A Fig. 9 — Schematic of change in stored energy in Al3003 foil during the following: A — Conventional thermomechanical processing; B — UAM, VHPUAM, and postprocessing heattreatment. when the build got higher. The result also showed that the average required power tended to increase with increasing vibration amplitude, i.e., from 28 to 34 μm or 38 μm. Although it is difficult to distinguish whether the power increased with normal force at constant vibration amplitude at first, the result of samples SL-80-34-4000 and SL-80-34- 8000 revealed that higher power was needed when higher normal force and vibration amplitude were used. However, at a higher weld speed of 42.7 mm/s, the trend of decreasing in average power with increasing layer number no longer existed. Thus, in order to produce a certain combination of vibration amplitude and normal force at a higher build height, the actual amount of power required may increase or decrease with build height. Discussion Effect of Process Parameters on Hardness Variation The average hardness of Al3003- H18 foil after VHP-UAM varied with vibration amplitude and normal force as well as weld speed used to fabricate the samples. The power level used during welding increased with higher vibration amplitude and normal force during process parameter settings. It was also learned that the power level drawn also changed with weld speed used. In order to correlate the average input power to the average bulk hardness of Al3003-H18 foil after VHPUAM, Fig. 8 plots the correlation between these two of all samples made with the TB machine and the SL7200 machine for those layers bonded at a constant 35.6 mm/s weld speed. It can be seen that the data from the sample made with low amplitude (28 μm) belonged to low power (below 650 W), and those made with high amplitudes (34 and 38 μm) belonged to high power (above 650 W). It was noted the vertical line at 650 W was drawn and delineated the two data points and facilitated the interpretation of the data in this study. It was found there is an obvious correlation between a decrease in hardness of Al3003-H18 foil with increasing power level used during VHP-UAM for both machines. Also, the average bulk hardness values of samples made with TB machine was above those of samples made with the SL7200 machine, and the hardness of samples made with low amplitude was usually larger than those made with high amplitude. Since the VHP-UAM power supplies were engineered to provide specific amplitude at the horn face under all conditions, the vibration amplitude for each sample was considered to be constant in each sample regardless of the actual power level measured. As the build got higher, the stiffness of the build was reduced, meaning less power was required to produce the same amount of amplitude when bonding upper layers. In addition, the design of the fixture was very different between the TB machine and SL7200 machine; typically, it was relatively difficult to get as solid a grip on the baseplate on the TB machine as compared to the SL7200 machine. Thus, the TB machine provided less stiffness during VHP-UAM and caused different amounts of energy dissipation into the foil, resulting in higher final hardness in the asprocessed condition despite using similar power. However, this subject is not the current focus of this research and the subtle difference of the existing ultrasonic actuators is the subject of ongoing research at Fabrisonic. The data in Fig. 8 also shows hardness drop from the original Al3003- H18 foil hardness. There is a larger drop in hardness (i.e., more softening behavior taking place in the bulk of the foil during VHP-UAM processing) when higher vibration amplitude and power were used. Although the hardness values of samples TB-10-38-4000 were slightly lower than the hardness of sample TB-10-38-8000, there was hardly any difference in hardness values between samples SL-80-34-4000 and SL-80-34-5340. This implied that there existed some ranges of vibration amplitudes and power levels at which increasing in normal force resulted in higher bulk hardness of Al3003-H18 WELDING RESEARCH 190-s WELDING JOURNAL / JUNE 2016, VOL. 95 B
Welding Journal | June 2016
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