Research On NC Incremental Forming Forvertical Wall Parts

CNC incremental forming, as a new sheet metal dieless forming technology, is committed to overcoming shortcomings, such as long design cycle, high cost, diversity production mode, in traditional sheet metal forming field which has drawn great attention from scholars and researchers all over the world. However, according to cosine law of incremental forming, parts with vertical wall characteristics are prone to excessive thinning even rupture.In this paper, incremental forming technology dealt with vertical wall parts was studied. Firstly, the forming mechanism and process planning of multi-stage forming strategy was discussed. Variable angle and height strategy was used for negative forming, which could be accomplished without support, but come up with a step defect and inaccurate height. Positive forming process mainly adopted the parallel strategy, which could have uniform thickness and good quality. Secondly, two new methods had been proposed, the one was called incremental forming assisted by bending and stretching strategy, the other was called incremental deep drawing process. The former one could have access to the cylindrical products with less wall thinning and more uniform wall thickness distribution. Furthermore, the processing time was significantly shorter so as to cater for production needs. Preformed angle directly determined the final wall thickness. By increasing the preformed angle, the wall thickness was sharply declined. Under the influence of circumferential stress, the phenomenon of an increase in thickness occurred in local area of vertical walls, and the thickened area got larger with the decline of the preformed angle. For the latter, circumferential stress in the flange and tensile stress at the round corner were the main two reasons contributed to failure. Spiral circle method was the optimal path. The limited D/d was between 1.18 and 1.25 under the annealing condition. Finally, based on above forming technology, forming method of irregular parts was analyzed. Compared with bending and stretching strategy, multi-stage forming strategy with a parallel line method was more suitable for forming irregular parts, but the thickness distribution was different due to the structural asymmetry. Thickness distribution of the convex area was significantly greater than that of concave fillet. Dangerous section existed at the bottom of the concave fillet.