Patent Application
20140271030
The present invention relates to a fastening material or member and a screw hole burring method. More particularly, the fastening portion structure and the screw hole burring method for a thin metal plate material, for burring around the screw hole to reinforce the screw fastening structure.
In a known structure, a plate member (fastening material) of metal and a fastening object material of metal or resin material are fixed by a screw (thread). The fixing using a screw is widely used in manufacturing devices or exchanging of parts, because the fixing and removing is easy. In the case of the fastening material and the fastening object material having quite large thicknesses, the fastening material and the fastening object material are fixed with each other by engaging the screw with the screw hole provided in the fastening object material.
Also in the case of thin fastening material (metal plate) having a small thickness such as about 1 mm, it is necessary to assuredly fix the fastening object material to the fastening material by a screw for a thin plate. To accomplish this, the screw hole portion of the fastening material to be engaged with the screw is subjected to a burring process to assure the screw hole depth (burring height). A method is known to increasing a thickness of the screw engaging portion by a burring process as compared with the case of simple screw boring processing the fastening material.
Japanese Laid-open U.M. Application Hei 6-66821 proposes a burring processing structure for a prepared hole for tapping in which an inner surface adjacent a free end portion of the prepared hole where the screw is formed is expanded by plastic deformation to provide a thickened portion which has an inner diameter smaller than the prepared hole.
By such a structure, a effective thread ridge engaging ratio is made 100% to enhance a confining torque, thus increasing the strength of the fastening portion as compared with the prior art structure.
Using the burring process, the number of the processing steps increases, and therefore, Japanese Laid-open Patent Application Hei 09-164431 proposes the following method in order to reduce the processing step number and the processing cost in the burring process for the fastening material and enhancing the processing efficiency.
It is a burring step without a preliminary drawing step including a burring except for small diameter pierce-burring such as prepared hole through one step. That is, Japanese Laid-open Patent Application Hei 09-164431 discloses such a burring forming process.
Japanese Laid-open Patent Application 2009-214151 discloses a structure in which an emboss portion forming and a piercing process are effected through a single step, and a so-called work confining mechanism such as a pad and a stripper are omitted. By cooperation of a lower mold including a button die having a die hole and an upper mold including a piercing punch, the formation of the emboss portion of the panel and the pierced hole formation for the emboss portion are effected by a single step. The pierced hole is first formed using a shear action cause by the piercing punch and the die hole at the time of lowering operation of the upper mold, and then the emboss portion is formed by pressing and confining the circumference of the pierced hole by the emboss forming surfaces of the upper and lower molds.
Referring back to Japanese Laid-Open Utility Model Application Hei 6-66821, an inner surface adjacent the free end portion of the prepared hole is expanded inwardly to provide a thickened portion, by the burring process. The inner diameter of the burring is equal to that of the prepared hole, and the fastening object material can be fastened by a metric coarse screw or a self-tapping screw.
The object of the burring process is to provide a screw crest contact portion as much as possible to assure the screw fastening force. To accomplish this, it is required to increase the burring height, and for this purpose, a thickness measure between the inside circumference and the outer position of the burring has to be decreased, but the thickness must not be fractured by the engagement of the ridge of the screw thread.
However, with the decrease of the plate thickness of the fastening material, the thickness between the inside circumference and the outer configuration portion of the burring becomes insufficient, with the result of fracture of the thin portion by the screw ridge, and therefore, the sufficient fastening force is unlikely assured. In addition, the burring process result is formation of round portion (flank) at the root of drawn portion. For this reason, when a step screw is used, no sufficient seat surface against the step portion is assured. Therefore, with the increase of the number of steps, the size of the entire screw portion increases, with the result of the bulkiness of the device.
The process of Japanese Laid-open Patent Application Hei 09-164431, is advantageous in the one step is enough for the burring process, the bent circumference portion of the burring is rounded, and therefore, similarly to Japanese Laid-Open Utility Model Application Hei 6-66821, the problem with the step screw arises again. Between the burring height and the scrap material removed by the burring, there is a relation that with the increase of the burring height, the amount of the scrap decreases. However, using the above-described processing, the attempt to increase the burring height may result in cracking in the burred portion.
It is not possible to increase the bur thickness without production of the scrap material, and therefore, there is a limit in use with a thin plate.
In addition, in Japanese Laid-open Patent Application 2009-214151, the formation of the embossed portion and the piercing process can be effected through a single step advantageously, and the tapping process can be carried out into the pierced hole, and the emboss portion is effective for reinforcement. However, from the standpoint of screw fastening for a thin plate, when a shearing force is applied to the screw portion after fastening, the fastening screw may easily tilt due to deformation of the thin plate.
In addition, since the screw engagement amount is small, the strength is not sufficient so that the necessary fastening torque can be provided.
In addition, looking in a direction facing the surface, the embossed portion is circular, and at the stepped portion of the emboss edge, the cross-sectional configuration of crank-like, and therefore, the bending strength is high. However, this does not reinforce the central pierced hole portion.
An example of the screw fastening to a thin plate provided with burred through a conventional burring process.
A screw 3 includes a screw head and a screw leg 32 (screw portion). The top of the screw head is provided with a cross-hole configuration (unshown) by which the screw 3 is rotated by a cross-slot screwdriver or the like. The outer peripheral surface of the screw leg 32 is provided with a male screw 32a. The screw head 31 is provided with a screw flange portion 34 at a screw leg (32) side having a large diameter. The screw flange portion 34 contacts the fastening object material 2 at a flange contact portion 2a.
The fastening material 1 which is a metal plate such as a thin steel plate is provided with a drawn burred portion 1′ having a burring height (h) by a burring process.
When a commercially available screw 3 having a flat flange for enhancing the fastening torque (RS tight tradename, available from Nitto Seiko Kabushiki Kaisha, Japan, for example) as shown in
Accordingly, it is a principal object of the present invention to provide a fastening portion structure and screw hole burring method in which the rupture of the screw hole can be suppressed.
According to an aspect of the present invention, there is provided a fastening material for fastening a fastening object material between itself and a screw, said fastening material comprising a burred portion forming a screw hole and projecting in a substantially cylindrical shape in a screw inserting direction, wherein said burred portion has a wave-like shape portion waving in a circumferential direction of the cylindrical shape.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.
Parts (a), (b) and (c) of
As shown in the Figures, in a fastening portion structure 90 of this embodiment, a screw 3 is threaded into the fastening material 1, sandwiching the fastening object material 2, thus fastening the fastening object material 2 with the fastening material 1.
The screw 3 includes a screw head 31 and a screw shank 32. In this embodiment, a screw flange portion 34 having a large diameter is integrally provided on the screw head 31 at a screw shank 32 side. The screw flange portion 34 is a part of the screw head 31 and provides a seat portion 31a of the screw head 31.
As shown in part (b) of
As shown in part (c) of
The fastening object material 2 is a thin metal plate of steel or the like and is provided with a screw hole 21. The fastening material 1 is a thin metal plate of steel or the like, with which an upper surface thereof is called a front side Ba, and the opposite side is called a back side Bb. The fastening material 1 is provided with a wave shape (corrugated) burring 11 provided by drawing a part of the fastening material 1 from the front side Ba to the back side Bb into a burring height h by a burring process.
In this specific example, the fastening material 1 is a thin electrolytic zinc-coated steel plate (JIS SECC-SD) provided by plating of an ordinary rolled steel plate (cold-rolled steel plate (JIS SPCC)). Or, it may be a so-called high-tension material (JIS G3134, JIS3135 SPFH, SPFC, or CA steel available from HTSS JFE, Japan). The plate thickness thereof is 0.4 mm, and it is not less than 0.3 mm and less than 0.8 mm approximately, when a M3 screw (metric coarse screw) is used.
A versatile steel plate ordinarily available in the market can be selected with increment of 0.1 mm (SPCC), and in the case of electrolytic zinc-coated steel plate, a next thickness above 0.6 mm is 0.8 mm. The present invention is applicable to high formability stainless steel, brass, aluminum or the like.
In the case of 0.8 mm of the plate thickness (t), it is possible to form the female screw by M3 tapping process (JIS/ISO metric coarse screw) using an ordinary burring process. Therefore, with the M3 screw, the practical range is 0.3 mm-0.6 mm of the plate thickness (t).
However, as will be described hereinafter, the wave shape burring 11 of the present invention is a means for providing a high screw fastening strength using a thin metal plate, and therefore, it is not limited to M3 but applicable to a meter fine pitch screw, small precision screw such as M1 screw to a large screw such as M4, M5 or the like.
In this embodiment, the fastening material 1 has a thickness 0.4 mm and is provided with a wave shape burring 11 for M3 size, and the fastening object material 2 (plate member) is provided with a screw hole 21 at a central portion in alignment with the wave shape burring 11. The screw 3 is a M3 RS tight (tradename) available from Nitto Seiko Kabushiki Kaisha, Japan, which is a hexagonal cross-recessed metric coarse tapping screw with a flange.
The wave shape burring 11 of the fastening material 1 will be described in detail.
As shown in part (a) of
When fastened, a side of the screw head 31 which contacts the fastening object material 2 is provided with the dish-like screw flange portion 34, and the flange contact portion 2a (diametrically outermost portion) contacts the fastening object material 2. Thus, the fastening object material 2 is fastened to the fastening material flat surface portion 1a by the screw 3. Therefore, the contact portion is farther from the center than a normal screw case by the projection size of the screw flange portion 34, and therefore, the screw is less loosened, that is, the required loosening torque is higher.
A self-tapping formation portion of the screw shank 32 of the screw 3 (tapping screw) is threaded into the wave shape burring 11 portion by rotation, by which a female screw is formed in the inside circumference 11c of the wave shape burring 11, and the screw 3 is fastened to complete the fastening.
Referring to
In
In this embodiment, the plate thickness (t) of the fastening material 1 is 0.4 mm, and an inner diameter (d11) of the cylindrical portion is 2.459 mm which is a prepared hole diameter of a cut tapping or a rolling tap of metric coarse screw M3, or is 2.78 mm which is a prepared hole diameter of a self-tapping screw. The thickness (h11) of the thickened portion which is a one half of a difference between the inside diameters (d11) and the outside diameter of the wave shape burring 11 is 0.8 mm. It is the same as the plate thickness of 0.8 mm which is a normal process limit of burring for M3 screw. Therefore, if 0.8 mm thickness is accomplished by the thickening, a fastening force of torque 1.4N·m which is 70% of a screw rupture torque 2N·m can be provided.
Normally, the fastening force of the screw is approx. 70% of the rupture torque. In the case of the burring process for a metric coarse screw M3 and plate thickness 0.8 mm, a prepared hole diameter (d11) of the burring is 0.9 mm, and therefore, a burring height (h) is 1.4 mm including the plate thickness (t) because of constancy of volume (part (c) of
In this embodiment, the plate thickness is 0.4 mm, and the prepared hole diameter (d11) of the burring 0.8 mm. Under these conditions, the wave shape burring 11 has been formed, by which the burring height (h) including the plate thickness was 1.6 mm. By doing so, the screw engagement amount of three leads could be provided. In addition, since an engaging lead of the screw is long, the torque in the fastened state can be dispersed, with the result of less damage to the burring and reduction of wearing in the case of repeated threading.
On the other hand, in the case of the burring for providing a proper fastening force of a M3 metric coarse tapping screw to a thin plate material of 0.4 mm thickness (t) of the fastening material 1 of metal material such as electrolytic zinc-coated steel plate or the like, a female screw hole 12 is formed in an inner surface 11c of a cylindrical of the wave shape burring 11 by tapping process or by tapping screw (screw 3).
This embodiment, the thickness (t) of the thin plate material (fastening material 1) is 0.4 mm, and a pitch of the metric coarse screw is 0.5 mm in the range of approx. 20%.
In the case of the thickness (t) of 0.3 mm, the applicability ranges from meter fine pitch screw M1 (screw pitch 0.2 mm) to M3 (screw pitch 0.35 mm), and metric coarse screw M1 (screw pitch 0.25 mm) to M3 (pitch 0.45 mm).
Similarly, in the case of metric coarse screw M4, the screw pitch is 0.7 mm, and therefore, the applicable plate thickness (t) ranges from M2 (screw pitch 0.4 mm) to M6 (screw pitch 1 mm). The present invention is applicable to a thickness smaller than the height of thread which is a pitch substantially equivalent to the different between the bottom and crest of the screw. Therefore, the applicability ranges between approx. ±40% of the pitch.
Reference
Parts (a) and (b) of
Parts (a) and (b) of
The first step to the fastening material flat surface portion 1a is a deep drawing process, in which the deep drawing is effected into a semi-spherical shape to form a spherical portion which is convex (recessed) toward the back side Bb from the front side Ba of the fastening material flat surface portion 1a. The second step is piercing and radial bead forming process, in which a through-hole 12 which is going to be a screw hole is formed at the central portion of the drawn spherical portion 1b. In addition, drawn beads 11′a expanding radially and outwardly from the central portion are formed. The third step is a gathering and thickening step, in which the spherical drawn portion 1b of the back side Bb is gathered toward the center of the through-hole 12 as indicated by arrows C in part (b) of
In the first step, the fastening material 1 of the thin steel plate which is difficult to machine in the flat state is formed into a convex (recessed) toward the back side Bb, by which the fastening material 1 becomes easy for plastic deformation, and in addition, the beads 11′a can be formed.
In the third step, the spherical portion 1b is squeezingly gathered in the directions indicated by arrows C in part (b) of
However, the increase of the strokes leads to increase of the number of metal molds, and therefore, the number of the strokes may be as small as possible as long as the height h11 of the waveform, that is the thickness of the wave shape burring can assure the necessary thickness.
The bead shape is not limited to those having channel like cross sections, but may be semicircle U-like configuration (part (d) of
In the fourth step, if the inner diameter portions of the screw hole 12 are not even, the engagement amount of the screw substantially decreases with the result of reduction of the screw ridge rupture torque. Therefore, it is preferable to insert a shaft having a desired prepare hole diameter (d11) into the hole and the burring is pressed from the outside to the shaft. Or, in order to enhance the circularity or cylindricity of the inside circumference, the pressing is effected so as to form the burring with a slightly smaller diameter, and then a finishing step such as a broach machining, shaving or the like may be carried out.
It is determined depending on the actual use, as to whether the ridges are formed by a rolling tap or a tapping screw is used. Particularly, in the case of screw fastening of a printed board with which an electrical conductivity is required, a tapping using a rolling tap may be used, since then an assured torque management is possible so that the contact pressure for the electrical contact is assured.
Furthermore, after the press work, it is preferable that cleaning or the like is effected to remove chips and/or oil so as to avoid the cut chips resulting from the self-tapping of the tapping screw or the like falling to the electroconductive portion.
As described above, the cylindrical portion thickened by the wave-like (folded) shape burring can be provided.
Reference
In this embodiment, in addition to the wave shape burring 11, the fastening material 1 of the thin plate material is provided with radially outwardly extending beads 4 which are disposed concentrically about the center of the female screw hole 12 by pressing.
Parts (a), (b) and (c), of
Above-described in the foregoing with Embodiment 1, the wave shaped cylindrical burring 11 provides the effective thickness (h11) of 0.8 mm for a plate thickness (t) of 0.4 mm, and therefore, the fastening strength is improved. Here, in order to meet more the improved strength, the strength of the fastening material flat surface portion 1a is enhanced by the provision of the radial drawn beads 4. It makes the plate thickness correspond to 0.8 mm, and therefore, the screw fastening reinforcement with good balance can be provided.
As shown in part (c) of
The first step is a spherical drawing process, in which a spherical portion 1b convex to the back side Bb from the front side Ba of the fastening material flat surface portion 1a is formed. The second step is a piercing and radial bead forming step in which the beads 11′ for the wave shape burring 11 is formed. The third step is a drawing and gathering step (thickening) of forming a wave-like shaped burring. The fourth step is a flattening and tapping process (if necessary) step, and similarly to Embodiment 1, the wave shape burring 11 is formed.
In this embodiment, a fifth step is used for the bead forming process. More particularly, the radial drawn beads 4 concave (recessed) toward a downstream side in the screw inserting direction are provided around the wave shape burring 11.
In this embodiment, they equally divide the circumference into 10, but the number is not limiting, and may equally divide into 3, 4 or the like. The beads 4 are arranged circularly, but may be arranged triangularly, rectangularly, polygonaly or into another shape having an arc. The radial drawn beads 4 are effective to enhance the strength in the fastening portion structure 90 of the fastening material 1, and the jack-up deformation upon screw fastening is reduced.
Referring to
This embodiment is different from the foregoing embodiments in that the above-described additional radial drawn beads 41 of Embodiment 2 is continuous and integral with the projections of the wave shape burring 11.
As shown in
As shown in
The first step is a deep drawing step for the fastening material flat surface portion 1a, in which a spherical portion 1b convex from the front side Ba to the back side Bb of the fastening material flat surface portion 1a is formed. The second step is piercing and radial bead forming process, in which a through-hole 12 which is going to be a screw hole is formed at the central portion of the drawn spherical portion 1b. In addition, beads 11′a extending radially from the center are formed. The drawn beads 11′a formed at this time are longer than those in Embodiments 1 and 2. The third step is a gathering and thickening step, in which the spherical portion is gathered toward the center into a cylindrical shape 11′b, while forming the radial beads 11′a. The beads 11′a do not entirely form into the cylindrical shape 11′b but partly remains as parts of the bead 11′a. The fourth step is a flattening and tapping process step, in which the spherical portion 1b is flattened by pressing to be flush with the original fastening material flat surface portion 1a to provide the radial beads 41 continuous with the wave shape burring 11.
Referring to
This embodiment is different from Embodiments 2 and 3 in that the radial drawn beads 4 concentrically with the wave shape burring 11 have configurations expanding toward outside in the fastening material flat surface portion 1a of the fastening material 1 (substantially sector-shaped).
Parts (a), (b) and (c) of
A flange contact portion 2a where the strength decreases by the screw fastening as the distance from the wave shape burring 11 increases, is reinforced, so that the deformation of the thin plate fastening material 1 by the screw fastening force is reduced. Simultaneously, upon the spherical drawing of the first step in the pressing step, the sector-shape portion can push the material so that it gathers in the central portion, and therefore, the thinning of the central portion of the fastening material 1 can be suppressed.
According to the present invention, a thin metal plate material is subjected to the burring process so that the screw fastening can be effected with a high fastening torque.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments.The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims priority from Japanese Patent Application No. 052547/2013 filed Mar. 14, 2013 which is hereby incorporated by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013-052547 | Mar 2013 | JP | national |
