Milling process
Within milling, however, there are very real differences. For example, the German Institute for Standardization (DIN) divides milling processes according to the type of workpiece surface produced, the kinematics of the cutting process and the profile of the milling tool:
- Face milling: Face milling is milling with straight-line feed motion to produce flat surfaces and is differentiated into face milling, circumferential face milling and circumferential face milling.
- Screw milling: Screw milling refers to milling processes in which helical surfaces are created on the workpiece under helical feed motion (e.g. threads and cylindrical screws).
- Gear hobbing: Gear hobbing is one of the most important manufacturing processes for producing gears. In hobbing, a cutter with a reference profile performs a hobbing motion simultaneous with the feed motion. In this process, the tool and workpiece hob against each other during the cutting process, similar to a worm in a worm gear.
- Profile milling: Profile milling is milling using a tool with a workpiece-bound shape. It is used to create straight (straight feed motion), rotationally symmetrical (circular feed motion) and arbitrarily curved profile surfaces in one plane (controlled feed motion).
- Shape milling: Shape milling is milling in which the feed motion is controlled in a plane or spatially, thereby creating the desired shape of the workpiece.
In addition to these basic processes, milling is differentiated into contour milling and up-cut milling depending on the direction of tool rotation and feed. In contour milling, the direction of rotation of the milling cutter and the movement of the workpiece in the area of tool engagement are in the same direction. In up-cut milling, on the other hand, the direction of rotation of the milling cutter and the movement of the workpiece in the area of tool engagement are in opposite directions.
In direct comparison, the chip thickness in contour milling decreases progressively between the entry and exit of the cutting edge, which also reduces the cutting force and avoids so-called chatter effects. In addition, chatter vibrations do not occur. This means that better surface finishes can generally be achieved with contour milling. This is why this process is preferably used for finishing operations.
One disadvantage, however, is that the cutting edges of the milling cutter plunge into the workpiece with maximum chip thickness. With up-cut milling, on the other hand, the cutting edges of the milling cutter emerge from the workpiece with maximum chip thickness. This results in squeezing and friction processes when exiting, which causes high wear of the tool.
