JP4490358B2 - Tapping screw - Google Patents

Description

  The present invention is a screw for attaching a part to a workpiece made of a soft material such as an aluminum alloy, a magnesium alloy, or a resin, and a female screw is formed in an unthreaded pilot hole formed in such a workpiece made of a soft material. The present invention relates to a tapping screw that eliminates the generation of workpiece shavings (swarf) when screwing in while forming a screw.

  In recent years, electrical appliances such as mobile phones, personal computers, and portable music players are widely used because of their light weight, small size, and good workability. Many screws are used. Various types of screws used in such products have been developed to maintain the fastening strength to soft material workpieces, but those that have sufficient functions of fastening properties and screwability have not yet been obtained. is the current situation.

  In view of such a current situation, for example, those disclosed in Japanese Patent Application Laid-Open No. 2002-89526 are recently being used for workpieces made of a soft material. This is a screw mainly used for a resin work, and has been developed especially to increase the tightening efficiency, and is shown in FIGS. In order to reduce the screwing torque, the outer diameter of the two threads 111 of the three threads is a JIS standard normal thread. The height of the other one thread 112 is about ½ of the height of the other two threads, and the thread angle of each thread 110 is 30 degrees. The three-threaded screw 110 is formed by making the outer diameter shape a triangular rice ball shape and gradually decreasing the outer diameter toward the tip. In addition to those used for the purpose of preventing seizure between the tapping screw and the workpiece, for example, as shown in Japanese Utility Model Publication No. 2571805, a single thread is used, and a part of the thread is raised near the tip. There are also things.

JP 2002-89526 A Noto 2571805 gazette

  However, since this screw is basically a triple thread screw, the screwing time is shortened, but the pitch of the screw thread is narrowed and the strength of the female screw tends to decrease. In addition, during screwing work, all the screw threads are always in surface contact with the female screw formed on the workpiece, so that the screwing resistance increases, and this resistance causes a heat generation phenomenon. When used for a workpiece, there arises a problem that seizure occurs and the screw is not completely screwed. Furthermore, the screw thread bites into the pilot hole of the workpiece at the start of screwing to form a female screw, but a large thrust (force that presses the screw against the workpiece) is screwed to cause the screw thread to bite into the pilot hole. If this thrust is weak, the end face of the pilot hole may be shaved in the early stages of screwing, and the chips may be scattered on the electronic parts fixed to the workpiece and damage the electronic parts. It is a cause of defects. In addition, since a large thrust is required, the operator's fatigue may be accumulated or tendonitis may occur in the screw tightening operation by the electric driver. Furthermore, in the case of a tapping screw having a thread that is partially raised near the thread tip of the leg part, the thread on the tip side suddenly increases, and this often prevents idling and scrapes the pilot hole. Therefore, it still has problems such as requiring a large thrust.

  The object of the present invention is to provide a tapping screw that eliminates such problems and has good biting ability to the pilot hole even if the thrust during screwing is reduced, and that can easily correct the fall of the screw in the initial stage of screwing. Is to get.

An object of the present invention is composed of a head 2 having a drive hole 4 and a leg 3 integral therewith, and a screw thread 10 formed on the leg 3 is a single same thread from the tip to the head side. in tapping screw having a normal threaded portion 11 of the shape, the guiding thread portion 12 having a diameter of crest diameter than the normal threaded portion 11 at the tip of the leg portion 3 is provided, the leg tip of the guiding thread portion About one mountain
Same diameter as or larger than the diameter of the pilot hole (21) formed in the workpiece (20)
A smaller crest diameter than the crest portion normally form a large-diameter female screw forming portion 13 from the threaded portion 11 between the guide thread portion 12 and the normal threaded portion 11, moreover, a guiding thread portion 12 It is accomplished by providing a gradual touch <br/> pin thread configuration that crest diameter is continuously connected to be greater toward the female screw forming portion 13.

  In addition to the above-described configuration, the object of the present invention is an asymmetrical shape in which the thread has a leading flank angle (α) and a small pressure flank angle (β). By using a tapping screw formed by (θ) larger than each flank angle of the normal thread 11, the resistance at the time of screwing can be reduced and seizure with the workpiece can be prevented.

According to the present invention, a single screw thread has a guide screw thread at the tip of the leg, and gradually increases the screw thread from the guide screw thread to provide a large-diameter female thread forming part. From the head seating surface to the head thread surface, since a normal thread part having a smaller diameter thread than the female thread forming part is formed,
Since the thread pitch can be made relatively large , the spacing between female thread threads is increased.
, A decrease in the strength of the female screw is prevented. Further, in the screwing operation, since the screw thread hardly comes into surface contact with the female screw except for the female screw forming portion, the screwing resistance is reduced, the screwing torque can be lowered, and the heat generation phenomenon is lowered. In particular, when this screw is used for a work made of an aluminum alloy, the seizure phenomenon occurs and the screw is not completely screwed. Furthermore, since the screw thread has a so-called tapered shape in which the thread gradually becomes higher from the tip of the leg portion, the screw can bite into the pilot hole of the workpiece without cutting the workpiece at the start of screwing. Therefore, it is not necessary to apply a large thrust to the screw and it is possible to screw in with a relatively small thrust. Therefore, the end surface of the pilot hole is shaved and the chips are scattered on the electronic component fixed to the workpiece, thereby damaging the electronic component. This is also eliminated, and there is no product defect due to this. In addition, since a large thrust is not required, the operator's fatigue is not accumulated and the occurrence of tendonitis is reduced in the repeated screw tightening operation by the operator with the electric screwdriver. In addition, about 1 thread at the tip of the guide screw thread is the same diameter or slightly smaller than the diameter of the pilot hole.
The diameter is set smaller than the normal thread, and the thread diameter gradually increases from this guide thread to the female thread forming part. It can be corrected at the time of screwing, and screwing with the screw center tilted with respect to the center of the pilot hole is reduced, and the screw floating phenomenon is eliminated . And screwed open
By the beginning, the screw tip can enter the workpiece's pilot hole.
There are specific effects such as the leg portion being reliably guided and the inclination of the screw before screwing is reduced .

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 and 2, reference numeral 1 denotes a tapping screw comprising a head 2 and a leg 3 formed integrally therewith. The head 2 is screwed into a screw 1 from a driver bit (not shown). Is formed in the drive hole 4. A single thread 10 is formed on the leg 3 integrally formed with the head 2 from the vicinity of the seating surface 5 of the head 2 to the tip of the leg 3. A normal thread portion 11 having the same height as a general tapping screw is formed on the portion side. The leg 3 has a triangular cross section so that the resistance during screwing can be reduced even slightly.

  On the other hand, a guide screw thread portion 12 having a screw thread diameter smaller than the screw thread diameter of the normal screw thread portion 11 is provided on the distal end side of the leg portion 3, and this guide screw thread portion 12 is usually about one thread. The outer diameter of the thread formed by combining the maximum radii of the guide thread 12 is the same as or slightly larger than the diameter of the pilot hole 21 formed in the workpiece 20 and smaller than the normal thread 11. The thread diameter is set. For this reason, the streak-like female screw 22 by the thread ridgeline is slightly formed in the prepared hole 21 at the start of screwing.

  Between the guide screw thread part 12 and the normal screw thread part 11, a female screw forming part 13 having a diameter larger than that of the normal screw thread part 11 is formed. Specifically, the thread diameter of the female thread forming portion 13 is normally set to be about 0.01 to 0.05 mm larger than the thread diameter of the thread portion 11, and the nominal diameter of the screw 1 is set. Depending on, the setting may be larger. Moreover, a continuous thread connecting portion 14 is formed between the female screw forming portion 13 and the guide screw thread portion 12 so that the thread diameter gradually increases from the guide screw thread portion 12 to the female screw forming portion 13. As shown in FIG. 3, the thread connecting portion 14 from the guide thread 12 to the female thread forming portion 11 is tapered as shown in FIG. That is, since it is continuously connected from the guide thread portion 12 to the female thread forming portion 13 by the thread connection portion 14 that gradually increases in diameter, the generation of chips at the start of screwing and the screw fall down. Can be easily corrected.

  Further, these screw threads 10 have an asymmetrical shape in which the advance side flank angle (α) is large and the pressure side flank angle (β) is small, and the flank angle of the thread 10 of the female thread forming portion 13 is the normal thread portion 11. Is formed larger than each flank angle by (θ). The reason why the flank angle of the female screw forming portion 13 is increased by (θ) is to reduce the contact between the female screw 22 and the screw thread 10 of the normal screw thread portion 11, and thereby the screwing torque at the time of screwing. Will fall. Furthermore, the pressure-side flank angle is small because when the screw 1 is screwed and tightened, an axial force is applied to the screw 1 between the workpiece 20 and the fastening force is increased.

When the tapping screw 1 obtained in this way is started to be screwed into the pilot hole 21 formed in the workpiece 20 in advance, as shown in FIG. 21 is pushed to some extent . In this state, since the tapping screw 1 is rotating, the screw thread connecting portion 14 continuing to the tapping screw 1 bites into the prepared hole 21 and is screwed in while forming the female screw 22 without idling. At this time, the tapping screw 1 is the work 2
Be slightly fall to the lower hole 21 of 0, the lower hole 21 is Oite worker at the time of this screwing start
Since it is easy to correct the inclination of the screw 1 along the, tapping screw 1 with respect to the prepared hole 21 is to be screwed into the smooth, the seating surface 5 of the screw 1 from the surface of the workpiece 20 floating In other words, the occurrence of screw floating is also reduced.

  By this screwing operation, the female screw 22 is formed in the female screw forming portion 13 as shown in FIG. 5, and the screw thread 10 of the normal screw thread portion 11 is screwed in a state where the contact with the female screw 22 is relaxed. It is. When the seating surface 5 of the tapping screw 1 is seated on the workpiece 20 in this way, the screwing operation is completed, an axial force is generated on the leg 3 of the screw 1, and the pressure side flank surface of the thread 10 is generated on the female screw 22. Will come into contact with each other and a strong fastening force will be obtained.

  Regarding the occurrence of the screw floating, the workpiece 20 is inclined in two ways of 7.5 ° and 10 ° with respect to the tapping screw, and the tapping screw 1 as a sample is shown in Patent Document 2 as a conventional example and the present one. Table 1 shows the results of preparing the inventions and screwing them into the pilot holes 21 to compare the presence or absence of screw floating. The measurement conditions are: tightening torque is 1.0 N · m, thrust applied to the sample is 9 N, 5 samples are prepared for each measurement type, screwed into the workpiece 20 having the pilot hole 21 of a predetermined size, and screw floating The presence or absence of was measured.

  As a result, as shown in Table 1, in the conventional example, no screw lift occurred in all samples when the tilt was 7.5 °, but screw lift occurred when the tilt was 10 °. On the other hand, in the present invention, when the tilt is 7.5 °, the screw float does not occur in all the samples, and only one of the five samples occurs when the tilt is 10 °. As a result, it has been clarified that even if the tapping screw 1 is slightly tilted with respect to the pilot hole 21 of the workpiece 20 at the start of screwing, this is corrected in the present invention and screwed without causing screw floating.

  Further, FIG. 6 and FIG. 7 show another embodiment of the present invention. In the embodiment, the leg portion 3 on which the screw thread 10 is formed has a triangular cross section. The cross-sectional shape is not limited to the above. And the thread 10 formed in this way also makes the female thread forming part 13 larger in diameter than the normal thread part 11 in the same manner as in the above embodiment, and from the guide thread part 12 having a small diameter of about one thread to the female thread forming part 13. The thread connecting portion 14 may be formed so that the diameter gradually increases toward the end of the thread, that is, the top of the thread is tapered, and the flank angle of the thread 10 is asymmetrical. An effect is produced.

It is a front view which shows embodiment of this invention. It is a right view of FIG. It is a principal part expanded sectional view of FIG. It is a partial cross section enlarged view which shows the screwing start state of this invention. It is a partial cross section enlarged view which shows the screwing state of this invention. It is a front view which shows another embodiment of this invention. FIG. 7 is a right side view of FIG. 6. It is a front view which shows a prior art example. It is a principal part expanded sectional view of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tapping screw 2 Head part 3 Leg part 4 Drive hole 5 Seat surface 10 Screw thread 11 Normal thread part 12 Guide thread part 13 Female thread shaping part 14 Screw thread connection part 20 Work 21 Pilot hole 22 Female thread

Claims (2)

A head (2) having a drive hole (4) and a leg (3) integral with the head (2) are formed, and a screw thread (10) formed on the leg is a single thread from the tip to the head. In a tapping screw having a normal thread portion (11) having a mountain shape,
A guide screw thread portion (12) having a screw thread diameter smaller than that of the normal screw thread portion is provided at the tip end of the leg portion, and about one leg tip end of the guide screw thread portion is formed on the workpiece (20). Pilot hole (21
) And a larger thread diameter than that of the normal thread portion, and a female thread forming portion (13) having a larger diameter than the normal thread portion between the guide thread portion and the normal thread portion. forming a, moreover, tapping screw, characterized in gradually it has a configuration in which the crest diameter is continuously connected to be greater toward the female screw forming portion from the guide thread portion. The thread has an asymmetrical shape with a leading flank angle (α) and a small pressure flank angle (β), and the thread in the female thread forming part is usually formed by (θ) larger than the respective flank angle of the thread part. The tapping screw according to claim 1, wherein the tapping screw is provided.

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