Threaded – headed fastener – or washer making: process and apparat – Implement – e.g. – die – etc. – Tap
Reexamination Certificate
2002-07-10
2004-02-03
Tolan, Ed (Department: 3725)
Threaded, headed fastener, or washer making: process and apparat
Implement, e.g., die, etc.
Tap
C470S198000, C408S222000
Reexamination Certificate
active
06685573
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a thread forming tap, and more particularly, to a thread forming tap which is capable of reducing tapping torque as well as improving durability by avoiding an increase of an apparent area of margins of external thread that causes interference with a grinding stone.
BACKGROUND OF THE INVENTION
Typically, a tap is used to form internal threads. Taps are mainly classified into two types, a cut thread tap for cutting the surface of a prepared hole (hole before threading), and a thread forming tap for performing plastic deformation on the surface of the hole before threading. The cut thread tap, however, requires an elimination process due to the chips generated by the tapping, and the finished surface comes out rough. On the other hand, in the thread forming tap, no chips are generated during the tapping process, and the finished surface of the internal thread comes out smooth as well as durable, resulting in a wide range of use.
A conventional thread forming tap is shown in
FIGS. 6A and 6B
. As shown in a front view of
FIG. 6A
, the tip of the conventional thread forming tap
100
is established with an external thread
101
for rolling internal threads. A taper shaped chamfer
101
a
and a full thread part
101
b
are established on the external thread
101
, and ridges are formed along the helix with a predetermined lead angle. Further, as shown in
FIG. 6B
, the external thread
101
has a square shape in cross-section, where four radially projected margins
102
and four reliefs
103
linked to the respective margins
102
are alternately established on the external thread
101
in the direction of the screw thread, i.e., along the helix of the ridges. In the example of
FIG. 6A
, each margin
102
is aligned in parallel with an axis O of the thread forming tap
100
.
When forming an internal thread, the chamfer
101
a
of the thread forming tap
100
is spirally advanced on the surface of the prepared hole on a workpiece. By this spiral movement, the margins
102
on the chamfer
101
a
bite into the prepared hole on the workpiece, allowing the plastic deformation (plastic flow) while proceeding on the surface of the hole, thereby creating the internal thread. This internal thread is then finished by the margins
102
on the full thread part
101
b
which helically advances as well.
In the conventional thread forming tap
100
, however, as shown in
FIG. 7
, the ridges (crests and roots) on the external thread
101
are at a lead angle &kgr;, unlike the margins
102
which are parallel with the axis O. Therefore, during the grinding process for producing the thread forming tap, in which a grinding stone having ridges on the outer surface thereof proceeds along the lead of the ridges to grind a screw thread onto the external thread
101
, an interference is occurred by the grinding stone with the margins
102
, resulting in the increase of an apparent width (area) of the margins
102
. This increase in the apparent width (area) causes a rotational resistance during tapping, i.e., an increase in tapping torque, resulting in an increase in the rolling load which also causes breakage of the margins
102
.
SUMMARY OF THE INVENTION
Therefore, the object of the present invention is to solve the above noted problems involved in the conventional technology by providing a thread forming tap with low tapping torque and high durability that is capable of preventing the increase of the apparent area of the margins caused by the interference with the grinding stone.
In order to achieve this object, the thread forming tap in the first aspect of the present invention comprises an external thread established with radially projecting margins and reliefs smaller in diameter than that of the margins. The margins and the reliefs are alternately linked to one another on the external thread in a screw thread shape. When forming internal threads, the margins on the external thread bite into the surface of a prepared hole of a workpiece, where plastic deformation is performed. The margins are aligned helically in a direction opposite to a direction of a helix of the external thread.
In the thread forming tap in the second aspect of the present invention, the external thread has a lead angle &agr;. The margins on the external thread have a helix angle &bgr;, where the helix of the margins is in the opposite direction of the helix of the external thread. Further, the helix angle &bgr; of the margins is larger than 0° but smaller than 10° or 4&agr;.
In the thread forming tap defined in the third aspect of the present invention, oil flutes established on the external thread are directed either in parallel with or diagonal to the axis of the external thread. The oil flutes are extended in a straight line over either a part of or the entire external thread.
In the thread forming tap in the fourth aspect of the present invention, the oil flutes established on the external thread is inclined in the same manner as the margins of the external thread. The oil flutes have a helix angle &bgr;, where the helix is in the opposite direction of the helix of the external thread. The oil flutes are extended over either a part of or the entire external thread.
REFERENCES:
patent: 3656197 (1972-04-01), Van Vleet
patent: 3775792 (1973-12-01), Leonard
patent: 6217267 (2001-04-01), Sugano et al.
patent: 58-186527 (1983-10-01), None
patent: 10-86019 (1998-04-01), None
Andoh Haruyasu
Hikosaka Kensuke
Muramatsu & Associates
OSG Corporation
Tolan Ed
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