Influence of die guidance systems on the angular deflection of press slide and die under eccentric loading

Journal of Mechanical Working Technology, 2ll (1989) 463-475 Elsevier Science Publishers B.V., A m s t e r d a m - Printed in The N e t h e r l a n d s

46~

INFLUENCE OF DIE GUIDANCE SYSTEMSON THE ANGULAR DEFLECTION OF PRESS SLIDE AND DIE UNDER ECCENTRIC LOADING H.W. WAGENER1 and C. SCHLOTT2 1 Metal Forming Laboratory, Kassel U n i v e r s i t y , FRG 2Daimler-Benz AG, Sindelfingen, FRG SUMMARY In sheet metal working of large automobile parts, for the alignment of the upper and lower dies two types of guidance systems are used, namely the p i l l a r guides and the heel block guides. The objective of the project is the determination of the angular d e f l e c t i o n , the l a t e r a l o f f s e t and the angular spring constant of the die guidance systems with regard to the performance of the press s l i d e under central and eccentric loading. The results of the experiments reveal that the heel blocks with brass plates produce optimal improvement with regard to die and s l i d e t i l t i n g and l a t e r a l o f f s e t . The use of a combination of heel block guides and p i l l a r guides produces only a small increase of angular s t i f f ness. INTRODUCTION In the competitive conditions of a world wide market the production engineers in metal forming technology are forced to increase the accuracy of the products. Due to the fact that in the FRG more than I0,000 tons of steel sheet metal are used in the automotive industry on a working day basis, t h i s makes sheet metal forming a very important manufacturing process in Germany. To improve the q u a l i t y and the accuracy of sheet metal products and to narrow the range of the required tolerances an important influence is derived from the role played by guidance systems of the presses and of the forming dies. Because of the great number of progressive dies in sheet metal working the influence of the v e r t i c a l s t i f f n e s s and the angular spring constant of presses were the topics of several research projects (refs. I - 6 ) .

Investigations on the influence

of the d i f f e r e n t types of guidance systems of large dies for sheet metal working (e.g. deep drawing) in the automotive industry appear to be sparse. In sheet metal working of large automobile parts, two types of guidance systems or t h e i r mutual combination are used f o r the alignment of the upper and lower die, -

p i l l a r guides consisting of guide pins and guide pin bushings of d i f f e r e n t design and size,

- heel blocks of d i f f e r e n t size with d i f f e r e n t wear plates of brass or PTFE. 0378-3804/89/$03.50

© 1989

Elsevier Science PublishersB.V.

DEFINITIONS In the center of the press bed, a system of coordinates is assumed which describes the x-, y- and z-directions. The positive x-axis indicates the l e f t to right direction with regard to the press front. The z-axis is congruent to the vertical press and die centerline (see Fig. l ) . The vertical spring constant (refs. I-4) is defined by &F cz = ~ ftot

kN/mm

'll

The total elastic deformation f t o t of a press consists of two parts. The f i r s t part is the i n i t i a l deflection, which shows large values of f t o t at r e l a t i v e l y low values of F. This is due to the clearances and gaps of press elements in the line of force. The second part is the linear function of the elastic deflection against the force acting in the press. I f a series of values of the spring constant of several types of presses is available, an empirical function of the spring constant against the nominal force of a press can be used as cz = p *

V~

kN/mm

(2',

By this equation, the press spring constant cz could be determined before the press is made (refs. 3-5).

B

~ BREADTHOF SLIDE

LF

, GUIDE LENGTH

hm , HEICHT OF POLE H ~ POLE Vx : OFFSET IN X-DIRECTION Ky

F1

Fig. I. Slide t i l t

z ANGULARDEFLECTION ABOUT Y-AXIS

Kby I DISTANCEP-P' SLIDE TILT Fu i OEFD~ATION FIERCE Vp

: LATERAL OFFSET

and instantaneous height of pole

I f the t i l t i n g of a press slide under eccentric loading (the angular stiffness of the press) should be described, the angular spring constant is used. I t is defined by the r a t i o of the moment of t i l t i n g Mb to the angular deflection kx,y,z (see Fig. l ) .

465

The angular spring constant (refs. 4-6) of a press is Mb ckx,y,z =

(3)

kNm/mm/m kx,y,z

The moment Mb is the product of the eccentric forming force Fu times the e c c e n t r i c i t y r x , y . The angular d e f l e c t i o n kx,y,z describes the angle of s l i d e tilting

and of s l i d e r o t a t i o n respectively. The c h a r a c t e r i s t i c of the curves

of the diagrams f o r the angular d e f l e c t i o n kx,y,z against the moment Mb is quite s i m i l a r to the curves for the v e r t i c a l spring constant cz. Another parameter which describes the value of s l i d e t i l t i n g purposes is the s l i d e t i l t kbx,y =

for comparison

(see Fig. I)

kx,y * LF

kNm/mm/m * m

(4)

which is the product of the angular d e f l e c t i o n kx,y times the hight of the s l i d e LF and represents the l a t e r a l distance between upper s l i d e edge P' to the lower s l i d e edge P in Fig. Io EXPERIMENTAL SET-UP For the present i n v e s t i g a t i o n an experimental die with p i l l a r guides and heel block guides is employed. The p r i n c i p l e arrangement and the die dimensions

are shown in Fig. 2. ~~

~"-"(~

]ower ~ upper upper lower ~ il

SLIDE

'-- ~L

b+__

BED

I 2 3 4 5

:

: : : :

~

l

UPPERDIE LOWERDIE LVDT-TUBE REFERENCESLAB LVDT (DEFLECTION)

S: 7: B: g: ID:

LVDT (SLIDE TRAVEL) LOADCELL BOLSTERPLATE ANVIL SPECIMEN

Fig. 2. Experimental die set-up

820

T2 . . . T6 rx, ry

LVDT ECCENTRICITY OF LOAD F

466

C y l i n d r i c a l steel test specimen (do = 24 or 38 mm, ho = 40 mm) are deformed in the press e i t h e r in the die center or with an e c c e n t r i c i t y r x , y . The deformation force Fu and the signals of the various LVDTs are recorded. By means of the force reading and the e c c e n t r i c i t y rx,y the moment which is acting on the slide-upper die u n i t can be determined. The values of the LVDT measurements give the basic informations f o r the angular d e f l e c t i o n of the s l i d e - d i e unit about the x-, y- and z-axes by central compression of the steel specimen and by eccentric loading in x- and y - d i r e c t i o n s . For the determination of the influence of the die guidance system on the angular d e f l e c t i o n and on the l a t e r a l o f f s e t of the s l i d e - d i e unit the f o l l o w i n g types of die guides were tested: (a) combination of brass heel block guides and p i | l a r guides (d = 50 mm) (b) brass heel blocks only (c) p i l l a r guides (d = 50 mm) only (d) combination of PTFE (DELRIN) heel block guides and p i l l a r guides (e) PTFE heel block guides only The case (f ) characterises the t i l t i n g

and o f f s e t of the press s lid e alone

(before the die set-up is incorporated in the press).

I

i

[WEINGARTENIiJ ii

J

,

I

.- 2L,00

,,..

58o0

Fig. 3. Test presses The tests were done in three d i f f e r e n t presses (see Fig. 3): I. a s t r a i g h t - s i d e eccentric press of 2,500 kN nominal force, one point suspension, front-to-back eccentric shaft. 2. a s t r a i g h ~ s i d e hydraulic press of 5,000 kN nominal force, one main c y l i n d e r , two motor-pump units. 3. a s t r a i g h ~ s i d e crank press of 6,500 kN nominal force, four point suspension, front-to-back crank shaft.

467

The main press characteristics of the three presses are mentioned in Table I. TABLE I TYPE OF PRESS

UNIT

ECCENTRIC PRESS

NOMINAL FORCE

kN

WORK CAPACITY

kNm

30

LENGTH OF STROKE

mm

400

HYDRAULICPRESS

158

7 to

mln

15

SLIDE HEIGHT

mm

1 160

1 600

PRESSTABLE-DIMENSION

mm

1 200

2 750 x 1 500

MOTOR POWER

kW

2 x

38

MAKE

700

1 070

NUMBER OF STROKES

830 x

6 300

5 000

2 500

• -1

CRANK PRESS

1 900 3 500

x 1 900

132

MOLLER

KRUPP

20

132 WEINGARTEN

TILTING OF PRESS SLIDE OF 2,500 kN ECCENTRIC PRESS The f i r s t series of tests is carried out with the 2,500 kN eccentric press for the determination of the angular deflection of the press slide alone, without the influence of the guidance systems of the experimental die. 1.5 Imm/mI o SPECIMEN . . , , I POSITION OF SPECIMEN : I .,~2

~ o.g ~--] O. 3

UJ

J

-0.3 -o. 9

<

MOMENT Mb
PRESSFRONT

MOMENT Mb>O X'Oi Y ~ 8 2 [mm]

v~'" ~ f/...

2500 NN STRAIGHT-SIDE ECCENTRIC PRESS MAKE : KRUPP

~

-1.5 -180 -140 -100

-60 -20 MOMENT

20

60

100

140

180

] = O.40 mmCLEARANCE 2 = (]. 25 turn 3 = O. 05 mm

Mb [kNm]

Fig. 4. Angular deflection of press slide - t i l t i n g about y-axis. Fig. 4 shows that under off-center loading by the upsetting operations, i t could be observed that for small values of the moment Mb, the values of angular deflection kx increase very steeply. This is called the i n i t i a l t i l t i n g . In this phase the closing of slide clearance and of gaps and the squeesing of lubrication films out of the bearings occur. When the slide guides have close contact with the press gibs, the planes of contact are e l a s t i c a l l y deformed under larger off-center loads; the behaviour of the angular deflection kx has a linear characteristic in this part of the curves, which is the elastic t i l t i n g . Fig. 4 shows also the influence of the clearance between slide guides and press gibs. I f the clearance is reduced from 0.4 mm to 0.5 mm, the t i l t i n g of the slide about the x-axis, i . e . the eccentric loading is in the front-to-back

4~ d i r e c t i o n , is reduced correspondingly from 0.1 mm/m (approx. 7/]00 ° ) to 0.6 mm/m (approx. 3 / I 0 0 ° ) . This also means t h a t the angular spring constant of the press increases from ckx = 160 kNm/mm/m to approx. 266 kNm/mm/m. One other phenomenon can also be observed. The t i l t i n g

of the s l i d e is not

completely symmetrical which indicates t h a t the e l a s t i c behaviour of the press

frame, the e c c e n t r i c s h a f t , the pitman

and the s l i d e guides i s not symmetrlca].

When the press i s loaded on the f r o n t

side or on the r e a r s i d e , d i f f e r e n t

d e f l e c t i o n s are encountered. One o t h e r reason i s the f a c t t h a t the guide system c o n s i s t i n g of the f o u r 4 5 ° - g i b s i s s t a t i c a l l y

i n d e t e r m i n a t e and t h e r e f o r e cannot

be in a s t a t u s of i d e a l a l i g n m e n t . TILTING OF SLIDE AND UPPER DIE I f the experimental die set-up is incorporated in the eccentric press, the behaviour of the press s l i d e is changed considerably with regard to t i l t i n g

of

the s l i d e and upper die. Fig. 5 demonstrates f o r the normal s l i d e clearance of 0.25 mm t h a t the angula~ d e f l e c t i o n is approximately reduced to h a l f i t s values by the d i f f e r e n t guidance 1.5 x[mm/m] x

o

0.9

0.3

~

POSITION OF SPECIMEN :

SPECIMEN f

j

MOMENT Mb>O X-Of Y--B2

PRESSFRONT

MOMENT Mb
d.~6 cl -0.3

~

~

2500 kN STRAIGHT-SIDE

% -o.g

z -1.5 <

X-O: Y-82 [mm]

.... ECCeNTRC i PRESS

CLEARANCE :

MAKE: KRUPP

Sst=0, 25

mm

I

-180 -140 -lO0 -60

-20

MOMENT

20

BO

I00

140

180

Mb [kNm]

" BRASS HEEL BLOCKS & PILLARS ; b " BRASS HEEL BLOCKS c " PILLARS : d = PTFE HEEL BLOCKS & PILLARS e - PTFE HEEL BLOCKS : f " NO DIE GUIDANCE

Fig. 5. I n f l u e n c e of d i e guidance - T i l t i n g

about x - a x i s

TABLE 2 DIE GUIDANCE SYSTEM

INITIAL TILTING [mm/m]

ELASTIC TILTING [mm/m]

ANG. S P R I N G

IMPROVEMENT

CONSTANT [kNm/mm/m

[%]

OF K(f)

0,025

0.38

438

0.03

0.4

416

58

0.09

0.52

320

4[

61

0.06

0.45

370

5O

0.06

0.45

370

5O

0.29

0.74

225

/

4(;!)

systems. Detailed informations about the curves of Fig. 5 can be taken from Table 2 where the data for the maximumeccentric load (Fu = 2,000 kN; Mb = 165 kNm) are recorded. These numerical values describe the effect of the different types of guidance systems on the angular spring constant ckx. The angular spring constant increases from ckx = 225 kNm/mm/m for the t i l t i n g of the slide only (f) to values between 320 to 438 kNm/mm/m, i f the guidance is performed by p i l l a r s (c) or by the combination (a) of brass heel blocks and p i l l a r s . The guidance system (a) shows the best performance with regard to angular s t i f f ness. For this combination (a) the improvement (with regard to the slide t i l t i n g without any guidance system) is 61%. I f the brass heel blocks are employed alone (b), i t can also be observed that the improvement is only s l i g h t l y less (58 %), i . e . in most of the cases i t is not economical to make use of a combination of two types of guidance systems because the improvement of angular stiffness is negligible. The evaluation of the experimental results indicate, that the values of t i l t i n g are strongly influenced by the position of the die guidance system with regard to the z-axis and to the height of the pole of t i l t i n g . I f the values of the angular deflection are multiplied with the height of the slide, one gets the slide tilt

kb, which is the horizontal distance between the upper slide edge and i t s

lower corresponding edge (see Fig. l ) . This is shown in Fig. 6 derived from the curves of Fig. 5 and the slide height of 1,160 mm. This diagram should be plotted i f a comparison of the effect of eccentric loading on different presses is intended. 1.5

oSPECIMEN

~-~ ~

~ ~

-0.3

O

-0. 9

~ ~e

MOMENT Mb>O MOMENT Mb
b o

~.A.~.,~_~ ~ ' ~ " :~f ~,d,e i I -60

POSITIONOF SPECIMEN:

J ~~'--"

,~r

-].5 -IBO -140 -100

! ~

X=O= Y=B2

2500 kN 5TRA]GHT-5IDE ECCENTRIC PRESS

HAKE: KR~P -20

20

60

lOO

140

CLEARANCE: Sst=O. 25 mm

180

MOMENT Mb [kNmI a = BRASSHEELBLOCKS & PILLARS ; b = BRASSHEEL BLOCKS c = PILLARS ; d : PTFE HEELBLOCKS & PILLARS e = PTFE HEELBLOCKS : F = NO DIE GUIDANCE Fig. 6. Slide t i l t

under off-center load - t i l t i n g about x-axis

The comparison of the improvement of the various die guidance systems under eccentric loading about the x-axis (Fig. 5) with the results of the eccentric loading about the y-axis, ( i . e . loading in the l e f t - t o - r i g h t direction) reveals that the values of angular deflection are considerably incredsed (see Fig. 7). The angular spring constant of the press-die unit is 148 to 173 kNm/mm/m only

470

(133 kNm/mm/m f o r the s l i d e ) , i . e . the s t i f f n e s s of the various die guidance systems and the press is reduced to less than h a l f i t s values i f e.g. the press is operated with a progressive die with eccentric loading in the l e f t - t o - r i g h t d i r e c t i o n compared with the s t i f f n e s s in the f r o n t - t o - r i g h t d i r e c t i o n ( t i l t i n g about x - a x i s , see Fig. 5). 1.5

[mm/m] o SPECIMEN

POSITION OF SPECIMEN :

~c Dog c~ i--

MOMENT Mb>O X-82: Y=O

pRESSFRONT

,,-J - 0 . 3 w

MOMENT Mb
¢=l

o. ,..~d,i , ~

J

2500 kN STRAIGHT-SIDE

a~ - 0 . g ~ <

ECCENTRIC PRESS MAKE : KRUPP

-1.5 -180

-140

-100

-BO

-20

20

SO

100

140

CLEARANCE : Sst=O. ~5

mrn

leo

Mb [kNm]

MOMENT

Fig. 7. Influence of die guidance systems - t i l t i n g

about y - a x i s

The reason f o r the good performance of t h i s press and the dies about the x - a x i s is the front-to-back eccentric shaft and the saddle type bearing (center~ l i n e in y - d i r e c t i o n , breadth 189 mm) of the pitman-slide j o i n t . Hence the t i l t i n g s l i d e is supported by the saddle type bearing in addition to the s l i d e guides and press gibs. Fig. 8 c o l l a t e s the r e s u l t s of the test carried out on the 2,500 kN eccentric ANG.DEFLEC. K x ANG. OEFLEC, KX 80 ~

-

~

7oi LLFZ- Bo _I i-/---~

so ~ I z 3oJ A

\

\

"

80 70

\/

BO 50 40 30 20

50----I j , W " x 3o ....I( .

"

\

/i i ! II !I '-q'°

Io o F=O b

% %

O~E G~~o~C~

~e

Go~o~c~

o - BRASS HEEL BLOCKS & P I L L A R S j b - BRASS HEEL BLOCKS c - P I L L A R S z d - PTFE HEEL BLOCKS & P I L L A R S = = PTFE HEEL BLOCKS = ~ - NO D I E GUIDANCE

=ig. 8. Influence of s l i d e clearance and die guidance system on the improvement of the angular d e f l e c t i o n by the die guides.

4?] press. The percentage of improvement of the angular s t i f f n e s s of the guidance system (a-e) r e l a t i v e l y to the behaviour of the press s l i d e alone ( f ) is plotted against the s l i d e clearance of the various die guidance systems. The improvement due to the die guidance is maximum f o r large values of s lide clearance; brass heel blocks and the combination of brass heel blocks with p i l l a r guides have the optimum results. LATERAL OFFSET By the t i l t i n g

of the press s l i d e , a corresponding l a t e r a l o f f s e t vx of the

s l i d e and the upper die is encountered with regard to the press centerline and with reference to the s l i d e face plane (see Fig. I ) . The curves f o r the o f f s e t can also be devided in two parts. At small values of moment Md we have a steep increase of the o f f s e t vx due to the diminishing clearance of the s l i d e and other gaps in the l i n e of force. Af t er that we f i n d the l i n e a r part of the curve, which stands f o r the e l a s t i c d e f l e c t i o n of s l i d e guidance and press gibs and causes the main non-parallelism of s lid e and upper die to the centerline of the press. POSITION OF

~ 0.2

0.4 ,f

SPECIMEN:

~

e

D.D.-q

" 0 _] -0. 8. -C nIJ.I ~-

< d

-1.2

', Q 2500 XN ECCENTRIC PRESS MAKE , KRUPP

800 1600 2400 FORCE Fu [RN]

~ -0.

~

"-~ d "-'- e

2.

X-Ol

Y'-82

1

qC f~.

~ -0.2 _~

0 800 1600 2400 FORCE Fu [J~N]

PRESSFRONTI

0 = BRASS HEEL BLOCKS & PILLARS = b = BRASS HEEL BLOCKS c = PILLARS = d = PTFE HEEL BLOCKS & PILLARS e = PTFE HEEL BLOCKS = £ = NO DIE GUIDANCE CLEARANCE Sst = D. 05 mm

Fig. 9. Influence of the die guidance systems on the l a t e r a l o f f s e t In Fig. 9, l e f t diagram, the influence of the die guidance systems on the offset vy in y - d i r e c t i o n is p l o t te d f o r a s l i d e clearance of 0.05 mm. The o f f s e t is caused by the s l i d e t i l t i n g

about the x-axis shown in Fig. 5 (here f o r a

press slide clearance of 0.25 mm). The curve (f) describes the o f f s e t of the press slide without the experimental die. For the o f f - c e n t e r force of 2.000 kN at a distance of ~ 82 mm from the press c e n t e r l i n e an o f f s e t of + 0,2 mm and - 0,3 mm respectively was measured. By means of the various guidance systems (a-e) the l a t e r a l o f f s e t due to the eccentric loading is very much decreased ( r i g h t diagram). The guidance system (a) and (b) have optimum performance, while the other systems allow s t i l l

an o f f s e t of 0.I to 0.15 mm only; i . e . with

regard to the o f f s e t of the press s l i d e (curve f ) the brass heel block reduce the values of l a t e r a l o f f s e t up to approx. 94 %.

472

The corresponding values of the o f f s e t in x - d i r e c t i o n

(left-to-right)

for

the s l i d e - d i e units (a-e) are up to + 0.3 mm. Because of the large values of angular d e f l e c t i o n

about the y - a x i s (see Fig. 7) t h i s had to be expected. The

reason is again that in x - d i r e c t i o n the press s lid e is supported by the s lid e guides and the press gibs only, because the saddle type bearing of the pitman acts as a free l i n k about the y - a x i s . One f u rt h e r information was gained by these tests. The o f f s e t of the press slid e alone is strongly influenced by the value of the s lide clearance; the initial

offset is approximately a proportional function of the s l i d e clearance.

On the other hand, once a die guidance system is made use of the l a t e r a l o f f s e t is only s l i g h t l y influenced by the value of the s lid e clearance. SLIDE TILTING ON THE 6,300 kN CRANK PRESS During the tests i t is observed that the experimental die-set is quite small f o r the use in the crank press and in the hydraulic press, so that the comparison of the performance of the die on the three test presses is not f u l l y s a t i s f a c t o r y . For determination of the angular d e f l e c t i o n and of the angular spring constant of the larger presses, i t is obvious that the values of e c c e n t r i c i t y had to be increased. Fig. I0 demonstrates that the angular s ti ff n es s of the crank press (which is of the four point suspension type) is very high. The angular spring constant is approx. 1.632 kNm/mm/m which is more than 7 times larger than the value of the 2,500 kN eccentric press about the corresponding x-axis (225 kNm/mm/m, Fig. 5 and Table I ) . Another fact which is indicated by t h i s diagram is that the p o s i t i v e e f f e c t of the die guidance systems is r e l a t i v e l y small

compared with

the guiding properties of the s l i d e guides. This is caused by the small dimensions of the die set, which gives The s l i d e t i l t

i n s u f f i c i e n t eccentric load on the press.

kby is decreased in the case of the crank press to

kby = 0.4 mm/m/m (at Mb = 160 kNm) compared with the value of the eccentric press (kby = 1.0 mm/m/m at Mb = 160 kNm, Fig. 6). The reason f o r t h i s phenomenon is a t t r i b u t e d to large dimensions, the mass of the s lid e and of the four pitmans of the crank press compared with the eccentric press (see also results of hydraulic press). ROTATION OF PRESS SLIDE One of the most i n t e r e s t i n g findings of the tests is that due to the eccentric loading the press s l i d e and also the s l i d e - d i e u n i t rotate about the z-axis in the case of a l l three presses. For the 2,500 kN eccentric press under an eccentric load of Mb = 160 kNm the angular d e f l e c t i o n of the s l i d e - d i e unit about the z-axis is kz = 0.1 mm/m; i . e . the s l i d e rotates approx. 6/1000 ° about the centerline of the press. For the 6.300 kN crank press, Fig. I I shows, that during the upsetting test

473

>- o.e

[mm/m]

~C

~ Ld -J

,

.au

- 1 0 0 0 - 7 5 0 -500 -250 0 MOMENT

:

MOMENT

c,de

Mb > 0 X=7041 Y=O

MOMENT Mb < 0 X=-704:Y=0

6300 kN ERAN~( PRESS MAKE : WEINGARTEN

u~ - 0 . 8

z <

~

I

LJ

-0.4

~

...J

PRESSFRONT

0.0

OF

POSITION SPECIMEN

= SPECIMEN

250 Mb

500

750

[mm]

1000

CLEARANCE Sst=O.I

[kNm]

o = BRASS HEEL BLOCKS & PILLARS; b = BRASS HEEL c = PILLARS; d = PTFE HEEL BLOCKS & PILLARS e = PTFE HEEL BLOCKS; F = NO DIE GUIDANCE

:

mm

BLOCKS

Fig. I 0 . I n f l u e n c e of the d i e guidance systems - t i l t i n g

E

0. I0

o SPEC|MEN

"L~ b. e

E

O. 0 5

PRESSFR0.T

N 0. 00

~

'l~=.~l" ~

~- -0.05

~ ~ /.,4"~

POSITION

OF

SPECIMEN

:

about y - a x i s

x-o, Y--740 t,.]

~ '

CLEARANCE : S s t : O . I mill

~

6300 kN CRANK PRESS .

MAKE : WEINGARTEN

-0.

10, 0 -I000 - 7 5 0 - 5 0 0 - 2 5 0 MOMENT

Fig. I I .

250

500

Mb

[kNm]

750

1000

Influence of d i e d i e guidance systems on s l i d e r o t a t i o n .

at small values of e c c e n t r i c moment (Mb = 370 kNm) the s l i d e i s r o t a t i n g in the negative direction

(kz = -0,02 mm/m). With i n c r e a s i n g moment the d i r e c t i o n of

r o t a t i o n is changed and at the end of the e c c e n t r i c compression of the steel specimen (Mb = 910 kNm) a p o s i t i v e r o t a t i o n of 0.05 mm/m takes p l a c e . This f i n d i n g i s an e f f e c t of the s t a t i c a l

indeterminateness of the s l i d e

guidance and suspension system, which is in the case of a f o u r p o i n t suspension of a higher degree than the one p o i n t suspension of the e c c e n t r i c press. The r e s u l t s i n d i c a t e also t h a t the s e l f - e q u i l i b r a t i n g

f o r c e s of the s l i d e guidance

system and of the d i e guidance system are f o r c i n g the s l i d e - d i e u n i t during the c l o s i n g of the s t r o k e in an a n t i - c l o c k w i s e r o t a t i o n .

While the s l i d e and the

upper d i e t u r n in clockwise d i r e c t i o n when under heavy o f f - c e n t e r l o a d i n g the a c t i o n of these redundant forces i s reduced. TILTING AND OFFSET ON THE HYDRAULIC PRESS When the t e s t s are c a r r i e d out on the 5.000 kN h y d r a u l i c press, i t

i s ob-

served t h a t due to the size of the experimental d i e t h i s press also cannot be loaded to i t s f u l l

e x t e n t . There i s another d i s t u r b i n g i n f l u e n c e by which the

e v a l u a t i o n of the instrument readings i s made d i f f i c u l t .

Due t o the l a r g e mass

474 2.50

o SPECIMEN __

=.e

1.2s. ~"

•

/l~l

O.O0

~:~

PRESSFRONT:.e

-1 2 5 - - - ~ , j

~

~-

~' 4~d -BOO -BOO -400 -200

POSITION OF SPECIMEN :

Jc ~

''-

"~,°

r

MOMENT > 0 X-525: Y=O MOMENT< 0 X--525: Y'O

;mOOWNHYOL

-2" 50

[mm]

WamE, mOLOm

0

200

400

BOO BOO

MOMENT Mb [kNm] HEEL B L O C K S & PILLARS; b

o = BRASS c = PILLARS; e = PTFE HEEL

d = PTFE BLOCKS:

= BRASS HEEL HEEL BLOCKS & PILLARS F = NO O I E G U I D A N C E

BLOCKS

Fig. 12. Influence of the die guidance systems - t i l t i n g about y-axis.

UPPERDIE PAD

UPPERDIE PAD

1.2

POSITION OF SPECIMEN:

S cl.e job

O.B

,T. 0.4

k

~ o.o

o.o

I. X-O= Y-82

I

TM

-

J

-0.4

800 lBO0 2400 FORCEFu [kN]

-0. 4

o

800 1600 2400 I I ~ J

]

FORCEFu [kN]

Fig. 13. I n f l u e n c e of d i e guidance systems on l a t e r a l

offset.

of the press slide and hydraulic piston (approx. 40 tons), the slide and the upper die h i t the upsetting specimen with a certain impact (impulse) so that the whole system vibrates at the beginning of the forming process. This phenomenon is visible in Fig. 12 which shows the angular deflection of the slide if~ and of the slide-die units (a-e) under off-center loading. The angular spring constant of the slide (f) is approx. 300 kNm/mm/m, while the values of the die guidance systems are only s l i g h t l y higher. Even under these large values of moment there is no clear positive influence of the d i f f e rent die guidance systems because of the large impulse of the slide-piston mass and the dominant effect of alignment of the large slide guides alone. Fig. 13 shows for the hydraulic press that the performance with regard to lateral offset is also not s y ~ e t r i c . The front-to-back offset of the slide under the e c c e n t r i c ]oad (Fu = 2.000 kN, rx = + 82 mm) i s l , l respectively (left

mm and 0,2 mm

diagram). The r i g h t diagram i n d i c a t e s the i n f l u e n c e of the

d i e guidance systems. There i s a c l e a r l y defined tendency of the s l i d e - d i e u n i t f o r a displacement in y - d i r e c t i o n .

Also in t h i s h y d r a u l i c press the brass heel

blocks p e r m i t a small angular d e f l e c t i o n and o f f s e t of the s l i d e - d i e u n i t on!y;

475

i . e . the brass heel blocks produce optimum angular stiffness among the tested die guidance systems. CONCLUSIONS By means of the tested die guidance systems the values of slide-die t i l t i n g , offset and rotation are reduced considerably; the improvement is in some cases (brass heel blocks) about 60 % compared with the t i l t i n g of the slide without any support by the die guides. The second best performance show the PTFE heel blocks and f i n a l l y the p i l l a r guides only. I f a combination of heel blocks and p i l l a r guides is used, only a minor improvement of the angular stiffness is observed. Also very small values of slide clearance (0,05 mm) have only very l i t t l e positive effect on the angular stiffness of the slide-die unit. Due to the results of the experiments the die designers

additionally gain

by the following informations for an optimal selection and design of the u t i lized die guidance system: -

Moment and lateral forces due to eccentric loading are mainly borne by the die guidance. For this reason the strength of the guidance elements should be maximum and the pressure between area of contact of slide guides and press gibs should be minimum. - The height of die guidance should be maximum, so that the alignment is effected before the forming process is i n i t i a t e d . The height of the upper die should be minimum,to reduce the height of pole of t i l t i n g . - Because of the fact that the guidance system of the slide and the guidance system of the die are s t a t i c a l l y indeterminate a very accurate manufacturing and alignment of the two systems individually and as a combination are the prerequisites with a view to optimum angular stiffness.

REFERENCES ( a l l in German) I. C. Krug and G. Schneider, The stiffness of machine tools, Werkstatt und Betrieb 87 (1954)2, p. 50-65 2. H.D. Watermann, The accuracy performance of forging hammers and percussion spindle presses under off-center loading, Werkstattstechnik 53 (1963)8, p. 413-420 3. W.Schwer and H.Hoppe, The accuracy of mechanical presses, Mitt. DFBO (1968)7, p. 90-95 4. H.W.Wagener, Stiffness of mechanical and hydraulical presses for impact extrusion of steel, wt - Z. ind. Fertigung 62 (1972) p.257-261 5. M.Hanisch, The performance of straight-side mechanical presses for impact extrusion under central and off-center loading, Dr.-Ing.-Dissertation Techn. Universit~t Hannover 1978 6. G.Silberbach, G.Mareczek and W.Wegener, Slide alignment of metal forming machinery, ll.Umformtechnisches Kolloquium Hannover, M~rz 1984, 4 1-17