METHOD FOR COLD FORGING HIGH STRENGTH FASTENER WITH AUSTENITIC 300 SERIES MATERIAL

METHODE PERMETTANT LE FORGEAGE A FROID DE DISPOSITIF D'ATTACHE HAUTE RESISTANCE AVEC MATERIEL AUSTENITIQUE SERIE 300

English Abstract

The present invention pertains to a method for cold forging high
strength fastener with austenitic 300 series material comprising the
procedures of initially preparing a raw austenitic shaft and then
proceeding through a cold forging method to reduce its diameter for
thereafter generating a preliminary shank, which can undertake above
1/2 force more than the raw shaft; further passing through the following
formations of the head, the drilling portion and threads in sequence
to build an integral fastener. Thus, the entire cold forging facilitates
to fabricate the fastener with high strength and hardness by lower
manufacturing cost and with effective corrosion resistance, so as to
firmly drill the fastener into objects and increase the screwing
security.

French Abstract

La présente invention se rapporte à une méthode qui permet de forger à froid une pièce de fixation à haute résistance avec un matériau austénitique série 300. Les opérations applicables sont comme suit. La préparation initiale d'une tige austénitique brute et l'application ensuite de la méthode préconisée pour réduire son diamètre, ce qui permet de produire par la suite une queue préliminaire pouvant subir une force égale à plus de la moitié de la force que pourrait subir la tige brute; la réalisation ultérieure successive des formations de la tête, de la partie perçage et des filets, pour fabriquer une fixation intégrale. Par conséquent, le forgeage à froid complet facilite la fabrication de la fixation avec une haute résistance et une dureté élevée, des coûts de fabrication moindres et avec une résistance à la corrosion efficace, de façon à aléser fermement la fixation dans des objets et à accroître la sécurité du vissage.

Claims

WHAT IS CLAIMED IS:
1. A method for cold forging high strength fastener with austenitic 300
series material comprising the steps of:
preparing a raw austenitic 300 series shaft having a first diameter,
said first diameter being initially squeezed by cold forging for reducing
said first diameter greater than 15% thereof for generating a preliminary
shank, said preliminary shank having a second diameter smaller than said
first diameter and being capable of bearing above 50% applied force
greater than said raw shaft;
forming a head by forming a screw head at one end of said shank;
forming a drill point by forging a drilling portion at the other end
of said shank, opposite to said screw head; and forming threads by
continuously rolling a plurality of screw threads between said head and
said drilling portion, hence an integral fastener is accomplished.

2. The method as claimed in claimed 1, wherein, a procedure of whitening
is subsequently proceeding after said procedure of thread formation for
retrieving original colors of raw austenitic 300 series materials.
3. The method as claimed in claimed 1, wherein, a procedure of corrosion
resistance is subsequently proceeding after said procedure of thread
formation in order to coat an outer surface of said integral fastener
with a rust-resistant layer on for corrosion protection.
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Description

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METHOD FOR COLD FORGING HIGH STRENGTH FASTENER
WITH AUSTENITIC 300 SERIES MATERIAL
BACKGROUND OF THE INVENTION
1. Field of the Invention
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
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

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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.
However, the conventional method may have some disadvantages:
1. Higher manufacturing cost and more procedures
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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
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thereof or difficultly drilling the fastener into objects. Therefore,
it would affect the screwing security.
SUMMARY OF THE INVENTION
The aspect 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.
According to one aspect of the present invention there is provided
a method for cold forging high strength fastener with austenitic 300
series material comprising the steps of: preparing a raw austenitic 300
series shaft having a first diameter, said first diameter being initially
squeezed by cold forging for reducing said first diameter greater than
15% thereof for generating a preliminary shank, said preliminary shank
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having a second diameter smaller than said first diameter and being
capable of bearing above 50% applied force greater than said raw shaft;
forming a head by forming a screw head at one end of said shank; forming
a drill point by forging a drilling portion at the other end of said
shank, opposite to said screw head; and forming threads by continuously
rolling a plurality of screw threads between said head and said drilling
portion, hence an integral fastener is accomplished.
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
4a

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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.
BRIEF DESCRIPTION OF THE DRAWINGS
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;
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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
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
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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).
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
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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.
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 #12X35 are adopted in the
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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
402423 HVO.3
Hardness-Thread
Surface
395432 HVO.3
Hardness-Drill Point
Equating with
124.15-124.28in.lb
Torsional Strength 143.08-143.20kg.cm
(Maximum value)
(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 M8x1.25x32mm are adopted in the
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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

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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)
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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.
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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
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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.
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Representative Drawing