Improving Formability of Ti-6Al-4V Alloy Using the Pulsating Sheet Hydroforming Process and Associating with Microstructure

Türköz M.(Executive), Livatyalı H. , Dilmeç M., Kotan H.

TUBITAK Project, 2020 - 2023

  • Project Type: TUBITAK Project
  • Begin Date: July 2020
  • End Date: January 2023

Project Abstract

Sheet metals are widely used in industries such as automotive and aerospace where the strength/weight ratio is significant. In these industries, light alloys are preferred in order to reduce the component weights. However, the limited formability of light alloys such as aluminum, magnesium, and titanium at room temperature requires research on new and innovative manufacturing methods. One of these methods is hydroforming (HF) where metals are shaped by the liquid pressure. The hydroforming method, which has many advantages over conventional methods, provides low cost and high product quality. Efforts are being made to improve process parameters and to develop new hydroforming methods for successful forming. In the previous work of the project team, the formability has been improved in processes such as sheet metal hydroforming and warm hydroforming. However, optimum process parameters are difficult to determine and the application of processes is laborious and costly. In addition, although warm hydroforming is an alternative in shaping materials such as titanium alloy with limited formability at room temperature, it is not preferred due to its high cost and application difficulties.

In this project, it is aimed to improve sheet formability by applying pulsation (sinusoidally) instead of continuously increasing pressure during the process of sheet metal process. In literature, a limited number of studies have shown that formability can be improved by applying pressure pulsating sinusoidally with a certain amplitude and frequency. However, all of these studies are related to tube hydroforming, which is completely different from the sheet hydroforming method in terms of part shape and process. There are no studies in which fluid pressure is applied sinusoidally in the sheet metal forming method. In the literature, tensile tests with pulsation were used to investigate mechanisms that improve formability, and ductility in stress-strain curves was significantly increased while flow stress was somewhat reduced. The reason for this is explained by stress relaxation resulting from dislocations re-ordering under more stable lower boundaries and thus dislocation density is reduced. The low-frequency oscillation to be applied in this project is thought to achieve a formability improving effect similar to stress relaxation.

In this project; it is aimed to improve the formability of Ti6Al4V alloy sheets, which have limited shape at room temperature and which are widely used in aviation industry, with pulsating HF process. For this purpose, effect of amplitude, frequency and initial hydraulic pressure parameters on product geometry will be investigated in pulsating sheet metal process. Thus, the effect of pulsating application of pressure on formability and part quality of sheet metal will be investigated and microstructural causes of the predicted increase in formability will be examined and its relation with stress relaxation will be revealed. In addition, the effect of different initial microstructure on optimal pulsation parameters will also be investigated. 

Project main parts can be summarized as follows:

1-Experimental analysis of the mechanical properties of the material
2-Design of pulsating sheet hydroforming process using FEA
3-Forming limit analysis
4-Experimental verification

This is a multidisciplinary project gathering researchers from mechanical, material, and mechatronics engineering departments of three different universities. Design of pulsating sheet HF process, installation of experimental setups, investigating optimum pulsation parameters, FEA simulations are related to mechanical engineering; investigation of microstructure and linking results to formability are related to material science; and integration, automation, and programming of experimental setups are related to mechatronics.

The pulsating sheet hydroforming process has the potential to be a preferred method of shaping materials of limited formability, such as Ti-6Al-4V, especially in the aerospace, defense, and automotive industries. It is expected that the presses to which this method will be applied will contribute to the national economy with domestic production.