**Algorithm 1** Automatic Mode


#### *2.3. Testing of the Positioning Accuracy*

The measurement process of the designed device with the DIC system is based on a mutual change in the position of the DIC system and the milling cutter. At first, the position of the milling cutter (MC) is adjusted to the analyzed area A1 of the specimen (see Figure 3). Subsequently, the milling tool is shifted to a new position A2, where distance L corresponds to the distance between the camera(s) and the axis of the milling cutter. In this position, the DIC system captures a reference image of the analyzed specimen area, after which the milling cutter is returned to A1 position, and the drilling process starts. After drilling the first step, the milling cutter moves to A2 position again, and the digital image corresponding to the first drilling cycle is captured. The process is repeated until the desired depth of the hole is achieved.

**Figure 3.** Principal scheme of the device positioning used for drilling of the hole and capturing digital images of the analyzed area by DIC in a series of steps.

Several methods based on different physical principles were used for the validation of the device positioning accuracy. The testing aimed to verify the real change of the milling tool position adjusted by the control software (by servo driver). The experimental procedures were performed in two stages:


**Figure 4.** Testing of the positioning accuracy in: (**a**) horizontal direction; (**b**) vertical direction; (**c**) measuring string.

The measurement in which the mutual position between the camera of the 2D DIC system and the milling cutter changed 30× was performed to obtain information about the accuracy and repeatability of the device positioning. The horizontal direction shift was

adjusted to the value L = 81 mm corresponding to the distance between the lens of the 2D DIC system and the milling cutter axis (Figure 3). The results obtained, which showed high accuracy of the desired value and achieved repeatability, are given in Figure 5. The detailed analysis suggested that deviations from the reference device position (after its move to a new position at a distance of 81 mm adjusted by the control software and return) were 10−<sup>3</sup> mm. The same graph shows that the deviations registered by the inductive displacement transducer WA-100 mm (HBM, Darmstadt, Germany) and 2D DIC system Q-400 (Dantec Dynamics A/S, Skovlunde, Denmark) are similar.

**Figure 5.** Deviations from the reference position of the device obtained for 30 repetitions of its movement to a new position at the distance 81 mm and subsequent return captured by the inductive displacement transducer WA-100 mm and 2D DIC.

Testing of the developed hole-drilling device positioning accuracy in a vertical direction, and analyzing the shape of the drilled hole were carried out on the specimen made from EN AW-5083 material, in which the blind holes were drilled using milling cutters provided with the RS 200 device, concretely the miller with a 3.2 mm tool diameter (Figure 6a). Measurements were performed according to the methodology set forth in the ASTM E837-13a standard, i.e., blind hole drilling up to 2 mm deep performed in 20 steps [1]. In this phase, all the steps were set up with the same increment of 0.1 mm (used to examine stresses uniformly distributed over the depth of the specimen).

**Figure 6.** Testing of the positioning accuracy: (**a**) milling cutters F1, F2, F3 with a diameter of 3.2 mm and denotation of the sides; (**b**) location of the drilled blind holes.

For the measurement of the drilling device vertical shift, the inductive displacement transducer WA-100 mm and digital indicator ASIMETO series 405 (ASIMETO, Weissbach, Germany) were used (Figure 4c). In several cases, the above-mentioned transducers captured any higher deviations towards the value adjusted in the control software than in the horizontal direction (see Table 2).


**Table 2.** Experimentally determined values of depths and diameters of the blind holes drilled by the designed prototype of the drilling device.

\* Note: The final depth of the drilled blind hole adjusted by the control software was 2 mm. \*\* AV—Average value (mm), \*\*\* SD—Standard deviation (mm).

> The analysis of dimensions was carried out on a series of drilled blind holes (Figure 6b), whereby the influence of the cutting speed and the milling cutter wear was reviewed. It was experimentally proved that the developed drilling device can cut blind holes in accordance with the requirements specified in ASTM E837-13a standard. Examination of the shape of blind holes, i.e., analysis of their circularity achieved after the last (twentieth) drilling step and their cylindrical shape along the depth was undertaken using a specially adapted microscope TM-505B (Mitutoyo, Kanagawa, Japan), (Figure 7). The averaged distances of two antipodal points measured three-times in two mutually perpendicular directions are listed in Table 2.

**Figure 7.** Measurement of the blind holes circularity in two mutually perpendicular directions.

The circularity of the cut holes was validated by checking the cylindrical part shape of the blind holes carried out on a split specimen using a specially adapted microscope TM-505B (Figure 8). These measurements also provide information about the real depth of the drilled blind hole, which was set to 2 mm by the control software. Table 2 shows that the real depth (registered by microscope) of the drilled blind hole is 2.002 ± 0.0003 mm and, thus, the achieved accuracy is equal to the top commercially produced drilling devices.

**Figure 8.** Measurement of the blind holes depth performed on the split specimen.

It can be stated that if the control of the vertical shift will be realized by the inductive displacement transducer WA-100 mm, the real depth of the drilled blind hole could be assessed based on the results in Table 2. It has to be noted that the control measurements of the depth of the drilled hole using an electron microscope cannot be used for real structures.

### **3. Experimental Measurements**

After performing testing measurements with satisfying results, the authors carried out analysis of the displacement/strain fields evaluated in the vicinity of the hole cut by the designed prototype of the drilling device into the testing specimen loaded by a known loading.

The full-field strain analysis was undertaken on the specimen made from the PS-1D material (Vishay Precision Group, Malvern, PA, USA) loaded by uniaxial tension loading (Figure 9a) registered by the RSCC-50 kg sensor (HBM, Darmstadt, Germany) (Figure 9b). The given mechanical/optical properties of the analyzed strain-sensitive plastic coating are: Young's modulus of elasticity E = 2500 MPa, Poisson's ratio μ = 0.38, thickness t = 0.5 mm and the fringe value of coating f = 3790 μm/m/fringe. The dimensions of the specimen are given in Figure 9a. The through-hole lying on the specimen's longitudinal axis was cut when the specimen was loaded by the uniaxial tension force of 250 N, and the relieved strains were observed using a polariscope based on the PhotoStress method as well as 3D DIC system. Measurement performed on any specimen in the near vicinity of the cut through-holes (due to the specimen's thickness) was performed under the same cutting conditions (cutting speed and velocity of horizontal and vertical positioning). The advantage of such a measurement method is that the results in the form of the relieved strain fields obtained by two different optical methods are observed on the specimen made from the same material and can be further analyzed (compared).

**Figure 9.** Testing specimen made from the PS-1D material: (**a**) the overall view with dimensions; (**b**) loading mechanism.
