Research On The Inner Surface Roughness Of The High Qualified Aluminum Rectangular Tube During Cold Drawing Process

The high quality aluminum rectangular tube is widely used in the aviation, radar,and aircraft for microwave transmission.Due to the specialty of the usage conditions ofthe aluminum rectangular tube, it is required that the dimensional accuracy of therectangular tube is very high while the roughness of the inner surface must be lowenough. The aluminum rectangular tube with highly dimensional accuracy can bemanufactured now, but the inner surface roughness is disqualification.The macro-scale finite element model of multi-passes cold drawing process forAl6061rectangular tube with dimensions of91.62×48.26×2.05mm had been establishedfirst in this paper. The meso-scale finite element analyses for some parts of the finaltube wereconducted based on the macro-analysis results and the theory of crystalplasticity. The couple of the macro-scale and meso-scale analysis provided a new way tosolve the inner surface disqualification problem during drawing process. To simulate thesurface roughness evolution with different material parameters after plastic deformation,a simple plastic deformation process, such as uniaxial tension, was chosen in this paper,for the reason that material deformation during drawing process was so complex. Themain research contents were as follows:1) The three passes drawing scheme was determined after the analysis of therectangular tube forming feature. Then the macro-scale finite element model had beenestablished according to the three passes drawing scheme. The experiment resultsverified the validity of macro-scale FEM analysis.2) As the dimensional accuracy and surface quality are determined by the thirdpass, so the meso-scale analyseswere conducted at several special positions in the thirdpass, such as the midpoints of the long and short sides with boss, and the end of the longand short sides without boss. Considering the measurement error, the differencebetween Raand Sqand the simplification of FEM model, the surface roughness obtainedin simulation was generally in agreement with that in experiment, which inspected thefeasibility ofsurface roughness revolution analyses under cold drawing withmacro-meso coupling analysis method.3) The influences of initial roughness value and initial grain size on the surfaceroughness evolution were simulated. In uniform plastic deformation stage, thelargerinitial roughness value, the smaller effect of tension strain to surface roughness. A small grain size would lead to a uniform deformation and small surface roughnessvalue.4) The influences of grain texture on surface roughness under uniaxial tension weresimulated. Different textures have different abilities of plastic flow, which will result indifferent surface topographies. Cube and Goss textures were effective in reducing theroughness value during uniaxial RD stretching. The key reason was the effect of Taylorfactor. Taylor factor is a measure of the ability of a given texture to accommodateplastic flow or grain anisotropic kinematic hardening. A small Taylor factor will resultin a more uniform strain distribution.5) The influence of texture density was simulated by using models with differentmixed ratio of Cube texture and Random texture. The results indicated that a smallsurface roughness value could be obtained in a model with high density of Cube texture.The reason was that high texture density of Cube texture can reduce the misorientationbetween grains.6) The influence of die on surface roughness was investigated. Surface roughnesswas reduced with the increasing of thickness reduction. When thickness reductionreached a certain value, surface roughness remained constant. The results indicate thatdie has flatting effect on the surface topography.7) The Al6061uniaxial tension experiments were carried out with different initialsurface roughness, initial grain size andtexture. Experiment and simulation results werein a good agreement, which confirmed the conclusions obtained by simulations.This paper makes a successful transition from macro-scale drawing analysis tomeso-scale analysis. The influence of several parameters on surface roughnessrevolution was discussed under uniaxial tension, which lays the foundation for solvingthe inner surface roughness problem after cold drawing in the future.