How Do You Compare Up Milling And Down Milling For CNC Machining

The Golden Rule Of Milling – From Thick To Thin

When milling, the formation of cutting must be considered. The decisive factor of cutting formation is the position of the milling cutter. It is required to form thick chips when the cutting edge cuts in and thin chips when the cutting edge cuts out, so as to ensure a stable milling process. Be sure to remember the golden rule of milling “from thick to thin” to ensure that the chip thickness is as small as possible when the blade is cut out.

Up Milling

In up milling, the cutting tool feeds in the direction of rotation. As long as the machine tool, fixture and workpiece allow, up milling is always the preferred method. In edge up milling, the chip thickness will gradually decrease from the beginning of cutting and finally reach zero at the end of cutting. In this way, the cutting edge can avoid scratching and rubbing the part surface before participating in cutting.

Large chip thickness is advantageous, and the cutting force tends to pull the workpiece into the milling cutter to keep the cutting edge cutting. However, because the milling cutter is easy to be pulled into the workpiece, the CNC machine tool needs to eliminate the backlash to deal with the feed gap of the worktable. If the milling cutter is pulled into the workpiece, the feed will increase unexpectedly, which may lead to excessive chip thickness and fracture of the cutting edge. Back milling should be considered at this time.

Down Milling

In down milling, the feed direction of the cutting tool is opposite to its rotation direction. The chip thickness increases gradually until the end of cutting. The cutting edge must be forcibly cut in, resulting in scratching or polishing due to friction, high temperature and frequent contact with the work hardened surface caused by the front cutting edge. Will shorten the life of CNC tools.

The thick chips and high temperature produced by the cutting edge will lead to high tensile stress, shorten the tool life, and the cutting edge will usually be damaged quickly. It may also cause chips to stick or weld to the cutting edge, which will then carry them to the starting position of the next cutting, or cause the cutting edge to collapse instantaneously.

The cutting force tends to push the milling cutter and the workpiece away from each other, while the radial force tends to lift the workpiece from the workbench. When the machining allowance changes greatly, down milling is better. down milling is also used when machining superalloys with ceramic blades, because ceramics are sensitive to the impact when cutting into the workpiece.

Feed Direction Of Workpiece Fixture Tool

Different requirements are put up for workpiece fixture. It should be able to resist the lifting force during the down milling process. It should be able to resist downforce during down milling.

Comparison Between Up Milling And Down Milling