JP2018161717A - drill - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a drill that is able to securely prevent sudden breakage of a drill body in highly efficient processing of a hard brittle material.SOLUTION: In a drill in which a chip discharge groove 4 is formed in the outer periphery of the leading end of a shaft-like drill body 1 rotated around an axis O and in which a cutting blade is formed in the leading end of the drill body 1, the bottom face 6 of the chip discharge groove 4 in a cross-section orthogonal to the axis O has a projecting curved central part 6A in a circumferential direction of the drill body 1. Both circumferential end parts 6B, 6C of the bottom are disposed in contact with the projecting curve of the central part 6A and formed in a recessed curved or straight shape that does not recede further than a line L extended from the projecting curve.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a small-diameter drill for drilling a workpiece made of a hard and brittle material such as ceramics.

  In drilling hard and brittle materials with such a small-diameter drill, in addition to the life due to wear of the drill body, the life due to sudden breakage of the drill body under high-efficiency machining conditions becomes a problem. If the drill body breaks during the drilling process, the broken tip end of the drill body remains inside the machining hole, and a very expensive workpiece may become defective, resulting in a large loss. For this reason, it is difficult to perform high-efficiency machining, and the machining time becomes long, resulting in high costs.

  Here, chip clogging is mentioned as a cause of such a sudden breakage. When drilling a hard and brittle material with a small-diameter drill, the amount of cutting may be extremely small, and the chips become a fine powder. The fine powdery chips are mixed with the cutting fluid to form a paste and adhere to the chip discharge groove. Then, as the number of processed holes increases, the amount of adhesion increases, and the resistance increases at a stroke due to clogging of chips, causing sudden breakage. In particular, under high-efficiency machining conditions, the amount of chip discharge increases and sudden breakage is likely to occur.

  In order to prevent sudden breakage due to such a cause, the drill body is pulled out from the workpiece by fine step processing and chip is discharged, and when it is pulled out, the cutting oil is sprayed on the drill body and attached to the chip discharge groove. It is conceivable to wash away. However, in a chip discharge groove in which a cross section perpendicular to the axis of the drill body forms a concave curve like a general drill, there are many cases where the chips cannot be reliably washed away.

  Also, in the case of a small-diameter drill, there is a risk of breakage if the cutting fluid is sprayed on the drill body at high pressure. On the other hand, if the cleaning time is increased instead of spraying the cutting fluid at low pressure, the processing time is very short in fine step processing. It becomes long. Furthermore, the dry life without using cutting fluid drastically reduces the life of the drill.

  Therefore, in Patent Document 1, as a tool for cutting hard and brittle materials such as ceramics, a tip of a tool body rotated around an axis is a polygon whose cross section perpendicular to the axis forms a polygonal shape. There has been proposed one that is formed in a columnar shape and is provided with a cutting edge portion at the tip thereof. According to such a cutting tool, it is easy to wash away the attached chips with the cutting fluid as compared with the drill having the chip discharge groove having the concave curved cross section described above, and if the cross section area of the chip discharge groove is the same, the core thickness is reduced. It is possible to secure a large amount to improve the rigidity, and it is also possible to make it difficult for sudden breakage to occur.

Japanese Patent Laid-Open No. 2005-022102

  However, in such a cutting tool (drill), paste-like chips tend to adhere to both ends in the circumferential direction of the chip discharge groove at the tip of the tool body having a polygonal cross section. Then, once the chips adhere to both ends in the circumferential direction in this way, the chips attached to the central portion in the circumferential direction lose the escape place and continue to adhere even if the cutting fluid is sprayed. Therefore, there is a risk of chip clogging, and it is difficult to reliably prevent sudden breakage in high-efficiency machining of hard and brittle materials.

  The present invention has been made under such a background, and provides a drill capable of reliably preventing breakage of a drill body suddenly in high-efficiency machining of hard and brittle materials as described above. It is aimed.

  In order to solve the above problems and achieve such an object, the present invention provides a chip discharge groove formed on the outer periphery of the tip of a shaft-shaped drill body that is rotated around an axis, A drill having a cutting edge formed at a tip thereof, and in a cross section orthogonal to the axis, the bottom surface of the chip discharge groove is formed with a convex central shape in the circumferential direction of the drill body, and Both end portions in the direction are formed in a concave curve shape or a straight line shape that is in contact with the convex curve in the central portion and is not recessed from an extension line of the convex curve.

  In the drill configured as described above, the center portion of the bottom surface of the chip discharge groove in the circumferential direction of the tip end portion of the drill body is formed in a convex curve shape in the cross section orthogonal to the axis, so When the cutting fluid is sprayed when the tip portion is pulled out from the workpiece, the cutting fluid sprayed on the central portion flows into both end portions in the circumferential direction of the bottom surface of the chip discharge groove along the convex curve.

  And since the cross section of the bottom face of the chip discharge groove is formed in a concave curve shape or a straight line shape in contact with the convex curve of the central portion and not recessed from the extended line of the convex curve at the both end portions. The chips adhering to both ends can be made to flow easily so as to be pushed out by the cutting fluid that has flowed in from and can be quickly washed away. For this reason, it is possible to prevent chip clogging even if the cleaning time is short.

  Moreover, since the center part in the circumferential direction of the bottom face of the chip discharging groove has a convex cross section, the core thickness of the tip end part of the drill body can be further ensured, and the rigidity can be further improved. Therefore, in a small-diameter drill that drills holes in hard and brittle materials such as ceramics, even if high-efficiency machining with a large step amount in step machining, sudden breakage of the drill body occurs. It becomes possible to prevent reliably.

Here, the surface of the tip portion of the drill body is coated with one of a diamond coating, a CVD coating such as Al ₂ O ₃ and TiCN, and an electrodeposited abrasive coating, so that the diamond of the coated coating is obtained. Drilling can be performed by grinding hard and brittle materials with particles, CVD particles, or electrodeposited abrasive grains.

  The core thickness at the tip of the drill body is desirably in the range of 0.5 × D to 0.9 × D with respect to the diameter D of the cutting blade. If the core thickness is larger than the above range, the chip discharge groove may become shallow and chip clogging may occur. On the other hand, if the thickness is smaller than the above range, the rigidity at the tip of the drill body is impaired and breakage is likely to occur. There is a risk that.

  Further, in the cross section orthogonal to the axis, the radius of curvature of the convex curve formed by the central portion in the circumferential direction of the bottom surface of the chip discharge groove is in a range of 0.25 × D or more with respect to the diameter D of the cutting edge. It is desirable that If the radius of curvature of the convex curve formed by the cross section of the central portion of the bottom surface is smaller than the above range, the core thickness d may be reduced, and the rigidity of the tip end portion of the drill body may be impaired.

  Furthermore, when a plurality of the chip discharge grooves are formed at intervals in the circumferential direction on the outer periphery of the tip portion of the drill body, and a portion between the chip discharge grooves adjacent in the circumferential direction is a margin part. In addition, the width of the margin portion in the cross section orthogonal to the axis is in the range of 0.05 × D or more with respect to the diameter D of the cutting blade and less than the core thickness of the tip of the drill body. It is desirable. If the width of the margin portion is smaller than the above range, it may be difficult to sufficiently guide the tip of the drill body, and if it is larger than the above range, the resistance may increase.

  As described above, according to the present invention, even if high-efficiency machining with a large step amount is performed in drilling of hard and brittle materials, it is possible to prevent sudden breakage due to chip clogging of the drill body. It is possible to prevent the broken drill body from being left inside the workpiece.

It is a perspective view of the front-end | tip part of the drill main body in the 1st Embodiment of this invention. It is a side view of the front-end | tip part of the drill main body in embodiment shown in FIG. It is a front view of the front-end | tip part of the drill main body in embodiment shown in FIG. It is sectional drawing orthogonal to the axis line of the front-end | tip part of the drill main body in embodiment shown in FIG. It is a perspective view of the front-end | tip part of the drill main body in the 2nd Embodiment of this invention. It is a side view of the front-end | tip part of the drill main body in embodiment shown in FIG. It is a front view of the front-end | tip part of the drill main body in embodiment shown in FIG. It is sectional drawing orthogonal to the axis line of the front-end | tip part of the drill main body in embodiment shown in FIG.

  1 to 4 show a first embodiment of the present invention. In the present embodiment, the drill body 1 is formed of a hard material such as cemented carbide in the shape of an approximately multi-stage cylindrical shaft centered on the axis O, and the tip thereof has a small diameter cutting edge having a diameter of about 6 mm or less. The rear end portion (not shown) is a cylindrical shank portion having a diameter larger than that of the cutting edge portion 2. In such a drill, the shank portion is gripped by the main shaft of the machine tool and is sent around the axis O while being rotated in the drill rotation direction T, and is sent to the front end side in the axis O direction to a workpiece made of a hard and brittle material such as ceramics. Drilling is performed by the cutting edge portion 2.

  In the present embodiment, the front end surface of the cutting edge portion 2 is notched into a quadrangular pyramid surface that is 180 ° rotationally symmetric with respect to the axis O as shown in FIGS. A cutting edge 3 is formed at the intersecting ridge line portion between the cone surface having a large fan angle centered on the axis O and the cone surface having a small fan angle located on the opposite side of the drill rotation direction T. The diameter of the circle formed by the outer peripheral end of the cutting blade 3 around the axis O is the diameter of the cutting blade portion 2 and is the diameter D of the cutting blade 3.

  Further, on the outer periphery of the cutting edge portion 2, a plurality of (two) chip discharge grooves 4 that twist to the opposite side to the drill rotation direction T from the front end surface toward the rear end side (left side in FIG. 2). The outer peripheral end of the cutting blade 3 is interposed in the circumferential direction of the drill body 1 and is also formed 180 degrees rotationally symmetric with respect to the axis O. A portion between the chip discharge grooves 4 in the circumferential direction is a margin portion 5 and is disposed on a cylindrical surface with the axis O as the center, and the cutting edge 3 intersects the margin portion 5. That is, the drill of this embodiment is a two-blade twist drill.

  The bottom surface 6 of the chip discharge groove 4 has a center portion 6A in the circumferential direction of the drill body 1 formed in a convex curve shape in the cross section orthogonal to the axis O, and both ends in the circumferential direction. The portions 6B and 6C are formed in a concave curve shape or a straight line shape that is in contact with the convex curve of the central portion 6A and is not recessed from the extended line L of the convex curve, and intersect the margin portion 5.

  Here, in the present embodiment, in the cross section perpendicular to the axis O, the central portion 6A in the circumferential direction of the bottom surface 6 of the chip discharge groove 4 is formed in a convex arc shape centering on the axis O, and this convex arc The radius of curvature (the radius of the convex arc) R is 0.25 × D or more with respect to the diameter D of the cutting blade 3. In this embodiment, twice the radius of curvature R is at the tip of the drill body 1. The core thickness d of a certain cutting edge portion 2 is set. The core thickness d in the present embodiment is in the range of 0.5 × D to 0.9 × D with respect to the diameter D of the cutting blade 3. When the central portion 6A in the circumferential direction of the bottom surface 6 is not formed in a convex arc shape with the axis O as the center, the core thickness d is the diameter of a circle inscribed in the central portion 6A with the axis O as the center. It becomes.

  Moreover, in this embodiment, the end 6B on the opposite side to the drill rotation direction T out of both ends 6B and 6C in the circumferential direction of the bottom surface 6 of the chip discharge groove 4 is in contact with the convex curve formed by the center 6A. It is a concave curve shape that is not recessed more than the extended line L of the convex curve, particularly a concave arc. In this embodiment, the radius of curvature of the concave curve (the radius of the concave arc) is 1.0 × D or more with respect to the diameter D of the cutting edge.

  On the other hand, of the both end portions 6B and 6C, the end portion 6C on the drill rotation direction T side is in contact with the convex curve formed by the central portion 6A in this embodiment, and is a straight line that is not recessed from the extended line L of the convex curve. It is made into a shape. That is, the curvature radius of the end portion 6C on the drill rotation direction T side in the bottom surface 6 of the chip discharge groove 4 is infinite.

In addition, the surface of the cutting edge portion 2 of the drill body 1 includes a diamond coating, a CVD coating such as Al ₂ O ₃ or TiCN, including the tip surface, the margin portion 5 and the bottom surface 6 of the chip discharge groove 4. , And one of the electrodeposited abrasive coatings. Further, in the present embodiment, the width W of the margin portion 5 is set in a range not less than 0.05 × D and not more than the size of the core thickness d with respect to the diameter D of the cutting edge 3.

  When drilling a workpiece made of a hard and brittle material such as ceramics with such a small-diameter drill, the drill body 1 is fed in a predetermined step amount toward the front end side in the axis O direction, and the workpiece is cut by the cutting edge portion 2. After drilling, the cutting edge part 2 is pulled out from the workpiece to discharge the chips, and after being drilled by sending out by the next step amount, step machining is repeated to repeat the operation of extracting from the workpiece and discharging the chips. Of course, when the cutting edge portion 2 is pulled out from the workpiece during drilling, cutting oil is sprayed on the cutting edge portion 2 to promote the discharge of the chips from the chip discharge groove 4.

  At this time, in the drill having the above-described configuration, the bottom surface 6 of the chip discharge groove 4 is formed in a convex curve shape in the cross section orthogonal to the axis O, and thus the cutting edge portion 2 is moved to the workpiece in step machining. When the cutting fluid is sprayed when it is pulled out from, the cutting fluid sprayed on the central portion 6A flows into both end portions 6B and 6C in the circumferential direction of the bottom surface 6 of the chip discharge groove 4 along a convex curve formed by the central portion.

  And in these both ends 6B and 6C, the cross section orthogonal to the axis O of the bottom face 6 of the chip discharge groove 4 is in contact with the convex curve of the central portion 6A and does not dent more than the extension line L of this convex curve. Since it is formed in a curve or a straight line, the chips adhering to the central part 6A and the chips adhering to the central part 6A so as to be pushed out by the cutting fluid flowing from the central part 6A can easily flow and be washed away quickly. it can.

  That is, even if at least one of these both end portions 6B and 6C has a concave cross section, if it is recessed with respect to the extension line L of the central portion 6A, chips accumulate and adhere to the recessed portion in this way. In the drill having the configuration, both end portions 6B and 6C extend smoothly and continuously toward the outer peripheral side with respect to the center portion 6A, so that it is possible to prevent chips from remaining on both end portions 6B and 6C. The cleaning time by spraying the cutting fluid can be shortened.

  Further, since the central portion 6A of the bottom surface 6 of the chip discharge groove 4 is a convex curve, the core thickness d of the cutting blade portion 2 can be further increased, and the rigidity of the cutting blade portion 2 can be further improved. Can do. Therefore, according to the drill having the above-described configuration, even if high-efficiency machining with a large step amount in step machining is performed in a small-diameter drill for drilling a hard and brittle material such as ceramics, it is unexpected. It is possible to reliably prevent the drill body 1 from being broken, and to prevent the broken drill body 1 from being left on the workpiece.

Furthermore, in this embodiment, the surface of the cutting edge portion 2 that is the tip portion of the drill body 1 is coated with one of a diamond coating, a CVD coating such as Al ₂ O ₃ and TiCN, and an electrodeposited abrasive coating. Therefore, even a hard and brittle material such as ceramics can be reliably drilled by grinding with coated diamond particles, CVD particles, or electrodeposited abrasive grains.

  Moreover, in this embodiment, the core thickness d of the cutting edge part 2 is made into the range of 0.5 * D-0.9 * D with respect to the diameter D of the cutting edge 3, and ensuring higher rigidity. The occurrence of chip clogging can be reliably prevented. That is, if the core thickness d is smaller than 0.5 × D, the cutting edge portion 2 is not sufficiently rigid, and there is a risk of breakage even if chips easily flow. The core thickness d is less than 0.9 × D. If it is large, the chip discharge groove 4 becomes too shallow, and there is a risk that breakage due to chip clogging is likely to occur.

  Furthermore, in the present embodiment, the curvature radius R of the convex curve formed by the central portion 6 </ b> A in the circumferential direction of the bottom surface 6 of the chip discharge groove 4 in the cross section orthogonal to the axis O is 0. 0 with respect to the diameter D of the cutting edge 3. It is set as the range of 25 * D or more, and favorable chip discharge | emission property is securable, maintaining the rigidity of the cutting-blade part 2. FIG. That is, if the radius of curvature R of the convex curve formed by the cross section of the central portion 6A of the bottom surface 6 is smaller than the above range, the core thickness d becomes small and the rigidity of the cutting edge portion 2 is impaired. The circumferential length must be shortened, and the chip discharge performance may be impaired. However, even if the radius of curvature R of the convex curve formed by the central portion 6A is too large, the cross section of the central portion 6A becomes almost linear, and particularly when the cross sections of both end portions 6B and 6C are made linear. Since the cross section of the cutting edge portion 2 becomes nearly polygonal like the drill described in No. 1, the curvature radius R of the convex curve formed by the central portion 6A is preferably 5.0 × D or less. .

  Furthermore, in the present embodiment, the margin portion 5 is formed on the outer periphery of the cutting edge portion 2, and the width W of the margin portion 5 is 0.05 × D or more with respect to the diameter D of the cutting edge 3. Since the thickness is in the range of the core thickness d or less, the cutting edge portion 2 is surely guided along the axis O without increasing the resistance to the processing hole more than necessary to form a processing hole having a high degree of straightness. Can do. That is, if the width W of the margin portion 5 is smaller than 0.05 × D, the cutting edge portion 2 may not be reliably guided. On the other hand, if the width W is larger than the core thickness d, the resistance increases and the chips are removed. The cross-sectional area of the discharge groove 4 is also reduced.

  Further, particularly in the present embodiment, among both end portions 6B and 6C in the circumferential direction of the bottom surface 6 of the chip discharge groove 4, the end portion 6B opposite to the drill rotation direction T is in contact with the convex curve formed by the center portion 6A. The end 6C on the drill rotation direction T side is in contact with the convex curve formed by the central portion 6A, and is formed as a concave curve that is not recessed from the extended line L of the convex curve. It is a straight line that does not dent more than L. For this reason, a large thickness can be ensured on the opposite side of the margin portion 5 from the drill rotation direction T, damage to the margin portion 5 can be prevented, and the guide performance of the cutting edge portion 2 can be maintained.

  However, in this embodiment, while the end 6B on the opposite side to the drill rotation direction T is formed in a concave curve shape in this way, the end 6C on the drill rotation direction T side is linear. Conversely, the end 6C on the drill rotation direction T side may be formed in a concave curve, and the end 6C on the opposite side to the drill rotation direction T may be linear. Moreover, both the end portions 6B and 6C of the chip discharge groove 4 may be formed in a concave curve shape in contact with the convex curve formed by the central portion 6A, or may be formed in a straight line shape.

  Next, FIG. 5 to FIG. 8 show a second embodiment of the present invention, and the same reference numerals are assigned to parts common to the first embodiment. In the second embodiment, the cutting edge portion 2 is formed to be 120 ° rotationally symmetric with respect to the axis O, and the chip discharge grooves 4 are formed on the outer periphery of the cutting edge portion 2 at three equal intervals in the circumferential direction. Unlike the first embodiment, the front end surface of the cutting edge portion 2 has a regular triangular pyramid shape, and a total of three cutting edges 3 are formed at the intersecting ridge line portions of the conical surfaces adjacent in the circumferential direction. Yes. That is, the drill of the second embodiment is a three-blade twist drill.

  Also in the drill according to the second embodiment, the same effect as that of the first embodiment can be obtained. The present invention can also be applied to a drill having four or more cutting blades 3 or chip discharge grooves 4 or a single drill. In the first embodiment, the central portion 6A of the bottom surface 6 of the chip discharge groove 4 and the end 6B opposite to the drill rotation direction T in the cross section orthogonal to the axis O are convex or concave arcs. In addition, the radius of curvature is constant, but the radius of curvature may be changed, including the second embodiment.

DESCRIPTION OF SYMBOLS 1 Drill main body 2 Cutting blade part 3 Cutting blade 4 Chip discharge groove 5 Margin part 6 Bottom surface of chip discharge groove 4 6A Center part in the circumferential direction of bottom surface 6B End part of bottom surface 6 opposite to drill rotation direction T 6C Bottom surface 6 Drill rotation direction T side end O Drill main body 1 axis T Drill rotation direction D Diameter of cutting edge 3 d Core thickness of cutting edge 2 R Center of circumferential surface of bottom surface 6 in cross section perpendicular to axis O The radius of curvature of the convex curve formed by 6A W The width of the margin portion 5 in the cross section perpendicular to the axis O

Claims (5)

A chip discharge groove is formed on the outer periphery of the tip of the shaft-shaped drill body rotated about the axis, and a drill having a cutting edge formed at the tip of the drill body,
In the cross section perpendicular to the axis, the bottom surface of the chip discharge groove is formed in a convex curve shape at the center portion in the circumferential direction of the drill body, and both end portions in the circumferential direction are in contact with the convex curve in the central portion. A drill characterized in that it is formed in a concave curve shape or a straight line shape that does not dent more than the extended line of the lever convex curve.   2. The drill according to claim 1, wherein one of a diamond coating, a CVD coating, and an electrodeposited abrasive coating is coated on a surface of a tip portion of the drill body.   The core thickness of the tip of the drill body is in a range of 0.5 × D to 0.9 × D with respect to the diameter D of the cutting blade. The drill described.   In the cross section orthogonal to the axis, the radius of curvature of the convex curve formed by the central portion in the circumferential direction of the bottom surface of the chip discharge groove is in a range of 0.25 × D or more with respect to the diameter D of the cutting edge. The drill according to any one of claims 1 to 3, wherein the drill is characterized.   A plurality of the chip discharge grooves are formed on the outer periphery of the tip end portion of the drill body at intervals in the circumferential direction, and a portion between the chip discharge grooves adjacent to each other in the circumferential direction serves as a margin portion, and is orthogonal to the axis. The width of the margin in the cross section is 0.05 × D or more with respect to the diameter D of the cutting blade and is not more than the size of the core thickness of the tip of the drill body. The drill according to any one of claims 1 to 4.

Images