For each blade, the way the cutting edge leaves the workpiece when exiting the cutting is important. The material remaining near the retraction may reduce the blade clearance somewhat. When the chips are detached from the workpiece, an instantaneous tensile force is generated along the rake face of the blade and burrs are often generated on the workpiece. This tensile force jeopardizes the safety of the cutting edge in hazardous situations.
There are two ways to feed the workpiece and the direction of rotation of the milling cutter: the first one is the down-cut milling. The direction of rotation of the milling cutter is the same as the direction of the cutting. The milling cutter bites when starting the cutting. Work on the workpiece and cut the last chip.
The second type is up-cut milling. The direction of rotation of the milling cutter is opposite to the direction of feed of the cutting. The milling cutter must slide over the workpiece before starting the cutting. The cutting thickness starts at zero and the cutting thickness reaches the end of the cutting. maximum. When three-sided milling cutters, some end milling or face milling, the cutting forces have different directions. In face milling, the milling cutter is just outside the workpiece, and the direction of the cutting force should be especially noticed. When milling, the cutting force presses the workpiece against the table, and the cutting force causes the workpiece to leave the table during up-cut milling. Since the cutting effect of the down-milling is the best, the down-cutting is usually preferred. Only when the machine has a thread gap problem or a problem that cannot be solved by the down-milling, the up-cutting is considered. Ideally, the cutter diameter should be larger than the width of the workpiece, and the cutter axis should always be slightly off the workpiece centerline. When the tool is placed against the center of the cutting, burrs are easily generated. The direction of the radial cutting force will change continuously as the cutting edge enters and exits the cutting. The machine tool spindle may vibrate and be damaged. The blade may be broken and the machined surface will be rough. The milling cutter will be slightly off center and the cutting force will no longer fluctuate. The milling cutter will get a preload. We can drive the center milling to the center of the road. Each time the milling insert enters the cutting, the cutting edge is subjected to an impact load depending on the cross section of the chip, the material of the workpiece and the type of cutting. Whether the correct engagement between the cutting edge and the workpiece is an important direction when cutting in and out.
When the milling cutter axis is completely outside the width of the workpiece, the impact force at the time of the cut is received by the outermost tip of the blade, which means that the initial impact load is absorbed by the most sensitive part of the tool. Finally, the milling cutter also leaves the workpiece with the tip of the tool, which means that the cutting edge is cut from the beginning to the cutting edge, and the cutting force acts on the outermost cutting edge until the impact force is unloaded. When the center line of the milling cutter is just on the edge line of the workpiece, the blade is out of the cutting when the chip thickness reaches the maximum, and the impact load is maximized when cutting in and out. When the axis of the milling cutter is within the width of the workpiece, the initial impact load at the time of the cutting is carried along the cutting edge from a portion farther from the most sensitive cutting edge, and the blade exits the cutting relatively smoothly when the blade is retracted.
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