The Difference Between Down Milling and Up Milling in CNC Milling

1. CNC milling machining: down milling and up milling

In CNC milling machining, the rotation direction of the milling cutter is generally unchanged, but the feed direction is changed. There are two common phenomena in milling: down milling and up milling. The cutting edge of the milling cutter is subjected to an impact load every time it cuts. In order to successfully mill, you must consider the correct contact between the cutting edge and the material when cutting in and cutting out.

When CNC milling machining, the formation of chips must be considered. The decisive factor for chip formation is the position of the milling cutter. We must strive to form thick chips when the blade cuts in, and thin chips when the blade cuts out to ensure a stable milling process.

Keep in mind that the golden rule of CNC milling is "from thick to thin" to ensure that the chip thickness is as small as possible when the blade is cut out.

2. CNC milling machining: down milling

In down milling of CNC machining service, the cutting tool is fed in the direction of rotation. As long as the machine tool, fixture and workpiece permit, down milling is always the preferred method. In edge down milling, the chip thickness will gradually decrease from the beginning of the cutting, and eventually reach zero at the end of the cutting. This prevents the cutting edge from scratching and rubbing against the surface of the part before participating in the cutting.

3. CNC milling machining: reverse milling

In up-milling, the feed direction of the cutting tool is opposite to the direction of rotation. The chip thickness gradually increases from zero until the end of the cutting. The cutting edge must be forcibly cut in to produce a scratching or polishing effect due to friction, high temperature, and frequent contact with the work-hardened surface caused by the front cutting edge. All this will shorten the tool life.