Research On Mechanical Grinding Efficiency Modeland Precision Control Method Of Diamond Conical Indenter

Nano-indentation is an advanced measurement technology which is used to test materials micro-mechanical properties and has been widely used in Micro-ElectroMehcanical-System manufacturing,bioengineering and Thin-Film technology.In order to improve the detection accuracy,it is necessary to use high-precision diamond indenters.Diamond conical indenter has its own unique characteristics.Sharp conical indenter can avoid the complex deformation phenomena caused by the sharp edges of Berkovich and Vickers indenters,so the indentation results analysis is simpler.Spherical tip conical indenter can be used in situation of pure elastic contact or transition from elastic contact to plastic contact.However,because of strong anisotropy of diamond crystals,grinding of conical indenters is extremely difficult.Comparing with pyramidal indenters,there are complex phenomena such as “roughness petals”,“tip pyramidation”and “pitting damage” when grinding conical indenters.In order to solve these problems,this paper researches the mechanical grinding theory and the precision control method of diamond conical indenter.In this paper,diamond conical indenter mechanical grinding efficiency model is established.Diamond crystal has strong anisotropy and its grinding efficiency has significant difference on different crystal planes and in different orientations.In order to solve the problems in the grinding of diamond conical indenter,it is necessary to choose the axis direction and grinding angle reasonably.Based on diamond typical crystal plane dynamic micro shear strength model and the weighted superposition model,the evaluation theory model of the grinding-ability factor for general crystal plane in any orientation is constructed.The cone face forming method of diamond conical indenter is analyzed and the mechanical grinding precision control theory for typical crystal axis is established.Then the grinding characteristics evaluation factors along different grinding angles of sharp and spherical diamond conical indenters are established.Precision control theoretical model for diamond conical indenter with a general crystal orientation axis is also established in this paper.It can accurately evaluate the grinding-ability factor along different grinding angles of the conical indenter which has arbitrary crystal orientation axis and arbitrary half-cone angle.Based on this model,the axis direction optimization method of conical indenter is discussed.In this paper,precise dressing of diamond grinding wheel and cast iron scaife are carried out to solve the problem that the tip of diamond conical indenter is easy to break in mechanical grinding.Mechanical grinding experiments of two types of diamond conical indenter along different grinding angles are carried out and the topography ofindenters are detected by atomic force microscopy.The experiment results are consistent with the theoretical calculation results,which verifies the practicability of the conical precision control theory.Based on the theoretical and experimental results,the axis direction and the mechanical grinding angles of two types of diamond conical indenters are optimized.For diamond conical indenter,besides the anisotropy of diamond crystals,machine tool errors can also cause grinding errors.When the diamond conical indenter is grinded along the optimized grinding direction,the influence of anisotropy of diamond crystal on grinding errors will be weakened significantly,and the machine tool error will be the main source of the grinding error.In order to reduce the influence of machine error,firstly,precision measurement and calibration of the rotation error of the rotary fixture are carried out.Then the grinding errors of two types of diamond conical indenters are analyzed,and the geometric model of the indenter tip is established.This paper analyses the influence of the amplitude and frequency of the fixture rotary error on the grinding precision of conical indenter,and proposes a control method which is reducing the amplitude and increasing the frequency of the rotary error of fixture to improve the diamond conical indenter grinding accuracy.This paper also proposes the solutions for the non-coincidence error between the fixture rotary axis and the pendulum rotary center in the mechanical grinding of spherical diamond conical indenter.In the last section,this paper establishes grinding accuracy measurement schemes for two types of diamond conical indenters.