Ultra-precision Turning Of Grazing Incidence Reflector Mandrel

Nested focusing X-ray telescope is used to observe physical phenomena such as transient sources and violent outburst objects in the X-ray band.Generally,X-ray detection is carried out with a grazing incidence Wolter-I imaging system,which has an endoscopic tube structure consisting of two rotationally symmetrical aspherical surfaces.And it has the advantage of high imaging quality and high spectral reflectance.As a commonly used mould material for optical components,the electroless nickel-phosphorus alloy has good ultra-precision cutting properties and is widely used as a surface chemical plating material for the grazing incident reflector mandrel.The large size grazing incidence reflector is generally machined by the mandrel replication method.Due to the specificity of its structure,the mandrel surface shape requires a high degree of accuracy,which is no more than 1 μm.It has been a great challenge to achieve ultra-precision processing and accuracy checking of large-aperture grazing incident reflector mandrel.The subject of this thesis was to focus on the grazing incidence reflector mandrel,and the mechanical properties of its chemical plating material,the amorphous electroless nickelphosphorus alloy,were investigated.The influence of tool geometry and cutting parameters on the surface quality in ultra-precision turning of amorphous electroless nickel-phosphorus alloy was analysed,and the ultra-precision turning process was optimised.Ultra-precision turning and in-situ inspection techniques were used to obtain the grazing incident reflector mandrel which complied with the requirements for form accuracy and surface quality.Firstly,the behaviour of the micro and nano mechanical response of amorphous electroless nickel-phosphorus alloy was investigated.Nanoindentation experiment was carried out,and its mechanical property parameters were obtained,including the elastic recovery rate of 30%to 34%,,the nano-hardness of 6.5 GPa to 7.0 GPa,and the Young’s modulus of 114 GPa to 131 GPa.The shear bands and micro bulges were observed around the indentation,which exhibited the plastic flow behavior.It was shown that amorphous electroless nickel-phosphorus alloy was a typical plastic material.Then,the micro and nano scratching experiment with variable depth of cut was carried out of this amorphous coating material.And there were no brittle features such as cracks and fractures in the scratch mark,and the chips were concentrated at the tool retraction.In addition,scratch edge defects such as plastic bulges and burrs were created due to the lateral flow of the material.The experimental results provided a theoretical basis for the ultra-precision turning of amorphous electroless nickel-phosphorus alloy.Secondly,the study on the ultra-precision cutting process and cutting mechanism of amorphous electroless nickel-phosphorus alloy was carried out.The influence of cutting parameters and tool geometry on physical quantities of the machining process(cutting forces and cutting temperatures)and surface quality was investigated for ultra-precision turning of amorphous electroless nickel-phosphorus alloy.And the mechanism of material removal was further explored through the observation and analysis of chip morphology.The experimental results showed that as the spindle speed increased,the cutting forces decreased and the surface quality subsequently improved,but the friction coefficient rose significantly.Increasing depths of cut and feed rate would increase cutting forces and reduce the friction coefficient.The cutting temperature at the tool tip was most significantly affected by variations in spindle speed(cutting speed).And the use of lower spindle speeds would result in thinner chips,which effectively reduced the cutting temperature.In addition,the use of diamond tools with large nose radius was also effective in reducing cutting temperature.Predicted values of surface roughness and experimental results showed that the feed rate would significantly affect the machined surface roughness.The tool was machined with a large nose radius and a negative rake angle,although it was subjected to higher cutting forces,the surface quality was significantly improved.Due to the plastic flow in the primary shear zone,a periodic laminar chip was generated during the cutting process,which formed the primary shear zone and the secondary shear band on the chip free surface,and the secondary shear band enhanced the plasticity of the material.The spindle speed and the tool rake angle influenced the formation and spacing of the shear zones.Finally,the ultra-precision turning and the contouring accuracy of the grazing incidence reflector mandrel was carried out.The reversal method of the contour accuracy of the mandrel was proposed.Ultra-precision turning of cylindrical roller with effective length of 140 mm was carried out,and the spectral confocal probe was used to measure the cross-section profile of the roller in the forward and reverse directions,which effectively separated the inherent error of the machine and the contour error of the roller,and the validity of the measurement method was verified.A large-diameter dual-zone(hyperbolic and parabolic)aspheric grazing reflector mandrel turning trajectory was produced,which considered the nose radius compensation of the diamond tool.Furthermore,ultra-precision turning was carried out and the surface roughness of the mandrel was less than 3.5 nm.The contour measurement of the mandrel was performed by reversal method,which produced outputs of 3.0 μm and 3.2 μm for the forward and reverse positions,respectively It was calculated that the shape accuracy of the grazing incidence reflector mandrel was within 1μm and the roundness was 0.4 μm.It was obtained the mandrel which conformed to the form accuracy and the surface shape accuracy.The tool wear profile of the semi-finish and finish machining was compared,and slight wear and scratches were found at the tool tip after the finish machining with no obvious chipping.