DE20022113U1 - Milling tool for milling soft materials, in particular for a device for producing predetermined tear lines in decorative epidermis layers in motor vehicles - Google Patents

Description

Description

Milling tool for milling soft materials, in particular for a device for producing predetermined tear lines in decorative

Epidermal layers in motor vehicles

The invention relates to a milling tool for milling soft materials, in particular for a device for producing predetermined tear lines in decorative upper skin layers in motor vehicles that cover airbag covers and dashboards.

For aesthetic reasons, airbag covers in the interior of motor vehicles are designed in such a way that the cover cannot be recognized as such from the top or visible side of the cover. This is achieved by covering the airbag cover and the parts in which the airbag is housed with a continuous, decorative top skin layer. However, so that the airbag can emerge at the desired location when it is used, the decorative top skin layer and the airbag cover underneath have predetermined breaking lines that tear open when the airbag is triggered and clear the way for the airbag. The predetermined breaking lines in the actual airbag cover are provided by trenches and grooves or by reducing the layer thickness of the airbag cover. The production of the predetermined breaking lines in the decorative top skin layer is critical because, on the one hand, the top skin layer must reliably tear when the airbag is triggered and, on the other hand, the predetermined breaking lines should not be visible from the visible side of the top skin layer. There are various methods and devices for producing the tear lines in the decorative epidermis layer.

[File:ANM\HG0509B1.doc] Description, 03.01.01
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From EP 0 428 935 B1 it is known to create this weakening and thus the predetermined breaking line by means of a pulling cut. The pulling cut results in a tapered furrow or groove that is visible on the visible or front side of the airbag cover. However, this is not desirable for aesthetic reasons. A further disadvantage is that the decorative top layer of skin can have different densities across its thickness. This leads to difficulties in making the pulling cut when cutting through areas of different densities.

From DE 196 36 428 A1 it is known to construct the weakening line from irregular perforations that extend right up to the front of the decorative epidermis layer. Since these perforation lines are very thin, they cannot be seen from the front, but their application is very complex due to their fineness and the resulting large number of them.

From US-PS 5,744,776 it is known to apply the weakening line or perforation line using laser beams. This method is also relatively complex because a laser processing unit has to be used.

It is therefore an object of the present invention to provide a milling tool for milling soft materials, in particular for a device for producing predetermined tear lines in decorative upper skin layers in motor vehicles that cover airbag covers and dashboards.

This object is achieved by a milling tool according to claim 1 and by a device equipped with such a milling tool according to claim 9.

[File:ANM\HG0509B1.doc] Description, 03.01.01

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Using a milling cutter instead of a pulling knife provides an additional degree of freedom, as the rotation speed of the milling tool can be varied in addition to the speed at which the milling tool is moved relative to the workpiece to be machined. The semi-conical shape results in two cutting edges at the interfaces where a cone becomes a semi-cone. It has been empirically proven that the semi-conical shape produces very clean and unfrayed cuts in the epidermis material. By guiding the milling tool across the course of the predetermined tear line, a tapered channel is avoided.

According to an advantageous embodiment of the invention according to claim 2, the tip of the semi-conical cutting edge is rounded, so that the predetermined breaking line does not end in a point in its deepest area, but is rounded. A transverse guide of the milling tool is therefore not necessary.

According to a further advantageous embodiment of the invention according to claim 3, the tip of the semi-conical first region lies on the axis of rotation. This allows precise positioning of the milling tool and precise guidance of the milling tool on the epidermis to be processed.

According to a further advantageous embodiment according to claim 4, the cutting edge comprises a second region, which in its basic form is a truncated cone, which tapers in the direction of the material to be machined or in the direction of the first region. A straight chip groove is machined or ground into this truncated cone-shaped basic form, which in the pointed

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zen angle to the direction of rotation. This results in cutting edges that have a stronger chip-removing effect than the cutting edges of the semi-conical first area.
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According to a preferred embodiment of the invention according to claim 5, the cone angle, i.e. the angle spanned by the cone, has the same size in both the first region and the second region.

This makes the manufacture of the milling tool considerably easier, since the straight chip groove only has to be ground out of a conical, tapered basic shape and the semi-conical first area is created automatically with the appropriate choice of grinding wheel. This also applies to the embodiment according to claim 6.

According to a further preferred embodiment of the invention according to claim 7, the taper angle is in the range between 15° and 30°. According to a further preferred embodiment of the invention according to claim 8, the angle between the direction of extension of the chip groove and the axis of rotation is not greater than 10°. With taper angles in this interval, both for the first and the second region of the cutting edge and with these orientations of the chip groove, the most satisfactory results were achieved in the machining of workpieces.

Further details, features and advantages of the invention will become apparent from the following description of preferred embodiments of the invention with reference to the drawing.

It shows:
35

[File:ANM\HG0509B1.doc] Description, 03.01.01
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Fig. 1 is a schematic representation of an airbag cover in the dashboard of a motor vehicle from the front, ie viewed from the optical side,
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Fig. 2 is a sectional view through the representation according to Fig. 1.

Fig. 3 shows a schematic representation of the operation of the milling tool or the device with the milling tool according to the present invention,

Fig. 4 shows a sectional view of the shape of a predetermined breaking line,
15

Fig. 5a, 5b and 5c show a first embodiment of the milling tool, and

Fig. 6a and 6b show a second embodiment of the invention.

Fig. 1 shows a schematic of a dashboard 2 with an airbag container 4 for an airbag (not shown in detail) installed therein. The airbag container 4 is covered by an airbag cover 6 shown in Fig. 2. The airbag cover 6 and the entire dashboard 2 are covered by a decorative upper skin 8 so that - in contrast to the illustration in Fig. 1 - the airbag cover 6 and the area of the airbag are not visible from the outside. A predetermined tear line 10 is shown in dashed lines in Fig. 1, along which the airbag cover 6 and the decorative upper skin 8 tear open when the airbag is triggered.

From Fig. 2, which is a sectional view of the representation in Fig. 1, it can be seen

[File:ANM\HG0509B1.doc] Description, 03.01.01

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that the airbag cover 6 is covered by the decorative upper skin 8. The airbag cover 6 is a plastic structure which has a groove 12 or a reduced layer thickness in the area of the intended tear line 10. The decorative upper skin 8 lying above it also has a reduced layer thickness in the area of the intended tear line 10 due to a V-shaped channel 14 which is incorporated into the upper skin 8 from the rear.

Fig. 3 shows schematically the structure and the functioning of an exemplary embodiment of the invention. The device comprises a milling spindle 20 with a milling tool 22 clamped therein, the milling spindle 20 and the milling tool 22 clamped therein rotating about an axis of rotation 24. The milling spindle 20 with the milling tool 22 is held, guided and controlled in a known manner by a device designated by the reference numeral 26. The milling tool 22 comprises a tip 0 cutting edge 28 tapering towards a workpiece, e.g. an upper skin 8. The cutting edge 28 plunges into the workpiece or the upper skin 8 to a depth T and, through rotation, mills out the V-shaped channel 14 along which the predetermined tear line 8 runs, as shown in Fig. 4.

Fig. 5a, 5b and 5c show different views of a first embodiment of a milling tool 22 according to the invention. The milling tool 22 according to the first embodiment is shown in Fig. 5b rotated by 90° compared to the representation in Fig. 5a. Fig. 5c shows a detail of the milling tool according to Fig. 5a or 5b in the same view as Fig. 5a.

The milling tool 22 is cylindrical in its basic form and is clamped into the milling spindle 20 at a first end 30. The other end of the cylindrical

[File:ANM\HG0509B1 .doc] Description, 03.01.01

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Milling tool 22 is designed as the cutting edge 28. The cutting edge 28 has the shape of a half-cone 32 with a tip 34, a base 36 and two cutting edges 38. The tip 34 is rounded and points towards the workpiece 8.

An exemplary milling tool 22 according to the present invention has a length L of 50 mm. The cutting edge 28 in the form of the half-cone 32 extends over a length L _s of 10 mm, ie the half-cone 32 is 10 mm high. The cone angle α, which the beveled outer side of the half-cone 32 encloses with a direction running parallel to the axis of rotation 24, is between 50° and 30°. The rounded tip 34 of the half-cone 32 has a radius of curvature in the range between 0.4 and 0.8 mm.

Fig. 6a and 6b show a second embodiment of the invention. The second embodiment of the invention according to Fig. 6a and 6b differs from the first embodiment according to Fig. 5a and 5b in the shape of the cutting edge 28. The representation in Fig. 6a is again rotated by 90° compared to the representation in Fig. 6b. The representation in Figs. 6a and 6b is not drawn to the same scale.

The cutting edge 28 comprises a first region 40 which, as in the first embodiment, is semi-conical with a rounded tip 34. This is followed by a second region 42 which is a truncated cone in its basic form. The second region 42 is followed by a third region 44 which is cylindrical and corresponds to the cylindrical basic form of the milling tool 2 2. The semi-cone 32 of the first region 40 sits on the truncated cone-shaped basic form of the second region 42 and both enclose the same cone angle α. In the

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A straight chip groove 46 is ground into the third and second areas 44 and 42, the direction of extension 48 of which forms an acute angle β with the axis of rotation 24. The angle β is in the range of up to 10°. The straight chip groove 46 ends in the third area 44.

The chip groove 46, which is ground at an acute angle β to the direction of rotation 24, results in cutting edges 50 which engage the material 8 to be milled at a flatter angle than the cutting edges 38 of the half-cone 32. This improves the material removal.

The embodiment of the milling tool 22 according to Fig. 6a and 6b is produced by grinding the basic shape, a conically pointed cylinder, into the pointed cone at an angle - angle β - using a grinding wheel with a large diameter. The size of the grinding wheel diameter results in the 0 straight chip groove 46 and by selecting the appropriate dimensions, the half-cone 32 of the first area 40 is automatically created.

A milling tool is created for milling soft materials, in particular for a device for producing predetermined tear lines in decorative upper skin layers in motor vehicles that cover airbag covers and dashboards. The milling tool comprises a rotary axis with a first end that can be clamped into a milling spindle and a second end that is designed as a cutting edge. The cutting edge comprises a first area that has the shape of a half-cone with a tip pointing towards a material to be machined. Using the special milling cutter instead of a pulling knife results in an additional degree of freedom, since the rotation speed can also be adjusted.

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The speed of the milling tool as well as the speed with which the milling tool is moved relative to the workpiece to be machined can be varied.

[File:ANM\HG0509B1 .doc] Description, 03.01.01
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List of reference symbols:

2 Dashboard

4 airbag containers

6 Airbag cover

8 decorative epidermis

10 Tear line

12 groove

14 V-shaped channel 10

20 Milling spindle

22 Milling tool

24 Rotation axis

2 6 Device for holding, guiding and controlling

and 22

2 8 Cutting edge

30 first end of

32 half cones

34 top of 32

36 Base of 32

38 cutting edges

40 first area

42 second area

44 third area

46 flute

48 Extension direction of

50 cutting edges

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Claims (9)

1. Milling tool (22), in particular for a device for producing predetermined tear lines (10, 12, 14) in decorative upper skin layers (8) which cover airbag covers (6) and dashboards (2), with a rotation axis (24), a first end (30) which can be clamped into a milling spindle (20), and a second end which is designed as a cutting edge (28) which comprises a first region (40) which has the shape of a half-cone (32) with a tip (34) pointing towards a material (8) to be processed. 2. Milling tool according to claim 1, characterized in that the tip (34) of the semi-conical region (40) is rounded. 3. Milling tool according to claim 1 or 2, characterized in that the tip (34) of the semi-conical region (40) lies on the axis of rotation (24). 4. Milling tool according to one of the preceding claims, characterized in
that the cutting edge (28) comprises a second region (42) which adjoins the first region (40) in the direction of the milling spindle (20),
that the second region (42) in its basic form is a truncated cone which is tapered towards the first region (40), and
that a straight chip groove (46) is incorporated in the basic shape of the second region (42), the extension direction (48) of which encloses an acute angle (β) with the axis of rotation (24). 5. Milling tool according to claim 4, characterized in that the cone angle (α) of the first region (40) is equal to the cone angle (α) of the basic shape of the second region (42). 6. Milling tool according to one of the preceding claims 5 to 6, characterized in
that the cutting edge (28) comprises a third region (44) which adjoins the second region (42) in the direction of the milling spindle (20),
that the third region (44) is cylindrical and has a diameter equal to the diameter of the base of the second region (42), and
that the straight chip groove (46) extends into the third region (44) and ends therein. 7. Milling tool according to one of the preceding claims, characterized in that the cone angle (α) of the first region and the cone angle (α) of the truncated cone of the second region are between 15° and 30°. 8. Milling tool according to one of the preceding claims 4 to 7, characterized in that the angle (β) between the direction of extension (48) of the chip groove (46) and the axis of rotation (24) is not greater than 10°. 9. Device for producing predetermined tear lines (10, 12, 14) in decorative upper skin layers (8) which cover airbag covers (6) and dashboard (2), with a milling tool (22) according to one of the preceding claims rotating about an axis of rotation (24).