Effect of Milling Parameters on DEM Modeling of a Planetary Ball Mill

The effects of the milling parameters involving shape of powder particles, rotation speed, and ball-to-powder diameter (BPDR) on DEM modeling in the planetary ball mill were investigated. BPDR was varied from 1 to 10. The results revealed that the size and shape of the powder particles do not give a significant change in simulation results when BPDR attains maximum value of 10. The increasing of BPDR leads to the increase of simulation time and size. Hence, the effect of change of the powder particle shape on the calculated data size is not significant. The results also revealed that the increasing rotation speed increases impact energy between powder particles.

Influence of Minimum Quantity Lubrication Parameters on Tool Wear and Surface Roughness in Milling of Forged Steel

The minimum quantity of lubrication（MQL） technique is becoming increasingly more popular due to the safety of environment.Moreover,MQL technique not only leads to economical benefits by way of saving lubricant costs but also presents better machinability.However,the effect of MQL parameters on machining is still not clear,which needs to be overcome.In this paper,the effect of different modes of lubrication,i.e.,conventional way using flushing,dry cutting and using the minimum quantity lubrication（MQL） technique on the machinability in end milling of a forged steel（50CrMnMo）,is investigated.The influence of MQL parameters on tool wear and surface roughness is also discussed.MQL parameters include nozzle direction in relation to feed direction,nozzle elevation angle,distance from the nozzle tip to the cutting zone,lubricant flow rate and air pressure.The investigation results show that MQL technique lowers the tool wear and surface roughness values compared with that of conventional flood cutting fluid supply and dry cutting conditions.Based on the investigations of chip morphology and color,MQL technique reduces the cutting temperature to some extent.The relative nozzle-feed position at 120°,the angle elevation of 60° and distance from nozzle tip to cutting zone at 20 mm provide the prolonged tool life and reduced surface roughness values.This fact is due to the oil mists can penetrate in the inner zones of the tool edges in a very efficient way.Improvement in tool life and surface finish could be achieved utilizing higher oil flow rate and higher compressed air pressure.Moreover,oil flow rate increased from 43.8 mL？h to 58.4 mL？h leads to a small decrease of flank wear,but it is not very significant.The results obtained in this paper can be used to determine optimal conditions for milling of forged steel under MQL conditions.

Discrete Element Simulation of Asphalt Pavement Milling Process to Improve theUtilization of Milled Old Mixture

In order to improve the utilization of milling materials,save stone resources and reduce milling energy consumption,the aged Styrene-butadiene-styrene(SBS)modified asphalt was used as a binder to prepare AC-16 asphalt mixture to simulate old asphalt pavement materials.First,the test and discrete element simulation results of uniaxial compression tests were used to calibrate the parameters of the parallel bonding contact model between asphalt mortar and aggregates.On this basis,a microscopic model of the asphalt mixture was established to simulate the old asphalt pavement.Then,the discrete element software PFC(Particle Flow Code)was used to simulate the milling process of the old asphalt pavement.Analyzed the force of the cutting tool and the utilization rate of milling materials,and the optimal milling speed and milling depth were determined.Finally,the energy consumption in the milling process was measured.It is concluded that in the process of milling the old asphalt pavement,using a cutting angle of 42°,milling speed of 0.5 m/s and milling depth of 20 mm can reduce the wear of the cutting tool.In this case,the direct utilization rate of milling materials is 85.3%,and the rate of energy consumption reduction is 33.53%.After parameter optimization,the utilization rate of milling materials can be increased by 17.4%.

A Facile Way to Large-scale Production of Few-layered Graphene via Planetary Ball Mill

Abstract In the field of polymer/graphene nanocomposites, massive production and commercial availability of graphene are essential. Exfoliation of graphite to obtain graphene is one of the most promising ways to large-scale production at extremely low cost. In this work we illustrate a facile strategy for mass production of few-layered （≤ 10） graphene （FLG） via the newly explored ball milling. The achieved FLG concentration was determined by UV/Vis spectroscopy. The formation of FLG was proved by measuring the flake thickness by atomic force microscopy （AFM）. Further Raman spectral studies indicated that the crystal structure of exfoliated flakes was preserved satisfactorily during this shear-force dominating process. To increase the maximum concentration obtainable, it＇s critical to make a good parameter assessment. N-methylpyrrolidone （NMP） was used as a dispersing medium and the effect of milling parameters was systematically and quantitatively investigated, thus providing a criterion to optimize the milling process. We established the optimal values for solvent volume and initial weight of graphite. As for milling time, the production of FLG was enhanced with continuous milling according to the power law, but not linearly with increasing milling time. Moreover, the possible mechanism involved in milling process was also explored. Our work provides a simple method for graphite exfoliation and has great potential for improving thermal and electrical conductivity of polymer composites in the fields of engineering.