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The use of tube hydroforming process to produce integrated parts is growing in various industries. In this research, the hydroforming process has been used to convert the circular cross-section of the tube into a square one. In this process, due to the high hydrostatic pressure of the fluid, the friction in the contact area between the tube and the die surface increases significantly. High friction prevents the metal flowing of the tube material on the die surface and therefore it becomes very difficult to completely form the tube inside the die and obtain sharp corners. In this research, in order to improve the tube formability, applying ultrasonic vibrations to the hydroforming die has been used, which causes a temporary gap to be created in the contact surface of the tube and the die, and therefore the amount of friction is reduced and the tube material can slide more easily. By developing a 3D finite element model, the ultrasonic tube hydroforming process was evaluated. Modal analysis was used to evaluate the different shape modes of the die. The effects of ultrasonic vibrations on the deformation process have been evaluated using two variables: corner radius of square die and average wall thickness. An ultrasonic hydroforming setup was designed to form the annealed copper tube and was stimulated using selected resonance frequencies. The results of the finite element model were validated with the deformed tube in the experimental test. After confirming the results, the numerical model was used to evaluate the process parameters.

In this paper, a new nonlinear optimization model for multi-state multi-components systems considering with random and economic dependence is presented for Grate Cooler Fans maintenance problem in Cement industries. The objective function minimizes failure unreliability in future missions subject to cost and time constraints. Actually, the applied constraints caused operation time of carrying out maintenance can be extended to the predetermined time in return to pay its penalty. In the proposed model, economic dependence with the positive effect of simultaneous maintenance executions start time in different components is investigated. Furthermore, grate cooler fans performance is considered under the impression of effects of propagated failures with global effect and failure isolation phenomena that the occurrence probability of propagated failures with global effect on both of the drive and dependent components is discussed. Also, existing more than one drive components based on technical structures of grate cooler fans is possible. The computational results are presented on a real-world case study. Furthermore, sensitivity analyses on the main parameters of the problem are performed to derive some managerial insights that can help corresponding decision makers provide suitable and homogeneous maintenance services in the case study environment.