JP2007307642A - Drill - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the quality of the wall surface of a machining hole and repolishing performance by exhibiting the characteristics of a two-blade drill while assuring hole position accuracy comparable to that of a single-blade drill. <P>SOLUTION: In the front end of a body 1, two cutting edges 3, 3 and two twisted grooves 4, 4 for discharging scrapes generated by each cutting edge are provided. The grooves 4, 4 are joined at a position retracted by a prescribed distance from the front end of the body 1, and made into a single groove 4A behind a meeting place c. Thus, the characteristics of the single-blade drill and the two-blade drill are exhibited together. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a drill used for drilling printed circuit boards.

  For drilling a printed circuit board, a small diameter drill having a blade diameter (diameter) of less than 0.5 mm is used.

  As examples of conventional printed circuit board drills, for example, there are those proposed by the present applicant in Japanese Patent Application No. 2005-32482 and those disclosed in Patent Documents 1 to 3 below.

These are all single-edged drills, and by using a single-edged blade, the number of grooves (blade grooves) for discharging chips is reduced to one to increase the rigidity of the body (drill body).
JP 2004-82318 A JP 2004-34213 A Japanese Utility Model Publication No. 7-33514

  A two-edged drill having two cutting edges and two grooves for discharging chips is superior in cutting balance compared to a single-edged drill having only one cutting edge and one groove. However, if a small-diameter drill with a blade diameter of less than 0.3 mm represented by a drill for a printed circuit board is made into two blades, the two grooves are formed over the entire area, so the rigidity of the body is reduced. It is inevitable that drilling and bending of the drill during workpiece biting or during machining is likely to occur, which causes machining hole positions and straightness to vary, and this is one of the required characteristics for drills. The position accuracy of the hole is degraded.

  Therefore, as a method for compensating for the lack of rigidity, single-blade drills disclosed in the above-mentioned Patent Documents 1 to 3 have been proposed, but single-blade drills have higher rigidity than double-blade drills. While the position accuracy of the split holes is improved, the cutting balance is poor, and a large stress is applied to the wall surface of the hole.

  In addition, in terms of machining efficiency, since it is a single blade, it is used under substantially the same machining conditions as a double-edged drill, so the load on the machining surface increases and the quality of the wall surface of the machining hole decreases. In addition, the flank at the front end of the body has a special shape, which makes it difficult to grind the flank, and it is difficult to perform re-polishing for regenerating the blade edge in existing equipment.

  Therefore, the present invention can improve the quality of the wall surface of the drilled hole and improve the re-polishing property while ensuring the same hole position accuracy as that of the single-edged drill while exhibiting the characteristics of the double-edged drill. The challenge is to make it.

  In order to solve the above-described problem, in the present invention, the tip of the body has two cutting edges and two twisted grooves for discharging chips generated by the cutting edges, and the two grooves are the tip of the body. The drills have a structure in which they are merged at a position retracted by a predetermined amount and have a groove behind the merge point, so that the features of the single blade drill and the double blade drill are exhibited together.

Preferred forms of this drill are listed below.
(1) The distance from the front end of the body to the merging point is set to ½ or less of the blade groove length.
(2) Set the twist angle of the two grooves to at least 2D (D = blade diameter) from the end of the body to the rear, and make the difference between the twist angles of the two grooves at positions exceeding 2D. The two grooves are merged.
(3) The groove width w1 of the grooves joined together is made larger than the groove width w of each groove before joining.
(4) A twisted ridge having a wavefront-like cross section formed at a portion where the two grooves interfere with each other is left at the bottom of the groove formed by joining.

In addition, the joining point of the groove | channel said by this invention points out the place where two groove | channels began to interfere.
The blade groove length is the length from the tip of the drill to the rear end of the groove, and the maximum insertion length of the drill into the work material within the range in which the chip discharging function by the groove is maintained by this blade groove length. Is determined.

  In the drill of the present invention, the cutting edge portion has the same structure as that of the two-blade drill, so that the machining with a good cutting balance can be performed, and the performance equivalent to that of the two-blade drill can be obtained with respect to the quality of the wall surface of the machining hole. In addition, since the cutting edge portion has the same structure as that of the two-blade drill, re-polishing for regenerating the cutting edge can be easily performed using a polishing equipment for a normal two-blade drill.

  Further, since the groove divided into two on the tip side of the body merges into a single part at a position retracted by a predetermined amount from the tip of the body, it is located on the body of the single-edged drill on the rear side of the junction point of the groove. It has an approximate structure, and the body rigidity is higher than that of the 2-flute drill, and its high rigidity suppresses bending and bending during the biting of the work material and during machining, so that high hole position accuracy can be obtained. Is also possible.

  The operations and effects of the other preferred configurations will be described in the next section.

Embodiments of the drill of the present invention will be described below with reference to FIGS. 1 to 10 of the accompanying drawings.
FIG. 1 shows the overall configuration of a drill according to an embodiment (for a printed circuit board). 2 is an enlarged view of the tip side surface of the drill of FIG. 1, and FIG. 3 is an enlarged view of the front surface. 4 to 7 are enlarged sectional views showing changes in the groove width of the drill.

  As shown in FIGS. 1 to 3, a body 1 (drill body) is integrally formed at the tip of the shank 2. The body 1 may be a body formed separately from the shank and attached by shrink fitting into a hole formed in the center of the tip of the shank.

  At the tip of the body 1, two cutting edges 3 and 3 having a centrally symmetric shape are provided. Moreover, the two groove | channels 4 and 4 which discharge the chips produced | generated by each cutting blade are also provided. 5 is a flank at the front end of the body, and 6 is a land portion.

  The grooves 4 and 4 are twisted grooves. The two grooves 4 and 4 are located at a position 180 degrees out of phase at the front end of the body 1 and have a centrally symmetric shape, but approach each other from a position retracted by a predetermined amount in the axial direction from the front end of the body. The merging is performed at a position retracted by a predetermined amount from the front end of the body, and a single groove is formed in the axially rearward direction from the merging point c. Here, for convenience of explanation, the groove after joining is denoted by reference numeral 4A.

  The joined groove 4A extends to the vicinity of the rear end of the body 1. The blade groove length L is from the front end of the body 1 to the end of the groove 4A. The distance l from the tip of the body 1 to the confluence point c shown in FIG. 2 is preferably ½ or less of the blade groove length L in order to suppress a decrease in rigidity on the body root side close to the shank 2. .

The two grooves 4 and 4 can be joined at a desired position by making a difference in the twist angle of the grooves. As shown in FIG. 8, if the twist angle β1 of one groove 4 is β1, and the twist angle β2 of the other groove 4 is made larger or smaller than β1, the two grooves 4, 4 approach each other and merge at point c.
When the groove width w1 of the groove 4A after merging becomes narrow to a certain point, the processing of the other groove is stopped, and the groove width from that position to the end of the groove 4A becomes constant at the width of one groove. In addition, when a web taper is attached to the blade groove portion, the groove width of the terminal portion is smaller than that of the tip portion, as in a normal two-blade drill.

  In the example drill, the torsion angles β1 and β2 (see FIGS. 2 and 8) of the two grooves 4 and 4 are in the range from at least 2D (D = blade diameter, see FIG. 2) from the front end of the body to the rear. Are the same angle, and the two grooves are merged with a difference between the twist angles β1 and β2 at a position exceeding 2D. With this structure, the positional relationship between the two grooves and the twist angle of both grooves are kept constant even when re-grinding for cutting edge regeneration is performed in the range from the tip of the body 1 to 2D. Re-polishing can be easily performed using equipment for a two-blade drill.

  In addition, by setting the range in which the twist angles β1 and β2 of the two grooves are the same angle to at least 2D from the body tip, it is possible to secure the number of re-polishings to the extent that it is normally performed and enhance the economic effect. .

Further, by making the groove width w1 of the groove 4A after merging larger than the groove width w of the groove 4 before merging, even if the number of grooves is reduced to one, better chip discharging performance than in the case of w1 = w. Can be secured. As one of the methods for setting the groove width w1> w, the two grooves 4 and 4 are joined, and then when the groove width w1 of the groove 4A becomes narrow to some extent as shown in FIG. There is a method of making the angles β1 and β2 constant.
As another method of setting the groove width to w1> w, after the two grooves merge as shown in FIGS. 5 to 7, the groove width w1 of the groove 4A after the merge gradually narrows toward the end of the groove. It may be made to become. In this case, after the two grooves merge, the twist angle β2 of the other groove may be made closer to the twist angle β1 of the one groove.
When the groove width is w1> w, it is not always necessary to maintain this relationship up to the end of the groove, but maintaining the relationship of w1> w to the end of the groove can further improve chip discharging performance. it can.

  A twisted ridge 7 having a crest-like cross section is formed at a portion where the two grooves interfere behind the junction point c. The protrusion 7 gradually decreases in height as the groove width of the groove 4A after joining decreases. The ridges 7 serve as reinforcing ribs and contribute to improving the rigidity of the body 1. Therefore, it is better to leave without removing.

  The two-blade drill usually provides a margin at the front edge of the land portion in the drill rotation direction, but the drill of the present invention may omit the margin depending on the blade diameter. The small-diameter drill has a small absolute value of the contact area even when the entire outer periphery of the land portion comes into contact with the work material, and therefore can be machined without any trouble even without a margin. The example drill has no margin. Since there is no margin, drill machining is not complicated even if the twist angle of the groove 4 is changed in the middle.

The results of tests conducted to evaluate the performance of the drill of the present invention are described below. The test was performed using the drill of the present invention (one of which the processing of the other groove was stopped after the joining of the two grooves, l = 1.5 mm), and the single blade drill and the double blade drill having the same blade diameter. Conducted under conditions.
-Test conditions-
・ Drill size: φ0.25mm (blade diameter D) x 4.0mmL (blade groove length)
-Work material: High heat-resistant printed circuit board 0.8 mm (thickness t) x 3 layers-Address plate: Lubricating resin coating sheet-Rotation speed: 250 Kmin ^-1
・ Feeding speed: 20μm / rev
・ Number of hits: 4,000

  The performance was evaluated for the two items by measuring the amount of displacement of the processed hole position and the inner wall roughness (surface roughness) of the hole. The results are shown in FIGS. The white marks in FIG. 10 represent average values.

As can be seen from this test result, the drill according to the invention is not inferior to the single-edged drill in terms of the displacement amount of the hole position, and it can be understood that the rigidity equivalent to the single-edged drill is secured from this. .
Moreover, about the inner wall roughness, the performance equivalent to a two-blade drill is ensured, and a result superior to that of a single-blade drill is obtained.

  The present invention is particularly suitable for a small-diameter drill whose drilling diameter for drilling a printed circuit board or the like is less than 0.3 mm. However, other drills such as a flexible Even if it is applied to a deep hole drill (long drill) where bending is likely to occur, the effectiveness is demonstrated.

Side view showing an example of the drill of the present invention The figure which expands and shows the front end side of the drill of FIG. 1 is an enlarged end view of the front side of the drill of FIG. FIG. 1 is an enlarged cross-sectional view taken along line II of FIG. Expanded sectional view along the line II-II in FIG. Enlarged sectional view showing a state in which the groove width after merging is further narrower than in FIG. An enlarged cross-sectional view showing a state where the groove width after merging is further narrower than that in FIG. Schematic diagram showing changes in torsion angle of grooves The figure which shows the result (hole position accuracy) of the performance evaluation test The figure which shows the result (inner wall roughness) of the performance evaluation test

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Body 2 Shank 3 Cutting edge 4 Groove 4A Groove 5 after merging 5 Relief face 6 Land 7 ridge D Blade diameter c Merge point β1, β2 Twist angle L Flute groove length l Distance from body tip to groove merging point w Groove width w1 before merging groove width after merging

Claims (5)

  The tip of the body (1) has two cutting edges (3, 3) and two twisted grooves (4, 4) for discharging chips generated by each cutting edge, and the two grooves (4, 4) ) Joins at a position retracted by a predetermined amount from the tip of the body (1), and is a drill (4A) behind the joining point (c).   The drill according to claim 1, wherein a distance (l) from the tip of the body (1) to the junction (c) is set to ½ or less of the blade groove length (L).   The torsion angles β1, β2 of the two grooves (4, 4) are set to the same angle in the range from the front end of the body to at least 2D (D = blade diameter), and the grooves (4, The drill according to claim 1 or 2, wherein the grooves (4, 4) are joined by making a difference in the twist angles β1, β2 of 4).   The drill according to any one of claims 1 to 3, wherein the groove width w1 of the groove (4A) joined to become one is larger than the groove width w of the groove (4) before joining.   Claim 4 wherein the ridge (7) having a wave-head-like cross section formed in the portion where the two grooves (4, 4) interfered is left at the bottom of the groove (4A) that is merged into one. The drill described.

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