Ball nose end mill

Details Ball nose end mill Ball nose end mill

1999-09-10

2001-05-15

Tsai, Henry (Department: 3722)

Cutters, for shaping

Rotary cutting tool

Including holder having seat for inserted tool

C407S054000, C407S063000, C407S065000

Reexamination Certificate

active

06231275

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a ball nose end mill, and more specifically, to an indexable type ball nose end mill used for high speed, high precision machining of ball groove of a uniform joint and the like.
2. Description of the Background Art
Conventionally, when high speed and high precision machining is required in cutting a ball groove, for example, a solid ball nose end mill in which a holder body and a cutting edge are integrated, or a tipped ball nose end mill in which a cutting edge is fixed on a holder body by brazing, for example, has been used. In such ball nose end mills, however, when the cutting speed is increased to improve cutting efficiency, wear or chipping of the cutting edge increases. Therefore, in the ball nose end mills described above, as the degree or amount of wear or chipping increases, it becomes necessary to regrind the cutting edge or to exchange the ball nose end mill body more frequently, resulting in low economical efficiency.
In view of the foregoing, an indexable type ball nose end mill has come to be widely used, in which an indexable insert having a cutting edge formed on an indexable plate-shaped insert is mounted. The indexable type ball nose end mill is used with the plate-shaped insert inserted into a slot at a tip end of the holder body. The plate-shaped insert is attached to the holder body by closing the slot by clamping force of one damp screw. More specifically, an end surface of the plate-shaped insert is brought into contact with a bottom surface of the slot, and the end surface of the plate-shaped insert is pressed to the bottom surface of the slot of the holder body, so that rotation of the plate-shaped insert is restricted, and the plate-shaped insert and the holder body are integrated.
More specifically, in the above described indexable type ball nose end mill, a central portion of the plate-shaped insert is fixed and pressed to the bottom surface of the slot using a clamp screw, so that the bottom surface of the slot and an end surface of the plate-shaped insert are brought into contact with each other, thereby securing the plate-shaped insert. Therefore, in order to maintain exact securing of the plate-shaped insert even when cutting force variation occurs periodically during cutting, it is necessary to improve the precision of screw-fixing by the clamp screw. With the improved clamping precision, a clamping force sufficient to maintain the friction force between the male screw thread on the clamp screw and the female screw thread on the holder body is ensured.
For this purpose, various proposals related to the shapes of portions around the clamp screw have been made. In Japanese Patent Publication No. 64-1248, a slit is provided at the center of the bottom surface of the slot.
FIG. 14
is a cross section of a ball nose end mill in accordance with this one example of the prior art in which a slot
101
of a holder body
100
is viewed from one side. The ball nose end mill having a slit
103
at the central portion of the bottom surface
102
of slot
101
has such a structure as described below, with reference to FIG.
14
.
At the center of bottom surface
102
of slot
101
at the tip end of holder body
100
, there is provided a slit
103
. Plate-shaped insert
104
is inserted into slot
101
. The space of slot
101
is made narrow by applying the clamping force of clamp screw
105
, and a rear end surface of plate-shaped insert
104
is in contact with bottom surface
102
of slot
101
. Therefore, in the conventional ball nose end mill having a slit a
103
provided at the central portion of the bottom surface
102
of slot
101
, plate-shaped insert
104
is fixed in tight contact with bottom surface
102
of slot
101
of holder body
100
with its mechanical rotation suppressed.
In this prior art example, as slit
103
is provided at an equal distance from opposing side surfaces of slot
101
, one half
106
and the other half
107
bend equally. Accordingly, plate-shaped insert
104
is fastened firmly, as it contacts the entire area of the side surfaces of the slot
101
, that is, whole areas of the inner side surface of one half
106
and the side surface of the other half
107
.
This prior art, however, has the following problem. Here, half
107
is inclined with respect to clamp screw
105
because of slit
103
, and therefore accurate screw-fixing between the male screw portion of clamp screw
105
and female screw portion of half
107
is not attained. Further, by the method of clamping in which only the damp screw
105
is simply passed through a through hole, there remains a space between damp screw
105
and the through hole of plate-shaped insert
104
, and therefore the plate-shaped insert
104
cannot be forced onto the bottom surface
102
of slot
101
. As a result, restricting force is insufficient in the direction of extension of slot
101
and in the direction of rotation of damp screw
105
, and therefore plate-shaped insert
104
may possibly be displaced when cutting force varies significantly.
Another ball nose end mill having a plate-shaped insert fixed therein is disclosed in Japanese Patent Laying-Open No. 8-252714. Two types of ball nose end mills disclosed in this laid-open application will be described with reference to
FIGS. 15 and 16
.
FIG. 15
shows an example of the ball nose end mill having the plate-shaped insert with the rear end thereof formed in an arcuate shape, and
FIG. 16
shows an example of a ball nose end mill having the plate-shaped insert with the rear end thereof formed in a V-shape.
First, the technical idea for fixing the plate-shaped insert of the ball nose end mill shown in
FIG. 15
will be described. The plate-shaped insert
131
having a cutting edge is inserted in a slot traversing the central portion of the tip end of holder body
130
as shown in FIG.
15
. Plate-shaped insert
131
is fastened as the width of the slot is narrowed by clamp screw
132
.
At this time, when the rear end surface
131
a
of plate-shaped insert
131
is adapted to have the same radius of curvature as the bottom surface
133
of the slot, or when the radius of curvature of rear end surface
131
a
is made larger than that of bottom surface
133
, plate-shaped insert
131
is automatically aligned with its center line moved to a position overlapping the center line of holder body
130
. This significantly improves finishing accuracy of the cutting process.
In order to attain high accuracy of cutting process, however, it is necessary to improve fitting accuracy of the through hole of plate-shaped insert
131
and neck diameter of damp screw
132
. In addition, the position accuracy of the screw hole of holder body
130
must also be improved. More specifically, rear end surface
131
a
of plate-shaped insert
131
and the arcuate contact surface of bottom surface
133
of the slot must be in contact entirely. Though it may be possible if actual parts are gauged in selective attachment, it is difficult to attain the expected accuracy when plate-shaped insert
104
, holder body
130
and clamp screw
132
are assembled at random.
The technical idea for fixing the plate-shaped insert of the ball nose end mill shown in
FIG. 16
will be described in the following. A plate-shaped insert
141
having a cutting edge is inserted into a slot traversing the central portion of the tip end of a holder body
140
in the similar manner as the ball nose end mill of
FIG. 15
, and fastened as the slot is closed by clamp screw
142
as can be seen from
FIG. 16. A
rear end surface
141
a
of a plate-shaped insert
141
is formed to have a V-shape, and a bottom surface
143
of the slot, which is formed to have a V-shape opposing that of the rear end surface
141
a
, abuts the rear end surface. Therefore, the center line of the plate-shaped insert
141
is automatically moved to a position overlapping the center line of holder body
140
and aligned.
If the accuracy of the V-shaped contact surfaces of plate-shaped insert
141
and bottom su

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