An Analytic Solution for an Expanding/Contracting Strain-Hardening Viscoplastic Hollow Cylinder at Large Strains and Its Application to Tube Hydroforming Design

This paper presents a semi-analytic rigid/plastic solution for the expansion/contraction of a hollow cylinder at large strains. The constitutive equations comprise the yield criterion and its associated flow rule. The yield criterion is pressure-independent. The yield stress depends on the equivalent strain rate and the equivalent strain. No restriction is imposed on this dependence. The solution is facilitated using the equivalent strain rate as an independent variable instead of the polar radius. As a result, it reduces to ordinary integrals. In the course of deriving the solution above, the transformation between Eulerian and Lagrangian coordinates is used. A numerical example illustrates the solution for a material model available in the literature. A practical aspect of the solution is that it readily applies to the preliminary design of tube hydroforming processes.

Thickness Improvement and Calibration Pressure Reduction of Stepped Tubular Components Using Axial Hydro-pressing Method

A new tube axial hydro-pressing method was proposed to solve the problems of high forming pressure and severely uneven wall thickness distribution of traditional tube hydroforming methods to form stepped tubular components. The forming pressure of the traditional hydroforming and the tube axial hydro-pressing method is studied theoretically, the mechanical model of the fillet area is established, and the forming pressure calculation formula is given. Based on this, an investigation of the tube axial hydro-pressing method is carried out by numerical simulation and experimental methods, and compared with the traditional tube hydroforming method. The key to the tube axial hydro-pressing method is to precisely control the relationship between the protrusion height and the axial feed, which is achieved by precisely controlling the feeding pressure and the axial displacement. Therefore, the constant pressure device in the experiment was used to eliminate the influence of the pressure rise caused by the volume compression on its cooperation relationship, to achieve accurate control of the loading path, eliminate wrinkles and flash defects. A qualified workpiece is successfully manufactured when the internal pressure is 18.0 MPa and the feed on each side is 15.0 mm. The forming pressure is reduced by 88.0%, and the feed is increased by 6.5%, which reduces the wall thickness reduction by 9.0%. The wall thickness difference of the workpiece can be controlled within 7.0%. The tube axial hydro-pressing method is suitable for forming stepped tubular components, which can achieve more replenishment at lower pressures, thereby effectively improving the uniformity of wall thickness and significantly reducing the forming pressure.

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.

Detection methods for springback of assembled camshaft under hydraulic expansion

The assembled camshaft under hydraulic expansion has the advantages of low cost, lightweight and high performance, which is an advanced technology with great development potential. By applying the tube hydroforming to the fabrication of assembled camshaft, the expansion principle is due to the different degrees of resilience of the cam and the shaft. Therefore, the effective detection method of elastic recovery of camshaft is of great significance to research how to improve the connection strength of the assembled camshaft. This paper introduces several springback detection methods for assembled camshaft under hydraulic expansion, namely resistance strain detection method, gap dynamic detection method and finite element simulation.

Material Characteristics Evaluation for DC04-Welded Tube Hydroforming

Tube hydroforming (THF) technology is widely applied, especially in the automotive and aircraft industries. Material characteristics of tubular workpieces should be evaluated in terms of bending and THF processes. A mathematical model, which combines the assumption of elliptical contour of a bulged wall and the prediction equation of wall thickness, is provided to analyze the THF process and to obtain the strain-stress relationship of tubes. Material characteristics of a DC04-welded tube is obtained by using a self-designed THF test machine. Considering the effects of pre-work hardening, we discuss the material strain-stress relationships of the tube and original sheet blank. An approximate determination method is proposed to obtain the stress-strain curve of the tube by using the curve of the original sheet blank and the hardness of the tube and sheet blank. A suitable constitutive equation with pre-work hardening is applied to the DC04-welded tubes through simulation and experimental methods.