Ashkan Alimoradi

In the present work, it is studied how the wire electrical discharge turning factors influence the surface integrity and subsequent fatigue life of Inconel 718. Discharge current, pule on time and spindle speed were taken into account as factors while characteristics to be studied are fatigue life, surface roughness, residual stress, and hardness. It was identified that a sample which is machined by discharge current of 5 A, pulse on time of 600 µs and work rotational speed of 250 rpm yields maximum fatigue life about 14,400 cycles. After finding the optimum level, statistical models of responses were also generated to correlate input-output relationship as well to identify which parameters has the greatest impact on performance measures. It was found from the results that fatigue life and residual stress is majorly influenced by pules current; while the surface roughness and hardness are significantly affected by spindle speed and pulse o time, respectively.

Turn-milling is a hybrid machining process which used benefits of interrupted cutting for proceeding of round bars. However, number of controllable parameters in the hybrid process is numerous that makes optimizing the process complicated. In the present study, an optimization work has been proposed to investigate the trade-off between production rate and cutting force in roughing regime as well surface roughness and tensile residual stress in finishing regime. Number of 43 experiments based on response surface methodology was designed and carried out to gather required data for development of quadratic empirical models. Then, the adequacy and importance of process factors were analyzed using analysis of variances. Finally, desirability function was used to optimize the process in rough and finish machining regimes. The obtained results showed that selection of eccentricity and cutter speed at their maximum working range can effectively enhance the quality characteristics in both the roughing and finishing regimes.

Generally, coil‐tubes are utilized to extract heat from solar ponds. There are different coil‐tubes in which their thermal and hydraulic characteristics depend on configuration and geometrical parameters. In this study, the performance of three well‐known coil‐tubes, namely helical, colubrine, and spiral, as the core of solar ponds is investigated at both smooth and twisted forms. Moreover, different levels of coil‐pitches and twist‐lengths are examined to explore the effects of geometrical parameters. First, the validity of the results is checked by the previous correlations proposed for the coil‐tubes. A good agreement is found, so that the average absolute deviation is about 6%. The results show that the heat extraction is affected by the configuration of coil‐tubes so that at the same geometrical parameters and operating conditions, the highest values are obtained for the spiral coil‐tube and the helical and colubrine coil‐tubes come in the second and third, respectively. It is found that, in all cases, twisting walls lead to higher rates of heat extraction. The enhancement range for the helical, colubrine, and spiral coil‐tubes is 0.3–19.8%, 0.3–46.1%, and 0.6–27.0%, respectively. At the same time, the pumping power augments in the range of 1.0–31.7%, 0.6–70.1%, and 0.4–43.5%. Furthermore, the models with lower level of coil‐pitch and twist‐length provide higher values of heat extraction and pumping power. At the considered ranges, the greatest overall performance is obtained for the colubrine coil‐tube with high coil‐pitch and twist‐length, which presents the performance index of 1.14.