DE102007004650A1 - Injection molding tool for producing plastic air bag covering which has tear line, comprises two injection molding halves with hollow space in between for filling airbag covering with plastic - Google Patents

Abstract

The injection molding tool (1) comprises two injection molding halves (2,3) with a hollow space (4) in between for filling the airbag covering with plastic (5). A molding measurer (8) has a molding edge (9) with a contour according to the tear line. A measuring adjustment mechanism (11) is adjusted by molding measurer along the measuring guide (6). An independent claim is also included for manufacturing of airbag covering.

Description

The The invention relates to an injection molding tool and a method for Making a tear line having airbag cover made of a plastic.

One used in a motor vehicle airbag usually includes a housing, a arranged therein container (= Container) and the rest Interior components such as airbag and gas cartridge. The case is on the side facing the passenger compartment with a cover Mistake. When the airbag trips, the airbag is suddenly filled with the gas. The housing cover bursts at least one extra for this provided tear line on, so that the filled Unfold the airbag in the passenger compartment to protect the occupant can. The tear line (= Splitline) is a deliberately introduced on the housing cover predetermined breaking point in shape a material rejuvenation on the inner components facing the back of the housing cover.

at The previous manufacturing process are injection molding tools used, which at the one injection mold in the area of the tear line a firmly projecting web have, which is overmoulded with the liquefied plastic becomes. The cover has at the tear line only a wall thickness of a few 1/10 mm. Ask in the known injection molding tools the protruding bridge and the opposite wall of the other Injection mold is a bottleneck, which is the injected plastic difficult and sometimes not done in the desired way. It thus happens that the case cover not everywhere has the intended surface quality and the tear line the passenger compartment facing visible side of the housing cover strong signs. The latter is undesirable for optical reasons.

A The object of the invention is an injection mold of to specify at the beginning designated type, the precise production of airbag covers allows.

to solution This object is an injection molding tool according to the features of claim 1. The injection molding tool according to the invention has a first and a second half injection mold, between which a cavity for filling formed with the plastic of the airbag cover, an embossing knife, the one embossing edge with a contour corresponding to the tear line and that in one provided in the first injection half mold and open to the cavity knife guide is arranged, and a Messerverstellmechanismus, by means of which the embossing knife along the knife guide is displaceable, so that the embossing edge protrudes into the cavity.

at the injection molding tool according to the invention let yourself the embossing knife especially before the injection process in a retracted position (= Injection position) bring, so that in the area of the tear line either no bottleneck or bottleneck compared to the known injection molding a significantly larger opening width has, exists. This distributes the injected plastic better and, above all, more consistent within the cavity than in the prior art. Only after filling with the plastic, especially during the so-called Nachdruckphase, the embossing knife for the production of tear in a selection advanced, in which it protrudes with be embossing edge in the cavity and the tear line impresses very precisely in the still malleable plastic.

at the ancestor of the embossing knife a part of the plastic is displaced. The resulting Additional pressure on the plastic mass located in the cavity can be used when adjusting the compression pressure during the Repressing phase taken into account become.

The in the injection molding tool according to the invention within the knife guide in both longitudinal directions, So back and forth, slidably mounted embossing knife allows one very precise production the airbag cover overall and especially the tear line. The committee leaves significantly reduce in this way. Due to the achievable high production precision is also ensures a high level of functional reliability. Continue to draw in a product produced by means of the injection molding tool according to the invention Airbag cover on the visible side virtually no on the back impressed tear from.

advantageous Embodiments of the injection molding tool according to the invention result arising from the features of the dependent claims of claim 1.

Cheap is a variant in which the embossing edge is rounded. This results in a very age-resistant tear line. It also comes after a longer one Operating time to no unwanted Bursting of the airbag cover in the area of the tear lines. In particular, at the top of the embossing edge is a rounding radius of a few 1/10 mm, for example, of 0.3 mm provided.

Furthermore, preferably between side walls of the knife guide and the embossing knife only a small game of particular no more than a few 1/100 mm, in particular of at most 0.1 mm, be provided. Particularly favorable is a game with a value of about 0.01 mm. Then no separate sealing is required at the opening to the cavity. The existing at such a small clearance between the side wall of the knife guide and the embossing knife gap is too small for wetting with the liquid plastic mass.

According to one Another preferred variant is in fully extended position in the cavity of the moulder between the embossing edge and one opposite Wall portion of the second injection mold half an opening width in the range between 0.15 mm and 0.3 mm. The injection molding tool with the displaceable embossing knife allows a very precise Production of airbag covers with tear lines, the uniform one small residual wall thickness according to said range for the opening width. Especially For the first time, extremely small residual wall thicknesses of only 0.15 mm can be produced. An indication on the visible side is also with these small ones Residual wall thicknesses safely avoided.

Preferably In addition, the blade adjustment mechanism also includes two each of an inclined plane having wedge-like guide plates, with their inclined planes abut each other and in the direction of slope the inclined planes are relatively displaceable, wherein the embossing knife with one of the embossing edge facing away from the end facing away from the inclined plane Side of one of the guide plates is appropriate. In this case, the connection between the embossing knife and the guide plate either directly or indirectly by means of one or more intermediate elements be executed. Due to the inclined planes become a very exact positioning of the moulder and a high stamping force effect reached.

at another advantageous embodiment of the Messerverstellmechanismus at least one end stop, which can be optionally queried can. This will ensure that the embossing knife especially not over the respectively desired End position, namely the injection position or the Prägestellung moved out. In the queriable variant, reaching the end position can also be detected and evaluated or monitored as part of a process control become.

Cheap is Furthermore, a variant, in the position detection means for monitoring the position of the embossing edge are provided. This position detection can be done directly on the embossing knife or indirectly to a component of the blade adjustment mechanism respectively. Deviations in the positioning accuracy can be recognize and, if necessary, also automatically correct.

A Another object of the invention is a method of the initially indicate type specified, the precise production of airbag covers allows.

to solution This object is a method according to the characteristics of Patent claim 9 specified. In the method according to the invention the plastic is liquefied Condition in between a first and a second injection molding half-mold injection molding tool formed cavity. After this Injecting the plastic becomes an embossing knife, which has an embossing edge with a contour corresponding to the tear line, from a retracted one Injection position in an extended and with the embossing edge in filled with the plastic Cavity projecting embossing position brought, causing the tear line is impressed in the still malleable plastic.

advantageous Embodiments of the inventive arrangement arise from the dependent of claim 9 Claims. The inventive method and its embodiments offer essentially the same advantages, already in connection with the injection molding tool according to the invention and its variants have been described.

Furthermore is a variant of the method particularly favorable, in which the embossing knife after the extension into the embossing position until the airbag cover is ejected from the injection mold, So in particular even while the subsequent one (Remaining) cooling phase, in the embossing position is held. This ensures the high production quality in the area the tear line. One too early return of the moulder could otherwise an undesirable later Deformation of the tear line and thus lead to a poorer manufacturing precision.

Further Features, advantages and details of the invention will become apparent the following description of an embodiment with reference to the partially only schematic drawing. The only figure shows one Cross-section through an injection molding tool in the region of a tear line of the to be manufactured airbag cover.

In the figure is an embodiment of an injection molding tool 1 shown in a sectional view. The injection mold 1 is for the preparation of a housing cover a einzu to be inserted in a motor vehicle airbag, for example, a knee airbag provided. It comprises as main components two half-molds, namely a lower injection mold 2 and an upper injection mold 3 , which are separably assembled and in the assembled state shown in the figure, an internal cavity 4 limit. The injection mold 2 takes the ejector not shown in the figure, whereas the Spritzgussgegenform 3 includes the injectors, also not shown. Both forms 2 and 3 are in particular designed in several parts.

In this cavity for producing the airbag housing cover is a liquefied plastic 5 injected. The plastic then fills, as shown in the figure, the entire cavity 5 out. For airbag housing covers, a soft plastic is used, which is a polypropylene type in the embodiment.

In the injection mold 2 is one to the cavity 5 open knife guide 6 intended. It is a recess that is perpendicular to the cavity 5 in the injection mold 2 hineinerstreckt and running in this direction longitudinal side walls 7 having. In the knife guide 6 is an embossing knife 8th arranged at its the cavity 5 facing longitudinal end face a tapered and rounded at the top embossing edge 9 includes. The latter has a contour corresponding to a tear line to be introduced into the airbag housing cover 10 , In the figure is an example only an embossing knife 8th shown. Basically, the injection mold 1 but also several such embossing knife 8th contain. Between the longitudinal side walls 7 the knife guide 6 and the respective facing longitudinal sides of the embossing knife 8th a small clearance is provided with a lateral distance d1 of about 0.01 mm each.

The embossing knife 8th is longitudinally displaceable in the knife guide 6 stored. It can be located within the knife guide 6 move back and forth in its longitudinal direction, leaving the embossing edge 9 more or less far in the cavity 4 protrudes. In the figure is the embossing knife 8th shown in its maximum extended position. This is the embossing position with an opening width d2 between the embossing edge 9 and the opposite wall portion of the injection mold counter-mold 3 , The opening width d2 determines the (residual) wall thickness that the airbag housing cover to be produced in the region of the tear line 10 Has. In the exemplary embodiment, the opening width d2 is about 0.25 mm. Otherwise, the airbag housing cover to be produced has a wall thickness of about 3 mm. A corresponding distance d3 is between the injection mold 2 and the injection mold counterpart 3 intended. At its widest point, ie in the plane of the rear side of the airbag housing cover, the tear line 10 a line width of about 2 mm.

For longitudinal displacement of the embossing knife 8th within the knife guide 6 has the injection mold 1 a knife adjustment mechanism 11 with two wedge-shaped, superimposed guide plates 12 and 13 , Both guide plates 12 and 13 have an inclined plane on a first main surface 14 respectively. 15 with an inclination angle of about 2 ° each. The inclined planes 14 and 15 both guide plates 12 respectively. 13 lie against each other. The upper guide plate 12 is in the longitudinal direction of the embossing knife 8th movable, but not in a direction perpendicular thereto. According to the double movement arrow entered in the figure, it can thus move up and down in relation to the orientations indicated in the figure. In contrast, the lower guide plate 13 a perpendicular to this oriented mobility, which is indicated by the also entered in the figure further movement double arrow. By means of a mechanically connected drive in the form of a hydraulic cylinder 16 can the guide plate 13 perpendicular to the longitudinal direction of the embossing knife 8th and in the slope direction of the inclined planes 14 and 15 be moved. The embossing knife 8th is with its from the embossing edge 9 opposite longitudinal end fixed to one of the inclined plane 14 remote from the second main surface of the guide plate 12 coupled. Optionally, this mechanical connection can also take place via an additionally provided intermediate plate.

The guide plate 13 moves driven by the hydraulic cylinder 16 under the unit from the upper guide plate 12 and the embossing knife 8th time. According to the illustration shown in the figure, the embossing knife 8th at a feed of the guide plate 13 raised in the right direction and into the cavity 4 driven into it. Conversely, the embossing knife lowers 8th off, if the guide plate 13 is moved to the left. The knife adjustment mechanism 11 So causes a direction and force deflection. A transverse movement 17 the guide plate 13 becomes in a longitudinal movement 18 of the moulder 8th implemented. Due to the only slightly inclined inclined planes 14 and 15 In addition, a particularly high stamping force effect is achieved.

The guide plates 12 and 13 are in the injection mold 2 forcibly guided almost without play. For this purpose, the lower guide plate 13 at a perpendicular to the transverse movement 17 oriented narrow side one in the direction of the transverse movement 17 extending projecting guide bridge 19 on that in a guide groove 20 engages in this area on the injection mold 2 is provided and whose shape to that of the guide bar 19 is adjusted.

Furthermore, there is also between the Füh approximately plates 12 and 13 among themselves a forced operation, which ensures that the guide plate 12 in a transverse movement of the guide plate 13 moved accordingly with up or down. This is on the guide plate 13 again at the perpendicular to the transverse movement 17 oriented narrow side up, ie towards the upper guide plate 12 protruding wall projection 21 molded or attached. The wall projection 21 is with a tilting direction of the inclined planes 14 and 15 extending guide groove 22 provided, in which another guide bar 23 engages the upper guide plate 12 at the perpendicular to the transverse movement 17 oriented narrow side and also in the direction of inclination of the inclined planes 14 and 15 runs. Also the guide groove 22 and the guide bar 23 are adapted to each other in their respective form.

The means for positive guidance are, as shown in the figure so in each case on the rear narrow sides of the guide plates 12 and 13 intended. In principle, embodiments with differently configured forced operation are possible. Due to the positive guidance largely play-free shifts of the guide plates can be 12 and 13 and thus ultimately the required to achieve the embossing effects shifts the embossing edge 9 even then make reliable and highly accurate when the injection mold 2 and the injection mold counterpart 3 , such as B. during injection or in the plastic 5 filled condition, with very high pressure pressed against each other. In this operating condition, extremely high forces, for example, corresponding to the weight of up to several 100 t occur.

The knife adjustment mechanism 11 has an end stop 24 to which the guide plate 13 on reaching the maximum permissible position for movements in the legal direction. In this position shown in the figure, the embossing edge protrudes 9 so far in the cavity 4 into that she is in the embossing position. The latter can change from use case to use case. It will be determined separately. Accordingly, then changes the exact location of the end stop 24 , For movements of the guide plate 13 in the other direction, so to the left is another end stop 25 intended. When reaching this other end position is the embossing knife 8th as far as possible from the cavity 4 moved out and thus in the injection position. The embossing edge 9 is then either completely in the knife guide 6 retracted or only a small piece protrudes into the cavity 4 into it. The end stop 25 is executed in the embodiment as queriable limit switch. Basically, this is also for the end stop 24 possible.

Next to the end stops 24 and 25 includes the blade adjustment mechanism 11 a sensor 26 for detecting the exact position and / or the traversed displacement of the guide plate 13 , This serves the sensor 26 indirectly also for monitoring the position of the embossing edge 9 inside the cavity 4 , The sensor 26 has as well as the hydraulic cylinder 16 and the interrogatable end stop 25 via an electrical connection, by means of which in each case a connection to a control and evaluation unit 27 can be produced. The end stop 24 is optionally also provided with such an electrical connection. At the control and evaluation unit 27 it is in particular the central electronic control assembly of the injection molding machine, in which the injection molding tool 1 used to manufacture the airbag housing cover.

The following is the mode of action and other benefits of the injection molding tool 1 described in more detail.

By means of the injection molding tool 1 the airbag housing cover can be produced particularly precisely. This is especially true for the area around the tear line 10 , Despite the here provided only very small residual wind strength, the tear line 10 on the visible side of the finished airbag housing cover not from. The visible side is the side of the plastic 5 who are interested in injection molding 3 is applied.

During an injection phase, the embossing knife becomes 8th placed in the injection position, where the embossing edge 9 in the direction of the knife guide 6 has moved back. This is the most uniform possible filling of the cavity 4 with the liquefied plastic 5 reached. This would not be possible due to the remaining small opening width d2 of only a few 1/10 mm when the embossing knife 8th already in the extended embossing position during injection.

Only during the subsequent repressurization phase, during the injected and even inside the cavity 4 distributed plastic 5 is subjected to a compression pressure and during the cooling and reconsolidation of the plastic 5 is used, the embossing knife 8th shifted to the embossing position. The embossing edge 9 is in the still deformable plastic 5 pressed, causing the tear line 10 is produced. This is due to the monitoring and (after) controllable movement of the embossing knife 8th highly accurate.

It is followed by the Restabkühlphase, after the completion of the finished airbag housing cover from the injection mold 1 is ejected.

During this last phase, the embossing knife remains 8th in the embossing position, around the shape and the exact dimensions of the tear line 10 to secure.

Only after ejecting the airbag housing cover is the embossing knife 8th by means of a corresponding left movement of the guide plate 13 put back into the injection position. The associated movements of the guide plate 13 and the embossing knife 8th are in the figure by the movement arrows 17 and 18 indicated. After that, a new production cycle can begin.

Claims (11)

Injection molding tool for making a tear line ( 10 ) comprising a plastic ( 5 ) comprising a) a first and a second injection molding half-mold ( 2 . 3 ), between which a cavity ( 4 ) for filling with the plastic ( 5 ) of the airbag cover is formed, b) an embossing knife ( 8th ), which has an embossing edge ( 9 ) with a contour corresponding to the tear line ( 10 ) and that in one in the first injection molding half-mold ( 2 ) and to the cavity ( 4 ) open knife guide ( 6 ), and c) a knife adjustment mechanism ( 11 ), by means of which the embossing knife ( 8th ) along the knife guide ( 6 ) is displaceable, so that the embossing edge ( 9 ) in the cavity ( 4 ) protrudes. Injection molding tool according to claim 1, characterized in that the embossing edge ( 9 ) is rounded. Injection molding tool according to claim 1, characterized in that between side walls ( 7 ) of the knife guide ( 6 ) and the embossing knife ( 8th ) is in each case only a small game (d1) of in particular at most a few 0.01 mm, preferably of 0.01 mm, is provided. Injection molding tool according to claim 1, characterized in that when completely in the cavity ( 4 ) extended position of the embossing knife ( 8th ) between the embossing edge ( 9 ) and an opposite wall portion of the second injection mold ( 3 ) is given an opening width (d2) in the range between 0.15 mm and 0.3 mm. Injection molding tool according to claim 1, characterized in that the blade adjustment mechanism ( 11 ) two each an inclined plane ( 14 . 15 ) having wedge-like guide plates ( 12 . 13 ) with their inclined planes ( 14 . 15 ) abut each other and in the direction of slope of the inclined planes ( 14 . 15 ) are displaceable relative to each other, wherein the embossing knife ( 8th ) with one of the embossing edge ( 9 ) facing away from one end of the inclined plane ( 14 ) facing away from one of the guide plates ( 12 ) is attached. Injection molding tool according to claim 5, characterized in that the guide plates ( 12 . 13 ) are forced. Injection molding tool according to claim 1, characterized in that the blade adjustment mechanism ( 11 ) a particular interrogatable end stop ( 24 . 25 ) having. Injection molding tool according to claim 1, characterized in that position detection means ( 26 ) for monitoring the position of the embossing edge ( 9 ) are provided. Process for making a tear line ( 10 ) comprising a plastic ( 5 ), in which a) the plastic ( 5 ) in a liquefied state into one between a first and a second injection mold ( 2 . 3 ) of an injection molding tool ( 1 ) formed cavity ( 4 ) and b) after injection of the plastic ( 5 ) an embossing knife ( 8th ), which has an embossing edge ( 9 ) with a contour corresponding to the tear line ( 10 ), from a retracted injection position into an extended position and with the embossing edge ( 9 ) in the plastic ( 5 ) filled cavity ( 4 ) projecting embossed position, whereby the tear line ( 10 ) in the still malleable plastic ( 5 ) is impressed. Method according to claim 9, characterized in that the embossing knife ( 8th ) after the extension into the embossing position until the ejection of the airbag cover from the injection molding tool ( 1 ) is held in the embossing position. Method according to claim 9, characterized in that the position of the embossing knife ( 8th ) is monitored.