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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.

Rotated clinching is a novel cold plastic deformation joining process, which is suitable for the multi-point simultaneous joining of sheet metals. However, the effect of various parameters on the mechanical properties of joints using rotated clinching remains unclear. The purpose of this study is to analyse the important parameters that affect the joint’s shearing strength and relationship between them. The relational expression between the four process parameters (die depth, rotation angle, small fillet radius and large fillet radius) and joint shearing strength was established using the response surface method. Additionally, the quantitative relationship between them was expressed by this relational expression, and the significance of process parameters were evaluated using the analysis of variance. The results revealed that the most significant parameter regarding the shearing strength was die depth h, with the contribution of 47.1%, followed by rotation angle α and small fillet radius r1, with the contributions of 26.8% and 8.2%, respectively, whereas the large fillet radius R1 is the least significant, there is a significant interaction effect between R1 and α, with the contribution of 5.4%. The shearing strength had a negative relationship with the die depth h and small fillet r1, whereas it had a positive relationship with rotation angle α. The predicted maximum value of the shearing strength was 1231.92 N at h = 2.29 mm, r1 = 0.46 mm, R1 = 1.27 mm and α = 18.45° in the range of given design parameter values. The experimental values of the shearing strength comprised approximately 74% of the predicted values.

Purpose This paper aims to study frictional characteristics of thin-walled tubes in the liquid impact forming (LIF) process. Design/methodology/approach LIF experiments under various impacting velocities were performed on SUS304 stainless steel tubes with various guiding lengths on a custom-designed measurement system to investigate the effects of impacting velocity and guiding length on the coefficient of friction (COF) in the guiding zone. Findings The results indicate that the COF changes dynamically in the guiding zone and decreases with the deformation process. The reduction range of the COF is wider in LIF than in both the conventional and pulsating hydroforming (THF), which may be contributed to the impacting velocities in a short time. Moreover, the COF decreases faster in the first half of the LIF process than in the second half. Under different impacting velocities and guiding lengths, the decreasing rate of the COF in the first half is more sensitive and obvious than that in the second half. Originality/value A method for determining the COF in the guiding zone in LIF is proposed and the frictional characteristics in LIF are studied. Comparing the COF of tubes in conventional THF, pulsating THF and the LIF process is valuable for improving and predicting the tubular formability in various hydraulic environments for industrial production. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-07-2019-0269

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.

Liquid impact forming (LIF) is a rapid tube hydroforming technique. The deformation behaviour of a metal tube may be different in LIF from that in tube hydroforming. A constitutive equation or equivalently an equivalent stress-strain relationship is generally used to describe the deformation behaviour of metals. The purpose of this work is to model the deformation behaviour of tubular materials in LIF using the Johnson-Cook (JC) structural model. LIF hydro-bulging experiments combined with the analytical approach based on the membrane theory and the force equilibrium equation were used to determine the model coefficients A, B, C, and n in the equations for SS304 stainless steel tubular materials. Finite element (FE) simulations of hydro-bulging under various impact velocities were carried out to validate the resultant JC model. The relationship between the strain rates and impact velocities was determined, the bulging heights between the equivalent stress-strain curves at different impact velocities were analysed, and the bulging heights obtained by FE simulations and experimental results were compared. The results show that the proposed approach using the JC model is suitable to define the stress-strain behaviour of tubular materials in LIF.

Tube hydroforming (THF) experiments were performed on TP2 copper tubes under different loading velocities and fluid velocities using a self-developed measurement system to investigate dynamic frictional characteristics in the guiding zone. The results show that the coefficient of friction (COF) dynamically changes during forming experiments and decreases with tube deformation. The average descending rate and amplitude of the COF increase with increasing loading velocity. Microscopically, the micro-protrusions on the tubular surface are flattened, and the surface scratches are finer and more uniform, as the loading velocity increases, resulting in a decrease in COF. At the same external loading velocity, the COF increases with increasing fluid velocity and is also extremely sensitive to it. Moreover, improving and predicting the formability of such tubes by accurately adjusting and controlling fluid velocity in THF is valuable and critical for the future.

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.

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.

Pulsating hydroforming is a novel forming technique that applies pulsating hydraulic pressure to deform tubular materials. Larger expansions and more uniform wall thicknesses in tubes have reportedly been achieved using this technique. However, periodic oscillations of hydraulic pressure acting on the tubes during pulsating hydroforming make the tube deformation behaviour and formability unpredictable. Forming limit diagrams, which consist of two forming limit curves in a major–minor strain coordinate system, are widely used to indicate the formability of sheet materials in plastic deformation. The comparable use of forming limit diagrams to indicate the formability of tubular materials under the pulsating action of hydroforming has not been previously established. In this study, pulsating and non-pulsating hydro-bulging experiments were performed on SS304 stainless steel tubes. Under distinct tension–compression and tension–tension strain states with and without active axial feeding, the forming limit curves for the deformed tubes were constructed based on the experimental data. The effects of various hydraulic pressure pulsating parameters, including pulsating amplitude and frequency, on the forming limit curves were analysed and compared. The experimental results showed that each of the forming limit curves under pulsating hydro-bulging was higher than the forming limit curves under non-pulsating hydro-bulging, thereby confirming the influence of the pulsating parameters. In general, the height of the forming limit curves increased as the pulsating amplitude and frequency increased, largely independent of the tension–compression and tension–tension states. Overall, the results showed that the proposed method for determining the forming limit curves (and the subsequent forming limit diagram) for tubes during pulsating hydro-bulging is feasible.

Tube hydroforming (THF) under pulsating hydraulic pressures is a novel technique that applies pulsating hydraulic pressures that are periodically increased to deform tubular materials. The deformation behaviours of tubes in pulsating THF may differ compared to those in conventional non-pulsating THF due to the pulsating hydraulic pressures. The equivalent stress-strain relationship of metal materials is an ideal way to describe the deformation behaviours of the materials in plastic deformation. In this paper, the equivalent stress-strain relationships of SS304 tubes in pulsating hydroforming are determined based on experiments and simulation of free hydraulic bulging (FHB), and compared with those of SS304 tubes in non-pulsating THF and uniaxial tensile tests (UTT). The effect of the pulsation parameters, including amplitude and frequency, on the equivalent stress-strain relationships is investigated to reveal the plastic deformation behaviours of tubes in pulsating hydroforming. The results show that the deformation behaviours of tubes in pulsating hydroforming can be well described by the equivalent stress-stain relationship obtained by the proposed method. The amplitude and frequency of pulsating hydraulic pressure have distinct effects on the equivalent stress-strain relationships-the equivalent stress becomes augmented and the formability is enhanced with the increase of the pulsation amplitude and frequency.

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.

Ultrasonic vibration assisted plastic forming is a process method for assisting the forming of metal materials by means of ultrasonic vibration devices. It is proved that the ultrasonic vibration could reduce the forming force, improve the friction environment, and enhance the formability of the metal material. However, there are some differences in forming characteristics for different materials under different vibrational plastic forming processes. In this paper, the forming principles, the vibration application modes and the forming characteristics of the ultrasonic vibration assisted the wire drawing, equal channel angular pressing (ECAP), upsetting, drawing of the sheets and hydroforming of the tube are reviewed. It emphasizes on the various processes’ improvement of the forming efficiency and the quality of the formed parts under the aid of ultrasonic vibration. Finally, the future development trend of ultrasonic vibration assisted plastic forming was prospected.

Tube hydroforming technology is an advanced manufacturing technology adapted to lightweight structure. The technology has the advantages of low production cost, high material utilization rate and light part quality. Forming equipment is the basis for implementing the technology, the performance of the equipment greatly affects the product quality. However, the key problems affecting the performance of the equipment include: loading path, axial feeding and sealing method, etc. The article is for the purpose of key question carrying on the system combing with the discussion. Among them, several hydraulic pressure control methods are summarized, the influence of different loading path on tube hydroforming is shown, A loading method that axial stress - circumferential stress is always proportional in the forming process is proposed. Meanwhile, the control method of axial feed is summarized, it is expressed that axial feeding can improve tube forming ability. Besides, five kinds of common pipe sealing methods were compared, the reliable and effective sealing structure is summarized.

The Forming limit diagram (FLD), also known as a forming limit curves (FLC), is generally used in metal forming for predicting forming behavior of metals. The purpose of the study is to clarify the difference among the FLC of tubes with initial wall-thickness difference under tension-compression strain states using finite element (FE) simulation of tube hydroforming (THF) and different instability criteria. Firstly, geometrical models for SUS304 stainless steel tubes with initial wall-thickness differences were built by introducing an index ‘wall-thickness deviation rate’. Secondly, forced-end hydro-bugling of the tubes was modeled and the forming process was simulated by using the commercial finite element (FE) code ABAQUS/Explicit 6.10. Afterwards, the limiting strains of the material in the hydro-bugling process were calculated based on the simulated resultant data and three instability criteria--strain change criterion, strain rate change criterion and strain path change criterion, respectively. Finally, the FLD for the tubes was established and the effect of wall-thickness deviation rate on the FLD was analyzed and the differences among the FLC based on the three instability criteria were compared. The results showed that the FLC are observed to shift in the major–minor strain coordinate system due to the initial non-uniform wall-thickness; however, no distinct differences among the FLC based on the three instability criteria were observed.

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.

Due to the low price, the seamed tubes are used more and more widely in various industrial fields in recent years. The difference in material properties between the weld zone of the parent metal zone of the thin-walled seamed tubes, the deformation of the hydraulic bulging under the same conditions will also be different, thus resulting in an inconsistency in the overall bulging of the seamed tubes. In this paper, the hydraulic bulging experiment of the seamed tubes at low and medium velocity, and the shape deviation law of the seamed tubes at different velocity are obtained. In the first half of the bulging, the seamed tubes at the medium velocity drops faster than the low velocity shape deviation rate, and the medium velocity is closer to circle; in the second half of the bulging, the medium velocity is go up faster than the low velocity. The shape deviation rate is higher before the tubes are burst, but the medium velocity’s radial average bulge height is smaller than the low velocity.

Torsional vibration is an important factor in the transmission process of mechanical shaft. The torque is also a part of the important parameters for working state of the mechanical shaft. In recent years, research on the measurement method of contactless torque of mechanical transmission shaft has been studied by many scholars. The contactless torque measurement methods have been continuously improved to achieve high precision and high reliability.The methods of contactless torque measurement is presented. The advantages of contactless torque measurement methods are introduced. The development of contactless torque measurement methods in the industry is discussed. Finally, the prospect of contactless torque measurement methods is prospected.

Compared with the traditional integrated camshaft, the assembled camshaft has the advantages of lowering production cost, reducing engine weight and improving engine performance, with a broad development prospect. The assembled camshaft is connected by different processes will cause residual stress which will seriously affect the mechanical properties of camshaft. Therefore, the measurement of residual stress is of great importance to the safety and reliability of assembled camshaft. This paper mainly introduces three detection methods currently applied to the residual stress of the assembled camshaft, namely X-ray diffraction method, Hole-Drilling method and Finite element simulation.

The hydraulic expansion of the heat exchanger tube and tubesheet is an important method in the uniform expansion. Compared with other methods, the advantages of hydraulic expansion are high productivity, low labor intensity and reliable expansion performance. This paper describes several common methods for the determination of the residual contact pressure between the tube and tubesheet, and describes the principle, characteristics and the current status of the measurement at home and abroad. This paper also summarizes the development of future methods for measuring the residual contact pressure in the hydraulic expansion joint.

Loading path plays a dominant role in tube hydroforming (THF), and the pulsating loading path has been reported capable of improving the formability of a tube in hydrobulging with axial feeding. As a new THF process, the tube hydroforming with radial crushing (THFRC) is receiving increasing attention; however, knowledge on the process still remains insufficient to extend its application to various other fields. In this study, the experiments of THFRC under both the pulsating and the linear hydraulic pressures were carried out to investigate the deformation behavior. The influences of the amplitude and the frequency of the pulsating hydraulic pressure on the shape precision, wall thickness, and the microstructures of the deformed parts were analyzed. Subsequently, metallographic examinations of the deformed specimens were conducted in an attempt to clarify the relationship between the microstructural evolution and deformation behavior. The mechanism of formability improvement in THFRC by the pulsating hydraulic pressure was explored from the perspective of microstructure. Compared with the linear hydraulic pressure, the pulsating hydraulic pressure could generate a higher shape precision, a more uniform wall thickness, as well as less martensites, and larger grain. The microstructural evolution induced by the pulsating loading path is supposed to contribute to the formability improvement of SUS304 stainless steel tubes.

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.

The rotating Rayleigh-Timoshenko beam element based on B-spline wavelet on the interval (BSWI) is constructed to discrete short shaft and stiffness disc. The crack is represented by non-dimensional linear spring using linear fracture mechanics theory. The wavelet-based finite element model of rotor system is constructed to solve the first three natural frequencies functions of normalized crack location and depth. The normalized crack location, normalized crack depth and the first three natural frequencies are then employed as the training samples to achieve the neural networks for crack diagnosis. Measured natural frequencies are served as inputs of the trained neural networks and the normalized crack location and depth can be identified. The experimental results of fatigue crack in short shaft is also given.

Autofocus method based on the analysis of image content information is investigated to reduce the alignment error resulting from mark positioning uncertainty due to defocus in microstructure layered fabrication process based on multilevel imprint lithography. The applicability of several autofocus functions to the alignment mark images is evaluated concerning their uniformity, sharpness near peak, reliability and measure computation efficiency and the most suitable one based on power spectrum in frequency domain (PSFD) is adopted. To solve the problem of too much computation amount needed in PSFD algorithm, the strategy of interested region detection and effective image reconstruction is proposed and the algorithm efficiency is improved. The test results show that the computation time is reduced from 0.316 s to 0.023 s under the same conditions while the other merits of the function are preserved, which indicates that the modified algorithm can meet the mark image autofocusing requirements in response time, accuracy and robustness. The alignment error due to defocus which is about 0.5 μm indicated by experimental results can be reduced or eliminated by the autofocusing implementation.

A low-cost quasi-LIGA process is proposed, in which, instead of using thick resist technique, micro-structure with large structural height is achieved by multilevel imprinting and through-mask plating. To achieve precise alignment between individual layers, an alignment system based on computer micro-vision is developed and the experimental results show an average overlay accuracy within 1.5@mm with a standard deviation within 0.33@mm. Good adherence of resist on seed layer is achieved by substrate surface oxidation and using a coupling agent, which establishes a chemical bond between substrate surface and the resist layer. The deposit uniformity is improved by electroplating process optimization to enhance the cathode polarization. Through electrolyze etching on previous layer before next level of metal deposition, the fresh metal surface is obtained and the bonding strength between adjacent metal layers is enhanced. With the developed process, tri-layer photoresist and metallic structures with a pattern feature size of 20@mm were successfully fabricated.

Assembled camshaft (AC) technology is a type of neo-manufactured technology of camshaft by which components are machined separately and assembled together. Compared with traditional integral-type camshaft, AC has advantages of lighter weight, material saving, compact structure and excellent performance, etc. Joint structure between the shaft and cam lobes has significant influence on the process and joint strength in AC. In this paper, three familiar joint structures are introduced, and the influences of some parameters on process and strength are analyzed. Then the non-circular joint structures are proposed as outlook of future development.