Cold and Hot Forging: Fundamentals and Applications / Edited by Taylan Altan, Gracious Ngaile, Gangshu Shen

Подождите немного. Документ загружается.

Process Modeling in Impression-Die Forging Using Finite-Element Analysis / 203

further deformation, the workpiece contacted

the uppermost wall of the top die, and a gap

formed between the inside wall of the top die

and the workpiece. At the ﬁnal stroke position,

a small gap remained along the inside wall of

the upper die, but no buckle was formed. Figure

16.12(a–c) shows the ﬁnish die operation with

the modiﬁed blocker output. Upon deformation,

the upper die pushes the workpiece down until

contact is made with the outer wall of the lower

die. With further reduction, the workpiece con-

tacts the outer web region of the upper die. As

the stroke continues, the inside corner ﬁlls up

without any indication of defective ﬂow pat-

terns. With further upsetting of the workpiece,

the uppermost ﬁllet of the top die and the outside

ﬁllet of the bottom die continue to ﬁll, and the

die cavity ﬁlls up completely. Hence, the result

from the ﬁnisher simulation indicates that the

modiﬁed blocker workpiece ﬁlls the ﬁnisher die

without defects.

16.6.4 Investigation of Tool Failure

Hot forging is a widely used manufacturing

process in the automotive industry. High pro-

duction rates result in severe thermomechanical

stresses in the dies. Either thermal cracking or

Fig. 16.16 Forging sequence of the aircraft wheel. Part geometry courtesy of Weber Metals Inc.

Fig. 16.15 Forging sequence of the titanium ﬁtting. Part geometry courtesy of Weber Metals Inc.

204 / Cold and Hot Forging: Fundamentals and Applications

wear governs the life of the dies. In the forging

industry, the tooling cost alone can constitute up

to 10% of the total cost of the component.

This example deals with the investigation of

the effect of thermomechanical stresses on the

tool life in the hot extrusion of the automotive

component shown in Fig. 16.13 [Brucelle et al.,

1999]. The workpiece was from austenitic stain-

less steel AISI 316L. The punch was from tool

steel (X85 WCrMoV6-5-4-2). The resulting

stresses in this process are a combination of the

purely mechanical stresses due to forging and

the thermomechanical stresses as a result of ther-

mal cycling of the punch surface due to the al-

ternating hot forging and waiting periods. The

stresses due to thermal cycling were found to

comprise approximately 75% of the total stress

ﬁeld. This cycling causes tool damage, known

as heat checking. Originally, the punch had to

be changed approximately every 500 cycles due

to cracking as a result of thermal cycling (Fig.

16.14). It is a commonly known fact that ge-

ometry changes are not the best way to reduce

the stress level with regard to thermal stresses.

From this study, it was determined that increased

tool life could be achieved by modifying the hot

forging process parameters such as billet tem-

perature and the forging rate.

Finite-element modeling simulation and ex-

perimental work were used to conduct a para-

metric study to determine the optimum process

parameters to achieve higher life expectancy of

the tools. This combined numerical and experi-

mental approach can be summarized as:

●

A two-step numerical simulation:

a. Process simulation to determine the

purely mechanical stresses, forging loads,

and thermal boundary conditions for the

punch

b. Thermoelastic simulation for thermal

stress analysis of the punch

●

A two-step experimental stage:

a. Metallurgical validation of the constitu-

tive laws of the workpiece material

b. Industrial forging test validation of the

thermal boundary conditions for the

punch

The surface temperatures on the punch are a

factor of the heat-transfer coefﬁcient at the tool/

workpiece interface. This coefﬁcient is a func-

tion of various factors, such as surface topog-

raphy, contact pressures, temperature difference,

and duration of contact [Snaith et al., 1986].

Forging tests were conducted on an industrial

press using a test punch with ﬁve thermocou-

ples. Several numerical iterations (FEM simu-

lations) were performed by using different

heat-transfer coefﬁcients until the calculated

temperature distribution was in agreement with

that from the experiments.

In order to reduce the thermal stresses, a re-

duction of the thermal gradient during forging

must be obtained. There are two options: 1)

modiﬁcation of process parameters to decrease

the temperature (reduction of the punch speed,

thus reducing the ﬂow stress, or decreasing

workpiece temperature, resulting in an increase

in ﬂow stress) or 2) use of lubricating/insulating

Fig. 16.17 Sections taken along the ﬁtting to check for die ﬁlling at the blocker stage [Shirgaokar et al., 2002]

Process Modeling in Impression-Die Forging Using Finite-Element Analysis / 205

products during forging to reduce the heat trans-

fer, which is an empirical approach. The ﬁrst

option was selected, since the available press

could handle increased forging loads as a result

of increased ﬂow stress.

A parametric study was conducted to inves-

tigate the inﬂuence of forging speed and initial

workpiece temperature on the ﬁnal thermome-

chanical stresses. The optimum process param-

eters were thus determined, resulting in a 30%

decrease in the stresses. Thus, a combination of

process simulation and experimental veriﬁcation

resulted in an increase in the tool life for the

punch in this hot forging process.

16.6.5 Multistage Forging Simulations of

Aircraft Components

Multistage forging simulations of two aircraft

components (a titanium ﬁtting and an aluminum

wheel) were run to study metal ﬂow, tempera-

ture distribution, die ﬁlling, and die stresses

[Shirgaokar et al., 2002]. The commercial FEM

code DEFORM-3D was used for these simula-

tions. The two components considered for this

study are produced by closed-die forging with

ﬂash. Since the parts are forged at elevated tem-

peratures, it was necessary to run nonisothermal

simulations. Flash removal between the forging

stages also had to be considered for the simu-

lations in order to ensure appropriate material

volume in the dies for the subsequent forging

stage. Each of the components was forged in

three stages, namely, two blocker stages fol-

lowed by a ﬁnisher stage. Figures 16.15 and

16.16 show the forging sequence of the titanium

ﬁtting and the aluminum wheel, respectively.

The results obtained at the end of the simulations

were the effective stress distribution, die ﬁlling,

metal ﬂow during forging, temperature distri-

bution, and strain distribution.

The simulation strategy adopted for the two

components was to remove the ﬂash in-between

stages. This was done by using the Boolean ca-

pability of DEFORM, i.e., volume manipula-

tion. Die ﬁlling was checked by examining vari-

ous cross sections along the length of the forging

(Fig. 16.17 and 16.18).

The simulations were stopped when die ﬁlling

was achieved, and it was this stage of the simu-

lation that was used to determine the stresses in

the dies. In order to reduce computational time,

the dies were kept rigid throughout the simula-

tion. At the last step, they were changed to elas-

tic, and the stresses from the workpiece were

Fig. 16.18

Section A-A of the ﬁtting after the ﬁrst blocker

operation [Shirgaokar et al., 2002]

Fig. 16.19 Forging of AISI 4340 aerospace component

206 / Cold and Hot Forging: Fundamentals and Applications

interpolated onto the dies. The results obtained

from the die stress analysis simulations were the

effective stress, the maximum principal stress,

and the temperature distribution. Using these re-

sults, an effective die design was established.

16.6.6 Precision Forging of

an Aerospace Component

The simulation of a precision-forged aero-

space component was conducted as part of a

study to develop guidelines for the design of

prestressing containers for dies used in forging

of complex parts. The simulated part is shown

in Fig. 16.19(b). Experiments for this compo-

nent were conducted in a previous study con-

ducted at Batelle Columbus Laboratories

[Becker et al., 1972]. The results from the sim-

ulations were compared to the experimentally

determined loads and were found to be in good

agreement. The simulation results are used to

obtain the loading on the die and the punch. The

load on the die is used to perform stress analysis

and design a cost-effective prestressing con-

tainer. The loading on the punch is used to per-

form a stress analysis and correlate the punch

deﬂection to thickness measurements taken at

various locations of the forgings.

16.6.7 Die Design for Flashless

Forging of Connecting Rods

In conventional hot forging of connecting

rods, the material wasted to the ﬂash accounts

for approximately 20 to 40% of the original

workpiece. It is essential to accurately control

the volume distribution of the preform to avoid

overloading the dies and in order to ﬁll the cav-

ity. It is equally important that the preform be

simple enough to be mass-produced. Thus, the

design of a ﬂashless forging operation is more

complex than that of a conventional closed-die

forging with ﬂash. In order to accelerate the de-

velopment process and reduce prototyping costs,

it is essential to conduct a substantial amount of

the design process on the computer.

The requirements for conducting a successful

ﬂashless forging process are [Vasquez et al.,

2000]:

●

The volume of the initial preform and the

volume of the die cavity at the ﬁnal forging

stage must be approximately the same.

●

There must be neither a local volume excess

nor a shortage, which means that the mass

distribution and positioning of the preform

must be precise.

●

If there is a compensation space provided in

the die, the real cavity must be ﬁlled ﬁrst.

The 2-D and 3-D FE simulations were used

extensively to analyze and optimize the metal

ﬂow in ﬂashless forging of the connecting rod

shown in Fig. 16.20(a). In order to verify the

applicability of the simulation results, physical

modeling experiments were conducted using

plasticine. Figure 16.20(b) shows the initial pre-

Fig. 16.20 Development of the preform shape for ﬂashless forging of a connecting rod [Vasquez et al., 2000]

Process Modeling in Impression-Die Forging Using Finite-Element Analysis / 207

form design along with the ﬁnal modiﬁed pre-

form. Finite-element simulation predicted un-

derﬁlling with the initial preform, which was

modiﬁed accordingly to give a defect-free con-

necting rod (Fig. 16.21).

16.6.8 Integrated Heat

Treatment Analysis

The forming of a medium-carbon manganese

steel bevel gear was analyzed using DEFORM

3D. This gear was hot forged with ﬂash. The

simulation was conducted utilizing rotational

symmetry. Thus, only

⁄

th of the total volume

was simulated. Mesh density windows were

used for local mesh reﬁnement during simula-

tion. Contours of effective strain (darker areas

indicate higher strain) are shown in Fig.

16.22(a). After the forging simulation, the gear

geometry was modiﬁed to account for the ﬂash

removal and drilling the inside diameter.

The modiﬁed gear geometry was used to sim-

ulate a heat treatment operation. In this simula-

tion, the gear was austenized by heating to 1560

⬚F (850 ⬚C) and cooled in 60 s with a heat-transfer

coefﬁcient representative of an oil quench. A

time-temperature-transformation diagram for

medium-carbon manganese steel determined the

Fig. 16.22

(a) The deformation simulation of a hot forged gear with ﬂash. (b) The volume fraction of martensite (dark is higher) in

a steel gear after quenching [Wu et al., 2001]

Fig. 16.21 Deformation sequence for ﬂashless precision forging of a connecting rod [Takemasu et al., 1996]

208 / Cold and Hot Forging: Fundamentals and Applications

diffusion behavior during the austenite-pearlite/

bainite transformation, whereas the Magee equa-

tion was used to model the martensite response.

In Fig. 16.22(b), the volume fraction of marten-

site is shown after quenching. The dark regions

represent a more complete martensite transfor-

mation, and the light areas indicate a mixture of

bainite and pearlite [Wu et al., 2001].

REFERENCES

[Becker et al., 1972]: Becker, J.R., Douglas,

J.R., Simonen, F.A., “Effective Tooling De-

signs for Production of Precision Forgings,”

Technical Report AFML-TR-72-89, Battelle

Columbus Laboratories, 1972.

[Brucelle et al., 1999]: Brucelle, O., and Bern-

hart, G.,” Methodology for Service Life In-

crease of Hot Forging Tools,” Journal of Ma-

terials Processing Technology, Vol. 87, 1999,

p 237.

[Hardwicke et al., 2000]: Hardwicke, C., and

Shen, G., “Modeling Grain Size Evolution of

P/M Rene 88DT Forgings,” Advanced Tech-

nologies for Superalloy Affordability, K.-M.

Chang, S.K. Srivastava, D.U. Furrer, and K.R.

Bain, Ed., The Minerals, Metals, and Mate-

rials Society, 2000.

[Howson et al., 1989]: Howson, T.E., and Del-

gado, H.E., “Computer Modeling Metal Flow

in Forging,” JOM, Feb. 1989, p 32–34.

[Jenkins et al., 1989]: Jenkins, B.L., Oh, S.I.,

Altan, T., “Investigation of Defect Formation

in a 3-Station Closed Die Forging Operation,”

CIRP Annals, Vol. 381, p 243.

[Knoerr et al., 1992]: Knoerr, M., Lee, J., Al-

tan, T., “Application of the 2D Finite Element

Method to Simulation of Various Forming

Processes,” Journal of Materials Processing

Technology, Vol. 33, 1992, p 31.

[Ngaile et al., 2002]: Ngaile, G., and Altan, T.,

“Simulations of Manufacturing Processes:

Past, Present and Future,” Proceedings of the

Seventh ICTP, Oct 2002, Japan, p 271.

[Oh, 1982]: Oh, S.I., “Finite Element Analysis

of Metal Forming Problem with Arbitrarily

Shaped Dies,” Int. J. Mech. Science, Vol. 24

(No. 4) 1982, p 479.

[Sellars, 1990]: Sellars, C.M., “Modeling Mi-

crostructural Development during Hot Roll-

ing,” Materials Science and Technology, Vol.

6, 1990, p 1072.

[SFTC, 2002]: DEFORM 7.2 User Manuals,

Scientiﬁc Forming Technologies Corporation,

Columbus, OH, 2002.

[Shen et al., 1993]: Shen, G., Shivpuri, R., Sem-

iatin, S.L., Lee, J.Y., “Investigation of Micro-

structure and Thermomechanical History in

the Hammer Forging of an Incoloy 901 Disk,”

Annals of the CIRP, Vol. 42/1, 1993, p 343–

346.

[Shen et al., 2000]: Shen, G., “Microstructure

Modeling of Forged Components of Ingot

Metallurgy Nickel Based Superalloys,” Ad-

vanced Technologies for Superalloy Afforda-

bility, K.M. Chang, S.K. Srivastava, D.U.

Furrer, and K.R. Bain, Ed., TMS, 2000, p

223–231.

[Shen et al., 2001]: Shen, G., Denkenberger, R.,

Furrer, D., “Aerospace Forging—Process and

Modeling,” Materials Design Approaches

and Experiences, J.C. Zhao, M. Fahrmann,

and T.M. Pollock, Ed., TMS, 2001, p 347–

357.

[Shirgaokar et al., 2002]: Shirgaokar, M.,

Ngaile, G., Altan, T., “Multi-Stage Forging

Simulations of Aircraft Components,” ERC/

NSM–02-R-84, Engineering Research Center

for Net Shape Manufacturing, 2002.

[Snaith et al., 1986]: Snaith, B., Probert, S.D.,

O’Callaghan, P.W., “Thermal Resistances of

Pressed Contacts,” Appl. Energy, Vol. 22

1986, p 31–84.

[Takemasu et al., 1996]: Takemasu, T., Vas-

quez, V., Painter, B., Altan, T., “Investigation

of Metal Flow and Preform Optimization in

Flashless Forging of a Connecting Rod,”

Journal of Materials Processing Technology,

Vol. 59, 1996, p 95.

[Vasquez et al., 1999]: Vasquez, V., Walters, J.,

and Altan, T., “Forging Process Simulation—

State of the Art in USA,” Proceedings of the

Conference on New Developments in Forging

echnology, Stuttgart, Germany, May 19–20,

1999.

[Vasquez et al., 2000]: Vasquez, V., and Altan,

T., “Die Design for Flashless Forging of Com-

plex Parts,” Journal of Materials Processing

Technology, Vol. 98, 2000, p. 81.

[Wu et al., 1992]: Wu, W.T., Oh, S.I., Altan, T.,

Miller, R.A., “Optimal Mesh Density Deter-

mination for the FEM Simulation of Forming

Processes,” NUMIFORM ’92, Sept 14–18,

1992, France.

[Wu et al., 1996]: Wu, W.T., Li, G.J., Arvind,

A., Tang, G.P., “Development of a Three Di-

mensional Finite Element Based Process

Simulation Tool for the Metal Forming In-

dustry,” Proceedings of the Third Biennial

Joint Conference on Engineering Systems

Process Modeling in Impression-Die Forging Using Finite-Element Analysis / 209

Design and Analysis, Montpellier, France,

1996.

[Wu et al., 2001]: Wu, W.T., Oh, S.I., Arimoto,

K., “Recent Developments in Process Simu-

lation for Bulk Forming Processes,” Journal

of Materials Processing Technology, Vol. 111,

2001, p 2–9.

SELECTED REFERENCES

●

[Devadas et al., 1991]: Devadas, C., Sa-

marasekera, I.V., Hawbolt, E.B., “The Ther-

mal and Metallurgical State of Strip during

Hot Rolling: Part III, Microstructural Evo-

lution,” Met. Trans. A, Vol. 12, 1991, p 335–

349.

●

[Shen et al., 1989]: Shen, G., Im, Y.T., Al-

tan, T., “Effect of Flash Dimensions and Bil-

let Size in Closed-Die Forging of an Alu-

minum Alloy Part,” Transactions of the

NAMRI of SME, Society of Manufacturing

Engineers, 1989, p 34–40.

●

[Shen et al., 1995]: Shen, G., Semiatin, S.L.,

Shivpuri, R., “Modeling Microstructural De-

velopment during the Forging of Waspaloy,”

Met. Trans. A, 26, 1995, p 1795–1802.

●

[Shen et al., 2001]: Shen, G., Kahlke, D.,

Denkenberger, R., Furrer, D., “Advances in

the State-of-the-Art of Hammer Forged Al-

loy 718 Aerospace Components,” Superal-

loys 718, 625, 706 and Various Derivatives,

E.A. Loria, Ed., 2001, p 237–247.

●

[Vasquez et al., 1996]: Vasquez, V., and Al-

tan, T., “Investigation of Metal Flow and

Preform Optimization in Flashless Forging

of a Connecting Rod,” Journal of Materials

Processing Technology, Vol. 59, 1996, p 95.

●

[Walters et al., 1998]: Walters, J., Wu, W.T.,

Arvind, A., Guoji, L., Lambert, D., Tang,

J.P., “Recent Developments of Process

Simulation for Industrial Applications,” Pro-

ceedings of the Fourth International Confer-

ence on Precision Forging—Cold, Warm and

Hot Forging, Oct 12–14, 1998, Columbus,

Ohio.

●

[Wu et al., 1985]: Wu, W.T., and Oh, S.I.,

“ALPID—A General Purpose FEM Code

for Simulation of Non-isothermal Forging

Processes,” Proceedings of North American

Manufacturing Research Conference

(NAMRC) XIII, Berkeley, CA, 1985, p 449–

460.

CHAPTER 17

Cold and Warm Forging

Prashant Mangukia

Fig. 17.1

Schematic illustration of forming sequences in cold forging of a gear blank. (a) Sheared blank. (b) Simultaneous forward

rod and backward extrusion. (c) Forward extrusion. (d) Backward cup extrusion. (e) Simultaneous upsetting of ﬂange and

coining of shoulder [Sagemuller, 1968]

17.1 Introduction

Cold forging is deﬁned as forming or forg-

ing of a bulk material at room temperature

with no initial heating of the preform or inter-

mediate stages. Cold extrusion is a special type

of forging process wherein the cold metal

ﬂows plastically under compressive forces into

a variety of shapes. These shapes are usually

axisymmetric with relatively small nonsym-

metrical features, and, unlike impression-die

forging (see Chapter 14, “Process Design in

Impression-Die Forging”), the process does not

generate ﬂash. The terms cold forging and cold

extrusion are often used interchangeably and

refer to well-known forming operations such

as extrusion, upsetting or heading, coining,

ironing, and swaging [Feldmann, 1961; Wick,

1961; Billigmann et al., 1973; Watkins, 1973;

and Altan et al., 1983]. These operations are

usually performed in mechanical or hydraulic

presses, which are discussed in Chapter 10,

“Principles of Forging Machines,” and Chapter

11, “Presses and Hammers for Cold and Hot

Forging.” Several forming steps are used to

produce a ﬁnal part or relatively complex ge-

ometry, starting with a slug or billet of simple

shape, as shown in Fig. 17.1. Some basic tech-

niques of cold forging are illustrated in Fig.

17.2. Through a combination of these tech-

niques, a very large number of parts can be

produced, as illustrated schematically in Fig.

17.3.

In warm forging, the billet is heated to tem-

peratures below the recrystallization tempera-

ture, for example, up to 1290 to 1470 F (700

to 800 C) for steels, in order to lower the ﬂow

stress and the forging pressures. In cold forg-

ing, the billet or the slug is at room tempera-

ture when deformation starts.

Cold and Hot Forging Fundamentals and Applications

Taylan Altan, Gracious Ngaile, Gangshu Shen, editors, p211-235

DOI:10.1361/chff2005p211

www.asminternational.org

212 / Cold and Hot Forging: Fundamentals and Applications

Fig. 17.3 Examples of cold forged tubular or cup-shaped parts [Feldmann, 1977]

Fig. 17.2 Various types of cold forging (extrusion) techniques (P, punch; C, container; W, workpiece; E, ejector) [Feldmann, 1977]

Cold and warm forging are extremely impor-

tant and economical processes, especially for

producing round or nearly round parts in large

quantities. Some of the advantages provided by

this process are:

●

High production rates

●

Excellent dimensional tolerances and surface

ﬁnish for forged parts

●

Signiﬁcant savings in material and machin-

ing

Cold and Warm Forging / 213

Fig. 17.4 Cold forging as a system

●

Higher tensile strengths in the forged part

than in the original material, because of

strain hardening

●

Favorable grain ﬂow to improve strength

By far the largest area of application of cold

and warm forging is the automobile industry.

However, cold forged parts are also used in

manufacturing bicycles, motorcycles, farm ma-

chinery, off-highway equipment, and nuts and

bolts.

17.2 Cold Forging as a System

A cold forging system, as shown in Fig. 17.4,

comprises all the input variables such as billet

or blank (geometry or material), the tooling (the

geometry and material), the material at the tool/

material interface, the mechanics of plastic de-

formation, the equipment used, the characteris-

tics of the ﬁnal product, and ﬁnally, the plant

environment where the process is being con-

ducted. The “systems approach” in forging al-

lows study of the input/output relationships and

the effect of process variables on product quality

and process economics. The key to a successful

metal forming operation, i.e., to obtaining the

desired shape and properties, is the understand-

ing and control of metal ﬂow. The direction of

metal ﬂow, the magnitude of deformation, and

the temperatures involved greatly inﬂuence the

properties of the formed components. Metal

ﬂow determines both the mechanical properties

related to local deformation and the formation

of defects such as cracks or folds at or below the

surface. The local metal ﬂow is in turn inﬂu-

enced by the process variables.

17.3 Materials for Cold Forging

All metals that exhibit ductility at room tem-

perature can be cold forged. This group consists

primarily of steels and aluminum alloys. How-

ever, alloys of copper, zinc, tin, titanium, beryl-

lium, and nickel are also cold forged for special

applications [Gentzsch, 1967].

Examples of steels that are used extensively

for producing cold extruded parts are:

●

Case hardening steels: unalloyed: 1010,

1015; alloyed: 5115, 5120, 3115

●

Heat treatable steels: unalloyed: 1020, 1035,

1045; alloyed: 5140, 4130, 4140, 8620

●

Stainless steels: pearlitic: 410, 430, 431; aus-

tenitic: 302, 304, 316, 321

Stainless steels usually are not easily forged.

Especially, cold forging of austentic or austen-

tic-ferritic steels (which work harden very

strongly) require high forces and tool pressures.

Furthermore, these materials are difﬁcult to lu-

bricate. Cold forging of stainless steel is some-

times limited due to lack of information on the

behavior of the material [ICFG, 2001a].

Examples of commonly cold forged alumi-

num alloys are:

●

Pure or nearly pure aluminum alloys: 1285,

1070, 1050, and 1100

●

Nonhardenable aluminum alloys: 3003,

5152, and 5052

●

Hardenable aluminum alloys: 6063, 6053,

6066, 2017, 2024, and 7075

Aluminum may be used as an alternative to

steel to save weight [ICFG, 2002]. Table 17.1

summarizes the properties of aluminum alloys

suitable for cold forging.