## 5 Conclusions  
In this study, the ultrasonic vibration effect on CBN abrasive grain movement behavior and distribution in the fabrication of structured CBN grinding wheel was studied. The numerical simulation method was introduced to simulate the ultrasonic vibration-assisted laser cladding process. The main conclusions are summarized as follows:  
(1) The micro-morphology of the laser cladding CBN printing layer subjected to ultrasonic vibration was compared. The surface profile of the printing layer was uneven without applying ultrasonic vibration, and the protruding height of the CBN abrasive grains varied. With the addition of ultrasonic vibration and the gradual increase in the amplitude to a power ratio of 30%, the surface of the printing layer tended to be smooth. The protruding height of the CBN abrasive grains gradually became consistent. When the ultrasonic amplitude continued to increase, the CBN abrasive grains on the surface of the melt pool with a protruding height were detached from the printing layer due to strong vibration. This resulted in a small number of abrasive grains on the surface of the printing layer, and the remaining abrasive grains on the surface were almost level with the surface of the printing layer. (2) A two-dimensional Gaussian cross-section heat source model was established, whose energy density conforms to Gaussian distribution in both space and time. The results of the temperature field simulation and analysis show that the temperature of each part of the printing layer exhibited the distribution form of an approximate Gaussian curve. When the simulation time was 100 ms, the temperature inside the printing layer reached more than 1100 K, and all the Cu-Sn-Ti alloy bond melted into the liquid state. When the simulation time was 240 ms, the maximum temperature of 1568 K was reached, which did not reach the CBN abrasive grain burnout temperature. (3) The results of the fluid field simulation analysis show that the fluid in the melt pool exhibited symmetric circumference. The flow velocities at different locations in the melt pool varied considerably, with the highest velocities at the surface of the melt pool, especially near the substrate. The flow velocity was lower at the bottom, the two centers of circumference, and the top of the melt pool. The maximum velocity of the molten metal in the melt pool was 0.319 m/s, and the minimum velocity occurred at the bottom of the melt pool at 0 m/s. (4) Under the condition without ultrasonic vibration, the CBN abrasive grains in the melt pool started to move under the joint action of gravity, buoyancy, and the drag force formed by the molten metal flow. The CBN grains located near the boundary of the printing layer moved at a higher speed, while the grains located at the bottom of the melt pool had the smallest speed. The CBN grains moved with the two circumfluences of the molten  
Figure 15: CBN abrasive grain movement trajectory: (**a**) without ultrasonic vibration; (**b**) with ultrasonic vibration. metal, which suggests that the molten metal flow played a dominant role in the drag force of the CBN grains. The CBN abrasive grains eventually accumulated on the boundaries on both sides of the printing layer, while there was no abrasive grain distribution on the top of the printing layer. (5) Under ultrasonic vibration conditions, the CBN abrasive grains in the melt pool were subjected to ultrasonic forces in addition to gravity, buoyancy, and drag forces. However, in contrast to the case where ultrasonic vibration was not applied, the CBN abrasive grains no longer flowed in the direction of the circumfluence of the molten metal in the melt pool but began to flow to the top surface of the melt pool. This indicates that the force generated by the ultrasonic vibration was comparable to the drag force of the metal fluid, which changed the direction of the combined force and the movement direction of the CBN grains.