Optimization And Experimental Validation Of Multi-pass Cold Drawing Process For Manufacturing The High Qualified Aluminum Rectangular Tube

The aluminum rectangular tube with high accuracy is a widely used component inthe aviation, radar, and aircraft for microwave transmission. Due to particular conditionof usage, not only the requirement for dimensional accuracy is high, but also for theinternal surface finish is stricter. Therefore, it is difficult to obtain the accurate tubeforming. The research for the high accuracy rectangular tube in our country has a veryshort history, so the forming process has not been developed to manufacture the eligibletube for lacking of technology and experience. The situation leads to the long-term tubeimportation from abroad which greatly restricts the development of our military industry.Therefore, it is necessary to obtain our own production process for this type ofaluminum rectangular, which can break out the technique monopolization of developedcountries and has a strong contribution to our national defense industry construction.The research object in the paper is the aluminum rectangular tube with dimensionsof91.62×48.26×2.05mm, the dimensional deviation±0.12mm and internal surfacefinish Ra=1.0um. Nowadays, the production of rectangular tube has some formingproblems for the influences of process, machine and so on, such as tube wall concave,wrinkle, uneven wall thickness distribution, especially the rough internal surface andevident ‘orange texture’ phenomenon in tube inner surface. All of these are greatlyaffecting the particular usage of the rectangular tube. Based on the analysis, theinvestigation of forming process for manufacturing this rectangular tube has beencarried out in this paper and the main content are as follows:①The three passes drawing scheme is determined after the analysis of therectangular rube forming feature, that is, the first pass is tube sinking drawing withoutplug for proper transition section; The middle pass plays a role of rectangular correctionfor the first pass tube; and the last one is the significant drawing pass with plug forassuring the finial dimension, geometry and surface accuracy. The section dimension forthe three passes is:φ92.8×2.15mm—96.38×57.26×2.15mm—92.8×50.0×2.1mm—91.62×48.26×2.05mm②The finite element model of aluminum rectangular tube multi-pass cold drawingprocess has been established in the paper. Through series of FEM analysis, the tubemetal flow and deformation feature is summarized. Meanwhile, the reason for maindrawing defects such as tube wall concave, wrinkle and uneven wall thickness is also explanted in our study. And the proper measurements are proposed to solve this problemwhich guarantees the eligible tube geometry accuracy.③To improve the uniformity of tube metal deformation in drawing process, thestudy is carried out to optimize the five significant drawing factors (drawing velocity v,friction coefficient, drawn tube sizing zone length L, die semi-angle, transitionarc radius R). Two evaluate index (deformation uniformity criteria θ and tube ear height H)are determined to analysis the simulation results. And the optimal parameterscombination for assuring the tube drawing stability is obtained after results institutiveanalysis, that is, v=12.5mm/s， L=9mm，=0.05， R=5mm，=9°④Aiming to solve the unqualified accuracy of rectangular tube inner surface, thenew type of “convex hull” shape die configuration and plug with “tinny boss club” areproposed to replace the traditional ones. The contact status between the tube innersurface and plug, the plastic strain-stress distribution, the dimensional accuracy of theformed part, and the forming load have been compared between the conditions that thetraditional die and this new type one have been used respectively. The results showclearly that the new type drawing die and plug design are beneficial to increase thedeformation uniformity and improve the tube forming accuracy.⑤The experiment on the cold drawing process of the aluminum rectangular tubehas been performed. The comparisons of the drawn tube dimensions, e.g. height/widthand wall thickness, have been made between simulation results and practical production.Meanwhile, the surface finish has also been measured. The experimental result exhibitsthat the drawn tube can better fulfill the requirements of the design and usage when theoptimized forming scheme is adopted.The investigation in the paper achieves the development of this high qualifiedaluminum rectangular tube, enriches the drawing deformation theory of special-sectiontubes and can also provide an effective guideline and reference to the research of thiskind of tube.