Research On Mechanism And Technology Of Machining Precision Joint By Abrasive Flow Machining

Precision pipe joints,valves,transfer switches and other components are widely used in aerospace field.The reliability of the components affects the stability of the system directly.A kind of precision joints used on a certain type of aircraft is made of 30 CrMnSiA.Due to the plasticity of 30 CrMnSiA,burrs occur at the intersection of the joints after drilling which affect the safety of hydraulic system.In the practical production,the burrs are removed by hand.However,the burrs are difficult to remove effectively and efficiently by hand,because the burrs are inside the joints.In addition,the surface quality of the central hole in the precision joint also has a significant effect on the system performance.Abrasive flow machining technology has unique advantages in deburring of inner cavity and polishing inner passageways.After overall consideration,abrasive flow machining technology is introduced into deburring and polishing inner passageways.The mechanism and technology of processing precision joints were studied by theoretical analysis,simulation and experiments.The main contents include:The rheological properties of pseudoplastic non-newtonian fluid abrasives were studied and the viscosity-temperature characteristics of abrasives were explored by water bath experiments,which showed that the viscosity of abrasive decreased with the increase of temperature.In addition,the velocity distribution in the precision joint during machining was analyzed.To know the removal of material,the forces acting on abrasive particles in the contact area were analysed and the wears were studied including deburring and polishing.After analyzing workpiece,planning abrasives path,designing structures and verification,two sets of fixtures for deburring and polishing inner hole were designed.The removal amount along the flow direction is uneven,so the variable-diameter core mold was set in the joint.In order to solve the problem that the size of guide section can not be determined due to the fluctuation of workpiece size in mass production,the gap-guide section was applied.By the generalized Reynolds number,it was found that the abrasives were in laminar flow.The changes of velocity and pressure in simulation results were observed to explore the influences of different abrasive particle size and processing pressure on deburring.Some single factor experiments were designed to verify the results of simulation.According to the results of simulation by Fluent,the gap of guide section was 3mm.About the size of core mold,the diameter of bottom surface is 5 mm and that of top surface is 6 mm.At last,the effects of the gap-guide section and the variable-diameter core mold were verified by experiments.Single factor experiments were done to study the influences of naphthenic oil,white oil and silicone oil with different content on the viscosity.What's more,the best combination of additives for adjusting viscosity was found through the orthogonal experiment,the content of silicone oil was 3%,the content of white oil was 2% and the content of naphthenic oil was 3%.In the processing experiments,the optimal parameters of deburring and polishing were found by orthogonal experiments.The optimized parameters for deburring were abrasive particle size 46 meshes,processing pressure 20 MPa and abrasive dosage 6000 ml.The optimized parameters for macroporous polishing were abrasive particle size 180 meshes,processing pressure 20 MPa and abrasive dosage 10000 ml.Finally,effective cleaning schemes were found and the detergent was environmentally friendly by testing.The mechanism and technology of processing precision joints were studied,which provided valuable experiences for the application of abrasive flow machining in more complex and refractory aeronautical precision parts.