Effect of drill bit structure on sample collecting of lunar soil drilling

The influence of the drill bit structure on the lunar soil drilling process is an important factor in the sampling mechanism design. The drilling process was simulated by a previously proposed discrete element model. The stress distribution showed that the boundary effects were within acceptable limits. By analyzing the source of the samples, the velocity field and the trajectory of the sample particles, a motion behavior of jumping and falling of the sample particles was observed and a bubble-shaped sample collecting law was summed up. The downward motion behavior of sample particles was verified by analyzing the sample length of a drilling experiment. Finally, based on the engineering requirement, the drill bit structure was optimized. The simulation results showed that the injection amount of the particles into the bit could be significantly increased by changing the cutting teeth from cylindrical to prismatic and adding complement ring to eliminate the protruding of the cutting teeth to the inside of the bit, and the sample leakage could be effectively prevented. The axial force and torque decrease obviously by changing the drill bit body from the cone shape to a funnel shape. The inner diameter expansion caused by the internal structure design of drill stem at the joint of the drill bit and stem had little effect on the injection quantity.