JP4136169B2 - Manufacturing method of airbag cover - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing an airbag cover in which a method for forming a portion to be broken is improved.
[0002]
[Prior art]
An air bag is inflated by a large amount of inert gas generated by an inflator that is activated by an activation device that detects a collision or the like, and between an occupant and a part of the vehicle interior, such as an instrument panel or a steering wheel. It develops and prevents or reduces injuries to the occupant due to the so-called secondary collision in which the occupant collides with the vehicle compartment at the time of collision.
[0003]
The airbag before activation is folded and covered with a resin cover body, and is attached to the indoor part. The cover body covering such an airbag is in harmony with the surroundings as part of the interior of the vehicle. Are arranged. That is, for example, injection molding is performed using a resin material that has a color tone and luster close to the skin of an instrument panel and a mold that transfers a texture such as leather tone.
[0004]
The covering portion in which the opening for inflating the airbag of the airbag cover is formed has a predetermined thickness, and a flat, substantially H-shaped or U-shaped groove portion is provided there, for example, and the opening can be opened by breaking from this groove portion. However, the gloss on the surface side of the covering part provided with the groove part of the airbag cover in order to make a deep groove that becomes sharply thin with respect to the overall thickness of the covering part so that it can be cut and opened at the groove part. Has a problem that it is different from the peripheral portion. That is, when injection molding the airbag cover, the flow cross-section of the resin rapidly decreases at the thin wall portion, which is the bottom of the deep groove, the flow velocity increases, shearing heat is generated, the resin pressure is not applied, and the wall thickness rapidly decreases. For this reason, a minute recess called so-called sink or gloss unevenness occurs 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 depth of the deep groove portion is set to be less than 0.8 mm, and the width of the deep groove portion is also about several mm. Only it is. Therefore, even if the mold surface is uniformly textured so as to visually conceal minute defects on the surface, there is a difference in gloss 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 for improving the appearance, a special elastomer resin that hardly causes 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 problems are addressed without painting. There is also a method. However, applying such a very special material and a molding machine capable of processing the material so as to have a suitable appearance and ensuring extremely limited processing conditions lead to an increase in product cost.
[0005]
Thus, while there is a method of forming the conventional airbag cover so as to obtain the final shape of the fractured part at the time of molding, there is also a method of processing the fractured part after molding. For example, Japanese Patent Application Laid-Open No. 6-218811 discloses a technique for applying a pressing member to which an ultrasonic vibration is applied to the skin to melt the skin to form a groove.
[0006]
[Problems to be solved by the invention]
However, since the method using the ultrasonic wave involves melting of the resin by heating, the influence on the gloss of the surface is unavoidable. Therefore, in order to maintain the fracture reliability, the appearance of the surface is improved. Naturally, there are limits.
[0007]
The object of the present invention is to solve the problem of the appearance on the surface side due to the formation of the thin part (broken part) of the airbag cover by a simple method without requiring painting or using a special resin. There is.
[0008]
[Means for Solving the Problems]
As a result of intensive studies, the present inventor has found that it is effective to form by engraving the breaking groove of the airbag cover, and has reached the present invention.
[0009]
That is, the present invention
(1) Air in which a weak portion is formed on the inner surface of the covering portion of the resin-made airbag cover that is broken by inflation of the airbag to a thickness (t ₁ ) smaller than the overall thickness dimension (t ₀ ) of the covering portion. In the bag cover manufacturing method, after engraving the weak part into a groove shape, the boundary part between the engraved part and its peripheral part is heated so as to melt the resin forming the airbag cover, and the bottom part of the groove at that time A method for manufacturing an airbag cover, comprising: forming a boundary portion so that heating is not applied to the case .
( 2) The groove-shaped weak part is formed in advance to a thickness dimension (t _m ) smaller than the overall thickness dimension of the covering part, and then further to a predetermined thickness dimension (t ₁ ) using an engraving blade. The manufacturing method of the airbag cover as described in said (1) to engrave.
( 3) The method for manufacturing an airbag cover according to (2), wherein the preformed thickness dimension (t _m ) is equal to or more than 1/3 of the overall thickness (t ₀ ) of the covering portion.
( 4) The covering portion is previously formed with a protrusion along the weak portion having a groove shape, and forms a weak portion having an inclined surface inclined in the depth direction of the weak portion from the protrusion. Manufacturing method of airbag cover.
[0010]
In the method for manufacturing an airbag cover of the present invention, a method of forming a weak portion that is a groove-like fracture planned portion provided on the inner surface side of the covering portion is important, and other matters are not particularly limited. For example, the airbag cover of the present invention is molded in advance by injection molding. And it forms by engraving a groove-shaped weak part in the predetermined position of the inner surface side of the coating | coated part.
[0011]
In the engraving, it is preferable to form a predetermined groove using an engraving blade, preferably a rotary blade. Since the grooves are formed by engraving instead of heating and melting, the surface side is not affected by heating, and there are no defects such as sink marks seen when forming grooves by injection molding. The appearance can be improved. In addition, the groove forming portion is formed in advance as a thin portion to some extent during the injection molding of the airbag cover, so that the next engraving amount can be reduced, the processing is easy, and the chips generated by the processing The resin can be used effectively. In the case where the thin portion is formed in advance, it is preferable to secure a thickness that does not cause defects during resin molding on the surface side of the covering portion, and the thickness of the thin portion is 1/3 of the total thickness of the covering portion. It is good to be the above.
[0012]
Further, when the groove-shaped weak part is formed by engraving, a fine burr-like or thin skin-like cutting burr may occur at the boundary part (the corner part of the groove) between the engraved part and its peripheral part. In that case, it is preferable to apply a heated trowel to the boundary portion to melt the rough surface and shape it smoothly. However, since heating is not applied to the bottom of the groove, it does not affect the appearance on the surface side of the covering portion on the opposite side. By shaping and smoothing the rough surface of the boundary portion, it is possible to prevent burrs from being scattered at the time of breakage.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an airbag cover according to an embodiment of the present invention will be described with reference to the drawings.
[0014]
1 is a single perspective view of the airbag cover 11, and FIG. 2 is a state in which the airbag cover 11 in the AA cross section of FIG. 1 is assembled to the airbag module 10 for the passenger on the passenger seat and attached to the instrument panel of the vehicle body. FIG.
[0015]
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 the bottom by welding a bracket 35, and the stud bolt 34 of the bracket 35 is attached to the steel of the instrument panel 1. It fixes to the attachment plate 3 of the made reinforcement 2 with the nut 4.
[0016]
A hook 21 a is provided on the peripheral edge of the retainer 21 on the opening side, and the airbag cover 11 is attached so as to hook the hook 21 a on the rectangular through hole 17 of the vertical wall 13. The hook 21 a is loosely engaged with the through-hole 17 and is positioned so as to close the opening 5 of the instrument panel 1, and a minute 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 engages with the edge of the opening 5 and the airbag cover 11 is positioned without being lifted or dropped from the outer surface of the instrument panel 1.
[0017]
The airbag cover 11 is injection-molded using an olefin-based elastomer resin (TPO). The airbag cover 11 has a substrate portion 12 that is cleaved by the pressure caused by the expansion of the airbag 22 to form a door 18. A texture 12a, which is a fine unevenness indicating only a portion, is uniformly engraved on the entire upper surface. Reference numeral 12b denotes a concave portion that is recessed by a minute step and carved with fine irregularities and characters having a pattern different from that of the texture 12a. Except for the recessed portion 12b, the substrate portion 12 of the airbag cover 11 has an overall flat shape with only the embossed portion 12a as an appearance, and a tear line 30 that is a substantially U-shaped recessed groove on the inner surface is provided on the inner surface.
[0018]
A method for forming the tear line 30 will be described with reference to FIGS. In FIG. 3, the inner surface is placed on the support die 51, and the clamp 52 is pressed from above to fix it so that it does not float, and the support die 51 is provided with a suction port 53 and connected to a vacuum pump (not shown) for adsorption. As a result, the airbag cover 11 can be held on the support mold 51 without a gap. The injection-molded airbag cover 11 is not provided with any thin portion. Therefore, it has a very uniform texture without any influence on the surface appearance due to the tear line. In general the thickness of the substrate 12 is t _0, those embodiments are 4.3 mm.
[0019]
Reference numeral 54 denotes a rotating chuck, which is controlled by a numerical control device (not shown) in a three-axis (X axis, Y axis, Z axis) direction by a milling machine (not shown) to the airbag cover 11 that is a workpiece. It is movable so as to draw a predetermined trajectory relatively up, down, left and right.
[0020]
A milling blade 56 is attached to the tip of the rotating chuck 54. Details of the milling blade 56 are shown in FIG. The blade 57 in this embodiment is one piece in the circumferential direction and has an inclination angle of 15 °. Further, since the cutting blade 57 with the inclination angle is longer than the depth of the tear line 30, a side wall forming a slope intersecting with the flat portion of the substrate portion 12 is formed. Even the minute height of the substrate portion 12 can be dealt with within the height range of the cutting blade 57.
[0021]
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 the first tear line portion 30a. A third tear line portion 30c that extends parallel to the tear line portion and starts from the terminal of the second tear line portion 30b, and a fourth tear line portion 30d that further extends from the terminal toward the first tear line portion, and is substantially bilaterally symmetric. A groove in the shape.
[0022]
The milling blade 56 is lowered to a position corresponding to the end portion 30e of one 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. Similarly, the thickness of the third tear line portion is 1.0 mm. Further, the direction is changed, and the second tear line portion 30b is carved so as to leave a thickness of 0.8 mm in the immediate vicinity of the inside of the vertical wall 14 in parallel with the vertical wall 14. The direction is changed in front of the vertical wall 13, and the first 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, the second, third, and fourth tear line portions 30b, 30c, and 30d are engraved in a single stroke so as to leave the wall thickness in the order, 30f is reached. These thicknesses correspond to t ₁ in FIG. 4, and the thickness t ₁ is slightly different at each portion because of the preferred tear line 30 breaking. Here, the engraving is finished and the milling blade 56 is raised. FIG. 5 shows a cross-sectional outline of the tear line 30 in a state where the engraving is finished. A thin burr-like or thin skin-like cutting burr 33 is formed at the corner portion (boundary portion with the peripheral portion) 32 of the groove of the tear line 30.
[0023]
Next, the corner portion 32 is chamfered by applying the pressing die 58. The pressing die 58 may be formed separately according to the shape of each tear line portion 30a to 30d, or the entire shape of the tear line 30 may be covered with one pressing die. Alternatively, as a pressing die having the minimum length of the tear line portion, for example, the length of the fourth tear line portion 30d, the die is pressed so as to be sequentially fed along the groove of the tear line 30, the corner portion 32 is melted, chamfered and cut. The burr 33 is welded or integrated. The pressing die 58 is made of a steel material. The pressing die 58 is put into a high-frequency heating device, which is an external heating device of a size that can accommodate the pressing die 58, heated to a predetermined temperature, and immediately applied to the tear line portion. The corner portion 32 is melted and shaped together with the burr 33.
[0024]
Preferably, in this state, the pressing mold 58 is rapidly cooled, that is, a passage through which a fluid flows is formed inside the pressing mold, and a low temperature water, oil, or other fluid is flowed to cool the pressing mold 58, and the temperature of the pressing mold 58 is adjusted. Then, the resin of the airbag cover 11 that contacts the pressing mold is solidified, and the pressing mold 58 is pulled away from the airbag cover 11. Thus, the corner portion 32 is shaped according to the shape of the pressing die.
[0025]
The pressing die may be an internal heating type (incorporating a bar heater or the like), or may generate heat on the contact surface by applying ultrasonic vibration.
[0026]
Further, the milling blade 56 may be a straight blade shape as described above, or may have a shape that can be engraved in advance to a shape close to the final shape, for example, a substantially S-shape following the pressing die 58 of FIG. .
[0027]
As shown in the cross section of FIG. 7, the height does not reach the bottom 31, so heat that affects the surface appearance is not given to the bottom 31. Therefore, the formed uniform surface appearance can be maintained.
[0028]
Another embodiment of the invention will be described with reference to FIG. The same parts as those in the above embodiment are denoted by the same reference numerals and the description thereof is omitted. The airbag cover 11 has a groove portion 40 formed integrally 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 mm. The general thickness t ₀ of the base plate portion of the airbag cover 11 is usually 4.0 mm inside and outside, and the thickness of the bottom 36 of the groove portion 40 is about 1/3, which is about 1.3 mm. The normal limit of t ₀ is 3.0 mm. Therefore, the thickness t _m in this case is 1.0 mm as a practical lower limit. By setting the thickness of the bottom 36, even if the thermoplastic elastomer resin, which normally required a coating finish in order to conceal sink marks and gloss unevenness appearing on the surface side of the groove during injection molding, gloss unevenness appears. Therefore, the milling blade 56, which can have an external appearance that does not require painting, has a smaller diameter than the width of the groove 40, and further engraves a groove on the bottom 36 of the groove 40 (FIG. 8II). The thickness t _{1 at} this time conforms to the dimensions of the above-described embodiment. The groove has a two-stage shape, and a cutting burr 33 is formed at the boundary portion 32 between the milling blade 56 and the bottom 36. Next, the cutting die 58 is applied to chamfer the cutting burrs 33 so as to be uniform, 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 gloss change occurs on the surface side. By forming the shallow groove portion 40 in advance in this way, the amount of cutting by the milling blade 56 can be reduced, so that processing is facilitated and the amount of resin that becomes chips can be reduced, so that the processing of chips can be performed. It is easy and the capacity of the suction system is small, or the maintenance of the suction system is small, leading to a reduction in cost as a whole.
[0029]
FIG. 10 shows a modified example of the substrate unit 12. For example, a bead 37 having a semicircular cross section is provided in advance at the engraving portion of the tear line 30 (FIG. 10I). Since the contact angle between the substrate portion 12 and the blade 57 of the milling blade 56 is close or coincides with the bead 37 and does not become an acute edge (FIG. 10 II), the cutting burr becomes minimal or does not come out. Is easy or does not require a shaping process. In addition, the board | substrate part 12 may be about 4.3 mm and the height of a bead about 0.5-0.8 mm, and there is no problem to the surface external appearance in injection molding. Since the bead 37 is formed smoothly along the periphery of the door 18, there is also an effect of reinforcing the door 18 and an effect of reducing a sliding contact resistance of the airbag 22. By using a means for detecting the bead 37, the airbag Individual differences of the cover 11 and minute variations in the set state on the support die 51 can also be easily detected. If processing is performed while detecting the bead 37, there will be fewer burrs and the finish of the tear line will be improved.
[0030]
In addition, the airbag cover 11 shown in FIG. 1 is U-shaped so that the cutting path of the milling blade 56 is drawn with one stroke, but it is of course applicable to various shapes such as an H-shape. . Furthermore, although the said Example demonstrated embodiment with a rotary blade, the 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 tip is directed in the moving direction of the blade. For such cutter blades, when engraving a groove to the desired depth, the engraving is performed in several steps, and the load applied to the blade and therefore the force applied to the workpiece (airbag cover) are appropriate. It is possible to be within a range.
[0031]
Furthermore, the corner portion can be formed by chamfering with a non-rotating cutter blade in addition to shaping by heating.
[0032]
The milling blade 56 rotates to generate frictional heat with the resin. For this reason, since it affects the cutting ability of the blade 57, the blade 57 is cooled to prevent the temperature from rising. The method using a liquid such as water or oil, which is commonly used for metal milling, needs to take into account the complexity of subsequent processes such as cleaning and removal of cutting waste. Therefore, for example, an air nozzle (not shown) is positioned near the tip of the blade 57 and blows air, or an air passage 59 is provided in the milling blade 56 as shown in FIG. The cutting waste can be removed from the groove 40 and the like by the cooling air.
[0033]
In addition to the cover for the passenger seat airbag module described above, it can be applied to a driver seat airbag module, etc. The shape of the tear line may be a U-shape in addition to a flat U-shape, and may be three-dimensional. It can be manufactured by applying a normal numerical control (NC) processing machine along the shape of the undulating coating.
[0034]
【The invention's effect】
As described above, the present invention uses a sculpture means that does not rely on heat melting of the resin to form a groove that is a broken part of an airbag cover, so that the surface side corresponding to the groove part has conventionally suffered sink marks and gloss. It can be prevented from appearing. For this reason, conventionally, in order to conceal the defects on the surface side, the required coating can be omitted.
[Brief description of the drawings]
FIG. 1 is a perspective view of an airbag cover of the present invention.
FIG. 2 is a cross-sectional explanatory view of FIG. 1A-A, showing a state where an airbag module is assembled.
FIG. 3 is an explanatory view of a method for forming a groove on the inner surface side of the airbag cover covering portion, and shows a state in which the airbag cover is held by the support die 51;
FIG. 4 is an explanatory view of the same as above and shows a state in which grooves are formed by engraving with a rotary blade.
FIG. 5 is an explanatory view of the same as above and shows a cross-sectional state of the formed groove.
FIG. 6 is an enlarged view of the tip of an example of a rotary blade.
FIG. 7 shows a state in which a corner portion (a boundary portion between an engraving portion and a peripheral portion) of a groove portion is chamfered by a hot pressing die (trowel).
FIG. 8 is a diagram for explaining another embodiment of the present invention and shows a case where the groove configuration position is thinned in advance.
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 for forming a weak part (groove) in the present invention, where I indicates a state in which a bead 37 is provided in advance in a portion to be engraved in a tear line. II shows a state where a weak part (groove) is formed by engraving with a rotary blade.

Claims (4)

An air bag cover having a thickness (t ₁ ) smaller than the overall thickness (t ₀ ) of the covering portion on the inner surface of the covering portion that is broken by inflation of the airbag. In the manufacturing method, after this weak part is engraved into a groove shape, the boundary part between the engraved part and its peripheral part is heated so as to melt the resin forming the airbag cover, and at that time, the bottom part of the groove is heated. A method for manufacturing an airbag cover, characterized by forming the boundary portion so as not to be applied . The groove-shaped weak portion is formed in advance to a thickness dimension (t _m ) smaller than the overall thickness dimension of the covering portion, and then engraved to a predetermined thickness dimension (t ₁ ) using an engraving blade. Item 2. A method for manufacturing an airbag cover according to Item 1. The method for manufacturing an airbag cover according to claim 2, wherein the thickness dimension (t _m ) formed in advance is not less than 1/3 of the total thickness (t ₀ ) of the covering portion.   2. The airbag cover according to claim 1, wherein a ridge along a weak portion having a groove shape is formed in the covering portion in advance, and a weak portion having an inclined surface inclined in the depth direction of the weak portion from the ridge is formed. Production method.

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