Climb milling and conventional milling
In machining, the direction of rotation of the milling cutter is generally constant, but the direction of feed is varied. There are two common phenomena in milling: climb milling and conventional milling.
(1) Definition of climb milling and conventional milling
1) Climb milling: The rotation direction of the contact part between the milling cutter and the workpiece is the same as the feed direction of the workpiece, as shown in Figure 2-6-21a 2) Conventional milling: The rotation direction of the contact part between the milling cutter and the workpiece is opposite to the feed direction of the workpiece, as shown in Figure 2-6-21b.
(2) Characteristics of conventional milling and climb milling
1) At the beginning of conventional milling, the cutter teeth begin to contact the workpiece and can not cut the chips within a certain distance thereafter, initially only rubbing the surface of the workpiece, and with the rotation of the tool, the cutter teeth cut more and more artificial parts, and the thickness of the chips increases to the maximum value at the end of cutting. Conventional milling creates a process of extrusion, friction and gnawing on the machined workpiece, which creates a work-hardening layer on the workpiece, resulting in increased tool wear and periodic vibrations. 2) The depth of cut is maximum when milling into the workpiece, and then gradually decreases. It avoids the phenomenon of extrusion, friction and gnawing when cutting artificial parts by conventional milling, and the cutting distance of the cutter teeth is short, the wear of the milling cutter is small, the tool life can be increased by 2~3 times compared with conventional milling, and the quality of the machined surface is also better. In particular, the effect is more pronounced when milling difficult-to-machine materials that have a tendency to harden. (3) The application of down milling and conventional milling Although the advantages of down milling are obvious compared with block milling, there will be some problems when using down milling in some cases.
For example, when there is a gap between the feed screw and the lead screw nut, the reverse gap of the movement will be generated during the movement of the lead screw driving the worktable, as shown in Figure 2-6-21 (pay attention to the direction of the lead screw gap on the figure). The direction of movement of the tool tip is consistent with the direction of the workpiece and the lead screw during the milling, and the cutting force of the tool at this time will cause the workbench to displace in the direction where the lead screw has a gap, and the displacement within the clearance range of the lead screw and nut mechanism is called channeling or creeping phenomenon. This phenomenon will not only reduce the quality of the machined surface, but also cause the phenomenon of "knife punching". Therefore, when using climb milling, the gap of the feed mechanism must be eliminated; There is another situation, that is, there is a hard skin on the surface of the workpiece to be processed, and the tip of the cutter is cut from the workpiece when the workpiece is cut out, so the phenomenon of the cutter tooth chipping is easy to occur during the down milling. If these two situations exist in machining, it is better to use conventional milling.
