Experimental Study On Shear Thickening Polishing Technology Of Cemented Carbide Twist Drill

Micro-defects such as saw teeth and burrs,as well as high surface roughness,often occur in the twist drill after grinding,which are generally improved by polishing process.However,for the complex curved surface geometry of twist drill,the existing polishing technology has great limitations.As a new fluid polishing technology,shear thickening polishing(STP)can polish hard,brittle and difficult-to-machine materials with high efficiency and high quality.In this paper,the cemented carbide twist drill is taken as the object,and the polishing process simulation and experimental research are carried out by using the shear thickening polishing technology,so as to achieve the overall polishing of twist drill body clearance,margin and spiral flute.The main research contents of this paper are as follows:(1)The principle of STP polishing for twist drills was analyzed,and the STP polishing experimental scheme was introduced.The preparation process of the polishing fluid was formulated,the main components and proportions of the polishing fluid was determined,and the rheological properties were tested.The results show that the viscosity of the prepared STP slurry is divided into three intervals with the shear rate: shear thinning-shear thickening-shear thinning intervals.The increase of the abrasive particle mass fraction will increase the overall viscosity of STP slurry but keep the rheological properties unchanged.At the same time,the viscosity characteristic curve of the STP slurry was fitted by Gaussian multi-peak method.(2)The fluid simulation of the STP polishing process of the twist dril was carried out,and the distribution nephograms of fluid velocity,dynamic pressure,viscosity and wall shear stress was obtained.The Influences of polishing groove rotation speed and workpiece rotation speed on STP slurry viscosity,workpiece wall shear stress and material removal rate were analyzed.The results show that with the increase of polishing groove rotaion speed and workpiece rotation speed,the STP slurry thickening area near the twist drill expands,and the wall shear stress and Material removal rate of workpiece increase accordingly.(3)Single factor experiment method was used to analyze the influences of the four process parameters,namely polishing groove rotation speed,workpiece rotation speed,polishing time and workpiece inclination,on the surface roughness and material removal rate of the cemented carbide twist drill body clearance,margin and spiral flute.The orthogonal experiment method was used to optimize the four polishing process parameters,namely abrasive particle mass fraction,abrasive particle size,polishing groove rotation speed and workpiece rotation speed.The results show that after STP polishing of cemented carbide twist drill for 30 min under the optimal parameter combination,the surface roughness of the twist drill body clearance,margin and spiral flute decreases to about 10 nm,the material removal rate is 3.497 μm/h.The grinding traces disappear,and the surface defects are basically removed.Studies have shown that STP polishing can effectively improve the overall surface quality of cemented carbide twist drills and achieve precision machining.