JPS5937136B2 - How to make crownless front fork material for bicycles - Google Patents

Description

[Detailed Description of the Invention] The front fork of a bicycle is composed of three parts: a stem, a shoulder (crown), and two sheaths or legs (hereinafter referred to as legs). That is, the crown is omitted and the curved part of the leg is used instead, in an attempt to reduce the cost of manufacturing the bicycle.

In summary, the present invention consists of two legs each made from a straight welded steel pipe, and a stem sandwiched between these two legs and welded.

The welded steel pipe that is the starting material of the present invention may be easily available on the market, and has a length of 400-450 m including the crown part.
m, outer diameter 21.2-24.0, inner diameter 20.0
mm) Use one with a wall thickness of 1.2-1.4 mm.

The composition of the steel is Co, 12% or less, Si 0.35% or less, Mn0.25-O, 60%, Po, 040%, and the balance is Fe, and its physical properties include tensile strength of 32-4
2kg/Cd) Elongation 30-40%, Brinell hardness 80-
It is a common and common steel type called 120.

In addition, a welded joint with a straight line parallel to the pipe axis is used, but it would be satisfactory if a seamless pipe was used, but there is a problem in terms of cost. When setting a welded steel pipe in a mold, care should be taken so that the weld seam faces inward at the shoulder. An embodiment of the invention will now be described in detail with reference to the accompanying drawings.

FIG. 1 shows a known front fork with a bicycle crown (shoulder), which consists of a stem, a crown, a foot or sheath, and a pawl.

FIG. 2 is a sectional view of the front fork according to the invention, which, as is readily apparent when compared with FIG. 1, is crownless.

In FIG. 2, the curved portion 5 consists of an outer circumferential portion, that is, a crown 5a, and an inner circumferential portion 5b of the tube material 1, and the outer circumferential portion 5a is the inner circumferential portion 5b.
This shows that the wall thickness has become approximately twice as thick. FIG. 3 shows a straight welded steel pipe 1 with a straight welded seam 1a of the starting material used in the invention.

FIG. 4 shows the tip (right end in the figure) of the tube material 1, which is the starting material of the present invention, cut at an angle of approximately 200 to 500 degrees with respect to the tube axis before being set in the mold 6. shows. FIG. 5 shows the state immediately before the pipe material 1 at the tip of the beveled cut is inserted into the split mold 6 and is then press-fitted from the left end using the mandrel 7 in the figure.

FIG. 5 shows a cross-sectional view of the mold 6. As shown in this cross-sectional view, the tube material 1 is pressed by the mandrel 7 from the left end in the figure, and the beveled tip is placed in a curved shape installed at the right end of the mold 6. The tube material 1 is curved along the curved portion 8a of the mandrel 8. FIG. 6 shows that the tube material 1 has completed the required steps in the mold 6.

Figure 7 shows pipe material 1 with both mandrels 7 and 8 inserted.
After removing the mandrels 7 and 8 from the mold 6, the mandrels 7 and 8 are attached to the pipe material 1.
Shows how to pull it out.

The mandrel 7 consists of a linear cylindrical body 7a, an intermediate cylindrical body 7b, and a base 7c.
The outer diameter of a is made to be approximately equal to or smaller than the former, so that it can freely slide within the tube.

The outer diameter of the intermediate cylindrical body 7b of the mandrel 7 is such that it sufficiently contacts the end surface of the tube material 1 and extends into the mold 6, that is, the beveled tip is approximately 9
Set the length so that it can be press-fitted until it bends 0 degrees.

The concave portion 6a of the mold 6 has a size corresponding to the thick portion 5a of the curved portion of the tube material 1 shown in FIG. The mandrel 8 has a curved portion 8a, which has a volume corresponding to the recess 6a, which will be explained in more detail below.

As an example, if the length of the front hawk's legs is 40,011 and the crown part is 5,011, the total length is 45.
A tube material 1 of No. 011 is taken and inserted into a mold 6 shown in FIG. 5 and set.

The tip of the tube material 1 is cut obliquely as described above. This mold 6
The size of the curved concave portion 6a is designed to cooperate with the curved cylindrical body 8a which is removably installed in the mold 6 so that the curved portion of the tube material 1 has a required thickness.
In other words, the concave portion 6a is determined as follows.

If the initial wall thickness of the tube 1 is 1.211, the method of the present invention increases the wall thickness to 2.81u, and if the initial wall thickness is 1.411, the wall thickness increases to 3.011u. It was found that the size of the concave portion 6a was 2.8.
It seems that a distance of ~3.0m would be sufficient. Fifth
When the tubular material 1 is set in the mold 6 as shown in the figure, care is taken to ensure that the welded seam 1a of the tubular material occupies the inside of the curved portion of the tubular material 1, that is, the position 5b (FIG. 2), as described above.

Next, a pressing mandrel 7 is brought into contact with the other end of the tube material 1, that is, the end opposite to the tip of the oblique cut.

As mentioned above, the mandrel 7 is made of three integral parts, so first the leading part 7a of the mandrel 7 is inserted into the tube 1 to support the tube 1 from inside, and then , the intermediate body 7b abuts the entire end surface of the tube material 1,
It is pressed into the mold in the direction of the arrow with a pressing force of 20,000 to 25,000 kg. The press-in speed of the mandrel 7 is a slow speed of about 1 m per minute. When the tip 7a of the press-fitting mandrel 7 comes into contact with the tip 8a of the curved mandrel 8 in the mold 6, the pressing is stopped, but at this time, the intermediate cylindrical body 7b of the mandrel 7 enters the inside of the mold 6. This is the time when the base portion 7c comes into contact with the mold 6. That is, when the intermediate cylindrical body 7b is sufficiently press-fitted into the mold 6, the obliquely cut tip of the tube material 1 curves along the curved mandrel tip 8a and comes into contact with the base portion 8 of the mandrel, completing the curve forming process. , the desired wall thickness of the tube material 1 in the concave portion 6a of the mold 6 becomes the required wall thickness. The length of the intermediate portion 7b of the mandrel 7 corresponds to the length of the curved portion of the tube material 1, and once the length of 7b is determined, the length of the tip portion 7a can be easily determined.

FIG. 6 is a sectional view showing the point at which the pressure forming process using only pressing according to the present invention is completed, and is a continuation from the point immediately before FIG. 5, and is an intermediate step from FIG. 5 to FIG. 6. has been omitted. As shown in Fig. 6, the tip of the pipe material 1 is the mold 6.
The above-mentioned pressure is applied at the above-mentioned speed along the curved mandrel 8a to form the required bulge 5a (Fig. 2).After the forming is completed, the upper die of the mold 6 is removed, and then Remove the tube material 1 with both mandrels 7 and 8 still inserted from the lower mold, pull out the straight mandrel 7 in the direction of the arrow, and then pull out the curved mandrel 8 in the direction of the arrow, as shown in FIG. As shown, the crude material for the crownless front fork is taken out by pulling it out in an arc as shown, and is subjected to subsequent processing to obtain the desired finished product for the crownless front fork. The present inventor is Japanese Patent Publication No. 53-12460 (May 1, 1982)
As disclosed in U.S. Pat. This should be seen as bulge formation.

As mentioned above, the metal components of the tube material 1 find a so-called escape place in the concave portion 6a provided in the mold 6, and as a result, they aggregate there.
It is assumed that the wall thickness of the curved portion 5a of the pipe material 1 becomes thicker.

The rate of increase in wall thickness is as described above. Align the two curved hawks 3 taken out from the mold 6, and make the two hawks 3.
Then, as shown in Fig. 2, by sandwiching the stem 2 and welding the parts 9 and 9a, the crownless front fork is completed.

Although the figure shows the welding points 9 and 9a between the right-hand fork and the stem, the same applies to the welding points between the left-hand fork and the stem. From this, a finished product can be obtained by subjecting it to various known processing steps as a bicycle part. As is well known, the bicycle parts industry is currently struggling with how to reduce the production costs of each part, and even though the crown (shoulder) is missing as in the present invention, there is no problem in practical use. It is considered to be extremely meaningful to be able to provide Hawk wood to the market.

[Brief explanation of drawings]

The drawings show the method of the present invention; FIG. 1 is a known front fork, FIG. 2 is a sectional view of the crownless front fork according to the present invention,
FIG. 3 shows the raw material, FIG. 4 is a sectional view of the starting material with one end beveled, and FIGS. 5 and 6 show the initial and final steps of the mold in the method of the invention. FIG. 7 shows a method for pulling out both mandrels from the tube into which both mandrels are inserted, which have been taken out from the mold. 1...Raw material pipe, 2...Stem, 3...Legs,
4...Tlaw, 5...Curved part, 6...
... Mold, 7... Pressing mandrel, 8...
...Curved mandrel.

Claims (1)

[Claims] 1 Starting material is a straight welded steel pipe with a beveled tip, and the tip of the tube is inserted into a split mold that is to be bent approximately 90 degrees, and the mold is relatively large at the bending point of the tube. A straight mandrel that can be inserted from the other end of the pipe material, with a recess designed so that the wall thickness at the curved outer circumference part, that is, the shoulder part of the front fork material for a bicycle, is relatively small and thicker than the curved inner circumference part. and a curved mandrel that can be inserted from the tip, the weld seam of the tube is set in the mold with the weld seam facing inward in the curved region, and the straight mandrel is inserted from the other end of the tube, The mandrel is press-fitted with a predetermined pressing force and a predetermined speed, a pipe material having a predetermined curved portion at the tip of the pipe material is manufactured, and the pipe material is taken out from the mold as one front fork material, and then the fork material is A method for producing a crownless front fork for a bicycle, which comprises preparing two pieces of front fork, installing a stem in the center, and welding the tips of the two front forks having the curved portions to both sides of the stem, respectively. .