*2.4. Validation of the Developed Tool*

The cost estimation tool was subjected to a series of validation tests, being used for two case studies. For Case Study 1, the validation consisted of the analysis of a total of 24 parts, 3 for each different complexity level. The tool was used to estimate the total production time of these parts (for all the mentioned production steps), which were then produced, and their production times were clocked by the machine operators (after each production step the worker would register the time taken up to perform the said task, this would later be compared to the estimated machining times). These times were then compared to the estimated ones, and the percentual deviation from each of the produced parts' production time was registered. The percentual deviations are presented with either a positive or negative value, with it representing a time over-estimation and underestimation, respectively. This comparison of time estimation is key, as the tool performs the calculation of total operation cost based on these production times.

Regarding Case Study 2, the validation was performed in the same manner; however, the machine types for this case study were slightly different, being CNC milling centers with vacuum tables. These machines performed the same operations as those of Case Study 1; however, the part complexity of the workpieces produced on these machines is somewhat constant, with the parts having low amounts of detail with low complexity (in terms of geometry). Additionally, the finishing operations for these machines are usually performed by the machine itself (differing from the manual finishing operations conducted for parts produced in the machines considered for Case Study 1). For Case Study 2, a total of 10 parts were produced, registering the machining time that was estimated, then, producing the workpiece and timing this manually (as for Case Study 1). These deviations were then averaged and are subsequently presented in the Results section of this study.

### **3. Results**

The cost estimation tool was successfully developed and tested, and in the present section the application is going to be presented in Section 3.1, showing the interface while explaining each of the different main interface elements. Furthermore, the accuracy of this tool was tested by estimating and producing various machined parts and then comparing the deviation of the predicted times from the real times. The data obtained from these tests will be presented in Section 3.2.
