JPH1076559A - Method for molding plastic article with channel for breaking - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture an air bag cover wherein a channel part for breaking is formed on the back face without generating fluctuation on the surface and with good appearance. SOLUTION: When a movable mold 12 is clamped to a fixed mold 11 of a mold 10, a core part 12b of the movable mold is slid to the fixed mold 11 in such a way that a cavity 13 is expanded more than the thickness of molding of an air bag cover. After a molten resin is filled under this condition, the core part 12b is slid so as to make the cavity 13 to the thickness of molding. The air bag cover as a plastic article is molded by a low pressure injection molding method like this.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steering apparatus equipped with an airbag for a motor vehicle, such as an airbag cover for covering a folded airbag or a column cover for covering a connecting portion of a steering shaft in the steering apparatus. In addition, the present invention relates to a method for molding a plastic article having a groove that is broken by impact.

[0002]

2. Description of the Related Art In a steering apparatus of an automobile equipped with an airbag, the airbag is disposed at a central portion of a steering wheel. Air bags are usually
It is folded and stored in the center of the steering wheel, and is covered by a plastic airbag cover. This airbag cover
Grooves are formed on the back surface of the peripheral portion and the central portion so that the air bag is easily broken when inflated by an impact applied to the vehicle. The portion thinned by the formed groove is broken by the impact of the inflation of the airbag, and the airbag that has protruded from the airbag cover is inflated.

Similarly, the connecting portion of the steering shaft in the steering device is covered with a plastic column cover, and a groove is also formed on the back surface of the column cover to reduce the thickness. Then, when an impact is applied to the steering shaft, the column cover is broken along the groove, the connecting portion of the steering shaft is released, and the steering shaft falls.

[0004]

Such an airbag cover or a column cover is usually formed integrally by injection molding. However, the thickness of the airbag cover or the column cover is about 3 mm, whereas the thickness is reduced to about 0.1 to 0.4 mm by a groove formed on the back surface. . For this reason, in normal injection molding, the molten resin filled in the cavity of the mold at a high pressure does not sufficiently flow into the thin portion forming the groove, and the resin is in a disturbed state, and the surface of the thin portion is disturbed. There may be unevenness or no gloss. Since the airbag cover and the like are arranged in the vicinity of the driver's seat and exposed to the driver's seat side, the defective appearance product needs to be painted again.

[0005] Further, a weld mark may be generated on the surface of the thin portion. When a weld mark is generated in the thin portion, the strength is weakened, and there is a possibility that the thin portion may be broken even if no impact is applied.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and an object of the present invention is to eliminate the possibility that unevenness or the like will occur on the outer surface of a portion thinned by a groove formed on the back surface, and It is an object of the present invention to provide a method for molding a plastic article having excellent breakability and having a groove for breakage capable of obtaining a predetermined strength in a thin portion.

[0007]

According to the method of molding a plastic article having a groove for breakage of the present invention, the groove for breakage is formed on the back surface to be thin, and the thin portion is broken by an impact. A method of molding a plastic article, wherein a predetermined cavity is formed by clamping a movable mold to a fixed mold, and a molding thickness of the molded plastic article is determined. Using a mold in which the core of the movable mold is slidable with respect to the fixed mold so that the cavity is in an expanded state, slide the core of the movable mold that has been clamped. After filling the molten resin with the cavity wider than the molded thickness of the plastic product, the plastic is pressed by a low-pressure injection molding method in which the core is slid so that the cavity has the molded thickness. Characterized by shaping the click article.

[0008]

Embodiments of the present invention will be described below in detail with reference to the drawings. The molding method of the present invention is applied to manufacture an airbag cover of a steering device equipped with an airbag in an automobile, or a column cover of a steering device. In the present embodiment, a method of molding an airbag cover will be described. I do.

The airbag is stored in a folded state in a storage portion provided at the center of the steering wheel, and is covered by an airbag cover. A groove is formed on the back surface of the airbag cover at a central portion or a peripheral portion, and a portion thinned by the groove is broken by an impact when the airbag is inflated. The airbag jumps out of the broken airbag cover and inflates.

[0010] The airbag cover is 3
In contrast to the thickness of about 0.1 mm, the thickness of the groove is reduced to about 0.1 to 0.4 mm.

In the present embodiment, such an airbag cover is manufactured by molding a molten thermoplastic molding material by a low-pressure injection molding method. FIG. 1 is a cross-sectional view illustrating an example of a mold used in the present embodiment. The mold 10 has a fixed mold 11 and a movable mold 12, and the fixed mold 11 is provided with a concave portion 11a having an inner surface corresponding to the surface of the airbag cover.

The movable mold 12 is provided with a recess 11 of the fixed mold 11.
a, a convex portion 12a is provided to fit into the fixed mold 11, and the movable mold 12 is clamped with respect to the fixed mold 11.
Inner surface of concave portion 11a of fixed mold 11 and convex portion 1 of movable mold 12
A cavity 13 having a thickness corresponding to the shape of the airbag cover to be formed is formed on the surface 2a.

The movable mold 12 is provided with a core 12b at the center of the projection 12a. This core portion 12b
From a state flush with the peripheral portion, the cavity 13 is retracted from the peripheral portion so that the thickness of the cavity 13 is increased. A plurality of protrusions 12c are formed on the surface of the core 12b facing the inner surface of the recess 11a of the fixed mold 11 so as to form a plurality of grooves on the back surface of the airbag cover.
Are formed.

Using such a mold 10, the method of the present invention is carried out as follows. First, the movable mold 12 is clamped to the fixed mold 11. In this case, the movable mold 1
The second core portion 12b is retracted by about 1 to 2 mm from the surface of the peripheral portion of the core portion 12b so as to be wider by about 1 to 2 mm than the molded thickness of the airbag cover which is a molded product. Slides like

In such a state, a molten thermoplastic molding material is used as a plastic molten material by an injection molding machine.
The cavity 13 is filled.

At this time, the core 12a of the movable mold 12
Is in a state of being retracted by about 1 to 2 mm with respect to its peripheral portion, so that the cavity 13 has a wider interval than the molding thickness of the airbag cover. The thermoplastic molding compound is filled at low pressure. Then, due to the injection pressure of the molten thermoplastic molding material filled in the cavity 13, the core portion 12b of the movable mold 12 tries to slightly retreat in a direction away from the fixed mold 11, but resists the pressure. Then, the core portion 12b of the movable mold 12 is slid so as to approach the fixed mold 11. Then, the surface of the core portion 12b is
And the cavity 13 is made equal to the molding thickness of the airbag cover.

In this case, the sliding pressure of the core portion 12b is lower than the pressure of 500 tons required for clamping the movable mold 12 at the time of ordinary injection molding, and is a low pressure of about 300 tons.

As described above, when filling the molten thermoplastic molding material with the injection molding machine, the gap between the cavities 13 is made larger than the molding thickness by sliding the core portion 12b of the movable mold 12 so that the air is removed. The molten resin sufficiently flows into the portion thinned by the groove formed on the back surface of the back cover. And movable mold 1
When the molten thermoplastic molding material is cooled and solidified by sliding the second core portion 12b at a predetermined low pressure so as to have a predetermined molding thickness against the filling pressure of the molten resin. Shrinkage is compensated.

As a result, the formed airbag cover has a thin portion of about 0.1 mm formed by the groove on the back surface, and the surface of the thin portion may be uneven or a weld mark may be generated. Therefore, an airbag cover having excellent appearance can be obtained. In addition, since a thin portion of 0.1 mm is reliably formed, a predetermined strength is obtained, and the thin portion formed by the groove is reliably broken only by the inflation of the airbag.

In the above-described embodiment, the airbag cover in which the groove that is broken by the inflation of the airbag is formed has been described. It can also be applied to a column cover that breaks as the shaft falls. The column cover,
A plurality of grooves are formed on the back surface so that the steering shaft is broken by an impact.

[0021]

As described above, the present invention is directed to molding a plastic article such as an airbag cover having a groove for forming a thin section which is broken by an impact.
Using a mold in which the core of the movable mold can slide, the core is slid so that the cavity becomes wider than the molding thickness, and after filling the molten resin, the core is removed. Since the cavity is slid so as to have a predetermined molding thickness, it is possible to obtain a plastic product with excellent appearance without the risk of generating unevenness or weld marks on the surface of the thin portion. it can. Moreover, since the molten resin is surely filled also in the part thinned by the formed groove, the thin part is
Sufficient strength is obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of a mold used in a method of molding a plastic article having a breaking groove according to the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 11 fixed mold 11 a concave 12 movable mold 12 a convex 12 b core 12 c ridge 13 cavity

Claims (1)

[Claims] 1. A method for molding a plastic product, wherein a thin groove is formed on a back surface and the thin portion is broken when an impact is applied. The core of the movable mold is fixed so that a predetermined cavity is formed by clamping the movable mold against the mold, and the cavity is wider than the molding thickness of the plastic product to be molded. After using a mold that is slidable with respect to the mold, slide the core of the movable mold that has been clamped and fill the molten resin with the cavity wider than the molded thickness of the plastic product. Forming a plastic article by a low-pressure injection molding method in which a core is slid so that the cavity has a molding thickness. Method.