Research On The Key Problems 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 method only to mass production. Recently, customer's demand in product diversification in this field calls for new manufacturing processes appropriate for small-lot production. Among various kinds of processes developed over the past few years, the research of the NC incremental sheet forming process which utilizes a simple tool has been paid great attention to.The NC incremental sheet metal forming process is a flexible forming process without dedicated forming dies, in which the NC program is designed according to the forming requirement of sheet metal components. The sheet metal is formed step by step with a forming tool according to a certain trace prescribed by the feed system of the NC forming machine until the required shape is obtained. The forming trace of the forming tool can be adjusted by correcting the numerical model of the product. Thus, its forming period is short and products can be quickly renovated. This process is very suitable for small-lot, varied and complex sheet metal products. Based on the programmable multi axis controller PMAC, an open architecture CNC system is built to suit with the flexibility of the sheet metal incremental forming. Being separately realized on different hardware --- the upper PC and the lower PMAC, the real-time control and the equipment management cooperate with each other through the high speed dual port RAM.Full coordination method of gantry motors is applied to provide the tightest and smoothest possible link. Meanwhile, acceleration negative feedback and notch filter are added to the servo loop to restrain the mechanical oscillation. Because the X axis has long travel range, the equipment drives the Y axis gantry by the use of double motors in the direction of X to balance the torque in the Z plane. After theoretical analysis of different control projects, full coordination method is adopted and practically verified that it can keep well synchronization between the two motors. The unstable forming force, which comes from the material stacking and hardening, will induce the mechanical oscillation. Experiments testify that the acceleration negative feedback and notch filter based on the conventional PID control algorithm can effectively attenuate this oscillation. System software HrpDSF is designed and realized by the component program method.The component program method is applied to the development of CNC software system which has multi-layer multi-module structure constructed by the binary reusable components. The System software HrpDSF has open architecture which accords with CNC hardware platform.NC data is stored and managed by structured storage method. On the basis of component program method, HrpDSF organizes the NC data into compound document format to realize the file system in the NC data following the forming logic. The NC component document has advantages of legible structure and fast access.The integration of trajectories and man-machine interactive modification algorithm are realized. The integration of trajectories not only compresses and simplifies the NC data but prepares for the further trajectory layout. To response to the flexibility of the technology varieties, the Man-machine interactive modification permits the operator to rapidly modify the local trajectories by the mouse instead of returning to the CAD model.The engage/retract points dispersing algorithm and loop reversing algorithm are realized. The engage/retract points dispersing algorithm is used for avoiding the accumulation of impacting pits, and loop reversing algorithm for wrinkling and buckling. The system and algorithm are all testified to be effectivity and reliability.The point bolster incremental forming, which adopts point rod as bolster instead of the conventional model bolster, eliminates the constraint of the mould and realizes the real incremental forming. The feasibility of this new forming method is verified by plenty of experiments on the axisymmetric part and FEM simulation. The forming instability flaws and these solutions are studied.