Extrusion die and manufacturing method of same

An extrusion die having on the front surface thereof a bearing opening of the shape of a given section; a bearing surface corresponding to the section of the bearing opening formed over a length from the front surface to the rear surface of the die; and a draft formed from the bearing surface toward the rear surface; the bearing surface at each position on the inner circumferential line of the bearing opening being formed in such a fashion as to have a bearing length which is substantially determined in accordance with the shape of the bearing opening at that position wherein, when viewed with respect to a sectional face orthogonal to the inner circumferential line, a straight line corresponding to the bearing surface and a straight line corresponding to the draft intersect at a depth position substantially equal to or larger than the bearing length at that position, and the depth position where the intersection point exists is in a depth position which is substantially determined in accordance with the shape of the bearing opening at the respective positions on the inner circumferential line of the bearing opening, and a method of making the same.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates generally to an extrusion die and a method of making 
the same, and more specifically to an extrusion die having on the front 
surface thereof a bearing opening of the shape of a given section, and a 
draft formed over a length from the bearing opening toward the rear 
surface of the die wherein all or part of the bearing surface and the 
draft constituting the inner circumferential surface of the bearing 
opening are formed by means of the wire- gutting discharge machining 
equipment, and a method of making the same. 
2. Description of the Prior Art 
An extrusion die as illustrated in FIGS. 1 (A) through (C) is known as a 
conventional type of extrusion die for extruding aluminum extrusions. FIG. 
1 (A) is a plan view, FIG. 1 (B) is a sectional side elevation taken along 
line A-A' in FIG. 1 (A), and FIG. 1 (C) is a bottom plan view of the 
conventional type of extrusion die, respectively. In the figures, 
reference numeral 1 refers to an entrance portion; 2 to a bearing opening; 
3 to a draft; and 4 to a shouldered portion of the draft 3, respectively. 
In general, when manufacturing an extrusion, like an aluminum sash, by 
forcing material through an extrusion die, an aluminum slug fed into the 
entrance portion 1 is forced toward the bearing opening 2 by means of an 
extrusion press (not shown), formed into a given shape by the bearing 
opening 2, and forced out of the draft 3 in the form of an extrusion. 
Consequently, to manufacture an extrusion with high precision, it is 
necessary to keep the rate of aluminum slug passing through the bearing 
opening 2 uniform. To achieve this, it has been conceived that the bearing 
length (1 as shown by arrows in FIG. 1 (B)) of the bearing opening 2 is 
adjusted in accordance with the shape of the bearing opening 2, as will be 
described later, referring to FIGS. 2 and 3. In the following, the bearing 
length 1 will be described. 
FIGS. 2 (A), (B) and (C) are crosssectional views taken along lines A-A', 
B-B' and C-C', respectively in FIG. 1, and FIG. 3 is a development of the 
bearing surface. Reference numerals 2 through 4 throughout the figures 
correspond with like numerals in FIG. 1, and 5 refers to a bearing surface 
and 6 to a draft tapered surface, respectively. 
As noted earlier, the bearing length 1 (as shown in FIG. 1 (B)) in the 
bearing opening 2 is predetermined in accordance with the shape of the 
bearing opening 2. That is, the bearing length, 1.sub.c is made larger, as 
shown in FIG. 2 (C), in a bearing opening portion having a larger width 
and the adjacent portions thereof, de is shown by arrows in FIG. 1 (C), 
while the bearing length, 1.sub.b is made smaller, as shown in FIG. 2 (B), 
in bearing opening portions, bc and fg having a smaller width, as shown by 
arrows in FIG. 1 (C). Furthermore, the bearing length, 1.sub.a is made 
further smaller, as shown in FIG. 2 (A), in a bearing opening end portion, 
ha as shown by arrows in FIG. 1 (C), which has the same width as the 
adjacent portions thereof but involves retarded metal flow. The bearing 
surface thus formed assumes a shape shows in FIG. 3 in a developed form. 
Arrows a through h in FIG. 3 correspond to the arrows a through h in FIG. 
1 (C). 
The bearing surface 5 of the bearing opening 2 in the conventional type of 
extrusion die described above is machined by the wire-cutting discharge 
machining equipment, while the draft shouldered portion 4 and the draft 
tapered surface 6 are machined by an ordinary discharge machining 
equipment, milling machine or other type of machine tool. The machining of 
the draft shouldered portion 4 is required because it is difficult to form 
with high precision the aforementioned bearing lengths 1.sub.a, 1.sub.b 
and 1.sub.c, and the portions between ab, cd, ef and gh as shown in FIG. 3 
merely by machining the bearing surface 5 and the draft tapered surface 6. 
As a result, the following problems are encountered in manufacturing an 
extrusion die of the conventionad type. 
(i) Complex die manufacturing processes are needed, and the workpiece has 
to be positioned precisely in each manufacturing process. 
(ii) As described above, the machining of the draft 3 with ordinary 
discharge machining equipment requires the manufacture of several types of 
machining electrodes, all of which have to be machined with high 
precision. The machining of the draft 3 with a milling machine also 
requires sophisticated machining techniques. 
(iii) The high-prescision machining of an extrusion die of thc conventional 
type with the abovementioned machining methods is difficult because of 
electrode consumption in discharge machining, and because of cutter 
wobbling in milling. 
Due to the aforementioned problems, the conventional type of extrusion die 
involves a large number of manhours and high manufacturing costs. 
Furthermore, provision of the draft shouldered portion 4 tends to decrease 
mechanical strength in the portions close to the bearing opening 2, 
leading to deformation and cracks in the thin-walled portions around the 
bearing opening 2. 
SUMMARY OF THE INVENTION 
It is an object of this invention to provide an extrusion die having an 
improved mechanical strength, which can be used for manufacturing 
extrusions with high precision, and can be manufactured with reduced 
manufacturing manhours and cost by automating all the machining operations 
of the bearing opening and draft thereof with the workpiece placed, 
through the operations, on the work table of a die manufacturing equipment 
combining wire-cutting discharge machining equipment and a milling 
machine, for example, and a method of making the same.

DETAILED DESCRIPTION OF THE INVENTION 
Each embodiment of the extrusion die of this invention will be described in 
the following, referring to FIGS. 4, 5 and 6. In the figures, reference 
numerals 2, 3, 5 and 6 correspond to like numerals in FIG. 2, and 7 to a 
notched portion. Each embodiment shown in FIGS. 4 through 6 is concerned 
with the extrusion die corresponding to the conventional type of extrusion 
die shown in FIGS. 1 through 3. 
FIGS. 4 (A), (B) and (C) are crosssectional views taken along lines A-A', 
B-B' and C-C' in FIG. 1 (C) illustrating the extrusion die of this 
invention, whose bearing surface 5 and draft tapered surface 6 are 
manufactured with the wire-cutting discharge machining equipment, which 
will be described later. The bearing surface 5 in the embodiment shown in 
FIG. 4 is machined in the same manner as with the conventional type of 
extrusion die. The draft tapered surface 6 constituting the draft 3 is 
also machined with the wire-cutting discharge machining equipment shown in 
FIG. 7, as will be described later, by controlling the inclination angle 
and/or travelling position of the wire electrode in accordance with the 
shape of the bearing opening 2 (the manufacturing method will be described 
in detail later). Consequently, the embodiment of this invention shown in 
FIG. 4 is an extrusion die having a bearing opening 2 defined by a desired 
bearing surface 5, as shown in the development shown in FIG. 3 without 
providing a draft shouldered portion 4 (shown in FIG. 2) as provided in 
the conventional type of extrusion die. 
In the embodiment shown in FIG. 5, the bearing surface 5 having different 
bearing lengths (for example, l.sub.a, l.sub.b, l.sub.c, etc. as shown by 
arrows in FIG. 3) at predetermined positions in accordance with the shape 
of the bearing opening 2 is formed by machining the draft tapered surface 
6 while controlling the inclination angle and/or travelling position of 
the wire electrode so as to ensure the uniform flow rate of an aluminum 
slug passing through the bearing opening 2. The results of actual 
extrusion tests using the extrusion die thus manufactured, however, 
revealed that the bearing length of the bearing surface 5 has to be 
corrected in some cases. The amount of correction of the bearing length is 
usually so small that it can be corrected with a file. To do this, 
however, the intersection line of the bearing surface 5 and the draft 
tapered surface 6 has to be made visible. In the embodiment shown in FIG. 
4, however, it is difficult to visually inspect the intersection line of 
the draft tapered surface 6 and the bearing surface 5 because of the small 
inclination angle of the draft tapered surface 6. Furthermore, when 
manufacturing extrusions using the extrusion die shown in FIG. 4, the 
extruded material may stick to the surface 6, depending on the nature of 
the material being extruded. This may cause flaws on the extrusion, 
leading to deteriorated product quality. As an extrusion die that can, 
solve the aforementioned problem, another embodiment of this invention 
will be described in the following, referring to FIG. 5. 
The embodiment shown in FIG. 5 is an extrusion die in which, after the 
draft tapered surface 6 has been machined in the same manner as with the 
embodiment shown in FIG. 4, a notched portion 7 is provided within a range 
that can be visually inspected and corrected and can prevent the extrusion 
from sticking, that is, to a depth of 0.1 to 1.0 mm, for example, on the 
draft tapered surface 6 at the intersection line of the bearing surface 5 
and the draft tapered surface 6, and thereafter the bearing surface 5 is 
formed in the same manner as with the embodiment shown in FIG. 4. (The 
manufacturing method thereof will be described later.) FIGS. 5 (A), (B), 
and (C) are cross-sectional views taken along lines A-A', B-B' and C-C' in 
FIG. 1 (C). FIG. 5,(D) is a cross-sectional view at a point D shown by an 
arrow in FIG. 1 (C) (a corner portion of the bearing opening). The bearing 
surface 5 of the embodiment shown in FIG. 5 can be developed as in the 
case of FIG. 3. The notched portion 7 is not provided at the corner 
portion of the bearing opening 2 in the embodiment shown in FIG. 5 (at a 
point D shown by an arrow in FIG. 1 (C)), as shown in FIG. 5 (D). This is 
partly because of the manufacturing method, which will be described later, 
and partly because the bearing surface 5 need not be corrected at the 
intersection line of the bearing surface 5 and the draft tapered surface 6 
at the corner portion of the bearing opening 2. Furthermore, in view of 
the fact that a larger pushing force is exerted on the corner portion than 
on other portions, elimination of the notched portion leads to increased 
reinforcement of the corner portion to withstand the pushing force 
Now, still another embodiment of this invention will be described in what 
follows. In the embodiments shown in FIGS. 4 and 6, the depth positions of 
the intersection line of the bearing surface 5 and the draft tapered 
surface 6 from the front surface of the die agree with bearing lengths 
(1.sub.a, 1.sub.b, and 1.sub.c shown by arrows in FIGS. 4 and 5) at 
positions determined in advance in accordance with the shape of the 
bearing opening 2. This makes not only the control operation required for 
machining the draft tapered surface 6 complicated, but also the 
manufacturing process troublesome. Consequently, another embodiment of 
this invention (not shown), which has the same basic construction as the 
embodiment shown in FIG. 5, is constructed so that, after the draft 
tapered surface 6 has been machined in such a manner that the depth 
positions of the intersection line of the bearing surface 5 and the draft 
tapered surface 6 are made larger than the predetermined bearing lengths, 
or equal to the maximum value of the predetermined bearing lengths, the 
bearing surface 5 having the bearing lengths determined in accordance with 
the inner circumferential line of the bearing opening 2 is formed by the 
abovementioned notching operation. The extrusion die may have small 
bearing lengths at corners D, D,- - - , as shown in FIG. 6. FIG. 6 shows a 
development of the bearing surface 5 in another embodiment of this 
invention. The embodiment shown in FIG. 6 also has the bearing opening 2 
of the same shape as the extrusion die of the conventional type shown in 
FIG. 1. The cross-sections taken at positions A-A' and B-B' correspond to 
FIG. 5 (B), and the cross-section taken at positions C-C' corresponds to 
FIG. 5(c). As is apparent from these crosssectional views, the embodiment 
shown in FIG. 6 has a similar construction as the embodiment shown in FIG. 
5. As described earlier, the flow rate of an aluminum slug passing through 
the bearing opening 2 varies with the shape of the bearing opening 2, and 
decreases particularly at corner portions. Taking this fact in mind, the 
bearing lengths at corners D, D, - - - in the embodiment shown in FIG. 6 
are made smaller than at other portions, as is apparent from the 
development shown in FIG. 6. 
In the foregoing, extrusion dies embodying this invention have been 
described. Now, before describing the manufacturing method of these 
extrusion dies, the manufacturing equipment used for the manufacture of 
the extrusion die of this invention will be described, referring to FIG. 
7. 
In FIG. 7, reference numeral 8 refers to a work table; 9 and 10 to control 
motors for driving the work table 8 in orthogonally intersecting 
lengthwise and widthwise directions; 11 to a work piece; 12 to a wire 
electrode; 13 to a wire electrode feeding roller; 14 and 17 to tension 
rollers; 15 to an upper guide; 16 to a lower guide; 18 to a scrap roller; 
19 and 20 to control motors for driving the upper guide 15 in orthogonally 
intersecting lengthwise and widthwise directions to adjust the inclination 
angle of the wire electrode 12; 21 to a cutter arbor; 22 to a milling 
cutter; 23 to a control motor for controlling the feed of the cutter arbor 
21, respectively. 
The manufacturing equipment shown in FIG. 7 is a combined wire-cutting 
discharge machining equipment and milling machine for manufacturing the 
extrusion die of this invention. Since the wire-cutting discharge 
machining equipment and the milling machine used are well known types, 
description of them will be made only briefly 
In FIG. 7, the work table 8 is driven in orthogonally intersecting 
lengthwise and widthwise directions by the control motors 9 and 10. The 
wire electrode 12 for cutting the workpiece 11 placed on the work table 8 
is wound up by the scrap roller 18 via the wire electrode feeding roller 
13, the lower guide 16, and the tension roller 17. The wire electrode 12 
stretched between the upper guide 15 and the lower guide 16 is tensioned 
by the tension rollers 14 and 17 and caused to travel in a taut state. 
Since the upper guide 15 is constructed so as to be moved in orthogonally 
intersecting lengthwise and widthwise directions by the control motors 19 
and 20, the inclination angle of the wire electrode 12 between the upper 
guide 15 and the lower guide 16 can be adjusted to any desired angle. 
Consequently, the work piece 11 on the work table 8 can be machined freely 
so long as linear cutting is concerned. Other machining operations (such 
as the machining of the notched portion as described earlier), which 
cannot be accomplished by the wire-cutting discharge machining equipment, 
can be achieved by performing desired milling operations by the use of the 
cutter arbor 21 set on the same bed, or by jig grinding operations by 
replacing the milling cutter 22 with a grinding wheel, through the control 
of the control motor 23 for controlling the feed of the milling cutter 22 
and the control motors 9 and 10 for driving the work table in lengthwise 
and widthwise directions. In addition, discharge machining is also 
possible by replacing the cutter arbor with an ordinary discharge 
machining head (not shown). 
The manufacturing equipment described above is capable of machining the 
workpiece in accordance with a predetermined program, or in a numerically 
controlled mode. In other words, the manufacturing equipment described 
above is capable of virtually automatically machining the bearing opening 
2 and the draft 3 of the extrusion die of this invention. As the relative 
positions of the center of the milling cutter 22 and the wire electrode 12 
are predetermined, it is possible to continuously and automatically 
perform wire-cutting discharge machining and milling operations. The 
abovementioned program may be considered as determined by the calculations 
performed based on the information on the shape of the bearing opening 2 
being machined, the bearing length of the bearing surface 5, the 
inclination angle of the draft tapered surface 6, and the amount of 
notching of the notched portion 7. In the following, an example of the 
manufacturing method of the extrusion die of this invention will be 
described, referring to FIGS. 7 and 8. 
The extrusion die of this invention as shown in FIGS. 4 through 6 is 
manufactured by machining in advance a die stock into a state before the 
machining of the bearing opening 2 and the draft 3, that is, a state where 
only the front surface, rear surface, recessed portion and outer 
circumferential surface of the extrusion die have been machined, as shown 
in FIG. 1 (in this Specification, the extrusion die machined in this state 
is called a workpiece). And then, the work piece 11 is heat treated and 
machined to form the bearing opening 2 and the draft 3 with the 
abovementioned manufacturing equipment. 
First, the machining method of the bearing opening 2 and the draft 3 in the 
embodiment shown in FIG. 4 will be described. The workpiece 11 is placed 
on the work table 8 in such a state that the front surface of the 
workpiece 11 comes in contact with the upper surface of the work table 8 
of the manufacturing equipment shown in FIG. 7 (that is, a state where the 
bearing opening 2 being machined is directed downward, with the draft 3 
faced upward, as shown in FIG. 8). Then, the workpiece 11 is cut by 
wire-cutting discharge machining while controlling the position and 
inclination angle of the wire electrode 12 with numerical control based on 
a predetermined program so that a machining allowance for the bearing 
surface 5 (as shown by dotted lines in FIG. 8 (A)). The program for 
numerical control is determined by calculations made based on the 
information on the shape of the bearing opening 2, the bearing length 1 of 
the bearing surface 5 at each position of the bearing opening 2, and the 
inclination angle of the draft tapered surface 6 at each position. FIG. 8 
(D) shows an embodiment where the workpiece is NC-machined, with the 
inclination angle .theta. of the draft tapered surface 6 maintained 
constant. With this arrangement, therefore, any desired draft tapered 
surface 6 can be machined by controlling the position of the wire 
electrode 12. As the information on the shape of the bearing opening 2, 
for example, the coordinates of a point P corresponding to the bearing 
surface 5 being machined and a bearing length 1.sub.l at each coordinate 
point are given. As a result, the coordinates of the position (a point 
P.sub.1 shown by an arrow in the figure) of the wire electrode 12 
corresponding to the point P can be obtained from the following 
expression. 
EQU t.sub.1 =l.sub.1 cot .theta. (1) 
Thus, the wire electrode 12 is caused to pass over the desired intersection 
point (a point P.sub.1 ' as shown by an arrow in FIG. 8 (D)) of the 
bearing surface 5 and the draft tapered surface 6 by controlling the 
position of the wire electrode 12 based on the coordinates of the point 
P.sub.1 obtained from Expression (1) above. 
When the bearing length l.sub.2 is given, the coordinates of a point 
P.sub.2 shown by an arrow in the figure corresponding to the point P can 
be obtained from the following expression. 
EQU t.sub.2 =l.sub.2 cot .theta. (2) 
By controlling the position of the wire electrode 12 based on the 
coordinates of the point P.sub.2 obtained from Expression (2), the wire 
electrode 12 is caused to pass over the desired intersection point (a 
point P.sub.2 ' shown by an arrow in FIG. 8 (D)) of the bearing surface 5 
and the draft tapered surface 6. 
Although a machining control method when the inclination angle of the wire 
electrode 12 is set at a predetermined angle .theta. (the angle 0 should 
preferably be within a range of 83.degree. to 88.degree.)has been 
described in the foregoing, the inclination angle .theta. may also be 
controlled together with the control of the position of the wire 
electrode. 
In this way, the desired draft tapered surface 6 is formed by cutting the 
workpiece 11 to the shape of the bearing opening 2 with the wire electrode 
12. Needless to say, a block 11' separated from the workpiece 11 is 
removed after this machining operation. 
Next, the machining process of the bearing opening 2 will be described. 
This machining process may be performed after a small notched portion, 
which will be described later, has been formed, or before the draft 3 is 
machined. The bearing opening 2 is cut with the wire electrode 12 by 
positioning the wire electrode 12 vertical to the work table 8 (shown in 
FIG. 7), as shown in FIG. 8 (B), and controlling the position of the wire 
electrode 12 based on the coordinates (the coordinates of the point P 
shown by an arrow in FIG. 8 (D)) corresponding to the given shape of the 
bearing opening 2. With this cutting operation, the extrusion die shown in 
FIG. 4 where the bearing surface 5 and the draft tapered surface 6 
intersect with each other at the positions (points P.sub.1 ' and P.sub.2 ' 
shown by arrows in FIG. 8 (D)) corresponding to the desired bearing 
lengths 1 on the inner circumferential surface (i.e., the bearing surface 
5) of the bearing opening 2 can be manufactured. 
Next, the manufacturing method of the embodiment shown in FIG. 5 will be 
described. The embodiment shown in FIG. 5 has a notched portion 7 (shown 
in FIG. 8 (C)) provided on the draft tapered surface 6 at the intersection 
line of the bearing surface 5 and the draft tapered surface 6 in the 
embodiment shown in FIG. 4. The notched portion 7 may be machined with the 
milling cutter 22 shown in FIG. 7 in a state where the extrusion die is 
kept placed on the work table 8 as it is after the draft tapered surface 6 
described in the manufacturing method of the embodiment shown in FIG. 4 
has been completed. After that, the bearing surface 5 may be machined on 
the workpiece 11. By machining in this sequence, burrs produced by the 
abovementioned notching operation can be removed. Since the information 
required for controlling the relative positions of the workpiece 11 and 
the milling cutter 22 during the notching operation, that is, the shape of 
the bearing opening 2 (the coordinates of the point P shown by an arrow in 
FIG. 8 (D)), the bearing lengths l.sub.a, l.sub.b, l.sub.c, etc. as well 
as the information necessary for forming the notched portion 7 have been 
given, the desired notched portion 7 can be formed. The state of the 
relative movement of the milling cutter 22 and the workpiece 11 during the 
notching operation is shown in FIG. 8 (E). That is, the milling cutter 22 
moves in the direction shown by an arrow line in the figure with respect 
to the workpiece 11. As is apparent from the figure, the tip of the 
milling cutter 22 moves along the corner portion D in such a manner that 
the cutter 22 comes in contact with the corner portion D. For this reason, 
the aforementioned notching operation is not performed on the corner 
portion D. In this way, the extrusion die shown in FIG. 5 is manufactured. 
In the description of the manufacturing method of the embodiment shown in 
FIG. 5, mention has been made that the draft tapered surface 6 is machined 
in the same manner as with the embodiment shown in FIG. 4. The bearing 
surface 5 having the predetermined bearing lengths (for example, l.sub.a, 
l.sub.b, l.sub.c) at the positions as shown in FIG. 5 may be formed by the 
abovementioned notching operation after the draft tapered surface 6 at 
each position on the inner circumferential line of the bearing opening 2 
has been machined to depth positions larger than the bearing lengths (for 
example, l.sub.a, l.sub.b, l.sub.c, etc. shown in FIG. 5) or equal to the 
maximum value of the bearing length l, with the inclination angle of the 
draft tapered surface 6 kept constant or not kept constant. 
Furthermore, the extrusion die in the embodiment shown in FIG. 6 can be 
easily manufactured by combining the manufacturing processes of the 
embodiments shown in FIGS. 4 and 5. That is, the embodiment shown in FIG. 
6 is essentially the same as the embodiment shown in FIG. 5, with the 
exception that the bearing length at the corner portion D of the bearing 
opening 2 is made smaller, as shown in the development showh in FIG. 6. 
The bearing surface at the corner portion D having the desired bearing 
length l by controlling the position and inclination angle .theta. of the 
wire-cutting electrode 12 since the bearing length l at the corner 
portion.D has been given in the machining process of the draft 3 in the 
embodiment shown in FIG. 4. In this way, the extrusion die in the 
embodiment shown in FIG. 6 can be manufactured. 
In the above description of the manufacturing method of the extrusion die, 
mention has been made that the bearing surface 5 is machined with the 
wire-cutting discharge machining equipment. The bearing surface 5, 
however, may be machined with the aforementioned milling, jig grinding or 
ordinary discharge machining. Furthermore, the notching operation may be 
performed by the abovementioned milling, jig grinding or ordinary 
discharge machining. 
FIG. 9 shows still another embodiment of the manufacturing method of the 
extrusion die according to this invention. In the embodiment shown in FIG. 
9, the inclination angle of the wire electrode is capable of being 
controlled easily, and bearing surface machining and notching processes 
are performed in the same manner as in the manufacturing method described 
with reference to FIG. 8. In the figure, reference numeral 2 refers to a 
bearing opening; 3 to a draft; 11 to a workpiece; 12 to a wire electrode; 
24 to a first profile; 25 to a second profile, respectively. Points 
represented by P', P'- - - indicate depth points (hereinafter referred to 
as bearing depth points) substantially equal to the bearing lengths (for 
example, l.sub.a, l.sub.b, l.sub.c, etc. shown by arrows in FIG. 5) at 
each predetermined position corresponding to the shape of the bearing 
opening 2. The first profile 24 may be considered as a profile described 
on the die front surface (11-1 shown by an arrow in the figure) by the 
wire electrode 12 which passes the second profile 25 representing open 
profile of the draft 3 on the die rear surface (11-2 shown by an arrow in 
the figure) and the bearing depth points P', P'. 
In the embodiment shown in FIG. 9, both the first and second profiles 24 
and 25 are given, and pairs of two corresponding points are given on each 
of the profiles 24 and 25 to be followed by the wire electrode 12 at a 
predetermined angle to machine the workpiece 11. Needless to say, an NC 
machining technique is adopted in machining the workpiece 11. The first 
and second profiles 24 and 25, and the pairs of two corresponding points 
on both profiles are given as the information for NC machining so that the 
wire electrode 12 passes over the bearing depth points P', P', - - - as 
shown in FIG. 9 corresponding to the points P.sub.1 ', P.sub.2 '- - - 
shown in FIG. 8 (D). As described above, the manufacturing method shown in 
Fig. (9) permits the inclination angle and travelling position of the wire 
electrode 12 to be easily and accurately controlled during the machining 
of the draft 3. In the manufacturing method shown in Fig. (9), the 
machining of the bearing surface 5 and the notched portion 7 as described 
referring to FIGS. 8 (B) and (C) is performed after the draft tapered 
surface constituting the draft has been machined. Although mention has 
been made in describing the manufacturing method shown in Fig. (9) that 
the first and second profiles 24 and 25 are set on the die front surface F 
and the die rear surface R, this invention is not limited to this 
arrangement. That is, the first and second profiles 24 and 25 may be set 
at any given positiohs. Furthermore, in the manufacturing method described 
referring to FIG. 9, the first and second profiles 24 and 25 are set so 
that the wire electrode 12 passes over the bearing depth points P', P', - 
- - , the first and second profiles 24 and 25 may be set so that the wire 
electrode 12 passes over points (not shown) deeper than the bearing depth 
points P', P', - - - or equal to a maximum bearing depth point (for 
example, l.sub.c in the embodiment shown in FIG. 5). In this case, the 
bearing surface having predetermined bearing lengths is formed by the 
aforementioned notching operation after the draft tapered surface 
constituting the draft has been machined. 
As described above, the manufacturing method of this invention makes it 
possible to manufacture the extrusion dies shown in FIGS. 4 through 6 by 
performing the entire machining process with the workpiece 11 placed on 
the work table 8, and to machine the workpiece 11 automatically with an NC 
machining technique. This enables the manufacture of extrusion dies with 
high precision at substantially reduced machining cost. In view of the 
fact that the performance of the wire-cutting discharge machining 
equipment in terms of machining rate has recently been substantially 
improved, the time required for the manufacture of the extrusion die of 
this invention, which relies on wire-cutting discharge machining for most 
of machining operations, can be substantially reduced compared with the 
conventional manufacturing processes. 
Depending on the shape of the bearing opening 2, the machining process of 
the draft 3 of the extrusion die using the manufacturing method of this 
invention may sometimes involve an unwanted phenomenon where fine metal 
chips (what is referred to as separated fine metal chips in this 
invention) are separated from the workpiece on the front surface of the 
extrusion die being machined. The formation of the separated fine metal 
chips is attributable to the factors which will be described later 
referring to FIG. 10, and may result in unstable wire-cutting discharge 
machining. This may pose an obstacle in automating the entire machining 
process since the separated fine metal chips have to be removed by 
interrupting the machining operation. The mechanism of the formation of 
separated fine metal chips will be described in the following, referring 
to FIG. 10. In the machining process of the draft 3 of the extrusion die, 
the wire electrode 12 inclined to an inclination angle .theta. 
corresponding to the inclination angle of the draft tapered surface 6 
constituting the draft 3 is moved so as to pass over the point P.sub.1 
having a depth of the bearing length l at each position of the desired 
bearing opening 2, as shown in FIG. 10 (A). The trajectory of the 
travelling wire electrode 12 may sometimes intersect at a point O, as 
shown in the figure, depending on the value of the inclination angle 
.theta. of the wire electrode 12. FIG. 10 (B) is a diagram illustrating 
the trajectory of the wire electrode 12 during machining to facilitate the 
understanding of the state of machining of the draft 3. Where the 
intersection point O exists between the front surface 11-1 and the rear 
surface 11-2 of the workpiece 11, a separated fine metal chip 26 is 
generated on the rear surface 11-2, as shown in the figure. Reference 
numeral 27 in the figure refers to a trajectory of the point P.sub.1 ; and 
arrow a to the direction of travel of the intersection point P.sub.2 of 
the front surface 11-1 of the workpiece and the wire electrode 12; and 
arrow b to the direction of travel of the intersection point P.sub.3 of 
the rear surface 11-2 of the workpiece 11 and the wire electrode 12. 
The mechanism described above gives an explanation of the formation of the 
separated fine metal chip 26. The formation of the separated fine metal 
chip 26, however, can be prevented by setting the inclination angle 
.theta. of the wire electrode 12 to a larger value during the machining of 
the draft tapered surface 6 at portions where the separated fine metal 
chips are likely to be generated. 
As described above, this invention makes it possible to provide an 
extrusion die which can be used for manufacturing extrusions with high 
precision and a method of making the same; and to substantially reduce the 
manufacturing manhours and cost and improve the mechanical strength of the 
die by automating the entire machining process of the bearing opening and 
the draft, with the workpiece placed on the work table of a manufacturing 
equipment combining the wire-cutting discharge machining equipment and the 
milling machine.