# Low-Cost Digitalization Solution through Scalable IIoT Prototypes
## 4 Case Study
### Analysis of the Collected Data  
The analysis of the broaching process was performed on the pressure. Figure 7 shows the characteristic pressure progression during one single cut in the Zerynth Dashboard.  
The pressure in bar is plotted in light green over time in the format HH:MM:SS. The user can zoom and/or slide along the time axis to see the data of the entire day or to search for a cut conducted at a known time. However, any operation of the broach is detected, and cuts are identified automatically by the system. Any day can be selected through a calendar. The dashboards also display the timestamps for every time a control button has been pressed. The pressing of the extension button is indicated with a blue dotted vertical line, and the retraction button with an orange dotted vertical line. The system provides a basic statistical analysis of the data shown on the screen by displaying the minimum, the average, and the maximum pressure values. The initial plateau after the blue dotted vertical line resembles the extraction phase of the piston. This comparably high value without an external load can be explained through the design of the control valve. During  
Figure 5: Final system overview.  
Figure 6: Flowchart of the broaching process digitization solution.  
Figure 7: Characteristic pressure progression during one single cut shown in the Zerynth Dashboard.  
the forward movement of the piston, the valve connects both cylinder chambers equally to the oil pump. In both chambers, the same pressure prevails. Nevertheless, the piston moves to the left due to the different effective surface areas of its piston head. When the piston is fully extracted, the valve is closed and the pressure drops. This characteristic plateau can be observed before every cut. Hence, it can be used to identify cuts from a large number of data points automatically. The entering phase of the broaching tool can be well observed in the plot too. The pressure increases step-wise whenever one circular array of teeth enters the tube and starts cutting the material. The opposite, less pronounced behavior occurs at the end of the pipe.  
During the cut, the digital pressure transmitter detected fluctuations in the pressure. The plateau is not as flat as during the extraction, but shows several peaks instead. The delivered polypropylene tubes have deviations in circularity, concentricity, and diameter, so that the broaching tool has to cut more material in some areas and less material in others. Additionally, a misalignment of the four bracket pairs and too-tight clamping of the tubes could deform them. The implementation of the measurement system eventually allows the authors to investigate these effects.  
Figure 8 shows the pressure progressions while broaching tubes of three different diameters with three different tools (tool diameters of 80, 102, and 110 mm). Every tool has its characteristic cutting pressure and can therefore be identified easily. The cutting force, and hence, the hydraulic pressure, are proportional to the removed cross-sectional area inside the tube. The cut area increases with the tube, and respectively, the tool diameter, which explains the difference between the 80 and 110 mm tool diameters (yellow and orange graphs). The graph with the highest pressure belongs to the new tool presented in Figure 2, with a diameter of 102 mm. This tool cuts in two stages instead of one stage, as in previous tools. Therefore, the material removal is about twice that of a previous tool with the same diameter [70]. This explains the higher pressure. The step-wise increase and decrease do not occur in the previous tools, due to their different design. Additionally, in the chosen representation in Figure 8, the distance traveled by the piston is plotted on the x-axis instead of the time. This, for instance, allows a pressure peak to be related to a position, and also to understand the length of the different tubes.  
Figure 8: Pressure progressions when broaching tubes of three different diameters with three different tools.