Analysis of the behaviour of two coupled hydraulic Müller-presses equiped with multi-die-sets

Analysis of the behaviour of two coupled hydraulic

Müller-presses equiped with multi-die-sets

Citation for published version (APA):

Singh, U. P. (1975). Analysis of the behaviour of two coupled hydraulic Müller-presses equiped with multi-die-sets. (TH Eindhoven. Afd. Werktuigbouwkunde, Laboratorium voor mechanische technologie en

werkplaatstechniek : WT rapporten; Vol. WT0370). Technische Hogeschool Eindhoven.

Document status and date: Published: 01/01/1975

Document Version:

Publisher’s PDF, also known as Version of Record (includes final page, issue and volume numbers)

Please check the document version of this publication:

• A submitted manuscript is the version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website.

• The final author version and the galley proof are versions of the publication after peer review.

• The final published version features the final layout of the paper including the volume, issue and page numbers.

Link to publication

General rights

Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain

• You may freely distribute the URL identifying the publication in the public portal.

If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license above, please follow below link for the End User Agreement:

www.tue.nl/taverne

Take down policy

If you believe that this document breaches copyright please contact us at:

openaccess@tue.nl

providing details and we will investigate your claim.

c.orrec'hdJ I.I:.,f ok>/: &9-I-~

Analysis Of The Behaviour Of Two Coupled

Hydraulic Muller - Presses Equipped With

Multi~Die-

Sets

U. P. Singh

Report Nr. PT 370

December 1975

Division of Production Engineering

Eindhoven University of Technology

The Netherlands

Correc list:

Page 6-_ y ~ll N

L

3

nun

Page 28: Model 2 ~s represented by fig. 7.2.

Pages 34 and 35: in equations (8.4), (8.6) and (8.8) "N" is changed by "tTl! Page 53: a being small i.e. a 5° instead of d = 5.

1 • 2. 3.

4.

5. 6. 3.1. 3.2. 3.3.

3.4.

Notation Introduction Process

The external forces acting on the system The technological force

The spring force The cylinder force The damping force

The behaviour of the press and tool during punching The finite element method

The beam element

Page 3 7 11 12 12 14 16 16 20 22 23 7. The modelling of two hydraulic coupled Muller presses 25 7.1. The cylinder force implication model (model 1) 25

7.2. The hydraulic spring model (model 2) 27

8. The analysis of a die-set 32

8.1. The modelling of two hydraulic coupled Muller presses equipped 32 with multi die-sets.

8.2. Th.e analysis of the bottom plate of the die-set by means of the 36 classical method of Mechanics.

Conclusion 45

Appendixes:

Appendix 1: Geometrical accuracy of a press. 47 Appendix 2: The influence of the clearance between the sliding 55

surfaces of ram and guide columns of a press on the misalignment of the die and punch.

Appendix 3: The material characteristics. 58

Appendix 4: The optimal clearance between a die and punch 60 Appendix 5: The hydraulic system of the 2000 Ton Muller press. 62 Appendix 6: The control system for the parallelism of the ram 70

References Sunnnary

of two hydraulic coupled Muller presses.

72

73

3 -NOTATION

=

= =

=

=

=

=

the punching force perimeter of cut

initial thickness of the blank

ultimate tensile strength of the blank material shearing coefficient

diameter of punch

compression force per unit area g shear modulus

A relative elongation

=

=

=

the cylinder force

liquid pressure inside the cylinder liquid pressure inside the delivary pipe diameter of the piston

FIl' F2l' F3l "" forces in the cylinders KO·i, K03 & K02 of left hand press respectively

FIr' F2r , F3r

=

forces in the cylinders KOl, K0₃

&

K02 of right hand press respectively

Fldl' F2dl Fldr' F2dr Cl, C2 er the the 1 the Ml the Mr

=

the

=

the distances of the points of application of FIl' F 21 from the center of the ram L of the L. H. P.

=

the distances of the points of application of FIr' F2r from the center of the ram R of the R.H.P.

= the damping forces on the ram L the damping forces on the ram R

=

_{the distances of the points of application of F 1dl ,}

F2dl from the center of the ram L

=

the distances of the points of application of F1dr' F2dr from the center of the ram R

=

coupling forces on the coupled rams Land R

= the technological force on the ram R

distance between the point of application of Ftr

&

center of the ram

length of each of the coupled rams moment on the left ram L

moment on the right ram R

[NJ; [ton

J

[NmJ;

[N~

; [ N/nnn2] [ N/nnn2]

[nnn

J

[ ton]

[ rom]

[ ton] [ tonJ

[ rom]

[

rom]

[rom]

[ ton

~

[ ton m]

nl' n Z E F I a V W cp (F) (K) (X) (K-I) R a

=

the nodal points number

=

the modulus of elasticity of the beam material

=

cross sectional area of the beam

=

second moment of area of the cross section of the beam the angle between the local x-axis of the beam and the global x-axis of the structure

displacement in x-direction

=

displacement 1n z-direction rotation about the y-axis

=

force

stiffness matrix displacement inverse matrix

=

the force applied to the clamping bolt for die plate

=

the force exerted by Press

= the length of the

be-de

hole

=

the distance between the clamped edge and the edge of the downfall hole in the bed

[ degrees] [mm]

[ rrnn

J

~ad

] [ N ]

[ - J

[ rrnn ]

[

-

]

[ rrnn

J

X

=

the distance between the clamped edge of the die plate and

b h Z n d H

e

liZ par llpar

the place.where the guide pin or the bush is fixed the breadth of the bott.om die plate

=

the thickness of the bottom plate

the clearance between the die and punch number of guide pins

diameter of guide pins

=

the height of the bush or the guide pins

=

the angle of rotation of the section of the plate

the misalignment of the die and punch due to non-parallelism _, of the surfaces of the bed and ram

=

non pHralle.lism of the surfaces of the bed and ram

[ rrnn

J

[rrnn]

[rom

J

[ rrnn

J

[

-

]

[ rrnn ]

[ nun

J

~ad

]

[rrnnJ

hI = the magnitude of the. stroke depending on the kind of process

1 the length of the ram

~Zperp the magnitude of misalignment of the die and punch due to nonperpendicularity of the guide columns to the bed

~perp the magnitude of the nonperpendicularity of the guide columns to the bed

~Zpl

=

the magnitude of the misalignment due to non-planeness of the meeting surfaces of the bed and the ram

~pl

=

the magnitude of nonplaneness of the meeting surfaces of the bed and the ram

a distance between the axes of bed and the die

~Zc

=

the total amount of misalignment equal to the sum of the misalignments ~Zcl and ~ZC2

~ZcJ

=

the amount of the misalignment between the die and punch

due to horizontal displacement of the ram within the. limit permitted by the clearance between the Sliding Surfaces of the ram and the guide columns

=

the magnitude of misalignment between the die and punch due to fitting of the ram within the limit of the clearance

between the Sliding Surfaces of the ram and the guide columns C

=

the amount of clearance between the Sliding Surfaces of the

a1 a2

n

ram and the guide columns

=

the angle between the Sliding Surface of the guide columns and the central axis of the ram in horizontal direction the length of the Sliding Surface of the guide column

=

the distance to which the upper part of the die.set moves out of the Sliding Surface of guide columns

=

ultimate tensile strength of the blank material stress characterist s

=

strain hardening exponent

[mm

~

[mmJ

[mm ]

[mm

J

[ mmJ

[mm ]

[mmJ

[mm

J

[mmJ

e Re v d U llP_sr }.. s y 1 g E n llP th

=

2.7number of Neyer

correction factor in the Nadai formula

the Reynold number

=

the velocity of liquid flow

= the female diameter of the delivery pipe

= the viscosity of oil

=: _{the loss of pressure due to surface roughness}

= coefficient of friction

=

absolute surface roughness

=

the density of the oil the length of the pipe

=

gravi ta tional force

=

the loss of pressure due to local resistance (bending pipes)

coefficient of resistance

=

number of bends in the pipe

of

the total loss of pressure due to surface roughness and local resistance

[ -J

[ - J

[ N ]. [kg

mm2 ' cm2

J

the

[-J

[-J

[~2

]; [:!2

J

7

-1. Introduction

It was observed that the punches used for making holes in the sidemem-bers of(DAF) industrial vehicles were generally out of order after having punched nearly 2.000 products. This was considered being too small number of products for a single set of tools. Hence

search regarding:

was requested to start

re-explanation of the reasons of the short tool-life. 2(a) increase of the life of the present tools.

(b) design of new tools with higher pE'..r£ormanceand longer life.

Punching of holes in sidemembersis performed on two hydraulic coupled presses (fig. 1) equipped with multi-die-sets (fig. 2). The rams of these presses are coupled together to provide the possibility of reaching two purposes:

1 punching of sidemembers(f . 3) of length ranging from -5 to -9m. 2 creation of countermoment through coupling against rotation of

rams due to eccentric loadings.

The loading capacity of each of the presses is 2.000 tons. Each of them is equipped with its seperate control system to protect against overloadings. When the rams, however, of these presses are coupled together, only the left-hand press is being controlled (see Appendix 6). The number of holes to be punched in single sidemember is nearly 200. With a V1ew to the large number of holes to be punched, the punching process is done in four consecutive steps to avoide an eccessive loading of the presses.

It is known that among other factors, misalignment of die and punch has a vital influence on too~life, whereas misalignment depends upon:

I. The geometrical accuracy of press and subpress (die-sets) (See Appendix 1).

2. The clearance between the guiding surfaces of press and subpress (See Appendix 2).

3. The deflection due to the bending of several parts of press and subpress.

Although an attempt has be'~n made to determine the magnitude of the misalignment caused by and 2, the main part of the investigation deals with detailed analysis of the misal due to the deformation (3) of press and subpress, as deformation of press and subpress has dominating

in-, upper platen 2 rnam cylinder k0₂ 3 main cylinder k03 4 rna in cylinder k0₁ 5 coupling unit 6 ram 7 column 8 press table

Ill!

~---I---t I" i I I I I , I

I

II II I "I I

I

I I

I

ij~

sc!oo._ .. _

---~-i

Fi g.1

9

-fluence on the misalignment of die and punch.

In order to calculate the displacements due to the distortion of the e.ntire system of press and subpress under the condition of eccentric loads~.

a beam model computer programme based on the method of finite elements was applied with fair success [1J.

-o

Fig. 2 The block of die-sets

I.-top plate; 2,3,4,8.-auxiliary plates; 6.-rubber-spring-plate; 7.-guide bush; 9.- punch; 10.-die-plate; 11.-bottom plate;

12.-blank; 13.-bush holder; 14.-guide-pin; 15.-fixator; 5.-guide-pin holder. L 830 2135

64S

tt 1

~+i+++

+++ +

+

I·· .•

+

+

_{+ ...}

~

-+ 41 + + + + . $ ..

+

₊

+

e

+

\

+

+ +

j:§+

+ + + + + _{\ •• $ ••}

....

• • ++

!~

I~

~

+

+

+ + ~U')

+

+ + + +

--

c - - _ _ _ . _ _ _ _ .____ _ _ _ c:--. t--- _-==-

2. Process

The sidemembers are made of steel 37 and steel 52. The length of the sidemember, depending upon the requirements,varies from ~5 to -10 m and its width is 400 rr~. The thickness of the sidemember from 6.5 mm to 7.5 mm. The total number of holes to be punched is about 200. These holes are of mainly ~ 10mm; ~ 11.5mm; ~ 13mm; ~ 15mm;

$

17mm; ~ 20.5mm; ~ 24mm;

$

50mm and

$

60mm.

Keeping in v~ew the economical aspect of the process, the present die-sets consist of several blocks. Each of these blocks may contain several

seperate tool-units to provide the possibility of quick adaptibility to the punching process of sidemembers of different lengths.Each of the tool-units

is equipped with its own spring system to plate.

the punches out of the

blank-Considering the large number of holes, the punching process ~s per-formed in four consecutive steps to avo ide the excessive loading of the pres-ses. Calculation for determining the punching forces and the distortions of the system due to these forces needs to be done seperately for each of the successive steps.

Each of the coupled presses equipped with its own hydraul dampers to overcome the effect of the possible dynamic impact on the system, which often occurs at the end of the punching process.

3. The external forces acting on the system

Fig. 3.1 shows a schematic view of two hydraul ic presses equipped with

F1dl

F2dl

F.1dr

r

F

Il

F _~l

c!

~

F

r

~~

Frz

r

~

~

i3r

~'

_1'-'"

_~"

_~""

_~'"

_~

~"-

_~

"-

_~"-

~.",

~

~~

V

_~

_~

_~

_~

_~

~v _po.::

_~

_{~ ~}

_~

_~

_~

_~

V

V

J!I ~ E:I rt

V

[V'

~ I f:1 It ~ iU

_./

"""

f"III

'"'"

'"

I""" t2'ZZ

If

~ l

-It

""

V

l/

_/'

V

/

~

_~

_{~ ~}

_~

I

t:\V

V~

!

~

~ ~

~

1

R:

/

~

_14-

~V

_Vi

I"';" ~

/

...

-

...

/

/

I

!

I

I

V

l,/

I

i

I

/'

/ I I

/

~~ ~

'"

~

~

~

'i V1

~:r

~

~

~

'~M~

'Ff"

.~~

"J

_!/

~

V

v

_/'/~-~

/

_V

V /

. •

m

/

1

/

I P71f7f "VM'A

41

V

/

I.. \. '\...~'f T,{'\. ,N

V

'" '"

"".

~

"" ""

'"

'"

/

~ ~.

' "

~

"'e'l'\.

~

~

1/

V

V /

/

/

/

/

/ / /

V

_/

V////rF{/'

/

I l '\. '\... '\. .'\. '\. '\. '\.'\.'\.'\.'\.'\. !'\. '\... \. '\... '\.'\.'\.'\. '\. '\. '\. '\. '\. '\. '\. '\. I.J

tj~~/~

r.~)(

Ir-'~ '\ T\

~f{~'\

(~ \

1;-'",_\\

\

~

'\

<~

Fig. 3.1 two hydraulic coupled presses.

multi~ie-sets.Ihese presses are coupled through their rams and are under the action of the following external forces:

3.1. The technological (punching) force Fp 3.2. The spring force F

sp

3.3. The cylinder force F or FR _L 3.4. The damping force Fn

3.1. The technological force

The formula for the force required to punch a given material assuming that there is no shear on the punch or is given bye 2 ]

or where L = d = ho °B K f =

for any shape

for round holes

perimeter of cut in rom diameter of punch in rom

thickness of the blankplB.te in rom

ultimate tensile strength of the blank material in shearing coefficient

(3.1.1.)

(3.1.2.)

In case of a product (sidemember), where holes of different diameters are to be punched simultaneously, the fonuula (3.1.1) can be written as

where d. ~ n. 1. = = m I: i=l 1T d. n. ~ ].

diameter of i-holes to be punched in i-number of diameters to be punched.

rom.

The characteristics of the material used for sidemembers table 3.1.

Table 3. I .

Kind of material

(3.1.3.)

given in

Detail information about material properties and about the calculation of punching force are given in Appendixes 3 & 4 ively.

3.2. The spring force

For stripping the punches out of blank holes generally springs are used. Once the punches are in contact with the blank, the springs are being compres-sed gradually with downward movement of the ram. The compression of the springs continues to increase throughout the last two successive steps.

The following two types of springs are being used in the present die-set:

3.2a. rubber springs (fig. 3.2.) with nonlinear characteristics 3.2b. coil springs with linear characteristics.

The formula for determining the compression forceof a rubber spring,the application of which is confined to tool-units only, is given by [~.

where f g A f g (A - 1/1.. ) 2 2

compressionforce per unit area (N/mm ) shear modulus

S

S

o

=

relative elongation.

The results of the calculation of compression force of rubber springs for each of the tool units are placed in table 3.2a.

3.2b. Coil springs are used in the two front blocks of the die-sets and their compression forces, which have been taken from the tool design section of the DAF, are placed in table 3.2b.

Table 3.2b.

no. of steps I II III IV compression

Table 3-2a ₁₅

-S no. Rubber Dimensions of rubber plates Compression

\ of Hardness Force (x104 N) units (SH) S

I

L B N Ao Step Step (mm) (mm) (mm) number (mm2 ) III IV 00 60 2 x 20 100 200

I

36000 5.4 9 80 200 02 60 2 x 20 100 200 36000 5.4 9 80 200 03 60 2 x 20 80 150 2 24000 3.6 6 05 60 2 x 20 80 200 36000 5.4 9 100 200 I ! 06 60 2 x 20 80 250 2 40000 6 10 07 60 2 x 20 70 160 24000 3.6 6 80 160 08 60 2 x 20 100 200 2 40000 6 10 09 60 I 2 x 20 100 200 2 40000 6 10

~

10 60 2 x 20 100 200 2 40000

I

6 10 I \

L

I !

/

/

)\

i

I

I

~~)

'/

I

I

,

I

Fig. 3-

20

Rubber plate

I

1 1 60 2 x 20 100 230 23000 3.45 5.75 70 200 5 15 60 2 x 20 70 300 3 156600 23.5 39.15 ! 70 240 2 , 16 60 2 x 20 100 220 I 37400 5.61 9.35 70 220 17 60 2 x 20 70 250 8 140000 21 35 18 60 2 x 20 70 250 2 35000 5.25 8.75 19 60 2 x 20 I _{135 275 37100 5.6 9.3} . 20 60 2 x 20 70

!

100 2 I I 14000 I _{2. 1 3.5}

-!

21 60 2 x 20 70 200 2 28000 4.2 7 23 60 2 x 20 80 120 , 2 19200

[ Z.

88 3.8

3.3 The cylinder force:

~~en the loss of pressure in the delivery pipe due to its geometry

and surface roughness (see Appendix 5) is inconsiderable, the pressure in the main cylinders can be regarded to be the same as in the delivery pipe. Then the force exerting on the piston of the cylinder (see Appendix 6) can be written as:

where P P

=

PI

=

D

=

PI liquid liquid F '" p • c pressure pressure diameter of the 2 'lTD inside inside piston (3.3.1) the cylinder (N/mm2) the delivery pipe

(mm)

In case the system is activated by cylinders of different diameters, the formula (3.3) can be written as:

where D. 1. n. ~

=

F c 'IT P

4"

D.n. ~ 1.

diameters of i-pistons (rom) i-number of diameters

3.4 The damping force:

(3.3.2)

In view of the insufficient information available about the design geometry of present damper in the system, it was not within the easy catch to find out the damping force either analytically or experimentally for each of the successive steps of punching. However, this difficulty is to overcome assuming that for particular moment of punching, the damping force, which is of dynamic nature, is constant. Then the magnitude of this damping force can be determined from system of equilibrium, pro-vided other parameters of the system are known.

Fig. 3.4-1 The force-scheme acting on the coupled rams. When Fn == _F31 F_1r == F 3r FIdl F2dl F1dr = F1dr and 11 12 13 == ₁₄ c 1 c3 ;:: c4

the above force scheme of the coupled rams in fig. 3.4-1 can be simpli-fied as

Fl

- - - _ ....

111--Lf

Fig. 3.4-2 The simplified scheme of fig. 3.4-1

where F1 =

_Fll

_{+ F21 + F3l} (3.4.1) F _r == _Fir + _F2r + F_3r (3.4.2) Fdl Fldl +< F2d1 (3.4.3) F dr == F1dr + F2dr (3.4.4) F tr == F p + F sp (3.4.5) e + e (3.4.6) r sp

The positions of the forces F

11, F21, F3l, F1dl, F2dl, FIr' F2r, F3r, F

ldr, F2dr, Fcl & Fc2 with respect to the center of each ram are known from the geometry of the presses, whereas the position of the techno-logical force F can be determined as

r m e = (3.4.7) m • Z 1 (F . + F . ) 1."" pr1 Sp1

where FSPi e . pr1 e . Sp1 = forces FP₁, FP2' FP3t ••• FP m due to 1, 2, 3, •• m cutters (N) = forces FsP

1, FSP2' Fsp~.FsPm due to I, 2, 3, •• m spring plates(N)

the positions e

1r, e2r, e3r, . eprm of the I, 2, 3,.m cutters (mm)

= the positions e I' e , e 3, •• e of 1, 2, 3,.m springs sp sp2 sp spm

block plates (mm)

Now from the system of equilibrium as shown in fig, 3.4.2, yields~

LYI = 0; FI ± F - Fdl :::: ₀ (3.4.8) cl LY 0; F r r

+

Fc2 Fdr 0 (3.4.9) EMI 0; _{Fl x 0 + Fdl x} 0 ± F x 1/2 = 0 (3.4.10) cl EM = 0; F x 0 + F dr x 0

+

x 1/2 + F

.

e = 0 (3.4.11) r r tr r

From the effectiveness of the control system, it is known that the move-ment (M) on each of the ram can not exceed 600 ton m, provided this occurs beyond the time limit 0.2 sec.

Hence Ml = ± M = :;: r F c) • 1/2 < 600 t.m F • 1/2 + F • e < 600 c2 tr r t.m (3.4.12) (3.4.13)

Substituting the value of Fel from equation (3.4.12) into (3.4.8), yields

Fdl

=

FI ± F _c1 (3.4.14)

Similarly

F

dr = F r :;: F e2 (3.4.15)

where _Fdl the resultant damping force on the left ram (L) F

dr the resultant damping force on the right ram (R) FI = the resultant cylinder force on the left ram F ;::; the resultant _{inder force on the right ram}

r F

c I' Fc2 = coupling forces.

However the damping forces have been neglected in further calculation because of their points of appl

the coupled rams.

4. THE BEHAVIOUR OF THE PRESS

&

TOOL DURING PUNCHING

During the process of punching the system of presses and subpresses is loaded like a closed power flow circuit (fig. 4.1), Under the action of eccentric loads the distortion of the system occurs and its magnitude depends upon the magnitude of moments about the rams.

Power Upperframe cylinder of the press

t

Columns of

Piston the press

t

Bed of the press Ram

t

I

Bottom plate of

I

die-set'

t

Top plate of die-set _Die

t

Punch Blank

Fig. 4. 1 Power flow cycle scheme of the system.

As a result of the distortion, the coupled rams of the aforesaid system try to form the shapes as shown in fig. 402 a, b, c, d.

--0~-a)

EI--"_-9_"

----I~-"~-=-t--r---b}

q-·3-- -'

---'---1" c) d)

Fig. 4.2 a), b), c), d) - various shapes of the coupled rams.

Die-sets, which are mounted on the coupled rams, will consequently tend to follow the shape of distorted rams and the magnitude of the mis-alignment of the die and punch v,lill great

the displacement of these rams.

5. THE FINITE ELEMENT HETHOD

The finite element method an analytical procedure whose active development has been persued for a relatively short period of time. The basic concept of the method, when applied to problems of structural ana~

lysis, is that a continuum (the total structure) can be modeled analyti-cally by its subdivisions into regions (the finite elements) in each of which the behaviour is described by a seperate set of assumed functions representing the stresses or displacements in that region. These sets of functions are often chosen 1n a form that ensures continuity of the des-cribed behaviour throughout the continuum. In other cases, the chosen fields do not ensure continui and nevertheless enable satisfac-tory solution but do not feature the rigorous assurances of convergence possessed by the fully continuous analytical models. If the behaviour of the structure is characterised by a single differential equation, then the finite element method, in common with the series and the finite dif-ferential schemes, represents an approach to the approximate solution of that equation. If the total structure is heterogeneous,being composed of many separate structural forms in each of which the behaviour is described by a distinct differential equation, the finite element approach continues to be directly applicable [~.

In common with the alternative procedures for the accomplishment of numerical solutions for practical problems in structural mechanics, the finite element method requires the formation and solution of systems of algebraic equations. The special advantages of the method reside in suitability for automation of the equation formation process and in the ability to represent highly irregular complex structures and loading

si-tuations.

The type of the elements, which are commonly employed in practice various such as beam element, triangular element, rectangular element, tetrahedronal element, rectangular hexahedronal element etc, Considering the economical aspects of the elements, the beam element was preferred to use for our purpose of investigation.

6. THE BEAM ELEMENT

All the elements of press and subpress (die-set) can be described as slender elastic beams. Because of the product size (L x b

=

5000 ~

10000 x 400) the moment Mx about the x-axis compared to the moment My about y-axis, can be regarded as negligible. Therefore the displacements due to the moment My are much more important than displacements due to Mx and henceforth only the displacements in the X-Z plane are taken into account. The model was built with finite number of such elastic beam ele~

ments and for each of these elements the following features are given:

n l , n2 == E F I Q

z

x

---._.x

Fig.6.1 Beam element nodal point numbers

modulus of elasticity of the beam material cross-sectional area of the beam

second moment of area of the beam cross section (m4) the angle between the local x-axis of the beam and the global x-axis of the structure.

Each of the nodal points contains three degrees of freedom.

1. 2. 3.

u

w

c:p displacement 1n X-direction displacement 1n Z-direction rotation about the Y-axis.

In each nodal point other elements can be coupled. When two or more

elements have the same nodal point number ,it means there is fixed coupling between them. It also possible to couple one or more of free-dom of different nodal points and thus a hinge can be simulated (see fig. 6.2).

---n~1~·~~n~2---Fig. 6.2

The stiffness characteristics of an element are calculated from E, I, F and 1. These characterist of all the elements of the model are

joint together in a big stiffness matrix

(K).

The relation between the loading (F) of the press and the displacement (X) due to this

can be written as

[5] :

or (F) (X) (K) (X) (K)-l (F) (8.1) (8.2)

Thus coupling the inverse matrix (K)-l of the stiffness matrix (K)

25

-The Modelling of the two coupled Hydraulic M~ller Presses.

The modelling of the hydraulic presses can be successfully done in two ways:

1. Applying the forces directly in place of hydraulic column cylinder (Cylinder force implication model).

2. Representing the hydraulic columns of the cylinders in the structure as springs (Hydraulic spring model).

Both types of model possess their own merits and demerits. Though the total number of elements in the spring model 2 of a structure compared to that of the cylinder force irilplication model 1 is larger, the model 2 has got wide range of practical pos 1i as, e.specially when van.ous types of products need to be manufactured. Variation in types of the product automatically leads to completely different cases of loading in the cylinders whose determination experimentally proves to be laborious and expensive. This is all true when the pressure Ln the oil columns of the cylinders remains unaltered. Once the pressure in the oil columns starts to vary; the spring model seems to be unreliable~ Therefore the utility of the spring model with respect to the model is limited one. The present hydraulic coupled M&ller presses, which

are equipped with the ram parallelism control systems, have been modelled in both ways. The analysis of the computed results indicates that while model responds satisfactorally to the experimental facts, the model 2 fails to respond the same. This can be explained in a way that under the condition of eccentric loads on the coupled rams of the system, the pressuresin the cylinders of the left hand press (fig.7.2.). are kept

on varying by the regulating system of the control device throughout the punching process, which can be easily verified from the experimental pressure data as shown in table 7. I .

. 1. The cylinder force implication model (model I).

The nodal points 1,2,3,5,9,7,31,30,28,26,22 and 24, as shown in fig.7.1., represent the vertical columns of the left hand press (L.R.P.) of the coupled presses, while 11,15 and 20 represent its top frame. Similarly the nodal points 32,33,35,37,39,62,61,60,58 and 56 represent the vertical columns of the righthand press (R.H,P.) and the nodal points 43,48 and

52 represent the top plate of the frame. The nodal points 4,6,8,12,13,10,14, 16,17,18,21,19,23,25,27 and 29 represent the ram of L.H.P., while 34,36, 38,40,44,45,42,46,47,49,50,53,51,5.5,57 and 5.') represent the R.H.P. rarn.

Each pair of the nodal points 9,10;21,22;41,42;53,54;3,4;27,28~29J34~35,36; and 59,60 may establish contact to each other within the pair itself

under the condition of an eccentric load to the system of coupled presses. In the model I and model 2 the aforesaid nodal points of each pair are

coupled in X-direction, but they, except 29 and 34, are free in Z-direction. The coupling of these nodal points of each pair in ~-direction is subject to the consideration of the direction of the moment on each of the L.H.P. and R.H.P. rams. For instance, when the direction of the moment on both coupled rams is clockwise as sho~~ ln

21,22; 35,36 and 53.54should be coupled

.4.2.c, the nodal points 3,4; ~-direction. But, in case when the direction of the moments is ant~clockwise (fig.4.2.b.), these nodal points are to be kept free in ~-direction and nodal points 9,10;

27,28; 41,42 and 59,60 should be coupled in the moment on the L.H.P.-ram is clockwise and

ion. In case, when

ant~clockwise on the

R.H.P.-ram (fig.4.2.a.), the nodal points 3,4; 21,22; 41,42 and 59,60 need to be coupled in ~-direction. For the reversed case i.e the moment on L.H.P,-ram ant~clockwise and clockwise on the R.H.P.-ram (fig.4.2.d.),

the nodal points 9,10; 27,28; 35,36 and 53, should be coupled in ~-direction. The nodal points 29 and 34 in both the models ! and 2 are coupled in

X and Y-direction, while in the dire~tion ~ they are free. The axes of the cylinders KO

l, K02 and K03 of L.H.P. coincide with the respective assumed straight lines passing through the pa~r of nodal points 11,8; 15,16; and 20,23. The axes of the same tern of cylinders for R.H.P. coincide with those respective assumed straight lines passing through the pair of nodal points 43,40; 48,47 and 52,55.

The directions of the resultant action of the damper for L.H.P. and R.H.P. coincide with those of the direction of the assumed vertical lines passing through the respective pair of nodal points 15,16 and 48,47.

When the rams of L.H.P. and R.H.P. are coupled together, for each of the punching steps the resultant technological force on every ram needs to be taken into account seperately. In model lone of the resultant forces together with F

1L, F2L, , FIR' and F3R should be introduced, while

the point of action of another one should be suppressed in vertical direction only. However, when there one such resultant force, the point of its action should be suppressed. For the case of sidemewher 513262 the point of action (nodal point 44) of resultant technologicalforceFTR has been suppressed in vertical direction and for sidemember 179738 the point of action of FTR has been suppressed and the magnitude of the resultant technological force FTL has been introduced.

The results of the computation of the model I, for punching cases of

sidemembers 513262 and 179738 are placed in tables 7.1.1 and 7.1.2. respectively. On the basis of both the experimental and the computed results for the above reffered sidemembers. the shape formations of the coupled rams, as shown in figures 7.1.1 and 7.1.2, have been determined.

2. Hydraulic spring model (model 2).

The frames and the rams of both the coupled hydraulic presses are represented by the same number of nodal points as model 1. The elements 59,60 and 61

represent the cylinders KOI' K03 and K02 of L.R.P. respectively. The nodal points 63,64,65,66,67 and 68 are coupled with respective nodal points 11,8,15,16,20 and 23 in the direction Wand U and are free in ~-direction.

Similarly the elements 62, 63 and 64 represent the cylinders KO

l , K03 and

K02 of R.R.P. respectively and the nodal points 69,70,71,72,73 and 74 are coupled with respective nodal points 43,40,48,47,52 and 55 in the direction Wand U only. The conditions for coupling the nodal points 3,4; 21,22~9,10;

27,28~35,36;53,54;41,42;59,60 and 29~34 remain the same as for model I.

The results of the computation of the model 2 for punching case of sidememb er 513262 are placed in table 7.1.1 together with the results for model I.

Model 1 @ 11 @ 15 @ 20 @ 24 39 ® 43 @ 1.8 @ 52 @ 56

t

F2L ® 26 37 _® 58 ® F'L ® F21 @ F,JL @l ®

.~0~~®~~@~@~@~®~~~@.~~@+@~~~@~@~*@~.@!!.~@~7~@~~~~~~~~+=@4

31 I. 6 8 12 13 14 17 18 19 23

VS

21 29 34 35 36 38 1,0 47

~9

50 51 55 57 59 ® @ 11 63 @ ® 31 L ® 2 CD ® z ₃₀ ~===:::::C>X 31 33 • Nodolpoint number

o

E~~m-eot number

fj~ .Beom model of the two c~.l.d hydraulic Muller Pr.sse.

Model 2 @ 15 @ 20 _® 21. 39 @ t.J @ 1.8 @ 65 67 69 71 ® Z 30 33

lL:,

(j) 31

~

F/g.?-2. ModeL 2. ® 62 52 @ 56 73 ® ® 58 @ ~ Lo 57 59 @ 61 ® 62

Table 7. 1.1.

,

.

Side member 513262; Length = 4925

rom;

Thickness = 7.5

rom;

St 52 KFS

S. No vertical displacements

{W)

of nodal points

(rom)

Left hand side press Right hand side press

of computed

steps

r-__

I I _ _ - r __ - . ____ - r __ -4 ____ - r __ - r __ - . ____ - , ______

~~--~~~~E-xp--e-r,i-III-en-t-a-l_.--

__

+-____

M~od~e-l--l-.--

__

=~===:M=0=d=e~l=2==~====;==

FIL _F2L

J

F3L

I

_{FT•L jeL} FIR tF2R

I

F3R r FT. R eR

;~S.NO.Ofp~~:;;

4 I 29(34) 59 4 29(34) 59 4 129(34)

!

59

'

(Ton) ,(Ton)(Ton)I' (Ton) !,I (m) (Ton) I(Ton) (Ton) (Ton) (Ton) S.No. I

I

' I

of s tens i • I i II 17 21 ~ if 17 -I

I

!

I

7,140

1 92 -IV

I

226 282

i

226 1 -I

i

I Side member 179738; ~ S. No

Left hand side press of steps 107 134 107'348 : 1.16 I 10 0.9 13.7 0 0.96 4.3610 1 _{6 • 5} - 262 333 262 677 1.266 I I - 326 404 326 943 0.734 III

J

1377 r 302 808 -0.388

IV

Table 7.1.2.

Length = 6090

rom;

Thickness == 7.5

rom'

,

Right hand side press

I

I

2.5 2.37

-2.51

vertical

o

o

o

1.4 _3.35

_I

₀ ,0.3 2.95 0 I 0.6 -3.45 0 St 52

KFS.

displacements (W) of Experimental model

I

2.05 1-9.4 0.8 -IS 1.

35 /-8

j

a

o

o

nodal points (rnm) computed 1 model 2

!

I

I

I

FIL

I

F2L

i

_{F3L , FT. L eL} FIR

I

F2RJ F3RI FT•R

I

eR S .No.of nodal 4 29(34) 59 I 4 129(34)

I

59 4 129(34)

~

i

(Ton) ITon)(Ton); (Ton)1 (m) (Ton) (Ton)(Ton): (Ton) I (m) _{S.No •}

I

!

I

! r

!

I

I

, i j I 1 I i of steps

i

I

100, I I I 124 324 i 1.265 I 0 1.5

I

3.5

a

0.9 4.4

-I

-

-

-

-

-

100 1-46

I

=~:

i

=~~

i

256 325 2561 677 1.266 I I 2.3 0

[I.

3 ! 2.62 0 1.8

-

-I -I _,

-

-

i 14 I 330/ 978

_:

I

III 1-11 60 2.91 330

i

414 0.523 III

_I

0.3 0 0.75 0 0.13

-

I

-i

.

I

-+

1 1 . 4 T

1-1.

2

1

I

19

I

!

18 1 16 1 I 3401 I 0 3 0

-

-IV

16 90

I

1.69 340 4211 1011

I

-0. 68 1 IV !

_I

, i i I !

I

15.4

I

i

I 1. 1 ! i 14

I

i5

I I

I

I

,

59

-t I

I

I

I

N

'"

2

nd

Step

3 rd

Step

4 th

Step

--

... '-....lL---- - - -

---.---,

---

\

_4'----,

---

--

----fig

7 -1-1

Lf) N I Experimental d

- -

- - -

Computed

without

tool

2nd step

-

.... ....

-tIl

r--

---3rd

step

r--"IiiiiE"':-~~-=:§:'t::_~_==_=+:'--~::::::----:::?'"=--I ~ - - - - . _ _ _ -" _ _ _ _ _ _ _ _ _ _ _ -..J

4th

step

- - - - Experimental

- - - Computed without tool

7-1-2

N

-8. rhe analysis of a die-set.

In view of the complexity of the press-structure it is economically advantageous, in case of necessity, to modify the structure of a die-set only from the system of press and subpresses (die-sets). With this

purpose an attempt has been made to investigate the influence of some significant parameters of the die-set on the misalignment of a die and punch.

From literature [6, 7J it is known that the bending of the guide pins and the bending of the bottom plates are the most dominant factors causing the misalignment of the die and punch. The influence of the geometry (length and diameter) of the guide pins on the misalignment of the die and punch has been evaluated by means of beam model 3 of the coupled Muller presses equipped with mult~ie-sets as shown in figure 8.1. While the influence of bottom plate geometry\as shown 1n fig.8.6 has been analysed by the classical method of Hechanics.

The numerical analysis of the coupled presses equipped with multi die-sets has been done in the same way as in the case of four columns under drive C.V.A. press

[8].

8.1. Modelling of hydraulic coupled Muller presses equipped with multi die-sets (model 3).

The nodal points 1,2,3,4,5,6,7,8,9,10,11,12,13,14 and

IS,

as shown in fig.8. I., represent the frame of the left hand press (L.H.P.) and the nodal points 31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47 and 48 represent its ram. Similarly the nodal points 16 to 30 represent the frame of the right hand press (R.H.P.) and the nodal points 49 to 70 represent its ram. Both the L.H.P. and R.H.P. rams are coupled together at nodal points 48 and 49 in U and W-direction. The elements 67 to 78 represent the top plates of the six blocks of die-sets and the elements starting from 91 to 102 represent the guide pins of the die-sets. These blocks are constrained to rams by coupling of nodal points 73,33; 74,37:79,38; 80,41; 81,43; 86,45; 87,46; 88,51; 89,52; 94,53; 95,57; 100,59; 101,61; 102,64;

103,66; 108,67; 109,68 and 110,69 in the directions U,W and <po

Assuming the bed of the coupled presses sufficiently stiff, the bottomplates of die-sets have been neglected. The extreme end points of the guide pins represented by the nodal points 71,76,77,83,84,91,92,97,98,105,106 and 112 have been suppressed in the horizontal direction.

6 @

I

I

® F1L F2l. 5 ,35 ® F1L @ I ® @ @ 3 31 32 ,33 3/' 73 _@ @ @) 72 75 @ @ ® 71 z l""====~>X ® 10

I

F3L _® J.O, 12 11 @ @) 79@ 80 @ _© 78 82 85 @) _® @ ® 11. 15 21 ® 19 ® ® 17 16 22 @

I

F1R @ 20 156 F1R ®

j@

51. @ • Nodalpoint number

o

Element number

Flg.8-1 Beam model of the two coupled hydraulic Muller Presses equipped with multi die-seh

23 21. 25

I

F2R F3R _@

6, 27

® 26 ® @ W W 29 30

The conditions for coupling of nodal points 5,35; 13,47; 3,31; 12,40; 20,56; 28,10; 18,50 and 27,63 and also for introduction of technological forces together with F_1L, F_2L, F_3L, FIR' F_2R, and F3R are the same as for model 1.

Keeping in view the inadequacy of the effectiveness of the tilting control-system, the relationship of different parameters of the die-set with respect to horizontal and vertical displacement have been established for the most critical situation i.e.when the t ting of the ram is 3 rom.

From conventional theory [9J it is known that the displacement of a beam, which is supported at one end and is subjected to a moment on its

another end, is given as:

M H2

U

=

_{2 EI}

(8.1.)

However, when there are n.number of such beams (guide pins) the expression (8.1.) can be written as:

u

n 2 EI (8.2.)

where

M

=

the moment on the guide pins

g

H

=

the closing height of the guide pin

E = modulus of elasticity of the guide pin material

I

=

second moment of the guide pin cross~section For circular bar (guide pin):

where

d = the diameter of the guide pin

SUbstituting equation (8.3.) in equation (8.2.) we get:

u

(8.3.)

35

-From the theory of elasticity QOJ it is known that the displacement of a structure is directly proportional to the load applied to it. The analysis of the computed results of model 3 also confirms the above statement. Therefore it can be assumed that there is a linear relationship between the moment (M

=

F e) on the ram and the moment

p

M on the guide pins, I.e. g

M

g M

=

F p e

Substition of (8.5.) in equation (8.4.) yields

64 F e H2 U _'" p 21fE nd4

or

U ""K -1 K} 64 F e H2 K

=

p

21f

E where K J

=

nd4

F = the technological force

p

e = the magnitude of eccentricity.

(8.5.)

(8.6.)

(8.7.)

(8.8.)

From equation (8.6.) it is clear that an optimisation on the design of a die-set can be achieved. The numerical computation of the beam model of the system of presses and subpresses as shown in fig.8.1. has been performed to determine the influence of the diameter (d),

length (1) and number (n) of the guide pins of the specific set of die-sets on the misalignment of the die and punch. The relationships between

horizontal displacement (U) of the top plate of the die-set and the length of the guide pin, between horizontal displacement of the top plate and diameter (d) of the guide pins and similarly between vertical displacement (W) of the top-plate of the die-sets and the diameter of the guide pins have been illustrated in figures 8.2.; 8.3. and 8.4 respectively. A cyclic diagram, as shown in figure 8.5, has been plotted to demonstrate how in pract knowing the blank thickness

or the clearance between the die and punch, the diameter and number of guide pins of a die-set can be chosen.

2. The analysis of the bottom plate of a die-set by means of the classical method of mechanics.

When the bottom plate of a die-set is rigidly mounted on the bed of the press, as shown in fig.8.6., the displacements of its end edges can be considered to be negligible. In case of the central loading

e

F

of the die-plate the support reactions Rl and R2 must be equal to each other.

Fi 9

8-6

For the immovability of the points A and B of the die-plate the bolts on the plate must be tightened with a force

3 P 12

R := p

The maximum angle of rotation 8 of the point "T", where the bushes are located can be written as [I~

For a rectangular plate

2 2 x a

e

= E I (R

'2 - 6)

bh2 1 = -12 (8.11.) (8.12)

where b the breadth of the bottom plate of the die-set h == thickness of the plate.

But 8 = Smax' when x = a.

Substituting equations

(8.10)

and

(8.12)

into equation (8.11) yields:

8

max _{8 E bh}3 ₍₂

+ 3£) a

(8.13)

From the condition of the over-stresses of the bush and guide pins, the displacement of the point "T", as shown l.n fig.8.6., must not exceed

10%

of the amount of the clearance Z between the die and punch

[12J;

1. e. U Z max 10 (8.14) But U _{8 H} max max (8.15) Hence - = Z

_e

H 10 max (8.16)

Substituting equation (8.16) in equation (8.13) and solving:

The relationship between the technological force (F ) and the thickness

p

of the bottom plate of a die-set has been established in figure 8.7a. In order to facilitate the designing possibilities the correction factors K₂, K3 and K4 for h, as shown in figures 8-7b; 8-7c and 8-7d

respectively, due to changes in b, Z and H respectively have been determined. For any desired change of any refevred parameters in equation (8.17),

the corresponding change in plate thickness (h) can be determined as:

h (8.18)

where hI = the original bottom plate thickness K

Z correction factor due to the length (b) K2 = correction factor due to the clearance (Z) K3 = correction factor due to the height (H) •

It is known that the die-set. which has symmetrical positioning of the guide pins with respect to the cut counter. has better stability.

However, the symmetrical positioning of the guide pins does not indicate the exact places of their positioning on the bottom plate of the die-set. Analysing the elastic deformed line of the die-plate under load F ,

P

as shown in figure 8-6, it is possible to find the plate section between supports

A

and

D

and similarly between

C

and

B,

where the angle of

rotation (6) is equal to Zero. Thus the influence of the horizontal displacements of the guide pins and the bushes, due to bending of the die-plate. on the misalignment of the die and punch can be eliminated, provided these pins or bushes are positioned mainly on the referred ,points. The position of such a point can be easily determined, when equation (8.11) is equal to zero; I.e.

or or 2 2

e

_{= -}1 ( x _{R - - R -}a ) EI 2 6

x

2 a 0.577 a;

o

When the die-plate is rigidly clamped at its ends, the angle of inclination

e,

despite the variation in the magnitude of the load(Fp ) on the plate and of its point of application between the internal supports (section DC), will retain its zero magnitude at a point a-X

=

0.423 a from the end D of the downfall hole in the bed table. Therefore it is important to note that the centers of the guide pins or the bushes should be clamped particularly to these points.

Number of pins n

=

21.

Ml=-1.20tm.} thO t'lt' f th f 3

Mr= 780 tm, IS means a I lOgo e ram 0 mm,

diameter of guide pin~ d=

63

300

~

280 "

E

.... b

260

Slw

I ~

21.0

15

.$ .9 a. a. o

...

~ 0 :::J

-

_-

c: 41 E 41 (J 0

...

a. 11'1 '"0 - ' 0

...

_c: 0 N 'C

£

180

160

140 120 100 80 60 40 20 0

₁₁₀

₁₂₀

₁₃₀

_{140 150}

length of the guide pins of the die-sets (l) [mmJ Fig. 8-2

The influence otthe ~th of t~~ide ~in5on the aliQt:!ment of die and punch

Num ber of pins 24

Ml =-4 20

tm.} thO t·lt·

f

th f 3

Mr=

780

tm. IS means a ling 0 e ram 0 mm.

l:: length of the guide pins

400

-

<II

~

380

"I

<II "tJ

360

15 (II

-

0

340

... a. a. 0

--

0 ::J l=~·

-

-

_c cv

E

<II

₂₆₀

u 0 - ' a.

240

""

:.a

...

220

0

1:

0 .t:!

₂₀₀

'-0

l =80

J:

180

80

60

40

20

0

I I I I

I

30

40

50

60

70

80

Diameters of guide pins of the die-sets (d) ...

[mn]

~

_ret

'"

I

E

.~ (""') "C I

15

0 <lI

W

..fJ 0 - . J 0 ..fJ ~

--

0 .-... ~ ..fJ C <lI

i

_u 0

...

'"

"C

...

0 .~ ..fJ l.. ell

>

4000

• Number of pins

24

~~ :-~;~ :~:}

this means 0

tilting of

the rom

of

3mm.

l

=

length

of

the guide p.ins

W48- W31

•

I •

•

•

•

Diameter

of

the guide pins

of

die-sets

(d) ...

Fig.8-4

[mmJ

The influence,of the-cljometer of the guide Qins

of

the die set on the

vertical

disQlocer:nent Of the

ram..:

(1Q8mm4)

I

Ml=-1.20tml. . .

j

this means a tilting of the ram

Mr= 780 tm of 3mm. Dotted line-- - for a tilting of 1,5mm.

L = length of the guide pins

I

10

Y

d·---t·~--t···-···--t----i0.8 1.0 z (mml 70 80 z =a.h Umox.= b.z

I

i/

;1

/

/

I I,

JJLY2Z

Umax.:: the max. horizontal displacement of die and punch

I i " number of p'!n S

d" pin diameter

Fig.8-5 Nomogram; showing the relations hi p~etw~!l..!'l~~_!!'~~ I'll, numl:l~rLr!l~!5!lJici~JJ.iI).~_4J.fl'!J.~_E£.tim~di?~!tE!r:.(d.L of the..ei.!l~JEr:..._C1gi!"!fl.lerl9.th of the guid epil'l~

p

-K

For plates having small thicknesses

p

[17J

Fig. 8.8 : Unified components of casted die-plates.

,Dimension of

I

a I K M

I

b

I

I

I

I

I

plate lxB d I

I

D

I

AxA nun nun nun I

I

I • I

I

H

I

It R

I

e I nun 1 130 : 40180 \80 I M24160 160 130 110012501 ---~~~~--~-~ 1500;< 1000 I 60 1200X 200' > 1500>< 1000 It' 35 45 90 1 1 90

I

M27 'i 70 70113511:,11011280 .:$ 2000X 1500 - - - i - - - i - - - I I I

I

___

~_4_2~._000_0;_· 2_1g_go_0_-,-14_0-,-1_50~I~otool

M30

rl

80 1 40 1120[3001

[17J

Table 8.1 70 1250X250 280><280 100 1 320X 320

d diametl of the bolt for clamping the die-set to the bed of the press

D = diameter of p~ns

Dimension of all the parameters in Table 8.1 is given in rom.

~ b(mm)

~

21,00 \ \ \

I

2200 \ \

,

2000 1800 \ \ 1600

\

H.OO \ 1200 \ "

~

1000 800 ll. 1.5

a-

7 b Correctiro foetor Kl ~!~_~

\

t;

r

! 1,3 \

\

1,2 1.1 1,0

t

0,7 0,6 0,5 0,7 0.8 0,9 1,0 1,1 1,2 1.3

Fig.8--/c Correction foetOf ~iOf h

.c:.

E

E '" 1.5

'"

ILl ~ U :z:. ~ <1.1 ...., 40 0 1l. E 0

....

15 ..a ₃₅ -0 c: -6> 'C 0 30 25 20 V. 1.5

I

. / . / . / 60 1,0 1.1 -7-a 240 mm b=1500mm

rig.8-7d Correction foctor KI, for h

--~

----o

-yg~ _ '\SfJ_--' \,.::>-'

----1. The metrological investigation of the two hydraulic coupled Muller presses shows that the misalignment of the die and punch due to nonperpendicularness of the guide columns with respect to the bed and due to the nonparallel ism of the meeting surfaces of the bed and the ram is well within the norm established by Schuler, but this exceeds the norm established by Gost 9408-60. Considering the controversy over the different norms and also the overall inclination of the bed with regard to the horizontal plane (as shown in fig.lA-4), it is advisable to pay some attention to this point.

2. When a nonsyrometrical product (length » breadth) has to be manufactured in large scale, it is better to choose a press, whose guide columns and the ram are so designed that the influence due to the clearance between the sliding surfaces of them on the misalignment of die and punch (as shown in fig. 2A-3) is minimum.

3. Among other factors, the selection of the optimal clearance between a die and punch has significant influence on the tool-life. For investigated materials having thicknesses of 6.5 rom and 7.5 rom, the satisfying

quality of shear surface is obtained when the clearances between the die and punch are 15% and 12% of the initial blank thickness (ho). Within this range of clearances both the technological force and the back pull force of the punch, shown

minimum.

fig. A-I, were found to be

4. Analysis of the forces of the main cylinders of the hydraulic coupled Muller presses and also of the vertical displacements of the extreme

ends (nodal points 4 and 59 of model I) of coupled rams, shown in table 7.1., indicates that the tilting control system of coupled presses is not

effective enough to cease the tilting of the coupled rams adequately. Therefore, when designing the new die-set, the inefficiency of the control system must be taken into account.

5. Considering the error in pressure measurements due to calibration in oscillogramme curves ani also due to the leakage of oil from cylinders the discrepancy between the experimental results and the computed results can be estimated about 15-20%. The computed results did not take into account the additional stiffness of the die-sets mounting on the model 1. An attempt was made to determine the stiffness of the model of the coupled Muller presses equipped with multi-die-sets.

46

-It was found that overall distortion of this model decreased by 10% with respect to that of model 1 without tool. When taking all these

factors into account the over all discrepancy could be said to be about 10%.

6. The analysis of the computed results of the model 3 reveals that the die-sets, used for punching of holes both in sidemember 513262 and in 179738, are working at a very extreme point of permissible tolerance on the misalignment of the die and punch (shown in .8.5.).

Moreover it is interesting to note that the diameters of guide pins of the die-set for optimal condition of working of the tool, computed wi th the help of model 3, is in good agreement with the findings of

D

7]

as illustrated in table 8.1.

7. The analysis of the computed results of model 3 similarly indicates that the closing length of the die-set, as shown in figure 8.2. has a significant influence on the misalignment of the die and punch.

Therefore when designing a die-set as minimum as possible.

S closing length should be kept

8. In stepwise punching it would be always possible to choose a group of combination of the cutters of different diameters, which may result in achieving a smaller magnitude of eccentricity. Hence a special attention should be paid to this point, as it has a direct influence on the distortion of the system of the press and subpress (die-set).

ACKNOWLEDGEt1ENT

The author 'dishes to thank Prof.Dr. P.C. Veenstra and Prof.Dr.lr. A.C.H. van der Wolf for their and guidance and Dr.lr. J.A.H. Ramaekers~

Ir. J.A.W. Hijink, Ir. W. Knaven, Ir. Franken, J. Katsman and Drs. N.A.L. Touwen for their contributions to this ect. The author appreciates the dedicated assistance of Van Hoek, Vall der Meulen, De Groot, Van Ier-land, Hisses Van Boxte~,

ration of this manuscript.

a-Appendix 1

Geometrical accuracy of a press.

The geometrical accuracy of a press is characterised by:

a. nonparallel ism (~ ) of the bottom plane of the ram with respect to par

the plane of the bed.

b. nonperpendicularity (~ ) of the movement of the ram to the perp

horizontal plane of the bed.

c. nonplaneness (A_pl) of the ram and bed surfa.ces.

Nonparallelism ):

When a di~et is clamped tightly to the ram 1 and to the bed 4 of a press, the punch, during closed position of the upper and lower parts of the die.setwill hold the position of the bottom plane of the ram as shown in fig. lA-I. The misalignment for this case can be written as:

L

I I

10---I

3

m77;~::~!

D, Z par (IA-) )

where: 1

=

the length along which the measurement of D, is taken.

par

48

-Non perpendicularity (~perp):

The misalignment due to nonperpendicularity of the movement of the ram can be considered for the case, when the die and punch are in contact (closed position of a die-set) as shown in fig. IA-2.

When the stroke hI of the ram is downward, the working face of the punch 2 deviates with regard to the die 3 by an amount ~Z and is

perp given by: Nonplaneness (~ 1): p t:.z perp ( IA-2)

Assuming that the meeting surfaces of the ram and the bed of the press, as shown in fig. lA-3, are made of an arc of a circle of the finite radius, the misalignment ~Zp1 due to nonplaneness of the ram and the bed can be written as: