DE10122312A1 - Controlled weakening of cuttable material bodies along contour line, e.g. for motor vehicle airbag cover, by heating blade, applying to material contour, and applying pressure to cut to predetermined thickness - Google Patents

Abstract

The method involves abutting the material body (36) against a predetermined surface (10), and heating or maintaining at least one cutting blade (22) whose cutting edge has the shape of at least part of the predetermined contour, to or at a predetermined increased temperature. The blade edge is brought towards the contour line of the material body to be weakened. Pressure below or equal to a maximum value is applied via the edge to the material body, to effect cutting up to a predetermined residual material thickness, and then removing the blade from the cut. Independent claims are also included for a cutting machine, a combined cutting and punching machine, a cutting tool, and a material body.

Description

STATE OF THE ART

The present invention relates to methods and pre direction for the dosed weakening of material that can be cut body, and especially for the production of predetermined breaking nien for airbag covers in motor vehicles.

Although the invention provides a much greater protection has a specific status of Technology used in the manufacture of airbag covers is used, delimited below.

Airbags have the job of vehicle occupants at one To protect impact. In particular, the breast and head area from a front airbag and the side Areas of the body with any side Airbags are protected. To fulfill this protective task in particular, a front airbag must be exposed Place in the vehicle interior trim who to protect people in the event of an impact to be able to. In particular, the front airbag Particularly high aesthetic requirements on the passenger side made an effort to install the airbag in this way, and by one  Airbag cover that surround the presence of a Airbags if possible, except in the event of an impact takes. So there are airbag covers created especially in the dashboard on the passenger side are integrated.

The dashboard mostly contains the essential ele ment for this also serves as an instrument panel body that generally spans the full width of the car interior extends. It is usually in one piece trained to ensure a perfect appearance.

Such an instrument panel is usually more layered: a carrier layer made of relatively hard Material, usually a thermoplastic material such as ABS or a thermoset, possibly in association with a company server reinforcement made of glass fibers, etc. forms the lower one Layer that essentially forms the dashboard gives balance.

A second layer often consists of a plastic foam, such as polyurethane foam, around the surface a certain to give palpable softness. The layer thickness of the foam layer is 8 mm, for example.

In order for an attractive appearance and a reasonable The visible side of the instrument panel becomes a haptic formed by a third layer, the decorative layer. The Decorative layer often consists of a plastic film, the one has a grained surface or as leather or imitation leather  is trained. It generally has a strength from 0.8 to 2 mm. In other parts of the vehicle interior, for example with a door panel or a spar panel a similar situation is encountered in principle. The Airbag cover mentioned above is now in the state of Technique formed from the instrument panel itself.

To ensure that the airbag deploys properly To be able to guarantee the person to be protected must do so be made sure that the explosion corresponds to one opening in the airbag cover through which through which the airbag can deploy. For that are in the booth technology along a given contour line weakening against the material thickness of the aforementioned layer structure seen. With appropriate pressure caused by the explosion of the airbag cushion then becomes the airbag cover broken open along this contour line and the desired one Opening arises.

Given the high aesthetic demands increasingly the predetermined breaking lines in the airbag Cover only from the back of the instruments made here to any contour of the predetermined breaking line to make it invisible from the visible side.

For this it is necessary in the process used to produce this line of weakness or predetermined breaking line as little pressure as possible on the visible side of the airbag Exercise cover to avoid an imprint.  

Problematic in the creation of the weakening line is now in particular that the material of all three layers must be weakened to open the airbag cover ensure safely.

Given the different strengths of the used Layers in the layer structure and the different hardness th of these layers is used in the prior art - for example as in DE 44 09 405 described - the decorative layer (there outer skin not weakened at all, be it when using one Cutting laser or when using a knife, in particular of a hot knife.

To weaken the outer skin anyway, perhaps because of this would be necessary due to stricter standards two different operations needed to do one hand to weaken the backing and foam and others on the one hand an extremely thin decorative layer with the highest precision to weaken. Because when creating the line of weakness in the thin decorative layer of 0.8-2 mm should according to such Vorga ben a residual decorative thickness of about 0.3-0.8 mm depending on the original crack wall thickness stop. It must be increased th accuracy can be worked, for example 2 to Is 5/100 mm. The remaining wall thickness is too low, so there is a possibility that by the claims the dashboard in everyday life intends to tear open. On the other hand, if the remaining Wall thickness is too large, there is a risk that the Opening in the event of an airbag explosion does not form and Airbag does not deploy towards vehicle occupants can.  

The cutting method disclosed in DE 44 09 405 cannot meet such high accuracy requirements:
Because the disclosure there shows only a weakening process to cut through a double layer of high-density foam (inside) and a layer of lower density (outside, towards the visible side) with complete separation of the inner layer and a weakening of the outer layer to form about 1 mm, whereby a relatively large residual thickness of about 4 mm may remain.

For this purpose, DE 44 09 405 proposes a La to use the beam along the specified contour is never carefully managed and by precisely metered lasers power and speed of the beam along the Line the required cut with the required cutting quality lity. The The aforementioned 2-layer composite can be processed without Schwä the decorative layer.

The second disadvantage of the proposed in DE 44 09 405 gene method, however, is that the laser beam what must be performed along the specified contour line on the one hand, for example when using a robot, is expensive and on the other hand, the production process is delayed because it is long takes until the cut is made. Furthermore, it is Laser cutting machine itself compared to mechanical Cutters relatively expensive.

If the process instead of a cutting laser with egg nem (hot) knife performed as in DE 44 09 405 as  Proposed alternative, so there is no incentive how to achieve such high accuracy. There are therefore two separate operations required, what has the disadvantage that the production of instrument tapes feln, in this sense the manufacture of the weakened In instrument panel, is difficult because the weakened Parts must then be placed on top of each other with a perfect fit.

The object of the present invention is therefore a improved method for producing lines of weakness with a given contour.

ADVANTAGES OF THE INVENTION

The attenuation method according to the invention with the Merk paint the claim 1 or the corresponding device accomplishes this task.

Advantageous Further can be found in the subclaims education and improvements of the respective subject of Invention.

According to its main aspect, the present inven creates a process using the material body that can be cut weakened finely dosed along a given contour line can be a precise control or regulation is provided to control the cut. You can One or more cutting knives can be used to make one corresponding number of sections of the contour line to be work.  

In its basic form, the process contains the following steps:

• a) Pressing the material body in contact with egg a given contact area,
• b) heating or holding the or knife, the Cut the shape of the given contour has, to a or a predetermined (n) increase te (n) temperature,
• c) Approaching the knife edge (s) to match Contour line of the material body to be weakened,
• d) Applying pressure less than or equal to one predetermined maximum value over the cutting edge (s) to the Material body to make a cut until a predetermined residual material thickness has been reached, and
• e) bringing the cutting knife (s) out of the Kerf.

Limiting the depth of cut can be done in a preferred manner via a precisely executed mechanical stop follow that between a knife holder and the contact surface is provided. These measures result in the pre part that by the predetermined maximum pressure limit, the heated knife edge (s) and the presence of the Contour knife (s) in with a cutting contour in two or three-dimensionally curved shape a precise, stan zend-cutting weakening of the material is possible without to leave an imprint on the visible side, whereby through the 2D or 3D knife an efficient, faster  Cutting process is made possible. This results in costs reductions in the production process. The cutting speed is the result of the print specification and Temperature specification. She is also individually at work processing of different materials.

If the procedure also includes the steps:
Detecting the remaining uncut material thickness at one or more points on the contour line,
Generation of a corresponding path signal,
Evaluating the signal,
Stopping the application of pressure when the signal indicates that a predetermined limit value for the uncut material thickness has been reached,
an additional cutting control is then possible, with which very high accuracy requirements for the cutting depth along the contour can also be realized.

If the procedure contains the steps beyond the basic procedure:
Detect the cutting speed, and
Reducing the pressure when a predetermined maximum value of the cutting speed is exceeded,
so there is the advantage of a further control possibility of cutting, especially in the area of the decor or with hidden material inhomogeneities in the body to be weakened. A cut that is too deep is then not produced, for example because an otherwise too rapid cutting movement of the knife would be stopped too late.

If when the specified residual material thickness is reached the knife edge for a specified period of time on The bottom of the cut, there is the advantage that the editing room is melted further, essentially lichen without further deepening the cut.

If furthermore after reaching a minimum remainder strengthen the knife with a predeterminable retraction speed is pulled from the material, there is the advantage to exert targeted influence: if withdrawn too slowly the knife gets dirty too easily. If it's too is quickly pulled out, residual particles remain from the Cut in the trench and can be when using the Ver driving to create a predetermined breaking point for airbag covers in the event of subsequent airbag explosion are harmful to health act well, for example because they could get in the eye.

The main area of application of the method according to the invention rens lies in the production of a predetermined breaking contour line in the cover of an airbag in a vehicle.

If in a single cutting a beam layer and an intermediate foam layer at least in intersect essential sections of the contour line and a layer forming the visible side of the airbag cover in not essential sections of the contour line who only cut, i.e. weaken, results in  the advantage of this is that only a single operation is needed instead of two, as in the prior art partially se available.

If the procedure includes the additional step, one according to the duration and size of the preselectable pressure value Break through or weaken a layer, see above there is also an alternative to evaluating the Ge speed signal for the purpose of control or regulation development. It is advantageously applicable to one in the layer follow last layer to be cut, especially the Transparent film that has to be weakened very precisely.

For example, the pressure when cutting through of the decor can be shut down in a targeted manner in order to to be able to meet the tolerances more easily and around the To reduce rejects.

If the process is designed so that the mate rial body in one and the same system from a blank is especially formed by punching out and dosed weakened along the specified contour line the production of the products can still be inexpensive tiger.

A weakening device according to the invention is in the for example, designed as a cutting system for metering Weaknesses of material bodies that can be cut along one predetermined contour line, and contains facilities for Carrying out the method or its modifications. Wesent Heatable cutting knives are a structural component  in a given line contour, as well as at least op tionally precise stop pieces that the penetration depth of the Limit knives and / or a path measuring system around which Measure cutting progress and if necessary for a control o to make the control of the cutting movement accessible.

A combined cutting / punching system is also invented claimed in accordance with, containing facilities for through management of the combined cutting-punching process. Doing it the cutting preferably does not follow at the same time the punching process in order to avoid cutting precision through mecha reduce vibrations.

An essential part of the cutting device is a Cutting tool containing at least one cutting knife if necessary, 3D-curved cutting line contour for installation in a aforementioned system.

DRAWINGS

Embodiments of the invention are in the drawing shown and in the following description nä ago explained.

Show it:

Fig. 1 shows a schematic sectional view of a work tool the basic structure of the present invention for weakening a single direction,

Fig. 2 is a detailed enlarged detail (detail C) of Fig. 1, showing how the cutting blade is inserted into the tool,

Figure 3 OF INVENTION tool to the invention variant, the directions of the prinzipiel len construction of a tool for two attenuation for the preferred use with strongly curved ge products shows. A schematic sectional view of a,

FIG. 4 to FIG. 7 is a sectional view of respective weakening of a weakening process of the invention without on the attenuating material to the body,

Fig. 8 to Fig. 11 is an illustration according to FIG. 4 to FIG. 7 for an inventive process for weakening a reduced in thickness and a carrier not pre schwächtes decor,

Fig. 12 to Fig. 15 is an illustration according to FIG. 4 to FIG. 7 for a non-reduced in thickness and a carrier ge before foaming a foam layer schwächtes decor,

Fig. 16 to Fig. 19 is a representation according to FIG. 4 to FIG. 7 for an inventive process for weakening a reduced in thickness and a weakened carrier before the foaming decor,

Fig. 20 is a view showing a directly electrically heatable cutting blade with the blade in front of handenen gears,

21 is a schematic sectional view of an OF INVENTION to the invention the cutting blade, the nen by Heizpatro is indirectly heated FIG.

Fig. 22 is an illustration according to FIG. 21, with Temperierkanä len in the cutting knife,

Fig. 23 to Fig. 29, the top view of various exemplary contour lines that can be generated with one or more tools according to the invention who.

DESCRIPTION OF THE EMBODIMENTS

In the figures, the same reference symbols designate the same or functionally identical components.

A cutting or weakening device designed according to the invention is installed in a fixed system connected to the ground. The manufacturing tool for weakening the material according to the invention on an exemplary car instrument panel consisting of a 3-layer composite is explained in more detail below with reference to FIGS. 1 and 2:
A fixed system fitting 10 has a negative shape matching the shape of the resulting instrument panel. It serves as a receptacle and a form-fitting counterpart for the so-called product, here the instrument panel, the material of which is to be weakened.

Another part of the tool is formed by a hold-down device 12 that matches the shape of the product being produced and that serves as a fixing device for the product.

The hold-down device 12 is guided with a preferably hydraulic drive on the one hand via guides 14 from a guide cylinder 14 a and a fitting bush 14 b with a suitable fitting bolt 14 c and on the other hand via springs 16 and spacers 18 fit precisely onto a product inserted into the system fitting 10 of the cutting device hazards.

In the embodiment shown in Fig. 1 is a central mounting unit for the guides 14 and springs 16 and the tool itself - see below - a Ba sisplatte 15 is provided, on which the above-mentioned Füh approximately 14 and the compression spring 16 with spacers 18 in the longitudinal direction of the cutting contour is repeatedly reversed. Since the hold-down device 12 is thus guided on both sides of its longitudinal axis and fixed by spring force, its precise positioning and stable fixation with respect to the actual cutting tool is ensured even with a considerable longitudinal extension of the product.

In the closed position shown in FIG. 1, the product can be found with its visible side in relatively light contact, which can be set via the pressure force of the springs 16 , with the form fitting 10 .

The two devices 14 and 16 and 18 repeat at a certain distance in pairs in the longitudinal direction - not shown in Fig. 1, since the longitudinal direction leaves the paper plane - to uniformly hold down and fix the product over the entire length of the contour to weaken guarantee for the subsequent cutting process.

The hold-down is preferably made of metal, for example stainless steel, of a suitable thickness in order to be able to have a suitable stability. Alternatives would be accordingly rigid plastic constructions, provided that they have the necessary rigidity and strength corresponding to the desired tool life. The hold-down device 12 is thus flat, has an opening in the loading area where the product is to be weakened, is guided here in the example below and is at the top under a preload supplied by the spring 16 , with which he interacts with the spacers presses against the product. The product therefore remains securely fixed.

The knife holder 20 extends beyond the plane of the drawing in FIG. 1 to accommodate one or more cutting knives 22 in their entire length. It has a suitable holder for the cutting knife, which allows the quick replacement before. The knife holder 20 is preferably made of a rigid, hard material to ensure a long service life of the tool. The further material properties of the knife holder preferably depend on how the cutting knife or knives 22 are heated.

In general, the knife holder 20 for this purpose has a heating device, by means of which the cutting knife or knives 22 can be heated to a predetermined temperature. For this purpose, a temperature control channel 26 is sketched in FIG. 1, which optionally passes through the knife holder in several turns or can be present several times. This channel is then loaded with a suitable medium, such as water, oil or steam, etc., in a suitable manner in order to bring the cutting knives 22 to the desired temperature (for example approximately 480 Kelvin for frequently occurring plastics) and to hold them there. For this purpose, a large-area contact between the base of the cutting knife 22 and the Messerhal ter 20 is preferably provided and the knife holder consists of a Ma material high thermal conductivity. The set temperature of the cutting knife should be adapted to the material to be cut in a suitable manner, for which a total consideration is necessary, in which the cutting pressure is an essential component.

Alternatively or in combination with the aforementioned temperature channels 26 , heating cartridges 24 can also be present, or the cutting blades themselves can be designed as ohmic resistors with a corresponding current, so that the predetermined temperature is reached.

The knife holder 20 is attached to the base plate 15 with a shoulder 21 and carries as an essential part the two cutting knives 22 , which are shaped so that their cutting edges each form a three-dimensional contour line that has exactly the 3D shape that is in the To be generated in the instrument panel. The latter is not apparent from Fig. 1, since this is a sectional view through the tool. Contour lines are, however, shown in FIGS . 23 to 29. These themselves are dealt with below.

If the cutting knife as electrical resistance sele elements are operated, they are from the surrounding measurement seraufnahmeteil preferably electrically isolated, however firmly connected to this. This happens, for example through a ceramic insulation covering the base part of the Surrounding cutting body. The base part is thus electrical isolated from the rest of the system, but still with a knife receiving part firmly connected.

A temperature sensor 28 is located in the area of the knife base and takes the temperature of the knife edge at a point where it does not interfere with the cutting process itself and sends a corresponding temperature monitoring signal to a control unit or a controller (not shown) for the cutting process.

The knife holder 22 is in suitable, for example, analogous to the guides of the hold-down tool guides 30 via a hydraulic drive (not ge records) together with the base plate 15 and the neck 21 back and forth. Precisely fitting spacers 32 (also available in the upper part of FIG. 1, but not drawn for reasons of increased clarity) in conjunction with column holder 29 and socket holder 31 ensure that the movement into the depth of the cut through a precisely defined end stop between the spacers 32 is stopped, the cutting depth of the cutting knives 22 thereby being limited:
At the stop, the two spacers 32 come into contact with each other, which in turn are attached to column base 29 on the base plate 15 or via the socket holder 31 on a common base with the contact fitting 10 , thereby ensuring a stable, precise counter bearing for the cutting process is reached.

In the following, the weakening method according to the invention is itself described in further details:
After the product 36 is inserted into the cutting device and fixed there by an initial movement of the hold-down device, the two cutting knives 22 are brought into contact with the material body 36 to be weakened by the hydraulic control via a control cylinder (not shown) in contact with the intended location of the weakening line contour to be generated on the instrument panel 36 .

The two knife edges have a wedge shape and taper to a cutting edge of about 1 to 2 tenths of a millimeter in width. The cutting edge itself has a thickness (width) of about 1 mm and is brought to a minimum temperature of about 480 Kelvin with the temperature control channel 26 and circulating hot medium therein and / or by the heating cartridges which are often used or by resistance heating. If special, high requirements for a homogeneously distributed heat in the knife are to be met, then any desired combinations of the heating devices can be combined at different points on the knife.

Now the knife edges are pressed with a certain, predetermined maximum value exercised. As a result of that this pressure value for the subsequent weakening process never is exceeded, is with an unproblematic shift Construction of the product already ensures that a cut through the material can be done.

In an advantageous manner, the depth of cut is limited by several mechanical stops of the stop pieces 29 on the dance pieces 32 at several points at the same time. This mechanical stop is provided with a fine adjustment that can be precisely maintained even over long tool life. Hardened, finely ground spacers and additional disks are advantageously provided for this purpose, which ensure high mechanical stability for long service lives. This enables precise cuts to be made with a cutting depth accuracy of approximately 1-3 / 100 mm.

If the spacers 32 rest against each other with their end faces, the required depth of cut is sufficient, and the cutting blades can be retracted after a given dwell time for a retraction movement in the opposite direction by a corresponding hydraulic control from the previously created trench.

When the cutting knives 22 are retracted, the actual cutting process is completed. Now the base plate 15 can optionally be moved together with a weakened instrument panel into an open position, from which the instrument panel can be removed manually or mechanically and is available for further processing or installation.

As from the previous description for the subject man can be seen, the maximum mentioned above can now Pressure value on the materials used in the layer structure be adjusted. For example, a low pressure worth about an effective cutting force of approx. 10 N per Corresponds to the millimeter cutting length by a corresponding Force control on the control cylinders of the knife edges be generated. A relatively low pressure value ensures Connection with the increased temperature of the cutting knife that a cut can be made as long as the cutting edge temperature near or above the respective enamel point of the material to be cut. Then can invent accordingly, a cut with low speed speed - if due to increased cutting accuracy wishes - take place in the depth of the material, at that only very low pressure forces are required. Despite However, the slow processing time is invented still relatively short in relation to the laser beam processing.

However, the low contact pressure of the knife edges 22 ensures that no impression is produced on the visible side of the product, here in the exemplary embodiment of the instrument panel. Due to the low thermal conductivity of the materials to be cut - it is mostly plastics, especially thermoplastic materials or thermosets - as well as a short dwell time of the cutting knife at the turning point at maximum depth of cut, it can be excluded that the decorative layer is exposed to the heat of the knife edge suffers an optically visible damage.

As a person skilled in the art further recognizes, according to the inventions method according to the invention by a single, comparatively short controlling cutting movement essentially vertical to the area of the precision material to be cut cut can be carried out without it being an expensive Control of cutting knife or laser beam in the longitudinal direction tion of the specified contour line is required, because fiction The entire contour, including the decorative layer, is preferred simultaneously or at least in sections at the same time cut.

This increases the cycle times in production, which increases productivity. At the same time is one Checking the depth of cut is possible because the knife can only be reversed for the retraction movement if the mechanical stop has occurred. The signal for reverse control, for example by an electri contact with one or more of the intended contacts strikes generated directly, or in connection with egg ner sensor control, as described below.  

In a further exemplary embodiment of the cutting system according to the invention, a plurality of displacement sensors for displacement measuring systems from the prior art, which are fixedly connected to the knife holder 20 , are present, which measure the distance traveled by the knife in relation to a predetermined starting position, whereby in addition to the waypoints for the cutting step preferably associated time values and in particular this data are stored at the point of reversal, ie at maximum cutting depth for control evaluation and logging. The starting position is preferably a zero position of the knives in the above-mentioned closed position of the system. There are preferably at least two position measuring systems at the two longitudinal ends of the cutting contour.

Furthermore, based on the measured by the distance sensors in the pro programmed logic for cutting control or if necessary Cutting control provided a speed control. This is preferably programmed so that when it is exceeded a predefinable cutting speed of the original neuter control pressure is reduced, which increases the Cutting movement slows down again.

This can make the layer structure rather problematic Layer sequences can be cut precisely without an un controlled cutting takes place. This is particularly so important if first a relatively hard layer with re relatively high melting point, such as a thermoplastic with Reinforced glass fibers can be cut  and then a relatively soft layer with a counter also low melting point.

According to the invention, the position sensors are used The signals from the control logic are monitored and output evaluates. If this evaluation shows that, for example the required for two out of a total of four displacement sensors Depth of cut is reached, so the pressure on the a (central) control cylinder for the cutting knife ge aims to decrease or stop to an appropriate order control for the retraction movement.

There are several control cylinders for the cutting pressure can then even specifically target the cylinder be depressurized, while others on a ge remain of lesser value to the cut in "their" areas to accomplish.

Advantageously, one or more Path signals and a time source the current one Cutting speed calculated by the control unit become. Now there is a very sudden increase in Cutting speed, it can be concluded from this that the knife has just shifted from a hard layer into one soft layer has pushed into it. So a sudden too steep or too high a climb to be exploited lower the pressure on the control cylinders to a precise, controlled cutting movement with min to be able to perform different cutting speeds.  

The displacement sensors give a signal that instead of or in combination with the mechanical stop as he continues has been described above, can be exploited to the Stop forward movement of cutting knives, slow down men or to pull back.

For this the programmable logic unit of the control tion device only via a correspondingly predetermined Limit of the route. If this limit at Distance measurement achieved, and this via the signal evaluation of the Logic communicated, so a corresponding withdrawal process triggered by the control device.

In a further modification of the Schwä invention chichungsverfahren can advantageously the retraction speed of the cutting knives out of the material stant or alternatively depending on the location of the knife be specified in the trench. To do this, the double controllable control cylinder with a corresponding predetermined pressure controlled, which corresponds to a appropriate retraction speed.

For example, with an initially slow, but then increased, and at the edge of the trench, such as the deliberately reduced retraction speed, a good result can be achieved, on the one hand avoiding excessive contamination of the knife and on the other hand ensuring that the knife edges are retracted slowly enough in order to leave a clean cut, in which possibly existing cut remnants are melted away by abrasion, etc. In particular, the bead 50 in FIGS. 4-19 can be rounded off in order to avoid residues which are dangerous for humans in the event of an airbag explosion.

More details on the actual cutting through different material composites are still below wrote.

Fig. 2 shows how the knife edge 22 is vorgedrun gene in a 3-layer composite of carrier 38 , foam 40 and decor 42 of the product until shortly before the start of the decorative layer 42 . From Fig. 2, which shows realistic layer thickness ratios, it can be seen that the cutting process according to the invention is not trivial, since a high degree of precision is required especially when the last, often very thin, decorative layer is weakened. The cutting device according to the invention realizes a cutting depth accuracy of approximately 1 to 3/100 millimeters.

In Fig. 3, in addition to the description of Fig. 1, a further variant of the embodiment of the cutting device according to the invention is shown, which instead of only one hydraulically moved knife holder 22 has two, which are used one after the other. The use of several knife holders and cutting knives is recommended when the surfaces of the product to be cut have a relatively strong curvature and it is important that the movement of the knife edges is parallel to the knife surface. In the vast majority of cases, this is a relatively imperative boundary condition in order to create a clean cutting geometry, to avoid undercuts and to achieve long tool life.

Fig. 3 shows a structure similar to Fig. 1, in particular with regard to the storage of the product in the Anla molded piece 10 , and the hold-down 12 and its gene gene, and the base plate 15 and the base 13th

However, they are two separate cutting knife units provided that work independently. The one Cutting knife device is in the upper part of the figure extended state shown in engagement with the product.

It essentially contains a hydraulic cylinder 44 A, which is firmly connected to the hatched frame element, which is designed as a stop piece 46 of the upper tool. The cutting unit also has a slide guide 49 a, which permits a linear displacement of the knife holder 20 a from a retracted state - see lower knife unit - into an extended state - see upper cutting unit. The cutting pressure can be fine-tuned as described above to suit current cutting situations.

When the one cutting process with the slide shown in Fig. 3 above has ended and the knife holder 20 a has been moved back into the retracted position, the second cutting process can be carried out in which the lower cutting unit with the knife holder 20 B and the slide 48 B is used. The cutting result can be checked by means of a specific evaluation by comparing the respective stored actual values, in particular those at the reversal point of the cutting movement and predetermined target values. Reject products that are hazardous to safety can thus be reliably identified.

If both cuts have been carried out successfully, the cutting result has possibly been checked and the cut can be qualified as successful, the second slide can also be retracted and the product can be removed from the cutting device, as was previously the case in connection with FIG. 1 has been described.

In Figs. 4 to 7, a sequence during he inventive cutting operation is shown, wherein a Trä ger is used, which is not pre-weakened at the point of weakening himself. In the figures, the hold-down device 12 , carrier 38 , foam layer 40 , decorative layer 42 and the contact molding 10 are drawn as a contour counter in each case in a sectional view from top to bottom. An arbitrarily chosen form is taken as an example.

The thickness of the decorative layer is et what is shown too large.

As mentioned at the beginning, the carrier layer 38 is usually harder than the underlying foam layer 40 and the decorative layer 42 . In Fig. 4 the knife edge is shown when putting on the support layer through an opening in the hold-down. In Fig. 5, the knife edge due to the pressure acting on it downward and its melting effect almost completely penetrated the carrier layer 38 , with a bead 50 of melted material depositing on both sides of the knife edge.

In Fig. 6 the knife has completely penetrated the foam layer 40 and the decorative layer is weakened 42 up to the required residual wall thickness. This is the phase in which either the mechanical stop, as mentioned above, has been reached or, alternatively or in combination with one another, a displacement sensor generates a corresponding reversing signal in conjunction with the control logic mentioned above.

In Fig. 7 the knife is shown in the retracted position. The cutting geometry itself corresponds to the cross-sectional contour of the knife. The material from the cut trench is partially recognizable in the melted form as a bead 50 or already evaporated during cutting itself.

In FIGS. 8 to 11 an analog interface sequence is shown, but the carrier 38 was beitsgang in a separate Ar already pre-weakened, for example directly during the casting of the shaped support part. The advantage of cutting an already weakened carrier 38 can be seen in the fact that the cutting with the cutting device according to the invention is restricted to what is really essential, namely the complete severing of carrier layer 38 only through recess 52 , foam layer 40 and the “only - Weaknesses "of the decorative layer 42 . Another advantage is that the foaming of the foam layer 40 is still possible without restriction, despite the weakening of the carrier 38 , since the carrier is still closed.

For the further description of FIG. 4 can be made to the description to Fig. 7 are referred to.

12 to 15, an analog section is shown, in which the carrier 38 has not been weakened, but instead the decorative layer 42 has already been weakened in a separate operation, see FIG . Recess 54 . Such a procedure can be recommended if very high accuracy requirements are imposed on the depth of penetration of the knife into the decorative layer. This can be the case, for example, if the decorative layer itself is very thin - about 1 to 1.5 millimeters and the remaining thickness after weakening should be about 2/10 mm to 3/10 mm or less. In such a case, the fact that it is easier to weaken the decorative layer separately if it lies in one plane and can be processed there can be exploited.

In Fig. 14 the knife edge has advanced so far that a certain remaining wall thickness X remains in the foam layer, so as not to risk the knife penetrating into the decorative layer. An unintentional pushing through of the decorative layer would then be feared if the focus was, for example, on very fast (and therefore coarser) machining of the workpieces.

According to the invention, the cutting method can therefore also be used for cases in which the decorative layer has already been weakened. However, unlike Fig. 14 and 15 may, if it is wanted, the foam layer can be completely penetrated 40 when this is required. However, if a complete penetration of the foam layer 40 is dispensed with, there is the advantage that the layer structure can be made with a far lower depth of cut accuracy, since the decorative layer 42 has already been weakened before. The foam layer 40 has such a low tensile strength that there are no difficulties in tearing open the predetermined breaking line.

Fig. 16 to Fig. 19 shows an analog section sequence, wherein a pre-weakened carrier and a pre-weakened decorative layer is used. For such a combination in the layer structure, what was said above for the individual cases - weakened decor or weakened carrier - applies alone.

In Fig. 20 an electrically heatable cutting knife 22 is shown with existing teeth in the blade with connec sen to the poles of a DC voltage source. The meter is therefore heated directly and completely in coherent, electrically conductive sections.

In FIG. 21, heating cartridges 24 embedded in the knife holder 20 , which are preferably formed as an ohmic resistor embedded in sand and / or ceramic in a metal tube, heat the cutting knives indirectly. There should be good heat conduction between the holder 20 and the cutting edge 22 .

In Fig. 22, a temperature control channel 26 is provided in the holder 20 of the cutting blade 22. This heats up the holder and also the cutting blades via heat conduction. A suitable hot medium is permanently flowed through in order to maintain a constant temperature on the knife.

In Figs. 23 to 29 different attenuation contours are shown. All weakening contours shown here are in principle suitable to form a suitable airbag breakout opening.

Fig. 23 shows, as a contour line of a horizontal line 37, which can be produced, for example, by using a single cutting blade. Fig. 24 shows an H-shaped contour line 37 , which can be made depending on the curvature by using a single (little curvature), two or three (a lot of curvature along the vertically drawn lines of the H) cutting knives. The same applies to Fig. 25 and Fig. 26, in which 37 aufwei sen the outer vertical portions of the contour lines of a specific shape, either a semi-circle or a square being imaginary C.

Fig. 27 shows a weakening contour 37 , in which we weaken essentially three sides of a rectangle, and the fourth - a long side - not. The standing long, long side takes over the function of a "hinge niers", that is, when the predetermined breaking line tears open, the aforementioned lower side remains and the detached piece of the airbag cover folds forward, down on.

FIG. 28 shows a weakening contour line 37 resulting from FIG. 27, with the lower side additionally having weakened sections coming from the outside.

FIG. 29 in turn results from FIG. 28, with the area remaining in FIG. 28 additionally including two additional linear weakening areas which are not connected to one another and are arranged symmetrically. The measures indicated in FIGS. 28 and 29 can be recommended if the material of the layer composite has a relatively high tensile strength or its rigidity is so great that the hinge effect, that is, the folding movement of the detached part of the cover, must be further supported ,

Also in sections, overlapping at a short distance Cuts (not shown) can be made to determine effects of tearing or stopping of material to effect.

Although the present invention is preferred based on one th embodiment has been described above not limited to them, but in many different ways modifiable.

The cutting system described above can now in front part way according to another embodiment of the invention as a combined cutting-punching system be det in which in a separate process section  Instrument panel from a blank provided is punched and in another process section material weakening according to the invention is itself carried out. The system described above is only for this purpose punching tools.

This has the clear advantage that the product or the blank for the product only one Times inserted or removed in the system becomes, which makes production processes much more efficient can be executed.

According to the invention, all the conventional designs of the cutting edge of the cutting knife 22 can be used, depending on the intended effect: for example, the cutting thickness of the material to be cut, the depth of cut, the material hardness, the speed of cut, and the intended speed Service life of the knife be adapted to the type that the most optimal possible miss can be achieved from the aforementioned sizes.

The same applies to the cutting edge angles and "Point angle" (with sectional view of the knife edge). Again, the knife should be designed so that a sufficient mechanical stability and thus durability acceptable cutting force is present. For example for this, the cutting edge should be designed so that it initially runs slenderly towards the cutting edge and then in egg nem ends duller in comparison, tip angle ends. This leads to a good compromise between cutting quality and Tool life, because the tip is somewhat defused.  

Furthermore, the cutting edges of the cutting blades used can also have serrations - see. also Fig. 20 - or other, for example, have wavy bulges. As a result, in principle, as is known in the prior art, a reduction in the urgent knife cross-section or volume is sufficient. As a result, reduced pressure can be used, particularly when the decorative layer is weakened. However, the teeth should be arranged parallel to the cutting direction so as not to form undercuts which can result in very heavy contamination of the knife after the cutting process. Basically, a corresponding compromise between cutting force, tool life and the cross-section of the remaining cross-section remaining through the toothing should also be aimed for.

The cutting method according to the invention can also be based on Mo nolayers or other layer compositions or Layered composites can be applied. So it's not on limits the scope of the airbag covers.

In particular, the path detection makes sense with a Control of the cutting pressure can be combined, even at very inhomogeneous layer sequences z. B. - soft / hard / very soft / hard - a controlled, yet efficient and pre to enable precise contour cutting.

Finally, the features of the subclaims in essentially freely with each other and not by those in the claims  present order combined with each other if the characteristics are independent of each other.

Claims (15)

1. Method for the metered weakening of cutable material bodies ( 36 ) along a predetermined contour line ( 37 ), comprising the steps,
Bringing the material body ( 36 ) into contact with a predetermined contact surface ( 10 ),
Heating or holding at least one cutting knife ( 22 ), the cutting edge of which has the shape of at least a part of the predetermined contour, to a predetermined, elevated temperature (s),
Approaching the knife edge to match the contour line ( 37 ) of the material body ( 36 ) to be weakened,
Applying pressure less than or equal to a predetermined maximum value via the cutting edge on the material body ( 36 ) in order to carry out a cut until a predetermined residual material thickness is reached, and
The at least one cutting knife ( 22 ) is brought out of the trench. 2. The method of claim 1, further comprising the steps
Detecting the remaining, uncut material thickness at one or more points on the contour line,
Generation of a corresponding path signal,
Evaluating the signal,
Stop the pressure when the signal shows that a predetermined limit of the uncut material thickness has been reached. 3. The method according to claim 1 or 2, further comprising the steps,
Detection of the cutting speed,
Decrease the pressure when a predetermined maximum value of the cutting speed is exceeded. 4. The method according to claim 1 to 3, further comprising the steps to leave the cutting edge when reaching the predetermined residual material thickness, the knife edge ( 22 ) for a predetermined period of time on the Bo. 5. The method according to any one of the preceding claims, applied to the processing of material bodies ( 36 ) with several layers ( 38 , 40 , 42 ) made of different materials, in particular with one or more layers of thermoplastic and / or thermoset material of different hardness , comprising the step of adapting the pressure value specification during the cutting process to the hardness of the material layer, in particular by checking the cutting speed. 6. The method according to any one of the preceding claims, further comprising the step of pulling the knife ( 22 ) from the material at a predeterminable, constant or location-dependent retraction speed after the minimum residual thickness has been reached. 7. The method according to any one of the preceding claims, used to produce a predetermined breaking contour line ( 37 ) in the cover of an airbag in a vehicle. 8. The method according to the preceding claim, in which in a single cutting process a carrier layer ( 38 ) and an intermediate foam layer ( 40 ) at least in we significant sections of the contour line ( 37 ) and cut through the visible side of the airbag cover decorative layer ( 42 ) in essential sections of the contour line can only be weakened. 9. The method according to the preceding claim, containing the step Setting one according to the duration and the size that can be specified Pressure value for breaking through or weakening a layer. 10. The method according to any one of the preceding claims, in which the material body ( 36 ) is formed in one and the same system from a blank, in particular by punching cutting and is weakened in doses along the predetermined contour line. 11. Cutting system for the metered weakening of cutting capable material bodies along a given contour never, including facilities for performing the method according to one of the preceding claims 1 to 9.   12. Combined cutting / punching system containing equipment the implementation of the method according to claim 10. 13. Cutting tool containing at least one cutting knife ( 22 ) for installation in a system according to the two preceding claims. 14. Cutting tool in which at least one cutting knife ( 22 ), in particular two cutting knives, are provided, which form a three-dimensional contour. 15. Material body ( 36 ), in particular a motor vehicle interior trim part or motor vehicle instrument panel, comprising a material weakening carried out according to a method according to one of claims 1 to 10 along a contour line ( 37 ).