Flexible-die forming methods such as hydroforming (HF) and rubber pad forming (RPF) allow producing a variety of complex tubular components that are difficult to fabricate by means of conventional forming. In this paper, firstly, in the bulging of a tube with oil pressure using numerical approach, weld-seam was modeled as a mechanical defect and non-homogeneity factor was calibrated by experimental observations and Vickers micro-hardness testing. Forming limit diagram (FLD), as well as effective plastic displacement factor, was utilized to estimate the initiation and evolution of damage, respectively. Then, with the aim of achieving a defect-free part in RPF process, the effect of lubricating conditions was experimentally and numerically examined. The sound parts were obtained using nylon and drawing oil, respectively, at the tube/rubber and the tube/die interaction surfaces. The results represented that by utilizing the accurate non-homogeneity factor, the numerical method can closely predict the...

Experimental and numerical study on formability in tube bulging: A comparison between hydroforming and rubber pad forming

Prediction of the optimal pressure is one of the objectives in the die design for the extrusion process. In this study, the concept of Equi-Potential Lines (EPLs) was applied for an accurate definition of the deforming zone in the upper-bound solution of the extrusion process. To implement the concept for the extrusion process, the initial and final shapes were considered and two different potentials were assigned to these. Then, the EPLs were drawn between the two shapes while minimizing the work path from the initial billet to the desired final shape. Bilinear, cubic Bezier, and polynomial curves were used for the definition of the deforming zone. It was shown that the coefficients of cubic Bezier curve could be replaced by the values obtained from the EPLs method. Moreover, accurate 3D streamlines representing material flow path in the deforming zone were obtained from the present method. Finally, forming pressures in the extrusion process were computed using the proposed geometry. To show the effectiveness of the proposed method, the estimated values were compared with experimental results. It was shown that the proposed method had a remarkable agreement with the experimental results.

Application of equi-potential lines method for accurate definition of the deforming zone in the upper-bound analysis of forward extrusion problems

Forming pressure plays a key role in extrusion processand widely affects product quality. Therefore, prediction of the optimal pressure is the main objective for effective extrusion process. In this study, the notion of Equi-Potential Lines (EPLs) was applied to pressure estimation in extrusion process for the first time. To implement analogy in the extrusion, the initial billet and square die were considered and two different potentials were assigned to them, and then EPLs were drawn between two shapes that show the minimum work path between the entry and exit cross sections. The drawn EPLs were connected to each other to buildup a 3D-die. In the following, cubic polynomial curve was fitted between the initial and final shapes in the designed die. The constructed curve was the accurate assumption for deformation zone in the extrusion that was later used in a written code and upper bound formulation for pressure estimation. Effectiveness of the proposed method was examined via theory and experiment. From ...

Application of the Equi-Potential Lines Method in Upper Bound Estimation of the Extrusion Pressure

Quantitative analysis of orange peel during tension of 6063 alloy spun tubes

A new ironing method entitled hydroironing is proposed for producing cup shaped components especially those with lower formability to overcome the problem of low ironing limit ratio in the conventional ironing process. Lower ironing limit ratio in conventional ironing process increases the number of ironing stages and also manufacturing time and expenses. In this new method, unlike the conventional ironing process, forming punch is pushed to reduce the thickness from the inner surface of the cup starting from the cup edge while at the same time applying hydrostatic pressure onto the inner surface of the cup. The tools required for the proposed method were designed and manufactured and hydroironing tests were carried out. The results showed that a higher thickness reduction of about 70% was achieved only after a single hydroironing stage. The proposed hydroironing operation compared with the previous methods was observed to have three important advantages including higher thickness reduction, lower fluid p...

Hydroironing: A Novel Ironing Method with a Higher Thickness Reduction

The quality of a tube-hydroformed component and the tooling cost and processing time involved in the process are notably affected by the component's preform Hence, it is necessary to produce a proper preform shape for the successful hydroforming from the initial tube to final shape In this article, a new technique based on the equi-potential line (EPL) designed in the electric field was used for the first time to find an appropriate preform shape in THF (Tube Hydroforming) process The equi-potential line generated between two conductors of different voltages show similar trends for minimum work path between the initial and final shapes Based on this similarity, the equi-potential line obtained by arrangement of the initial tube and final die was used for preform design The finite element (FE) method was employed to find the forming pressure to form the preform shape in the die cavity, and then the effectiveness of this method was compared with previous methods It was shown that the new method was si

S. M. Tabatabaee

Papers

Preform Shape Design in Tube Hydroforming Process Using Equi-Potential Line Method