Patent Description:
T-shaped tools comprising a shank and a head (tool body) connected to the tip of the shank have been conventionally well-known. For example, Patent Literature <NUM> describes a T-shaped cutter (T-groove milling cutter) in which a cutting head having a cutting edge on the outer periphery thereof is detachably attached to the tip of the shank by means of a screw. The cutting head has an annular projection in the central portion of the side surface facing the shank, and the cutting head and the shank are connected by bringing the end surface of the annular projection into contact with the end surface of the shank, inserting a fixation screw into a head hole formed in the center of the cutting head from the opposite side surface of the cutting head, and engaging the screw with an internal thread formed on the tip of the shank.

In the T-shaped tool described in Patent Literature <NUM>, the shank is tensioned by the fixation screw in a state in which it is in contact with the end surface of the projection of the cutting head. Thus, an axial tensile load is continuously exerted on only one side of each thread of the internal thread of the shank engaged with the fixation screw. Shanks are generally formed from cemented carbide, and cemented carbide has a high compressive strength but a low tensile strength. Thus, in the invention of Patent Literature <NUM>, since the thread lacks rigidity, it is difficult to firmly secure the cutting head to the shank.

Thus, the present invention aims to solve such problems of the prior art by providing a highly-rigid T-shaped tool which can easily be manufactured and a method for the manufacture thereof.

In order to achieve the object described above, according to the present invention, there is provided a T-shaped tool as defined in claim <NUM>.

Furthermore, according to the present invention, there is provided a method for manufacturing a T-shaped tool as defined in claim <NUM>.

According to the present invention, a tool which is approximately T-shaped in a side view is formed by engaging the tapered external thread of the shank with the tapered internal thread of the tool body. Due to the tapered threads, the shank can be tightly engaged with the internal thread of the tool body with a high fastening torque even without, for example, abutting the end face of the shank onto the tool body. Thus, when the tool body is threadedly connected to the shank, a tensile load is not exerted on the tapered external thread of the shank, unlike in the invention of Patent Literature <NUM>, and as the threads are tightened, a compressive load is exerted on each thread of the tapered external thread of the shank, which is composed of cemented carbide, from both sides in the axial direction. Thus, cemented carbide having high rigidity can be used for the shank, and also the rigidity of the connection part between the shank and tool body becomes higher, whereby machining speed (cutting speed) can be increased to improve machining efficiency. Furthermore, by forming the shank from cemented carbide, the shank is less likely to be deformed, whereby machining accuracy can be improved.

The preferred embodiments of the present invention will be described below with reference to the attached drawings.

A T-shaped tool <NUM> comprises a shank <NUM> which is mounted on the tip of a spindle or tool holder of a machine tool and a head <NUM> which is coupled to the tip of the shank <NUM>. The shank <NUM> is composed of a highly rigid cemented carbide rod-shaped member having a substantially cylindrical shape, and an external thread <NUM> is formed on the tip thereof. The external thread <NUM> is a tapered thread, the diameter of which decreases in the tip direction of the shank <NUM>. The external thread <NUM> can be a tapered thread having, for example, a pitch of <NUM> to <NUM>, a thread height of <NUM> to <NUM>, and a taper ratio of <NUM>/<NUM> to <NUM>/<NUM>. It is desirable that the maximum outer diameter of the tapered thread be substantially equal to the diameter of the shank <NUM>.

A coolant pathway for the supply of coolant to the cutting edge can be formed in the shank <NUM>. The coolant pathway can include an axial pathway <NUM> which passes through the shank <NUM> along the central axis O and radial pathways <NUM> which pass radially through the shank <NUM> from the axial pathway <NUM>.

The head <NUM> forms the tool body of the T-shaped tool <NUM> and is composed of a steel material. A plurality, and in the present embodiment, six, of blades are formed on the head <NUM>. In the present embodiment, the blades are formed by inserts <NUM>, <NUM> attached to the head <NUM>. The inserts <NUM>, <NUM> can be formed from, for example, cemented carbide, which has high wear resistance. The inserts <NUM>, <NUM> include three upper inserts <NUM> which protrude on the proximal side of the T-shaped tool <NUM>, i.e., the shank <NUM> side, and three lower inserts <NUM> which protrude on the distal side of the T-shaped tool <NUM>, i.e., the side opposite the shank <NUM>.

A plurality, and in the present embodiment, six, of grooves <NUM>, <NUM>, corresponding to the number of inserts <NUM>, <NUM>, are formed in the head <NUM>. The grooves <NUM>, <NUM> extend from the proximal surface 30a of the head <NUM> facing the shank <NUM> to the tip surface 30b facing opposite the shank <NUM>. The grooves <NUM>, <NUM> include first grooves <NUM> for receiving the upper inserts <NUM> and second grooves <NUM> for receiving the lower inserts <NUM>. A lower seat 32a for attachment of an upper insert <NUM> is formed in each first groove <NUM>. A lower seat 34a for attachment of a lower insert <NUM> is formed in each second groove <NUM>. The upper inserts <NUM> and the lower inserts <NUM> are attached to the upper seats 32a and the lower seats 34a using a suitable bonding technology such as brazing.

The upper inserts <NUM> and the lower inserts <NUM> are formed in the same shape. Though only an upper insert <NUM> is illustrated in <FIG>, the lower insert <NUM> is identical thereto. The upper insert <NUM> has a rake face 36a on the side opposite the upper seat 32a, when attached to the upper seat 32a, and a flank face 36b which faces radially outward. A linearly extending main cutting edge 36c and an arc-shaped sub cutting edge 36d, which is connected to the main cutting edge 36c on the upper end of the upper insert <NUM>, are formed by the rake face 36a and the flank face 36b. A sub flank face 36e may be formed on the end on which the sub cutting edge 36d is formed. The shape and dimensions of the arc-shaped sub cutting edge 36d can be determined in accordance with the size of the fillet R of the machined surface to be machined on the workpiece.

The upper insert <NUM> is attached to the upper seat 32a so that the main cutting edge 36c protrudes from the outer peripheral surface of the head <NUM> and the sub cutting edge 36d protrudes from the proximal surface 30a of the head <NUM>. Likewise, the lower insert <NUM> is attached to the lower seat 34a so that the main cutting edge 36c protrudes from the outer peripheral surface of the head <NUM> and the sub cutting edge 36d protrudes from the tip surface 30b of the head <NUM>. Furthermore, the upper inserts <NUM> and the lower inserts <NUM> are alternatingly arranged at regular intervals in the circumferential direction of the head <NUM>. In order to prevent chatter, the upper inserts <NUM> and the lower inserts <NUM> may be alternatingly arranged at irregular intervals in the circumferential direction.

Referring specifically to <FIG> and <FIG>, the upper seat 32a is formed so that the rake face 36a of an attached upper insert <NUM> is oriented downward. Specifically, when viewed from the tip side of the T-shaped tool <NUM>, the upper insert <NUM> is inclined with respect to the head <NUM> so that the rake face of the upper insert <NUM> can be seen. Likewise, the lower seat 34a is formed so that the rake face of an attached lower insert <NUM> is oriented upward. Specifically, when viewed from the shank <NUM> side, the lower insert <NUM> is inclined with respect to the head <NUM> so that the rake face of the lower insert <NUM> can be seen.

Further, an aperture <NUM> is formed in a central portion of the head <NUM>. The internal thread <NUM> for engagement with the external thread <NUM> is formed on the inner circumferential surface of the aperture <NUM>. The internal thread <NUM> is a tapered thread, the diameter of which decreases in the tip direction of the T-shaped tool <NUM>. A circumferential groove <NUM> (<FIG>) is formed in the inner circumferential surface of the aperture <NUM>. The circumferential groove <NUM> is arranged so that when the external thread <NUM> of the shank <NUM> is engaged with the internal thread of the aperture <NUM> and the head <NUM> is connected to the shank <NUM>, the radial passages <NUM> can open into the circumferential groove <NUM>.

Branch passages 46a, 46b which pass from the circumferential groove <NUM> radially through the head <NUM> and which open in the grooves <NUM>, <NUM> on the side surface on the side opposite the upper seat 32a and the lower seat 34a, respectively, are formed in the head <NUM>. More specifically, the branch passages 46a, 46b extend in the direction in which coolant is ejected toward the rake faces 36a of the upper insert <NUM> and the lower insert <NUM> attached to the upper seat 32a and the lower seat 34a, respectively. By providing coolant from the coolant passage toward the upper insert <NUM> and the lower insert <NUM>, heat generated by cutting can be reduced, and tool life and swarf discharge are improved.

By engaging the external thread <NUM> of the shank <NUM> with the internal thread <NUM> of the aperture <NUM> of the head <NUM>, the head <NUM> is fastened and coupled to the shank <NUM>. At this time, the head <NUM> is coupled to the shank <NUM> with a fastening torque that is greater than the maximum torque due to the cutting acting on the head <NUM> during machining. This is a measure to prevent the tapered threads from being further tightened by the torque based on the cutting, thereby deforming the head <NUM> and changing the posture of the inserts <NUM>, <NUM>. Engagement holes <NUM> which engage a tightening tool (not illustrated) for imparting the head <NUM> with the desired fastening torque can be formed in the tip surface 30b of the head <NUM>. Further, a plurality of threaded holes <NUM> may be formed in the tip surface 30b of the head <NUM>, and screws (not illustrated) may be attached thereto for balancing the rotation of the T-shaped tool <NUM>.

Furthermore, in order to prevent loosening of the connection between the internal thread <NUM> of the head <NUM> and the external thread <NUM> of the shank <NUM> due to vibrations or the like that occur during cutting using the T-shaped tool <NUM>, at least one recess <NUM> may be formed in the tip of the shank <NUM>, and the shank <NUM> and the head <NUM> may be welded at the recess <NUM> after the head <NUM> is coupled with the shank <NUM>. Due to the weld, the molten metal of the weld rod is integrated with the steel material of the head <NUM> and flows into the recess <NUM>. Since shank <NUM> is composed of cemented carbide, it cannot be welded, but the metal that flows into the recess <NUM> and solidifies acts as a key, thus forming a detent. When loosening the connection between the external thread <NUM> and the internal thread <NUM> to separate the shank <NUM> and the head <NUM>, the shank <NUM> and the head <NUM> can be easily separated by loosening the threaded connection while welding the weld part and melting the metal that has flowed into the recess <NUM>. Thereafter, the head <NUM> can be changed by newly connecting another head <NUM> to the shank <NUM> and performing the same welding.

Further, after the head <NUM> has been coupled with the shank <NUM>, the T-shaped tool <NUM> can be finished by grinding so that the main cutting edges and the sub cutting edges of the upper insert <NUM> and the lower insert <NUM> have the desired sizes, shapes, and postures.

According to the present embodiment, the shank <NUM> does not have a characteristic portion that abuts the proximal surface 30a of the head <NUM>. Thus, when the head <NUM> is threadedly connected to the shank <NUM>, a tensile load is not exerted on the threaded portion (external thread <NUM>) of the shank <NUM>, unlike in the invention of Patent Literature <NUM>. Thus, cemented carbide, which has a high rigidity, can be used for the shank <NUM>, machining speed (cutting speed) can be increased to improve machining efficiency. Furthermore, by forming the shank <NUM> from cemented carbide (the Young's modulus thereof is about three times greater than that of steel), the shank <NUM> is less likely to become deformed, whereby machining accuracy can be increased.

According to the present embodiment, material cost and manufacturing cost can be remarkably reduced as compared with a T-shape tool in which the shank and head are cut from a single piece of cemented carbide and are integrally formed in a T-shape. Furthermore, in the present embodiment, it is not necessary to specially produce a reference surface for contacting the shank and the head and a fixation screw, unlike in the invention of Patent Literature <NUM>, whereby manufacturing cost can be reduced.

Claim 1:
A T-shaped tool (<NUM>) in which a tool body (<NUM>) having a cutting edge and a cylindrical shank (<NUM>) are connected in a T-shape in a side view, wherein
the shank (<NUM>) is composed of cemented carbide and has a tapered external thread (<NUM>), the diameter of which decreases in the tip direction, formed on a tip thereof,
the tool body (<NUM>) is composed of steel and has an aperture (<NUM>) formed in a central portion of said tool body (<NUM>), and wherein a tapered internal thread (<NUM>) for engagement with the tapered external thread (<NUM>) is formed on an inner circumferential surface of said aperture (<NUM>), and
wherein the shank (<NUM>) and the tool body (<NUM>) are configured such that the shank (<NUM>) and tool body (<NUM>) connect by engaging the tapered external thread (<NUM>) with the tapered internal thread (<NUM>) without abutting an end face of the shank (<NUM>) onto the tool body (<NUM>).