JPH0262342B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a finishing punch for cold plastic working bolts.

[Prior Art] Conventionally, when finish punching a hexagonal bolt with a flange, it is necessary to use a large force applied to each side of the hexagonal hole formed in the nib to break the hexagonal hole at each corner. Due to the large concentration of force exerted on the hexagonal hole, each corner of the hexagonal hole is prone to cracking. As a measure to prevent this, for example, as shown in Fig. 1, six small nib pieces 1 are combined to form a nib 2, the outer circumference of the nib 2 is processed into a circular shape, and then the inner circumference is fitted into a bush 3 whose inner circumference is circular. , moreover 3
was fitted into punch case 4. In this way, the bush 3 and punch case 4 absorb the lateral load and stress, thereby reinforcing the nib 2. However, even with such reinforcement, chipping and cracking of the nib 2 did not disappear, and further improvements were desired. Also nib 2
Since the nib pieces 1 are manufactured from cemented carbide, it is extremely difficult to process the outer periphery of the nib pieces 1 into a circular shape to fit into the bush 3 after assembling them.

[Problems to be Solved by the Invention] Therefore, in the present invention, first, intensive studies were conducted to reduce the occurrence of chipping and cracking of the nib 2. What I discovered was that the chipping and cracking of nib 2 was caused by nib 2 as shown in Figure 2.
This was found to occur more frequently on the inner circumferential hexagonal corner 5 and on the radial extension line of the corner 5. Therefore, we investigated the cause and formulated the following hypothesis. In other words, the thickness of the nib 2 is thinnest at the radial extension line from the corner 5 (that is, at the boundary between the nib pieces 1), and the thickness near the center between the corners 5 is equal to the length l.
The theory is that this difference in thickness causes an imbalance in the tightening force of the bushing 3, causing the heaviest load to be applied during punching, and causing damage near the thinnest part. . Therefore, in order to confirm this hypothesis, we studied the shape of the nib 2 that is thickest near the corner 5 where the greatest load is applied, and devised a finishing punch for bolts as shown in Figures 3 and 4. In the figure, reference numeral 1 denotes a small nib piece, which has an isosceles trapezoidal shape with legs 6 and 7 of equal length and an upper base 8 shorter than a lower base 9. Six small nib pieces 1 are assembled with the upper base 8 facing inside and the legs 6 and 7 in contact with each other to form a nib 2 having a regular hexagonal shape on both the inner and outer peripheries. A bush 3 whose inner circumference is a regular hexagon similar to the outer circumference of the nib 2 and whose outer circumference is circular is fitted on the outer circumference of the nib 2. The inner circumference of the bush 3 is slightly smaller than the outer circumference of the nib 2, and the nib 2 is press-fitted or shrink-fitted inside the bush 3. A punch case 4 is further fitted on the outside of the bush 3 by press fit or shrink fit.

In manufacturing bolts using the finishing punch for bolts configured as described above, when a punching force is applied by the punch pin 12 to the head 11 of the roughly pressed hex bolt clamped to the die 10 as shown in FIG. The head 11 is formed into a hexagonal shape corresponding to the inner circumference of the nib 2. Hexagonal hole 1 required during this molding
3 The load on each surface acts as a force that breaks each corner 5 of the hexagonal hole 13, but in this punch, the thickness on the line connecting the center 14 of the square hole 13 and the outer periphery of the nib 2 is determined by the length of the border between the nib pieces 1. It is thickest with S. In other words, the parts that require the most durability are made thickest. As a result, the resistance to cracking has improved even more than conventional products. Also,
The outer periphery of the nib 2 does not need to be processed into a circular shape unlike conventional products, and can be used as is by simply combining trapezoidal nib pieces 1. As a result, the time and effort required to process the cemented carbide was eliminated, making it possible to significantly reduce the manufacturing cost of punches.

However, even the finishing punches for bolts shown in FIGS. 3 and 4 do not have sufficient durability, and there is a demand for finishing punches for bolts with even higher performance.

[Objective of the Invention and Means for Solving the Problems] As a result of numerous experiments, the present inventor found that providing notches at specific locations further increases durability, and completed the present invention.

That is, the purpose of the present invention is to provide a finishing punch for bolts that is far more durable than conventional products, and this purpose is to provide a finishing punch for bolts that is far more durable than conventional products. In a finishing punch for bolts, which has a nib, a bush with a regular hexagonal inner periphery and a circular outer periphery, and a punch case fitted on the outside of the nib, a small nib piece near the intersection of the border of the nib piece and the outer periphery is used. This is achieved by a finishing punch for bolts, which is characterized by having a notch for stress relief.

[Function] The punch of the present invention combines a plurality of small nib pieces, a bush is fitted onto the outer periphery of the punch, and a stress relief notch is provided by cutting out a part of the nib piece. These notches absorb the internal pressure P that the nib receives radially from inside the processing hole 13 in Figure 3 during the forming process, as well as the tensile stress in the peripheral direction (also called hoop stress) that is applied from the bushing on the outer periphery. The incidence of cracks occurring at the interface between the nib and the nib pieces can be kept low.

[Example] The present invention will be explained in detail below. Fig. 5 shows an example of the present invention, and in this example, the nib small piece 1
A stress relief notch 17 is provided near the intersection between the boundary 16 and the outer periphery. This notch 17 prevents stress from concentrating on this portion, further reducing cracking of the nib 2. The reason for this is presumed as follows. That is, during punching, a strong internal pressure P acts on the hexagonal hole 13 as shown by the arrow in FIG. When a circular pipe receives internal pressure, the pipe wall experiences tensile stress in the circumferential direction (also called circumferential stress or hoop stress).
However, in this embodiment as well, circumferential stress is generated on the inner wall of the nib 2 due to the internal pressure P. This circumferential stress causes stress concentration at the corner 5 of the hexagonal hole 13 and the notch 17. Without the notch 17, stress would concentrate only on the corner 5, making it more likely to break. It is believed that the presence of the notch 17 disperses stress and significantly reduces cracking.

Note that, as a matter of course, the hexagonal hole 13 in both of the above embodiments may be a square hole.

[Effects of the Invention] As described in detail above, in the finishing punch for bolts of the present invention, the nib is less likely to be damaged during cold working, and cold working can be performed for a long time without replacing the nib.
The present invention is particularly useful during cold working of flanged hexagonal bolts, since the force that tends to widen the mouth of the nib acts even more strongly.

Further, the present invention has the advantage that manufacturing is simple and the cost is low because there is no need to process the outer periphery of the nib into a circular shape.

The reason why the present invention exhibits such excellent durability has not been thoroughly investigated theoretically. However, the following reasons are presumed, and it is thought that the following factors (1) to (4) are acting in a synergistic and complex manner.

(1) As mentioned in the above function, the stress relief notch absorbs stress.

(2) The notch allows air and machine oil trapped inside the forming tool to escape, preventing them from adversely affecting the air and hydro-cussion.

(3) It is difficult to precisely machine the cemented carbide, which is the material of the nib piece, into a curved surface in micron units, but in the present invention, the outer periphery of the nib piece is a regular hexagon, so precision machining is easier than when the outer periphery is circular. Easy to do.

(4) The notch function ensures that the tightening force is transmitted to the nib pieces inside.

[Brief explanation of the drawing]

Figure 1 is an exploded perspective view showing an example of a conventional finishing punch, Figure 2 is a front view showing a conventional nib breaking state, Figure 3 is another example of a conventional finishing punch, and A is an exploded perspective view. 4 and 5 are front views, FIG. 4 is a sectional view showing the same example in use, and FIG. 5 is a front view showing an embodiment of the present invention. 1...Nib piece, 2...Nib, 3...Button, 4...Punch case, 5...Corner, 10...
dice.

Claims (1)

[Claims] 1 A bolt consisting of six pieces of isosceles trapezoidal nib pieces combined to form a nib with a regular hexagonal inner and outer circumference, a bushing with a regular hexagonal inner circumference and a circular outer circumference fitted on the outside of the nib, and a punch case fitted on the outside of the nib. A finishing punch for bolts, characterized in that a stress relief notch is provided in the nib piece near the intersection of the boundary of the nib piece and the outer periphery.