Joints and connections – Interfitted members – Longitudinally splined or fluted rod
Reexamination Certificate
1998-10-20
2001-05-29
Knight, Anthony (Department: 3626)
Joints and connections
Interfitted members
Longitudinally splined or fluted rod
C403S359600, C403S359500
Reexamination Certificate
active
06238133
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention generally relates to mounting mechanisms for cutting inserts, and is particularly concerned with a mechanism for preventing the rotation of a round cutting insert mounted onto the body of a cutting tool.
The inserts used in tools such as milling cutters are mounted in complementarily-shaped pockets spaced around the periphery of the tool body. The inserts are typically secured within their respective pockets by clamping screws inserted through a hole provided in the center of the insert. During a cutting operation, such inserts often experience not only compressive and vibratory forces, but some amount of torque due to the angle between the cutting edges of the inserts and the workpiece. For cutting inserts of non-round shapes, such torque does not result in the rotation of the insert due to the interference-type fit between the angled sidewalls of such inserts and the complementarily-shaped walls of the pocket that receive them. By contrast, round inserts can rotate within their respective pockets since no such mechanical interference naturally arises between the cylindrical or frustro-conical sidewalls of round inserts and the circular walls of the pockets which receive them. The resulting rotation can loosen the clamping screw that secures the insert within its respective pocket. If the clamping screw should become sufficiently loosened, it can vibrate within the surrounding pocket severely enough to become chipped or cracked not only ruining the insert, but also jeopardizing the quality of the cut on the workpiece.
To prevent such unwanted rotation, several anti-rotation mechanisms have been developed in the prior art. In one such mechanism, a plurality of deep semicircular recesses are provided around the sidewall of the insert. A pin is provided adjacent to the sidewall of the insert-receiving pocket in the tool body that is complementary in shape to the recesses around the insert. In operation, the insert is installed in the pocket of the milling cutter or other tool with the pin of the pocket inserted into one of the semicircular recesses of the insert. During use, the insert is indexed to even out the wear on its cutting edges by periodically removing it from the pocket, partially rotating it, and reinstalling it so that the pin is received by a different recess. In another type of anti-rotation mechanism, a polygonal pattern of facets are provided around the circular sidewall of the insert. Such a mechanism is disclosed in U.S. Pat. No. 5,346,336. The insert-receiving pocket is provided with a complementarily-shaped pattern of polygonal walls for receiving the facets of the insert. The indexing of the insert is performed generally in the same manner as described in the first mechanism.
While both of these mechanisms effectively prevent the rotation of round inserts during a cutting operation, the inventors have noticed a number of shortcomings associated with each design. For example, the applicants have observed that, with respect to the first design, the edges of the full radius, semicircular recesses formed in the hard, carbide material of the insert can slowly cut the steel pin in the pocket as the result of vibrations between the pin and the edge of the recess, which is oriented substantially orthogonally with respect to the axis of the pin. Additionally, the provision of such deep recesses around the bottom of the insert body result in an undesirable weakening of the insert body as a result of the removal of the material necessary to form the recesses. The stop mechanism disclosed in the '336 patent likewise has shortcomings, albeit different ones. For example, the facets provided around the body of the insert are angled at a slightly steeper angle than the flat walls provided around the insert-receiving pockets to avoid contact between the walls of the pocket and the weaker, bottom portion of the insert. However, the limited contact provided by such a design can result in one-point contact between the edges of the insert facets and the flat walls of the pocket. Moreover, because the only contact between the insert and the pocket is along the upper portion of the insert, this relatively small area of the insert must absorb all the stresses generated between the insert and the pocket when the insert cuts a workpiece. Hence the limited and sometimes one-point contact between the insert and the pocket can result in localized chipping, cracking, or breakage of the insert over time.
Clearly, what is needed is a stop mechanism for round inserts which effectively prevents such inserts from rotating without creating local stresses in either the body of the insert or the pocket that receives it. Ideally, such a stop mechanism should be relatively easy to integrate into conventional insert and pocket structures. Finally, such a mechanism should be substantially independent from the main interface between the pocket walls and the insert that supports the insert during a cutting operation.
SUMMARY OF THE INVENTION
The invention is an anti-rotation mounting mechanism between an indexable insert in an insert-receiving pocket that overcomes all of the aforementioned shortcomings associated with the prior art. To this end, the invention comprises a plurality of curved stop surfaces disposed around the insert side surface, each of which includes a portion which is obliquely oriented with respect to the side surface of the insert, and at least one complementarily-shaped anti-rotation surface in the insert-receiving pocket. The anti-rotation surface in the pocket is preferably integrally formed with the pocket walls and both the anti-rotation surface and the stop surfaces of the are preferably defined by a gentle sloping, partial radius curve. A small amount of space is deliberately provided between the insert stop surfaces and the pocket anti-rotation surface to allow the insert to rotate between 1° and 10° before the stop and anti-rotation surfaces to seat against one another in broad line or lenticular surface contact.
In order to prevent the removal of a weakening amount of material from the insert, the rounded stop surfaces are tapered relative to the side surfaces of the insert; i. e., the stop surfaces increase in depth between the upper and lower surfaces of the insert such that sidewalls of the insert appears to be scalloped in a continuous sinusoidal pattern. Additionally, in order to equalize stresses between the insert walls and pocket walls, the pocket preferably includes two anti-rotation surfaces for simultaneously engaging two of the rounded stop surfaces of the insert. Finally, the anti-rotation surface is preferably located on a lower portion of the pocket sidewalls, and the upper portion of these sidewalls engages an upper portion of the insert sidewall to provide the primary support between the insert and the pocket.
The obliquely oriented, interfitting surfaces defined by the partial radius curves around the insert sidewalls and the sidewalls of the pocket provide an interference joint characterized by either a broad line-type or lenticular-surface type contact between the insert and the pocket in the tool body, avoiding localized point-type stresses which could either chip or crack the insert body or create wear patterns in the walls of the insert-receiving pocket. The contact between the upper sidewalls of the pocket and the insert substantially insulates the interference joint created by the stop and anti-rotation surfaces from the load applied between the insert and the pocket as a result of a cutting operation.
REFERENCES:
patent: 1056466 (1913-03-01), Solem
patent: 1838520 (1931-12-01), Archer
patent: 3408722 (1968-11-01), Berry, Jr.
patent: 3831237 (1974-08-01), Gunsalus
patent: 3842470 (1974-10-01), Hertel
patent: 3946474 (1976-03-01), Hahn et al.
patent: 4202650 (1980-05-01), Erickson
patent: 4632593 (1986-12-01), Stashko
patent: 5147158 (1992-09-01), Riviere
patent: 5199828 (1993-04-01), Forsberg et al.
patent: 5346336 (1994-09-01), Rescigno
patent: 5558142 (1996-09-01), Ehrle et al.
patent: 5658100
DeRoche Kenneth G.
Hartshorn Jeffrey E.
Snyder Robert T.
Kennametal PC Inc.
Knight Anthony
Meenan Larry R.
Walsh John B.
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