Patent Application
20050183487
1. Field of the invention
The present invention relates to a method for cutting a continuous strip of sheet metal into finite length sections. The invention also relates to such a finite length section.
2. Description of related art
In a variety of manufacturing industries sheet metal is used. The sheet metal normally arrives at the manufacturing industry stored in coils comprising a continuous strip of sheet metal. Coiled sheet metal facilitate transportation and can be purchased in a variety of lengths, widths, thickness and material. However, before the sheet metal can be further machined, the continuous strip must be cut into finite lengths. For this purpose, machines for shearing, slitting and sawing a continuous strip of sheet metal into sections of finite lengths with linearly sheared, slit or sawn edges are known in the art.
To avoid excessive material wastage it is essential that the continuous strip of sheet metal are sheared, slit or sawn into sections which are not longer than required in the subsequent machining operation, e.g. a pressing operation. When the manufacturing volumes are high, even small length savings per section are essential.
However, during the subsequent pressing operation the outermost edge portion of the cut sections have to be firmly held by means of a holder device before the pressing tool is allowed to strike the sheet metal. Thus, the sections are made longer than if no such holding was required. Since these holder surfaces are cut off upon completion of the pressing operation they are considered as wastage.
Accordingly, related art methods for preparing finite length sections from a coiled continuous strip of sheet metal, which is to be used in a subsequent pressing operation, imply that sheet metal has to be rejected.
The object of the invention is to provide finite length sections from coiled sheet metal with a minimum of material wastage.
This object is achieved by means of a method comprising the steps of feeding out a continuous strip of sheet metal, and cutting the continuous strip into sections of finite lengths, wherein the cutting step is characterized by cutting the continuous strip into sections of finite lengths having wave shaped edge portions. The object is also achieved by means of a finite length section of sheet metal being fed out and cut from a continuous strip, the section comprising first edge portions being parallel with the feeding direction of the continuous strip, and second edge portions being transverse the feeding direction of the continuous strip, wherein the second edges portions are wave shaped.
Due to the wave shape of the edge portions, sheet metal material is saved since less material need to be rejected. By means of the method it is possible to provide finite length sections having wave shaped edge portions of the same length as if the sections were provided with linear straight edge portions, at the same time as material is saved. The reason is that the wave shaped edge portions of two, in the feeding direction, consecutive sections overlap each other. Thus, for every cut a distance corresponding to the height of the wave shaped, i.e. the over-lapping distance is saved. When production volumes are high a lot of material may be saved.
Moreover, if the cutting step is followed by the step of firmly holding the wave shaped edge portions in a subsequent sheet metal section machining operation, e.g. a pressing operation, the holder tool will be subjected to less wear if the edge portions are wave shaped instead of linear. The reason is that when the edge portions are wave shaped the material can more easily deform during the strike of the pressing tool. When the edge portions are linear such deformation is not possible to the same extent, so instead the holder tool will absorb the corresponding deformation forces.
Suitably, the wave shape is coplanar with the plane of the section, and the wave shaped edge portions comprise a plurality of mutually spaced notches.
Preferably, the notches have a height in the feeding direction in the interval 10-50 mm. Hereby, sections having wave shaped edge portions falling within this interval are suitable for many applications within car body manufacturing.
Suitably, the wave shape is sinusoidal. Hereby, tool manufacturing is simplified at the same time as a continuous, smooth cut is provided.
The invention will now be described with reference to accompanying drawings, on which:
Each finite length section 13, 15, 17 has first edge portions 21 which are parallel with the feeding direction f of the continuous strip, and second edge portions 23 which are transverse to the feeding direction f. The second edge portions 23 of the section comprise mutually spaced notches 25 and projections 27, which alternately extend between the first edge portions 21 of the section, thus forming the wave shape 23. The wave shape is in this embodiment sine waved, but is conceivable to adopt other wave shapes, such as square shaped waves or saw-toothed waves. Each sine shaped notch/projection has a radius rand the spacing between two adjacent notches/projections is denoted 2s (in
When comparing the figures, it should be apparent that the lengths l of the sections, irrespective of the form of the edge portions, are equal. Still, the amount of sheet metal required for producing the sections 3, 5, 7; 13, 15, 17 of finite length is greater when utilizing the related art solution (
These cut off sections are ready for further machining operations, e.g. a pressing operation. In such cases, the edge portions 23 of the sections 13, 15, 17 have to be firmly held or clamped before the pressing tool is allowed to strike the sheet metal, otherwise the section would not be properly pressed. A not shown holder device provides for the holding or clamping of the edge portions 23. When pressing is completed, these held edge portions 23 are considered as wastage and are rejected.
In addition to the material saving advantage, tool wear is decreased when the sections are provided with wave shaped edge portions, which in turn improves working life of the holder device. The reason is that mechanical stresses on the holder device is less during the pressing operation if the edge portions are wave shaped instead of linear, since the wave shape more easily can deform during the pressing tool strike compared with the linear form.
When the sections are provided with linear cuts, such deformation does not occur as easily and the holder device must absorb the forces concerned.
Obliquely cut sections (swivelling cuts) are known in the art, but not in combination with the wave shaped cuts 31. Accordingly, the same principles apply as for the embodiment relating to
Even though it is possible to use different cutting tools for creating wave shapes in a variety of sizes in dependence of the width and length of the coiled sheet metal strips to be used, it is not always realistic to choose such a solution since cutting tools are expensive to manufacture. Instead, it is likely that one or a few numbers of cutting tools are used in several applications. Accordingly, the size of the wave shaped created by the cutting tool will be a compromise depending on the pressed products in the manufacturing process.
It is preferable that for car body manufacturing, cutting tool which forms wave shapes having notches with a height in the interval 10-50 mm are used, and more preferable in the interval 20-30 mm, and most preferable 25 mm. As mentioned above, these measures are preferably equal to or less than half the distance between adjacent notches.
