Factors affecting the quality of the machined surface
First, the surface layer of the material microstructure changes in grinding burn refers to an outer temperature of the process exceeds the limit after article, metallurgical change occurs, the hardness and strength weakens, while the residual stress or microscopic fine marks appears. When grinding hardened steel, note the following burns: burns tempering, that lies between the grinding zone temperature phase transition temperature of hardened steel and martensitic transformation temperature, there will be transformed into tempered martensite low hardness tempered Organization (sorbite or prop's body) phenomenon. Quenching burns, namely the grinding zone temperature exceeds the phase transition temperature in case of cooling fluid, and the emergence of secondary hardening, secondary quenching martensite appears, its harder than first tempered martensite, due the bottom of the cold late, lower than the first hardness of tempered martensite (sorbite or prop's body) phenomenon. Annealing burns, namely the grinding zone temperature exceeds the phase transition temperature, before adding coolant, the outer metal hardness decreases rapidly and produce phenomena Annealing.
Second, the surface layer of cold work hardening materials processing plastic deformation, its texture become distorted, bent, grain scrolling longer, fibrosis, fragmentation, resulting in firmness workpiece outer metal toughness strong, this process is called work hardening (also called enhanced). The physical properties of the outer metal also changes, the plastic becomes weak, a direct result of deformation difficult. This time has been to strengthen the position of the metal into a different energy state of the body, and then into the usual steady, this change is called weakened. Degree weakened by the cold temperatures and the duration of effect. Since the degree of processing power and thermal energy act on the metal, so strengthening and weakening property directly determines the workpiece outer metal. The hardness of the outer layer of metal HV, case depth h, N is the assessment of the degree of hardening strengthening and weakening of three important criteria. Chilled increase of factors have contributed to the outer layer of metal are: increasing the cutting edge radius, the extrusion force increases flank wear resistance, etc., will result in enhanced plasticity changes, cutting faster, cutting Effect of heat generated when the metal outer faster feed becomes large, and larger plastic material itself, will have a serious phenomenon chilled.