WO1996023621A1

WO1996023621A1 - Double ply metal sheet with an upper boom and a lower boom

Info

Publication number: WO1996023621A1
Application number: PCT/EP1995/004813
Authority: WO
Inventors: Friedrich Behr; Klaus Blümel; Conrad Oehlerking
Original assignee: Thyssen Stahl Ag
Priority date: 1995-02-01
Filing date: 1995-12-07
Publication date: 1996-08-08
Also published as: DE19503166A1; DE19503166C2

Abstract

A double ply metal sheet for use in car construction has its stiffness increased and its weight reduced by comparison with metal sheets made of solid material. The embossed area of each boom raised above the base surface of the boom amounts to maximum 30 % of the total surface of each boom. A torque-transmitting auxiliary member is mounted between the centre lines of the bosses of each boom in contact with the bosses of the other boom. The torque vector lies in a plane parallel to the plane of the booms.

Description

Double-layer sheet made of an upper and a lower flange

The invention relates to a double-layer sheet for use in vehicle construction, which enables savings in weight by increasing the rigidity compared to sheets made of solid material.

It is already from Dilthey, U., Hachmann, B _.; Kopp, R., Marek, U., Rappen, J., lightweight structures and light components, VDI-Reports 1080, Werkstofftag 1994, pp. 657-666, VDI-Verlag 1994, known that a sandwich sheet made of top belt, intermediate layer made of wire mesh or expanded metal, lower flange, an increase in stiffness or a weight saving of up to 44%. The three layers are connected to each other by resistance welding (capacitor discharge welding). The intermediate layers behave like rigid humps when the electrode plates are pressed together.

It is also known that sheet metal components can be connected to one another by a projection weld. Here, hemispherical humps are embossed into a sheet (φ approx. 5 ... 10 x sheet thickness), the hump sheet is pressed against a flat sheet with electrode plates and connected with an electrical resistance weld, the humps being pressed by the pressing force and the heat softening of the Steel can be pushed back practically to zero height. In this form, the known technology cannot be used for the production of double-layer sheets with a required high surface moment of inertia. Three-layer sandwiches now have the following disadvantages:

1. The production of the intermediate layer from wire or expanded metal (web spacing up to approx. 5 mm with each 0.2 mm belt thickness) is expensive compared to only thinly rolled sheet metal;

2. The welding point spacing of <5 mm does not allow continuous production, i.e. no coil capability, because with the current state of welding technology, more than 500,000 humps per minute would have to be welded if a lower production speed of 10 m / min. with a bandwidth of>. Requires 1,250 mm.

It is an object of the invention to find a double-layer sheet which enables a weight saving like the three-layer sandwich, but which only consists of two sheet layers and which, by means of design measures, enables inexpensive production of a coil-capable product. In addition, it should have the same shape properties (isotropy) in all directions of the sheet metal plane, which neither enables a wire mesh due to the different geometric configuration of "weft" and "chain" nor an expanded metal.

In addition, it should be easy to recycle so that adhesive and filler plastics should be avoided.

It is a further object of the invention to provide a method for producing the double-layer sheet.

The task is solved by the measures of the first claim. It has now surprisingly been found that by installing an agent capable of transmitting a torque, the number and size of the necessary per ^{2 of} the sheet metal area to be welded can be significantly reduced. In addition, the welding method according to the invention leads to welding beads, the diameter of which is only about 1 to 4 times as large as the sheet thickness of the thinnest belt. The electrical current to be used per welding stud is correspondingly low. At Δs = 0.2 mm, for example, it is only approx. 0.5 kA in the case of stainless belt material (1.4301) and only approx. 0.9 kA in the case of galvanized deep-drawing steel of the same thickness. A conventional spot welding, on the other hand, leads to a welded connection with a diameter that would correspond almost to the area F with the diameter, thus to a much higher demand for electric current and also to a much rougher, often perforated surface of this thin surface Straps.

A force acting perpendicular to the sheet surface forms a moment with the lever arm (load application point - tip of a welded hump (knobs)), the vector of which lies perpendicular to the load / lever arm plane in a plane parallel to the sheet plane. A torque is also formed in the event that a belt wants to avoid a buckling load. The invention now consists in the fact that the torque is transmitted from the upper belt to the lower belt by means of a wide configuration of the nub tips which lie exactly on the counter belt or by means of unwelded support knobs. This leads surprisingly to l. only max. about 30% of the area of the pimpled belt has to be stamped out of the surface plane, this largely retains the tensile and compressive stiffness of the belts and 2. to reduce the number of pimples and weld beads to be welded while maintaining the high bending strength like that of a three Layer sandwiches according to the state of the art. A technical rule was also found with which the distances between the knobs to be welded can be determined. A typical width of an automotive sheet metal when installed may be 300 mm (L), the thickness of the upper and lower flange 0.2 mm each, the height of the studs after welding 1 mm (sum of "double-layer sheet" 1.4 mm) , then the lever arm (C) of the area moment of inertia to the neutral fiber of the double-layer sheet is 0.6 mm. According to the invention, the distance between the welded knobs can then be greater than / equal to 14 mm (1). The number of studs welded per m ² is thus reduced by a factor of about 10 or more compared to the prior art if a torque-transmitting means according to the invention is provided.

In order to be able to obtain isotropy of the double-layer sheet properties and at the same time a long lever arm (C), the invention further proposes to provide the knobs with circular cross sections in the manner of a truncated cone. If the stresses on a surface element made of this double-layer sheet require a preferred direction, the knobs could also be shaped oval. Since the embossing of the knobs in accordance with the method according to claim 11) is a plug-and-pull process which can severely restrict the embossing height or the length of the lever arm (C), in particular when using higher-strength steel qualities, the flank angle ( o;) the studs to be welded optimized at 45 ° + 10 °, which represents a compromise between the decrease in the tensile / compressive rigidity in the sheet metal plane and the achievable embossing height. - 5 -

The torque-transmitting means can consist of unwelded, pressure-only knobs with the steepest possible edges (ot = 55 ° ± 10 °). On the basis of a welding process found here, which is described below, the total amount embossed from the surface can still <. 30% are held.

However, it has been found in tests that the torque-transmitting means can better be formed only by a contact surface on the nub tips. If the knobs to be welded are embossed with a flank angle of approx. 45 ° and a spherical nub tip, then with the correct selection of the contact parameters at the welding time, there is no springing back of the nub tip (crack frog effect) with formation of an attachment ring. After the weld, the contact surface has only a small weld bead; it does not need to be completely welded to the entire belt with the counter belt. Surprisingly, this form is sufficient at φ _ 5 x ΔS to be able to transmit a sufficiently large torque 09, (P x X) so that the quotient 1 / L> 0.14 AS / C can be.

Of course, an adjacent, ring-shaped surface can also be formed from the nub tip, which is only partially welded to the counter belt.

The use of a double-layer sheet according to the invention, which consists of two belts, which both have knobs of the same shape, has been found to be particularly suitable for a vehicle interior wall or a support, the respective knot tips being welded together to form a contact surface. In this way, a large lever arm (C) is obtained from the belts with a relatively small surface area Area moment of inertia with large (φ) for torque transmission despite a small welded area share of φ.

The double-layer sheet according to the invention and its production method are described below using exemplary embodiments.

Trial 1:

A thinly galvanized sheet with a thickness of 0.2 mm on both sides and a sheet of galvanized steel of St 14, also 0.27 mm thick, were used.

1/7 of all 3.2 mm diameter holes of a 1.5 mm thick stainless steel perforated plate were equipped with a 90 "milling cutter with 45 ° flanks, the perforated plate was deburred in an electropolishing device and thereby rounded edges were rounded off the 0.20 mm thick sheet was placed on top of it, a 3 mm thick latex mat was placed on top of it and the whole package was loaded piece by piece with the help of a deep drawing press, in this way knobs with an approximately 45 ° flank angle with an embossing height of 1.3 mm with spherical nub tip, the smallest center distance of this nub type was 15 mm, as were 6/7 of all nubs with a maximum flank angle of 55 ° - 60 ° and also spherical nub tips with an embossing height of 1 mm.

The 0.27 mm thick sheet was placed on top of it and welded with a projection welding machine and plate electrodes made of a copper alloy (50 x 80 mm) by limiting the minimum gap between the two electrodes to 1.2 mm, but the welding current after the electrode had moved of 0.15 to 0.2 mm after the first electrical contact was switched on, i.e. before reaching the closest electrode spacing. The weld was also achieved with the help of a force limiter, because the 45 ° knobs act like a spring. For the production of the welded connections, 2/50 seconds of welding current with 0.9 K amperes per 45 ° welding studs was sufficient with a holding pressure holding time of 4/50 seconds. Surprisingly, the heat flowing out of the welding bead probably produced an exact one surface with a diameter of φ = 1.8 mm.

A double-layer sheet was obtained which has an elastic bending stiffness which corresponds to that of a 0.7 mm thick steel sheet and that of an approximately 1.2 mm thick aluminum sheet. However, the elongation under elastic tensile stress was so low that the 1.2 mm thick aluminum sheet showed.

Trial 2:

In a second experiment, only 1.5 mm high 45 ° knobs with a conical base circle diameter of 5 mm were stamped from a 0.2 mm thick sheet at a distance of 15 mm from the knob centers (1) with the help of a perforated plate and the latex mat. This sheet was welded as above with a 0.2 mm thick chord, but limited to a double layer sheet thickness of 1.4 mm. This double-layer sheet, with the same elastic bending stiffness as a 1.2 mm aluminum sheet, had a higher elastic tensile stiffness than that from test 1. The surprising cause is that the bending stiffness and buckling stiffness were maintained at the same level under pressure load even without unwelded support knobs presumably due to the shape of the overlying nub tip, which had formed during the welding process and the smaller surface area embossed from the nub belt proportion of. The diameter (φ) of the adjacent nub tip surfaces was approximately 2 mm.

The double-layer sheets obtained in this way were formed into pots using a deep-drawing tool with a drawing gap of 0.5 mm (first attempt) and 0.45 mm (second attempt). In both cases, the formation of pimples with a height of 0,1 0.1 mm in the area which is subject to stretching could only be avoided by previously compressing this area portion flat using the deep-drawing press. In order to prevent the knobs from being pushed through the top chord for outer skin parts, the invention proposes to manufacture the top chord from a higher-strength steel quality or to make it thicker than the bottom chord, and to use the surface areas that have a small radius of curvature as the finished component Making the board cuts to press flat. These areas already have a high rigidity due to their later shape, so that the loss of the high moment of inertia is irrelevant.

Based on the results of the welding tests, it has now been found that the welding process for double-layer sheet welding can be improved. With a medium frequency power supply, the pulse duration (welding time) can be optimized, with the help of an arrangement of the welding electrodes in the form of rollers which are connected in series with respect to the current flow, it is possible to work with increased voltage. In this way, welding is accomplished in a production line from the coils of the upper and lower chord, and a coil-capable product is obtained.

The pimples can also be embossed with the help of a roller stand. The flattened areas of the double-layer sheet can be welded with the prior art to "tailored blanks" with solid material sheets butt (laser) or in an overlap joint (pinch seam).

The invention is explained below with reference to drawings.

1 shows the design of the double-layer sheet according to the invention, FIG. 1 a shows the case found here, in which the surface (F) formed by the diameter (φ) has a welding bead in the middle, FIG. 1b shows the embodiment according to the invention in the form of non-welded support knobs with a steeper flank angle a.

Fig. 2 shows micrographs of welded

Knobs according to the exemplary embodiments, the weld bead not being struck in test 1, but the heat effect has led to the formation of (F).

Fig. 3 shows schematically the nub tip forms, which according to the invention can also transmit a torque (9 = P x X) from the upper chord to the lower chord at least in one direction of rotation. 3c-g represent the most favorable variants for the carrier. 4 shows a hat carrier as an example, which has flattened surface areas produced in the area of the folds before or during the shaping, and flattened surface areas on the edge of the hat as weld-on surfaces.

The advantages of the method and the device according to the invention can be seen from FIGS. 3b, 3c and 3g. All three types can be manufactured with the same embossing tool (embossing roller with inserted knob shape and soft counter material and smooth counter roller) or with a pair of embossing rollers.

Claims

claims

1. sandwich sheet made of an upper and a lower flange, one or both of which has (or have) embossed knobs, characterized in that the surface area embossed from the belt surface per belt is less than or equal to 30% and between the central axes of the knobs connected to the respective counter belt a tool capable of transmitting torque is arranged, the vector of the torque lying in a plane parallel to the belt plane.

2. Sandwich plate according to claim 1, d a d u r c h g e k e n n z e i c h n e t that the quotient of the distance (1) of the knobs, which are welded or soldered to the counter belt, to the length (L) spanned in the installed state by the sheet metal greater than or equal

0.14 ΔS / C

with ΔS as the thinnest sheet thickness of both belts and C as the distance from the center of the thinnest belt to the neutral fiber of the area moment of inertia of both belts and in the region of (1) between the nub centers a torque transmitting means is arranged,

and the knobs have an annular cross section in the manner of a truncated cone.

3. Sandwich according to claim 2, characterized in that the torque-transmitting means is formed by a bearing surface (F) with the diameter (φ) of the welded knob next to the weld with φ ≥ 5 x ΔS or from a ring with φ ≥ 5 x ΔS .

4. Sandwich according to the preceding claims, d a d u r c h g e k e n n z e i c h n e t that the torque-transmitting means is formed with the help of unwelded knobs.

5. Sandwich according to claim 4, d a d u r c h g e k e n n z e i c h n e t that the unwelded knobs have a flank angle (x) of 55 ° ± 10 °.

6. sandwich sheet according to the preceding claims, d a d u r c h g e k e n n z e i c h n e t that the welded knobs have a flank angle (α) of 45 ° ±

Have 10 °.

7. sandwich sheet according to the preceding claims, d a d u r c h g e k e n n z e i c h n e t that when used in the visible outer skin area of the smooth belt

(10-30%) is thicker, and / or consists of a higher-strength steel quality than the knob belt; When used in the non-visible vehicle area, the knob belt is 10-30% thicker than the smooth top belt, or both belts have knobs and are made of the same thickness of the same steel quality.

8. A method for welding the sandwich, so that the welding electrodes partially or force-limited compress the belts, at the same time forming the contact surface or the ring weld according to claim (3).

9. Method for welding or soldering the sandwich as a tape, so that the electrodes are made up of more than two, e.g. consist of three rollers, a power supply roller with approximately half the bandwidth, a counter roller with full bandwidth and a power discharge roller with approximately half the bandwidth.

10. Method for forming blanks from the sandwich material, so that the knobs of the surface areas, which in the deformed state have a smaller radius of curvature than 50 mm, are flattened when the blanks are cut or before the shaping.

11. Method for embossing the knobs, so that the belt is guided in the form of a band over a roller which has the shape of the knobs and is embossed between the counter roller and the band with the aid of a counter roller and soft, elastic material.

12. Sandwich according to the preceding claims, d a d u r c h g e k e n n z e i c h n e t that it is welded to one or more sheet (s) made of solid material in the manner of tailored blanks.