Patent Application
20060245837
The present invention relates to material cutting tools. The present invention more particularly relates to tool holders and cutting inserts. The tool holder and cutting inserts of the present invention comprise an antirotation stop to prevent rotation of the insert while secured in an insert pocket of the tool holder.
Early carbide cutting tools were typically carbide blanks brazed to steel holders. The blank would be resharpened by grinding. Clearance angles, cutting point radii, and other features could also be ground into the tools to suit a particular cutting operation. Although these early carbide cutting tools provide significant productivity increases over previous tools, certain disadvantages became apparent. Regrinding to sharpen the dulled tool would change the size and shape of the cutting insert. This would require an adjustment of the relationship between the cutting tool and the workpiece each time the tool is sharpened to compensate for the smaller sized tool.
Additionally, the brazed connection between the carbide insert and the holder could only withstand a limited range of operating temperature, thereby reducing the number of potential applications for the carbide tool. Additionally, carbide inserts which with coated surfaces could not be resharpened and had to be replaced.
Presently, replaceable, indexable inserts are more widely used. Indexable inserts resemble brazed tools except that the carbide insert is secured in the holder by clamping rather than brazing. When a cutting edge dulls, the insert may be removed, rotated, and replaced to provide a new sharp edge for further cutting. This eliminated the need for readjustment of the cutting operation between changes. Typically, an indexable cutting insert is held in place by a screw with a tapered head that fits a conical hole in the insert and thus holds the insert securely in the tool holder. Clamps on top of the insert may also be used in conjunction with the screw to further secure the cutting insert to the tool holder.
Consistency and ease of replacement are the main advantages of indexable inserts. Consistency of positioning of the cutting edge from index to index simplifies machine tool setup and helps ensure a more uniform product.
There may be a number of problems, however, in using a round shape inserts in a tool holder for metal machining, in particular in milling operations. Typical problems for machining with round inserts include inconsistent insert life in machining operations due to an imprecise indexing mechanism compared to square or diamond shape inserts, insecure clamping and positioning of a round inserts since no straight edge is available for indexing, cutting edge chipping may also result from rotation of a round shape insert in the pocket of the cutting tool holder, as well as other reasons.
Several tool holders and round cutting inserts have incorporated antirotation mechanisms in an attempt to overcome these problems in machining metals with round shape inserts in tool holders. For example, U.S. Pat. No. 5,658,100, describes a mechanism to secure the round shape insert in a pocket of a milling cutter wherein a plurality of depressions are built on the top surface of the round shape insert. The insert is then secured in the tool holder by a clamping claw supported on the milling cutter body, to prevent the rotation of a round shape insert in the pocket of a milling cutter. However, since the clamping claw described in U.S. Pat. No. 5,658,100 engages the top face of the cutting insert, the chip control geometry must perform the duel function of preventing rotation and to controlling the chip formation of the insert in operation.
In U.S. Pat. No. 6,053,671, a round shape insert is manufactured in a way that the edge surface of the insert consists of two portions separated by a step. The upper portion is a conical frustum which functions as a normal round cutting surface and the lower portion is in the shape of a polygon which creates an interface contact with the lower wall of the pocket, thus preventing the rotation of a round shape insert against the pocket.
In U.S. Pat. No. 5,346,336, another cutting insert comprising a polygonal pattern of facets is described. The polygonal pattern is located around the circular side surface of a round shape insert and then a complementary shaped polygonal pattern of the pocket is provided. The polygonal facet on a round shape insert interfaces with the complementary polygonal wall on the corresponding pocket of a milling cutter body, thus preventing the rotation of a round shape insert in the pocket.
U.S. Pat. Nos. 6,053,671 and 5,346,336 are basically similar in design, that is, the polygonal-shaped facets on a round shape insert interacts with the complementarily-shaped polygonal wall in the receiving pocket on a milling cutter body. The edges of the full radius formed by the polygonal pattern on the hard carbide material insert may slowly cut the relatively soft steel material of the pocket pin during the machining operations. In addition, the limited contact provided by the polygonal pattern-based design of these inserts may result in one-point contact between the edges of the insert facets and the flat wall of the pocket, which can result in localized chipping or cracking of the insert over time.
In U.S. Pat. No. 6,238,133, a insert and tool holder are described wherein a plurality of curved and obliquely 3-dimensional surfaces are built around the side wall of a round shape insert which interfaces with a substantially complementary curved surface, also 3-dimensional, in the insert-receiving pocket of a milling cutter body, therefore providing an anti-rotation mechanism for a round shape insert in the pocket on a milling cutter.
U.S. Pat. No. 6,238,133 provides a mechanism that uses curved stop surfaces around the side wall of the round shape insert and at least one complementary anti-rotation curved surface in the pocket of a cutter body. Both curved surfaces are defined by partial radius curves such that the interface can be in a form of either a broad/line-type contact or double convex, lenticular, contact. This is largely because there are no sharp edges on the insert to weaken the contact interface between the hard carbide insert and the relatively soft pocket on a steel cutter body.
There are several disadvantages and limitations in the mechanism described in U.S. Pat. No. 6,238,133, these disadvantages are primarily due to the complexity of the curved and oblique 3-dimensional surfaces in the pocket. Specifically, first, the complementarily-shaped oblique geometry can require complex machining procedures in the manufacturing of the insert and the corresponding pocket to ensure the necessary geometric and dimensional accuracy required to keep the desired functionality at the contact interface between the insert and the pocket. Second, the curved and oblique 3-dimensional surface limits the manufacturing methods for the pocket to an axial machining method along the pocket axis. Third, as a result of the manufacturing limitations of the complex geometry of the tool holder, it further limits number of pockets, thus the number of teeth, in a milling cutter.
The number of teeth on a milling cutter is an important factor affecting the cutting efficiency of the milling operation. A milling cutter should have enough teeth to ensure uninterrupted contact with the work piece. If the milling cutter has too few teeth, one tooth will lose contact with the workpiece prior to the next tooth is engaging the workplace. This will lead to vibration and chatter resulting in poor finishing, dimensional inaccuracies, and excessive tool wear. The quality of the surface finish is typically better using milling cutters with more teeth.
Although all the above-mentioned mechanisms provide feasible means of preventing undesired rotation of a round shape insert in the corresponding pocket on a milling cutter body, the mechanisms described all have some shortcomings.
Therefore, there is a need for an indexable cutting insert and tool holder that effectively functions to prevent rotation of the round shape insert in an insert pocket, but also are easy to manufacture and provides the necessary accuracy for stable and secure positioning. There is also a need for an indexable cutting insert, for example, a cutting insert made from tungsten based carbide or cermet and tool holder combination that allows the possibility to increase number of teeth on a cutter body.
The present invention relates to embodiments of a cutting tool holder having at least one insert pocket, wherein at least one insert pocket comprises a side surface and at least one antirotation stop protruding from the side surface. The antirotation stop may comprise at least two substantially planar surfaces. In certain embodiments, the cutting tool holder may have a pocket which comprises a bottom surface and an antirotation stop having three substantially planar surfaces that are substantially perpendicular to the bottom surface.
The antirotation stop may be integral to the tool holder or may be produced separately and attached, either permanently or temporarily, to the tool holder. Embodiments may further comprise additional antirotation stops if desired by the machining application.
In one embodiment, the cutting tool holder includes an insert pocket in the tool holder and at least one antirotation stop protruding from at least one of a side wall and the bottom surface of the insert pocket, wherein the antirotation stop comprises at least two substantially planar surfaces. A cutting insert made of tungsten based carbide or cermet may be secured in the tool holder, wherein the cutting insert has a recess having a shape that is non-complementary to the shape of the antirotation stop.
The cutting insert may be manufactured using a tangential machining method. The method includes tangentially machining at least one antirotation stop and an insert pocket in the tool holder, wherein the antirotation stop comprises at least two substantially planar surfaces. The method may further comprise milling a top surface of the pocket with a ball mill. The tangential method allows forming more pockets per a diameter of the tool holder than an axial machining method.
Embodiments of the tool holder includes at least one insert pocket. Each insert pocket comprises a bottom surface and a side surface, and at least one antirotation stop protruding from the bottom surface, wherein the antirotation stop comprises at least two substantially planar surfaces. The tool holder may be used for any machining operation such as, but not limited to, milling, turning, boring, planing, shaping, and reaming.
An embodiment of the tool holder may be a milling cutter tool 10 for an indexable cutting insert, such as shown in
The tool body 12 may be formed from any suitable engineering material such as a metal, alloy, plastic, or ceramic used in the fabrication of machinery, machinery components, structural shapes, tools, instruments, and other items. Their hardness, strength, machinability, dimensional stability, nonflammability, and resistance to corrosion, acids, solvents, and heat may characterize the properties of such suitable engineering materials. One example of a list of such suitable engineering materials include, but are not limited to, metals and alloys such as aluminum, beryllium, brass, bronze, cast iron, copper, lead, magnesium, steel, tantalum, zinc, zirconium, and various other trademarked and non-trademarked alloys; ceramics such as glass and porcelain; and plastics such as ABS resin, acetal resin, acrylic resin, fluorocarbon polymer, nylon, phenolformaldehyde resin, polybutilene terephthalate, polycarbonate, polyethylene, polyphenylene oxide, polypropylene, polystyrene, polyvinyl chloride, reinforced plastics (FRP), and ureaformaldehyde resin.
The tool holder of the present invention comprises at least one pocket. A pocket in a tool holder is designed to receive a cutting insert. In certain embodiments, such as shown in
Embodiments of the tool holder further comprise an antirotation stop. The antirotation stop prevents rotation of the insert within the pocket of the tool holder. A cutting insert comprising at least one recess may be secured in the pocket with the antirotation stop extending into the recess of the cutting insert. A round shape insert 20, as shown in
The phrase substantially planar indicates that the surfaces are flat or level. The surfaces of the antirotation step should be considered substantially planar if the surfaces are manufactured in such a way to maintain the engagement of the antirotation step and the recess at a point, or a localized section, contact. As used herein, point or point contact is defined as a contact between two components that is limited to a localized area.
The tool holder of the present invention does not require a complementarily shaped antirotation stop as compared to the recess. This non-complementary requirement allows the pocket and insert to be more easily manufactured and more accurately secured than tool holders and inserts which are complementary. The antirotation stop in the pocket provided in the present invention has at least two substantially planar surfaces instead of the obliquely oriented 3-dimensional surface of the prior art, such as in the recent U.S. Pat. No. 6,238,133. Therefore it allows the manufacturing of the pockets using the tangential method rather than an axial method. A tangential method involves the forming the pocket of the cutting tool by approaching the pocket in a direction tangent to the pocket bottom surface rather than in an axial (conventional) direction of the pocket as is the case in the method of forming the pocket as described in the recent U.S. Pat. No. 6,238,133.
In another embodiment, shown in
While the bottom surface 37 of the pocket 33 supports the insert during a cutting operation, the recessed surface, 26, or the edge 27 of the recess of the cutting insert 20, in
The antirotation stop need not be limited to the shape shown in
The embodiment of the tool holder in
Embodiments of the present invention allows accurate and secure positioning a round shape insert in a tool holder. An accurately and securely positioned insert may improve the performance and consistency of the insert life. The tool holder of the present invention may be used with any number of shapes of cutting inserts. The shape of a recess in the cutting insert that engages the antirotation stop is not required to be complementary to the shape of the antirotation stop. In fact, a cutting insert comprising multiple recessed surfaces in any form may be used. A simple spherical geometry around the side wall of a round shape insert may be used with the tool holder.
The insert contacts the pocket in at least three main two locations. As an example, an insert 50 may be seated in a pocket 51 as shown in
Embodiments of the tool holder of the present invention allow more accurate seating of the insert. A recessed surface of the insert contacts the pocket at a concave profile of the edge of the antirotation stop thus giving a stable contact. In one embodiment, the edge of the top of the antirotation stop is a result of the intersection between at least two substantially planar faces and a sphere formed by a standard ball mill when machining the upper portion of the pocket wall.
Embodiments of the tool holder provide significant advantages.
In this invention, the anti-rotation surface in the insert-receiving pocket consists of at least 2 substantially planar surfaces in a form of non-oblique 2-dimensional geometry, rather than the convex surfaces in a form of oblique 3-dimensional geometry as in U.S. Pat. No. 6,238,133.
In this invention, there need not be a complementary relationship between the positioning geometry of the insert and the pocket, rather than the complementarily shaped geometry in U.S. Pat. No. 6,238,133.
A regular round shape insert may contact at the upper portion of the pocket wall. For a round shape insert with anti-rotation mechanism, it needs to have at least one additional contact. In embodiments of the tool holder of the present invention, the insert contacts with the lower portion of the pocket wall at a point, rather than the linear contact of the pocket and tool insert described in U.S. Pat. No. 6,238,133. Therefore, tool holders of the present invention give a more stable contact, which improves the in-process performance and the seating consistency of the insert in the tool holder. In certain embodiments, the above-mentioned point contact result from the edge formed at the top the two substantially planar surfaces.
Because of the substantially planar geometry, this invention allows manufacturing of the pocket using the tangential method rather than the axial, or conventional, method. In the tangential method, the cutting tool approaches the pocket in a direction tangent, or parallel, to the pocket bottom face rather than in an axial direction perpendicular to the pocket bottom face as shall be in U.S. Pat. No. 6,238,133. Therefore, the design in this invention provides more options for ease of manufacturing.
It is a well-known that the conventional method, i.e. axial method, is typically used for manufacturing a pocket in a milling cutting tool. The tool used for manufacturing the pocket approaches and machines the pocket in a direction parallel to the axis of the pocket, thus the clearance space for the cutting tool must be provided along the pocket axis. In this sense, the axial method for manufacturing the pocket limits the number of pockets, or number of teeth, per diameter available for a milling cutter.
The tangential method for manufacturing the pocket is more flexible and one embodiment is shown in
The tangential manufacturing method allows more pockets or cutting teeth to be formed per diameter in a cutter body than an axial manufacturing method. Therefore, this invention can expand the machining applications.
There are several advantages in having the ability to produce tool holders with additional pockets. For instance, the life of the cutting inserts may be improved by reducing feed rates during machining while keeping or improving the material removal rate. A milling cutter with less distance between the teeth can also improve the life of cutter body by reducing the stresses distributed on each tooth. More teeth will also benefit in machining of some difficult-to-machine materials, like inconel, titanium, etc.
The recessed surface of the insert which may be, for example, tungsten based carbide or cermet in embodiments of the present invention may have a simple geometry, that is, an almost perpendicular, or preferably, slightly off perpendicular such as, 1 to 2 degrees perpendicular to the bottom surface and then smoothly extending to a simple spherical surface, rather than the complex geometry that is defined by partial curved radius and includes continuous sinusoidal curve around the insert circumference as well as tapered (about 15 degrees) curved stop surface at the central portion as in the prior art.
Embodiments of the tool holder have been described, however, different modifications, variations, and additions may become evident to persons of ordinary skill in the art. For example, while the anti-rotation stop has been described with respect to use on a tool holder in conjunction with a round insert, it may also may be incorporated into embodiments with other curved cutting edges or even straight cutting edges. In addition, the embodiments described herein comprise on antirotation stop, a greater number of antirotation stops may be incorporated into the tool holder comprising at least one antirotation stop comprising two planar surfaces.
Embodiments of the tool holder may be used to accurately and securely position a round shape insert, thus improving performance and consistency of the life of the insert in cutting operations. Embodiments of the tool holder are easy to manufacture due to the geometry of the pocket on the holder, and allow more number of pockets or teeth to be formed on a specific tool holder thus expanding the potential applications of the tool.
