Investigation Of Impact Hydroforming Technology And Equipment For Complex Thin-wall Aluminium Alloys Part

Aiming at the urgent need for lightweight and integration of sheet metal parts in the aircraft industry,the corresponding technology for manufacturing complex shaped thin-wall sheet metal parts of magnesium,aluminum,and titanium alloys with small features such as convexes,ribs,and small fillets has become the important issues that need to be solved.Light alloys such as magnesium,aluminum,and titanium have poor plasticity,and wrinkling and cracking are easy to occur during the forming process.Dropping press forming is mostly adopted by military aircraft manufacturer for manufacturing the sheet metal parts.The dropping press forming process requires a large amount of manual assistance through hammering,pad rubber,etc.to achieve the purpose of eliminating wrinkles and manually controlling the flow of materials to prevent cracking.It has low processing efficiency,poor forming precision,high reject rate,and poor working conditions and safety.Impact hydroforming(IHF)technology combines the advantages of hydroforming(HF)technology and high strain rate forming technology for solving the above problems.The basic principle of IHF is that sheet is deformed by the shock wave which is generated by impacting the liquid with the projectile.The forming limit of low-plastic lightweight alloys can be significantly increased by IHF at room temperature in the strain rate of 103 s-1-104 s-1.The technology has the following characteristics:small springback,no need of sealing,good surface quality,good filling ability of small features.This research investigated the high strain rate hydraulic forming limit of AA5A06,the load propagation characteristics of the solid-liquid-solid impact and the design and manufacture of new driven principle IHF equipment.The high strain rate frictionless full zone hydraulic forming limit of traditional aircraft AA5A06 was studied.The experimental results show that the elongation under high strain rate conditions increased 41.3%than that under quasi-static conditions.The characteristics of instantaneous high pressure of IHF were used to design the IHF forming limit test setup and to achieve the full zone forming limit diagram(FLD)with no substrate and no friction,which overcomes the difficulties of the traditional hydraulic forming limit testing method can't realize the experiment of tension-compression zone without base plate and obviously improved the forming limit of 5A06.IHF strain rate can reach 2.43×103s-1.The minor strain of the IHF increases 36.39%than that of the quasi-static hydroforming.The forming limit of 5A06 is theoretically calculated based on three forming limit theories of Swift,Modified Maximum Force Criterion(MMFC)and Marciniak-Kuczynski(M-K).The calculation results show that M-K theory is the best theory for calculating the high strain rate forming limit.The theoretical research on the load propagation characteristics of the solid-liquid-solid impact has been systematically analyzed according to the sequence of the generation,propagation,and action of shock waves.The influence of air on the pressure of solid-liquid impact interface was considered by introducing the attenuation coefficient.This research establishes a dynamic compression algorithm for the pressure of liquid generated by shock wave propagation in liquid media.Calculations have found that the mass and impact velocity of the impact body,the dimension of the liquid chamber,etc.all affect the liquid maximum pressure.It was found that the liquid shock wave acts on aluminum will produce interface pressure which is 1.87 to 2 times-of the liquid maximum pressure by solving the reflected wave and transmitted wave equation at the liquid-solid interface with Hugoniot relationship.It was found that there is a pressure double effect in the IHF.Load propagation characteristics experimental device was designed,and two impact types,single projectile impact and double projectile impact,were comparatively studied.Experiments were conducted for different impact speeds and projectile masses.The pressure doubly effect of IHF at the liquid-solid interface is verified by experiments.The experimental results show that the liquid chamber pressure maintaining effect and the liquid-solid interface pressure doubly factor of the large mass single projectile impact are larger than the double projectile impact form.The experimental results show that the impact form of the single projectile is superior to the double projectile based on the energy utilization rate.The pressure analysis at the liquid-solid interface found that increasing the mass and impact velocity of the projectile can delay the decay process of the shock wave at the liquid-solid interface and increase the time for the shock wave to act on the sheet,which is more conducive to forming.This research completed the design and manufacture of new gas-liquid combined high-pressure driven principle IHF equipment,the driven pressure is able to reach 20 MPa,which realize the high speed driving of big mass projectile.The impact energy of the equipment is as high as 225kJ,the maximum liquid pressure can reach 872MPa,and the liquid chamber diameter is 250mm,which can meet the needs of industrial automation production.The IHF process was verified for the 5A06 aluminum alloy aerospace complex thin-wall frame parts.Perfect part is obtained by quasi-static HF as pre-forming and IHF as final forming,there is no crack and wrinkle.Thickness strain analysis of the critical section of IHF parts and quasi-static hydroformed parts found that the thickness distribution of the two cavity regions of the IHF part is more even and more thinned.The IHF technology and equipment improve the production process of traditional drop press forming which is 7-8 steps by manual forming to a production process that requires only 2 steps which executes automatically,increasing the manufacturing efficiency by more than 4 times.