OBRABOTKAMETALLOV technology Vol. 25 No. 4 2023 a b Fig. 6. The direction scheme of the components of the cutting force in asymmetric up end milling in the top view: the position of the cutter tooth at a central angle ψ ≈ 50º from the point of contact to the considered position (a); large diagram of the action of the components Pvi and Phi, as well as Pz and Py and its resulting Phvi and Pzy at ψ ≈ 50º (b) The axial component Px changes slightly throughout the entire cycle (fig. 7, the range is between numbers 1 and 5), because along the end part, three teeth are in contact with the workpiece almost immediately having a four-flute cutter and milling depth of t ≈ d/2 (fig. 5, a, b) when decreasing the milling depth of t < 0.2d. That is, if the milling depth t is less than the cutter flute depth h, only one tooth will be in constant contact with the workpiece. This will cause large changes in the value of the Px component as the cutter rotates. The operating time of one tooth is t = d/2 and a four-tooth cutter (z = 4) has τ1 tooth = 60/(4∙n) (s). The graph of changes in the magnitude of the components Ph Pv and Px of the cutting force (fig. 7) shows that there is a non-synchronous change in its value. When analyzing changes in the milling forces, one should keep in mind that the Kistler dynamometer is installed across the milling table (perpendicular to the longitudinal feed of the table sm), and the workpiece is installed with its long part across the dynamometer, i.e., parallel to the direction of the longitudinal feed of the table sm. The workpiece is behind the cutter when viewed from the operator’s side. When a tooth cuts into a workpiece (fig. 7, the range is between numbers 1 and 2), the cutter tooth with its rounded cutting edge pushes the workpiece away from the axis of rotation of the cutter. That means that a component force Pv cut appears with a negative sign (in the signal processing program using the Kistler dynamometer, the sensors are “wired” and the positive sign of the force Fy (Pv during milling) will be when the force is applied towards the operator, i.e. as in turning). At the same time, the component force Ph of the cut acts with a positive sign, i.e., the cutter tooth pushes the workpiece in the direction opposite to the direction of the counter feed sm (fig. 8). The positive sign of the force Fх (Ph during milling) on the monitor will be when the force is applied from left to right, i.e. as in turning. When the tooth rotates further (fig. 7, the range is between numbers 2 and 3), the force Pv acts in the positive direction of the OY axis. That is, the cutter tooth attracts the workpiece to the axis of rotation of the cutter due to the positive main rake angle γ (fig. 8, but the position of the cutter after the workpiece is Fig. 7. Graphs of force changes during milling when turning a sharp cutter for one revolution. Up milling with a 4-tooth cutter d = 8 mm, t = 3.8 mm, B = 2mm, n = 500 rpm, sm = 28mm/min, specimen No.1 – carbide
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