## 4 Results and Discussion  
### Comparison of Mechanical Properties  
Figure 3 shows the SEM microtopography of the gel abrasive tool and the hot-pressing abrasive tool. The agglomerated abrasives can be observed in the micrograph of the hot-pressing abrasive tool. On the one hand, the preparation method of the hot-pressing abrasive tool involves dry mixing, whereby the fluidity of the mixed materials is much worse than that of the wet mixing method. Furthermore, there are density differences between different materials, which renders the mixing process more difficult. On the other hand, the abrasives have a high surface energy and large contact surface due to the small particle size, whereby agglomeration is prone to happen due to van der Waals forces between the particles. It can be observed from Figure 3a that abrasives were uniformly dispersed in the gel abrasive tool because the premixed solution of the gel abrasive tool had low viscosity. Moreover, under the action of chemical reagents such as the dispersant and wetting agent, the abrasive had a better dispersion effect. Pore structure is an important feature of abrasive tools; Archimedes' principle was used to test the density and porosity of samples. The porosity of the abrasive tool can be obtained by calculating the theoretical density and weighting dry weight, floating water weight, and water weight of the sample. The existence of pores in the abrasive tool enables the abrasive tool to have good debris-holding and heat-dissipation capabilities. It can be seen that there were many uniformly distributed pores on the surface of the gel abrasive tool, which were caused by the loss of water during the drying process. The DUH-211/211S Dynamic Microhardness Tester was used to establish force-displacement curves; the maximum test force was 500 mN and the loading speed was 7.0067 mN/s. Five points were chosen to test the microhardness, and the elastic modulus was obtained after the test. Figure 4 shows a comparison of the microhardness and elastic modulus of the gel abrasive tool and the hot-pressing abrasive tool; the results show that the microhardness of the hot-pressing tool fluctuated greatly due to the appearance of loosely distributed agglomerated particles. The flexural strength was tested using the three-point bending method; the span distance was about 60% of the sample's length, and the speed was 1 mm/min. The tensile strength was tested using the uniaxial stretching method; the stretching speed was 1 mm/min. The impact strength was tested using the pendulum impact method; the impact rate was 3.5 m/s, the pendulum potential energy was 5 J, the sample size was 10 mm \(\times\) 10 mm \(\times\) 50 mm, and the surface roughness Ra of the sample was about 1 \(\upmu\)m. Figure 5a shows the effect of PI resin content on the mechanical properties of the gel abrasive tool, where it can be seen that the mechanical properties showed an upward trend with the increase in mass fraction of the PI resin; however, when the mass fraction of PI resin was too high, the viscosity of the slurry was significantly affected, which worsened the uniformity of the abrasive tool. As shown in Figure 5b, the flexural and tensile strength of the gel abrasive tool was 25% and 23% higher than that of the hot-pressing abrasive tool, respectively, while the impact strength was 6% higher. The curing temperature of PI resin was much higher than the g  
Figure 3: Surface SEM microtopography: (**a**) gel abrasive tool; (**b**) hot-pressing abrasive tool. enabled the gel to wrap the uncured resin and abrasive particles in the uniformly dispersed microgel during the gelling process. During the sintering process, the gel component in the abrasive tool began gradually decomposing, and the polyimide resin gradually became the main body of the bonding agent.