# Influence of Ball-End Milling Strategy on the Accuracy and Roughness of Free Form Surfaces
## 4 Results and Discussion  
The predicted positive and negative deviations in the CAM system did not correspond to the actual values. Authors [PERSON] et al. [4] stated that the CAM prediction for 5-axis milling corresponded better to the actual state than that for 3-axis milling. In our case, it was not possible to determine the best or worst match rate. In all the cases, the CAM system predicted only negative deviations. The areas with negative deviations were differently distributed on the actual samples, and areas with residual material also occurred. Positive deviations mainly occurred at the two opposite edges of the sample. Because the specimens were clamped in these places, it is probable that they deformed during machining, owing to clamping forces. The authors of [4] present positive deviations with a maximum value of 42 \(\upmu\)m in 3-axis milling, and deviations in the positive region with an arithmetic diameter of 18 \(\upmu\)m in 5-axis milling. In our case, positive and negative deviations were achieved in both milling methods. In the 3-axis milling, a negative maximum deviation of 42 \(\upmu\)m was obtained. In 5-axis milling, the arithmetic mean of the negative deviations was 35 \(\upmu\)m and the positive deviations 30 \(\upmu\)m. One of the reasons for the different results may be the use of Cycle 32 Tolerance of the machine control system described by the authors [4]. Predicting the surface after milling using a CAM system is not sufficient; the results are merely indicative. As stated by the authors in ref. [21], the results obtained in this way cannot be generalized because each CAM system works with a different mathematical model, and the results, especially for 5-axis milling, depend on the setting of a number of parameters. However, such predictions are necessary because they allow CNC program  
Figure 8: Comparison of surface roughness for the strategies performed using 3- and 5-axis milling: (**a**) comparison of \(\text{R}_{\text{a}}\) and (**b**) \(\text{R}_{\text{z}}\) parameter values. Figure 9: Comparison of the surface roughness for the strategies evaluated using 3- and 5-axis milling: (**a**) comparison of \(\text{R}_{\text{t}}\) and (**b**) \(\text{R}_{\text{q}}\) parameter values. mers to evaluate the milling process better when selecting an effective toolpath strategy and milling method. A comparison of the scans showed that the two strategies (linear and spiral) yielded better results for 5-axis milling, and the offset strategy was better for 3-axis milling. The linear strategy and 5-axis milling achieved a maximum negative deviation of 29% less and a maximum positive deviation of 48% less than the 3-axis milling. With the spiral strategy, the maximum negative deviation was 71% smaller, the positive maximum deviations were the same. With the offset strategy and 5-axis milling, the maximum negative deviation was 17% greater and the maximum positive deviation was 32% greater than with 3-axis milling. This partially confirms the results reported previously [5]. Finishing operations account for 70-80% of the total machining time when making die and mold tools [6]. Surface roughness and surface texture are key indicators of the machined surface quality. Therefore, it is important to optimize the relationship between the milling parameters and these finished part indicators. This eliminates or minimizes finishing operations, such as grinding or polishing, respectively. When comparing the surface textures, a more uniform surface was obtained by 5-axis milling. The most significant is the difference in the planar parts of the surface. Circular traces left by the cutting-edge contact point, which rotates at a small radius, are visible on 3-axis milling samples. On samples machined by 5-axis milling, tool traces are even over the entire surface. On the textures in [5], the tracks are wider, which is caused by a fixed radial depth of cut. In our case, the scallop height value was set, and the CAM system adjusted the distances between the toolpaths accordingly.