Study On Principle And Process Of NC Incremental Sheet Metal Forming

Conventionally, a sheet metal component is manufactured with dies and punches.However, the high cost of dies and punches limits the traditional manufacturing methodonly to mass production. Recently, customer's demand in product diversification in thisfield calls for new manufacturing processes appropriate for small-lot production. Amongvarious kinds of processes developed over the past few years, the research of the NCincremental sheet forming process which utilizes a simple tool has been paid great attentionto. The NC incremental sheet metal forming process is a flexible forming process withoutdedicated forming dies, in which the NC program is designed according to the formingrequirement of sheet metal components. The sheet metal is formed step by step with aforming tool according to a certain trace prescribed by the feed system of the NC formingmachine until the required shape is obtained. The forming trace of the forming tool can beadjusted by correcting the numerical model of the product. Thus, its forming period is shortand products can be quickly renovated. This process is very suitable for small-lot, variedand complex sheet metal products. In this paper, the forming principle of the NC incremental sheet metal forming processis researched. The deformation law is obtained from the experiments performed on the NCincremental sheet metal forming machine. The stress, strain and deformation force in thedeformation process are analysed in detail and formulas are obtained. It is verified that theNC incremental sheet metal forming process is mainly a shear forming process by gridexperiment and metallurgical analysis. The key process parameters in the NC incremental sheet metal forming processconsist of sphere radius r of the tool head, forming half-apex angleα, ironing ratio, amountof feed, interval between the model and the forming tool, feed speed of the forming tool, IIIfriction, and so on. In this paper, the effect of all the process parameters on the deformationprocess and how to choose suitable process parameters are researched, which is animportant condition of success in the NC incremental sheet metal forming process. Theresearch on the forming principle provides a powerful rationale for the practical production. Because of being shear forming process, the relationship between the thickness (t) ofthe deformed region, the thickness (t0) of the raw sheet, and the angleαbetween sheetmetal forming surface and vertical direction z conforms to the sine law, i.e.,t = t0 sinα .Thesine law indicates that the thickness of the deformed region is close to zero when thehalf-apex angle of the box is close to zero. Therefore, the vertical wall parts can't beformed in a single process. To settle the problem, a method is given to form vertical wall parts, through which aconical part is gradually formed into vertical a wall part by multi-tool paths. The defects, such as fracture, wrinkle, springback, and so on, seriously affect thequality of formed parts. A good result has been achieved by taking a variety of measures toremove these defects. In this paper, a NC incremental sheet metal forming process is presented according tothe above-mentioned researches. The forming experiments of some panels and vertical wallparts have been made, and good results have been achieved.