Development Of Super-elastic Flexible Abrasive Tool And Its Experimental Investigation On High-Shear And Low-Pressure Grinding

Grinding is one of the most common precision and ultra-precision machining technologies.It is widely used in advanced manufacturing field such as aerospace,shipbuilding,and medical equipment.With the development of high-end equipment manufacturing industry and automation technology,higher requirements are needed on the surface quality of complex curved parts with difficult-to-machine materials such nickel-based alloy.Nickel-based alloys have many great material properties,such as high temperature resistance,thermal fatigue resistance and thermal stability.However,its excellent material properties are easy to cause some processing issues such as wheel blocking,grinding burn and poor surface integrity in traditional grinding.It is difficult to meet the quality requirements of cutting-edge industries.From the grinding mechanism analysis,the traditional grinding is a multiple-edge cutting technology which means the material removal mechanism is very complex.In the grinding process,the normal grinding force is usually 3-5 times that of tangential grinding force,which can even reach 10 times for difficult-to-machine materials.The high ratio of normal grinding force to tangential grinding force is the main cause of many of the above-mentioned grinding issues.In this thesis,a super-elastic composite flexible abrasive tool（ECAT）with shear thickening characteristics using super elastic materials and high-performance fibers was developed.A multi-degree-freedom“high-shear and low-pressure”precision grinding system was integrated.A serial of“high-shear and low-pressure”grinding experiments were carried out for Inconel718 superalloy.The influence of grinding parameters and abrasive layer microstructure composition parameters on surface roughness and grinding force was explored.The microscopic material removal mechanism of“high-shear and low-pressure”grinding was revealed.Through the“high-shear and low-pressure”grinding experiment,the“high-shear and low-pressure”characteristics and excellent grinding performance of the ECAT were verified.The main research contents are as follows:（1）According to the grinding characteristics of complex curved parts of difficult-to-machine materials,the structural scheme of the ECAT and the material of the abrasive layer were determined.The structure of the ECAT was optimized through finite element analysis.The rationality of its structural design was verified.（2）A multi-degree-of-freedom“high-shear and low-pressure”precision grinding integrated system was developed with an industrial robot,a three-dimensional precision platform,an electric spindle and the ECAT.Effective communication between the robot and the three-dimensional precision motion platform was established.A force control module for grinding force acquisition,analysis and feedback was developed.The multi-degree of freedom（6+3）linkage was realized through the attitude adjustment of the industrial robot and the movement of the three-axis precision motion platform.Precise force control grinding for complex curved parts can be achieved.（3）Based on the principle of“liquid body armor”and the“particle cluster”effect,the microscopic material removal mechanism of“high-shear and low-pressure”grinding for curved surface parts was revealed.According to the structure of the ECAT and the Hertz contact theory,the velocity field and pressure field in the grinding area were analyzed respectively.The material removal model of“high-shear and low-pressure”grinding with ECAT was established by the Preston equation.Its effectiveness was verified thought fixed-spot grinding experiments.The average error of the material removal theoretical model is about 4.563%.（4）The experimental investigation on“high-shear and low-pressure”grinding was carried out for Inconel718 planar workpiece.The influence of offset,abrasive tool speed and feed speed on the surface roughness and grinding force was explored.The results showed that the grinding quality was best when the offset was 1 mm,the abrasive tool speed was 600 r/min and the feed speed was 4 mm/s respectively.The surface roughness decreased from 385.6 nm to 44.5 nm.The surface of the workpiece was smoothened after grinding.The excellent grinding performance of the ECAT was verified.The grinding force during the grinding process was monitored.The results showed that the ratio of tangential grinding force to normal grinding force F_t/F_n reached about 0.427,which was much higher than the F_t/F_n of 0.166 with pure Kevlar fibre.The“high-shear and low-pressure”grinding characteristics of the developed ECAT was verified.（5）The experimental investigation on the microstructure composition optimization of abrasive layer was carried out for Inconel718 curved workpiece.The influence of nano SiO₂ mass fraction in abrasive layer base fluid,abrasive particle average size and abrasive mass fraction on surface roughness,material removal depth and grinding force was explored.The obtained optimal microstructure composition parameter of the abrasive layer was that SiO₂ mass fraction was 15%,Al₂O₃abrasive mass fraction was 5%and the Al₂O₃abrasive average particle size was 6.5μm respectively.The surface roughness of the curved workpiece decreased from the initial 308.1 nm to50.0 nm The material removal depth reached about 1.57μm.The ratio of tangential grinding force to normal grinding force F_t/F_n can reach about 0.2741.After grinding,the surface integrity of the workpiece was improved,while still maintaining a good surface profile.