US 7919036 B2
A process for preweakening the inside of an automotive trim piece cover layer of various constructions by use of a laser beam so as to enable formation of an air bag deployment opening in the trim piece formed at the time the air bag deploys. The laser beam impinges the inside surface of the cover to form a groove scoring or spaced perforations to form a preweakening pattern. A robot arm may be used to move a laser generator so as to form the preweakening pattern. The laser beam can be controlled in accordance with sensed conditions to achieve accurate preweakening, and may also be used to trim substrate panels and to perform other cutting operations.
1. A process for constructing a preweakened automotive interior trim piece comprising an instrument panel covering an air bag installation, said preweakening extending in a predetermined pattern enabling formation of an air bag deployment opening in said instrument panel by pressure exerted by an air bag deploying from said air bag installation mounted on the inside of said trim piece,
said process including the steps of:
constructing said instrument panel with a thin pliant plastic outer cover layer defining an outer surface extending smoothly and uninterruptedly over said predetermined pattern;
preweakening said constructed instrument panel by directing a laser beam at an inner surface of said instrument panel and along said predetermined pattern so as to produce a scoring therein partially penetrating an inner surface of said outer cover layer along said predetermined pattern; and
said preweakening step including controlling said scoring by said laser beam so as to cut a series of repeating spaced apart deep scoring penetrations extending partially into the inside of said trim piece cover with intervening uncut material between said deep scoring penetrations thereby forming a varying depth laser scored groove in said outer cover layer which has a lower resistance to tearing along said predetermined pattern by the pressure exerted by said deploying air bag because of the presence of said deep scoring penetrations while said intervening uncut material strengthens said outer cover layer to reduce any tendency for preweakening said pattern to become visible from said outer surface prior to air bag deployment or to develop cracks in said outer cover
sensing the remaining thickness of said instrument panel outer cover layer beyond said scoring during said laser beam scoring, and controlling said laser beam scoring in correspondence to said sensed remaining thickness so as to maintain a predetermined minimum remaining thickness of said instrument panel outer cover layer beyond said scoring to avoid cracking along said pattern.
2. The process according to
3. A process for constructing a preweakened automotive interior trim piece comprising an instrument panel covering an air bag installation, said preweakening extending in a predetermined pattern enabling formation of an air bag deployment opening in said instrument panel by pressure exerted by an air bag deploying from said air bag installation mounted on the inside of said trim piece,
said process including:
constructing said instrument panel with a thin pliant plastic outer cover layer defining an outer surface extending smoothly and uninterruptedly over said predetermined pattern;
preweakening said constructed instrument panel by directing a laser beam at an inner surface of said instrument panel and along said predetermined pattern so as to produce a scoring therein partially penetrating an inner surface of said outer cover layer along said predetermined pattern;
said laser beam is controlled during said scoring of said inner surface of said outer cover layer so as to score a series of closely spaced repeating partial penetrations into said inner surface of said outer cover layer while leaving unscored intervening cover layer material between said partial penetrations, said series of repeating partial penetrations extending along a path defining said predetermined pattern and comprising a stepped depth scoring into said inner surface of said outer cover layer; and
sensing the remaining thickness of said instrument panel outer cover layer beyond said scoring during said laser beam scoring, and controlling said laser beam scoring in correspondence to said sensed remaining thickness so as to substantially maintain a predetermined minimum remaining thickness of said instrument panel outer cover layer beyond said scoring such that said minimum remaining thickness of said instrument panel outer cover layer along said predetermined pattern is sufficiently thin to be readily severed by said pressure exerted by said deploying air bag but sufficiently thick so that said predetermined pattern will not be visible from said outer surface prior to air bag deployment nor develop cracks in said outer cover layer.
This application is a division of U.S. Ser. No. 09/816,955, filed Mar. 23, 2001 now U.S. Pat. No. 6,808,197, which is a division of U.S. Ser. No. 09/339,885, filed Jun. 25, 1999, which is now U.S. Pat. No. 6,267,918, issued Jul. 31, 2001, which is a division of U.S. Ser. No. 09/063,141, filed Apr. 20, 1998, which is now U.S. Pat. No. 6,294,124, issued Sep. 25, 2001, which is a division of U.S. Ser. No. 08/332,565, filed Oct. 31, 1994 which is now U.S. Pat. No. 5,744,776, issued Apr. 28, 1998.
The present invention concerns cutting and scoring of covers for automotive trim pieces enclosing air bag safety devices.
Air bag safety systems have come into widespread use in automotive vehicles and light trucks and have been proposed for use in passenger trains and airplanes.
Such systems comprise an inflatable cushion, commonly referred to as an “air bag” which is stored folded in a storage receptacle and then very rapidly inflated, as with gas from a pyrotechnic gas generator, when a collision of the vehicle is detected by sensors. The air bag is thereby deployed in a position to absorb the impact of the driver or a passenger.
It is necessary that the folded air bag be stored in an enclosed secure environment within the passenger compartment, protected from tampering, and yet be allowed to properly deploy into the passenger compartment as the air bag is inflated.
It is critical that the air bag deploy within milliseconds of activation of the system in order to protect the occupant.
As noted, the air bag is enclosed within a storage receptacle, which is typically mounted behind an interior trim piece, such as a steering wheel cover in the case of the driver's side air bag, or a section of the instrument panel, in the case of the passenger's side air bag. It has been proposed to also provide side impact air bags in the vehicle doors.
One or more air bag deployment doors normally overlie the air bag receptacle and are forced open when the air bag is inflated to allow deployment of the air bag through the opening created by the door panel movement.
As described in U.S. Pat. No. 5,082,310 issued on Jan. 21, 1992 for an “Arrangement for Providing an Air Bag Deployment Opening”, a seamless construction is advantageous in which the deployment door panels are not separately delineated within the expanse of the trim piece, but rather a smooth uninterrupted surface is provided extending over the deployment door substrate panels.
This construction necessitates severing portions of the covering of the trim piece in order to allow the door panels to hinge open.
Severing has been achieved by the pressure of the inflating air bag, or by various other methods which have been proposed, such as linear energy devices described in copending U.S. Ser. No. 08/279,225, filed Jul. 22, 1994. See also U.S. Ser. No. 08/027,114, filed Mar. 4, 1993, and U.S. Pat. Nos. 5,127,244 and 4,991,878 describing pyrotechnic elements used to cut the outer cover layer of the trim piece.
Cutter blades have also been proposed which are forced outwardly by the air bag inflation to assist in cutting the cover layer, but these outwardly swinging elements can present a potential hazard to a vehicle occupant seated in front of the deployment door.
Automotive interior trim covering materials such as vinyl plastic are relatively tough and difficult to sever, and also a predetermined severing pattern is necessary for proper door panel opening, such that heretofore preweakening grooves have been formed in the trim cover in a predetermined pattern to insure proper opening.
It has heretofore been proposed to provide an “invisible seam” installation in which the deployment door pattern is totally invisible to a person seated in the vehicle passenger compartment, and even faint outlines or “witness” lines are desirably avoided.
Scoring of the covering layer from the inside, if not done accurately, can over time become at least faintly visible from the exterior of the trim piece.
Fabrication of the automotive interior trim pieces with preweakening grooving particularly for invisible seam applications is thus a difficult manufacturing challenge.
First, the groove depth must be carefully controlled in order to achieve reliable rupture of the outer cover at exactly the right time during the air bag deployment event.
If the groove is too shallow, the thickness of the remaining material may be too great, presenting excessive resistance to severing, delaying air bag deployment. Conversely, if too little material remains, over time cracking may be result, or at least allow the appearance of externally visible “witness” lines.
The preweakening effect may also be less effective if the grooves are molded-in during the process since it has been found that cutting into plastic material such as vinyl has a better preweakening effect compared to molding-in the groove during the initial manufacture of the item.
The high pressures used in injection molding can cause a “crazing” effect at the thinned bridging material extending over the gap defined by the groove. This crazed zone is rendered more visible as the part is removed from the mold, particularly if the part is not completely cooled when it is being removed.
The net effect is that the molded groove becomes visible on the exterior side.
It is difficult to accurately and reliably control the depth of mechanical cutting of component materials such as sheet vinyl, since the material is variably compressed by the pressure of a cutting instrument.
U.S. Pat. No. 5,082,310, referenced above, describes a partial cutting procedure which is intended to enable accurate control over the depth of the cut into a sheet of pliant plastic material such as a vinyl skin. However, a purely mechanical cutting operation still has other inherent accuracy limitations and is slow to execute.
Also, some cover materials have irregular inside surfaces, i.e., dry powder slush processes create such irregularities. If the groove depth were constant, this results in an irregular thickness of the remaining material. This leads to erratic performance as the resistance to opening pressure will vary greatly.
The groove width is also important, in that if a too narrow groove is cut into many plastics, a “self healing” may occur, particularly at elevated temperatures in which the groove sides will re-adhere to each other, causing the preweakening effect to be erratic or neutralized.
The required groove width also varies with the notch sensitivity of the material being preweakened.
A further difficulty is encountered in assembling the preweakened component to the interior trim structure so that the lines of preweakening are properly registered with the other components. For example, the vinyl skin in a skin and foam instrument panel must be accurately positioned on the instrument panel substrate and the deployment door substrate panels so that the preweakening lines are stressed as the door edges hinge out under pressure from the air bag.
This alignment requirement creates manufacturing difficulties and increased costs particularly since a variety of forms of instrument panel structures are employed, i.e., skin and foam, vinyl clad, hard plastic with a finished surface, etc., since a variety of forming techniques are employed, i.e., vacuum formed calendared plastic sheet, dry powder slush molded, injection molded, etc. A leather covering later sometimes may be used in lieu of a vinyl plastic covering layer.
Accordingly, it is an object of the present invention to provide a process for preweakening trim components overlying an air bag installation by groove scoring which is highly accurate in production implementation, and which may be efficiently integrated into the trim piece manufacture to lower costs and improve results.
According to the invention, the preweakening groove scoring of a smoothly contoured trim piece cover material overlying an air bag receptacle is carried out by the use of a laser beam which is controlled and guided so as to produce grooves of a precise depth and width formed by the laser beam energy into the undersurface of various trim piece cover materials such as a vacuum formed sheet of vinyl.
A sensor provides a feedback signal allowing relative positioning of the workpiece and/or varying of the laser beam source intensity or to precisely control the groove depth to achieve a constant thickness of the remaining material.
The workpiece and laser beam source can be mounted for relative movement in a two-axis positioner table, or alternatively, a system of movable reflectors can optically generate the groove pattern.
A five axis robotic arm can also be used to guide the laser beam source in the required pattern extending in three dimensions, and in process or post-process gauging can also be utilized to correct the laser and robot control and improve results.
The laser beam preweakening groove scoring can be carried out on the cover piece prior to its incorporation into the trim piece or such groove scoring can be carried out after attachment to a substrate or other trim elements grooving the underlying substrate and partially scoring the cover layer at the same time to create a deployment door substrate panel while preweakening the cover material.
The laser beam apparatus can further be utilized to trim the assembled trim piece.
In the following detailed description, certain specific terminology will be employed for the sake of clarity and a particular embodiment described in accordance with the requirements of 35 USC 112, but it is to be understood that the same is not intended to be limiting and should not be so construed inasmuch as the invention is capable of taking many forms and variations within the scope of the appended claims.
The present invention is concerned with preweakening of an automotive interior trim piece such as a steering wheel cover or an instrument panel overlying an air bag receptacle stored behind the trim piece. The surface of the interior trim presented to the passenger compartment must be aesthetically pleasing rather than starkly utilitarian. There has also been developed a preference for eliminating any suggestion of the presence of the stored air bag. In the past, separately defined deployment doors have been fit into an opening in the instrument panel. In the case of a wheel cover, visible delineations segmenting the cover to form deployment doors have been provided.
Internal grooves have also been provided, typically molded into the trim piece itself.
As described above, molded grooves have sometimes resulted in exteriorly visible “witness” lines, since the high injection pressures forcing the plastic through the narrow gap remaining above the groove has resulted in a crazing pattern, as well as slight cracking when the part is removed from the mold.
The present invention comprises the process of laser scoring to obtain the preweakening internal groove after the cover has been molded or otherwise formed.
A laser beam is directed at the cover layer or other trim piece component to score the component along a path defining the desired pattern matching the deployment doors.
The laser scoring has been found to result in elimination of any exteriorly visible lines, even where minimum material remains above the scoring groove.
Referring to a first embodiment (
The width of the score line 20 is generally minimized in typical applications but self healing may be avoided when necessary by making wider cuts which may be backfilled with a material having physical properties having generally beneficial physical properties for improving bursting of the invisible seam during air bag operation in the vehicle.
For example and referring to
Typical focusing elements for infrared laser 12 comprise gallium arsenide or germanium refractive lens members, or gold reflective members. Several alternate laser types will achieve good results and laser source 12 may be an excimer, solid state, argon gas, or diode laser. However, the carbon dioxide laser is likely to be the least expensive in both initial cost and over the required lifetime.
If laser source 12 produces continuous output, the depth of the score line 20 is controlled by the laser output power density at the surface of cover 16 and the rate at which cover 16 moves relative the beam 14.
In another process, laser source 12 may be controlled to generate pulses of a laser output beam, each pulse removing by heat ablation or combustion a minute quantity of cover 16 material. Depth is therefore controlled by applying a particular number of pulses before moving to an adjacent, possibly overlapping, site on the inside of cover 16. The pulsed laser technique combined with a stepwise movement of cover 16 should result in superior control over the process when a computer based controller 26 is used.
Multiaxis positioning system 17 may be driven by a multiplicity of electric motors controlled by a small computerized controller 26 as shown, or alternatively, by electromechnical actuation of a multiplicity of cams and mechanical devices which move the cover 16 in a proper pattern at appropriately controlled rates.
In most industrial applications, the focusing elements 18 must be maintained clean and free of blowback debris emanating from the score line 20. A free flowing gas system 28 is frequently employed to achieve focusing element 18 cleanliness. Also, certain gases, if directed to the score line 20 formed at the laser impingement area, will alter the chemistry and thermodynamics at the scoring site. For example, inert gases such as nitrogen or argon can displace the oxygen in the air at the impingement site and prevent both charring and local combustion while keeping the focusing elements clean. Alternate gases and flow rates can dramatically alter the properties of the resulting score line 20 and create a wide range of physical properties of the cover 16.
The computer controller 38 may also be connected to a laser controller 44 which can vary the operation and power level of the laser generator 34.
The cover 42 is fixtured on an ultrasonic sensor 46 which generates signals corresponding to the thickness of material remaining after the groove scoring is produced by the laser beam 14B such as to provide a feedback signal to the central computer control 38 to vary the position of the laser generator 34 and/or its power output to precisely control the thickness of material remaining after the groove scoring is produced. The resistance to tearing of the remaining material above the groove is important to proper air bag deployment and hence its thickness should be controlled.
Such ultrasonic sensors capable of gauging internal features, such as material thickness, are commercially available, and hence details are not here given.
The laser generator 34 is preferably of the “diffusion cooled” type which does not require gas line hookups and thus is readily mountable to a robot arm manipulator. Accordingly, the optical system is simplified as the beam is directed by robot arm motion, lower costs and improving performance. A more rugged, reliable installation also results, suited to a production environment.
Diamond™ lasers available from Convergent Energy of Sturbridge, Mass. are perfectly suited for this application.
The laser beam can be directed to not only produce the scoring of the cover 42, but may produce cutout openings 54 therein. Further, the perimeter of a substrate panel 56 to which the cover 42 is assembled can be trimmed as well, achieving significant manufacturing economies.
Thus, gauging of the thickness t, as with an ultrasonic gage, is necessary, varying the depth of the groove 64 to maintain the thickness t.
In both examples, the covers 58, 66 are assembled in a mold after scoring, together with an instrument panel substrate (not shown), and foam injected into an intervening space to bond together the substrate and cover, as well as deployment door panels and frame, into a unitary trim piece.
The preweakening pattern consists of a series of laser scored grooves 78 in the inner or rear face 80.
The width w of the groove is sufficient to avoid self healing. The thickness tL of the material remaining above the laser beam scored groove 78 may be less than the remaining thickness tM of a molded groove and still remain invisible from the finished surface 76.
it is also noted that the laser scoring process can be carried out very rapidly, and saves processing time over the molding time where a long cooling interval is required to avoid cracking over the thinned out region above the preweakening groove.
The scoring depth can vary from 20%-80% of the total thickness depending on the available tearing force, the strength of the material used, and whether or not other assisting devices are employed.
The laser scored groove 95 penetrates completely through the backing scrim 94 and partially through the textile layer 92.
The power of the laser beam 114 can be controllably varied so as to completely penetrate the substrate panel 116 and foam layer 120, but only partially penetrate the inside of the cover 118, as indicated, creating the preweakening by a laser scoring.
A deployment door panel 122 is thus formed at the same time, perfectly aligned with the preweakening pattern of the cover 118.
The use of a laser beam enables preweakening by other forms than a straight groove.
As shown in
The preweakening process is readily applicable to all conventional types of trim piece construction, i.e., skin and foam with both vinyl and leather skins (vacuum formed, dry powder, molded, injection molded) vinyl clad, or hard plastic with a surface finish.