Note: Descriptions are shown in the official language in which they were submitted.
g3 765~2
BNs-101
INTRODUCTION
This invention relates to cold drawlng and particularly
to a cold drawing die for producing polygonal shapes from round
stock.
BACKGROUND OF TEE INVENTION
.
Cold drawing of polygonal shapes yieIds a finished shape
with harder surfaces, a higher yield strength, and con~ormed to
closer tolerances than hot formed stocks. These finished shapes
are suitable for machinl~g into hex nuts and other small parts.
~eretofore, in cold drawing of polygonal shapes such as hexagons,
a shape or hexagon larger than the-finished poly~on is used ~
as the starting ma~erial.~ This leads to several problems. -~
Typically, manufacturers of cold dra~n stocks produce
a number of different shapes and sizes. Without this invention
they must carry an inventory of raw material bar stock of the
same shapes and sizes as their finished products. This requires
j a much larger inventory overhead expense than is the case if it
were only necessary to keep an inventory of different sizes of
round stock.
Another problem com~only encountered is the result of-
a twisting defect in the starting material. The starting materialis a coil of a hot rolled form. In the coiling process a twist is
often imparted to the stock. During the cold drawing of this type
of stock material, the die through which the bar stock is being
drawn acts as a straightener. The twists are compressed into the
area just ahead of the die. At some point the stored twisting force
becomes greater than the compressive resistance of the stock as
it passes through the die. The stock then flips over. That is,
one corner of the polygon or hexagon shape moves laterally across
an adjacent straight side and settles into an adjacent corner.
Because the bar stock is continually moving through the die,
'~ ,,
.,.',." '~",
;,
. , .
~ 376S~2J
BNB-101
the corners are distorted as they move across the straight sides.
The whole section of stock that passes through the die
as the corners are flipping must then be scrapped. This flipping
over also frequently results in the fracturing of the die. Of
course, this does not happen if round stock is used as the starting
material because it is circumferentiall~ symmetrical.
In the prior art when trying to draw a polygonal shape
from a round bar, edge defects are oten encountered. Looking
at a cross-section of the stock perpendicular to its long axis
as it encounters a polygonally shaped die, we see that the initial
contact point is on the periphery o~ the cross-section of the
stock and the middle of a flat side of the die. The die acts on
this edge of the cross-section and pushes it back in reIation
to the central axis of the stock. Since this is the area of
greatest deformation or deepest draft, the force is considerable.
The adjacent areas of the perpendicular cross-section not con-
tacted by the die are also pulled back. This leaves~a void-
or lack of material at the apex of the angle between the-
two straight sides. If the round stock is only sli~htly larger
` 20 than the maximum cross corner radius of the finished polygon,
there will be gaps where material does not fill the corners and
the piece will be defective. If the diameter of the round stock
;~ is sufficiently large to prevent this defect, the force required
to draw this stock through the die is prohibitive. The lar~er
; 25 the original bar stock the greater are the stresses of deformation.
The greater the stress, the more force required to accomplish
~ the deformation. This extra force will also act to squeeze out
; lubricant from between the die and the bar stock and increase
. .,
frictional resistance.
BRIEF SUMMARY OF THE INVENTION
; The present invention provides an improved cold drawing
die for making polygonal shaped bars from round stock, wherein
. --2--
,
:.,,
'76~i22
BNB-101
edge defects are eliminated and sha~ply deined shapes may be
produced with a dra~ing force substantially equivalent to that
of the prior art.
In general this is acco~plished b~ providing a dle
having a polygonal bearing zone with at least one straight side,
and an entry zone characterized by a full round initial opening
or contact zone and shaping planes tangential to the round initial
opening which gradually lead into the straight sides such that
continuous full circumferential contact is maintained between
~ 10 the die and the stock throughout the draw.
-~ In a specific embodiment hereinafter described, the
entry zone has a circular cross-section at its forward end.
It contains semi-elliptical shaping planes equal in number to
the straight sides of the finished shape, and shaping corners
which lead gradually into the apex of the bearing corners. The
shaping planes angle inwardly from the initial circular contact
zone to meet the sides of the bearing zone. The preferred
shaping plane of this invention will be angled at successiveIy
smaller angles to the axis of the die as it approaches the bearing
zone but this invention also covers a flat shaping plane with a
~ fixed angle to the die axis.
;.'
;~ As used herein the term "polygon" refers to any multi-
surface section, including those with one or more non-flat por-
.
tions.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a block diagram of a cold drawing line;
FIGURE 2 is a view of a die in its holder;
FIGURE 3 is a cut-away of the die for drawing a
~, hexagonal bar from round stock;
FIGURE 4 is an end view of the die of FIGURE 3 from the
entry side of the die;
-3-
''"
~7~Z2
BNs-101
FIGURE 5 is a detailed view o~ a shaping corner;
FIGURE 6 is a detailed view of the cross-section of
an angled shaping plane taken along the intersection of the
shaping plane and the plane running through the axis of the die
and normal to the transverse surface of the shaping plane;
FIGURE 7 is a cut-away view of the die for drawing a
double D bar from round stock.
The angles and dimensions in Figures 3 through 7 are
exaggerated to bet~er show the detail of the invention.
10DESCRIPTION OF THE PREFERREI~ ~MRnnTM~N~.~
P~GURE 1 is a block diagram of a cold drawing line
in which round stock 2 is drawn through a shaping die and cut into
desired lengths. The bar stock 2 is received in coils which are
placed on a decoiler l which rotates in the same direction the
stock is coiled thus providing the force to uncoil the stock.
The stock then travels through a straightener 3 and
into a Wheelabrator sho-t descaler 4. The shot descaler takes
the rust and scale off the surface of the stock by forcible
impingement of small steel shot~ The clean stock then goes
through another straightener 5.~
After this the stock passes through a push pointer 6
which operates intermittently. The push pointer is only activated
~;to start the stock through the die with a pushing action. Once
`the pullers take over as hereinafter described, the pusher dis-
engages and lies idle.
-The bar stock then encounters the die held in the die
holder 7. The die is lubricated continuously and deforms the bar
stock to the desired shape.
Next, the puller 8 grips the stock and pulls it through
the die. There are two grippers 9 and 10 in the illustrated line.
They grip and pull alternately to give the stock a continuous
linear velocity.
--4--
765Z%
BNB-101
After passing through the puller the stock is straight-
ened once more in a straightener 11. The stock is then cut into
the desired lengths by a cutter 12 and stacked by a stacker 13.
The combined drawing apparatus used for drawing in these embodi-
ments is a commercially available product, for example a SchumagCombined Drawing Machine Model No. KZ-II-B.
The die body 66 is tapered and sets into the tapered
hole 71 in the die stand 7. The holder plate 67 holds the die in
; place, and in tuxn is held in place by the setscrews 68. The cir-
cumferential ridge 70 acts as a relief and facilitates removal
of the die from the holder.
The die 66 has a tungsten carbide heat fitted insert
69 to improve wear resistance. The stock to be deformed enters
the assembly through an orifice 72 in the holder plate 67. It
then passes through the passage of the die and is deformed to the
- desired shape.
FIGURE 3 shows a cut-away view of the die for forming
` a hexagon comprising a body 14 of high hardness material having
an axial passage 28 formed between opposite plane faces 75 and 76.
The axial passage 28 is divided into three zones: an entry zone
- 29, the bearing zone 20, and a reverse angled relief zone 15.
The entry zone 29 has a circular cross-section at its
forward edge 78. The initial contact point 17 is also circular in
cross-section. The internal surface of the entry zone 29 contains
the shaping planes 19 and khe shaping corners 18. ~he shaping
planes 19 take the form of a semi-ellipse with their forward ends
rounded and tangent to the circular cross-section of the initial
contact, point 17. The area on which the shaping plane exerts its
force on the stock starts out as a small point and gradually in-
30 creases in width until the shaping plane 19 meets the bearingzone 20. Concurrently, the shaping corner 18 gradually de~orms
the round bar section into a sharp angle. As the round
: .
n
~7
BNs-101
sections on either side of the apex of the corner become straighter,
the area contacted becomes less because of the widening shaping
planes. Hence, full circumferential contact between the stock
and the die exists along the entire axial length of the die;
i.e., there are no corner gaps. This gradual shapin~ allo~s the
use of stock only slightly larger than the maximum cross corner
diameter of the finished shape.
The next part of the die encountered by the deforming
stock is the bearing zone 20 which give5 the stock its final shape
to exacting tolerances. The reverse angled exit zone 15 allows
fGr expansion of the stock as it exits the die.
FIGURE 4 shows an end view of the internal surface of
- the die of FIGURE 3 from the side on ~hich the bar stoçk would
; enter the die. The axial passa~e 28 has an initial circular
cross-section 78. As the bar stock moves into the die opening 28
it encounters the initial contact point 17 around its full circum-
ference. The bar stock will then encounter shaping planes 19
and shaping corners 18.
-' The shaping plane 19 has the outline of a semi-eIlipse.
Its for~ard edge is tangent to the initial contact point 17 and
angles inwardly until it meets the straight side of the bearing
20. This way the straight sides of the final shape are formed
'`~ gradually rather than all at once. In between the shaping pl~nes
19 are the shaping corners 18.
FIGURE 5 gives the detail of a shaping corner. The
lines 21, 22 and 23 do not exist on the die but are in the figure
to show the changing shape of the cross-section of the die. The
,~ cross-section at the initial contact point 17 is round. In
sections of the shaping corner closer to the bearing, the angle
of the corner becomes more pronounced and the cross-sections
become straighter on either side of the apex of that angle. As
the shaping planes become wider, the sections of the shapin~
corner also become smaller until, at a point immediately in
--6--
, . '
3L~71 ii~2Z
BNB-101
front of the bearing, the edyes of the shaping planes meet and
the shaping corner degenerates into the apex of a sharp angle.
FIGURE 6 shows the cross-section of an angled shaping
plane. The shaping plane may be flat but the better form for it
to take is that of decreasingly smaller angles as the shaplng
plane approaches the bearing zone. The angling is generally done
in four zones. The stock initially contacts the die at initial
contact point 17 and gradually passes through the entry zone 29
until it contacts the bearing 20 and the relief zone 15. ~gain
angles and distances are greatly exaggerated to more clearly show
the detail.
In zone 27 of the die the angle 33 that the shaping
; ~lane takes to a line parallel to the axis 34 is ~reater than the
angle 32 in zone 26. The angles 31 and 30, being closer to the
bearing are increasingly smaller. The actual die will n~t have
four distinct flat zones but will show a smooth curve through all
four zones as shown by the line 36.
FIGURE 7 is a cut-away view of the die ~or drawing a
double D bar from round stock. With this die round stock 61 is
drawn to the finished shape 62. The double D bar has two round
sides 57 and 58 which take the form of two diametrically opposed
arcs of the same circle. The curved sides will be equal in length~
Two sides 59 and 60 are parallel to each other, e~ual in length
and diametrically opposed.
As with the die of Figure 3 this die has an entry zone
53, a bearing zone 5~ and reverse angle relief zone 55. The bar
`~ stock 61 enters the die at the initial circular cross-section 51
and contacts the die at the initial contact point 52~ One of the
two shaping planes of this die is shown at 56. It starts ~rom a
point near the forward edge of the die at the initial contact zone
52, angles inwardly from the initial circular cross-section 51 un
til it meets the straight side of the bearing zone 54. This
shaping plane 56 may be either straight or angled.
1~765;~
EXAMP_E I
This example relates to a die which will deform .891
inch round bar stock into a hexagon .750 inches across the
straight sides. A similar die is sho~n in FIGUR~ 3. The die is
an annular piece of high hardness material, generall~ steel with
a heat-fitted tungsten carbide insert. Those generally skilled
in the art will know othex materials which can be substituted.
The diameter of the circular cross-section of the
initial contact zone will be .891 inches. The entry zone will
have a length of .546 inches measured along the axis of the die.
The initial zone 27 of the shaping plane will take an angle of 9
with a line parallel with the axis of the die. It will be 1~4
of the length of the total shaping plane or .1365 inches~
The se~ond zone 26 will take an angle of 8 with a
line parallel to the axis of the die and have a like length. The
15 third zone 25 and fourth zone 24 will be 7 and 6 respectiveIy
from the axis of the die and have like lengths with the first
and second zones. The angles of the shaping plane will be
blended together so as to form a smooth curve.
; There will be 6 angled shaping planes and 6 shaping
.: ~
corners in this die. The shaping corner will be .546 inches in
length along the axis of the die. It will take a shape as
described earlier in this specification.
The stock then encounters the bearing zone 20 which is
-, .470 inches long in the axial direction. The bearing will have
a diameter across ~he straight sides of .74q inches to allow for
expansion of the stock as it leaves the die. Immediately behind
the bearing zone is the reverse angled relief zone where the inter-
nal surface o~ the die angles sharply away from the axis of the
die. This permits expansion of the stock as it moves out of
the bearing zone.
Since the diameter of the original bar stock is .891
' .
:, ' ' . ' ~ . .' ' , ~
9765Z;2
BNB-101
inches and the distance across the straight sides of the fini~hed
shape is .750 inches the draft in this area is .0,705'inches. That
is, 1/2 the decrease in the diameter. The draft on the shaping
corner will be ~0155 inches. When the bar is drawn through this,
die it will yield a hard cold drawn hexagonal shape 0'.75 inches across
the straight sides with, a tolerance of -.003 inches.
Drawing a hexagonal shape from round stock of this size
; without edge defects and with only a .0155 inch draft on the cor-
ners has not been done until the die of this invention. The
, 10 drawing force required in this example is only sli~htly more than
that required to draw hot formed hexagonal bar stock through'a
hexagonal die with recommended draft. If one drew round bax stock
, of a size large enough to avoid edge defects through a hexagonal
' shaped die, of the prior art, the drawing force required would
be 1 1/2 to 2 times as great as the drawing force in this example.
'' EXAMPLE 2
` This example relates to a die for forming a double D
bar. A cut-away view of the die is shown in Figure 7. This will
also illustrate the action of the shaping planes without shapin~
, 20 corners. A double D bar i5 a bar with a round cross-section
', except for two diametrically opposed, equal, parallel stxaight
sides.
~, The bar stock has an original diamet~r of .969 inches.
The initial contact zone 52 has a diameter of .969 inches also.
,, The two diametrically opposed shaping planes are of the angled
variety.
The zone of the angled shaping planes nearest the
initial contact zone 52 will taken an angle 33 o '12 with the
axis of the die 34. The second 26, third 25, and fourth 24 take
angles of 10, 8 and 6 respectively. Again the shaping planes
do not show distinct zones but the angles blend into a smooth
curve 36.
_9_
'. '
:
, ~
65;~Z
BNs-lOl
; The length of the entry zone 53 is .671 inches. The
length of the bearing zone 54 .i5 . 500 inches. The diameter
across the straight sides 59 and 60 of the finished bar is .756
inches. The diameter across the round sections 57 and 58 is
.938 inches.
The practice of this example allows the drawing of a
double D shaped bar with substantially less force than the prior
art die.
It will be understood that the invention has been
described with reference to specific illustrati~e embodiments
- and that the foregoing description is not to be construed in a
`~ limiting sense~
~ ..... ...
.. ~, .
., -.
. .j .
,, .
,,.1
.
': '.' "
~`
.. ~ ....
'`'
.~ .
`',, '
' ' ':
''' -10-
,. .
.~' .
,:. ' ~ :,,
.. . . .
