Comparison of Constitutive Models for predicting the formability of SS 304 by tubular hydroforming process

Finite Element (FE) simulation of sheet/tube forming precision depends mainly on the accuracy of the constitutive modeling. The present paper aim is to compare the constitutive models to fit the stress-strain curves. The accurate deformation behavior of the SS 304 tubes depends on the constitutive modeling of hardening behavior. Deformation data of the tensile specimens cut from tubular sample were collected by conducting Uniaxial tensile tests (UTT) at three different rolling directions. Five constitutive relationships were then recognized by fitting the true stress and strain data with the constitutive models of Hollomon, Power, Krupowsky, Voce and Ghosh, and the fitting accuracy were analyzed and compared. Effects of hardening models on Forming Limit Curves (FLC), pressure loading and bulge height of the hydroformed tube were then studied. The obtained FLC from the simulations were compared with experimental FLC to predict the accuracy of the hardening models.

Experimental Study of Ultrasonic Vibration Effects on Punch Radial in Sheet Hydroforming Process

Nowadays, one of the metal forming processes that are widely used in industries is sheet hydroforming. Because of high complexity and sensitivity, this process needs precise calculations in the die and method to control metal flow correctly and prevent defects. Therefore recently, new processes were combined to this process to increase precision and effectiveness. For example, ultrasonic vibration assistance forming. Using hydroforming and ultrasonic vibration as new methods were studied in several research types separately, and each of them redounded to different analyses and improvements in the process. Even synchronic use of these two methods was studied in some metal forming processes such as tube hydroforming, but it has not been studied in sheet hydroforming. Therefore the aim of this research is the experimental study of St14 sheet hydroforming ultrasonic vibration assistance. For this purpose, ultrasonic vibration (with 20 KHz frequency and 4μm amplitude) was applied to a hydromechanical deep drawing die into punch radial in the hydroforming process. Then process parameters consisting of LDR, maximum height, forming force, safe working zone, and thickness distribution were determined and compared in four case states conventional deep drawing(CDD), hydroforming deep drawing(HDD), ultrasonic vibration assistance deep drawing(UDD) and ultrasonic vibration assistance hydroforming deep drawing(UHDD). Results indicated that applying ultrasonic vibration into the sheet hydroforming process increases LDR and the maximum height of the cup, decreases forming force and develops a safe working zone. Also was very effective in thickness distribution and decrease of sheet thinning in critical sections.

Multi-step Hydroforming Process And Wall Thickness Optimization of 5A02 Aluminum Alloy Five-Way Tube With Different Branch Diameter

The different branch diameter of five-way tube affects the design of loading internal pressure in the hydroforming process, where the large-diameter branch is broken more easily than the small-diameter one due to the same ultimate stress of tube material in one-step forming method. Therefore, the first four-way and then five-way of multi-step forming (FFTF) method and the first three-way and then five-way of multi-step forming (FTTF) method were proposed to fabricate the 5A02 aluminum alloy five-way tube with two kinds of branch diameters to avoid the burst of large-diameter branch tube. The finite element simulation of five-way tube hydroforming process shows that the height of small-diameter branch tube is lower and serious wrinkles appear at the large-diameter branch tube in the one-step forming and FFTF method. By optimizing the length of punch, a five-way tube with a big branch height and uniform wall thickness was obtained with the FTTF method. The approach of lengthening the punch in the experiment increased the height of formed branch and reduced the wall thickness reduction rate of five-way tube in FTTF method. Overall, the findings mentioned above can not only offer guide in creating five-way tube with excellent quality, but also be taken as reference to the hydroforming studies on multi-way tube in the future.

Multi-objective Tubular Hydroforming Process Parametric Optimization using TOPSIS and PSI techniques

Tube Hydroforming (THF) process is widely used in the aerospace and automotive industries. The success of forming tubular components using the THF process generally depends on many influencing parameters such as geometry, coefficient of friction, loading pathways, material formability, etc. The objective of this study was to determine the effect of the corner radius, coefficient of friction and heat treatment temperature on the bulging of the tubular component using finite element simulations. To address the complexity of parameter selection correctly with different alternatives, the multi-criteria decision-making methods (MCDM) applied in the present work. Two decision models, namely Technique for Order Performance by Similarity to Ideal Solution (TOPSIS) and Performance Selection Index (PSI) methods with entropy weighting criteria were applied for obtaining the best combination of parameters to get a sound quality product. Finally, the proposed ranking was validated by conducting experimental trials and the error was observed to be in limits in comparison with the simulated data. ANOVA was also performed to distinguish the significant parameters and their contribution to the responses. Both the MCDM methods suggested the same favorable and unfavorable alternatives.