Cutting Tool and Cutting Insert With A Rearward Resilience Slit

[0001] The present invention relates to cutting tools, in which a cutting insert is resiliently and removably self-clamped in a tool shank holder, in general, and to a cutting insert having a rearward resilience slit for mounting into such a holder, in particular.

[0002] Cutting tools, and in particular drills, may include a cutting insert or cutting head which is removably secured in a tool holder, either by a fastening member (e.g., a screw), or by a resilience force. The cutting insert is fastened to the tool holder prior to operation in metal cutting, such as drilling. The cutting insert is typically made of a hard metal, such as cemented carbide or cermet. The tool holder may be made of steel, or also of a hard material, such as cemented carbide or cermet. Examples of such cutting tools and cutting inserts are disclosed in U.S. Pat. No. 5,228,812, U.S. Pat. No. 5,749,689, U.S. Pat. No. 6,485,235, U.S. Pat. No. 6,582,164, U.S. Pat. No. 7,048,480, US2010/155144 and US2010/143059.

[0003] It is an object of the subject matter of the present application to provide an improved novel drill cutting insert having a single resilience slit in the coupling portion thereof, for resilient self-clamping into a compatible tool shank holder.

[0004] In accordance with the subject matter of the present application, there is provided a cutting insert having a longitudinal insert axis extending in a forward to rearward direction, the cutting insert comprising a head portion and a coupling portion.

[0005] The head portion has two opposing major surfaces and a head peripheral surface extending therebetween, the head peripheral surface including a base surface at a rearward end of the head portion, the base surface defining a base plane perpendicular to the insert axis, each of the major surfaces intersecting with the base surface at a respective first intersection.

[0006] The coupling portion protrudes rearwards from the base surface along the insert axis. The coupling portion has a rear surface spaced apart from the base surface along the insert axis and a cylindrical coupling peripheral surface extending therebetween. The coupling peripheral surface intersects with the base surface at a transition area.

[0007] The coupling portion also includes a resilience slit extending from the rear surface in the forward direction, and opening out to the coupling peripheral surface. The resilience slit has two opposite inner walls converging in the forward direction towards a slit inner end which terminates at a slit inner end plane perpendicular to the insert axis.

[0008] The slit inner end plane is spaced apart from the base plane by a longitudinal distance and the inner walls of the resilience slit form a first acute slit angle therebetween.

[0009] Also in accordance with the subject matter of the present application is a cutting tool having a tool shank, with the aforementioned cutting insert resiliently secured to the tool shank by an interference fit.

[0025] It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity, or several physical components may be included in one functional block or element. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.

[0026] In the following description, various aspects of the present invention will be described. For purposes of explanation, specific configurations and details are set forth in order to provide a thorough understanding of the present invention. However, it will also be apparent to one skilled in the art that the present invention may be practiced without the specific details presented herein. Furthermore, well-known features may be omitted or simplified in order not to obscure the present invention.

[0027] Reference is made to FIGS. 1 and 2, depicting a cutting tool 100 in accordance with an embodiment of the present invention. The cutting tool 100 is a rotary cutting tool, such as a drill, having an axis of rotation B. The cutting tool 100 includes a tool shank 150 and a cutting insert 102, the cutting insert 102 removably mounted in a resilient self-clamping manner on the tool shank 150. The cutting tool 100 rotates about the axis of rotation B in a direction of rotation R.

[0028] The cutting insert 102 may be of the sort used in metal cutting operations and thus can be termed a metal cutting insert, meaning that the cutting insert may be used for cutting metal, not necessarily that the cutting insert is made of metal. In preferred embodiments, the cutting insert 102 is formed of hard metal, such as cemented carbide or cermet, and is employed for drilling or other metal cutting operations, sometimes also referred to as chip removing operations.

[0029] With further reference to FIGS. 3-5, different views of the cutting insert 102 are shown. The cutting insert 102 has a longitudinal insert axis A extending in a forward to rearward direction D_F, D_R. The cutting insert 102 has a head portion 104 and a coupling portion 116. The head portion 104 has a rearward end 112 and a forward end 136. The head portion 104 includes two opposing major surfaces 106 and a head peripheral surface 108 extending therebetween. The head peripheral surface 108 includes a base surface 110 at the rearward end 112 of the head portion 104. The base surface 110 defines a base plane P1 extending perpendicular to the insert axis A. Each of the major surfaces 106 intersect with the base surface 110 at a respective first intersection 114.

[0030] The head peripheral surface 108 further includes a forward surface 134 at the forward end 136 of the head portion 104. Each of the major surfaces 106 intersects with the forward surface 134. A portion of each such intersection forms a respective major cutting edge 138 at the forward end 136 of the head portion 104. An insert flute surface 107 extends rearwards from each of the cutting edges 138, on the respective major surface 106.

[0031] The base portion 110 includes two insert transverse abutment surfaces 123, extending perpendicular to, and symmetrically around the insert axis A. Each of the major surfaces 106 further includes an insert radial abutment surface 125, extending along the insert axis A. Each insert radial abutment surface 125 extends from the head peripheral surface 108 towards the insert axis A and the base surface 110, such that the two insert radial abutment surfaces 125 are arranged symmetrically around the insert axis A. A retaining ledge 133 extends circumferentially from the rearward end of each of the insert radial abutment surfaces 125, along a portion of the respective insert transverse abutment surface 123.

[0032] The coupling portion 116 protrudes rearwards from the base surface 110 along the insert axis A. The coupling portion 116 comprises a rear surface 118 spaced apart from the base surface 110. A cylindrical coupling peripheral surface 120 extends between the rear surface 118 and the base surface 110, forming a cylindrical envelope to the coupling portion 116. The coupling peripheral surface 120 is coupled with the base surface 110 at a circumferential transition area 122. The transition area 122 is spaced apart from the first intersections 114. Therefore, as depicted in FIG. 5, the transition area 122 is entirely surrounded by the base surface 110 and has a substantially circular boundary 132.

[0033] The coupling portion 116 also comprises a resilience slit 124 extending from the rear surface 118 in the forward direction D_F, opening out to the coupling peripheral surface 120. The resilience slit 124 has two opposite inner walls 131, converging in the forward direction D_F towards a slit inner end 126 which terminates at a slit inner end plane P2 extending perpendicular to the insert axis A. The slit inner end plane P2 is spaced apart from the base plane P1 by a longitudinal distance D, such that the resilience slit 124 ends in the coupling portion 116 and does not extend further into the head portion 104 of the cutting insert 102. In this manner, all of the resilient self-clamping of the cutting insert 102 occurs in the coupling portion 116, and in particular adjacent the rear surface 118 thereof. This provides stability to the head portion 104, and in particular to the transition area 122, which is particularly susceptible to side-forces acting on the cutting insert 102 during machining operations. Further, due to the longitudinal distance D, a cross section of the coupling portion 116 taken perpendicular to the insert axis A, between the slit inner end plane P2 and the base plane P1, has a full undivided cross section 128 (e.g., a circular or elliptical cross section). This is shown in the cross section of FIG. 12, as will be elaborated herein below.

[0034] The rear surface 118 of the coupling portion 116 defines an end plane P3 extending perpendicular to the insert axis A. The resilience slit 124 has a longitudinal slit length H between the end plane P3 and the slit inner end plane P2. The longitudinal distance D is typically smaller than the longitudinal slit length H. The resilience slit 124 divides the coupling portion 116 into two coupling legs 117. As shown in FIG. 5, a resilience slit plane P_S passes through the resilience slit 124, substantially centrally between the coupling legs 117, such that the coupling legs 117 are mirror-symmetric about the resilience slit plane P_S. The resilience slit plane P_S includes the insert axis A. The insert radial abutment surfaces 125 define first and second radial abutment planes P_A1, P_A2, which are parallel to one another and to the insert axis A. The resilience slit plane P_S is perpendicular to the first and second radial abutment planes P_A1, P_A2. The resilience slit 124 allows the coupling portion 116 to be elastically deformed, such that each of the coupling legs 117 approaches the insert axis A, when sufficient force is applied on the coupling peripheral surface 120 in the direction of the resilience slit plane P_S.

[0035] FIG. 4 depicts a side view of the cutting insert 100 viewed along the resilience slit plane P_S, when the cutting insert 100 is in its neutral position (i.e., not mounted into the cutting tool holder 150). This side view shows that the inner walls 131 of the resilience slit 124 form a first acute slit angle α1 therebetween, expanding from the slit inner end 126 toward the rear surface 118. This forms a rearwards V-shape of the resilience slit 124. As also seen in FIG. 4, each coupling leg 117 has a thickness T in a direction perpendicular to the resilience slit plane P_S, which thickness T decreases in the direction towards the rear surface 118.

[0036] As depicted in FIG. 2, the tool shank 150 has a generally cylindrical shape, having a shank forward end 154 with a receiving portion 152. With further reference to FIG. 10, the tool shank 150 is depicted in a perspective front view. The receiving portion 152 includes a rearmost receiving portion base 158, and a receiving portion peripheral surface 156. The receiving portion peripheral surface 156 extends from the rearmost receiving portion base 158 in the forward direction D_F, circumferentially about the axis of rotation B. The receiving portion peripheral surface 156 may have a substantially cylindrical cross section. Alternatively, the receiving portion peripheral surface 156 may have another shape, which is not necessarily cylindrical. With reference to FIGS. 12 and 13, the receiving portion peripheral surface 156 is shown to have a substantially cylindrical cross section.

[0037] The tool shank 150 further includes two shank radial abutment surfaces 160, located at the shank forward end 154, and extending parallel to the axis of rotation B. The shank radial abutment surfaces 160 are arranged symmetrically about the axis of rotation B. The tool shank 150 also includes two shank transverse abutment surfaces 162, each extending from a respective one of the shank radial abutment surface 160, perpendicular to the axis of rotation B. A retaining undercut 164 is formed between each of the shank transverse abutment surfaces 162 and the respective radial abutment surface 160, for receiving one of the retaining ledges 133 of the cutting insert 102.

[0038] The tool shank 150 also includes two shank flute portions 157, arranged at the circumference of the tool shank 150 symmetrically about the axis of rotation B. During metal cutting operations, metal chips removed from the work-piece are directed to flow from the cutting edges 138 of the cutting insert 102 along the insert flute surfaces 107, and further into the shank flute portions 157, thereby being evacuated from the cutting area.

[0039] Reference is further made to FIGS. 6 and 7, depicting top views of the cutting tool 100 in a partially assembled position and assembled position, respectively. FIGS. 8 and 9 are cross sections of the cutting tool 100 in the assembled position, according to the cutting lines VIII-VIII and IX-IX, respectively, noted in FIG. 7. The cross section of FIG. 8 passes through the intersections of the head peripheral surface 108 with the insert radial abutment surfaces 125, and through the insert axis A. The cutting line IX-IX includes the insert axis A, and extends parallel to the radial abutment planes P_A1, P_A2.

[0040] The cutting insert 102 is configured to be mounted on the tool shank 150 and securely affixed thereto in order to reach the assembled position, shown for example in FIGS. 1 and 7. The assembled position is suitable for employing the cutting tool 100 in metal cutting operations, such as drilling. In the disassembled position shown in FIG. 2, the cutting insert 102 and the tool shank 150 are separated from one another. With the insert axis A aligned with the axis of rotation B, the cutting insert 102 and the tool shank 150 are brought together until the coupling portion 116 is located in the receiving portion 152, in a partially assembled position (FIG. 6). From the partially assembled position, the cutting insert 102 is rotated about the insert axis A, relative to the tool shank 150, in an assembling direction R′, opposite the direction of rotation R, until reaching the assembled position, shown for example in FIGS. 2 and 7. In this position, the cutting insert 102 is resiliently secured to the shank forward end 154 by an interference fit applied between the coupling peripheral surface 120 and the receiving portion peripheral surfaces 156. In the partially assembled and assembled positions, the insert axis A coincides with the axis of rotation B. Further, in the partially assembled and assembled positions, the coupling portion 116 of the cutting insert 102 is entirely confined within the receiving portion 152 of the tool shank 150 (i.e., the coupling portion is not visible when observing the assembled cutting tool 100).

[0041] Reference is further made to FIG. 11, depicting a side view of the cutting tool 100 of FIG. 2. The outline of the hidden parts of the cutting insert 102, in this view, is depicted in dashed lines. FIGS. 12 and 13 depict cross sections of the cutting tool 100, according to the cutting lines XII-XII and XIII-XIII, respectively, noted in FIG. 11. The cutting line of FIG. 12 passes between the base surface 110 and the slit inner end 126 of the cutting insert 102, perpendicular to the insert axis A. The cross section of the coupling portion 116, in this longitudinal location, is the full undivided cross section 128.

[0042] The cross section of FIG. 13 passes forwards from, and adjacent to the rear surface 118 of the cutting insert 102, perpendicular to the insert axis A. This cross section demonstrates the interference fit between the coupling peripheral surface 120 and the receiving portion peripheral surface 156.

[0043] In the assembled position, each one of the insert radial abutment surfaces 125 of the cutting insert 102 abuts a respective one of the shank radial abutment surfaces 160 of the tool shank 150. Each one of the insert transverse abutment surfaces 123 abuts a respective one of the shank transverse abutment surfaces 162. Further, in the assembled position, each flute portion 157 of the tool shank 150 forms a continuous extension of the respective insert flute surface 107 of the cutting insert 102. The retaining ledges 133 of the cutting insert 102 are received within the retaining undercuts 164 of the tool shank 150. If a forward force is applied on the cutting insert 102, acting to pull the cutting insert 102 out of the tool shank 150, the retaining ledges 133 are stopped by the retaining undercuts 164, thereby preventing the cutting insert 102 from being pulled out. In the assembled position, the rear surface 118 of the cutting insert 102 is spaced apart from the receiving portion base 158, as shown in the cross-sections of FIGS. 8 and 9.

[0044] The coupling portion 116 and the receiving portion 152 are designed to have an interference fit between them so that in the assembled position the coupling portion 116 is secured in the receiving portion 152. Such an interference fit is achieved by the diameter of the coupling peripheral surface 120 being larger than the diameter of the receiving portion peripheral surface 156, at least in a portion of the circumference thereof. The coupling peripheral surface 120 may include two opposite indents 130, arranged symmetrically about the insert axis A. The indents 130 are formed in the coupling peripheral surface 120, and extend from the rear surface 118 in the forward direction D_F. FIG. 13 shows that the indents 130 reduce the diameter of the coupling peripheral surface 120, forming an elliptical cross section 129 of the coupling portion 116.

[0045] The resilience slit 124 provides elasticity to the coupling portion 116 enabling the diameter of the coupling portion peripheral surface 120 (that is, the diameter in any cross section of the coupling portion 116 taken perpendicular to the insert axis A), to be made smaller by applying an interference force from both sides of the resilience slit 124. By applying such a force, the coupling portion 116 is elastically deformed and the coupling legs 117 are urged towards one another, and towards the resilience slit plane P_S. A resilience force urges the coupling legs 117 apart to their original neutral position, thereby pressing the coupling peripheral surface 120 against the receiving portion peripheral surfaces 156.

[0046] In the embodiment depicted in the drawings, each of the indents 130 extends on both sides of the resilience slit 124, over the opening of the resilience slit 124 to the coupling peripheral surface 120. This is to ensure that the interference fit occurs such that the interference force is applied perpendicular to the resilience slit plane P_S, so as to press the coupling legs 117 towards the resilience slit plane P_S.

[0047] When the cutting tool 100 is employed in metal cutting, it rotates in the direction of rotation R, and a reverse force is applied on the cutting insert 102, in the opposite direction R′. This reverse force further assists in maintaining the cutting insert 102 clamped tight within the tool shank 150 during operation.

[0048] The cutting insert 102 may be removed from the tool shank 150, for example, when the cutting edges 138 have worn out and the cutting insert 102 needs to be replaced. In order to remove the cutting insert 102, it is rotated about the insert axis A, relative to the tool shank 150, in the direction of rotation R, until reaching the partially assembled position (FIG. 6). Then, the cutting insert 102 and the tool shank 150 are pulled apart until arriving at the disassembled position (FIG. 2).

[0049] Reference is further made to FIG. 14, schematically depicting partial side views of the coupling portion 116, taken along the insert axis A, when the coupling portion 116 is in the neutral position (shown in solid lines) and the assembled position (shown in dashed lines). The displacement towards the resilience slit plane P_S in the coupling portion 116 is evident when comparing the assembled position with the neutral position. As shown in FIG. 14, and according to results of mechanical analysis of the cutting tool 100, the largest displacement was recorded at, or immediately adjacent, the rear surface 118, in each of the coupling legs 117. The displacement decreased when approaching the slit inner end 126, and no displacement was recorded between the slit inner end 126 and the base surface 110, and in particular at the transition area 122.

[0050] The coupling portion 116 has a coupling portion width W extending between the coupling peripheral surface 120, on opposite sides of the insert axis A. In the neutral position, the coupling portion width W is substantially constant, along the coupling portion 116. In the assembled position, the coupling portion width W decreases when approaching the rear surface 118 from the slit inner end 126. The coupling portion width W remains constant between the slit inner end 126 and the transition area 122, both in the assembled position and in the neutral position.

[0051] As noted above, the slit inner end 126 is spaced apart from the base surface 110, (i.e., the slit inner end plane P2 is spaced apart from the base plane P1), making the cross section of the coupling portion 116 at that region, the full undivided cross section 128. Further, in the neutral position, the inner walls 131 of the resilience slit 124 form the first acute slit angle α1 expanding towards the rear surface 118, such that the thickness T of each coupling leg 117 taken in a direction perpendicular to the resilience slit plane P_S narrows down toward the rear surface 118. In the assembled position, the coupling legs 117 are displaced toward each other, on opposite sides of the resilience slit plane P_S, causing the inner walls 131 of the resilience slit 124 to form a second slit angle α2 therebetween, the second slit angle α2 being smaller than the first acute slit angle α1. Due to these attributes, the displacement towards the resilience slit plane P_S is the largest at the rear surface 118, while eliminated from the transition area 122 and its vicinity, thereby providing further durability to the transition area 122.

[0052] In a particular case of side-forces acting on a cutting insert during machining operations (e.g., angular drilling), the transition area may be particularly susceptible and prone to breakage and other mechanical damage. The suggested design of the cutting insert 102 according to the present invention provides better strength and durability of the transition area 122, thereby preventing such damage.

[0053] While the present invention has been described with reference to one or more specific embodiments, the description is intended to be illustrative as a whole and is not to be construed as limiting the invention to the embodiments shown. It is appreciated that various modifications may occur to those skilled in the art that, while not specifically shown herein, are nevertheless within the scope of the invention.