| The processing of large and ultra-large forgings has high standard and they are difficult to product. In the processing of forging, a manipulator is employed to take the heated billets out of the furnace,transfer it from furnace to press and place it on the lower die as quickly as possible. However, usually it is difficult to place it on ideal final position on the lower die by once, then the mislaid billet must be readjusted, sometimes several times. Not only does this incur security risks, but also incur enormous risks to heated-forming operation especially for the Non-ferrous metal after the excessive cooling of the heated billets. Therefore, it is necessary to further study and resolve how to realize the rapid and accurate positioning of large billets on forging dies, but up to now, however, there has been no relevant theoretical research.Multi-body dynamics simulation and the concept of design of experiment(DOE) were used to develop a new solution in this paper,with which the rapid and accurate positioning of the large and ultra-large billets on the lower die can be solved. In the meantime, In view of the friction characteristics between the billet and the die have quite an effect on the accuracy of analysis and the follow-up plastic forming process, this paper researched and optimized the test method of friction parameters in bulk forming process based on forward extrusion. The main conclusions are as follows:(1) The analysis method of positioning of large billets on forging dies includes steps as follows: first of all, constructing the 3D geometric models of the billet and die in CAD software and establishing the orthogonal table which represents the different initial relative position and posture of the billet and the die; Then, Multi-body dynamics simulation technology is used to analyze the placing process of the different initial status of billet, predict the position and posture of the billet after falling into the cavity of lower die from a manipulator with gravity and staying on the lower die steadily; Finally, analyzing the deviating level of that position and the ideal position of forging, combining with the FEM simulation technology of hot forming process, finding out the greatest impact index on deviation, indicating the billet position parameter that should be strictly controlled in the real operation. A representative example of 7050 Aluminum forgings was given to test the effectiveness of the approach, the results show that this method is feasible.(2) The geometry and the friction characteristics between the billet and the die have quite an effect on the positioning and controlling. For example, some billets enable “self-adjusting” along the vertical direction, the allowed range of deviation can be wider; The larger the friction is, the more strictly the initial billet position should be controlled.(3) optimized the test method of friction parameters in bulk forming process based on forward extrusion. The standard compression test with specimens made of Al 7050 and varying speeds was used to get the compression stress-strain curves; combining with the numerical simulation and physical experiment, researched the friction parameters in bulk forming process with varying speeds and varying friction condition, including no lubrication and MoS2 lubricated. The results of simulation and experiment indicated that too large or too small cone angle both caused the extrusion load increases. To avoid the influence of “barreling” effect, the recommended cone angle of the conical die ranges from 5 to 15 degrees.(4) established the correcting formula of the test method of friction parameters in bulk forming process based on forward extrusion. The result proved that the correcting formula can measure the friction parameters in bulk forming process effectively. Furthermore, the method is simple and easy to operate, the accuracy is high. |
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