| Nickel-based alloys have advantages such as high working temperature,stable structure,oxidation resistance,and corrosion resistance.They maintain high fatigue strength,tensile strength,fracture strength,and creep strength even under high-temperature oxidation conditions of 1000℃.Therefore,nickel-based alloys are important strategic materials in the aerospace and civil industries.However,due to their high hardness,strength,heat resistance,and pressure resistance,nickel-based alloys are one of the most difficult materials to process.As an important branch of machining technology,deep hole machining of nickel-based high-temperature alloys is even more challenging.According to statistics,hole machining accounts for about one-third of all mechanical processing in the machinery manufacturing industry,while deep hole machining accounts for more than 40% of hole machining.For example,aircraft engines,which are made of nickel-based high-temperature alloys,have tiny hole structures such as blind holes,step holes,and deep holes in components such as impellers,blades,slender shafts,nozzles,and turbine discs.These hole structures are extremely difficult to machine,and the pass rate is relatively low.Machining nickel-based small deep holes is one of the most challenging tasks.Compared with other small hole machining methods,gun drilling of deep holes in nickelbased high-temperature alloys has the advantage of a large length-to-diameter ratio.The most significant feature of gun drilling is that the guide bar’s "rolling" effect on the hole wall can improve surface smoothness,prolong the fatigue life of parts,and reduce electrochemical reactions on the surface of parts.From the perspective of ensuring the internal quality of the hole and the use of nickel-based alloy parts,gun drilling is still one of the most reliable methods for machining small deep holes in nickel-based alloys.However,the complex structure of gun drilling for small deep holes,small aperture,long drill rod,poor relative rigidity of the drill rod,and the inability to observe and correct the closed machining have made cutting performance,cutting temperature,cutting force,tool wear,and other issues particularly prominent during the gun drilling process for nickel-based high-temperature alloys.These issues also lead to serious problems such as low machining efficiency,drill rod vibration and bending,difficulties in chip removal,poor machining quality,and short tool life.This article focuses on the series of problems that exist in gun drilling of nickel-based high-temperature alloy Inconel 718 and conducts research on key technologies,mainly including the following research contents:In order to address the difficult issues in cutting nickel-based high-temperature alloys with gun drills,solid carbide gun drills were selected for drilling experiments.The influence of different drilling parameters and depths on surface roughness,chip formation,microstructure,and cutting force of the workpiece material during drilling was investigated,and the evolution of surface roughness,cutting force,and machining system stability with tool wear was observed.The types of hole surface defects and their causes were clarified;the optimal process parameter combination for gun drilling of nickel-based alloys was obtained;the main forms of gun drill wear were identified as abrasive wear and chip accumulation;the change pattern of cutting force during drilling was discovered,and the intrinsic connection between cutting force and tool wear was elucidated.It was proven that the primary cause of tool breakage during gun drilling of nickel-based high-temperature alloys was excessive axial drilling force.The reliable prediction factors for tool life were found to be cutting force,vibration,noise,and hole mouth morphology,and the influence of machining parameters on chip morphology was explored.A force analysis was conducted on the gun drilling process,using the edge micro-element model and based on the orthogonal cutting theory and the improved Oxley shear angle model.A drilling force prediction model was constructed considering material work hardening,cutting parameters,and tool geometry parameters,combined with the unequal division shear zone model.The contribution of the tool edge plowing force to the cutting force was established using the finite element analysis method.Deep hole drilling experiments on nickel-based alloys were carried out using a six-dimensional force sensor,and the cutting force values calculated by the experimental and predicted models under different cutting parameters were compared,verifying the effectiveness of the established cutting force prediction model.Due to the structural asymmetry of the main rotating system and the complex and variable external excitation forces in the operating environment of gun drilling,the gun drill rod system is regarded as a continuous beam rotor model,and the vortex models of the drill rod under three working conditions are derived: the gun drill is vertically installed without considering gravity and mass eccentricity;the drill rod vortex equation considering gravity and tilt motion is derived when the drill rod is horizontally installed;and the drill rod vortex model considering mass eccentricity and torque is derived based on the first model.The critical speed and bending vibration mode of the system are solved based on the established transverse vibration dynamic equation of the drill rod.The dynamic behavior and regularity of the drill rod system are analyzed and explored from three aspects: excitation force,damping,and geometric parameters.Various complex phenomena,including periodic and chaotic phenomena,were discovered.Through rich and complex numerical calculation results,a foundation has been laid for the research on vibration suppression of the deep-hole drilling rod system.To address the vibration problem during the drilling process of nickel-based hightemperature alloys using gun drills,a new type of electromagnetic sleeve-assisted vibration damping device was designed,and a sliding-mode active controller based on the fal function was proposed as the underlying control algorithm.The proposed active control strategy condensed a class of multi-channel uncertain generalized affine system manifold to describe the bending vibration state of the gun drill.By introducing an error-based state space,the internal perturbation and external uncertainty of the drilling rod dynamic system were concentrated in the same channel.Based on the fal function,a sliding-mode controller was constructed,combined with a reduced-order extended state observer,to effectively estimate the total uncertainty in the system.To ensure the effectiveness of the proposed active control strategy,the stability of the observer and controller were theoretically analyzed,and the closedloop stability of the entire system was ensured.Simulation analysis verified the effectiveness of the proposed control strategy.This technology can provide theoretical and engineering guidance for controlling the bending vibration of the drilling rod during the gun drilling process and has great practical significance. |
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