The various mechanisms that contribute to wear process are as below .
• Mechanical overload causing micro breakages (attrition).
• Abrasion
• Adhesion
• Diffusion
Attrition :
The grains of the various components of the tool material hold together at grain boundaries. Those on the rake face and on the flank are supported on at least half of their surfaces and can therefore be rather easily broken out, embedded in the machined surface and in the underside of the chip, and dragged over the tool surface. Some of them may then break out other grains and produce a kind of chain effect.
• Adhesion
• Diffusion
Attrition :
The grains of the various components of the tool material hold together at grain boundaries. Those on the rake face and on the flank are supported on at least half of their surfaces and can therefore be rather easily broken out, embedded in the machined surface and in the underside of the chip, and dragged over the tool surface. Some of them may then break out other grains and produce a kind of chain effect.
Abrasion :
Abrasion is the commonly known wear process in which a harder material scratches a softer material over which it is sliding under normal pressure. This mechanism is significant for tool wear only in those instances where the workpiece material is very hard or contains hard particles: cast iron with grains of cementite, various metal containing hard inclusions like hypereutectic aluminum with SiC grains, steel killed with aluminum and containing Al2O3 , and so on. The machined surface is cooler than the tool flank, and it may happen that tool material is softened more than some of the constituents of the workpiece materials, which creates the conditions for abrasion.
Abrasion is the commonly known wear process in which a harder material scratches a softer material over which it is sliding under normal pressure. This mechanism is significant for tool wear only in those instances where the workpiece material is very hard or contains hard particles: cast iron with grains of cementite, various metal containing hard inclusions like hypereutectic aluminum with SiC grains, steel killed with aluminum and containing Al2O3 , and so on. The machined surface is cooler than the tool flank, and it may happen that tool material is softened more than some of the constituents of the workpiece materials, which creates the conditions for abrasion.
Adhesion :
In the conditions of the intimate contact between the tool and the freshly created surfaces on the workpiece and on the underside of the chip, welding of the workpiece surface and of the chip to the tool can often be observed. The extreme case is the built-up edge, which is formed in the low and middle speed range. Layers of workpiece material welded to the tool are found in ductile materials like in ferritic and Tehran International Congress on Manufacturing Engineering Tehran, Iran austenitic steels, titanium alloy, and nickel-based alloys. The welded layers and points are periodically sheared away. This mechanism contributes to flank wear as well as to the formation of the crater.
In the conditions of the intimate contact between the tool and the freshly created surfaces on the workpiece and on the underside of the chip, welding of the workpiece surface and of the chip to the tool can often be observed. The extreme case is the built-up edge, which is formed in the low and middle speed range. Layers of workpiece material welded to the tool are found in ductile materials like in ferritic and Tehran International Congress on Manufacturing Engineering Tehran, Iran austenitic steels, titanium alloy, and nickel-based alloys. The welded layers and points are periodically sheared away. This mechanism contributes to flank wear as well as to the formation of the crater.
Diffusion:
Diffusion is an important mechanism and plays a significant role at higher cutting speeds in some workpiece/tool material combinations. The diffusion rate, that is, the amount of atoms of material penetrating into another material, depends on the affinity of the two, very strongly on temperature, and on the gradient of concentration of the penetrating atoms in the solvent material. The latter aspect is very special in cutting, because the chip materials that absorbs the atoms of the tool material is continuously being carried away, and all the time new, virgin, unsaturated material is always arriving.
Diffusion is an important mechanism and plays a significant role at higher cutting speeds in some workpiece/tool material combinations. The diffusion rate, that is, the amount of atoms of material penetrating into another material, depends on the affinity of the two, very strongly on temperature, and on the gradient of concentration of the penetrating atoms in the solvent material. The latter aspect is very special in cutting, because the chip materials that absorbs the atoms of the tool material is continuously being carried away, and all the time new, virgin, unsaturated material is always arriving.
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