Description CUTTING INSERT AND CUTTING TOOL THEREWITH
Technical Field
[11 The present invention generally relates to a cutting insert anJ a cutting tool
comprising the same.
Baclcground Art
[2] Cutting inserts, which proviJe cuttint; edges of a culling tool, ai'e made from a
material with high abrasion resistance such as mugsten carbide. Such cutting inserts are rigidly secured to a tool body by means of screws so that they can peifoim stable cutting during a cutting pr(x:ess. Pig, I is a pci-spective view of a milling cutter, to which a prior art cutting i/i.sen i.s applied. A screw is pejpendicuJarly fasleued to a cutting insert seatuig surface trf a cutter body, wherein a bottom surface of the cutting inseit is brougiit into coiitaci, thereby securing the cutting insert to the cutter body. In such a case, since the screw exerts only a perpendicular fastening force to the cutting insert, Ihe screw fails (o suiticiently support the reaction force corresponding to a cutting force and can be unfastened during operation nf the milling cutter. Ac¬cordingly, there is a problem in that the culring insert is not rigidly seemed to the cutter body.
[31 Fig. 2 is a perspective view of anothtir prior art milling cutter, wherein a screw-
fastening stmcture is modified in tiixlei' ro solve the above-mentioned problem. In this stnicture, a screw is fastened to a cutting insert seating suiface of a cutter body and is slanted at a predetermined angle. With the slantingly fastened screw, the fastening force of the screw is allowed to have both perpendicular and horizontal components. Thus, the screw can be maintained as faslened, despite the reaction force cor¬responding to the cutting force, and the cutting insert can be more stably secured to the cutter body. However, even with such screw-fastening stmctuie, there is a pioblem in that when subjected to a cutting environment accompanied by heavier vibrations, the screw Cannot withstand such an environment and thus becomes unfastened.
Disclosure of Invention Technical Problem
[4] The present invention is directed to solving the foregoing prablems of the prior ai1.
It is an object of Ihe present invention to provide a structure, wherein a screw for securing a cutting insert to a tool body is not unfastened under a working environment accompanied by heavier vibrations. Thus, the cutting insert can be maintained as rigidly secured to the tool body.
15J It is a further object of the present invention to provide a cutting inserl, which has a


I! 3] Fig. 4 is a sectional view tiiken aloii): (he line A-A of Fig. 3.
3


f32) Pig, 4 is a sectional view taken iiJo% rJie lii)e A-A of Pig. 3. Fig, 5 is a sectional
view taken along tiie line B-B ot Kig, 3. When the screw 30 is fastened to the threaded

hole 42 of the culler btuJy 40 so iis to secure ihe culling inserl 10, a head 32 of the
screw is contacted loone ponioii 0|-)posedtti a lateral portion 18 of the cutting insert 10
and to Ihe other portion opposed to the comei^ 12 wilh i^e^pect to the wall surface 16 of
the mounting hole 14 of the cutting insert 16 at different levels and at different contact
angles, respeciively. As used herein, a contact angle means an angle included between
two tangent lines, which extend I'especlively from two contact points where the head
32 of the screw is conlacledto [he wall surface 16 of the mounting hole 14, as seen
from a cross-section of the cutting inseit 10 of Figs. 4 anil 5. Fig. 4 sliows the contact
between the head 32 of the screw and Ihe wall surface 16 of the mounting hole in the
portion opposed to tlie lateral portion 1K of the cutting insert. The contact angle A
ranges from approximately $5 degrees lo approximately 65 degrees (preferably ap¬
proximately 60 degrees). Fig. 5 shows the contact between the head 32 of the screw
and the wall surface 16 of the mounting hole in the portion opposed to Ihe comer 12 of
the cutting insert. The contact portions lihown in Fig. 5 are formed at a higher location
than the contact portions shown in Fig. 4. The contact angle B ranges from ap¬
proximately 20 degrees to approximately 50 degi"ees (preferably approximately 40
degrees),
[331 Unclamping forces were measmed after fastening the screws by exerting the same
clamping forces to the cutting inserts, which provide the fastened screws with contact angles of 30 degrees and 60 degrees, respectively. The results of such a measurement arc shown in Table 1 below. The magnitudes of the clamping force and the unclamping force were measured by using a known method. It can be seen from Table I that ihe case of the contact angle of 30 degrees requires the unclamping force larger by ap-

18 of Ihe cutting insert and the contact angle of approximately 40 degrees at the

portion opposed to Hie corner 12 of ihe cutting insert are foniied simultaneously. With such a coiisritiKion, ihe screw unfastening causet! by the vibrstians, which occmfi during machining, \',as prevented. Funlier, the problem in which the screw is jammeiJ in the mounting hole of the ciitliiig insert during the unfastening of the screw also did not occur.
[36] Fig. 6 is a perepective view of the cutting insert, wherein the screw is fastened as
shown in Figs. 4 and 5 and the screw is thereafter unfastened. Fig. 6 shows thai contact lines 22, which are foimed when the head 32 of the screw is contacted to the wall surface 16 of the mounting hole opposed lo the lateral portion 18 of the cutting insert 10. Further, Fig. 6 shows contact lines 114, which are formed when the head 32 of the screw is contacted lo the wall surface 16 of the mounting hole opposed to the corner 12. The above contact lines aie located at diflerent levels. The contact lines 22 on the wall surface 16 of the mounling hole opposed to the lateral portion 18 of the cutting iii.vert iO are foitned a! a lower JeveJ uJong a loiigiludina] axis X of the mounting hole 14 than the contact lines 24 on the wall surface 16 of the mounting hole opposed to the comer 12. In such a case, when Ihe here w 30 Is fastened and the head 32 of the screw is contacted to the wall surface 16 of the mounting hole, the contact angle at the portions opposed 10 the lateral portion 18 of the cutting insert is appixiximately 60 degrees and the contact angle at (he portions opposed to the comers 12 of the cutting insert is ap¬proximately 40 degrees.
[37] As shown in Fig. 6, the contact lines, ul which the head of the sci'ew is contacted to
the wall suiface of the mounting hole, may be formed so as to be separated from each other.
f381 On the conirai-j', ihe contact lines, at which the head of the screw is contacted lo the
wall .surface of the niotniting hole, may be joined to each other, as .shown in Fig. 7. In other woids, the head 32 ol the screw and the mounting hole 14 are further coniacled to each other at one or more contact portions. ,Siich contact portions form a contact line, which is continuous an)und the periphery of the head of the screw, together with the contact portions between the head 32 of the .screw and the wall sutface 16 of the mounting hole in the portions opposed to the corner 12 of Ihe cutting insert and the contact portions betweeji Ihe bead 'M ol' the sci'ew and the waJ] smface 16 of Ihe mounting hole in die portions opposed lo lateral ponion 18 of the cutting insert. This can be accomplished by designing an ai^propiiate geomeliy of the wall suiface 16 of the mounting hole. Alternatively, it can be accomplished by choosing an appmpriate geometi7 of the head 32 of Ihe screw. As such, since the Joined contact lines fonn longer contact lines than Ihe sep^iraled cotuacl lines, the head of the screw with a relatively lower hardness is less damaged when the screw is fastened under heavy loads.

[391 The mounting hole 14 is symmetricul up and down, As shown in Fig. 3, the
motinllng hole is imuKl at (IN enlcitfic^ and is ceciangular shaped with rounded comers at its middle portion. Thus, adist;iiice between the lateral portion 18 of the cutting inseit and the wal) surf'aL-e 16 of the monnfing hole becomes increased as it proceeds to the middle portion. Accordingly, the cross-sectional area of the cutting insert is increased and the rijiidity of tiie cutting insert is thus enhanced.
[401 While the preseni invention has been described with reference to exemplai7 em-
bodiments thereof, tiie presenl invention may te embtxiied in various manners. For example, the cutting insert of the present invention may be used not only with respect to milling cutters btii also wilh any oiher cutting tools. Further, the cutting insert may have any other shape such as a trigonal prism in addition to the rectangular parallel piped shape. Those modifications will be obvious to those of ordinaiy skill in the art and naturally fall wichin the scope of the present invention. Industrial Applicability
[411 As described above, accoi-dhig to the present invention, theis are provided a cutting
insert, which has a screw-cojuact structure allowing an uiiclamping force of the already fastened screw to be greatly increased, Lind a cutting tool comprising such a cutting insert. Wilh such a conslitiition, the screw unfastening caused by the vibrations occun'ing during machining is prevente.l. Further, the problem where the screw is jammed in the mounting hole of the culling insert during the unfastening of the screw does not also occur.

Claims

]7j A cutting inseit having a moutiting hole for a screw to pass through, the cutting
insert being mounted to a tool body by the screw and providing cutting edges of the tool,
wherein a wall surtat.t; of the mounting hole contacts a head of the screw about at least one first coniacl portion and al least one second contact portion, the at least one first coniacl portion being formed at ii level different from that of the at

[SI [9]
[1]] The cutting iiiseil of any one of Claims 7 to 9, wherein the cutting insert has a
rectangular pai-allel piped shape, and wherein the mounting hole is symmetrical witii respect to a cenler pui-liofi tliereof and the rnocinlitig hole is found at the upper and lower ends and rectangular with rounded comers in the middle poll inn.