# Influence of Ball-End Milling Strategy on the Accuracy and Roughness of Free Form Surfaces
## 1 Introduction
Experimental results demonstrated the impact of milling strategies on machining times and their importance in reducing production time and, consequently, costs. Strategies also affect the tool deflection, material removal rate, cutting forces, and machining errors. The linear, concentric and spiral strategies for machining the alloy EN AW 7075 were investigated. The use of different tool path strategies in ball-end milling on convex, low-curvature surfaces has a significant impact on the cutting forces, surface texture, and machining time [11]. The authors compared linear, offset, spiral and radial strategies. The radial path of the tool provides advantageous results in terms of a more uniform structure and lower cutting forces, but with the highest total machining time. The resulting cutting force is highest when using a helical toolpath owing to the contact area between the tool and chip. Finishing convex surfaces with a small curvature using a helical toolpath strategy is not recommended. Three strategies, linear, linear rotated by 90\({}^{\circ}\) and 3D offset, when machining aluminum alloy are investigated in reference [12]. The 3D offset is the best finishing strategy; it combines the benefits of the linear and linear 90\({}^{\circ}\) strategies. Continuous machining strategy is ensured, which is favorable for milling. The tool life is increased, and a better surface quality is achieved. The impact of the strategies on the surface roughness for die and mold applications was studied in [13]. The path strategy influences the actual machining time, polishing time, and costs. Offset, spiral, radial and zig-zag (linear) strategies were compared. The best results were achieved by the 3D offset and a spiral that slits the part horizontally. [PERSON] et al. [14] compared three typical milling strategies when milling a freeform surface: radial, raster, and 3D offset. Their effects on surface roughness, texture, and dimensional deviations were evaluated. The sample was made of aluminum alloy. In this case, the 3D offset strategy proved to be the most suitable because it achieved the most favorable results for each of the monitored parameters. However, according to the authors,the results cannot be generalized; however, the study shows that there is a general trend when the machining areas are like those tested. In reference [15], three strategies for high-speed milling were evaluated: linear, linear in two perpendicular directions, and circular. The evaluated parameters were the surface roughness and texture. To achieve the lowest possible surface roughness, a linear path is recommended, and the most uniform surface structure is provided by the circular strategy. The authors recommend avoiding a linear strategy in two perpendicular directions while emphasizing that the results depend on the material being machined. Considering machining time and average residual load per unit area, [16] evaluated eight finishing strategies for 3- and 5-axis milling. A comparison was made using machine codes that were obtained directly from the CAM system and modified by the optimization software. The authors determined the best strategies for specific types of surfaces while ensuring that feed optimization balanced the machining times of the different strategies. By optimizing the feed rate, the machining time was reduced by 20-50%. The samples were made of aluminum alloy. Milling strategies were also evaluated based on durability and number of pieces produced, as in the case of a die forging tool [17]. On active tool surfaces, it is advantageous to use a milling strategy with toolpaths that follow the flow of material during the forging process. The aim of the experiments in the present article was to compare 3- and 5-axis ball-end milling using three machining strategies (linear, offset, spiral), which are commonly used in the production of parts with freeform surfaces. The deviation of the finished shape, the texture of the machined surface and its roughness on a sample specially designed for this purpose were evaluated.