Abstract
Harmonic decomposition is an analytical technique that is able to express a manifold surface as the sum of a number of simple surface harmonic components. By reconstructing the initial geometry using a reduced number of components, a similar surface is obtained with a lower level of geometric detail. Because small features are filtered out and the resulting surface lies equal parts above and below the original surface, a tailored multi-step SPIF (Single Point Incremental Forming) processing strategy can be devised. This sequential SPIF strategy uses three processing passes to form a workpiece. The first step is a regular SPIF operation using a conventional toolpath strategy to form the reduced geometry. Two finishing steps are then needed, one from the same side to form the smaller features that lies deeper than the reduced geometry and one backwards pass from the other side of the sheet. To add features that need to be shallower than the reduced geometry, the part is flipped around. The used sequence of these finishing steps and the toolpath strategy used significantly influence the final part accuracy and surface quality. The advantages and disadvantages of four of these combined strategies are examined and compared to regular SPIF.
Highlights
The Single Point Incremental Forming (SPIF) process remains a hot topic researched in many institutions around the globe
Because the low order manifold harmonic reconstruction positions equal parts of the target geometry above and below the original surface resulting from the first SPIF operation, the use of conventional spiraling toolpath strategies for the two final steps would mean that the tool only contacts the workpiece half of the time
The accuracy achieved for the low order reconstruction is shown in Fig. 3, along the resulting zones that need extra forming in both direction compared to the intended manifold harmonic behavior
Summary
The Single Point Incremental Forming (SPIF) process remains a hot topic researched in many institutions around the globe. When forming truncated conical or pyramidical geometries, the bottom edge is such a difficult geometry, often leading to stepped features due to rigid body motion of the part bottom when using multi-stage forming [5] This behavior can be taken advantage of through the use of a simultaneous Double Sided Incremental Forming (DSIF) strategy [6]. The workpiece is generated in three subsequent SPIF steps: a first step creates the intermediate shapes, while two finishing steps are needed to deform this shape to the desired final shape One of these finishing steps needs to be a back-drawing step [8,9], where the sheet is processed from the other side after having flipped the clamping rig. The two benefits of using multi-stage strategies, improved accuracy and improved part thickness uniformity, are studied for these sequences method
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