JP2012240179A - Tapping method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tapping method capable of starting processing while making a rotating direction phase of a thread cutting starting position being a starting position of an internal thread section a specific position at all times when tapping by a machine tool.SOLUTION: The tapping is conducted by mounting a preset tapping tool, in which a tap 16 is supported by a tool holder, on a main shaft of the machine tool, moving it to approach a pitch feed starting position for tapping a work, identifying the rotating direction, and applying pitch feed. Prior to tapping, the position of the tap 16 in the rotation direction is determined against the tool holder based on a rake face of a threaded section 17 of the tap 16 in a state that the preset tapping tool is not yet mounted and the length of the tool is preset based on a flank 31 of a peak 17a of a first peak of a complete peak section T1 among the threaded section 17 of the tap 16.

Description

  The present invention relates to a tapping method, that is, a method for processing a threaded portion using a tap.

  For example, as is well known, a spark plug (hereinafter simply referred to as a plug) that is mounted on a cylinder head of an internal combustion engine (engine) is screwed into a female thread portion on the side of the plug hole, as is well known. By being (screwed), it is fixed via a gasket so that the tip end side faces the combustion chamber. In that case, the direction (rotation direction position) of the outer electrode (ground electrode) that faces the combustion chamber and makes a pair with the center electrode is identified from the viewpoints of eliminating variations in combustion among cylinders, improving ignitability, and improving fuel efficiency. There is a request to match the direction.

  As countermeasures, for example, various techniques such as those described in Patent Documents 1 to 3 have been proposed. In particular, Patent Documents 1 and 2 arbitrarily set the starting position of the thread rolling process for the metal shell of the plug. Thus, a technique capable of accurately positioning is disclosed.

Japanese Patent Application Laid-Open No. 11-13613 JP 2001-284015 A JP 2003-323963 A

  The direction (rotational direction position) of the outer electrode (ground electrode) when the plug is tightened with a predetermined torque against the plug hole on the cylinder head side is not limited to the starting position of the male thread on the plug side, Naturally, this also depends on the starting position of the female thread portion in the plug hole on the cylinder head side (the rotational direction phase of the threading start position of the female thread portion). And, if it is going to manage the direction of the outer electrode as described above more strictly, it is not enough to manage the starting position of the male thread on the plug side, and in many cases the cylinder head side that is processed by tapping Similarly, if the plug hole is not managed so that the start position of the female thread portion is constant, the intended purpose cannot be achieved.

  The present invention has been made paying attention to such a problem, and when tapping with a machine tool, that is, when using a tap to process a threaded portion, rotation of the threading start position, which is the starting position of the female threaded portion. The present invention provides a tapping method capable of always processing a directional phase as a specific position.

  The present invention is a method of tapping a workpiece by attaching a tap to a spindle of an NC machine tool or the like represented by a machining center, for example. At that time, at the pitch feed start position for tapping, positioning (indexing) in the rotational direction of the tap with respect to the rake face of the tap screw portion is performed, and a specific peak of a complete peak portion of the tap screw portion, for example, The distance between the tap and the workpiece is set to a specified dimension based on the first or second flank (the inclined surface connecting the top and bottom of the mountain). In this state, a pitch feed for tapping is given to start tapping.

  If this technical matter is further related to tapping using a preset tapping tool by external presetting, a preset tapping tool with a tool holder supporting a tap is mounted on the spindle of the machine tool, and the preset tapping tool is screwed. Approach the workpiece in which the pilot hole (hole before tapping) is formed to the pitch feed start position for tapping, and give the pitch feed for tapping after indexing the rotation direction It is assumed that tapping is performed.

  At that time, prior to the above tapping, the preset tapping tool alone is positioned in the tap rotation direction with respect to the tool holder on the basis of the rake face of the tap screw portion, and a specific peak portion of the tap screw portion is specified. It is assumed that a tool presetting step for presetting the tool length based on the flank of the mountain, for example, the flank of the first mountain or the second mountain is included.

  According to the present invention, it is possible to always process the rotational direction phase of the start position of the internal thread portion as a specific position. Therefore, for example, when attention is paid to the relationship between the plug hole in the cylinder head of the engine and the spark plug screwed into the plug hole, the start position (rotational direction phase of the thread cutting start position) of the male thread side of the spark plug and the outside If the relative positional relationship with the electrode (ground electrode) is managed so as to be a specific positional relationship, the spark plug is tightened with a predetermined torque with respect to the plug hole in which the female thread portion is formed. It is possible to always adjust the outer electrode to a specific direction (rotational direction position) simply by inserting the outer electrode.

Cross-sectional explanatory drawing which shows the schematic structure of a cylinder head as a more concrete form for implementing this invention. The enlarged view of the a part in the plug hole of FIG. Cross-sectional explanatory drawing which shows the state which mounted | wore the plug hole of FIG. 2 with the spark plug. Explanatory drawing which shows the processing form of the seating surface of FIG. Explanatory drawing at the time of performing the tapping process of the internal thread part of FIG. 2 using a preset tapping tool. (A) is the principal part expansion schematic of the tap shown in FIG. 5, (B) is the detailed explanatory drawing. FIGS. 6A and 6B are diagrams illustrating a preset procedure of the preset tapping tool shown in FIG. 5, where FIG. 5A is an explanatory diagram when a tool presetter is calibrated using a master gauge dedicated to a bearing surface, and FIG. Explanatory drawing which shows the state which mounted | wore the gauge. FIG. 6 is a bottom explanatory view of a tool holder in the preset tapping tool shown in FIG. 5. FIGS. 6A and 6B are diagrams showing a preset tapping tool shown in FIG. 5 at the time of presetting, in which FIG. 5A is an explanatory diagram when creating a standard using both a master tap gauge and a locator, and FIG. 5B is a master tap gauge from a tool presetter. Explanatory drawing which shows the state which removed. FIG. 10 is an enlarged plan view showing the relationship between the master tap gauge shown in FIG. 9A and a contact on the locator side. FIG. 6A is a diagram illustrating a preset procedure of the preset tapping tool illustrated in FIG. 5, and FIG. 5A is an explanatory diagram when the preset tapping tool of FIG. 5 is mounted on the tool presetter and positioning in the rotation direction is performed; Fig. 4 is an explanatory diagram when setting the tool length of a preset tapping tool with a tool presetter. Explanatory drawing of the principal part at the time of the tool length preset shown to (B) of FIG.

  FIG. 1 and the following drawings show a more specific form for carrying out the present invention. Here, machining of a female thread portion into a plug hole in an engine cylinder head, that is, a plug into which a spark plug is screwed. The processing of the female thread portion in the hole is illustrated. In particular, FIG. 1 shows a cross-sectional view of the cylinder head, FIG. 2 shows an enlarged view of a part of FIG. 1, and FIG. 3 shows a state where the spark plug is attached.

  As shown in FIGS. 1 to 3, the cylinder head 1 is formed with a stepped hole-like plug hole (plug hole) 2 that opens into the combustion chamber Q for each cylinder, and a spark plug ( Hereinafter, it is simply referred to as a plug.) 3 is mounted by screwing. The metal shell 4 of the plug 3 is formed with a large-diameter barrel portion 5 and a hexagonal portion 6, and a screw portion 7 is formed adjacent to the barrel portion 5. Further, a gasket 8 is mounted in advance on the lower side of the neck of the body portion 5. On the other hand, the plug hole 2 on the cylinder head 1 side includes a small-diameter portion 2a close to the combustion chamber Q and a large-diameter portion 2b continuous therewith, and a seating surface 9 is formed at an intermediate portion therebetween, and the small-diameter portion 2a. A female screw portion 10 is formed. Then, by tightening the plug 3 with a predetermined torque, the plug 3 is fastened and fixed to the cylinder head 1 due to the screwing action of the male screw portion 7 and the female screw portion 10, and the body portion on the plug 3 side. 5 is seated on the seating surface 9 via the gasket 8. As a result, the center electrode 32 of the plug 3 and the outer electrode (ground electrode) 33 paired with the center electrode 32 face the combustion chamber.

  Here, for the plug 3, the rotation direction phase (rotation direction position) of the threading start position of the external thread portion 7 and the outer electrode 33 when tightened with respect to the female thread portion 10 on the plug hole 2 side with a specified torque. By managing the direction (direction in which the outer electrode 33 is directed) in the manufacturing stage, the relative positional relationship between the two is specified in advance. For example, the rotational direction phase and the prescribed torque of the threading start position of the external thread portion 7 are specified. The direction of the outer electrode 33 at the time of tightening is matched in advance.

  Most of the machining in the process of manufacturing the cylinder head 1 is performed by an NC type machine tool represented by a machining center. In particular, the machining procedure for the plug hole 2 including the small diameter portion 2a and the large diameter portion 2b. In the case where attention is paid to the above, after the cutting of the small diameter portion 2a and the large diameter portion 2b is performed as preprocessing, the cutting of the seating surface 9 and the threading of the female thread portion 10 are performed. The threading of the female thread portion 10 is performed by tapping, that is, tapping. Both the cutting process of the seating surface 9 and the tapping process of the internal thread portion 10 are performed using a common machining center which is an NC type machine tool, and the cutting process of the seating surface 9 is performed as a counterbore as a pre-processing. Subsequently, the tapping process of the female screw portion 10 is performed.

  The seating surface 9 is processed by mounting a counterbore cutter 11 as shown in FIG. 4 on the spindle of the machining center. The counterbore cutter 11 is a general-purpose HSK type tool holder 12 that supports a counterbore cutter 13 so as to be detachable. The counterbore cutter 13 is, for example, two throwaway type chamfers at the body tip. A chip 13a is attached. Then, while the counterbore cutter 11 is rotated at a predetermined speed, a cutting feed in the axial direction is given to the counterbore cutter 11 to perform a counterbore with a part of the chamfering to finish the seating surface 9 with a predetermined accuracy.

  The counterbore cutter 11 has a tool length when it is mounted on the spindle of the machining center, preset in advance using a known tool presetter, which will be described later, in a so-called external preset method to a specified dimension.

  On the other hand, the tapping process of the internal thread portion 10 is performed by attaching a preset tapping tool 14 as shown in FIG. 5 to the spindle of the machining center. The preset tapping tool 14 is a general-purpose HSK type tool holder 15 having a tap 16 removably supported in the same manner as described above. The tap 16 itself is, for example, a straight groove tap type as shown in FIG. A long shank tap type is used. Then, using the tapping process mode of the machining center, a pitch feed for tapping is given to the preset tapping tool 14, and the female thread part 10 is machined by using the small diameter part 2a as a screw pilot hole by a so-called one-pass method. 6A shows the outline of the threaded portion 17 of the tap 16, and FIG. 6B shows the details of the threaded portion 17. In FIG. 2B, T1 is a complete (thread) thread portion and T2 is a biting portion.

  In this case, if a position that is a predetermined distance L (known value) away from the seating surface 9 that has been previously cut and cut is the pitch feed start position M for tapping, the seating surface 9 is opened. The preset tapping tool 14 is approached to the pitch feed start position M toward the small diameter portion 2a as a screw pilot hole and the preset tapping tool 14 is positioned in the rotational direction at the pitch feed start position M. It is assumed that pitch feed for tapping is started.

  In addition, since the tool for tapping is the preset tapping tool 14, the tool holder 15 supporting the tap 16 is correctly attached to the spindle of the machining center only after the rotation direction position is determined at a specific position. Therefore, as will be described later, in managing the phase of the threading start position of the female thread portion 10, the rotational direction position of the tap 16 with respect to the tool holder 15 is indexed to a specific position by a so-called external preset method. Based on being preset. At the same time, based on the fact that the tool length when the preset tapping tool 14 is mounted on the spindle of the machining center is preset to a prescribed dimension by a so-called external preset method using a known tool presetter as will be described later. Yes.

  Both the counterbore processing of the seating surface 9 and the tapping processing of the screw thread portion 10 are performed by using a machining center which is a common NC type machine tool, and the cylinder head 1 which is a workpiece to be machined is mounted on the machining center. Once the work table is clamped, counterbore processing and subsequent tapping processing are performed at once by a so-called 1-clamp (1-chuck) system. That is, the cylinder head 1 is subjected to the tapping process following the counterbore process without being unclamped from the work table even after the counterbore process is finished. At the same time, if spot facing of the seating surface 9 is performed using, for example, the Z axis of the machining center, the subsequent tapping process is also performed using the same Z axis.

  As described above, the spot face machining and the tapping are performed on the plug hole 2 of the cylinder head 1 by the so-called one-clamp method using the same machining axis of the same machining center. Since there is a large correlation with the accuracy of the phase (position in the rotational direction) of the threading start position of the threaded portion 10, the plug hole 2 is used as described above in order to improve the phase accuracy of the threading starting position of the female threaded portion 10. This is because it is important that the counterbore processing and the tapping processing are performed on the same processing standard.

  Here, so-called external presetting of the preset tapping tool 14 using a known tool presetter (for example, TP-400 manufactured by Nippon ID System Co., Ltd.) is performed in the following procedure.

  First, as shown in FIG. 7A, the tool presetter is calibrated by using a seating surface dedicated master gauge 18 for processing the seating surface 9 prepared in advance. 4 is a master bar having the same diameter and the same length as the counterbore cutter 11 shown in FIG. 4, and is used for presetting the tool length of the counterbore cutter 11 shown in FIG. It is.

  This seat surface master gauge 18 is set on the spindle of the tool presetter, and the seat surface master gauge is used with the enlargement projection function by the tool presetter projector (may be the imaging enlarged display function by the CCD camera). The shape of the tip of 18 is projected, and a reference line as an index on the screen, that is, two cross-shaped reference lines 19a and 19b orthogonal to each other are respectively provided on the gauge tip surface and the cylindrical surface of the master gauge 18 for the seating surface. Calibrate to match. In addition, on the screen of the projector, apart from two orthogonal reference lines 19a and 19b, two reference lines 20a corresponding to a complete (thread) thread portion of the thread portion of the tap 16 as described later. , 20b are preliminarily displayed in a mountain shape.

  As described above, in this calibration, the positional accuracy of the seating surface 9 in the plug hole 2 has a large correlation with the accuracy of the phase (position in the rotational direction) of the threading start position of the female screw portion 10, and the female screw portion This is performed in order to improve the phase accuracy of the 10 threading start positions, that is, to eliminate the angle error. That is, it is important to preset the counterbore cutter 11 for processing the seating surface 9 and the preset tapping tool 14 for tapping the internal thread portion 10 on the same basis. However, this calibration work can be omitted if the tool presetter alone is sufficiently calibrated.

  When the calibration is completed, the bearing surface master gauge 18 is removed from the spindle of the tool presetter, and instead, the master tap gauge 21 is set on the spindle of the tool presetter as shown in FIG. The master tap gauge 21 is the same as the preset tapping tool 14 (including the tool holder 15) for actual processing shown in FIG. 5, and is stored as a master gauge and is not used for actual processing. is there. Then, as the posture of the master tap gauge 21 set on the spindle of the tool presetter, the posture equivalent to that when the preset tapping tool 14 is mounted on the spindle of the machining center as shown in FIG. 5 is reproduced.

  More specifically, as shown in FIG. 8, when the preset tapping tool 14 is mounted on the spindle of the machining center, the key block 23 is fitted into the groove portion 22 of the tool holder 15 to perform positioning in the rotational direction. At the same time, the information on the ID chip 24 is read and written between the ID chip 24 attached to the tool holder 15 and the ID chip sensor 25 on the spindle side. Therefore, similarly for the master tap gauge 21, as shown in FIG. 7B, a slidable key block 26 prepared in advance on the tool presetter side is fitted in the groove 22 of the tool holder 15. The positioning in the rotational direction is performed in the same manner as when the spindle is mounted on the machining center side. At the same time, necessary information is exchanged between the ID chip sensor and the ID chip 24 similar to those shown in FIG. 8 prepared in advance on the tool presetter side. As a result, on the tool presetter, the positioning of the master tap gauge 21 in the rotational direction with respect to the key block 26 is performed under the same conditions as when the spindle on the machining center side is mounted.

  When positioning in the rotational direction of the master tap gauge 21 set on the spindle of the tool presetter is performed in this way, as shown in FIG. 9A and FIG. 10, the threaded portion of the tap 27 in the master tap gauge 21 The contact 29 of the locator 28 is lightly applied to the rake face 27a to create a reference for the rotational direction at the tip of the tap 27 of the master tap gauge 21. The locator 28 has a flat contact 29 attached in a cantilevered state from the upper end of the magnet stand 30. If the reference can be established by the contact of the contact 29 with the rake face 27a, the magnet stand The magnetic stand 30 is attracted and fixed to the non-movable part of the tool presetter by the magnetic force of 30.

  Subsequently, the master tap gauge 21 is removed from the spindle of the tool presetter as shown in FIG. 9B while taking care not to change the position of the locator 28. Instead, as shown in FIG. 11A, the preset tapping tool 14 before presetting for actual tapping is set on the spindle of the tool presetter. As in the case of the master tap gauge 21, the slidable key block 26 prepared in advance on the tool presetter side is fitted in the groove 22 (see FIG. 8) of the tool holder 15, and the machining center side is fitted. Positioning in the rotational direction is performed in the same manner as when the spindle is mounted. At the same time, necessary information is exchanged between the ID chip sensor 25 and the ID chip 24 (both of which are shown in FIG. 8) prepared in advance on the tool presetter side. As a result, the positioning of the preset tapping tool 14 in the rotational direction with respect to the key block 26 is performed under the same conditions as when the spindle on the machining center side is mounted.

  Here, the preset tapping tool 14 is positioned in the rotational direction of the tool holder 15 with reference to the key block 26 attached to the tool presetter. The most functionally important tap 6 rotation direction and tool length setting remain incomplete.

  Therefore, when the tap 16 is unchucked with respect to the tool holder 15 of the preset tapping tool 14 and the tap 16 is appropriately rotated to position the tap 16 in the rotation direction, the case shown in FIG. Similarly, the rake face 16a of the threaded portion of the tap 16 is lightly applied to the contactor 29 of the locator 28, and the contactor 29 of the locator 28 is placed on the raked face 27a of the threaded portion of the tap 27 in the previous master tap gauge 21. Reproduce the lightly touched state. Accordingly, at least the positioning of the tap 16 in the rotation direction in the preset tapping tool 14, that is, the rotation direction phase of the tap 16 is determined. In addition, about the square part of the shank rear end of the tap 16, the rotation prevention function is made not to be exhibited.

  Subsequently, the tool length of the tap 16 in the preset tapping tool 14 is set. When the tool length of the tap 16 is set, if the tip surface of the tap 16 is used as a reference, the processing accuracy of the tip surface is not higher than the function of the tap 16, so that the tap 16 is used as described above. This is insufficient for managing the rotational direction phase of the threading start position of the female thread portion 10 to be processed.

  Therefore, in the present embodiment, when setting the tool length of the tap 16 in the preset tapping tool 14 (preset), the idea is greatly changed, and the complete (thread) thread of the thread portion 17 having a high machining accuracy among the taps 16. The flank of the specific mountain of the portion T1 (see FIG. 6) is assumed to be based on the inclined surface that connects the top of the thread and the bottom of the valley.

  More specifically, as shown in FIG. 11B, a preset tapping tool 14 is used by using an enlargement projection function by a projector of a tool presetter (may be an imaging enlargement display function by a CCD camera). The shape of the tip of the tap 16 is projected, and the reference lines 20 a and 20 b that are indices on the screen are superimposed on the tip of the tap 16. It should be noted that, in addition to the two cross-shaped reference lines 19a and 19b orthogonal to each other, two reference lines 20a and 20b having a mountain shape are displayed in advance on the screen of the projector. . The angle formed by the two reference lines 20a and 20b forming the mountain shape is made to coincide with the angle α formed by the flank on both sides of the complete (thread) thread portion T1 of the tap 16, as will be described later.

  As described above with reference to FIG. 6, the screw portion 17 of the tap 16 includes the biting portion T2 on the tip side and the complete (thread) thread portion T1 that follows, and the biting portion T2 is incomplete (screw). Yamabe. FIG. 12 is a further enlargement of FIG. 6B, and in the example of FIG. 12, the third peak 17a from the tip end side of the tap 16 is the first peak of the complete peak T1, and the rest are sequentially complete. The second mountain 17b of the mountain T1, the third mountain 17c of the complete mountain T1, and so on. As described above, the size (T2 itself) of the biting portion T2 that is an incomplete screw portion has a large variation and is not suitable for the reference of the tool length of the tap 16. The two reference lines 20a and 20b having the mountain shape on the screen side of the projector described above are displayed on the flank on both sides of each mountain 17a, 17b... (Inclined surface connecting the top of the thread and the bottom of the thread) 31 and 31 are made to coincide with each other in advance.

  When the reference lines 20a and 20b, which are indices on the screen of the projector, are superimposed on the projected shape of the tip of the tap 16, as shown in FIG. 12, a mountain shape is formed on the flank 31 of the first mountain 17a of the complete mountain portion T1. A pair of reference lines 20a and 20b that are formed so as to overlap each other and set so that the tool length becomes a predetermined dimension, that is, preset, and in that state, a chuck (not shown) built in the tool holder 15 is mounted. And chucking firmly. This is because the line that bisects the angle α between the flanks 31 of the specific peak 17a of the complete peak T1 is the horizontal reference line 19a, and therefore one peak of the complete (thread) peak T1. The matching of the pair of reference lines 20a and 20b having a mountain shape with the flank 31 of the eye peak 17a is based on the assumption that the peak of the peak 17a has an acute angle. There is nothing else. Thus, the preset operation of the preset tapping tool 14 is completed. It is also possible to use the second mountain 17b and the third mountain 17c instead of the first mountain 17a of the complete mountain portion T1.

  In this case, the intended purpose cannot be achieved with a chuck that slightly pulls the tap 16 toward the tool holder 15 during chucking, and therefore the tap is not pulled even if a clamping force is applied due to chucking. For example, a milling chuck or the like is adopted. Also, when setting the tool length of the tap 16, the intersection of the cross-shaped reference lines 19a, 19b is not directly matched with the tops of the peaks 17a, 17b ... Since it is a cylindrical surface when viewed microscopically as shown in FIG. 12, even when setting using a projector, the intersection of the cross-shaped reference lines 19a and 19b can be made to exactly match the cylindrical surface. It is difficult.

  As is clear from the above description, when presetting the preset tapping tool 14, the tool presetter is first calibrated by using the bearing surface master gauge 18 for presetting the tool length of the counterbore cutter 11, and then, Using the calibrated tool presetter, the preset tapping tool 14 is positioned in the rotational direction and the tool length is preset. This means that the counterbore cutter 11 for machining the seating surface 9 in the plug hole 2 and the preset tapping tool 14 for machining the internal thread portion 10 in the plug hole 2 are the same machining axis (Z Assuming that it will be used for machining on the axis), it is nothing but a preset based on the same standard.

  Then, the counterbore processing of the seating surface 9 is performed in the form of FIG. 4 using the counterbore cutter 11 preset with reference to the master gauge 18 for the seating surface. The depth) is managed by the dimension management function of the machining center itself.

  On the other hand, the tapping process of the internal thread portion 10 following the counterbore process of the seating surface 9 is performed in the form of FIG. 5 using the preset tapping tool 14 preset by the procedure described above. In this case, a position that is a predetermined distance L away from the seating surface 9 that has been subjected to spot facing is set as a pitch feed start position M, and this pitch feed is started toward the screw pilot hole 2a that opens in the seating surface 9. As described above, the preset tapping tool 14 is approached to the position M, the positioning of the preset tapping tool 14 in the rotational direction is performed at the pitch feeding start position M, and then the pitch feeding for tapping is started. It is. The reference position on the preset tapping tool 14 side with respect to the predetermined distance L is the first peak 17a in the complete peak T1 of the tap 16 described above.

  Then, in a state where the preset tapping tool 14 is approached to the pitch feed start position M and positioning in the rotational direction is performed at the pitch feed start position M, the predetermined distance L has a specified dimension and the tap 16 The rotational direction phase is determined at a specific phase angle position. Therefore, when the pitch feed for tapping is started from the pitch feed start position M, the tap 16 enters the screw pilot hole 2a by the screwing action of the screw and is n-th rotation from the pitch feed start position M and The threading of the screw thread portion 10 is started from a specific phase angle position of the n-th rotation, and finally the through hole type female screw portion 10 is finished. This means that the threading of the threaded portion 10 starting from the specific phase angle position of the n-th rotation from the pitch feed start position M can be similarly reproduced regardless of how many times tapping is repeated. Means.

  In other words, the counterbore process of the seating surface 9 and the tapping process of the female thread portion 10 are performed using the same machining axis (Z axis) of the same machining center, and the cylinder head 1 between the counterbore process and the tapping process. Assuming that the internal thread portion 10 of the plug hole 2 for the n cylinders of the cylinder head 1 is processed with the common preset tapping tool 14 on the assumption that the cylinder is not detached and attached, the seating surface for each cylinder 9 are all the same specific phase angle positions. This does not change even if the same processing is performed one after another in the mass production processing line of the cylinder head 1.

  When the plug 3 is installed in the plug hole 2 of each cylinder of the cylinder head 1 processed in this way as shown in FIG. 3, the start of the male threaded portion 7 on the metal shell 4 side of the plug 3 as described above. If the relative positional relationship between the position (the rotational direction phase of the threading start position of the external thread portion) and the outer electrode 33 is managed to be a specific positional relationship, that is, the threading start position of the external thread portion 7. If the rotation direction phase of the plug 3 and the direction of the outer electrode 33 when the plug 3 is tightened with a specified torque are matched in advance, the plug 3 is fixed to the female thread portion 10 of the plug hole 2 with a predetermined torque. It is possible to always adjust the outer electrode 33 to a specific direction (rotational direction position) in any cylinder by simply tightening the. As a result of the trial production by the present inventors, it was confirmed that the outer electrode 33 can be managed at about ± 10 ° with respect to the target specific direction.

  Here, in the present embodiment, the case where the threaded portion 10 of the plug hole 2 on the cylinder head 1 side where the plug 3 is mounted is described as an example, but the present invention is not limited to this. Of course, for the purposes of the present invention, the present invention can be applied to tapping of any threaded portion that requires management of the threading start position of the female threaded portion.

1 ... Cylinder head (work)
DESCRIPTION OF SYMBOLS 2 ... Plug hole 2a ... Screw pilot hole 3 ... Spark plug 9 ... Seating surface 10 ... Female thread part 14 ... Preset tapping tool 15 ... Tool holder 16 ... Tap 16a ... Rake face 17 ... Screw part 17a ... First mountain 31 … Frank T1… Complete Yamabe

Claims (6)

A method of tapping a workpiece by attaching a tap to a spindle of a machine tool,
At the pitch feed start position for tapping, the tap rotation direction is determined based on the rake face of the tap screw part, and the tap and workpiece are determined based on the flank of a specific peak part of the tap screw part. Set the distance between
A tapping method comprising starting pitch feed for tapping in that state.   2. The tapping method according to claim 1, wherein the distance between the tap and the workpiece is set to a specified dimension based on the first flank of the complete thread portion of the tap screw portion. A preset tapping tool with a tool holder supporting a tap is mounted on the spindle of the machine tool, and the preset tapping tool is approached to the pitch feed start position for tapping with respect to the workpiece on which a screw pilot hole is formed. A method of performing tapping by giving a pitch feed for tapping after indexing the rotation direction,
Prior to the above tapping, the preset tapping tool alone is positioned in the tap rotation direction with respect to the tool holder on the basis of the rake face of the tap screw part, and the flank of a specific peak part of the complete thread part of the tap screw part is determined. A tapping method comprising a tool presetting step of presetting a tool length as a reference.   4. The tapping method according to claim 3, wherein the tool length is preset based on the first flank of the complete thread portion of the tap screw portion. As a pre-process of the tapping process, including a process of processing the seating surface on the opening peripheral part on the tapping start side in the screw pilot hole of the workpiece,
Both this seating and subsequent tapping are performed on a common machine tool,
The tapping method according to claim 3 or 4, wherein the workpiece clamped during the seating process is subjected to the tapping process without being unclamped even after the seating process. The workpiece is an engine cylinder head,
A screw pilot hole is formed as a plug hole pilot hole in this cylinder head,
The tapping process according to any one of claims 3 to 5, wherein the seating surface is a seating surface on which a spark plug that is screwed into a tapped plug hole is seated. Method.

Images