Research And Development Of Cryogenic Minimum Quantity Lubrication Deep Hole Machining System

Hole machining accounts for more than 30%of the total amount of machining.Among them,depth diameter ratio L/D>5～10 deep hole accounts for more than 1/3,especially in aviation,aerospace,petrochemical and nuclear power industries,the proportion of deep hole processing is even greater.Because the deep hole processing belongs to the closed processing.the chip removal is di difficult,the cutting heat is not easy to emit,the cutting condition is bad,and the tool wear is serious,so a lot of high pressure cutting liquid is used to cool the cutting condition and removal chip.However,with the continuous improvement of environmental protection requirements,the use of cutting fluid is becoming more and more limited.Therefore,it is urgent to develop new cooling and lubricating methods.This paper aims at the shortage of micro lubrication technology in cooling and chip removing,so cold air is introduced into micro lubrication to form cryogenic minimum quantity lubrication,in order to solve the problem of cooling,lubrication and chip removal in deep hole machining,the research work has important theoretical and practical significance.In this paper,the writer aims at BTA drilling deep hole machining system which use large amount of cutting fluid,through the analyses of BTA drilling deep hole processing characteristics and requirements of cooling and lubrication,cryogenic minimum quantity lubrication system is formed by mixing oil and water to form micro lubrication,and then mixing with a large amount of cold air and finally the system is built.In ICEM CFD,a fluid dynamics model of multiphase flow and cold air mixing spray structure were established.In Fluent,the atomization characteristics of the flow field and the downstream flow field of the atomization nozzle were numerically simulated by Euler model and DPM model respectively.The influence of nozzle diameter and atomization parameters on the diameter of spray particles and the axial velocity at exit were analyzed.Deep hole machining test has been carried out to observe and analyze the operation and chip removal of deep hole processing under cryogenic minimum quantity lubrication,the chip shape and the quality of deep hole machining were also discussed.The analysis results show that,oil and water can be well blended with the mixing unit,and with the aid of porous medium,the oil and water mixed liquid column can be changed into smaller droplets before mixing with compressed air,thus,the pressure drop due to broken oil-water mixture column is reduced.The diameter of atomized particles is proportional to the nozzle diameter,water flow rate and the cold air pressure,and is inversely proportional to the air pressure and the cold air temperature in a certain range.The parameters of nozzle diameter,air pressure and water flow have great influence on the diameter of atomized particles.The results of orthogonal experiment show that the diameter of atomized particles is the smallest when the nozzle diameter is 1 mm,the compressed air pressure is 0.6 MPa,and the water flow rate is 42 ml/h.Deep hole machining test were carried out on 20CrMnMo alloy steel and 1Cr18Ni9Ti austenitic stainless steel using Φ19 mm BTA deep hole drilling.The result shows that the development of low temperature micro lubrication system can meet the needs of deep hole processing of general materials at present,but for some difficult to process materials,it needs to further improve lubrication performance of the system.