The operating principle of end mills
When cemented carbide end mills are used for milling operations, the feed direction of the workpiece can be either in line with or opposite to the rotation direction of the end mill, and this choice will affect the characteristics of the start and finish of the cutting process.
Climb milling is referred to the feed direction of the workpiece is consistent with the rotation direction of the cemented carbide end mill. The chip thickness gradually decreases from its initial maximum value until it reduces to zero at the end of the peripheral milling. In contrast, Descend milling is referred to the feed direction of the workpiece is exactly opposite to the rotation direction of the end mill, with the chip thickness starting from zero and increasing progressively throughout the cutting process.
During Descend Milling, the blades of the cemented carbide end mill begin cutting from a zero chip thickness, which generates significant cutting forces that can cause the end mill and the workpiece to repel each other. When the end mill blade is forced into the material, it often comes into contact with a work-hardened surface created by the previous cut, leading to frictional heat and a burnishing effect due to friction and high temperatures, which can even lift the workpiece off the table.
During the process of climb milling, the blades of the cemented carbide end mill start cutting from the maximum chip thickness, which helps to avoid the burnishing effect by reducing heat and the tendency for work hardening. Utilizing the maximum chip thickness is advantageous for cutting and allows the cutting force to more easily push the workpiece into the end mill, facilitating the cutting action of the blades.
Broken chips can sometimes adhere to or even weld onto the cutting edges and may accumulate around the starting point of the next cut. During Descend Milling, these chips are more likely to become trapped or wedged between the blade and the workpiece, potentially leading to blade breakage. However, during Climb Milling, the same chips are split, reducing the risk of damage to the cutting edges. Regardless of the specific requirements of the machine tool, fixtures, and workpiece, climb milling is usually the preferred method.
