4.2.4. Forming Forces

The forming force is an important parameter in the forming processes. The forming forces were studied under the same process parameters during simulations. The maximum forming forces in the horizontal direction (X and Y direction) and vertical direction (Z direction) observed during the simulation of ISF and ISF processes are presented in Table 5. The forming forces along Z-direction are 1350 N and 1225 N in ISF and ISH processes respectively. As the forming force in the Z direction is most significant during the incremental forming processes, therefore, the forming force in the Z direction for both the process have been plotted. Figure 17 shows the comparative forming forces in the Z direction observed during the simulation of ISF and ISH processes. As visible from the figure the trend of forming forces for ISH and ISF processes was increasing throughout the process; although, in the case of the ISH process, the force gets reduced after a certain forming depth compared to the ISF process. In the ISF process, the tool was in continuous contact with the sheet throughout the process. It results in a larger forming force as the deformation of the sheet must overcome the constraint impact of the entire sheet on the deformation area. In the ISH process, initially, the tool aligns itself to the first hammering position where it deforms the workpiece with predefined amplitude. In the next step, the tool retracts to its original position and then moves to the next hammering position and similarly deforms the workpiece. The same phenomenon was explained in Section 2.1 and shown with the help of Figure 2. In addition, when the tool deforms the sheet in two successive hammering positions, it forms an overlapping region, as mentioned earlier and shown in Figure 3a. In the present work, the overlapping region in the case of the ISH process was 25%, i.e., 1/4th of the trailing deformed area overlapped with the leading area. Further, the hammering amplitude considered in the present work is very small, i.e., 0.05 mm, which does not allow the tool to leave contact with the sheet. Due to the overlapping region, lower hammering amplitude, and spiral toolpath used in the present investigation, the force value does not fluctuate greatly; as the tool and sheet have intermittent contact, which leads to shorter deformation time, and it further leads to a reduction in forming forces. Thus, it signifies that the integration of hammering with the ISF process leads to the reduction of the forming forces compared to the ISF process.

**Figure 17.** Forming forces in Z direction during ISF and ISH processes.

**Table 5.** Forming forces in the components formed with ISF and ISH processes.


### *4.3. Statistical Analysis*

An indicative statistical analysis is performed to understand the experimental results obtained for both the processes. Figure 18 shows the percentage change in the values obtained with the ISH process in comparison to that with the ISF process. The statistical analysis helps in understanding the comparison of the ISF and ISH processes.

**Figure 18.** Experimental statistical analysis of the ISH process with respect to the ISF process.

The statistical analysis shows the differences mainly in terms of wall angle, forming depth, and surface quality of the components observed for the ISF and ISH processes. The forming depth and wall angle while forming the VWATC through the ISH process were found to be 1.5% and 5.2% higher, respectively, compared to the ISF process. These initial results are the foundations for the CWATC components for further study. When the CWATCs of the same wall angle were experimentally formed through both the processes, only 0.1% difference is observed in the ISH process compared to the ISF process, whereas the achieved depth is observed to be higher by 1.32% in the components formed through the ISH process. The major differences are observed in the parameters such as sheet thickness, surface quality and forming forces. The thickness distribution was compared for both the processes at a forming depth of 11.59 mm because this is the maximum depth achieved during the ISF process. It was found that the minimum sheet thickness was 15.37% higher for the ISH process compared to the ISF process. The surface quality was observed to be better through visual inspection of the components formed through the ISH process. The average roughness and maximum average roughness were found to be 16% and 35.37% higher, respectively, in the case of components formed through the ISF process compared to the ISH process. The maximum values of forming forces in the Z direction were found to be 13.16% lower for the ISH process. Further, it was observed that the ISH process would lead to an overall 10.99% improvement in the quality of the parts, where the majority of the improvement is contributed by surface finish and forming forces.
