Patent Application
20200189023
The invention is based on a method for producing an overlap composite material from sheet metal with the features specified in the preamble of claim 1, as is of known art from WO 2015/043951 A1. In the electrical industry, for example, overlapping composite materials made of copper and aluminium are used when heavy and expensive copper has to be partly replaced by lighter and more cost-effective aluminium.
A problem in the production of such overlap material composites is adhesion between the two sheets. This problem is particularly pronounced with metals such as copper or aluminium, as passivation surface layers, such as oxide layers, form very quickly on their surfaces. These interfere or impede contact between metal atoms of the joining partners that are capable of bonding.
An object of the present invention is to indicate a way in which the adhesion between the sheets used in the production of an overlap composite material can be improved.
This object is achieved by a method with the features specified in claim 1. Advantageous refinements of the invention are the subject matter of dependent claims.
In a method for producing an overlapping composite material from sheet metal according to the present invention, a first sheet of a first material and a second sheet of a second material, which has a lower strength, in particular a lower yield point, than the first material, are laid on top of one another overlapping in an edge region, and are then joined by rolling. Here the first sheet has a wedge-shaped edge in cross section, which can be formed, for example, by ablative machining of the sheet, such as by milling or grinding. The second sheet is then positioned with its edge against a side surface of the first sheet formed by the wedge-shaped edge, and is then joined by rolling. The side surface formed by the wedge-shaped edge of the first sheet has a greater width than a side surface of the edge of the second sheet, which is joined to the first sheet, so that the edge region of the second sheet is deformed more severely than the first sheet during the subsequent rolling operation.
It is important here that the edge of the second sheet is positioned against an inclined side surface of the first sheet, which is formed by its wedge-shaped edge. Thus the second sheet does not lie on a step or recess formed in the edge region of the first sheet, but rather on an inclined side surface of the wedge-shaped edge.
The inventive configuration of the relevant side surfaces of the sheets causes an increase in the shear stress and compressive stress between the two materials during the rolling process, and thus an increase in the local deformation of the edge regions due, on the one hand, to shear in the materials of the two sheets, and, on the other hand, to the improved extrusion of bondable metal atoms into the bonding zone as a result of effective compressive stresses. In particular, the rolling process achieves a considerable increase in surface area and thus a cracking of oxide layers or other passivation and covering layers in the edge regions of the two sheets.
The edge region of the second sheet is plastically deformed during the rolling over the wedge-shaped edge of the first sheet. The initially relatively narrow side surface of the second sheet is widened until the two adjacent side surfaces are of the same size. As the width of the initially relatively narrow side surface is increased by the rolling process, any oxide or other covering layers on this side surface tear open, so that the metal underneath comes to the surface and comes into contact with the first sheet. In addition, during the rolling process, the material of the edge region of the second sheet is pressed against the wedge-shaped side surface of the first sheet and flows, so to speak, onto the wedge-shaped side surface. Any passivation layers of the first sheet that may be present are torn open on the side surface, so that the metal of the first sheet underneath the passivation layers comes into contact with the metal of the second sheet and can enter into a joint with good adhesion.
Compared to the method known from WO 2015/043951 A1, this results in an improved joint between the two sheets. This is attributed to the fact that in the method known from WO 2015/043951 A1, the second sheet is not positioned on an inclined side surface, but on a step of the side surface. A higher degree of deformation is therefore achieved with the inventive method.
The side surface formed by the wedge-shaped edge of the first sheet preferably has a width that is at least twice that of the width of the side surface of the second sheet. Here the width of a side surface is to be measured from the front face of the sheet in question to its rear face. The width of a side surface corresponds to the distance between an edge on a front face of a sheet and the adjacent edge on the rear face of the sheet.
The width of the side surface of the wedge-shaped edge of the first sheet is generally greater, the flatter the wedge is formed. The width of the side surface of the second sheet is minimal if the side surface of the second sheet is at right angles to the front and rear faces of the sheet, and then corresponds to the thickness of the sheet. The more the side surface is inclined to the front or rear faces of the sheet, the greater is the width of the side surface.
In the simplest case, the relevant side surface of the second sheet can be at right angles to the front and rear faces of the sheet so that the width of the side surface corresponds to the sheet thickness and is a minimum. However, better results can be achieved by slightly enlarging the side surface of the second sheet, that is to say, by inclining it slightly. The second sheet then has an edge region in which the sheet thickness decreases from the front edge, which is positioned on the wedge-shaped edge of the first sheet, to the rear edge of the edge region. Here it is preferable if the edge of the second sheet, as seen in cross-section, tapers over a length, to be measured in the plane of the sheet, which is not more than a quarter of the maximum thickness of the second sheet, preferably over a length that is between one fifth and one twentieth of the maximum thickness of the second sheet. The side surface can, for example, subtend an angle of 80° to 89°, in particular 86° to 89°, with a front face of the second sheet facing the side surface of the first sheet. However, the side surface does not have to be designed as a flat surface, but can, for example, also be a curved surface, or can be composed of a plurality of flat surfaces.
In an advantageous refinement of the invention provision is made for the side surface of the wedge-shaped edge of the first sheet to have a width that is more than twice the thickness of the first sheet. The side surface can, for example, have a width that is two to four times the thickness of the first sheet.
The side surface formed by the wedge-shaped edge of the first sheet can be a flat surface that encloses together with a rear face of the first sheet an acute angle, for example an angle between 10° and 30°, in particular between 15° and 25°. However, such a shape is not optimal, since in an end section of such a wedge the ratio between the thickness of the stronger material and the thickness of the softer material becomes less and less favourable and thus the stronger metal is deformed less and less. An advantageous refinement of the invention therefore provides for the wedge-shaped edge to have a thickness that decreases in cross-section from a starting point to an end at the tip of the wedge, wherein the thickness in the end section decreases faster per unit length than in a main section adjacent to the end section. This can be achieved, for example, by blunting the edge between the rear face of the first sheet and the side surface. As seen in cross-section, the tip of the wedge is therefore blunted.
The side surface of the wedge-shaped edge of the first sheet can be shaped as a curved surface. A simple way to create a suitable side surface is to bound it with a plurality of flat surfaces. For example, a main section of the side surface can be bounded by a first flat surface which subtends an angle of between 10° and 30°, in particular between 15° and 25°, with the rear face of the first sheet, and an adjacent end section can be bounded by a steeper descending curve, or by a surface, for example a surface that subtends an angle of between 25° and 50°, in particular between 35° and 45°, with the rear face of the first sheet. It is advantageous if, in a region adjacent to the main section, the end section initially slopes only slightly more steeply than the main section, for example if it subtends an angle of 35° to 45° with the rear face of the first sheet, and only at the end of the end section is a greater angle subtended with the rear face of the sheet.
The thickness of the wedge-shaped edge in the main section is preferably reduced by at least three fifths, for example by 60% to 90%, in particular by 70% to 80%. For example, each tangent to the main section can subtend an angle of 30° or less with the plane of the sheet. Tangents to the end section of the side surface then subtend larger angles with the plane of the sheet, for example angles of 40° or more. The angle that tangents to the end section subtend with the plane of the sheet preferably increases to the tip of the wedge, for example to values of 35° or more, preferably of 35° to 45°.
In another advantageous refinement of the invention the second sheet is positioned on the wedge-shaped edge of the first sheet at a point where the edge has a thickness that is more than half the maximum thickness of the first sheet, for example between 55% and 90% of the maximum thickness of the first sheet, in particular between 70% and 90%. This point is defined by the point, or rather, the line, at which the first sheet comes into contact with the second sheet when the two sheets are oriented in parallel. Surprisingly, it is not ideal to place the second sheet on the edge of the first sheet such that half the sheet thickness is in front of the point of contact, and half behind. Better results can be obtained if the second sheet is positioned so that the distance from the point of contact to the tip of the wedge-shaped edge is greater than the distance to the base of the wedge-shaped edge. Here the second sheet can be positioned on the first sheet such that the second sheet overlaps the starting point of the wedge-shaped edge. However, better results can often be achieved if—as seen in cross-section—an initial region of the wedge-shaped edge of the first sheet does not overlap with the second sheet before the rolling process begins, for example this initial region, which does not overlap with the second sheet, can have a width of between one fifth and one half of the thickness of the first sheet, in particular between two fifths and one half of the thickness of the first sheet.
The first sheet can, for example, consist of copper or a copper-based alloy. The second sheet can, for example, consist of aluminium or an aluminium-based alloy. Aluminium has a much lower strength than copper and can therefore be plastically deformed more easily than copper by the rolling process.
In a further advantageous refinement of the invention provision is made for the thickness of the overlapping composite material produced not to exceed 60% of the thickness of the first sheet before the rolling process. The thickness of the overlap composite material can, for example, be half or less of the thickness of the first sheet before the rolling process, in particular 30% to 40%. The sheets are therefore severely plastically deformed during the rolling process, which is advantageous for good adhesion in the overlapping edge region.
The sheets used preferably have the same thicknesses within their manufacturing tolerances. However, it is also possible to use sheets of different thicknesses. In general, there are no problems if the thickness of the first sheet is between twice and half the thickness of the second sheet. Preferably, however, the thicknesses of the two sheets differ only by 20% or less from one another.
Further details and advantages of the invention are explained in an example of embodiment of the invention, with reference to the accompanying figures.
Here:
One of the first sheets 1 of
The width bF1 of the wedge-shaped edge region and the width of the side surface 3 measured as the arc length are more than twice the thickness of the first sheet 1. The width of the wedge-shaped edge measured from the tip of the wedge can also be considerably more than twice the thickness of the sheet. However, a width of more than 4 times the sheet thickness usually has no advantages.
In the sectional view of
The side surface 3 can be convex, in other words free of hollows or indentations. In the example shown the reduction of the thickness of the first sheet 1 in the wedge-shaped edge region is strictly monotonic.
In the design example shown, the side surface in the main section is a plane that subtends an angle α1 with the plane of the sheet metal, which can be between 10° and 30°, in particular between 15° and 25°, for example, and in
In the example shown, the side surface 3 is formed by planar sub-surfaces. The side surface 3 can, however, also be curved in design. More generally, the shape of the side surface can therefore be described such that, as seen in cross-section, each tangent to the side surface 3 in the main section with the plane of the sheet metal subtends an angle of at most 30°, preferably at most 20°, while each tangent in the end section with the plane of the sheet metal subtends an angle of at least 30°, preferably at least 35°, for example 40° or more. The angle that a tangent subtends on the end section with the plane of the sheet increases towards the tip, for example to values of 50° or more. For example, in a first part of the end section, each tangent with the plane of the sheet can subtend an angle of less than 50°, e.g. 35° to 45°, and the thickness can decrease from a value hβ1 to a value hγ1. From this thickness on, each tangent subtends an angle with the plane of the sheet of more than 50°, for example 55° to 80°. For example, the value hβ1 can be 10% to 40%, in particular 20% to 30%, of the maximum thickness of the first sheet 1, the value hγ1 can be 5% to 15%, in particular 5% to 10%.
The main section can be directly adjacent to the end section. However, there can also be a transition section between the main section and the end section.
In the main section, the thickness of the edge section is reduced by three fifths or more, for example by 60% to 90%, in particular by 70% to 80%. The main section has a width that is at least as large as the maximum thickness of the first sheet 1. The main section preferably has a width that is at least 1.5 times the maximum thickness of the first sheet 1. The end section has a width that is, for example, between one fifth and one seventh of that of the main section.
As
The side surface 4 can be a flat surface that subtends an angle of 80° to 89° with the plane of the sheet, e.g. 86° to 89°. The side surface 4 can, however, also be curved.
After the sheets 1, 2 have been laid against one another as shown in
During rolling, the edge region of the second sheet 2 is deformed particularly strongly so that it adapts to the contour of the edge region of the first sheet 1.
Before the execution of the described method, the sheets 1, 2 are degreased and cleaned. The sheets 1, 2 can then be annealed so as to adjust to a defined material state, especially for the more solid material. Alternatively or additionally, the sheets 1, 2 can also be brushed before the execution of the method.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2017 119 677.3 | Aug 2017 | DE | national |
This continuation application claims priority to PCT/EP2018/072739 filed on Aug. 23, 2018 which has published as WO 2019/042855 A1 and also the German application number 10 2017 119 677.3 filed on Aug. 28, 2017, the entire contents of which are fully incorporated herein with these references.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2018/072739 | Aug 2018 | US |
| Child | 16798745 | US |
