In conventional CNC machining, equal cutting and thick cutting are generally used when formulating tool paths. In other words, radial cutting has a constant value in a single pass. However, in the case of over-milling fillets, the machining problems will be exacerbated. This problem is especially important when milling thin structures at high speeds. You can see that when performing high-speed milling with rounded corners, the cutting force of the tool at the rounded corners has changed significantly.
How to improve the fillet tool path due to the problem of fillet machining. For equidistant cutting and thick milling, the cutting depth Qb increases as the tool transitions from a straight path to a circular path (see Figure 2 and Figure 3).
The corresponding formula in the figure is:
- Cos (Qb) = 1-Cl / r (1)
- Cos (Qb) = 1-Cc / r-Cc (r-0.5Cc) / rR (2)
- Qb-cut corners.
- Cl ——— Radial depth of cut in straight-edge milling.
- Cc ——— Radial gap when milling fillet.
- r ——— Milling cutter radius;
- R ————The radius of the tool center path at the fillet.
Obviously, when Cl = Cc, the tool transitions from a straight path to an arc path. Increasing the angle of entry will increase the contact area between the tool and the workpiece, resulting in a sudden increase in cutting force, which is prone to vibration. Due to the sudden change of the cutting force, the machining deformation of the tool and the workpiece increases, and the size error of the part increases. The cutting vibration produces vibration lines at the fillet, which affects the processing quality of the part.
How to improve the circular toolpath. The idea is to keep the cutting angle of the tool constant during the path or to add the path to the tool. This is to reduce the radial thickness of the tool at the fillet to avoid sudden changes in cutting force.
The tool path improvement program for milling fillet can effectively maintain stable cutting. Reduce machining deformation and possible cutting vibration caused by sudden changes in cutting force, and improve the machining quality of parts.
At the same time, the tip thickness goes from thin to thick counterclockwise. Due to the size effect of the cutting edge, when the cutting edge just touches the workpiece, the friction between the flank face and the workpiece increases, which is prone to vibration, and severe oblique vibration occurs at the corner. Clockwise milling is just the opposite. Down-milling cutting force is slightly greater than up-milling cutting force, but there is no big chatter when cutting corners. However, clockwise milling will reduce chip thickness and increase the impact on the workpiece and tool. Machining minimizes the overhang of the tool and increases the rigidity of the workpiece.
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