Shallow cutting is one of the main factors to be observed when high speed milling is used to finish hardened die steel. Cutting depth should not exceed 0.2/0.2 mm (ap/ae: axial cutting depth/radial cu
The main suggestion is to use forward milling as much as possible.
When the cutting edge has just been cut, the chip thickness can reach its maximum value in down milling. In reverse milling, it is the minimum value. Generally speaking, the tool life in reverse milling is shorter than that in forward milling, because the heat generated in reverse milling is obviously higher than that in forward milling. When the chip thickness increases from zero to maximum in reverse milling, more heat will be generated because the friction on the cutting edge is stronger than that in forward milling. The radial force in reverse milling is also obviously high, which has a negative impact on the spindle bearing.
In forward milling, the cutting edge is mainly subjected to compressive stress, which is much more advantageous to the effect of cemented carbide blade or integral cemented carbide tool than the tension produced in reverse milling. There are exceptions, of course. Back milling is preferred when side milling (finishing) is carried out with an integral carbide end milling cutter (see cutter in die sample C-1102:1), especially in hardened materials. This makes it easier to get smaller tolerances for wall straightness and better 90 degree angles. If there is no coincidence between different axes, the contact marks are very small. This is mainly due to the direction of the cutting force. If a very sharp cutting edge is used in cutting, the cutting force tends to "pull" the knife towards the material. Another example of the use of reverse milling is the use of an old manual milling machine for milling, which has a large clearance between the screw of the old milling machine. Reverse milling generates cutting force to eliminate clearance, which makes milling action more stable.