Study On An Incremental Die Forging Process Of The Even-thickness Helical Tube And Its Forming Mechanism

With the rapid development of petroleum and chemical industry, efficient production of capacity type screw pump, as one of the burgeoning artificial lifting methods, has broad development prospects. The even-thickness helical tube, as one of the important parts of screw pump, its forming precision is of great significance. However, there are little researches about the forming methods of the even-thickness helical tubes so far, in additional, in the forming process of existing methods: the movement mechanism is complex generally, besides, equipment and installation cost is very high, as a consequence, the economic benefit is not good enough. So, it's necessary to make study on the new forming process for the even-thickness helical tubes. In this study, an incremental die forging process is proposed to forming them.Two dies are applied in this study, for its movement mechanism is simple, which saves the cost greatly. Firstly, detailed mathematical analysis was made for the geometry of the even-thickness helical tube and the maximum central angle of a single die ? was calculated when two dies were used, which can avoid the interference between the dies and workpiece when dies opening, making the forming process go smoothly. To make further research, an orthogonal array L64(421) was designed considering the interactions between factors to analyze the influences of forming process parameters on the axial shrinkage based on FE method.The calculation result shows: the maximum central angle of a single die ? should be 140.7° to avoid interference. The most evident deformation occurs around the interface between pre-forging part and finish-forging part. The axial shrinkage exists since the effective stress releases when dies open. A larger area of tensile stress releases when dies open than that of the compressive stress, which directly results in the axial shrinkage.The orthogonal test results indicate: There is no interaction among t, p, q and l, but the significances of any single factor are all strong. Besides, the value of axial shrinkage ?p increases with the increase of t, p, q while decreases with the increase of l, and their influence rank is t>p>q>l. The optimized parameters group is t=6mm, p=400mm, q=1.05, l=40mm.To obtain the helical tube with t=6mm and p=400mm on the condition that q=1.05, the pitch of dies should be designed with 406.8mm by quadratic optimization. FE simulation results agree well with experimental results.