Shear forming, also referred as shear spinning, is similar to metal spinning. In shear spinning the area of the final piece is approximately equal to that of the flat sheet metal blank. The wall thickness is maintained by controlling the gap between the roller and the mandrel. In shear forming a reduction of the wall thickness occurs.
Before the 1950s, spinning was performed on a simple turning lathe. When new technologies were introduced to the field of metal spinning and powered dedicated spinning machines were available, shear forming started its development in Sweden.
Schematics
Figure 2 shows the schematics of a shear forming process.
1. A sheet metal blank is placed between the mandrel and the chuck of the spinning machine. The mandrel has the interior shape of the desired final component.
2. A roller makes the sheet metal wrap the mandrel so that it takes its shape.
As can be seen, s1 which is the initial wall thickness of the workpiece is reduced to s0.
Workpiece and roller tool profiles
In shear forming, the starting workpiece can have circular or rectangular cross sections. On the other hand, the profile shape of the final component can be concave, convex or a combination of these two.
A shear-forming machine looks very much like a conventional spinning machine, except that it has to be much more robust to withstand the higher forces necessary to perform the shearing operation.
The design of the roller must be considered carefully, because it affects the shape of the component, the wall thickness, and dimensional accuracy. The smaller the tool nose radius, the higher the stresses and poorest thickness uniformity achieved.
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