# A Decision-Making Tool Based on Exploratory Visualization for the Automotive Industry
## 3 A Real Case Study: Waterjet Cutting
### Intensifier  
The function of a water pump or intensifier (Figure 2) is to raise the water pressure to the level needed in the waterjet machines for an optimal operation. Explained in a very simple manner, the intensifier works like this: it begins when the low pressure water enters the intensifier (3-5 bar); after several filters, the water reaches a pump that raises the pressure to 10 bar, and then the water flows to the cylinders that will be compressed by a hydraulic group, which, using a plunger/piston system, will be able to reach an extremely high pressure (around 3000 bar) The intensifiers under study have two cylinders, as can be seen in Figure 2.  
According to the experience of the workers in the plant, it is known that before a failure happens, an increase in temperature in different zones of the cylinder is observed. Another problem directly related with the increase of temperature is the water leaking, which is caused by the deterioration of the cylinder, and which can be visually observed. As this could lead to a critical failure, specific sensors have been installed in order to measure the temperature in the seal head (SH) and the hydraulic piston (HP) of the intensifier. Additionally, leak sensors have been installed in each cylinder. With the installation of these sensors, as shown in Figure 2, a diagnosis of the status of the machine could be performed in order to prevent failures.  
The dataset analyzed in this research comprises 7414 samples (from February 2020) and 36 parameters (features), described in Table 1, which were gathered every 5 min (except for the increase of water leak).  
As the intensifier has two cylinders and each cylinder has two SH and two HP, there are 36 total features: 4 temperature features per SH, 4 temperature features per HP, and 1 feature per SH for the leak problem. There is one temperature sensor per SH and HP, and one leak sensor per SH. As the features are recorded for a given time period, the maximum, minimum, average and standard deviation statistics are calculated during this period, and stored. In the case of the leak sensor, the increment when compared to the previous period is stored.  
There are three main problems or failures that affect the intensifier:  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Feature Name** & **Description** & **Unit** \\ \hline HPXTemp\_oC\_avg & HP average temperature & \({}^{\circ}\)C \\ HPXTemp\_oC\_max & HP maximum temperature & \({}^{\circ}\)C \\ HPXTemp\_oC\_min & HP minimum temperature & \({}^{\circ}\)C \\ HPXXTemp\_oC\_std & HP standard deviation temperature & \({}^{\circ}\)C \\ SHDXTemp\_oC\_avg & SH average temperature & \({}^{\circ}\)C \\ SHDXTemp\_oC\_max & SH maximum temperature & \({}^{\circ}\)C \\ SHDXTemp\_oC\_min & SH minimum temperature & \({}^{\circ}\)C \\ SHDXTemp\_oC\_std & SH standard deviation temperature & \({}^{\circ}\)C \\ SHDXLeak\_mLm & SH increase leak of water since last period & 1.5 mL/increase \\ \hline \hline \end{tabular}
\end{table}
Table 1: Intensifier features. Variables gathered from each cylinder, SH and HP. XX in the feature name refers to the number of each sensor.  
Figure 2: Example of intensifier and sketch of sensors (blue and red circles). (**a**) Picture of the intensifier. (**b**) Sensors placement sketch.  
* Water leaks: the intensifier will stop working if there is a severe water leak. This is a critical failure with high associated costs, as it stops production;
* High temperature in a cylinder: if high temperature lasts a long time, it could lead to a break in the header;
* Detected SH malfunction; this means that it is necessary to repair the SH, or otherwise it will crash and stop the production. This malfunction/problem is perceived by the maintenance staff.