Cold Forging of Hollow Cylindrical Components Having an Intermediate Flange - Ubet Analysis and Experiment

H. Kudo (1). Yokohama National University/Japan; B. Avitzur und T. Yoshikai, Lehigh University/USA; J. Luksra, Stanislaw Staszic University of Mining and Metallurgy/Poland; M. Moriyasu. Toyo Denki Seizo K. K./Japan; S. Ito. Tokyo University/Japan

iummnry: I ' o s s i h l c i o l d i'ergint: opei.:it i o n < to Corv hol I O U c y l indric:il co:npo!ic:its having 3 circular intcrncdiatc flnngc n:.c firrr p r o p o s d . i h c n;atcl-i:iI deformat i n n :int! r o r g i n g prcsrurc.; Tor tlicsc opcr;it ions a r c then ::ilculatcd h!, : i i r ~ n i o F tllc L.oi;iputcr-:i idc<! u p p c r Iloun(l I lcircntal i ' echni$ ;uc iUIlT.7 I ]iro::r:im, the Iii~sic conccpt of \>hicII i s I>a.crcl on t h e Iini? i'lcnerlt I lcg ions d!ic f i r s t t o EuJo. :iit!i the emer:;cncc o f :hc coin]'utcr revolution, :!ic u r c o i ?l ie Unit i:lcncnt Rcqions I\:I.< i~rplementcJ a s tiic 1iIll:'i' program h y \\-it:ur a:iJ otlicrs.

In the ?resen? study it is a s ~ u s c d that t h e aatcrinl i s non-i:arrlcnin!:, ;+nil tlic fricrional stress over the :ool-i~orkliiece interfaces is negligible. Cold f o r g i n g cspcrimcnts bit11 anncalcd aluirinium billets or slugs are :il.so !ierForined to observe dcCornation, d e f c c t forlaation and iiorking pr iacntal rcsul ts a r c comparcJ iiith the tlieorct ical results whjcli a r e oht;tincd hy mod non-hardening rcsults to iillov f o r thc riork-!iardcning. The coincidcncc is found t o I I C iair. binall?;, thc relative iserits : ~ n d Llemcrits ar.ong the propcscd forging mcthods itith regar,! to tiic load . unit pre . s iurc , energy and defect iirc discusseJ on the hnsis o r the thcorctical anJ cxpcrimcntal results.

1 . Introduction

The present work attempts t o develop a method for optimisation o f deformation sequence to produce cold forged components. Kaiser(ll, Soackf?), Lengycl and Venkatasuhramanian(3) have presentcd computer methods of assessing the production cost for selected cold forging processcs. So systematic method, however, of designing p o s s i b l c deformation scquences that are to he evaluated has hitherto been suggested. In the first part of the present p a p e r , thcreforc, an a',- proach is attempted by marking every characteristic part of a component and hy constructing all possihle combination.s and arrangements of the marks. The shape and the dimensional symbols of the Component consider- ed - hollow cylinder having an intcrmediate flange - a r e shown in Fig. 1. Physically possible deformation sequences which start from a solid billet o r slug are first sorted out and thcn those which contain at least an operation that requires a press machine with triple or more actions are excluded. Those that contain meaningless extra operations are a l s o p u t aside. The sequences to he evaluated are thus ohtained.

In the second part of the paper, the industrially p o s - sible deformation sequences thus sclcctcd out a r e evaluated by means of the IJpper Round Elemental Tech- nique (URET) due to Avitzur , Iobst and McDermottlJ) in regard to the forging load, tool pressure, forging energy and material displacement. Experiments with aluminium are conducted of some of the deformation sequences considered to confirm the validity of the IJRET, since only a paper that compares the URET and experiincntal results has heen published by Thornton and Rramley(4) to date. The evaluation of the IJRET in the light of the present experimental results is done in the third part of the paper. Finally, the optimum deformation sequences are suggested and dis- cussed with regard to the force, energy, product defect, material loss and necessary number of opera- t ions.

2 . Suggestion of Industrially Possible Deformation Sequences

As is scen in F i g . 1 , each characteristic part of the finished component is marked first, i.e., the flange by I:, the tube wall by I<, and the through hole by H. In the following layout of the process, these symbols

(a) S l u p o r billet (h) Finishrd product

Fig. 1 Shapes and Dimensional Yotations for Starting Slug o r Rillet and Finiched Product

will denote the operations of finishing the parts. In mans cold forging opcrations, the final shape and di- mensions of a component part are attained after pre- forming operat ions. These rough shapes and, accord- ingly, preforming operations will he denoted by f, w and h corresponding resliectively to I:, W a n d ! I , see F i g . 1. The mark h denotes the cavities, the liottoni of which is punched out in tlic operation H.

The nirmher of permutations of the 6 marks is 7 2 0 . This means that the number of formally possible d e f o r - illation sequences is 7 2 0 when only a part i s formed in each operation. In a permutation, however, onc or rlore groups of neighhouring marks mav h e parenthesized to .shov that the plural parts a r e simultaneously formed in one operation. 'The number of possible sequences Ix'comcs, then, extremely high. Moreover, each sequence has B few variations dependinR on the shape and size of the starting hillet o r s l u ~ .

There is a rule for excluding physically impossible arrangements. .4 small lcttcr cannot be preceded hy the capital letter. A small letter parenthesized bith the capital letter is meaningless. .Any smcill letter that does not appear before the operation including the capital letter should then be deleted. There are also technically meaningless sequences. The operation W o r ( N i l ) that comes after h, F and w will be such that shown in Fig. 3 , in which w is backward extruded to form H without full support. The attain- able reduction in area i s low and there is a chance of forming folding defect when a small fillet radius between F and W is needed. The deformation sequence, therefore, will be considered only for difficult workpiece materials. The operation f that precedes F , see r i g . 4 , wil.1 not be significant, unless the mate- rial is s o hard as to require intermediate annealing. The operation F after W is liahlc to cause folding or skin inclusion defects in the material, see F i g . 3 , iinless the Flange volume is relatively small.

Lencrally, the combined opcrations that include a number o f marks require press machines having multi- action construction, c.g. Fig. 6 . Since triple o r more action presses are unusual, the deformation se- quences that need such presses are left out of consi- deration. On the other hand, the numhcr o f operations

r i a . 2 Votations f o r Fig. 3 Example of Oper - ation W Performed Preforms of

Component Parts after h , F , and w

Annals of the ClRP Vol. 29/1/1980 129

f a ) I: artcr I h ) I: after Li and I{ W and h

Fig. 4 Example of Operation F Fig. 5 Examplcs of Preceded by f Dpcration F after Y

advancing punch

(a) (h1:W) operation (b) (hW) oper:it ion

Fig. 6 Examples of Operation That Requires Press Machine Having Triple o r More Action Mechanism

in a sequence increases as the combined operations arc eliniinated. .After all. three families of deformation sequences are regarded as adequate and are summarized in Fig. 7 . The marks h,, h;, w1 and w2 represent upper and lower cavities and walls respectively. To avoid the use of triple action machine, forming of the upper and lower parts of the component is arranged to be carried o u t in two separate operations.

3 . Analysis and Evaluation of the Processes by Weans of the URET

The sclectcd deformation processes, see Fig. 7, a r e subjected to the UBET analysis t o obtain the load, pressurc, work donc, and material movement. The com- puter program 'Axiform' is used which is described elsewhere(4). In the analysis, the workpiece is di- vided into unit elemental discs and rings each having a rectangular section as has been proposed hy Kudo[GJ, and is illustrated I>y the broken lines in Fig. 8 . Thc zone boundaries are assumed to shift without rotation, satisfying the volume constancy. The current rate o f plastic work is calculated on the hasis of the von Flises yield criterion with a constant flow stress k, and the L6vy-Yises flow rule. The current rate of frictional work is also calculated with an assumption that the frictional stress is constant. The boundary velocities that minimise thc total ratc of work are assumed to give the most likely deformation mode and an approximate forming load is calculated from the minimised rate of work. In the present work, the frictional stress on the tool-material interfaces is disregarded.

Fig. 9 illustrates and compares the diagrams of thc load-flow stress ratio F/kf against the punch distance from the bottom dead point s-s , f o r the five deforma- tion sequences chosen from F i g . 7. The component dimensions to he produced are predetermined as d f - 4 5 mm, d c = 30 mm, d l = 2 4 mm, l i e = l l e = 2 5 . 9 mm and s, - 2 . 9 mm, sce Fig. 1. Thc slug volume is then 17810 m m 3 when the thickness of bottom t o he punched out I S assumed equal to s e . The curvcs for (hFW)H-1 and hH(FW)-1 show an intcrmediate step. This indicates that the expanding outer cylindrical surface of thc

hH[Fil) and h(HFY) Fan i l j . .

(hFW) Family

Fis. 3 Deformation Sequcnces Selected out for Considcration and Evaluation

undersized slug has reached the container surface, see Fig . 8 .

So curves for the punching operations are shown in Fig. 9. By assuming that no fracture takes place throughout the process, the maximum punching load and thc total work are given rcspcctively hy

The maximum load and punch pressure, and thc work done ohtained from Fig. 3 and F q u s . ( I ) and f I I arc s i ~ m m a - rized in rahle 1 f o r comparl\on.

130

hH ( F Y ) - I , H( FW) - 1 , 2. h(H%!!-I: 1st stage

N l 1 1, 3

1st 1 2 2 5 0

- 2nd ' 3100 Lf - .G

r - - I 1st 4300 = I

* 5 2nd 126 I E

the sale: 2nd stage I

I I 4.97 14160 1 47540 2 1 1

3.51 33380

3.57 37920 38100 2 1

0 . 2 8 180

the same: 3rd stage hH ( FU) -2, H( FV) -2, h(iiFU)-Z: a l l staqes

N I

I & I

1st 5000 5.-1 36640 - 36820 i z Y I

(hFW)H-l: (hFA)H-l : (hF:d)h-l: 3rd stage 1st staqe 2nd stage oIFW)H-2: all stages'

I

1 i I

F[hlUl)(h2W2)H-l: F(hlWl)(h2W*)H-4: F(hlWl)(hZU,)H-i, 2, 1st operation I 1 s t Operation 3 , 4: 2nd operation

t ' y I 1st I 2100

I

c s , < 1 2nd 1 I 2100

rl 1 3rd

E. h

1630

5 1 A 4th 126

-

Fig. 8 i)ivision o f Workpiccc into Unit Klemental Regions: Dottcd Zones Represent Currently Deforming \rca

I I

1.32 4960

4.64 12000 I ! . 26420 4

3.64 9280

I 0.28 180

s - 5 , m

!ig. 9 Load-Stroke Diagrams Calculated hy UBET in Some Deformation Sequence.; to Producc Component Havins df = 5 5 , d, = .in, J 1 = 2 4 , L l 0 = L i o = -75 .9 and se = 2 . 9 nim

The process [hFK)H-: requires the highest load, while F(hi t i ; I [li., I<, ) H - l requircs the minimum load and energy at the cost of a largcr number o f operations and more complex machinc mechanism. The loads required f o r (hlX)I.(-l and - 2 arc considerably lowcr than f o r h(lll~lV)-l and - 2 . Thc differences in thc load hetween l l ( l ~ F l ~ ' ~ - l and - 2 and betvecn ihf%"l- I and - 2 a r c rather trivial. 'The highest punch prcssure for the 1st oper- ation in hlllFW)-I is attributable partly to the thin interinediatr Iwttom thickness o f 2 . 9 inm, and partly t o

Table 1 Comparison of Maximum Loads, Punch Pressures, kork Done, Numhers o f Required Operations and Maximum Sumhers of Actions Seeded to Press Machine f o r Different Deformation Sequences to Produce Idcntical Component Specified in Caption of Fig. 9

the vclocity field adopted in the analysis. I f the thickness were increased, a lower punch pressure would result on the expense of a larger discard volume.

In order to make comparison between the results of the UHI'.T analysis and the following experiment with an- nealed aluminium, a mean equivalent straii F, is cal- culated in the way proposed hy Kudo[hl. The incremen- tal strain (d, , ,j i attained in the i-th deformation increment produced by an incremental punch stroke ( A H ) i is expresscd as

where F i denotes the average force for the i-th step and Vp the current deforming zone, this being shown by the dotted zone in Fig. 8 . The mean equivalent strain at the end of the i-th step is thus

lrm)i = Z(A?m)i (4) i

Ry expressing the f low stress curve of the workpiece material by

kf = kfl T " (5)

where kfl and n are the material constants, the mean flair. strcss kfm at the end of the i-th operation is given by

i k f m l i kfl Gm)in (6)

'The forging load F is then calculated from

-2. Experimental Work and Discussion

Thc cxperimental material is annealed aluminium of 99.80: purity Kith a Vickcrs hardness of 18.5. All specimens are turned to an outer diameter do of 30 f=d;), 5 8 or 45 (=df)mm and an appropriate length Lo. The specimcns to be used f o r the processes h(HFW)-1 and 2 are horcd beforehand so that the cup extrusion h and punching H are eliminated. The specimens are lubri-

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cated with Johnsons wax 1111 and are fo rged cold in a 1 WX hydraulic press at a speed of shout 12 mm/s. The load F and ram stroke H are (letected by a strain-gaugc type load cell and a differential transformer typc transducer and are recorded by an elcctro-magnetic type X - Y pen writing recorder. lhe 1:-tl diagrams thus rc- corded are illustratcd in Figs. 10 to 1 3 by the thick chain-dot, solid, and hroken lines.

Stroke H nm

Fig. 10 Comparison of 1:xperimcntal and Theore- t ical Load-Stroke Diagrams f o r l l ~ l W ) - l Process-[FW) Operation; d o = 38 me, thick line - experiment, thin line - theory

To calculate the load for the present material, a com- pression test of the cylindrical specimens is carried out u p to a logarithmic strain of 2 . of the flow stress curve indicates that it is approxi- mated well by Equ. (5) within thc strain range from 0.05 to 2 when 125 N / m m 2 and 0.272 are substituted for k f l and n respectively. The forging loads thus calcu- lated from Equ. (7) are shown in Figs. 10 to 13 by the thin chain-dot, solid, and broken lines. The coincidence between the experimental and theore- tical curves is generally fair, but the latter tends to lie above the former by an increasing distance 3s the deformation progresses. Thus the overestimatc made by the theory of the actual forging load reaches 30% in some instances. The same trend was observed by one of the authors[?]. In the calculation of I: hy the use of Equs. ( 4 ) and ( 6 ) , thc mean flow stress kfm often exceeds 180 N/mm2. Rut the maximum Vickers hardnesscs that are determined on the cross sections of forged specimens never exceed 5 4 , and the avcrage hardnesses are around 4 5 . From the generally accepted correlation between the flow stress and Vickers hard- ness. e.g., Ref. [ a ] , the flow stress values used in the calculation are supposed to be considerably higher than the actual. Since no consideration has bccn paid to the possible Rauschinger effect due to rota- tion of the relative direction of maximum strain to the material element, it is likely that Equ. (6) would have overestimated the actual flow stress[9].

A log-log plot

400

z Y

U

3 200 0 -I

0 C 10

Stroke H nm

Fig. 11 Comparison of Experimental and Theore- tical Load-Stroke Diagrams f o r H( I : lu ’ ) - ? Process-(ri\‘) Operation; do = d f = 4 5 mm, thick linc - cxperimental, thin line - theory

In Figs. 10 and 1 2 , the intcrmcdiatc rapid r i s e in the cxperimcntal curves is not so marked as the theo- t?tical. This is cou.;ed h y the fact that thc side surface o f the ilsnge has either a barrel- o r an over- hanging-shape and it cones i n t o contact with the con- tainer surface QraJual l y .

The levels of thc cxpcrimentally determincd maximiim load lower in the order of (hF#)ll-l-lst operation, IhFW)II-Z--lst o?cration, F(hl\t’i 1 Ch2li’> J H - l.-..lst opern- t ion, h(llFW)-l-2nd operation, and h(llFW)-2--2nd operation. Although the order of the first and second

I I I 1

Stroke H mi

Fig. 1 2 Comparison of Experimental and lhcore- tical Load-Stroke Diagrams for ( h F Y ) H - I Process-(hl:W) operation; do = 38 mm, thick line - experiment, thin line - theory

I d i = 2 7 , S , = 4 . 4 0 mm

L Y

LL

V

-I

\\ ---

I

f 1 I

5 10 Stroke H mn

Fig. 13 Comparison of Experimental and Tlieore- tical Load-Stroke Diagrams f o r (hl:W)II-2 I’roccss-(hPlv’) Opcration; d = df = 4.5 mm. thick line - experiment, th?n line - theory

132

proccsscs and that of the fourth and fifth processes arc the reversa15 of t'lclse of the IIHI:T aniiysis, the diffcrenccs arc sinall. This reversal would have heen caused by the higher flow stresses for fhWjH-1 and h[HI:W)-l due to the higher amount of work. The fact that the load of F(hlWIiIh,U,JH-l is the third highest results from harreling o f thc side surface of the flanye being deformed. In the cxpcriment an extra load iias needed to obtain the square edge of the flange. In the IJBET analysis, however, no barreling is assumed.

The levels of the total deformation *ork observed es- perimentally lower in the ordcr of hfHI:Wj-I, hfHFWj-2, ( I i F ' O H - I , (hFWjH-2 and F(hlIC1 j ( h 2 N 2 ) t l - l in accordancc with the theoretical result, sce Table 1.

V

(a) Folding in hH(FW)-I, fhl Skin inclusion in H(FWj-1, and hH(I;W) - 2 , H( FIVj - Z , F ( h I w I J [ h, 1\2 ) I I - 3 and hffilWJ-2

(c) Bore contrac- I d ) Peripheral i e ) Peripheral tion in hll(r#j-?, thinning in thinning and I l ( F l V ) - 2 and (hFh')Il-l and skin inclusion h (HfW) - 2 F(h,vl) (h,w2)H in (hlSjHF

- 2

Fie. 14 blcchanism of Ikfect Formatiol,

( a ) Fold in flange (b) Skin inclusion in flange

(c) Flange thinning (d) Skin inclusion in wall

Fig. I5 Photographs of Some Defects Ohserved in Cold Forged Products

The present experiment displays some product deiects that are not predictable by the U R E T analysis. In Fig. 14, they are summarized together with the schemata to show their formation mechanisms. Some photographs of them are shown in Fig. 15. The fold shown in (a) is hardly observable in the fhFlOti-1 process, though do IS 38 me. Since the overall upsetting took place first, see Fig. 8 , (hFW)H-1-1st stage, the period of the second stage would havc bcen too short to cause the overhanging flow, see Fig. 1J(aj. The skin inclusion of the type of F i g . 14(b) is not observed in (hFW)H-2. This is attributable to the fact that only a small volume o f material from thc flange part f l o u into the wall part in this process compared with hHIFY)-2, h IFW) - 2 and h (HFW) - 2 .

The contraction shown in Fig. I4(c) occurs when the flange thickness is reduced to, say, double the wall thickness(?). This results in a rough orange peel-like suriace of the product bore opposing the flange. The thinning of the flange periphery, see Fig. 14(d), is caused by the expansion of the flange due to internal pressure. When the flange diameter was large, say 60 mm, necking and fracture were observed in the flange, see Fig. 1S(c). The tvpe of thinning shown in lig. ll(c) is observed when'the material is extruded into the flange part from one side o f the central asis. In addition, the skin inclusion appears when the material is extruded from the wall part into the flange, see Fig. l5fd).

5 . Conclusion

In order to choose industrially possible deformation sequences t o produce hollow cylindrical components having an intermediate flange by cold forging. a method is proposed in which every characteristic part of the component is marked and the marks are arranged in different orders and comhinations. This enables us to envisage all possible dcformation sequences. After deleting physically impossible and industrially inade- quate sequences, several sequences are picked up that deserve consideration.

They are evaluated by the UBET analysis and the expe- rimcnt with aluminium in regard to the load, punch pressure, energy consumption, number of necessary operations, intricacy of machine mechanism needed, and product defect. Comparison of the theoretical and ex- perimental results reveals that t!ie IIBET analysis p r o - vides us with a proper references in regard to the Forces and energy. Rut it fails to predict most of the product defects encountered.

It is concluded that the process (hF1C)Il-Z is the most advantageous, sincc it produces sound products with a moderate energy consumption and thc least niimher o f operations in a single action press. The conclusion will be changed when harder vorkpiece materials are to he employed and the flangc volume is relatively small.

Acknowledgement The present authors thanks Doei Kogyo Co., Ltd. and The Furukawa Electric C o . , Ltd. f o r providing us with the experimental tools and aluminium bars. They also wish to cspress their thanks to blr. M. Tsuhouchi and Miss. Y. Harada o f Department of blechanical Engineer- ing, Yokohama National University, f o r the aid in carrying the experiment and preparing the type-script. It is also to be remarked that the present internation- al cooperative work has been done by the aid of the scholarship granted to Avit:ur by Japan Society for the Promotion o f Science.

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References KAISER, H., Umformcnde Rearbeitung in flexihlen Fertigungssystcmen, Bericht IFII, llniv. Stuttgart, R d a ( i a 7 - 1 I . . I * < . . . . XOACK, P . , Hechnerunterstut:te Arhcitsplaner- stellune und Kostenberechnune beim Kaltmassiv Urnforme; von Stahl. ihid.. B4: (19791. LENGYEL. B. and VENKATASUBRA~~ANI~K, 1.1'. , Optimi- sation in the Cold Forging of Steel, Proc. 18th Int. M . T . D . R . Conf., 153 (1977). A\'ITIUR, R . , IOBST. J%: and %lCDER;XOTT. R . P . . - . Asiform - A Computer Simulation Prograi for .\xi- symmetric Forging and rxtrusion, Proc. 6 N . A Y.R.C. 1 7 4 ( 1 9 7 8 ) THORKTON, j.1.. and BRkblLEY, 4 . S . , in .Approximate Vethod for Predicting !Ictal I'low in t:orging and Extrusion Operations, Proc. I .Y.E., 194 (1980) KUDO, H., Some Analytical and Expcrimcntal Studies of Axi-Symmetric Cold Forging and Extrusion - I , Tnt. J. Mech. Sci., 2 , 102 (1960). KllDn, f l . , the same as above - 11, ihid.,~,91~196])* TABOR, D . , The Physical Meaning of Indentation iiardness, Sheet Metal Ind., 31, 745) (Sept./l954). KUDO, t l . and OZAWA, S., Correlation between Plastic Deformation and Vickcrs Hardness, J. Hardness and Strength Study, 7 7 , 11 fWay/1968).

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