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Technology of watch production - part 19

A t the beginning the descending die (8 ) presses the part agains t the s tripper

( 7 ) which is thereby forced down, comp ressing the sp ring (4 ) . The punch

( 5 ) then pierces (or calibrates ) the hole . The slugs pass through the hole

in the die (8 ) and in the uppe r s hoe and are ejected . The centering nest ( 6 )

is also lowered, compressing the springs

( 3 ) .

FIGL:RE

2 5 . Piercing die for piercing a

central hole in gears

A fter the hol e has been pierced, the upper shoe retracts while the center

ing nest ( 6 ) and the s tripper ( 7 ) return to the ir original positions under the

action of their resp ective springs . The part is removed with the aid of pin
c e rs . Having a run- out of not more than 0 . 0 1 5 m m , the central hol e pierced

by this die is more conc entric than thos e made by the form erly us ed m ethod

of d rilling or bo ring on a machine with the wheel clamped in a collet.

DlNKING, SHAVING, AND BENDlNG

Dinking

is a process for blanking parts from mica, leather, cardboard

and other thin nonm etallic materials .

The clinking process consists in cutting the m aterial with a hollow punch

having a closed contour . The die is cons tituted by a s m ooth l ead o r mil d

steel plate . The punch i s hardened t o

= 52 to 56 and the ma rks left by

the punch on the s urface of the die are removed at certain fixed time
intervals .

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Typical punch designs for dinking dis ks and washers are s hown in Figure

2 6 . The punch s hear angle

is 1 5 to 1 8° .

Shaving.

Parts blanked from s tock more than 0 . 5 mm thick will have

rough edges and burrs .

Most watch parts are required to have a smoothly finished s hear ..surface

(class 7 - 8 ) perpendicular to the main plane and the parts are shaved afte r

blanking to achieve this finish. Shaving allowances are given in Table

3 .

These allowances should b e increas ed by 50- 6 0 o/o a t s harp angles and sharp

transitions where burrs are liable to attain dim ens ions as large as 50 o/o of

the blank thicknes s . The allowances are also increas ed by 0. 5 to 0. 8 o/o of

the major blank dimension when this dimension is larger than 2 0 mm .

FIGURE

2 6 .

Dinking dies :

FIGURE

2 7 .

0 3

shaving die

a-for disks; b-for washers

Parts may be shaved on both their exte rnal and their inte rnal contours .

The part to be shaved in the die set in Figure 2 7 is placed on the die

( 3 )

and

properly located by the nest ( 2 ) . When the punch ( 1 ) is lowered, the part

is forced through the die opening whose cutting edges shear the metal along

the desired contour.

TABLE

Shaving allowances for

mm-diameter blanks (total for both sides)

Material

Part thick-

1\lild steel and brass

Steel of aver age hardness

Hard steel

ness

min

max

min

max

min

max

0 . 5- 1 . 5

0 . 1 0

0 .1 5

0 . 1 5

0 .20

0 . 1 5

0 .25

1 .6 - 3

0 . 1 5

0 .2 0

0 .25

0 . 2 0

0 . 30

3 .1 - 4

0 . 2 0

0 .25

0 . 3 0

0 .2 5

0 . 35

-L�- 5 .5

0 .2 5

0 . 3 0

0 . 35

0 . 3 0

0 .40

7 4

In o rder that the allowanc e be uniformly removed, the nest ( 2 ) mus t be

accurately pos itioned relative to the die contour, and it is therefore punched
in s itu by the shaving-die punch its elf after which the opening is enlarged

by the value of the allowance, and chamfe red .

In watch p roduction it is frequently necessary to blank and shave parts

whose thickness is 2 - 5 times their width or diameter. In such cases the

blanking allowance is inc reased, and the blank is s haved on a die s et having

a punch la rger than the die opening.

In this type of shaving die the punch does not penetrate into the die, and

each part is ejected from the die by the following part . A surface thus

s haved has a bette r finis h, and the part is flatter, but the shaving force re
quired is much large r than that required in shaving by the usual method.

Springs of s top watches (see Figure 1 0 ) are shaved by this method.

When the contour of a part se rves as the bas e for subsequent operations

parts may be s haved two or three times . E

subsequent s having opera

tion removes a s maller and m o r e even laye r and the dies us ed i n the final

shaving must the refore be much more rigid than the firs t shaving die .

Multiple shaving p roduces more uniform dim ensions and a better s urface

quality. The parts mus t be shaved in the same direction in which they were

blanked, as otherwise burrs will appear on the edges .

Thin s teel parts are frequently sized ins tead of being shaved and this

p rocess pro duces a clas s 9 or 1 0 finish on the lateral s urfaces . In sizing,

the working edl;{es of the die are blunt, and as a result the part increases
in thickness (Figure 28 ).

FlGUHE ZR.

Schematic representation of the sizing

process

The s having force

is calculated from the formula

P = kl · ® s ,

where

perimeter, mm;

a =

allowance per side, mm;

a 5 "

shear strength, kg/mm2;

k =

coefficient allowing for the ejection force Q and the shaving depth

h .

For s teel with an ultimate s trength

au �

90 kg/mm2 , k " 1 . 5 to 1 . 6 ; fo r

b rass with

a u

up to 6 0 kg/ mm 2

k "

1 . 2 for a s tock thickness of 1 mm .

Example. lt is requireu to determine the force ? necessary for shaving a watch plate 38 n!ln in diameter

and

:! .2

mm thick . Table

after adding 0 . 8 °/o D , recommends an allO\vance of 0 . 52 mm. Further given are

= 3H kg/mm2 and

k = 1 .4. 11/e therefore obtain P =

1 .43X3 .14X38X 0 . 52°X38

3.4

t .

The force

P required for sizing is higher by 30"/o than that required for shaving and a minimum al101vance

of 0.03 to

O .OH

mm per side is fi xed.

•

[The value 0 .52, taken from Table 3 , constitutes the total al101vance , i . e . , 2 a. As, however, the above

formula operates with the al101vance on one side only, i. e . w ith a, it seems that 0 .26 should be substituted

for 0.52 , which of course would reduce P to

1 .7

t . )

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The same die s ets

are used for shaving dies as a re us ed for blanking

dies (Figure 2 7 ).

Dies with a fixed nest are us ed for shaving parts of thickness up to 1 m m .

Thicke r parts are s haved on dies with s wing- out nests (Figure 2 9 ) .

The nes t is first s wung clear of the wo rking zone of the die s et and the

die is carefully cleaned, rem oving all chips . The part to be shaved is then

ins e rted into the nes t . The adjus tm ent of the die s et (the positioning of the
punch relative to the die ) is much eas ier with s wing- out nests . On the othe r

hand, it should be kept in mind that the positioning accuracy o f swing- out

nes ts is inferior to that of fixed nests and that, with s wing- out nes ts , the

shaving action m ay be nonuniform. Accidental notching of s wing-out nests
is a possibility to be reckoned with .

FIG URE 2 9 .

Swing-out nest for a shaving die

FI GURE

30.

Combination blanking- shaving die

It should be mentioned that, according to safety rules , parts may be fed

into fixed nests with pince rs only.

C ombination blanking- s having dies are now widely us ed in watch produc

tion.

The des ign of such a combination die for plates and b ridges is shown in

Figure 30. The uppe r shoe of the die set carries the punch ( 1 ) and the s t rip

per (2 ) and on the lowe r shoe are mounted the blanking die (3 ), the pads (4 ),
and the shaving die ( 5 ) .

The first time the punch ( 1 ) descends , the s t rip i s p ressed against the

die block by the s tripper (2 ), a part is blanked, and remains in the die.

The s econd strike of the punch blanks anothe r part and the first part is

pus hed into the hole in the pads (4 ). During the third blanking the first part

is shaved by the die ( 5 ) . The shavings are removed by a jet of compressed
air through a lateral window between the pads . The two dies , togethe r with

the pads, are a single ass embly and are mounted on the lower shoe .

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