METHOD OF FORMING MODULE COVER OF AIR BAG DEVICE

Abstract: A method of forming a module cover, in which a gate mark (20) left after injection-molding on the cover (1) is positioned out of sight of the driver on the vehicle, and the metallic mold is provided with a submarine gate in such manner that the gate communicates with a part to be covered up when in use of the outer surface of a module cover to be formed, and is used for forming a module cover through injection molding.

Description: TECHNICAL FIELD The present invention relates to a method of producing a modular cover for containing an air bag assembly. BACKGROUND ART As is known, an air bag assembly includes an air bag adapted to be rapidly deployed in the event of a vehicle collision or emergency situations. As shown in Fig. 2, an air bag 2 is normally folded and covered by a modular cover 1. The air bag 2 as well as an inflator 4 is supported by a mounting plate 3 commonly referred to as a retainer. The modular cover 1 is also secured to the retainer 3 by means of rivets 5, screws or bolts. Usually, the modular cover 1 includes a rigid layer 1a (core layer) and a soft layer (outer layer) 1b. A groove or tear line 1A is formed in the modular cover 1 to permit the modular cover 1 to rupture when the air bag 2 is deployed. The tear line 1A is weaker and thinner (generally, 0.5 to 1.0 mm) than its adjacent portions. The modular cover 1 can rupture along the tear line 1A when the air bag 2 is deployed. In Fig. 2, 1C is a decorative line. Also, 6 is a body cover. A ridge 1B, referred to as a welting portion 1B, extends from the outer periphery of the modular cover 1 to cover the juncture of the body cover with the modular cover 1. GB-A-2 224 449 describes an air bag device modular cover having a core layer of a hard resin and an outer layer of a softer resin, the cover being produced by first molding the core layer and then molding the outer layer on the core layer. Conventionally, expanded urethane integral skin foam or thermoplastic is typically used as a material to produce a modular cover for an air bag assembly. The resin is introduced into a mold of a given shape. An injection molding is deemed best to produce such a modular cover for an air bag assembly in that it improves the production rate, the operability, and the accuracy of a product. However, when a modular cover is made by an injection molding, a gate mark may be left on the product to significantly deteriorate its aesthetic appearance. Particularly, in the production of a modular cover composed of a core layer and an outer layer, it is difficult to place a gate to form the outer layer, so that a gate mark may not be left on the outer layer. Such a gate mark inevitably appears on the surface of the product. DE-A-2315 905 describes a method of molding a plastics article of a single layer, the method including the use of a submarine gate having an outlet at a position where the remaining gate mark is hidden from an observer. DISCLOSURE OF THE INVENTION It is an object of the present invention to solve the problems encountered in the prior art and to provide a method of producing a modular cover having at least two-layers for use in an air bag assembly, which prevents any gate mark made during injection molding from been seen by a vehicle occupant, and which improves the aesthetic appearance of the modular cover. According to the present invention there is provided a method of producing a molded modular cover of an air bag assembly comprising the steps of forming a first mold with a submarine gate, placing second and third molds with said first mold to form a first cavity, introducing a first resin into said first cavity to form a core layer, replacing said second mold with a fourth mold to form a second cavity over the core layer, introducing a second resin into said second cavity to form an outer layer on said cover layer, and removing said modular cover from said mold, said method being characterised by forming a welt forming cavity on a top surface of said first mold, the submarine gate communicating with said welt forming cavity through an outlet located at an inner side of said welt forming cavity which is closer to a central portion of said modular cover than a lowest point of said welt forming cavity, placing said second and third molds with said first mold such that said second mold covers said welt forming cavity whilst forming said first cavity, said first resin being introduced into said first cavity to form said core layer replacing said second mold with said fourth mold so as to uncover said welt forming cavity to form said second cavity which communicates with said welt forming cavity, said second resin being introduced into said welt forming cavity and said second cavity through said outlet to form said outer layer on said core layer, thereby forming the molded modular cover with a welt portion having a gate projection on an inner side thereof; and removing said gate projection from said molded modular cover to leave a gate mark on said inner side of said welt portion so that when said modular cover is installed on a vehicle, said gate mark is situated behind the welt portion relative to a user of a vehicle, thus making the gate mark invisible to the user. The use of the submarine gate allows the gate to contact with a surface of the modular cover which is hidden in use. A gate mark can not be seen when the molded modular cover is in use. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a partial sectional view illustrating a method of producing a modular cover for an air bag assembly, according to one embodiment of the present invention; Fig. 2 is a sectional view of an air bag assembly; Fig. 3 is a perspective sectional view showing the principal part of the modular cover made according to the present invention; and Fig. 4 is a sectional view showing the manner in which the cover is produced. BEST MODE FOR CARRYING OUT THE INVENTION The present invention will now be described in more detail, by way of example, with reference to the drawings. As shown in Fig. 4, three molds 11, 12, 14 are first assembled to form a cavity. Resin is introduced into the cavity through a gate (not shown) placed in any one of the molds 11, 12, 14 so as to form a core layer 1a. After the mold 14 has been removed, another mold 13 is assembled to the molds 11, 12 to form another cavity 15 outwardly of the core layer 1a as shown in Fig. 1. The mold 12 has a cavity 15a to form a welting portion 1B of the modular cover 1. The cavity 15a is communicated with the cavity 15 which is formed by the mold 13. A submarine gate 16 is open to the inner side of the cavity 15a. That is, the outlet of the gate 16 is located closer to the central portion of the cover than the lowermost portion of the cavity 15a. Resin is introduced through the submarine gate 16 into the cavity 15 formed by the molds 12, 13 and the core layer 1a. This provides an outer layer 1b. After a two-layer structure has been molded by a two-color injection molding, a projection which corresponds in position to the submarine gate 16 during molding is removed from the molded product. A gate mark 20 is left, but on the rear surface of the welting portion 1B. When the modular cover 1 is attached to the air bag assembly, such a gate mark 20 can not be viewed by the occupant of a vehicle. The modular cover can thus have good esthetic appearance. One embodiment of the present invention has been illustrated, but the present invention is not limited to the illustrated method. A three-color or multi-color injection molding may be used instead of a two-color injection molding. In either event, a submarine gate is placed in the mold to form at least the outer layer of the modular cover. INDUSTRIAL APPLICABILITY As previously described in detail, with the modular cover of the present invention made according to the present invention, a gate mark can not be seen when the modular cover is in use. This improves the esthetic appearance and value of the modular cover.

Claims: A method of producing a molded modular cover (1) of an air bag assembly comprising the steps of: forming a first mold (12) with a submarine gate (16), placing second and third molds (14, 11) with said first mold (12) to form a first cavity, introducing a first resin into said first cavity to form a core layer (1a); replacing said second mold (14) with a fourth mold (13) to form a second cavity (15) over the cover layer (1a), introducing a second resin into said second cavity (15) to form an outer layer (1b) on said core layer (1a), and removing said modular cover (1) from said mold (11, 12, 13), said method being characterized by: forming a welt forming cavity (15a) on a top surface of said first mold (12), the submarine gate (16) communicating with said welt forming cavity through an outlet located at an inner side of said welt forming cavity (15a) which is closer to a central portion of said modular cover than a lowest point of said welt forming cavity; placing said second and third molds (14 and 11) with said first mold (12) such that said second mold (14) covers said welt forming cavity (15a) whilst forming said first cavity, said first resin being introduced into said first cavity to form said core layer (1a); replacing said second mold (14) with said fourth mold (13) so as to uncover said welt forming cavity (15a) to form said second cavity (15) which communicates with said welt forming cavity (15a), said second resin being introduced into said welt forming cavity (15a) and second cavity (15) through said outlet to form said outer layer (1b) on said core layer (1a), thereby forming the molded modular cover with a welt portion having a gate projection on an inner side thereof; and removing said gate projection from said molded modular cover to leave a gate mark (20) on said inner side of said welt portion so that when said modular cover is installed on a vehicle, said gate mark (20) is situated behind the welt portion relative to a user of a vehicle, thus making the gate mark (20) invisible to the user. A method of producing a molded modular cover according to claim 1 characterised in that said outlet extends downwardly from said top surface to a point which is higher than said lowest point of said welt forming cavity (15a).

Inventors: ZUSHI TAKAYASU - TOGA-CHO, ZUSHI, TAKAYASU, 255-6, TOGA-CHO
Applicants: TAKATA CORP, TAKATA CORPORATION
Application year: 1991
Main classification: B29C45
IPC codes: B29C45, B29L31