# Influence of Ball-End Milling Strategy on the Accuracy and Roughness of Free Form Surfaces
## 2 Research Methodology  
To achieve the set goal, the experiment was carried out in the following steps:  
1. Deviations in freeform surfaces were detected using a CAM prediction software and a scan of the actual surfaces. The degree of conformity and reliability of the CAM system were compared to predict the accuracy of the manufactured surfaces. Differences between the surface deviations made by 3- and 5-axis milling were obtained. 2. A comparison of surface textures was made using both milling methods. The areas were evaluated under a microscope, and the differences between the 3- and 5-axis milling surfaces were determined. 3. Measurements were obtained, and a comparison of the surface roughness of machined surfaces using both milling methods was made. A sample with a freely modeled 3D surface was designed for the experiment. To design a test sample, the SolidWorks CAD system and its tool, called Freeform, was deployed. The sample (Figure 1) had floor plan dimensions of 50 mm \(\times\) 50 mm, with a height of 19 mm. The workpiece material of the samples was aluminum alloy, EN AW 6061 T651. It is an Al-Mg-Si-Cu alloy for highly loaded structural applications with tensile strength 260 MPa. It is used in the production of blow molds, compression molds and low volume injection molds. The initial dimensions of the semi-finished product were 50 mm \(\times\) 50 mm \(\times\) 20 mm. A CAM system, SolidCAM 2021, was selected to create the NC program. A 5-axis continuous milling machine DMU 60 eVo (DMG Mori Corporation, Bielefeld, Germany) with a control system Heidenhain TNC 640 was used to fabricate the samples for both milling methods. The maximum spindle speed of the machine is 20,000 rpm. The control system has a Look Ahead function which detects changes in the direction of the milling tool in advance [18]. The system adjusts the tool feed rate based on the tolerance entered in the respective cycle. Related cycle 32 Tolerance was not used so as not to affect the results of NC programs obtained from the CAM system. A K5X 125 vise (supplier Schunk GmbH & Co. KG, Brackenheim, Germany) with a set clamping force of 25 kN was used to clamp the sample. The sample was clamped in the middle of the vise's jaws. Each sample was prepared in six operations. The first five operations focused on roughing and pre-finishing the shape. These operations were matched for all samples. After pre-finishing, an allowance of 0.25 mm remained on the surface. The last (sixth) operation was finishing, which was sample specific. As shown in Figure 2, the surface of the sample was prepared for the finishing operation. Three types of finishing strategies were selected for the comparison: linear, offset, and spiral. In the linear strategy, the tool transitions are parallel in the XY plane and follow the surface in the \(Z\)-axis direction. Using this strategy, the direction of the toolpaths can be selected. To shorten the machining time, a direction parallel to the longer side of the workpiece is typically chosen. In offset milling, toolpaths follow the circumference of the machined surface. The path can start at the circumference and progress to the middle surface, or vice versa. The spiral strategy creates a helical path for the tool from a given focus while maintaining a constant contact between the tool and workpiece. Each strategy was applied in 3- and 5-axis milling. The \"convert\" function of the CAM system was used to program the existing 3-axis operation to a 5-axis milling operation. This approach ensured that most of the parameters of the compared strategies were matched. The ball-end mill N.R.D.10,0.45\({}^{\circ}\).Z4.HA.K TI1000 (manufactured by WNT, supplier Ceratizit S.A., Mamer, Luxembourg) with a diameter of 10 mm was used to finish the  
Figure 1: Model of the proposed sample with freeform surface. Figure 2: Sample surface after roughing and pre-finishing operations. freeform surfaces.