| Aluminum alloy 6061(A16061),being one of Al-Mg-Si alloys,it has good processing property,plasticity,thermal stability,light weight and corrosion resistance.It is widely used in optical lighting,communications,medical equipment,automotive,military and aerospace and other fields.Currently,research on influencing factors of surface generated in ultra-precision diamond cutting are mainly related to machining parameters,environmental conditions,material properties of workpiece,tool geometry and vibration between tool and workpiece.Relevant research on material properties factors which include elastoplasticity,anisotropy,swelling of materials,crystalline phase characteristics and so on,shows that the effect of material properties on cutting surface generation should not be neglected in ultra-precision cutting.However,relatively little research has been done on surface quality due to the effects of crystalline phase in A16061 in ultra-precision cutting.Moreover,the parameters of physical properties,elastoplasticity and damage characteristics in ultra-precision diamond cutting under crystalline phase are not available.This paper studies the formation mechanism of cutting surface in ultra-precision diamond cutting based on the characteristics of crystalline phase in A16061 and develops a new method for obtaining the parameters of material constitutive equation.It aims to build a finite element model(FEM)of ultra-precision diamond cutting for A16061,considering the effect of its crystalline phase(AlFeSi phase).The research is going to analyze the effects of AlFeSi phase on cutting force,scratches on cutting surface and chip formation,as well as to propose an optimization method which reduces scratches on cutting surface in ultra-precision diamond cutting for A16061.The research outcomes have significant theoretical and application value in further revealing the formation mechanism of A16061 surface generated in ultra-precision diamond cutting and obtaining high quality optical components.The main research works is as follows:(1)To study cutting performance and factors affecting the surface quality of A16061 in ultra-precision diamond cutting,and analyze the effects of crystalline phase on cutting surface,chip shape and cutting force.It is observed that a large number of white phase,black phase,scratches and pits are distributed on the cutting surface and chip surface of A16061 in experiment of ultra-precision cutting.The scratches and pits on the cutting surface are the major factors affecting the surface quality and mainly produced by the white phase.(2)To study the formation mechanism and the size distribution characteristics of crystalline phase,and reveal the relationship between characteristics of crystalline phase and surface quality of cutting surface.Temperature-phase conversion characteristics in A16061 are analyzed to obtain influence rules of crystalline phase transition with aging temperature,aging time and phase transition type and to establish generation rules of crystalline phase in A16061 surface under different aging conditions.It is showed that crystalline phase of A16061 is mainly consisted of two types:the black phase(Mg2Si phase)and the white phase(needle-shaped phase(?-AlFeSi)and block-shaped phase(a-AlFeSi).It revealed that the size distribution of crystalline phase in A16061 is affected by aging temperature and aging time.Moreover,the surface roughness of A16061 is linearly correlated with the number of AlFeSi phase particles which size is more than 1?m.(3)To study the physical/thermophysical properties,elastoplasticity and damage characteristics of the white crystalline phase(AlFeSi phase),in order to build FEM of ultra-precision diamond cutting for A16061 with characteristics of AlFeSi phase.The physical and thermophysical properties of AlFeSi phase,the stress-strain curves under different temperatures and different strain rates,as well as the parameters of elastoplasticity constitutive equation and damage constitutive equation of AlFeSi phase are calculated.Lastly,it is verified that the parameters A?B?n?C?m of elastoplasticity constitutive equation and the parameters D1?D5 of damage constitutive equation of AlFeSi phase are valid under the scratch experiment and finite element calculation of AlFeSi phase.(4)To build FEM of ultra-precision diamond cutting for A16061 based on characteristics of AlFeSi phase and analyze the effects of AlFeSi phase particles on the cutting force,chip shape,scratches on cutting surface and the friction between chip and cutting tool with comparison to experimental results.The results showed that,compared with finite element model which neglected the effect of AlFeSi phase,the mean cutting force calculated by the finite element model which considered AlFeSi phase is more consistent with the experimental results.Due to the existence of AlFeSi phase,the peak value of cutting force increases and the fluctuation range of cutting force increases.It leads to the increase of instability of cutting force.Friction coefficient between AlFeSi phase particles and rake face is higher than that of A16061 and rake face,and friction coefficient of chip and rake face are linearly correlated with the number of AlFeSi phase particles(size more than 1?m).(5)To develop the optimization method of ultra-precision machining for A16061,so as to obtain cutting surface of Al6061 with higher precision.Based on the formation mechanism of AlFeSi phase and the influencing factors of shear deformation,different aging parameters,cutting parameters,environmental temperature in cutting process are designed for conducting experiment of ultra-precision diamond cutting.The effects of AlFeSi phase on scratches on cutting surface under different processing parameters are analyzed for optimizing the machining parameters. |
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