# Low-Cost Digitalization Solution through Scalable IIoT Prototypes
## 4 Case Study
### Selecting the Digitization Toolkit  
The displayed tool in Figure 2 is a special hollow broaching tool with 36 teeth arranged in a circular helical pattern around its outer cylindrical surface. It has been designed in previous research work by [PERSON] and [PERSON] [70]. Its unique chip evacuation concept eliminates the timely cleaning step required in traditional broaching, and thus reduces the lead time significantly. Furthermore, it decreases the cutting forces due to minimized friction. The cutting force is the sum of the axial forces of all teeth of the broach that are intruding in and removing material from the tube. It is equivalent to the longitudinal piston force required to pull the broaching tool through the tube. The following two different measurement principles according to the instruments appear generally suitable for achieving the required task:  
Figure 3: (**a**) Automation pyramid architecture used for ascertaining the current state of the factory and (**b**) IIoT stack used to present solution architecture.  
Direct measurement of the force through a dynamometer mounted between the broaching tool and the piston;
2. Indirect measurement of the force through the measurement of the cylinder pressure \(p\) using a digital pressure transmitter.  
The relationship between the hydraulic force and the pressure \(p\) is described by [PERSON] and [PERSON] [70]. A safety valve at 170 bar protects the hydraulic system against overload. Cylinder pressures up to 150 bar are common during broaching operations. These result in cutting forces of up to approximately 65 kN. Both measurement methods have their pros and cons. Therefore, several aspects had to be weighed for the specific application case. The direct measurement of the force via a load cell delivers the absolute force value accurately. A digital pressure transmitter does not measure the force, but the pressure. The force can be calculated [70]. There remains uncertainty regarding the correct absolute force value due to the potential losses of the hydraulic system. However, the prior formulated four main goals of monitoring the progression, and thus, the relative changes of the performance indicator, can still be satisfied. Additionally, to investigate the behavior adequately, especially during the entering and exiting phase of the broaching tool, a resolution of \(d=1\) mm is required. At an average forward rate of the broach of \(v=3\) m/min, this results in a minimum measurement frequency of \(f_{\min}=v/d=50\) Hz or a sample time of \(t_{\max}=20\) ms, respectively. This requirement can easily be achieved by both systems. A standard 100 kN dynamometer for tension and compression costs about 2000 EUR. However, these standard instruments are too big and do not fit inside the tube. Using option one would hence require specially manufactured measurement equipment, which is even more expensive and has long delivery times. Furthermore, the installation and implementation of a dynamometer inside the tube (regarding also the cabling) are complex. A digital pressure transmitter, on the other hand, can easily be swapped with or added to the existing analog manometer, and it can immediately be bought off-the-shelf for under 100 EUR. Lastly, a solution with the least possible intrusiveness to the existing system is desirable. The most critical factors that finally led the authors to choose the second option of the indirect force measurement via a digital pressure transmitter, were its instant availability and its immense cost advantage. These factors play a central role in IIoT prototyping.