to be 0A3 m z for AISI 4130 steel (average flow stress of AISI 4130 steel is 93.1 MPa at its hot working temperature range). Thus a simply shaped product can be forged in one blow on 140 MN press when the forged diameter is less than 740 rnm_

At the next forging step the shape complexity factor is determined to be 5. As a result, the forgible region is expanded from 740 mm to 964 mm in diameter. Since the forgible region in the second step covers the dimensions of the cup-shaped forging, the forging of this product can be, accomplished within two stages.

According to the above results, a preforming die was designed to forge the product up to 720 mm in diameter by cutting out the outside part of the finisher. Fig. 2 shows the preforming and finishing

Preforming Die

k

Finishing Die

i i Jj

Fig. 2. Preforming and finishing dies.

711

dies. It should be noted that the upper die for preforming is reused in the finishing step.

3. VERIFICATION OF THE PROPOSED FORGING PROCESS

3.1. Physical modeling approach Physical modeling with plasticine was

performed to prove the feasibiliW of the forging process proposed in Sec. 2. Flow stxesses of plasticine and AISI 4130 steel were obtained from the compression tests and fitted in the form of the following equation.

o (MPa) = K ~ " at T ' C (3)

The values of K and m with temperature are given in Table 1. It can be known that plasticine at 21°C has similarity with AISI 4130 steel at 1200~. A gravity drop hammer which has similarities with 35 ton counterblow hammer was constructed to simulate the hammer forging process [3]. The ratio of dimension between the real and the model was 12 : 1. In the modeling, the weight of upper tup and die was 3 kg and

Table 1. Values of K and m in F_xl. (3).

Material Temp.,°C

AISI 4130

Plas t ic ine

K m

245.5 0.040 800

185.1 0.031 900

134.5 0.066 1000

101.1 0.069 1100

69.6 0.110 1200

0.375 0.130 21

the drop height of them was 35.7 ram. A tissue paper was used as lubricant because the friction factor of 0.3 can be obtained in the physical modeling with plasticine by use of it [4]. The plasticine billet was 48 mm in diameter and 22 mm in height.

The preforming and finishing were performed on the model hammer. The cross sectional views of the preform and the final forging are shown in Fig. 3. The cup- shaped product could be forged successfully in the modeling following the proposed process.

Fig. 3. Cross sectional views of the preform and the final forging.

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3.2. F in i t e e l emen t approach A commercial FE code DEFORM [5]

was used to verify the proposed forging process. Nonisothermal analysis was perfermed since the forging of AISI 4130 steel is carried out at the elevated t e ~ a t u r e . Even though a hammer is used in the actual tryout, the simulation has been performed assuming that the press forging has been done. However, the forging load was checked whether it exceeded 140 MN or not, which is thought m be the limit capabilites of the hammer used in this investigation.

The dies were assumed to be made of H13 tool steel. The thermal properties of AISI 4130 and H13 steels were obtained from references [6,7]. At the start of each forging step, temperature of the dies and the workpiece were initialized to 250°C and 1200"(3, respectively. The speed of the upper die was 5 mm/sec and the lower die was at rest. The friction factor, m, between the die and the workpiece was 0.3. The billet was initially 360 mm in diameter and 668 mm in height. It was compressed with flat dies to

300 Finishing i

~ 200 Preformingi ,'~

" ~ _ ! - ~ [ t _ Lo_~_d . . . . . . . . . . . . . . ! . . . .

100 UpseHing~ / ]

STROKE

Fig. 5. Predicted load-stroke curve,

248 mm in height prior to preformms. The deformed shapes and the predicted

flownets of the workpiece at the end of preforming and finishing are shown in Fig. 4. The load-stroke curve is also shown in Fig. 5. The forging load does not exceed the limit value except at the very end of the finishing stage, However, the cup- shaped forging is managed to be forged successfully with the proposed process.

250

E so E v F- "1- (.9 ,~-lso I

-350 2O0 4OO

RADIUS (mm)

200

E 0 E

v

T

W ;200 -i-

Finishing

__t 1

0 2oo 4oo 6oo

RADIUS (mm)

Fig. 4. Deformed shapes and predicted flownets of the workpiece.

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3.3. K n o w l e d g e - b a s e d p r o c e s s pl:anning A knowledge-based process planning

prograr~ which is based on the empirical design rules for forging practices collected from technical references, has been developed to design hot forging processes for axisymmetric products [8]. It can be implemented on a PC and consists of five main parts such as input, process planning, die design, flow simulation and output modules. This program can predict the forging load and stresses, determine the process variables and design the preforms. All the results can be shown graphically. Five preforming methods based on the design guidelines have been built in the program to effectively design the preforrrL The designs produced by the program can be easily modified through the user- interactive routines.

The process variables for the cup-shaped product are given in Table 2. The dimensions of the flash are calculated from

DIE ,~S]~4BLY {

I i

L 1400 r

l LI

= ' , I D.D.

Table 2. Process variables for the cup- shaped product.

Net volume, mm 3

Net weight, kg

Shape d i f f i c u l t y factor

Max. radius, ram

Max. height, m

Centroid of half section, mm

Flash thickness, mm

Flash width, mm

Sectional area, nm 2

Perimeter of section, mm

Flash weight, kg

Scale weight, kg

B i l l e t weight, kg

6. 511×106

510.8

6.6

841.2

469.9

237.7

12.6

27.3

43596.9

1487.3

20.4

14.1

545.3

Wolf 's and Teterin 's equations [9], which consider the weight and the shape difficulty factor of the forgings.

Fig. 6 shows the graphical output of the preforming die for the cup-shaped forging. The required loads for the preforming and the finishing processes are estimated to about 127 and 441 MN, respectively.

Fig. 6. Graphical output of the preforming dies.

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Fig. 7. The as-forged cup-shaped product.

4. A C T U A L F O R G ~ G T R Y O U T

The actual forging tryout was carried out on 35 ton countevblow hammer following the proposed process. Dies were made of JIS SKT4 tool steel. The billet of AISI 4130 steel was initially 360 mm in diameter and 772 mm in height. The dies and the workpiece were heated to about 200 °C and 1200°C, respectively, prior to each forging step.

The billet was compressed with the fiat dies until pancake height reached about 290 mm. The preforming and the finishing could be completed with one heating each. Finally, the cup-shaped product can be forged successftflly by the proposed process and is shown in Fig. 7.

5. CONCLUSIONS

A forging process has been developed to forge a cup-shaped product with a capacity-limited equipment. The proposed process has been verified with three kinds of process modeling and design approaches prior to the actual forging. The cup-shaped

product in a real scale has been successfully forged without any modification of the actual dies as predicted in the modelings.

REFERENCES

1. J. A. Schey, introduction to Manufactur- ing Processes, McGraw-Hill, NY, 1977: Ch.4. S. H. Choi and T. A. Dean, Int. j Mach.

Tool Des. Res., 24 (1984) 105. N. C. Cho, S. H. Lee, S. S. Hong and j. S. Lee, J. Mater. Process. Tech., Accepted for publication.

4. G. A. Lee, Y. T. Irr~ J. S. Lee and S. S. Hong, Trans. Korean Soc. Mech. Engrs., 16 (1992) 2082.

5. S. I. Oh, W. T. Wu, J. P. 'Fang and A. VedhanayagalT~ J. Mater. Process. Tech., 27 (1991) 25.

6. Y. T. Im, ASME J. Eng. ind., 11i ([989) 337.

7. Metals Handbook, 9th ed., vol.1, ASM, Metals Park, OH, 1978.

8. J. C. Choi, B. M. Kim, S. W. Kim, J, S Lee, S. S. Hong and N. H. Kim, J: Kore- an Soc. Tech. Plast., 1 (1992) 20.

9. E. Sleeekx and J. P. Kruth, J. Mater'. Process. Tech., 31 (1992) 119.

3.