JP2000272451A - Manufacture of air bag cover - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of shrinkage and gloss at a surface side corresponding to a groove part by engraving a weak part to be broken into the shape of a groove formed on an inner surface side of a coating part, into the shape of a groove. SOLUTION: An air bag cover is provided with a groove part 40 integrally molded in advance. A thickness of a bottom 36 of the groove part 40 is 1/3 of a general thickness t0 of a base part of the air bag cover. By applying the thickness of the bottom 36, a milling blade 56 having a diameter smaller than a width of the groove part 40 is used for further engraving the groove on the bottom 36 of the groove part 40. The groove has two stages, and a cut burr 33 is formed on a boundary part 32 between the milling blade 56 and the bottom 36. Then a mold 58 is pressed for chamfering while levelling off the cut burr 3, and a side wall having the approximately S-shaped cross section is formed by shaping. On this occasion, since a point of the mold 58 does not reach a bottom part 31, the change of gloss is not generated at a surface side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an airbag cover with an improved method for forming a portion to be broken.

[0002]

2. Description of the Related Art An airbag is inflated by a large amount of inert gas generated by an inflator operated by a starting device which detects a collision or the like, so that an occupant and a part in a vehicle compartment, such as an instrument panel and a steering wheel, are inflated. This prevents or reduces injuries to the occupant due to a so-called secondary collision in which the occupant hits the interior of the vehicle during a collision.

[0003] Before activation, the airbag is folded and covered with a cover made of resin, and is attached to the above-mentioned room. The cover covering such an airbag serves as a part of the interior of a vehicle. Harmoniously arranged around. That is, for example, injection molding is performed using a resin material having a color tone and gloss close to the skin of the instrument panel and a mold for transferring grain such as leather.

The covering portion of the airbag cover, in which the opening for inflating the airbag is formed, has a predetermined thickness. For example, a substantially H-shaped or U-shaped groove portion is provided in the cover portion, and the groove portion is cut from the groove portion. The surface of the covering part where the groove of the airbag cover is provided so that the opening is made, but in order to make the opening cut by the groove part and to make the opening sharply thin with respect to the thickness of the whole covering part There is a problem that the gloss on the side is different from the peripheral edge. That is, when the airbag cover is injection-molded, the flow cross section of the resin rapidly decreases at the thin portion at the bottom of the deep groove, the flow velocity increases, and shear heat is generated,
Since the resin pressure is not applied and the thickness rapidly decreases, minute recesses called so-called sink marks or gloss unevenness occur on the surface due to a difference in resin shrinkage after molding. In a normal airbag cover, the normal thickness of the covering portion is about 4 mm, whereas the deep groove portion is dimensioned so that the thickness is less than 0.8 mm, and the width of the deep groove portion is also about several mm. It is only.
For this reason, even if the mold surface is uniformly embossed in order to visually hide minute defects on the surface, a difference in gloss appears on the product surface. Therefore, the appearance is improved by painting the airbag cover, but this method increases the manufacturing cost. In addition, as another method of improving the appearance, a special elastomer resin that does not easily produce a difference in gloss between the thin portion and the peripheral portion under the above conditions is used under specific molding conditions, and the above problem is solved without painting. There are ways. However, applying such a very special material and a molding machine capable of processing the material to have a suitable appearance and securing extremely limited processing conditions leads to an increase in product cost.

As described above, there is a method of forming the conventional airbag cover so as to obtain the final shape of the broken portion at the time of molding, but there is also a method of processing the formed portion after forming the broken portion. For example, Japanese Patent Application Laid-Open No. 6-218811 discloses a technique in which a pressing member having ultrasonic vibration applied to a skin is applied to melt the skin and form a groove.

[0006]

However, the method using the ultrasonic wave involves melting of the resin by heating, so that the influence on the gloss of the surface cannot be avoided.
There is naturally a limit to maintaining good fracture appearance to maintain fracture certainty.

SUMMARY OF THE INVENTION An object of the present invention is to solve the problem of appearance on the front side due to the formation of a thin portion (a broken portion) of an airbag cover by using a simple method without requiring painting and using a special resin. To solve the problem.

[0008]

As a result of intensive studies, the present inventor has found that it is effective to form the airbag cover by engraving the breakable groove, and has accomplished the present invention.

That is, according to the present invention, there is provided (1) a thickness dimension (t ₀ ) of the entirety of the covering portion of the resin airbag cover, in which a weak portion is formed on the inner surface of the covering portion which is broken by the inflation of the airbag.
A method of manufacturing an airbag cover having a smaller thickness dimension (t ₁ ), wherein the weak portion is formed by engraving the groove into a groove shape; After engraving the airbag cover, the boundary between the engraved portion and the peripheral edge is heated so as to melt the resin forming the airbag cover, and the boundary is shaped to form the boundary. manufacturing method, (3) a groove-like weak portion is formed in advance as a whole smaller thickness than the thickness of the covering portion (t _m), a predetermined thickness (t _l) with then further engraving blade a method of manufacturing the airbag cover (1) or (2) wherein the engraving so, (4) the thickness to be preformed (t _m) thickness (t ₀₎ of the whole of the covering part 1 3. The airbag according to (3), wherein (5) The covering portion is formed in advance with a ridge along the groove-shaped weak portion, and forms the weak portion having an inclined surface inclined from the ridge in the depth direction of the weak portion. 1) A method for manufacturing an airbag cover according to 1).

In the method for manufacturing an airbag cover of the present invention, it is important to form a weak portion which is a groove-shaped portion to be broken provided on the inner surface side of the covering portion, and other matters are particularly limited. is not. For example, the airbag cover of the present invention is formed in advance by injection molding. The groove is formed by engraving a groove-shaped weak portion at a predetermined position on the inner surface side of the covering portion.

In the engraving, it is preferable to form a predetermined groove using an engraving blade, preferably a rotary blade. Since the groove is formed by engraving without heating and melting, the surface side is not affected by heating, and there is no defect such as sink mark that occurs when forming the groove by injection molding, so it looks good Good appearance. In addition, when the airbag cover is injection-molded in the groove forming portion as a thin portion to some extent, it is possible to reduce the amount of engraving to be performed next. And the resin can be used effectively. In the case where the thin portion is formed in advance, it is preferable to secure a thickness such that a defect does not appear during resin molding on the surface side of the coating portion. The thickness of the thin portion is set to 1/3 of the total thickness of the coating portion. It is better to do the above.

Also, when forming a groove-shaped weak portion by engraving, a boundary portion (corner portion of the groove) between the engraved portion and its peripheral edge portion.
In some cases, fine bristles or skin-like cutting burrs may occur. In that case, it is preferable to apply a heated trowel to the boundary to melt the rough surface and to shape it smoothly. However, since the heating is not applied to the bottom of the groove, it has no effect on the appearance of the front side of the coating, which is the opposite side. By shaping and smoothing the rough surface of the boundary portion, it is possible to prevent burrs from scattering at the time of breaking.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An airbag cover according to one embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view of the airbag cover 11 alone, and FIG. 2 is a perspective view of the airbag module 11 for an occupant in the passenger seat, taken along the line AA in FIG. It is sectional drawing which shows the attached state.

The airbag module 10 includes an airbag cover 11, a retainer 21, an airbag 22, an inflator 23, and the like. The retainer 21 is attached to a bottom portion by welding a bracket 35, and a stud bolt 34 of the bracket 35 is attached to an instrument panel. 1 is fixed to a mounting plate 3 of a steel reinforcement 2 with a nut 4.

A hook 21a is provided on the opening side of the retainer 21. The airbag cover 11 is attached to the rectangular through hole 17 of the vertical wall 13 so as to hook the hook 21a. The hook 21 a is loosely engaged with the through hole 17, is positioned so as to close the opening 5 of the instrument panel 1, and has a small individual difference in the distance between the reinforcement 2 and the outer surface of the instrument panel 1 ( (Variation) can be absorbed. That is, the claw 16 is engaged with the edge of the opening 5, and the airbag cover 11 is positioned without rising or falling from the outer surface of the instrument panel 1.

The airbag cover 11 is formed by injection molding using an olefin-based elastomer resin (TPO).
There is a substrate portion 12 which is cleaved by the pressure due to the inflation of the airbag 22 to form the door 18. On the upper surface side, a grain 12a which is a fine unevenness showing only a part in FIG. 1 is uniformly carved on the entire upper surface. . Reference numeral 12b denotes a concave portion which is recessed by a minute step and has fine irregularities and characters in a pattern different from that of the grain 12a. Except for the concave portion 12b, the substrate portion 12 of the airbag cover 11 has a texture 12a
And a tear line 30 which is a substantially U-shaped concave groove on the inner surface.

The method of forming the tear line 30 is shown in FIGS.
It will be described based on. In FIG. 3, the support 52 is placed on the support mold 51 with the inner surface facing upward, and the clamp 52 is pressed from above to fix the clamp so as not to float. The support mold 51 is provided with a suction port 53 and connected to a vacuum pump (not shown) for suction.
As a result, the airbag cover 11 is supported without any gaps.
Can be held. The injection-molded airbag cover 11 has no thin portion. Therefore, it has a very uniform texture without any influence on the surface appearance due to the tear line. The general thickness of the substrate portion 12 is t ₀ , and that of the embodiment is 4.3 mm.

Numeral 54 denotes a rotary chuck, which is controlled by a numerical controller (not shown) in three axes (X-axis, Y-axis, Z-axis) by a milling machine (not shown), and is an airbag cover 11 to be processed. It is movable so as to draw a predetermined trajectory vertically and horizontally relative to.

The tip of the rotary chuck 54 has a milling blade 5
6 is attached. FIG. 6 shows the details of the milling blade 56.
Shown in In this embodiment, the number of the blades 57 is one in the circumferential direction, and the blade 57 has a tilt angle of 15 °. Further, since the cutting blade 57 with the inclined angle is longer than the depth of the tear line 30, it forms a side wall that forms an inclined surface that intersects the plane portion of the substrate portion 12. Even if the thickness of the substrate portion 12 is very small, the cutting blade 5
7 height range.

As shown in FIG. 1, the tear line 30 includes a first tear line portion 30a extending in the left-right direction of the airbag cover 11, a second tear line portion 30b extending forward from a terminal of the first tear line portion 30a, and A third tear line portion 30c extending parallel to the first tear line portion and starting at a terminal of the second tear line portion 30b; and a fourth tear line portion 30d extending further from the terminal toward the first tear line portion, It is a substantially symmetrical groove.

The milling blade 56 is lowered to a position corresponding to the end portion 30e of the fourth tear line portion 30d, and engraving is started. The fourth tear line portion is carved so as to leave a thickness of 1.0 mm. Then change the direction and carve the third tear line. The thickness of the third tear line portion is also 1.0 mm. The direction is further changed, and the second tear line portion 30b is carved so as to leave a thickness of 0.8 mm immediately inside the vertical wall 14 in parallel with the vertical wall 14. Change direction before the vertical wall 13 and
The tear line portion 30d is carved so as to leave a thickness of 0.5 mm. Change the direction in front of the vertical wall 14, and in the reverse order to the above,
Second, third, fourth tear line portions 30b, 30c, 30d
, In a single stroke so as to leave the above-mentioned thickness, and reach the terminal end 30f. These thicknesses are represented by t in FIG.
₁ , and the thickness t ₁ is slightly different at each part due to breakage of the tear line 30. Here, the engraving is completed, and the milling blade 56 is raised. FIG. 5 shows an outline of the cross section of the tear line 30 after the engraving. Fine hairs or thin skin-like cutting burrs 33 are formed at the corners (boundaries with the periphery) 32 of the grooves of the tear line 30.

Next, the pressing die 58 is applied to the corner 3
Perform chamfering 2. The pressing mold 58 is connected to each tear line portion 30a.
Each of them may be formed separately according to the shape of the tear line 30 to 30d, or the entire shape of the tear line 30 may be covered by one pressing die. Alternatively, the minimum length tear line,
For example, a pressing die having a length of the fourth tear line portion 30d is pressed so as to be fed forward along the groove of the tear line 30, the corner portion 32 is melted, chamfered, and the cutting burr 33 is welded or integrated. The pressing die 58 is made of a steel material. The pressing die 58 is placed in a high-frequency heating device, which is an external heating device large enough to accommodate the pressing die 58, and is heated to a predetermined temperature, and is immediately applied to the tear line portion. Corner 32
Is melted and shaped together with the burr 33.

Preferably, in this state, the pressing die 58 is rapidly cooled, that is, a passage for flowing a fluid is formed inside the pressing die, and a fluid such as low-temperature water or oil is allowed to flow therethrough for cooling. Is lowered, the resin of the airbag cover 11 that contacts the stamp is solidified, and the stamp 58 is separated from the airbag cover 11. Thus, the corner portion 32 is shaped according to the shape of the pressing die.

The pressing die may be an internal heating type (with a built-in bar heater or the like), or may generate ultrasonic heat to generate heat at the contact surface.

The milling blade 56 may have a straight blade shape as described above, or a shape that can be engraved in advance to a shape close to the final shape. You may.

As shown in the cross section of FIG. 7, since the height does not reach the bottom 31, heat that affects the surface appearance is not applied to the bottom 31. Therefore, the formed uniform surface appearance can be maintained.

Another embodiment of the present invention will be described with reference to FIG. The same parts as those in the above-described embodiment are denoted by the same reference numerals, and description thereof is omitted. The airbag cover 11 has a groove 40 integrally formed in advance (FIG. 8I). The thickness t ₀ of the substrate portion 12 of the airbag cover 11 is 4.3 _mm , and the thickness t _m is 2.0 m.
m. General thickness t of the substrate portion of the airbag cover 11
₀ is usually 4.0 mm inside and outside, and the thickness of the bottom 36 of the groove 40 is about 1/3 thereof, ie, about 1.3 mm, which is a preferable dimension. The normal limit of t ₀ is 3.0 mm, and therefore, the practical lower limit of the thickness t _m in this case is 1.0 mm. By setting the thickness of the bottom 36, uneven gloss is produced even with a thermoplastic elastomer resin which usually requires a coating finish to conceal sink marks and uneven gloss appearing on the surface side of the groove during injection molding. Since the milling blade 56 has a smaller diameter than the width of the groove 40, the milling blade 56 can have an appearance that does not require painting.
A groove is further engraved on the bottom 36 of FIG. The thickness t _{1 at} this time conforms to the dimensions of the above embodiment. The groove has a two-step shape, and a cutting burr 33 is formed at the boundary 32 between the milling blade 56 and the bottom 36. Next, the pressing dies 58 are applied to the cutting burrs 33.
Are chamfered so as to smooth out, and are shaped into side walls having a substantially S-shaped cross section (FIG. 8III). At this time, since the tip of the pressing die 58 does not reach the bottom 31, no change in gloss occurs on the front surface side. By forming the shallow groove portion 40 in advance in this manner, the amount of cutting by the milling blade 56 can be reduced, so that machining is facilitated and the amount of resin that becomes chips can be reduced. It is easy and requires little or no effort to maintain the suction system, leading to overall cost savings.

FIG. 10 shows a modification of the substrate section 12. For example, a bead 37 having a semicircular cross section is provided in advance at the engraved portion of the tear line 30 (FIG. 10I). With bead 37,
The contact angle between the substrate portion 12 and the blade 57 of the milling blade 56 becomes closer or coincides with each other, and does not become a sharp edge (FIG. 10).
II) Since shaving burrs are minimized or eliminated, the shaping step is easy or no shaping step is required. In addition, the board | substrate part 12 may be 4.3 mm and the height of a bead may be about 0.5-0.8 mm, and there is no problem in the surface appearance in injection molding. Since the bead 37 is formed smoothly along the periphery of the door 18, the bead 37 has an effect of reinforcing the door 18 and an effect of reducing the sliding contact resistance of the airbag 22. It is also possible to easily detect individual differences in the cover 11 and minute variations in the set state of the cover 11 on the support die 51. If processing is performed while detecting the bead 37, the burr is further reduced and the finish of the tear line is improved.

The airbag cover 11 shown in FIG.
Is U-shaped so that the cut path of the milling blade 56 is drawn in one stroke, but it is needless to say that the cutting path can be applied to various shapes such as H-shaped. Further, in the above embodiment, the embodiment using the rotary blade has been described, but a non-rotating cutter blade for cutting out a normal resin material can also be used. In such a cutter blade, the tear line 30 can be formed by performing control such that the blade edge is directed in the direction of travel of the blade. In the case of such a cutter blade, when carving a groove to the desired depth, a predetermined engraving is performed several times, and the load applied to the blade and, accordingly, the force applied to the work (airbag cover) is properly adjusted. It is possible to set it as a range.

Further, besides shaping by heating, the corner portion can be chamfered by a non-rotating cutter blade.

The milling blade 56 rotates to generate frictional heat with the resin. For this reason, since the cutting ability of the blade 57 is affected, cooling is performed so as to prevent the temperature of the blade 57 from rising. In a method using a liquid such as water or oil commonly used for metal milling, it is necessary to consider the complexity of the subsequent steps such as cleaning and removal of cutting chips. Therefore, for example, an air nozzle (not shown) is positioned near the tip of the blade 57, and air is blown,
Alternatively, as shown in FIG. 9, an air passage 59 is provided in the milling blade 56, and air is blown toward the blade 57. With this cooling air, the cuttings are again
0 and so on.

In addition to the above-described cover for the passenger seat airbag module, the present invention can also be applied to a driver seat airbag module and the like, and the shape of the tear line may be a flat U-shape or an H-shape. Further, it can be manufactured by applying a normal numerical control (NC) processing machine along the three-dimensionally undulating covering portion shape.

[0034]

As described above, the present invention utilizes the engraving means which does not rely on the heating and melting of the resin in forming the groove which is the breakage portion of the airbag cover. The appearance of sink marks and gloss on the surface can be prevented. For this reason, conventionally, the required coating can be omitted in order to conceal the defects on the surface side.

[Brief description of the drawings]

FIG. 1 is a perspective view of an airbag cover of the present invention.

FIG. 2 is an explanatory sectional view of FIG. 1A-A, showing a state where an airbag module is assembled.

FIG. 3 is an explanatory view of a method of forming a groove on an inner surface side of an airbag cover covering portion, and shows a state in which the airbag cover is held by a support die 51;

FIG. 4 is an explanatory view of the same, showing a state where a groove is formed by engraving with a rotary blade.

FIG. 5 is an explanatory view showing the state of the cross section of the formed groove.

FIG. 6 is an enlarged explanatory view of a tip of an example of a rotary blade.

FIG. 7 shows the corners of the groove (the boundary between the engraving and the periphery).
Shows a state in which the surface is shaped by a heating press die (trowel).

FIG. 8 is a view for explaining another embodiment of the present invention, and shows a case where a groove forming position is previously thinned.

FIG. 9 is a perspective view showing an example of a rotary blade used in the present invention.

FIG. 10 is an explanatory view of another embodiment in which a weak portion (groove) is formed in the present invention, and I shows a state in which a bead 37 is provided in advance at a place where a tear line is to be engraved. II shows a state where a weak portion (groove) is formed by engraving with a rotary blade.

Claims (5)

[Claims] An airbag cover made of resin has a thickness (t ₁ ) smaller than the overall thickness (t ₀ ) of the coating on the inner surface of the coating which is broken by the inflation of the airbag. A method for manufacturing an airbag cover, wherein the weak portion is formed by engraving a groove. 2. The method according to claim 1, wherein after engraving in a groove shape, the boundary between the engraved portion and the peripheral portion is heated so as to melt the resin forming the airbag cover, and the boundary is shaped. A method for manufacturing the airbag cover according to the above. 3. The groove-shaped weak portion is formed in advance into a thickness (t _m ) smaller than the overall thickness of the covering portion, and then further becomes a predetermined thickness (t _l ) by using an engraving blade. The method for manufacturing an airbag cover according to claim 1 or 2, wherein the engraving is performed. 4. The method for manufacturing an airbag cover according to claim 3, wherein the thickness dimension (t _m ) formed in advance is at least １ ／ of the thickness (t ₀ ) of the entire covering portion. 5. The coating portion according to claim 1, wherein a ridge is formed in advance along the groove-shaped weak portion, and the weak portion has an inclined surface inclined in a depth direction of the weak portion from the ridge. Method of manufacturing airbag cover.