GB2244449A

GB2244449A - Moulding a garnishing protection around the edge of a vehicle protective air bag cover

Info

Publication number: GB2244449A
Application number: GB9109518A
Authority: GB
Inventors: Takayasu Zushi
Original assignee: Takata Corp
Current assignee: Takata Corp
Priority date: 1990-05-24
Filing date: 1991-05-02
Publication date: 1991-12-04
Anticipated expiration: 2011-05-02
Also published as: GB9109518D0; JPH0428515A; GB2244449B

Abstract

The cover of the air bag comprises sequentially injection moulded inner and outer layers (15, 17) of respective hard resin and soft resin, and is characterized in that a die cavity (12a) for molding the garnishing projection and a cavity in between dies (11, 13) for forming the inner layer are isolated from each other in the step of forming the inner layer, and the garnishing projection is then formed integrally with the outer layer in the step of forming the outer layer in a larger cavity which communicates with the cavity (12a), formed by replacing the die (13) by a die (16). <IMAGE>

Description

A MOLDING METHOD OF A MODULE COVER OF AN AIR BAG DEVICE FIELD OF THE INVENTION AND RELATED ART STATEMENT The present invention relates to molding method of a module cover of an air bag device, and particularly to a method for molding a module cover, which is provided at its outer edge with a garnishing projection, of an air bag device by a multiple injection method.

As is well known, air bag devices have air bags which rapidly develop at emergency such as crashes or the like of the vehicles. As shown in Figure 3, in a normal condition, an air bag 2 is folded and covered with a module cover 1. This air bag 2 is held, for example, together with an inflator 4 by a mounting plate 3 called as a retainer, and the module cover 1 is also fixed to the mounting plate 3 by rivets 5, screws, bolts or the like. The module cover 1 is fixed so that it also covers a body cover 7 of a vehicle. For this purpose, the module cover 1 is provided at its outer edge with a garnishing projection 1B which serves as a screen for a contact portion thereof with the body cover 7.

This module cover 1 has a main plate portion 100 of a nearly oblong shape and four erected piece portions 110, 120, 130 and 140. (140 is not illustrated.) This module cover 1 is provided with a groove-like tear line 1A for tearing the cover when the air bag 2 develops. This tear line 1A has a strength less than that of the adjacent portions and is formed of a thin portion (generally, having a thickness of about 0.5-1.0mm) of a predetermined shape, so that the module cover 1 tears along a region of the tear line 1A when the air bag 2 develops.

Since an extremely large tensile force is generated in the tearing operation of the module cover, the illustrated module cover 1 includes an insert cloth 6 embedded therein to have a required tensile strength at the portion of the module cover 1 other than the tear line 1A. In Figure 3, a numeral 1C indicates a decorative line.

In the prior art, material used for the module cover of the air bag device thus constructed is generally foam urethane integral skin foam or thermoplastic plastics, and such resin material is injected into a mold having predetermined configurations.

The module cover of the air bag described above may be formed of an inner layer of hard resin and an outer layer of soft resin so that the tear may not be facilely generated by externally applied impacts or the like but it may rapidly tear when the air bag 2 develops. In a moLding method of the module cover having the two-layer structure described above, there has been such an effective method called as a double injection method that injection molding of the inner layer is performed using first and second dies, and subsequently, after removing the second die, injection molding of the outer layer is performed with a third die which is assembled to form a cavity for forming an outer layer without removing the molded inner layer from the dies.However, in the prior art, there has not been proposed a double injection method for fabricating the module cover provided at its outer edge with the garnishing projection.

For instance, a following method can be envisaged as a method for molding the module cover provided at the outer edge with the garnishing projection by the double injection method.

That is; as shown in Figure 2A, with a first die (fixed die) 21, a second die 22 having a cavity 22A for forming the garnishing projection and a third die 23, the inner layer is formed by injection of material 24 for the inner layer. Then, after removing the third die 23, a fourth die 25 is assembled, and an outer layer is formed over the inner layer 27 by injection of material 26 for the outer layer, as shown in Figure 2B. Thereby, a module cover 29 is fabricated to have the two-layer structure formed of the inner layer 27 and the outer layer 28 and also to include a garnishing projection 29A at the outer edge.

However, in the module cover 29 fabricated in this manner, there is exposed a seam of the garnishing projection 29A on an outer surface as a boundary 30 between the inner layer 27 and the outer layer 28, which impairs an appearance.

OBJECT AND SUMMARY OF THE INVENTION It is an object of the invention to provide a molding method of a module cover of an air bag device, overcoming these problems, which enables an industrially advantageous fabrication of a module cover of an air bag device, which is formed of an inner layer of hard resin and an outer layer of soft layer and has a garnishing projection at its outer edge, by a multiple injection method.

A molding method of a module cover of an air bag device according to the invention, in which the module cover of the air bag device having a garnishing projection at its outer edge is molded by a multiple injection method and which comprises the steps of forming an inner layer of hard resin and subsequently forming an outer layer of soft resin, is characterized in that a cavity in a die for molding the garnishing projection and a cavity in a die for forming the inner layer are isolated from each other in the step of forming the inner layer, and the garnishing projection is formed integrally with the outer layer in the step of forming the outer layer.

In the molding method of the module cover of the air bag device of the invention, since the cavity in the die for forming the garnishing projection is isolated from the cavity for forming the inner layer, material for forming the inner layer does not flow into the cavity for forming the garnishing projection.

Further, the garnishing projection is molded integrally with the outer layer in the step for forming the outer layer. Thereby, the garnishing projection is molded only by material for forming the outer layer, and thus a boundary between the outer layer and the inner layer is not exposed on the garnishing projection.

BRIEF DESCRIPTION OF THE DRAWINGS Figures 1A, 1B and 1C are cross sections of a major part for illustrating an embodiment of a molding method of a module cover of an air bag device of the invention; Figures 2A, 2B, and 2C are cross sections illustrating a molding method other than that of the invention; Figures 3 is a cross section of an air bag device; and Figures 4A, 4B and 4C are whole cross sections for illustrating a cover molding method, respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the invention will be described below with reference to the drawings.

Figures 1A, 1B and 1C are cross sections of a major part for illustrating an embodiment of a molding method of a module cover of an air bag device of the invention, and Figures 4A, 4B and 4C are cross sections illustrating whole views of Figures 1A, 1B and 1C, respectively.

In an illustrated method, as shown in Figures 1A and 4A, a first die 11, a second die 12 and a third die 13 are first assembled to form a mold. These three dies 11-13 form a cavity 14 into which material 15 for forming an inner layer is injected to mold the inner layer. Although the second die 12 is provided with a cavity 12A for forming a garnishing projection, this cavity 12A in the die 12 for forming the garnishing projection is isolated from the cavity 14 formed in the first to third dies 11-13 for forming the inner layer. That is; since both the second and third dies 12 and 13 are brought into intimate contact with each other at a boundary (indicated by A in Figure 1A) of the dies 12 and 13, the material 15 for forming the inner layer is surely prevented from flowing into the cavity 12A provided for forming the garnishing projection.

Then, after the material 15 hardens to form the inner layer 17, the third die 13 is removed, and then, as shown in Figures 1B and 4B, a fourth die 16 is mounted. Then, resin material 19 for forming the outer layer is injected into the cavity 12A for forming the garnishing projection and the cavity 18 for forming the outer layer, which are surrounded and defined by the second die 12, fourth die 16 and the inner layer 17 already formed in the previous step, whereby the outer layer and the garnishing projection are integrally formed by the hardened material 19.

Thereby, as shown in Figure 1C and 4C, the module cover 10, which has a two-layer structure including the inner layer 17 as well as the outer layer 20 (hardened layer of the material 19) integral with the garnishing projection 20A, is fabricated.

In this module cover 10, a boundary between the inner layer and the outer layer is not exposed on the outer surface, and thus it has a good appearance.

In the invention, there is no particular restriction with respect to the shape of the garnishing projection formed in the module cover, and shapes other than the illustrated semicircular shape may be employed.

Further, the method of the invention is not restricted to the double injection method, and may be applied to other multiple injection methods such as a triple injection method.

As described hereinabove, the molding method of the module cover of the air bag device according to the invention enables the easy and efficient fabrication with high accuracy of the module cover of the air bag device, which is formed of the inner layer of the hard resin and the outer, layer of the soft resin and has the garnishing projection at the outer edge, by the multipleinjection method. Further, the fabricated module cover does not have the exposed boundary between the inner layer and the outer layer, and thus has a good appearance.

Claims

WHAT IS CLAIMED IS:

1. A molding method of a module cover of an air bag device, in which said module cover of said air bag device having a garnishing projection at its outer edge is molded by a multiple injection method and which comprises the steps of forming an inner layer of hard resin and subsequently forming an outer layer of soft resin, characterized in that: a cavity in a die for molding said garnishing projection and a cavity in a die for forming said inner layer are isolated from each other in said step of forming said inner layer, and said garnishing projection is formed integrally with said outer layer in said step of forming said outer layer.

2. A manufacturing method of a module cover having a main plate portion, an erected portion erected from a side of said main plate portion and a garnishing projection projected from an outer edge of said erected portion, and including a hard inner layer and a soft outer layer, comprising the steps of:: assembling a first die for forming an inner surface of said module cover, a second die having a cavity for forming said garnishing projection and a third die which is fitted onto said first die with a cavity for forming said inner layer therebetween and is fitted to a second die in such a manner tha#t said cavity for forming said garnishing projection and said cavity for forming said inner layer are isolated from each other; injecting resin material only into said cavity for forming said inner layer and hardening it to form said inner layer; removing said second die and alternately assembling a fourth die to form a cavity for forming said outer layer between said inner layer and said fourth die in such a manner that said cavity for forming said outer layer and said cavity for forming said garnishing projection are communiçated with each other;; injecting resin material for forming said outer layer into said cavity for forming said outer layer and said cavity for forming said garnishing projection, and hardening it'to form said outer layer and said garnishing projection; and removing said first, second and fourth dies.

3. A method of claim 2, wherein said cavity for forming said garnishing projection is formed by a concave portion provided between opposed surfaces of said second die and said third die, and said third die is adapted to be assembled in such a manner that said third die covers said concave portion, whereby said cavity for forming said garnishing projection and said cavity for forming said inner layer are isolated from each other.

4. A method of manufacturing a module cover for an air bag device, substantially as hereinbefgre described with reference to the accompanying description and Figures lA,lB, 1C,4A,4B and 4C of the drawings.