Numerical Simulation And Structural Improvement Of The Milling Process Of Asphalt Pavement Milling Machine

In order to relieve the increasing pressure on road maintenance,it is necessary to improve the structure of pavement milling machines and improve their performance.The complex milling process of pavement milling machines is difficult to investigate due to limited testing techniques,hence the need for numerical simulation methods.In this paper the suitability of the pavement milling machine milling system for asphalt concrete pavements is evaluated by discrete element modelling.In addition,based on the analysis results of the simulation,structural improvements for better mobility are proposed,allowing the milling waste to be discharged from the milling system faster.The main work is as follows.(1)The composition of the milling machine and the working principle of the milling system are expounded.The motion model and mechanical model of the process of collecting waste by the spiral of the milling drum blade and the throwing process of the throwing plate are deduced,and the parameters that can affect the performance of the milling system are extracted.A three-dimensional model of the milling system is established.(2)Based on the discrete element theory and the structural composition of asphalt concrete,the Hertz-Mindlin and Bonding(legacy)contact models were selected for discrete element modelling of the asphalt concrete pavement.The discrete element model parameters of the asphalt concrete pavement were calibrated according to uniaxial compression tests and rest angle tests,and the pavement model was built using the block factory approach.The discrete element model of the milling operation was built in EDEM by fitting the real operation of the pavement milling machine.(3)The conventional milling chamber structure was improved by proposing a new tail plate structure and a front baffle structure with variable side inclination,respectively.The new tail plate structure makes the gap between the milling chamber and the milling drum smaller and the front baffle with inclination has a material collecting effect.The new structure of the milling chamber significantly improves the accumulation of waste material,increases the material transfer efficiency of the milling system and corresponds to a small increase in the milling drum torque.The dynamically adjustable tilting front baffle solution is more efficient in collecting material than the tilting front baffle solution and the conventional milling chamber structure.(4)The effects of four helix angles(16°,18°,20°,22°)of the milling drum blade on the waste discharge efficiency of the milling system were studied.The simulation results were consistent with the theoretical analysis of the milling drum’s spiral collection of waste.The total output mass of the milling drum of each group of single throwing plates and each group of double throwing plates is studied,and the influence on the radial force of the milling drum is considered.The milling drums with two throwing plates per set are considered to be more capable of conveying scrap.Overall,the designed milling chamber shows satisfactory performance and the study of the helix lift angle and throwing plates can provide a reference for further optimisation of the milling system design.