The formation of built-up edge and its influence on the cutting process

When the cutting speed is not high and continuous chips can be formed, when processing plastic materials such as steel, there is often a hard block with a triangular cross section at the cutting part of the rake face. Its hardness is very high (usually 2-3 times of the workpiece material), when in a stable state, it can replace the blade for cutting. This piece of cold-welded metal on the rake face is called a built-up edge or edge.

    How does scum tumor form?

    The chip and the rake face have strong friction to form a fresh surface contact. Bonding (cold welding) occurs when the blade-chip contact surface has a moderate temperature and pressure. As a result, the bottom metal of the chip is cold welded to the rake face and stays on the rake face, but the chips flow out continuously. Under the push of the subsequent chip flow, the front chip bottom layer facilitates the relative slippage of the upper layer and separates. Become the basis of built-up tumor. After that, the metal separates from the chip layer by layer, accumulates on the previous layer layer by layer, and finally grows into a built-up edge.

    The generation of built-up edge and its accumulation height are related to the hardening properties of metal materials, as well as the temperature and pressure conditions in the front area of ​​the blade. Generally, the stronger the work hardening tendency of the material, the easier it is to produce built-up edge; the temperature and pressure in the front area of ​​the edge are too low, and the built-up edge will not occur; if the temperature is too high, it will produce a weakening effect. Will not produce built-up edge. For carbon steel, the built-up edge is highest at about 3000, 500℃. It tends to disappear when it is above 500℃. The relationship between the height of built-up edge and cutting speed. In the low speed range I, there is no built-up edge; in the zone I, the height of the built-up edge increases to the maximum with the increase of the cutting speed; in the zone I, the height of the built-up edge decreases with the increase of the cutting speed; in the zone The crumbs no longer form.