Fabrication of micro shell parts by incremental forming of foil metal

研究了一种新的微细金属板材柔性成形工艺，该工艺不需要任何昂贵的模具，就可以由平板坯成形毫米级的超薄壳体。这一过程涉及到增量成形技术的使用。该工艺的基本操作是沿着目标形状的一条闭合轮廓线压入和移动一个小的针状工具。通过对所有轮廓线重复该操作，板材逐渐形成最终形状。该工艺可用于微机械壳体等微部件的柔性微细加工。在本研究中，使用了厚度从10到100微米的几种金属薄片，并通过实验考察了尺寸效应对渐进成形断裂极限的影响，由于待成形部件的小型化，很难无缺陷地完成该工艺。当一个非常薄的金属板形成…时多为锥形壳体，壁面陡峭，发生灾难性的壁面断裂。壳体壁厚由厚度的正弦定律表示。正弦定律表明，锥体的半顶角越小，壳体的壁厚越薄。研究了薄板厚度对不锈钢退火后断裂极限的影响。试验结果表明，断裂极限应变随初始厚度的减小而减小。但断裂极限应变大于常规挤压成形的断裂极限应变。但实验是为了保持板材的路径间距、尖端半径和尺寸不变，因此缩小比例仅指毛坯的初始厚度。为了估计结垢效果，在下一次实验中，改变进料量和尖端半径，并考察了它们的影响。第二个实验结果表明，减小进给量和尖端半径与初始厚度成正比，可以提高薄板的断裂极限。然而，薄板的极限应变小于厚板的极限应变，由于塑性变形引起的板材表面粗化导致了厚度的不均匀，超薄板材的断裂极限应变在很大程度上取决于这一现象。对薄片施加不同的增量变形量，并检测了厚度的不均匀性。实验结果表明，未接触触针的后表面粗糙度随总塑性应变的增加而增大，而前表面粗糙度保持不变。所有测试的板材具有几乎相同的最大高度粗糙度。因此，薄板的厚度不均匀性大于较厚的薄板，并且较薄的薄板有较弱的部分导致灾难性断裂。较少

A new flexible process for micro sheet metal forming was investigated, by which millimeter sized very thin shells can be formed from flat blanks without the need for any expensive dies. This process involves the use of the incremental forming technique. The elementary operation of the process is indentation and travel of a small stylus-like tool along one closed contour line of an objective shape. By repeating this operation for all contour lines, the sheet is formed into the final shape gradually. This process would be useful technique for flexible micro-fabrication of micro components such as a micro-machine shell-body. In the present study, several kinds of thin metal foils ranging in thickness from 10 to 100 micrometers were used and the scaling effect on the fracture limit of the incremental process was examined experimentally.With the miniaturization of the components to be formed, it was difficult to complete the process without any defect. When a very thin metal sheet was forme … More d into a conic shell with steep wall, a catastrophic rupture of the wall occurred. The thickness of the shell wall is shown by the sine law of thickness. The sine law indicates that the wall of the shell becomes thinner when the half apex angle of the cone becomes smaller. The influence of sheet thickness on the fracture limit of annealed stainless steel was investigated. The experimental results show that the fracture limit strain decreases with decreasing the initial thickness. However, the fracture limit strain is greater than that for the conventional press forming. But the experiment was conducted to keep the path-pitch, tip radius and size of sheet constant and thus downscaling refers only to initial thickness of the blank. In order to estimate the substantial scaling effect, in the next experiment, the feed and the tip radius were varied and the effects of them were investigated. The second experimental results show that by decreasing the feed and the tip radius proportional to the initial thickness, the fracture limit of thinner sheet was improved. However, the limit strain of the thin sheet was smaller than that of thick one.Since the surface roughening of sheet metals with the plastic deformation develops the non-uniformity in thickness, the fracture limit strain of very thin sheet metal appreciably depends on the phenomenon. The foils were subjected to various amount of incremental deformation and the non-uniformity in thickness was examined. The experimental results show that the roughness of the rear surface, which did not contact the stylus, increased as increasing the total plastic strain, while that of the front surface kept constant. The all sheets tested had almost the same maximum height roughness. Therefore, the non-uniformity in thickness of the thinner sheet was greater than that of the thicker sheet, and the thinner sheets had weaker portions to induce a catastrophic rupture. Less