*Background–Development of an Affordable and Simple Cost Estimation Tool*

The development of the cost estimation tool was made based on an SME manufacturing company that produces machined parts, primarily by the milling process. The analyzed company followed a conventional cost estimation process, shown in Figure 1. However, due to the high variability and small series of requested parts, the created budgets had some errors, usually resulting in over-estimated production costs and, in some cases, underestimated production costs, which resulted in company revenue loss. This was the case, especially for more complex parts. Thus, there is an opportunity to develop a tool that can be useful for this sector but also provide the necessary knowledge to be adapted and adopted by other kinds of industries.

**Figure 1.** Schematic representation of the conventional budgeting process.

To speed up the budgeting process and reduce the errors associated with it, a cost estimation tool based on the analyzed company's resources and conditions, such as machines, workforce, and client requests, was developed. In the subsequent sections, the methodology used for the development and validation of this tool, and the results obtained from this validation, are going to be presented. Furthermore, a discussion of the obtained data is going to be made, analyzing the advantages/disadvantages of the developed tool.

#### **2. Materials and Methodology**

To develop the cost estimation tool, it was decided that an approach based on the calculation of machining times and founded on the final part's dimension would be the best choice. The calculations were developed for each of the milling machine types considered for validation of the model. The different milling machines that were considered can be observed in Table 1, where the different specifications of each machine are presented.


**Table 1.** Considered CNC milling machining centers.

As observed in Table 1, the main difference between machines is the workspace volume, the amount of axis, and the workpiece fixation method. These machines were considered as they are selected based on the requested final workpiece (size, tolerances, number of needed axes, etc. ... ). The machines with vacuum tables are mainly used for the machining of parts with small heights or thickness. In Figure 2, some parts being produced on the mentioned machined can be observed.

**Figure 2.** The part being machined in an M1 milling machine (**a**), and an M4 milling machine (**b**).

The developed tool's working principle is shown in Figure 3.

**Figure 3.** Schematic representation of the working principle of the developed tool, for the cost estimation of machined parts.

The inputs for the tool, as observed in Figure 2, are the part's material, the initial required material amount (based on the part's dimensions), machining strategy (parameters and operations), and required machines to obtain the workpiece, and part complexity level definition. Based on all this information, the tool performs the calculation of machining time, which can be used to estimate the overall production cost for the machined parts.

Total production time and, consequently, the total production cost are obtained by determining the operation time for the five production steps that each part undergoes, as follows:

(1) CAD (2D/3D): The 2D technical drawings are needed for part production; additionally, the 3D drawings can be used to perform the CAM software. If these are not provided, they need to be made.


These five steps are applied for every part that is produced in the milling machines; however, due to the existing variability from part to part in terms of geometry complexity and required details, the determination of the operation times is insufficient to provide an accurate prediction. Thus, a part complexity level was created to be applied to each of the parts that are being analyzed in terms of cost, which influences the estimated times for each of the production steps.

In the following subsections, the operation time calculation method for each of the five production steps is going to be presented. Furthermore, the working principle of the model will be described in more detail, including the determination of the part complexity level and its influence on the estimated times are going to be explained. Furthermore, the methodology adopted for the validation tests is going to be presented.
