Rotary splitting — a novel sheet metal forming technique

Journal of Materials Processing Technology, 24 (1990) 225-233

225

Elsevier

ROTARY SPLITTING

-

A NOVEL SHEET METAL FORMING TECHNIQUE

BAUER Institut of P r o d u c t i o n E n g i n e e r i n g , U n i v e r s i t y P.O. Box 101240, D 5900 Siegen (FRG)

D.

Siegen,

SUMMARY A first attempt is given to analyse and describe Skinner's rotary splitting technique theoretically. It is found that this technique is of high kinematical compiexity and quite sensitive to changes in process parameters. Negiecting eiasticai deformation effects a piastomechanical theory is presented to predict the deformation force, depending on tooi geometry, workpiece properties, feed rate and mandrel speed. Results achieved by this theory are compared to those obtained by experimental work. A large difference between experimentei and theoretical values is found and attributed to neglecting eiastical effects. Therefore, in the next step of investigation the author intends to improve his theory and compietes it by these effects. Additionally friction and work hardening effects shali be considered in future, too. INTRODUCTION In 1963 W.J. Skinner has been taken out a patent for a combination of transverse facturing

roliing and metai spinning technology

V-beit puiiey and simiiar components

with round profile~

Skinner cailed this novei chipless forming technique ting

(ref.

I). In the meantime

sucessfully

in automotive

Skinner's

industry

(refs. 2-3).

patent has been appiied

But the theoreticai

metai working process is aimost compieteiy any resuit of research, has been pubiished

Skinner'a rotary spIitting of our investigations

process.

background

of

of this

forming technique

Therefore,

and theoretical

econo-

optimisation

unknown because not

dealing with Skinner's

up to the present.

we started experimental

Rotary Split-

ieading to considerabie

mic benefits with weight savings and structurai V-belt puliey

manu-

two years ago,

investigations

analysing

In this paper first results

wiil be presented.

FORMING PROCESS The principle machinery

of the forming process is shown in Fig. I. The

employed

is simiiar to that used for metal spinning

(ref. 4). Starting workpiece may be a blank of 3 - 6 mm thickness

0924-0136/90/$03.50

© 1990---Elsevier Science Publishers B.V.

226

Forming Railer

Blank

Fig. 1. Principle of Skinner's rotary splitting technique using a driving blank as workpiece and a driven forming roller as tool

227

or a similar workpiece

pre-form

machine.

Forming tool

suitable

material

(ref.

with a central

is centered

5). This

and clamped involved

and shape.

forming

cular to the axle of mandrel. contact too,

Simultaneously

perpendicular mation zone,

of friction

This

appearing

splitting

of

rolling

roller

comes

between tool

is starting

and work-

because the

tool forces

of the w o r k p i e c e - d i a m e t e r

into

it begins rotating,

plastic

defor-

RWS in the contact

2.

localized

plastic

deformation

in radial

and circumferential

workpiece

with an annular

Fig.

workpiece

feed rate of the rotating

and reduction Fig.

rotary

roller

This

of the

along a path perpendi-

When the forming

forces

flange.

mandrel

to transverse

is powered

with the rim of the rotating

by means

piece.

is a free running

Similar

roller

hub and circular

on the rotating

is continuoualy

direction

groove

delivering,

of V-ehape

processing

finally,

a

at its periphery,

1.

DEFORMATION MECHANISM The mechanism o f t h e d e f o r m a t i o n p r o c e s s i s up t o t h e p r e s e n t no a n a l y s i s e x i s t s point

of our i n v e s t i g a t i o n

analysis of the relevant

v e r y complex and

dealing with it,

has been t h e r e f o r e ,

Starting

a kinematical

process parameters e f f e c t i n g

t h e depth

o f p e n e t r a t i o n T and t h e c o n t a c t area o f t h e f o r m i n g t o o l causing p l a s t i c Assuming t h a t following

AK

deformation in the workpiece. elastical

s p r i n g b a c k can be n e g l e c t e d t h e

e x p r e s s i o n s can be d e r i v e d a c c o r d i n g t o

Fig.

2:

BK AK = 2 K2 f 0

(K1 eA + K2 s i n

Where K1 = RWZ - K2; BK = a r c s i n

(1)

a A) d B

K2 = RR; K3 = ( ~ - y ) / 2 ;

a A = K3 B/8 K

(2)

(b/Rwz)

(3)

a + c = RWS + RWZ a

2

+

b2

2 = RWZ

(4) (5)

b 2 + c 2 = (Rws + s) 2

Where B K : a n g l e o f ferential

c o n t a c t between r o l l e r

direction:

and w o r k p i e c e i n

a A = a n g l e o f c o n t a c t between r o l l e r

circumand

228

×

z~Y

Fig. 2. Kinematical process parameters determing the amount of contact area between tool and workpiece.

229 workpiece

in axial direction;

RWS = radius

forming roller; V-groove;

R o = original radius of workpiece;

of deepest point of V-groove; R R = radius

RWZ = outer radius of

of roller edge;

y = shoulder angle of

and s = feed rate of forming roller.

Notice that eqn.

(I) is a t r a n s c e n d e n t a l

one and can, therefore,

be solved only iteratively. The integration matical

of eqn.

expression

(I) is delivering,

finally,

a mathe-

in order to predict the amount of the contact

area A K at the interface

between tool and workpiece.

study of this expression

has been revealed that at constant values

of T the amount of A K is increasing y and s are increasing, that at constant

too.

DEFORMATION

if the values of Ro, RWZ,

R R,

On the other hand it has been found

values of Ro, RWZ,

decreases with increasing

A parameter

RR, y and s the amount of A K

vaiues of penetration

depth T.

FORCE

In the second part of our i n v e s t i g a t i o n s find a p i a s t o m e c h a n i c a i theory

we have been tried to

predicting the deformation

force

F z, Achieving this aim we fitted to our problem a proposai of M.W. S t o r o s c h e w and E.A.

Popow

(ref. 6). These research workers

for the normal stress distribution

o n produced

force on the contact area the foiiowing on = kf Where

(1 + ~A -

choosed

by the deformation

simplification,

Fig. 3.:

~)

(6)

kf is denoting the effective s t r e s s - s t r a i n

curve of work-

piece materiai. MultipIying this stress distribution, ponding

contact area, BK

F

Z

= 2 ~

(I), we get,

eqn.

(6),

by the corres-

finaliy:

~A kf

cos

8 ~

O

[(1+~ A -

~)

cos

e •

0

K 2 (K 1 + K 2 c o s

Eqn.

eqn.

(7) ~)]

d ~ d B

(7) can be soived by the assumption that

kf = kfm = constant.

This means that work hardening of workpiece material wiIi not be taken

into account.

A parameter study of this soiution

vering the following t h e o r e t i c a l results:

Choosing

is deii-

constant

for kfm ; Ro; RWZ ; RR; X and s the amount of the deformation

values force

230

!

--~X

o.

'/

0n=2,27

Fig. 3. A s s u m p t i o n a c c o r d i n g to (ref.

F z decreases regarding,

with

on the

F z is g r o w i n g

of stress 6).

increasing other

distribution

values

hand,

up at i n c r e a s i n g

on c o n t a c t

of p e n e t r a t i o n

constant values

values of kfm,

area

depth

T;

and

of T the

amount

of

R o,

R R and

s.

RWZ,

231

1600

I/,00

J

_J

1200

IOO0 rt

800

u~ o

600

U..

400

/0

200

0

5

15

10

25

20

Depth (mm)

Fig.

4.

Comparison

of e x p e r i m e n t a l

(a)

and t h e o r e t i c a l

(b)

forces.

RESULTS In the and

following

experimental

carbon micro

steel

roller

was

was

Lubricant tions

we

are

results

submitted.

Sheet

material

yield

stress

150 HV 0,05).

were

s = 0,03

employed observed

of our t h e o r e t i c a l

(4 mm t h i c k n e s s ;

R ° = 65 mm.

involved

choosed

work

Stw 24

hardness

deformed

first

RWZ mm/U

was

The

The

initial

geometrical

= 65 mm

and

Kooher

y = 34 ° at m a x i m u m

speed F i00

depth

used

RpO,2

of the

dimensions

R R = 0,3

at a m a n d r e l

of t y p e

radius

computations

mm.

was

blank

of the

The

low

= 290 MPa,

feed

forming rate

U = 180/minute. E. U n d e r

T = 25 mm.

these

condi-

232

E -i

160--i 150

Fig. 5, L i n e s steel S t w 24 1 5 0 HV 0 . 0 5 .

of constant a n d T = 25

microhardness mm. H a r d n e s s

of

HV 0 , 0 5 a t undeformed

low carbon material

233

The resuits

of the force measurement

the theoretical

results

F z was measured

by means

penetration

in Fig.

of high sensitive

depth T by an inductive

The theoreticai

vaiues

But in order to integrate Thus,

we measured

of the workpiece one.

The results

Looking

at Fig.

are presented

deformed

strain

dispiacement

have been computed this equation

the hardness

of our measurement

are presented

piace in the deformation kfm = 1,55

CONCLUDING

to eqn.

are showing

in Fig. hardening

zone.

5. of about

Regarding

this

• Rpo,2 = 450 MPa for the compu(7).

4 the results

not yed good agreement

The Iarge difference of deformation fore,

(7).

REMARKS

As can be seen from Fig.

friction,

eqn

in the cross section

155 % has been taken

of F z according

and the

it with that of the starting

we choosed, tation

gauges

we needed the vaiue of kfm.

distribution

and compared

force

transducer.

by soiving

5 it can be seen that a materiai

finally,

aiong with

4. Where the deformation

with those

between theoreticai

force Fz, couid possibiy

workhardening

computed

and eiastical

we intend to improve

by experiment.

and experimental

attributed

deformation

and compiete

by our theory

our theory

values

to negiecting effects.

There-

by these effects

in the next step of our investigations. REFERENCES I 2

3 4

5

6

C. Packham, Manufacture of one piece sheet metal V-belt pulleys with up to three grooves, Sheet Metal Industries, 55 (4) (1978) 441-445. D.H. Poiitt, The Practice and Potentiai of Flow Forming Processes, in: Proc. Ist. Int. Conference on Rotary Metai Working Processes, London, November 20-22, 1979, IFS-Pubiications, Kempston, pp. 21-32. R. Noppen, Neue Werkstoffanwendungen in der Fahrzeugtechnik, in: Proc. Fertigungstechnisches Koiioquium FKT 85, Stuttgart, October 10-11, 1985, Springer, Beriin, 1989, pp. 67-72. C. Maiiana, H.N. Nagarajan and M.E. Visveswaran, Process Parameters in Flow Forming and how they affect the End Product, in: Proc. Ist. Int. Conference on Rotary Metal Working Processes, London, November 20-22, 1979, IFS-Publication, Kempston, 1979, pp. 2 3 1 - 2 4 2 . G. Thompson and J . B . H a w k y a r d , Crack F o r m a t i o n i n T r a n s v e r s e Rolling, in: Proc. 1st. Int. Conference on Rotary Metai Working Processes, London, November 20-22, 1979, IFS-Publication, Kempston, 1979, pp. 171-184. M.W. Storoschew and E.A. Popow, Grundlagen der Umformtechnik, 1st edn., VEB Verlag Technik, Berlin, 1968.