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This paper introduces an evaluation method for the quality of assembled camshafts under pulsating hydroforming, aimed at laying a certain foundation for the automobile engine industry in the future. The novelty of the design lies in applying a pulsating hydraulic pressure to the interior of a hollow shaft such that it exhibits an interference fit with the cam (cam-bores with non-circular structure) after being deformed by the pressure. A camshaft with a trilobe polygonal inner profile is selected and studied by conducting experiments and finite element analysis. The quality of the camshaft varies with the process parameters (pulsating amplitude, pulsating frequency, and hydraulic pressure). The effects of these parameters are investigated by evaluating the filling rate of the shaft and torsion strength of the assembled camshafts. Moreover, a new measurement method for the filling rate of the shaft is developed. Finally, the quality of a pulsating, hydraulically assembled camshaft is compared with that of a non-pulsating hydraulically assembled camshaft, thereby validating the proposed evaluation method. The preliminary feasibility of the pulsating hydraulic connection for the assembled camshafts with a trilobe polygonal profile is demonstrated in this study.

The assembled camshaft is a recently developed split assembly technology that enables the realization of lightweight cars and improves engine performance. Residual shaft–cam contact pressure is affected by camshaft elastic recovery and affects connection quality. This study investigated a cam with an isometric–trilateral profile for tube hydroforming with a hollow shaft via experiments and finite element analysis. A novel, indirect residual contact pressure measurement method is herein proposed. Hydraulic parameter effects on residual contact pressure and elastic recovery were analyzed using the theory of plastic mechanics. For hydraulic pressure below 85 MPa, increasing hydraulic parameters increased residual contact pressure nearly linearly while decreasing elastic recovery.

Liquid impact forming (LIF) is a new type of composite forming method based on tube hydroforming (THF) and stamping forming. It has high efficiency and low energy consumption, with no need for external pressure source, so LIF has good development prospect and application value in the field of lightweight and integrated manufacturing. In order to investigate LIF technology, the generation mechanism of the internal pressure was analyzed in this paper. Firstly, based on the theory of the liquid volume compression, the change law of the cavity volume of metal thin-walled tubes was analyzed according to size parameters of the tube and dies during the forming process. The mathematical relationship between the internal pressure in the tube cavity and clamping parameters (clamping speed and clamping height) was obtained under the impact load. Then, the theoretical maximum internal pressure Pmax1 was discussed under different die cavities. Furthermore, the relationship between the internal pressure in the tube and the clamping time under different die cavities with a same clamping speed was obtained according to the transient dynamic analysis by ANSYS Workbench. At the same time, the simulated maximum internal pressure Pmax2 and the calculational maximum internal pressure Pmax were acquired under different die cavities. In addition, the LIF experiments were performed using a simple and suitable device to verify the calculational maximum internal pressures under die cavities with different side lengths. Through the comparison of the calculational and experimental maximum internal pressures, it is not difficult to find that the values of both showed a good agreement and the maximum deviation is 10.27%. The research results indicate that the theoretical equation of internal pressure of metal thin-walled tubes based on LIF is reliable, and it will lay a good foundation for further study.

Tube hydroforming (THF) is a unique forming technique, which can transform metal tubes into complex hollow parts using hydraulic fluid as the forming medium. The initial non-uniform thickness of as-received practical tubes significantly affects their formability in the hydroforming process. A forming limit diagram (FLD), also called as the forming limit curve (FLC), is often adopted to evaluate the forming behaviour of sheet metals in plastic forming processes to avoid forming failures. The purposes of this research are fivefold, namely to establish the FLCs of tubular blanks with varied initial thickness deviations in tensile and compressive strain states by means of finite element (FE) modelling of THF, to construct a non-uniform geometric model for practical tubes, to analyse the impact of initial thickness deviation on the FLCs, to clarify the differences in the FLCs obtained using three different instability criteria, and to validate the proposed non-uniform geometric model by conducting hydro-bulging experiments. Results show that it is possible to accurately predict the FLCs of practical tubes with initial non-uniform thicknesses using FE simulation combined with the proposed non-uniform geometric model. We found that the displacement of FLCs occurred in the major- and minor-strain coordinates because the thickness is initially not uniform; however, no significant discrepancies were observed in the FLCs obtained using the three instability criteria. The proposed approach, which combines FE simulation with a non-uniform geometric model, can be easily employed to predict the ultimate strains of tubes with initial non-uniform thicknesses in THF to avoid forming defects.

In tube hydroforming (THF), the friction between the tube and dies plays an important role. The coefficient of friction (COF) in THF is generally determined by assuming that the contact pressure between the tube and dies is equivalent to the hydraulic pressure acting on the internal surface of the tube so that the COF can be calculated by multiplying the hydraulic pressure by the contact area. For the pulsating hydroforming process of a tube, the pulsating amplitude and frequency of the hydraulic pressure may impact the friction and result in complicated frictional characteristics. This paper presents a method for determining the COF in the THF guiding zone by a self-developed measurement system. THF experiments were performed under pulsating and non-pulsating pressures on SUS304 stainless steel tubes to investigate the relationship between the contact and hydraulic pressures and the effects of fluctuations in the hydraulic pressure on the COF. The contact pressure increased periodically with fluctuations in the hydraulic pressure and was always less than the hydraulic pressure with a maximum pressure difference of 20 %. The pulsating amplitude and frequency of the hydraulic pressure impacted the fluctuations of the contact pressure and pressure difference. The COF decreased faster with deformation; the average COF was less under pulsating pressure than under non-pulsating pressure. Increasing the pulsating amplitude and frequency decreased the average COF but had little effect on the decreasing rate of the COF. The pulsating amplitude had a clearer influence than the pulsating frequency on the amplitudes of the COF curves.

In this article, tube hydroforming along with stamping, a compound forming technology of thin-walled tube using stamping and hydroforming processes, was presented to cut forming costs, reduce number of forming and assembly operations, and improve forming efficiency. A simple experimental tooling was designed and manufactured. Forming experiments of stamping and tube hydroforming along with stamping processes in two square cross-section dies were performed for SS304 tubes at different upper die velocities. The experimental results indicated that the better formability and the more uniform thickness distribution are obtained by the tube hydroforming along with stamping processes than by the stamping.

The forming limit diagram (FLD) has been widely used as a measure of the maximum formability of a material in tube hydroforming (THF). The geometric shape of the FLD varies owing to the influences of many factors, especially the strain path. Therefore, discussing the change rule of FLDs under various strain paths has practical significance. In the present study, strain paths generated from THF are classified as simple or complex ones. The FLDs for THF are established based on Swift’s diffused necking criterion and Hill’s localised necking criterion along both simple and complex strain paths. Through a comparison of the FLDs obtained from various strain paths, the influences of changing strain path are revealed. Some THF experiments under various strain paths are performed to verify the theoretical analysis. The theoretical analysis and experimental results prove that the position of the FLD changes with different strain paths. Compared with the FLD position established along a simple strain path, the FLD position under a two-stage linear strain path moves in the upper left direction with an initial uniaxial tensile strain path and in the lower right direction with an initial equibiaxial tensile strain path.

Tube hydroforming with radial crushing is a new tube hydroforming process to manufacture very long components with complex cross sections. A loading path is generally considered a major factor that greatly affects the formability of a component by tube hydroforming. In this study, the tube hydroforming with radial crushing process of a square cross-sectional component was investigated by using the finite element method, and a method to predict the optimal loading path for the tube hydroforming with radial crushing process was developed from the finite element simulation. A multi-object function was first built in terms of the die-filling ability, cross-sectional symmetry, and wall thickness uniformity. Subsequently, a multi-strategy approach, characterized by a genetic algorithm and the bisection method, was developed to predict the optimal loading path. The effectiveness of the prediction method was verified by comparing the formability of components deformed under the optimal and conventional loading paths. Furthermore, the developed multi-strategy approach was demonstrated to have high efficiency when the total calculation times for the multi-strategy approach and for genetic algorithm alone were compared.

The flow stress, used to describe the plastic deformation behavior of thin-walled tube, is one of the most important parameters to ensure reliable finite element simulation in the tube hydroforming process. In this study, a novel approach of on-line measurement based on digital speckle correlation method is put forward to determine flow stress of thin-walled tube. A simple experimental tooling is developed and free-bulged tests are performed for 304 stainless steel and H62 brass alloy tubes. An analytical approach is proposed according to the membrane theory and the force equilibrium equation. The developed method is validated by means of FE simulations. The results indicate that the present method is acceptable to define the flow stress in the tube hydroforming process.