Process of and apparatus for ironing work for bolt and the same work for bolt

A process of ironing a thread formation shaft portion of a work for bolt having a cylindrical portion and the thread formation shaft portion in axial alignment. The process comprises the steps of supporting the cylindrical portion of the work in radial directions and in a zero clearance state, and moving the thread formation shaft portion in the axial direction relative to a shaft portion ironing die, the supporting step and the moving step being executed simultaneously.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a process of and apparatus for ironing a work for 
bolt having a cylindrical portion and a thread formation shaft portion in 
axial alignment, specifically ironing the thread formation shaft portion, 
and also to the ironed work. 
2. Description of the Prior Art 
FIGS. 6(A) and 6(B) show a prior art ironing apparatus pertaining to the 
invention. This ironing apparatus 1 is used for ironing work w for bolt. 
The work w has a cylindrical portion wk, a thread formation shaft portion 
wn, and a connecting portion wt connecting the portions wk and wn. The 
portions wk, wt and wn are in axial alignment. The apparatus 1 irons the 
thread formation shaft portion wn of the work w to a predetermined finish 
diameter. After the thread formation shaft portion wn has been finished to 
the predetermined diameter, it is formed with a thread, thus completing a 
bolt. 
The ironing device 1 comprises a movable die 2 for guiding the work w while 
supporting the cylindrical portion wk thereof in radial directions, and an 
ironing die 4 for ironing the thread formation shaft portion wn. 
The ironing die 4 has a land (not shown) for ironing the thread formation 
shaft portion wn of the work w, and comprises two stages disposed one over 
another and secured centrally in a substantially cylindrical reinforcement 
ring 5. The reinforcement ring 5 is accommodated in a cylindrical die case 
8, and is positioned with its flange 5f clamped in the axial direction 
between the die case 8 and a die base 6. 
The movable die 2 is slidable through the die case 8 above the 
reinforcement ring 5, and has a central hole 2k for supporting the 
cylindrical portion wk of the work w in radial directions and coaxially 
with the ironing die 4. The hole 2k has a slightly greater diameter than 
the outer diameter of the cylindrical portion wk of the work w. 
A pair of spring retainer pins 2r are secured to the lower end of the 
movable die 2 and extend in the sliding direction through guide holes 5h 
formed in the reinforcement ring 5. Spring retainers 2e are coaxially 
secured to the ends of the spring retainer pins 2r, and slidably 
accommodated in recesses 6h formed in the die base 6. 
Springs 6g are accommodated in the recesses 6h to push the spring retainers 
2e upward. By the biasing forces of the springs 6g, the movable die 2 is 
pushed up together with the spring retainer pins 2r and is held at a 
position where the spring retainers 2e are in contact with the bottom face 
of the reinforcement ring 5. A work kick-out pin 9 extends upward through 
a central bore or hole 6k formed in the die base 6 and also through the 
ironing die 4. 
For ironing the thread formation shaft portion wn of the work w with the 
ironing apparatus 1 as shown above, the thread formation shaft portion wn 
of the work w is inserted in the ironing die 4 by passing the cylindrical 
portion wk of the work w through the hole 2k of the movable die 2 with a 
head of the work w held in engagement with a dodecagonal trimming punch 7c 
of a lifting mechanism 7, as shown in FIG. 6(A). Then, the lifting 
mechanism 7 is lowered from this position to push down the movable die 2 
together with the work w against the spring forces of the springs 6g, as 
shown in FIG. 6(B), so that the thread formation shaft portion wn of the 
work w is ironed by the ironing land. When the ironing process on the 
thread formation shaft portion wn is completed, the lifting mechanism 7 is 
raised, and the work w is kicked out from the ironing die 4 by the work 
kick-out pin 9. The diameter of the ironed thread formation shaft portion 
wn is adjusted to a predetermined dimension. 
In the above prior art ironing apparatus 1, however, the movable die 2 is 
moved vertically relative to the die case 8. Therefore, a predetermined 
clearance is formed between the movable die 2 and the die case 8. In 
addition, the cylindrical portion wk of the work w is inserted through the 
hole 2k of the movable die 2. Therefore, a predetermined clearance is also 
formed between the cylindrical portion wk of the work w and the wall 
surface of the hole 2k. The accumulation of these clearances has adverse 
effects of rattling of the work w when the thread formation shaft portion 
wn is ironed. It is thus difficult to stabilize the axial deflection 
accuracy (i.e., deflection of the head with reference to the thread 
portion) of the ironed work w for bolt to at least a predetermined level. 
SUMMARY OF THE INVENTION 
An object of the invention is to improve the axial deflection accuracy of 
the bolt by eliminating the clearance between the cylindrical portion of 
the work for bolt and the wall surface of the movable die hole, and to 
thereby permit the ironing of the thread formation shaft portion without 
adverse effects of rattling. 
The above object of the invention is attained by a process of ironing a 
thread formation shaft portion of a work for bolt having a cylindrical 
portion and the thread formation shaft portion in axial alignment, which 
comprises the steps of supporting the cylindrical portion of the work in 
radial directions and in a zero clearance state, and moving the thread 
formation shaft portion in the axial direction relative to a shaft portion 
ironing die, the supporting step and the moving step being executed 
simultaneously. 
In this process, the thread formation shaft portion of the work is ironed 
with the cylindrical portion thereof held continuously in radial 
directions and in a zero clearance state by a support member. No rattling 
is thus generated between the cylindrical portion of the work and the 
support member, and the axial deflection accuracy (i.e., deflection of the 
head with reference to the end thread portion) of the ironed work is 
improved. 
Preferably, the cylindrical portion is supported in radial directions while 
it is ironed by a cylindrical portion ironing die.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
First Embodiment 
Now, an ironing process and ironing apparatus according to a first 
embodiment of the invention will be described with reference to FIGS. 
1(A), 1(B), 2, 3(A) to 3(C), 4(A) and 4(B). FIGS. 1(A) and 1(B) are 
fragmentary sectional views showing an ironing apparatus according to this 
embodiment, and FIG. 2 is a sectional view showing the whole ironing 
apparatus. FIG. 3(C) is a side view showing a thread formation shaft 
portion wn before being ironed, FIG. 3(B) is a side view showing the 
thread formation shaft portion wn after being ironed, and FIG. 3(A) is a 
side view showing a product bolt. 
A work w for bolt which is to be processed, as shown in FIG. 3(A), has a 
head wh, a cylindrical portion wk, a connecting portion wt and a thread 
portion wm. Before the thread formation, the thread portion wm is swaged 
to increase its diameter to d3 (see FIG. 3(C)). It is then ironed by an 
ironing apparatus 10 according to the invention to reduce its diameter to 
d2 (see FIG. 3(B)). The ironed thread formation shaft portion wn is then 
formed with a thread in a subsequent step. The outer diameter d3 of the 
thread formation shaft portion wn before the ironing is set to be smaller 
than the outer diameter d5 of the cylindrical portion wk after being 
processed and greater than the outer diameter d6 of the connecting portion 
wt. A cylindrical portion ironing die to be described later has an inner 
diameter of d5, and the diameter d7 of the cylindrical portion before 
being processed is adjusted through the ironing to d5. Similarly, the 
diameter d3 of the thread formation shaft portion wn is adjusted through 
the ironing to d2, which is the inner diameter of a shaft portion ironing 
die. Naturally, d7&gt;d5, and d3&gt;d2. As noted above, d5&gt;d3. Consequently, 
d7&gt;d5&gt;d3&gt;d2. The length L2 of the thread formation shaft portion wn and 
the length L1 of the cylindrical portion wk are related as 
EQU L1: L2+X+xr 
where X is the land margin of an ironing land of a cylindrical portion 
ironing die 12 to be described later, and xr is the guide length of the 
cylindrical portion ironing die 12. 
FIG. 2 shows the ironing apparatus 10, which is used for ironing the swaged 
thread formation shaft portion wn and comprises the cylindrical portion 
ironing die 12 and the shaft portion ironing die 14. 
The cylindrical portion ironing die 12 supports the cylindrical portion wk 
of the work w for bolt in radial directions and in a zero clearance state 
when ironing the thread formation shaft portion wn of the work w. As shown 
in FIGS. 1(A) and 1(B), the die 12 has a land 12r formed at a 
predetermined upper position for ironing the cylindrical portion wk. The 
zone from the top of the cylindrical portion ironing die 12 to the land 
12r serves as a guide for guiding the cylindrical portion wk of the work w 
down to the land 12r. This distance, i.e., the guide length, is xr. The 
land margin X is set to about 2 mm. The cylindrical portion ironing die 12 
thus serves as a support member according to the invention. 
The shaft portion ironing die 14 serves to iron the thread formation shaft 
portion wn of the work w. This die 14 is positioned coaxially to the 
cylindrical portion ironing die 12. It has a land 14r for ironing the 
thread formation shaft portion wn, and the land 14r is formed at a 
position at a distance yr from the land 12r of the cylindrical portion 
ironing die 12. The distance yr is set such that the leading end of the 
thread formation shaft portion wn reaches the land 14r when the leading 
end of the cylindrical portion wk clears the land 12r. The zone from the 
land 12r of the cylindrical portion ironing die 12 to the land 14r of the 
thread formation shaft portion 14 serves as a guide for guiding the thread 
formation shaft portion wn of the work w down to the land 14r. 
The cylindrical portion ironing die 12 and shaft portion ironing die 14, as 
shown in FIG. 2, are accommodated in a coaxially superimposed state in a 
cylindrical die case 18. The die case 18, cylindrical portion ironing die 
12 and shaft portion ironing die 14 are coaxially secured to a die base 
16. A work kick-out pin 19 is disposed under the die base 16 and extends 
upward through a central hole 16k formed in the die base 16 and also 
through the shaft portion ironing die 14 and cylindrical portion ironing 
die 12. 
An ironing process according to the invention will be described with 
reference to FIGS. 1(A), 1(B) and 2. 
First, the lifting mechanism 17 is lowered to insert the work w, which is 
mounted vertically on a dodecagonal trimming punch 17c of the lifting 
mechanism 17, from the thread formation shaft portion wn through the 
cylindrical portion ironing die 12 and then the shaft portion ironing die 
14. FIG. 1(A) shows the state in which the cylindrical portion wk of the 
work w has been led along the guide xr down to the land 12r and the thread 
formation shaft portion wn has been led along the guide yr down to the 
land 14r. 
As the lifting mechanism 17 is further lowered form this state, ironing of 
the cylindrical portion wk of the work w by the land 12r is commenced, and 
slightly afterward, ironing of the thread formation shaft portion wn by 
the land 14r is commenced. When the work w is inserted through the ironing 
dies 12 and 14 to the extent that its head wh reaches the die 12, as shown 
in FIGS. 1(B) and 2, the ironing of the thread formation shaft portion wn 
and cylindrical portion wk are completed. 
When the ironing of the thread formation shaft portion wn of the work w is 
thus completed, the lifting mechanism 17 is raised to detach the processed 
work w from the dodecagonal trimming punch 17c, and the work kick-out pin 
19 is raised to kick out the work w from the cylindrical portion ironing 
die 12 and shaft portion ironing die 14. 
When the ironing process is completed, an upper portion of the cylindrical 
portion wk remains without being ironed, as shown in FIG. 1(B). However, 
no problem arises so long as the cylindrical portion wk is ironed during 
ironing of the thread formation shaft portion wn because the cylindrical 
portion wk is ironed for the purpose of supporting the portion wk in 
radial directions in a rattling-free state (i.e., zero clearance state). 
Since the cylindrical portion wk of the work w is supported in radial 
directions and in a zero clearance state by the cylindrical portion 
ironing die 12 while the thread formation shaft portion wn of the work w 
is ironed by the shaft portion ironing die 14, no rattling of the portion 
wk is caused, and the axial deflection accuracy (i.e., deflection of the 
head with reference to the end thread portion) of the ironed work w is 
improved. 
FIG. 4(A) is a graph showing the axial deflection of a plurality of works 
of bolt when the works are ironed in the ironing process according to this 
embodiment. FIG. 4(B) is a graph showing the axial deflection of a 
plurality of works w of bolt ironed in the prior art process. With the 
ironing process according to this embodiment, the axial deflection of the 
work w is reduced to about one half compared to the prior art. 
Second Embodiment 
An ironing process and ironing apparatus according to a second embodiment 
of the invention will now be described with reference to FIGS. 5(A) and 
5(B). 
The ironing apparatus 20 according to this embodiment is an improvement of 
the cylindrical ironing die 12 in the ironing apparatus 10 according to 
the first embodiment. The construction is otherwise the same as the 
ironing apparatus 10 according to the first embodiment. 
The ironing apparatus 20 comprises an upper support die 22 having a through 
hole 22k through which the work w for bolt is inserted. A ring-like oil 
hydraulic pressure chamber 22t is formed around the thorough hole 22k. The 
oil hydraulic pressure chamber 22t has a flexible side plate for forming a 
wall portion of the through hole 22k, so that, as shown in FIG. 5(B), the 
inner diameter of the thorough hole 22k is reduced when an oil hydraulic 
pressure is applied to the oil hydraulic pressure chamber 22t from an oil 
hydraulic unit (not shown). 
With this construction, the cylindrical portion wk of the work w is 
supported in radial directions and in a zero clearance state by the upper 
support die 22 when the thread formation shaft portion wn of the work w is 
ironed by the land 24r of the shaft portion ironing die 24. The portion wk 
is thus free from rattling, and the axial deflection accuracy of the 
ironed work w is improved. 
Thus, according to the invention, the cylindrical portion of the work for 
bolt is supported in radial directions and in a zero clearance state by 
the support member when the thread formation shaft portion of the work is 
ironed, thus eliminating rattling of the work and improving the axial 
deflection accuracy of the ironed work. 
While the invention has been described with reference to preferred 
embodiments thereof, it is to be understood that modifications or 
variations may be easily made without departing from the scope of the 
present invention which is defined by the appended claims.