Research On The Uniformity Of Wall Thickness For The Superplastic Bulging Forming Of Aluminum Alloy Thin Shell

5A06 Al-Mg alloy is a common structure material in aerospace.While in cold stamping,the plasticity of the alloy is poor so that the maximum elongation is only 16%with high springback.In the space field,it is inclined to adopt the superplastic bulging instead of cold stamping to produce the aluminum alloy shell,which can gain the better elongation and spontaneously avoid the springback.But the accompanied uneven wall thickness distribution leads to the serious stress concentration of parts in applications.This paper analyzed the regularities of wall thickness distribution on a particular basin parts after the superplastic bulging,at the same time,determined the thick and thin area of the parts.By using the positive and negative bulging,the wall thickness distribution is improved.At the same time the forming limit of spherical parts is obtained,and the particular spherical part forming process is also optimized.MSC.Marc was used to simulate the forming process of superplastic forming basin shaped parts,the thickness distribution is: the latest pasted bottom corner has the lowest wall thickness,the earliest pasted lateral wall has the highest thickness,the minimum wall thickness is only 0.69 mm,the wall thickness distribution is 0.1797 mm.The thickness distribution was improved using positive and negative bulging,with five main influencing factors of the negative bulging mold,through five-factors and three-levels orthogonal test,the optimal results considering the minimum wall thickness and the variance of wall thickness distribution are obtained as follows: R1=40 mm,R2=30 mm,R3=17.5 mm,a=180mm,b=0mm,compared with the direct positive bulging,the minimum wall thickness is increased from 0.69 mm to 0.94 mm,while the variance of the wall thickness is reduced from 0.1797 mm to 0.0790 mm at the same time.The design method of the negative bulging mold for this kind of basin part is provided,which is called reverse tracing method.It makes the design of the negative bulging mold more objective and reduces the work load.At the same time,through analyzing the superplastic forming process of the spherical parts,the maximum diameter ratio of the minimum of wall thickness is determined by using the free bulging,and then,narrow the scope,eventually it is determined that if the maximum thinning rate of the wall thickness is less than or equal to 10%,the forming ratio of height to diameter must be less than 0.147.This forming limit is obtained,which can provide the basis for forming method of spherical shell on aerospace in the future.Finally,through optimizing the forming process parameters of products,shortest time and the process parameters of minimum pressure forming are obtained: at the temperature of 400?,bulging pressure of 0.8MPa,and holding pressure time of 20 min,3mm thick 5A06 aluminum alloy products can be formed;at the temperature of 400?,bulging pressure of 0.3MPa,holding pressure time of 15 min,1.2mm thick 5A06 Aluminum Alloy products can be obtained;at the temperature of 425?,bulging pressure of 0.3MPa,holding pressure time of 5min,1mm thick 5083 Aluminum Alloy products can be obtained.