BACKGROUND OF THE INVENTION
1. Field of the Invention
[0001] The present invention relates to a method of forming a metal fastener, in particular
a method for cold forging high strength fastener with austenitic 300 series material.
2. Description of the Related Art
[0002] Referring to Fig.
1 and
2, a conventional method
1 of manufacturing a fastener comprises a sequence of procedures, which include a procedure
of preparation
11, a procedure of head formation
12, a procedure of drill point formation
13, a procedure of threads formation
14 and a procedure of heat treatment
15; wherein, a raw shaft
21, made of the austenitic 302 or 304 stainless steel, is initially arranged in the preparation
11 and provides with a first diameter
"d" for instance the specification of #12 (approximately of 5.5 mm) and a maximum shearing
force approached 2630 pounds. Further, the raw shaft
21 respectively forms a head
23 and a shank
24 extended therefrom and thereafter forms a drilling portion
25 disposed reverse to the head
23 by the formation procedures
12 and
13. Still, a plurality of threads
26 are sequentially convolved on the shank
24 by a thread roller machine, thus obtaining a preliminary fastener. Ultimately, the
fastener is susceptible of carburizing and quenching inside a heat furnace for altering
the molecular arrangement thereof and is also coated with a carburized layer
27 thereon for increasing the hardness thereof. The above apparatuses here are omitted
in Figures.
[0003] However, the conventional method may have some disadvantages:
- 1. Higher manufacturing cost and more procedures
Although the integral fastener includes higher strength than the raw shaft through
the concatenating procedures of formations, the fastener still requires the heat treating
procedure to enhance its case hardness, so that the fastener can be smoothly drilled
into objects. Additionally, the fastener would facilely become rusty and corrosive
by the carburized layer and the additional process for corrosion resistance is necessary,
whereby the conventional method results of increasing the cost and adding more excess
manufacturing procedures.
- 2. Descending the quality of the fastener
The procedure of heat treatment may assist the fastener to increase its case hardness
but may negatively soften its core hardness susceptible of the high temperature in
carburizing and quenching, thus decreasing the elongation of the fastener to result
in the broken thereof or difficultly drilling the fastener into objects. Therefore,
it would affect the screwing security.
SUMMARY OF THE INVENTION
[0004] The object of the present invention is to provide a method for cold forging high
strength fastener with austenitic 300 series material which facilitates to achieve
a high strength and an effective corrosion resistance, simultaneously to obtain a
rapid manufacture, a lower manufacturing cost and the using security.
[0005] The method in accordance with the present invention comprises in sequence a procedure
of preparation, a procedure of head formation, a procedure of drill point formation,
and a procedure of thread formation. That is, preparing an austenitic raw shaft and
reducing its diameter by cold forging so as to generate a preliminary shank, which
can bear above 1/2 force more than the raw shaft; further passing through the formation
procedures in sequence to build an integral fastener. In this manner, the entire cold
forging work facilitates to fabricate the integral fastener with high strength and
harness without any additional heating procedures, thus decreasing the manufacturing
cost and process; moreover, the fastener has a better elongation to avoid being broken
while screwing so as to increase the screwing security.
[0006] The advantages of the present invention over the known prior art will become more
apparent to those of ordinary skilled in the art upon reading the following descriptions
in junction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007]
Fig. 1 is a flow diagram showing a conventional method of manufacturing a stainless
fastener;
Fig. 2 is a schematic view showing the conventional procedures;
Fig. 3 is a flow diagram showing a first preferred embodiment of the present invention;
Fig. 4 is a schematic view for showing the procedures of Fig. 3;
Figs. 5a and 5b respective indicate the torque range in the experiment relating to
the torque value and the angle;
Fig. 6 is a flow diagram showing a second preferred embodiment of the present invention;
and
Fig. 7 is a schematic view shown an integral fastener of Fig. 6.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0008] Before the present invention is described in greater detail, it should be noted that
the like elements are denoted by the same reference numerals throughout the disclosure.
[0009] Referring to Fig.
3 and
4, a method
3 of a first preferred embodiment for cold forging a high strength fastener comprises
the steps of a process of preparation
31 for preparing a raw shaft
41 having a first diameter "
d1" fabricated of austenitic 300 series material, for instance of 302 or 304 stainless
steel, and the raw shaft
41 is initially squeezed by cold forging for reducing above 15% of the first diameter
"
d1" and a preliminary shank
42 with a second diameter "
d2" is hence generated. Assumed that the second diameter
"d2" is measured of 5.5mm, and the first diameter should be predetermined at least of
6.325mm, so that the second diameter
"d2" smaller than the first diameter "
d1" assists the shank
42 to undertake in excess of 1/2 force to the raw shaft
41, namely the shank
42 is subjected to the maximum shearing force of 4065.25 pounds, extremely larger than
the conventional method (2630 pounds).
[0010] Still further, the preliminary shank
42 forms a screw head
43 at one end thereof through a procedure of head formation
32 and the head
43 has a third diameter
"d3" greater than the second diameter
"d2" of the shank
42. In a procedure of drill point formation
33, a drilling portion
44 is thereafter cold forged at the other end of the shank
42, reverse to the head
43, so as to increase the hardness of the drilling portion
44. Further at a procedure of thread formation
34, a plurality of screw threads
45 are convolved on the shank
42 by a thread roller machine (not shown), hence an integral fastener
4 is accomplished. The fastener
4 increases its case hardness and strength by passing from the cold forging of the
preparation
31, thence to the head and the drill point formation
32, 33, and then to the thread forming formation
34 to impart multiple squeezing forces to the shank
42. Furthermore, the integral fastener
4 can additionally experience a procedure of whitening
35 for cleaning the remnants on the outer surface thereof, thereby retrieving primary
colors of the raw austenitic 300 series materials and maintaining a bright appearance.
[0011] Moreover, the fastener
4 has been previously tested in different areas and provides with some experimental
statistics as presented in tabled below:
(1) For utilized in construction industry
8 random samples of fasteners made by the present invention and providing with the
specification of #12×35 are adopted in the experiment and here the table 1 shows the
numerals relative to the hardness, torque, shearing force and loading weight while
in screwing: (Referring to Fig. 5a and 5b)
TABLE 1
CHARACTERISTICS |
RESULTS |
REFERENCE |
Surface Hardness-Thread |
402∼423 HV0.3 |
|
Surface Hardness-Drill Point |
395∼432 HV0.3 |
|
Torsional Strength |
124.15∼124.28in.lb (Maximum value) |
Equating with 143.08∼143.20kg.cm (metric system) |
Shearing Force |
4065.25 pounds |
|
Loading Weight |
6045 pounds |
|
(2) For utilized in automotive industry
8 random samples of fasteners made by the present invention and providing with the
specification of M8×1.25×32mm are adopted in the experiment and here the table 2 shows
the practical numerals by comparing to the standard level:
Table 2
CHARATERISTICS |
RESULTS |
STANDARD VALUE |
Core Hardness |
37-38 HRC |
33-39 HRC |
Axial Tensile Strength |
124-125kg/mm2 |
110 Min.kg/mm2 |
Elongation |
12-14% |
10 MIN.% |
In view of the austenitic 300 series materials devoid of the enough strength, the
standard value of TABLE 2 is defined according to the value of the fasteners fabricated
of iron materials. From the table 2, the elongation and the axial tensile strength
of the present invention obviously exceeds the standard level except for the core
hardness being located within the range of the level, which indicates the fastener
can be well adapted to the automotive demand. Those numerals of the two charts indicate
that the present invention is adapted to the relative fields and provides with high
hardness and high strength.
(3) Inspection on Corrosion Test
Further, the experiment carries out both Salt Spray Test and Kesternich Test procedure
per DIN 50018 for corrosion tests, and the results indicate that the fastener does
not appear patches of rust and corrosion thereon. Therefore, the fastener of the present
invention substantially achieves a better corrosion resistance.
Referring to Fig.
6, a second preferred embodiment of the present invention still comprises the same
procedures of preparation
31, the head formation
32, the drill point formation
33 and threads formation
34. Particularly, a procedure of corrosion resistance
36 can be carried out after the threads forming procedure
34 depend on the market demand in order to coat with a rust-resistant layer
46 (as shown in Fig.
7) on an outer surface of the integral fastener
4 for achieving superior corrosion protection.
In view of the above descriptions, the present invention has following advantages:
- 1. Higher strength without proceeding heat treatment
By means of the procedure of preparation, the raw shaft is initially squeezed by cold
forging to generate a preliminary shank with a smaller diameter, which results of
the shank providing with higher density and strength for bearing above 1/2 force greater
than the raw shaft. The subsequent procedures of formations also experience the conformity
forging method with the initially process so as to avoid breaking the molecular arrangements
of the austenitic materials and simultaneous reinforce the strength and hardness for
the fastener to be firmly drilled into the objects.
- 2. Effective corrosion resistance and more screwing security
Due to that the fastener is not susceptible of the carburizing and quenching, the
present invention is conducive to raise the producing speed and reduce the manufacturing
cost. Additionally, the core and case hardness of the fastener would not be influenced
while being devoid of the heat treatment procedure and the fastener would increase
its corrosion resistance without being carburized, hence the present invention can
have better elongation to prevent an unintentional broken, increase the screwing security
and achieve better corrosion resisting effect.
To sum up, the present invention takes advantage of cold forging for initially preparing
a preliminary shank with higher core and case hardness and subsequently passing through
the head, the drilling portion and threads formations to generate the integral fastener
with high strength and hardness. In this manner, the present invention deviates from
the conventional heat treatment, which facilitates to decrease the manufacturing cost,
improve the corrosion situation and simultaneously enhance the screwing security.
While we have shown and described the embodiment in accordance with the present invention,
it should be clear to those skilled in the art that further embodiments may be made
without departing from the scope of the present invention.
1. A method (3) for cold forging high strength fastener with austenite 300 series material
comprising the steps of:
a preparation (31) for preparing a raw austenite 300 series shaft (41) having a first
diameter (d1), which is initially squeezed by cold forging for reducing above 15%
of said first diameter (d1) and hence generating a preliminary shank (42) with a second
diameter (d2) smaller than said first diameter, thus said shank (42) undertaking above
1/2 force greater than said raw shaft (41) ;
a head formation (32) for forming a screw head (43) at one end of said shank (42)
;
a drill point formation (33) for forging a drill portion (44) at the other end of
said shank (42), opposite to said screw head (43); and
a thread formation (34) for continuously rolling a plurality of screw threads (45)
between said head (43) and said drilling portion (44), hence an integral fastener
(4) is accomplished.
2. The method as claimed in claimed 1, wherein, a procedure of whitening (35) is subsequently
proceeding after said procedure of thread formation (34) for retrieving primary color
of said raw austenite 300 series materials.
3. The method as claimed in claimed 1, wherein, a procedure of corrosion resistance (36)
is subsequently proceeding after said procedure of thread formation (34) in order
to coat with a rust-resistant layer (46) on an outer surface of said integral fastener
(4) for corrosion protection.