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CNC machining center should choose down milling or up milling

Release time: 2020-01-11 16:52:40

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应该挑选顺铣仍是逆铣 CNC machining center should choose down milling or up milling
In CNC machining centers, the rotation direction of the milling cutter is generally constant, but the feed direction is changed. It presents two common phenomena of CNC machining center machines in milling: down milling and down milling.
机床铣刀切削刃在每次切入时都会受到冲击载荷的作用。 The cutting edge of the milling cutter of the CNC machining center is subjected to the impact load every time it cuts. In order to successfully mill, it is necessary to consider the correct cutting method of the cutting edge and the material during cutting in one cutting. In the milling process, the workpiece is fed in the same or opposite direction as the rotation direction of the milling cutter, which will affect the cutting in and out of milling and whether the method of down milling or down milling is selected.
01 The Golden Rule of Milling-From Thick to Thin

When milling, it is necessary to consider the composition of the chips. The decisive factor for chip formation is the orientation of the milling cutter. It is necessary to strive to form thick chips when the cutting edge is cut in, and thin chips when the cutting edge is cut out to ensure a stable milling process. Keep in mind that the golden rule for milling is "thick to thin" to ensure that the chip thickness is as small as possible when cutting out.

02 Down milling

In down milling, the cutting tool is fed in the direction of rotation. As long as the machine, fixture and workpiece allow it, down milling has always been the preferred method.
In edge down milling, the chip thickness will gradually decrease from the beginning of cutting, after all it reaches zero at the end of cutting. This prevents the cutting edge from scratching and abutting the appearance of the part before participating in cutting.

Chip thickness is favorable, and cutting forces tend to pull the workpiece into the milling cutter, keeping the cutting edge stuck. However, because the milling cutter is easily pulled into the workpiece, the machine tool needs to handle the table feed slot by eliminating backlash. Assuming the milling cutter is pulled into the workpiece, the feed will unexpectedly increase, which may then result in excessive chip thickness and cutting edge splitting. In these cases, consider using up milling.

03 Up milling
In up milling, the cutting tool feeds in the opposite direction to its direction of rotation.

The chip thickness gradually increases from zero until the end of the cutting. It is necessary for the cutting edge to be forcibly cut in, and then a scratching or polishing effect may occur due to resistance, high temperature, and often touching the work-hardened appearance of the front cutting edge. All this will shorten the tool life.

The thick chips and higher temperatures that occur when the blade is cut out will cause high tensile stresses, which will shorten the tool life and the cutting edge will usually be damaged quickly. It may also cause the chips to stick to or weld to the cutting edge, which will then carry it to the starting position of the next cut, or cause the cutting edge to chip instantly.
Shear force tends to push the cutter and the workpiece away from each other, while radial force tends to lift the workpiece from the work table.

When machining allowances change significantly, down milling may be advantageous. When using ceramic blades to process high-temperature alloys, it is also recommended to use up-milling, because ceramics are more active when cutting into the workpiece.

04 Workholding

The feed direction of the tool places different requirements on the workpiece fixture. It should be able to withstand lifting forces during the up milling process. It should be able to withstand downforce during down milling.