JP2012071405A - Tap with drill - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely perform cutting working of a female thread in a tap with a drill performing the cutting working of the female thread while simultaneously performing cutting working of a prepared hole.SOLUTION: Heels of a plurality of lands 24 of a drill part 12 are provided with reverse rotation cutting edges 36 having an edge diameter of the same dimension as a drill diameter Dd. The cutting working at a positive rake angle β is performed when drawing the tap 10 with the drill after the cutting working of the female thread 52. Accordingly, when the inner diameter of the female thread 52 is smaller than the drill diameter Dd due to elasticity at the stage of performing the cutting working of the female thread 52 by the tap part 14 while performing the cutting working of the prepared hole 50 by drill edges 26, the inner diameter of the female thread 52, i.e. the thread crest part is cut and removed by the reverse rotation cutting edges 36. The dimensional accuracy of the inner diameter of the female thread 52 is thereby improved, there is no risk of generating burrs at the crest of the female thread 52, and the female thread 52 is precisely worked.

Description

  The present invention relates to a tap with a drill that cuts a female screw while cutting a pilot hole, and more particularly to a tap with a drill that can cut a female screw with high accuracy.

  A drill part having a drill hole for drilling a pilot hole and a tap part for cutting a female screw are integrally provided on the same axis, and the pilot hole is cut by the drill part and at the same time the tap hole is used to cut the pilot hole. A tap with a drill for cutting a female screw on an inner peripheral surface is known (see Patent Document 1). Such a tap with a drill is, for example, driven by a NC and controlled in sync with the rotational speed and feed speed so that one lead of the female thread to be processed per rotation is advanced, thereby cutting the pilot hole and the female thread. Therefore, the internal thread can be cut efficiently in a short time compared to the case where the pilot hole processing and the internal thread cutting are performed in separate steps.

Japanese Patent Laid-Open No. 10-100020

  By the way, although not yet known, it has been considered to cut a female thread into a bottomed hole provided in an aluminum alloy casting or the like using such a tap with a drill. In other words, the cast hole has poor dimensional accuracy and position accuracy due to the effects of solidification shrinkage at the time of casting. It is difficult to cut, and the size is such that the core hole is completely included by the tap with the drill against the center of the tap stand where the core hole is offset from the center of the core hole. The female screw is cut while cutting the pilot hole. Since aluminum alloy castings are relatively soft, it is possible to cut a pilot hole on the inner peripheral surface of the pilot hole simultaneously while cutting the pilot hole with high accuracy using a tap with a drill in this way. Is possible.

  However, when a female thread is cut into a core hole using a tap with a drill in this way, there is a problem that the inspection by the thread screw plug gauge (GP) is rejected and sufficient accuracy cannot be obtained. . FIGS. 6A and 6B are views for explaining the internal thread formed by the tap with a drill as described above, both of which are enlarged cross-sectional views of the thread, and the internal thread 90 of FIG. A state in which the pilot hole has been machined by the drill portion and then cut by the tap portion. (B) The internal thread 92 is in a state after the tap portion has passed when the tap with a drill is rotated in the reverse direction. ) The female screw 94 is in a state after the drill portion further passes, that is, the final shape, when the tap with a drill is rotated in the reverse direction and extracted. Then, in the final-shaped female thread 94 shown in (c), burr-shaped burr 118, 120 protruding to the flank 114, 116 side is recognized at the crest 112 of the thread, and the thread passes through these burr 118, 120. It is thought that the plug gauge gets caught and fails.

  Considering the above-mentioned burr 118, 120, the burr 118 is a flank on the bottom side of the hole of the thread of the initial female thread 90 shown in FIG. As shown in (b), a part of the surface layer portion of the flank 114 flows so as to squeeze toward the peak 112 as shown in (b), and a projection 122 is formed. Thereafter, the drill portion 100 ( It is considered that the projection 122 is formed by being crushed when passing (see FIG. 7). Even when the tap with a drill is synchronized and driven by NC control, the thread of the tap portion may be pressed against the flank 114 due to the rigidity of the device or the elastic deformation of each portion. The drill part 100 shown in FIG. 7 is a front end view of an example of a drill part of a conventional tap with a drill, and has an outer diameter equal to the drill diameter Dd continuously to the outer peripheral end part of the drill blade 102 in the same manner as a normal drill. A margin 104 is provided, and a second catching surface 106 is provided with a predetermined clearance dimension behind the margin 104, and a heel 108 at the rear end is chipped when being reversely rotated and extracted. Chamfering is performed to prevent chipping or the like due to biting. For this reason, when the tap with a drill is reversely rotated after the internal thread 90 is machined, the margin 104 having an outer diameter equal to or larger than the internal diameter of the internal thread 90 squeezes the protrusion 122 and returns. 118 is produced. The internal diameter of the female screw 90 is basically the drill diameter Dd, but an aluminum alloy casting is relatively soft, and is generally elastically reduced after being cut by the drill blade 102 and slightly smaller than the drill diameter Dd. Dd-α is small.

  Since the internal diameter of the female screws 90 and 92 is Dd-α as described above, the margin 104 of the drill portion 100 is pressed against the peak 112 when the tap with drill is pulled out, and the surface layer of the peak 112 is obtained. When a part of the portion flows toward the mouth side, a burr 120 protruding to the flank 116 side on the mouth side opposite to the flank 114 is generated. As for the burr 118 on the flank 114 side, not only the projection 122 but also the margin 104 may be pressed against the peak 112, so that a part of the surface layer portion of the peak 112 may flow to the bottom of the hole. is there. Such burr 118, 120 tends to occur in the case of a relatively soft workpiece such as an aluminum alloy casting. The inner diameter D1 of the final-shaped female screw 94 shown in (c) is such that when the tap 104 with a drill is extracted, a margin 104 whose outer diameter is equal to the drill diameter Dd is pressed against the peak 112, whereby the initial inner diameter Dd− Although it is larger than α, it is elastically reduced in diameter after the margin 104 passes and becomes smaller than the drill diameter Dd, so that Dd> D1> Dd−α.

  The present invention has been made in the background of the above circumstances. The purpose of the present invention is to cut a female screw with high accuracy in a tap with a drill that simultaneously cuts a female screw while cutting a pilot hole. There is in doing so.

  In order to achieve such an object, the first invention is provided with a drill part having a drill hole for drilling a pilot hole and a tap part for cutting a female screw, which are integrally provided on the same axis. In the tap with a drill that simultaneously cuts the female thread on the inner peripheral surface of the pilot hole by the tap portion while cutting the blade, the heel of the plurality of lands of the drill portion has a cutting edge diameter that is the same as the drill diameter Dd. Thus, a reverse rotation cutting edge that performs cutting at a positive rake angle β when rotated in the direction opposite to the pilot hole machining is provided along the chip discharge groove.

  According to a second aspect of the present invention, in the tap with a drill according to the first aspect of the present invention, the thinning provided at the tip of the drill portion is a front end view of the drill portion viewed from the tip side. The chip has a curved shape in which the boundary is convex toward the flank side, and the outer edge of the curved shape coincides with the heel or on the inner peripheral side of the heel, the chip discharge groove. It is characterized by having reached.

  According to a third aspect of the present invention, in the tap with a drill according to the second aspect of the present invention, the thinning provided at the tip of the drill portion is a front end view of the drill portion as viewed from the tip side. The boundary has an arc shape with a radius R within a range of 0.30 Dt to 0.38 Dt with respect to the tap portion outer diameter Dt.

  According to a fourth invention, in the tap with a drill according to any one of the first to third inventions, a rake angle β of the counter rotating cutting edge is in a range of 20 ° to 30 °.

  According to a fifth aspect of the present invention, in the tap with a drill according to any one of the first to fourth aspects, the outer peripheral surfaces of the plurality of lands of the drill portion are all outside the same dimension as the drill diameter Dd from the leading edge to the heel. It is a cylindrical surface having a diameter.

  6th invention is a tap with a drill in any one of 1st invention-4th invention, It is each outer diameter surface of the some land of the said drill part, Comprising: A drill diameter is each in the intermediate part between a leading edge and a heel. A spine is provided so as to have an outer diameter smaller than Dd.

  In such a tap with a drill, when a counter-rotating cutting edge is provided on the heel of a plurality of lands of the drill portion with a cutting edge diameter equal to the drill diameter Dd and rotated in the opposite direction to the drilling, in other words, When the tap with a drill is extracted after cutting the fit screw, the cutting is performed at a positive rake angle β. For this reason, when the internal diameter of the internal thread is smaller than the drill diameter Dd due to elasticity when the internal thread of the internal thread is cut by the elasticity at the stage where the internal thread of the internal thread is cut by the tap portion while cutting the pilot hole with the drill blade, When the reverse rotation is performed for extraction, the internal diameter of the internal thread, that is, the crest portion of the thread is removed by the reverse rotation cutting edge. That is, the internal diameter of the internal thread is substantially finished by the counter-rotating cutting edge, the dimensional accuracy of the internal diameter of the internal thread is improved, and the burr 118, 120 is prevented from occurring at the peak of the internal thread. As a result, the internal thread is machined with high shape accuracy.

  In the second invention, the thinning provided at the tip of the drill portion has a curved shape in the front end view, and the outer edge of the curved shape is cut at a position that coincides with the heel or on the inner peripheral side of the heel. Since it reaches the waste discharge groove, the reverse rotating cutting edge provided on the heel is not reduced by thinning, and the cutting action by the reverse rotating cutting edge can be obtained appropriately. That is, in the case of a blind hole, the axial length of the drill portion provided on the tip side of the tap portion is a useless dimension in which a female screw is not formed. When the thinning 109 is provided beyond the heel 108 as in the drill portion 100 of the above, the thinning 109 cuts the heel 108 and further the reverse rotation cutting edge provided on the heel 108, so the reverse rotation cutting edge becomes shorter. It may become impossible to cut the top of the female thread.

  In addition, since the thinning has a curved shape that protrudes toward the flank side, it is easy to set the thinning shape so as not to exceed the heel while ensuring chip discharge performance near the axis. Can do. That is, when the boundary with the flank is a straight line as in the thinning 109 of FIG. 7, it is difficult to apply the thinning 109 so as not to exceed the heel 108 while ensuring the chip discharge performance near the axis. is there.

  The third invention secures chip discharge performance in the vicinity of the shaft center when the boundary between the flank of the drill blade and the thinning has an arc shape with a radius R in the range of 0.30 Dt to 0.38 Dt. However, the thinning shape can be set more easily so as not to exceed the heel. That is, when the radius R is larger than 0.38 Dt, it is difficult to perform thinning so as not to exceed the heel while ensuring the chip discharging performance near the shaft center, and when the radius R is smaller than 0.30 Dt, the shaft The chip discharge performance near the heart may be impaired.

  In the fourth invention, since the rake angle β of the counter-rotating cutting edge is in the range of 20 ° to 30 °, a sharp sharpness is obtained, and the top portion of the thread of the female screw that is slightly reduced in diameter by elasticity is appropriately used. Can be removed by cutting. That is, when the rake angle β exceeds 30 °, the blade angle becomes small and the chipping of the blade is likely to occur. On the other hand, when the rake angle β is less than 20 °, the sharpness decreases, and depending on the processing conditions such as the cutting speed and the material of the workpiece Although it is different, it becomes difficult to appropriately cut the top portion of the thread of the female screw that is elastically slightly reduced in diameter.

  In the fifth invention, since the outer peripheral surfaces of the plurality of lands of the drill portion are cylindrical surfaces having the same outer diameter as the drill diameter Dd from the leading edge to the heel, the drill portion can be easily processed at low cost. When the axial length of the drill portion is made as short as possible, the frictional resistance due to contact with the pilot hole is small, and a cylindrical surface having the same outer diameter as the drill diameter Dd may be used.

  In the sixth aspect of the invention, the back surface is provided on the outer peripheral surfaces of the plurality of lands of the drill portion, and the frictional resistance due to contact with the pilot hole is reduced, and heat generation and processing torque are suppressed. This is particularly effective when the axial length of the drill portion is relatively long.

FIG. 2 is a diagram showing a drill tap according to an embodiment of the present invention, where (a) is a schematic front view, (b) is an enlarged view of the tip of the drill portion, and (c) is a view of the drill portion of (b) from the tip side. (D) is a rear end view as seen from the shank side. FIG. 2 is an explanatory diagram of a case where a female screw is machined with the center of the core hole shifted using the tap with a drill of FIG. 1, (a) is a state before processing, and (b) is a screw ( It is sectional drawing of a screw hole. It is an expanded sectional view explaining the change of the thread shape of a female screw at the time of cutting a female screw using the tap with a drill of FIG. It is a figure which shows the result of having test | inspected using a thread screw plug gauge (GP) and a pin gauge by cutting a female thread at several cutting speeds using the tap with a drill (product of this invention) and the conventional product of FIG. It is a figure explaining the other Example of this invention, and all are expanded front end views equivalent to FIG.1 (c). It is an expanded sectional view explaining the change of the thread shape of a female screw at the time of cutting a female screw using the conventional tap with a drill. It is a figure explaining the drill part of the conventional tap with a drill, and is an enlarged front end view corresponding to Drawing 1 (c).

  The tap with a drill of the present invention completely includes a cored hole with respect to a bottomed cored hole having a diameter smaller than the drill diameter Dd provided in a relatively soft casting such as an aluminum alloy casting. It is suitable for cutting female threads with a thread cutting blade provided in the tap part while cutting a pilot hole with a drill blade, but when cutting female threads on workpieces other than castings. It can also be used. It is also used when a female thread is cut while a pilot hole is cut from the beginning with a drill blade on a workpiece that is not provided with a preliminary hole such as a cast hole.

  When cutting a female thread into a core hole, the pilot hole is cut to a size that completely includes the core hole by a tap with a drill against the center of the tap stand at a position offset from the center of the core hole. Since a female screw is to be machined, a three-blade drill portion with excellent centripetality is desirable. In addition, a spiral oil hole (oil hole) that passes through the tap part and drill part and opens to the flank of the drill blade is provided so that lubricating oil can be supplied internally by MQL (Minimum Quantity Lubrication) or the like. It is desirable to make it. A three-blade drill part and an oil hole are employed as needed, and a general two-blade drill part can be used, or the oil hole can be omitted.

  The tap with a drill is synchronously driven at a rotational speed and a feed speed so that, for example, one lead of a female screw to be machined per revolution is advanced by NC control, and is retracted one lead per one revolution in the reverse rotation direction when being extracted. However, it is also possible to cut or extract while rotating along the lead of the screw by rotationally driving in a state having a predetermined play in the axial direction.

  The drill part and tap part are continuously provided with a chip discharge groove that is twisted with a constant lead, for example, but the drill part and the tap part lead with a twisted groove and a tap part with a straight groove. It is also possible to change. The tap part is formed with a thread cutting blade along the chip discharge groove, and this thread cutting blade cuts the flank and groove bottom of the female thread. In the present invention, when the tap with a drill is extracted, the top of the mountain is finished and cut by the counter-rotating cutting edge. For example, the drill part and the tap part are integrally formed, but the separately formed drill part is integrally fixed to the tool body having the tap part by a fixing means such as a screw or shrink fitting. Is also possible.

  Cemented carbide is suitably employed as the material of the tool, but other tool materials such as high-speed tool steel can also be used. It is desirable to coat the drill part and the tap part with a hard coating such as DLC (Diamond-Like Carbon), TiN, TiCN, TiAlN or the like.

  The heel of the land of the drill part is provided with a reverse rotation cutting edge, and when it is extracted by being rotated reversely, the top of the female thread is cut. The rake face of the reverse rotating cutting edge is the inner wall surface of the chip discharge groove, and the rake angle β is appropriately determined by the cross-sectional shape of the chip discharge groove. The rake angle β is an angle of inclination of the rake face with respect to the radial direction of the cross section perpendicular to the axis, and may be at least positive, but is preferably in the range of 20 ° to 30 °.

  In the second invention, the thinning provided at the tip of the drill portion has a curved shape in the front end view, and the thinning is applied so as not to exceed the heel. Similarly to the conventional drill portion shown in FIG. That is, when the axial length of the drill is relatively long, even if the heel is cut slightly by thinning, the axial length is sufficient to cut the peak of the female thread on the remaining heel. A reverse rotating cutting edge can be provided.

  In the third invention, the thinning provided at the tip of the drill portion has an arc shape with a predetermined radius R. However, when the second invention is implemented, the curvature of the boundary with the flank continuously changes. The thinning may be performed so as not to exceed the heel at least. In the first invention and the second invention, it is also possible to perform thinning so as to have an arc shape with a constant radius R exceeding the range of 0.30 Dt to 0.38 Dt.

  In carrying out the second and third inventions, since the heel is not shaved by thinning, the axial length of the drill portion can be made relatively short, for example, from the tip of the tap portion to the outer end (corner) of the drill blade. The drill length (axial direction length) L1 can be about 1.5P to 3.0P with respect to the thread pitch P of the tap portion. However, if a heel, i.e., a counter-rotating cutting edge, is provided on the thread winding of the thread of the tap part, the top of the thread of the female thread can be appropriately cut even if the axial length is shorter than 1P. The length L1 is appropriately determined within a range where the top of the female thread can be cut.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
1A is a schematic front view of a tap 10 with a drill according to an embodiment of the present invention viewed from a direction perpendicular to the axis O, and FIG. 1B is a drill portion 12 positioned at the left end in FIG. (C) is an enlarged front view of the drill portion 12 of (b) as viewed from the tip side (upper side of the figure), and (d) is from the side of the shank 18 located on the right side in (a). FIG. This tap 10 with a drill is provided with a drill portion 12, a tap portion 14, a neck portion 16, and a shank 18 coaxially and integrally from the tip end side in the axial direction (left end side in FIG. 1 (a)), The surface is made of a cemented carbide and the surface excluding the shank 18 is coated with DLC as a hard coating. This tap 10 with a drill is for right-hand thread machining, and the tap portion 14 is provided with a right-hand thread 20 corresponding to a female thread to be formed, and also has three cuts twisted clockwise. A scrap discharge groove 22 is provided so as to divide the male screw 20, and three thread cutting blades are formed along the chip discharge groove 22. The tap portion 14 includes a front biting portion 14a whose diameter dimension gradually decreases and a complete peak portion 14b having a constant diameter dimension, and the outer diameter of the complete peak portion 14b is the tap portion outer diameter Dt. . The external thread 20 corresponds to a female thread to be processed, and is M6 × 1 in this embodiment, the tap portion outer diameter Dt is 6.0 mm, and the tap length L2 is 8 threads (8.0 mm) in this embodiment. ) And 1.5 of them is the biting portion 14a. It should be noted that the proportions and angles of the dimensions of each part of the drawings are not necessarily described accurately.

  The three chip discharge grooves 22 are provided from the tip of the drill portion 12 to the front of the shank 18 with the same lead at equal angular intervals (120 ° intervals) around the shaft center. A drill blade 26 for cutting a pilot hole is formed at a portion where 22 is opened at the tip of the conical shape of the drill portion 12 by being rotated clockwise when viewed from the shank 18 side. The drill diameter Dd which is the diameter dimension of the drill portion 12 is the same as the inner diameter of the female screw to be processed, and is about 5.04 mm in this embodiment, and the valley diameter of the male screw 20 is about 4.9 mm and the drill diameter Dd. Smaller than. Further, the drill length L1 that is the axial length of the drill portion 12 from the tip end of the tap portion 14 to the outer end (corner) of the drill blade 26 is 1.5 P with respect to the thread pitch P of the external thread 20. Within the range of ~ 3.0P, it is about 2.0P or 2mm in this example.

  The chip discharge groove 22 is provided with a constant lead so that the twist angle is in the range of 20 ° to 50 ° in the complete peak portion 14 b of the tap portion 14. In the present embodiment, the tap portion 14 (complete peak portion 14b) is provided with a lead of about 24.34 mm so that the twist angle is about 38 °, and the twist angle in the drill portion 12 is about 34 °. Further, the tap 10 with a drill has three spiral oil holes (oil holes) 28 having the same lead as the chip discharge groove 22 from the end face on the shank 18 side to the tip of the drill portion 12. They are provided independently over the entire length so as to pass through the inside, and are opened on the flank faces 30 of the three drill blades 26, respectively. The diameter d of the oil hole 28 is about 0.5 mm in this embodiment.

  A thinning 32 is provided at the tip of the drill portion 12, and the inner peripheral side portion of the drill blade 26 is made to approach the axis O smoothly. The thinning 32 has a curved shape in which the boundary between the flank 30 and the thinning 32 is convex toward the flank 30 in the tip view of FIG. In addition, the outer edge of the curved shape is provided so as to coincide with the heel of the land 24. Specifically, in the front end view of FIG. 1 (c), the boundary between the flank 30 and the thinning 32 is a circular arc shape having a radius R within a range of 0.30 Dt to 0.38 Dt with respect to the tap portion outer diameter Dt. In this embodiment, the radius R≈2.04 mm = 0.34 Dt. Such thinning 32 can be performed using, for example, a grinding wheel having an arc-shaped grinding surface having a radius R on the outer periphery.

  Further, the outer peripheral surfaces 34 of the three lands 24 in the drill portion 12 are all cylindrical surfaces having the same outer diameter as the drill diameter Dd from the leading edge to the heel, and the heel is provided with a counter-rotating cutting edge 36. It has been. When the counter-rotating cutting edge 36 has a cutting edge diameter of the same dimension as the drill diameter Dd and is rotated in the reverse direction to the pilot hole machining, that is, when rotated counterclockwise in FIG. Cutting is performed with β, and is provided along the chip discharge groove 22 over the entire length of the drill length L1. The rake angle β is the angle of inclination of the rake face with respect to the radial direction of the cross section perpendicular to the axis O, and in this embodiment is about 25 ° within a range of 20 ° to 30 °. The rake face of the reverse rotation cutting edge 36 is the inner wall surface of the chip discharge groove 22, and the rake angle β is appropriately determined by the cross-sectional shape of the chip discharge groove 22.

  Such a tap 10 with a drill is used by being attached to a main shaft of a tapping machine 40 composed of an NC machine tool or the like, for example, as shown in FIG. A cutting fluid (coolant) is supplied from 42 to the three oil holes 28 at a predetermined supply hydraulic pressure. FIG. 2 shows a case in which a female screw 52 is cut into a bottomed hole 46 provided in the workpiece 44 by casting the workpiece 44 such as an aluminum alloy casting. Since the dimensional accuracy and position accuracy are poor due to the effects of solidification shrinkage, etc. during casting, it is possible to cut the female screw with high positional accuracy by performing tapping with the tap as it is to the core hole 46. It is difficult. For this reason, the punched hole 46 is provided in a small size, and the pilot hole 50 is cut by the tap 10 with a drill with respect to the target tap stand center S2 at a position shifted from the center S1 of the cast hole 46. The female screw 52 is cut. That is, with respect to the bottomed core hole 46 having a diameter smaller than the pilot hole diameter substantially equal to the drill diameter Dd, the tap stand center S2 at a position displaced from the center S1 of the core hole 46 by a predetermined displacement dimension e. Is the target center position, and the drill hole 12 is cut to a size that completely includes the core hole 46, and at the same time, the female screw 52 is cut by the tap portion 14. The tapping device 40 can independently control the rotation speed and the feed speed of the tap 10 with a drill, and the rotation speed and the feed to advance the tap 10 with a drill by one lead of the female screw 52 to be machined per rotation. By synchronously driving at a speed, the drill hole 12 is cut into the workpiece 44 by the preceding drill portion 12, and the inner peripheral surface of the pilot hole 50 is continuously threaded by the thread cutting blade of the tap portion 14. The screw 52 can be cut efficiently. The chips are discharged to the shank 18 side through the chip discharge groove 22 together with the cutting fluid supplied to the tool tip through the oil hole 28. 2A is a sectional view of the screw (screw hole) 52 to be cut by the tap 10 with a drill in a state before the female screw 52 is cut.

  Here, the tap 10 with a drill of this embodiment is provided with a counter-rotating cutting edge 36 with a cutting edge diameter equal to the drill diameter Dd on the heels of the plurality of lands 24 of the drill portion 12, and in the direction opposite to the drilling of the prepared hole. When rotated, in other words, when the tap 10 with a drill is extracted after cutting the female screw 52, the cutting is performed at a positive rake angle β. For this reason, the internal diameter of the female screw 52 is smaller than the drill diameter Dd due to elasticity at the stage where the female screw 52 is cut by the tap portion 14 while cutting the pilot hole 50 by the drill blade 26. When the tap 10 with a drill is rotated in the reverse direction and extracted, the inner diameter of the female screw 52, that is, the crest portion of the thread is removed by the reverse rotation cutting edge 36. In other words, the internal diameter of the internal thread 52 is substantially finished by the counter-rotating cutting edge 36, so that the dimensional accuracy of the internal diameter of the internal thread 52 is improved, and the top of the internal thread 52 is shown in FIG. The occurrence of burr 118, 120 as shown is prevented, and the internal thread 52 is cut with high shape accuracy.

  FIG. 3 is an enlarged cross-sectional view showing a change in the shape of the thread of the female screw 52 that is machined using the tap 10 with a drill, and is a view corresponding to FIG. 6, wherein the female screw 52a in FIG. A state where the tap 10 with drill is rotated forward and the pilot hole 50 is machined by the drill portion 12 and then cut by the tap portion 14, (b) The internal thread 52 b rotates the tap 10 with drill in the reverse direction. The state after the tap portion 14 has passed when extracting, (c) The internal thread 52c is the state after the drill portion 12 has further passed when the tap 10 with drill is rotated in the reverse direction, that is, the final shape. . 3 (a) and 3 (b) are the same as FIGS. 6 (a) and 6 (b), and the internal diameters of the internal threads 52a and 52b are elastic after being cut by the drill blade 26. By reducing the diameter, the Dd-α is slightly smaller than the drill diameter Dd. Further, when the tap 10 with a drill is rotated in the reverse direction and pulled out, the female screw 52b at the stage of (b) in which only the tap portion 14 has passed is threaded to the flank 114 on the bottom side of the hole of the female screw 52b. By being pressed, the projections 122 are formed by flowing so that a part of the surface layer portion of the flank 114 falls toward the peak 112 side.

  On the other hand, the internal thread 52c of (c) after the drill portion 12 is pulled out by rotating the tap with a drill 10 in the reverse direction is the reverse rotation cut provided in the drill portion 12 with the same edge diameter as the drill diameter Dd. The crest portion of the thread is cut off by the blade 36. As a result, the dimensional accuracy of the inner diameter D1 of the female screw 52c is improved, and the protrusion 122 formed on the peak at the stage of the female screw 52b is removed at the same time. Further, unlike the conventional case, the margin 104 is pressed against the top of the thread and there is no fear that the burr 118, 120 will be generated, and the female thread 52c is formed with high shape accuracy. The dotted line in FIG. 3 (c) shows, for comparison, the tip shape of the thread of the female screw 52b at the stage (b). The inner diameter D1 of the final shape female screw 52c shown in (c) is finish-cut by the counter-rotating cutting edge 36 having a rake angle β of positive, so that the drill diameter Dd which is the cutting edge diameter of the counter-rotating cutting edge 36 is shown in FIG. And approximately the same dimensions.

  On the other hand, in the present embodiment, the thinning 32 provided at the tip of the drill portion 12 has a curved shape in the front end view of FIG. 1 (c), and the outer edge of the curved shape coincides with the heel. Therefore, the reverse rotation cutting edge 36 provided on the heel is not reduced by the thinning 32, and the cutting action by the reverse rotation cutting edge 36 is appropriately obtained. That is, since the drill length (axial length) L1 of the drill portion 12 provided on the distal end side of the tap portion 14 is a useless dimension in which the female screw 52 is not formed in the case of a blind hole as shown in FIG. For example, when the thinning 109 is provided beyond the heel 108 as in the drill portion 100 of FIG. 7, the reverse rotation provided on the heel 108 and further on the heel 108 by the thinning 109 is desirable. Since the cutting edge 36 is cut, the reverse rotation cutting edge 36 may be shortened or lost, and the top of the thread of the female screw 52 may not be cut.

  Further, since the thinning 32 has a curved shape that is convex toward the flank 30 side, the thinning shape can be easily formed so as not to exceed the heel while ensuring chip discharge performance near the axis O. Can be set. That is, when the boundary with the flank is a straight line as in the thinning 109 of FIG. 7, it is difficult to apply the thinning 109 so as not to exceed the heel 108 while ensuring the chip discharge performance near the axis. is there.

  In this embodiment, since the boundary between the flank 30 and the thinning 32 has an arc shape with a radius R in the range of 0.30 Dt to 0.38 Dt, the chip discharge performance near the axis O is improved. The shape of the thinning 32 can be set more easily so as not to exceed the heel while ensuring. That is, when the radius R is larger than 0.38 Dt, it is difficult to perform the thinning 32 so as not to exceed the heel while ensuring the chip discharging performance near the axis O, and the radius R is smaller than 0.30 Dt. Then, chip discharge performance near the axis O may be impaired.

  In the present embodiment, the rake angle β of the counter-rotating cutting edge 36 is in the range of 20 ° to 30 °, so that a sharp sharpness is obtained and the thread of the female screw 52b that is slightly reduced in diameter by elasticity is obtained. The top of the mountain can be cut and removed appropriately. That is, when the rake angle β exceeds 30 °, the blade angle becomes small and chipping is likely to occur. On the other hand, when the rake angle β is less than 20 °, the sharpness decreases, and the processing conditions such as the cutting speed, the material of the workpiece 44, etc. However, it is difficult to appropriately cut the top portion of the thread of the female screw 52b that is elastically slightly reduced in diameter.

  Further, in this embodiment, the outer peripheral surface 34 of the three lands 24 of the drill portion 12 is a cylindrical surface having the same outer diameter as the drill diameter Dd from the leading edge to the heel, so that the drill portion 12 can be easily processed. Can be manufactured at low cost. Since the drill length L1 of the drill portion 12 is made as short as possible, the frictional resistance due to the contact with the pilot hole 50 is small, and the cylindrical surface having the same outer diameter as the drill diameter Dd may be left as it is.

Next, using the tap with drill 10 (product of the present invention) and the conventional product having the drill unit 100 shown in FIG. The results of cutting the female screw 52 and inspecting the shape accuracy and dimensional accuracy of the female screw 52 will be described. The preliminary hole diameter is a diameter of a preliminary hole provided in advance assuming a cast hole, and the misalignment dimension e of the female screw 52 with respect to the preliminary hole is 0.5 mm.
"Processing conditions"
Tap size: M6 × 1
Drill diameter (Dd): φ5.04
Work material: ADC12 (JIS standard; aluminum alloy for die casting)
Spare hole diameter: φ3.5
Tap stand length: 12mm (blind hole)
Cutting speed: 20, 50, 75 m / min
Cutting fluid: MQL internal oil supply (oil supply amount 200cc / min)
Machine used: Horizontal machining center

  FIG. 4 is a diagram for explaining the inspection results, in which the female screw 52 was cut by five holes at each cutting speed and inspected. “GP II” is an inspection using a thread plug gauge grade 2 that can comprehensively inspect the effective diameter, thread shape, pitch, etc., and the thread plug gauge is 12 mm long (thread 12P). The case where it completely passes through 52 is “pass”, less than 12P and 6P or more is “Δ”, and less than 6P is “x”. According to the product of the present invention, it was “pass” at any cutting speed, whereas the conventional products were all rejected. Further, the “inner diameter” is the maximum dimension when a pin gauge (inner diameter plug gauge PP) jumping 0.01 mm and the pin gauge completely passes through the female thread 52. The product of the present invention is 5.04-5. In the range of 06 mm, it is the same as or slightly larger than the drill diameter Dd, whereas the conventional product is reduced in diameter by elasticity within the range of 5.00 to 5.03 mm. The difference between the cutting speeds was almost the same between the products of the present invention and the conventional products, except that the conventional products were broken at the 5th hole at a cutting speed of 75 m / min.

  Next, another embodiment of the present invention will be described. In the following embodiments, parts that are substantially the same as those in the above embodiments are denoted by the same reference numerals, and detailed description thereof is omitted.

  5 (a) and 5 (b) are diagrams for explaining another embodiment of the present invention, and are front end views corresponding to FIG. 1 (c). In the drill portion 60 of (a), a spine 62 is formed at the intermediate position in the circumferential direction of the outer peripheral surface 34 of the three lands 24, that is, at the intermediate portion between the leading edge and the heel so as to be smaller than the drill diameter Dd. Is provided. In this case, the frictional resistance due to contact with the inner wall surface of the pilot hole 50 formed by the drill blade 26 is reduced as compared with the above embodiment, and heat generation and processing torque are suppressed. This is effective when the length L1 is relatively long.

  5 (b), the outer edge of the thinning 72 whose boundary with the flank 30 has a constant radius R in the front end view is formed in the chip discharge groove 22 on the inner peripheral side of the heel. In this case, the radius R is set in the range of 0.30 Dt to 0.38 Dt. Also in this case, the reverse rotating cutting edge 36 provided on the heel is not reduced by the thinning 72, and the cutting action by the reverse rotating cutting edge 36 can be obtained appropriately.

  As mentioned above, although the Example of this invention was described in detail based on drawing, these are one embodiment to the last, and this invention is implemented in the aspect which added the various change and improvement based on the knowledge of those skilled in the art. be able to.

  10: Tap with drill 12, 60, 70: Drill part 14: Tap part 22: Chip discharge groove 24: Land 26: Drill blade 30: Flank 32, 72: Thinning 34: Outer peripheral surface 36: Reverse rotation cutting edge 50 : Prepared hole 52, 52a, 52b, 52c: Female screw 62: Back removal O: Shaft center Dt: Tap portion outer diameter Dd: Drill diameter β: Rake angle

Claims (6)

A drill part having a drill hole for drilling a pilot hole and a tap part for cutting a female screw are provided integrally on the same axis, and the pilot hole is simultaneously cut by the tap part while cutting the pilot hole by the drill part. In a tap with a drill that cuts female threads on the inner peripheral surface of
The heel of the plurality of lands of the drill portion has a cutting edge diameter that is the same as the drill diameter Dd, and a counter-rotating cutting edge that performs cutting at a positive rake angle β when rotated in the direction opposite to the pilot hole machining. A tap with a drill, characterized in that is provided along the chip discharge groove. The thinning provided at the tip of the drill part is a curved shape in which a boundary between the flank of the drill blade and the thinning is convex toward the flank side in a front end view when the drill part is viewed from the tip side. The outer edge of the curved shape reaches the chip discharge groove at a position coinciding with the heel or on an inner peripheral side of the heel. Tap with drill. The thinning provided at the tip of the drill portion is a tip view of the drill portion viewed from the tip side, and the boundary between the flank of the drill blade and the thinning is 0.30 Dt to the tap portion outer diameter Dt. The tap with a drill according to claim 2, wherein the tap has a circular arc shape with a radius R within a range of 0.38 Dt. The tap with a drill according to any one of claims 1 to 3, wherein the rake angle β of the reverse rotation cutting edge is within a range of 20 ° to 30 °. The outer peripheral surfaces of the plurality of lands of the drill portion are all cylindrical surfaces having the same outer diameter as the drill diameter Dd from the leading edge to the heel. Tap with drill as described in. The outer peripheral surface of the plurality of lands of the drill portion, and an intermediate portion between the leading edge and the heel, is provided with a spine so as to have an outer diameter smaller than the drill diameter Dd. The tap with a drill of any one of Claims 1-4.

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