As the cutting speed goes higher, the mechanism of chip deformation will be changed significantly, i.e., continuous chip in low cutting speed will shift to serrated chip with shear localization. For the shear localize...As the cutting speed goes higher, the mechanism of chip deformation will be changed significantly, i.e., continuous chip in low cutting speed will shift to serrated chip with shear localization. For the shear localized chip, the parameters used to assess the chip deformation for continuous chip, such as shorten coefficient ξ, shear angle φ and shear strain ε, can not describe the chip deformation correctly or comprehensively. This paper deals with the assessment of chip deformation of shear localization. There are two deformation regions in shear localized chip, one is the chip segment body with relative smaller plastic deformation, another one is the boundary between segments with shear localization, so called shear band. Considering the two distinct deformation regions, two parameters are used to define their deformation respectively. According to the analysis of chip formation process, the equations have been deduced to calculate the shear strains of shear band ε, shear strain of chip segment ε 1 and shear rate so that the shear localized chip deformation can be assessed correctly and comprehensively. By use of this assessment, the chip deformation in machining selenium treated stainless steel (STSS) and common stainless steel at various cutting conditions is investigated. The experiment results obtained by the machining of stainless steel prove that: (1) the shear strain and strain rate increase with the increasing of cutting speed; (2) the shear strain in shear band can be over 10 when cutting speed exceeding 200 m/min for both types of stainless steel, and it is much higher than the strain of chip segment. The difference will be enlarged as the cutting speed increasing; (3) As the comparison, the shear strain for the STSS is a little lower than that for JIS304; (4) The stain rate is extremely high (= 2.5×10 5 1/s ). In range of cutting speed less than 180 m/min, the strain rate for STSS is lower than that for JIS304. However, when the cutting speed is higher than 180 m/min, the strain rate for STSS is higher than that for JIS304.展开更多
The cutting performance of particle reinforced meta ll ic matrix composites (PRMMCs) SiC p/Al in ultrasonic vibration cutting and comm on cutting with carbide tools and PCD tools was experimentally researched in the p...The cutting performance of particle reinforced meta ll ic matrix composites (PRMMCs) SiC p/Al in ultrasonic vibration cutting and comm on cutting with carbide tools and PCD tools was experimentally researched in the paper. The changing rules of chip shape, deformation coefficient, shear angle a nd surface residual stress were presented by ultrasonic vibration cutting. Resul ts show: when adopting common cutting, spiral chip with smaller curl radius will be obtained. The chip with zigzag contour is short and thick. There are lots of sheet cracking both on the face of the chip and on the machined surface. That i s to say, the cutting process of metallic matrix composites(MMCs) is not all lik e the cutting process of plastic material. It is akin to the breaking process of brittle material. By comparison, when adopting ultrasonic cutting, because tool contacts with workpiece intermittently in high frequency, deformation of chip i s small, loose spiral chip with larger curl radius is long and thin. The phenome non is just similar to vibration cutting of plastic material. But the chip still belongs to plastic or semi-plastic segmental chip due to the structure charact eristics of the material itself. Furthermore, the tangential residual compressio n stress of vibration cutting is larger than that of common cutting, axial resid ual stress has a relation to the feed rate and residual stress does not changes obviously with cutting depth and they are in the same order of magnitude on the whole. According to the test result analyzing, the following conclusions are put forward: 1) The extruding deformation is serious in common cutting PRMMCs, defo rmation of it’s chip is larger, and the chip with lesser curl radius is short. Whereas, the deformation of chip in vibration cutting PRMMCs is lesser, the curl radius is bigger, and the loose chips are obtained at every turn. 2) The cuttin g deformation coefficient of chip in vibration cutting is lesser than that in co mmon cutting, however the shear angle is bigger. 3) The tangential residual compression stress of vibration cutting is larger than that of common cutting, a nd residual stress does not change obviously with cutting depth, they are in the same order of magnitude on the whole.展开更多
文摘As the cutting speed goes higher, the mechanism of chip deformation will be changed significantly, i.e., continuous chip in low cutting speed will shift to serrated chip with shear localization. For the shear localized chip, the parameters used to assess the chip deformation for continuous chip, such as shorten coefficient ξ, shear angle φ and shear strain ε, can not describe the chip deformation correctly or comprehensively. This paper deals with the assessment of chip deformation of shear localization. There are two deformation regions in shear localized chip, one is the chip segment body with relative smaller plastic deformation, another one is the boundary between segments with shear localization, so called shear band. Considering the two distinct deformation regions, two parameters are used to define their deformation respectively. According to the analysis of chip formation process, the equations have been deduced to calculate the shear strains of shear band ε, shear strain of chip segment ε 1 and shear rate so that the shear localized chip deformation can be assessed correctly and comprehensively. By use of this assessment, the chip deformation in machining selenium treated stainless steel (STSS) and common stainless steel at various cutting conditions is investigated. The experiment results obtained by the machining of stainless steel prove that: (1) the shear strain and strain rate increase with the increasing of cutting speed; (2) the shear strain in shear band can be over 10 when cutting speed exceeding 200 m/min for both types of stainless steel, and it is much higher than the strain of chip segment. The difference will be enlarged as the cutting speed increasing; (3) As the comparison, the shear strain for the STSS is a little lower than that for JIS304; (4) The stain rate is extremely high (= 2.5×10 5 1/s ). In range of cutting speed less than 180 m/min, the strain rate for STSS is lower than that for JIS304. However, when the cutting speed is higher than 180 m/min, the strain rate for STSS is higher than that for JIS304.
文摘The cutting performance of particle reinforced meta ll ic matrix composites (PRMMCs) SiC p/Al in ultrasonic vibration cutting and comm on cutting with carbide tools and PCD tools was experimentally researched in the paper. The changing rules of chip shape, deformation coefficient, shear angle a nd surface residual stress were presented by ultrasonic vibration cutting. Resul ts show: when adopting common cutting, spiral chip with smaller curl radius will be obtained. The chip with zigzag contour is short and thick. There are lots of sheet cracking both on the face of the chip and on the machined surface. That i s to say, the cutting process of metallic matrix composites(MMCs) is not all lik e the cutting process of plastic material. It is akin to the breaking process of brittle material. By comparison, when adopting ultrasonic cutting, because tool contacts with workpiece intermittently in high frequency, deformation of chip i s small, loose spiral chip with larger curl radius is long and thin. The phenome non is just similar to vibration cutting of plastic material. But the chip still belongs to plastic or semi-plastic segmental chip due to the structure charact eristics of the material itself. Furthermore, the tangential residual compressio n stress of vibration cutting is larger than that of common cutting, axial resid ual stress has a relation to the feed rate and residual stress does not changes obviously with cutting depth and they are in the same order of magnitude on the whole. According to the test result analyzing, the following conclusions are put forward: 1) The extruding deformation is serious in common cutting PRMMCs, defo rmation of it’s chip is larger, and the chip with lesser curl radius is short. Whereas, the deformation of chip in vibration cutting PRMMCs is lesser, the curl radius is bigger, and the loose chips are obtained at every turn. 2) The cuttin g deformation coefficient of chip in vibration cutting is lesser than that in co mmon cutting, however the shear angle is bigger. 3) The tangential residual compression stress of vibration cutting is larger than that of common cutting, a nd residual stress does not change obviously with cutting depth, they are in the same order of magnitude on the whole.
