To evaluate the dynamic characteristics at all positions of the main spindle of a machine tool, an experimental point was selected using a full factorial design, and a vibration test was conducted. Based on the measurement position, the resonant frequency was distributed from approximately 236 to 242 Hz. The approximation model was evaluated based on its resonant frequencies and dynamic stiffness using regression and interpolation methods. The accuracy of the resonant frequency demonstrated by the kriging method was approximately 89%, whereas the highest accuracy of the dynamic stiffness demonstrated by the polynomial regression method was 81%. To further verify the approximation model, its dynamic characteristics were measured and verified at additional experimental points. The maximum errors yielded by the model, in terms of the resonant frequency and dynamic stiffness, were 1.6% and 7.1%, respectively.

The purpose of this study is to evaluate the fatigue life of an automotive engine valve spring when the micro defect is applied to a 2300 MPa-class oil-tempered wire (OT wire) with 2.5 mm of diameter as the critical flaw depth. First, the deformation of the surface flaws in the OT wire during the valve spring manufacturing processes was derived via FE analysis using the sub-modeling technique, and the residual stress of the final spring was measured and applied to the spring stress analysis model. Second, the strength of the valve spring was analyzed to examine the presence of residual stress and compare the applied stress levels by the surface flaw. Third, the influence of micro defects on the fatigue life of the spring was evaluated by applying the stress on the surface flaw derived through the spring strength analysis to the S–N curve derived through a rotary bending fatigue test with the OT wire. The flaw depth of 40 µm, which is the existing criterion for surface flaw management, does not reduce the fatigue life.

The use of carbon fiber-reinforced plastics (CFRP) is markedly increasing, particularly for the manufacturing of automotive parts, to achieve better mechanical properties and a light weight. However, it is difficult to manufacture multi-material products because of the problems due to the adhesive between CFRP and steel. The prepreg compression molding (PCM) of laminated CFRP can reduce the production time and increase the flexibility of the manufacturing process. In this study, a new manufacturing process is proposed for CFRP reinforcement on a hot stamped B-pillar using PCM. A finite element (FE) simulation of the hot stamping process is conducted to predict the dimensions of the B-pillar. The feasibility of PCM manufacturing is explored by the simulation of the thermoforming of a CFRP set on a shaped B-pillar. The temperature conditions of the CFRP and B-pillar for the PCM are determined by considering the heat transfer between the CFRP and steel. Finally, the PCM of the B-pillar consisting of steel and CFRP was performed to compare with the analytical results for verification. The evaluation of the B-pillar was conducted by the observation of the cross-section for the B-pillar and interlayer by scanning electron microscopy (SEM). As a result, a steel/CFRP B-pillar assembly could be efficiently manufactured using the PCM process without an additional adhesive process.

In this study, the feasibility of one-shot forming for manufacturing of steel/CFRP hybrid B-pillar was investigated using a steel sheet with a CFRP patch. The design of one-shot forming process has been described in three stages. First, CFRP reinforcement was designed to substitute for the steel reinforcements for weight reduction. The thickness of CFRP reinforcement was determined through structural analysis by comparing the strengths of the conventional and hybrid B-pillars. Second, the stamping of B-pillars using only the steel sheet was preliminarily designed to determine a proper blank shape that could be used as an initial blank shape in one-shot forming. Third, one-shot forming of the steel/CFRP hybrid B-pillar was designed by finite element (FE) simulation to investigate if fracture and wrinkling occur during the forming process. The feasibility of the designed one-shot forming was evaluated by experimentally manufacturing a steel/CFRP hybrid B-pillar. The FE simulation and experimental analysis indicated that one-shot forming is efficient and suitable for manufacturing steel/CFRP hybrid structures and can be used for mass production of automotive parts at low cost without an additional assembly process.

In metal product manufacturing, additive manufacturing (AM) is a method that has the advantage of fabricating complex shapes and customized production, unlike existing machining methods. However, owing to the characteristics of the AM process, anisotropy of macrostructure occurs because of various causes such as the scan direction, melting, fusion, and cooling of the powdered material. The macrostructure anisotropy is realized from the scan direction, and when a single layer is stacked in one direction, it is expressed as orthogonal anisotropy. Here, the classical lamination theory is applied to simply calculate the individual orthotropic layers by superimposing them. Through this, the authors analyzed whether the mechanical properties of the product are isotropically expressed with a periodic layer rotation strategy. To determine if the mechanical properties can be reasonably considered to be isotropic, a shock absorber mount for a vehicle was manufactured by AM. The tensile and vibration test performed on the product was compared with the finite element analysis and experimental results. As a result of the comparison, it was confirmed that the macroscopically of the product was considered isotropic as the load-displacement diagram and the fracture location coincided, as well as the natural frequency and mode shape.

Multi-materials of metal-polymer and metal-composite hybrid structures (MMHSs) are highly demanded in several fields including land, air and sea transportation, infrastructure construction, and healthcare. The adoption of MMHSs in transportation industries represents a pivotal opportunity to reduce the product’s weight without compromising structural performance. This enables a dramatic reduction in fuel consumption for vehicles driven by internal combustion engines as well as an increase in fuel efficiency for electric vehicles. The main challenge for manufacturing MMHSs lies in the lack of robust joining solutions. Conventional joining processes, e.g., mechanical fastening and adhesive bonding involve several issues. Several emerging technologies have been developed for MMHSs’ manufacturing. Different from recently published review articles where the focus is only on specific categories of joining processes, this review is aimed at providing a broader and systematic view of the emerging opportunities for hybrid thin-walled structure manufacturing. The present review paper discusses the main limitations of conventional joining processes and describes the joining mechanisms, the main differences, advantages, and limitations of new joining processes. Three reference clusters were identified: fast mechanical joining processes, thermomechanical interlocking processes, and thermomechanical joining processes. This new classification is aimed at providing a compass to better orient within the broad horizon of new joining processes for MMHSs with an outlook for future trends.

In a flexible roll-forming process, a metal blank is incrementally deformed into the desired shape with a variable cross-sectional profile by passing the blank through a series of forming rolls. Because of the combined effects of process and material parameters on the quality of the roll-formed product, the approaches used to optimize the roll-forming process have been largely based on experience and trial-and-error methods. Web warping is one of the major shape defects encountered in flexible roll forming. In this study, an optimization method was developed using support vector regression (SVR) and a genetic algorithm (GA) to reduce web warping in flexible roll forming. An SVR model was developed to predict the web-warping height, and a response surface method was used to investigate the effect of the process parameters. In the development of these predictive models, three process parameters—the forming-roll speed condition, leveling-roll height, and bend angle—were considered as the model inputs, and the web-warping height was used as the response variable. The GA used the web-warping height and the cost of the roll-forming system as the fitness function to optimize the process parameters of the flexible roll-forming process. When the flexible roll-forming process was carried out using the optimized process parameters, the obtained experimental results indicated a reduction in web warping. Hence, the feasibility of the proposed optimization method was confirmed.

Continuously cast large round blooms have gained widespread attention due to the improved quality, enhanced economy, higher yields, and lower operating costs obtained through continuous operation. Because the continuous casting (CC) process combines the cleanliness and radial solidification symmetry of the ingot casting process with the higher axial symmetry obtainable through bloom casting, it can deliver a more homogeneous product than conventional ingot casting. Herein, the shop floor manufacturing of a main shaft is discussed to confirm the feasibility of using continuously cast round bloom in the manufacture of heavy forgings. For comparison, the characteristics of a 1000 mm‐diameter continuously cast round bloom are assessed against those of a conventionally cast 20.6 ton ingot. To eliminate cavities at the centerline of the cylindrical bloom, additional studies on void closure efficiency at the center of the billet under various forging die geometries (e.g., flat, V, and round dies) are conducted, and the results reveal that the V‐die geometry is most effective in consolidating centerline voids. A comparison of the respective operational characteristics reveals that the round bloom CC method could be feasibly applied in the manufacture of main shafts.

Prepreg compression molding (PCM) is a well-known process for manufacturing of carbon fiber reinforced thermo-plastics (CFRTP) products with high quality and production rate. However, the design method used for the development of automotive parts has not been clearly presented. In this paper, we propose a process chain that can satisfy the stiffness of existing steel products. First, the CFRTP product of a B-pillar reinforcement to satisfy the bending deformation of an existing product is designed using a structural analysis and genetic algorithms. Next, forming conditions of the product are determined by a forming analysis. To investigate the feasibility regarding the mass production of the PCM process, a rapid heating and cooling system was applied to PCM molds. The heating and cooling times of the molds were calculated using a computational fluid dynamics analysis. Finally, a CFRTP product was fabricated and its bending deformation, dimensional accuracy, and weight were evaluated.

The purpose of this study is to apply Hot Forming Quenching (HFQ) on Patchwork Blank of AA6061 using Two-stage refilled Friction Stir Spot Welding (TFSSW). TFSSW is a developed joining method to improve joint strength of conventional Friction Stir Spot Welding (FSSW) and it consists of two stages. The first stage is a conventional FSSW process and second stage is a refilling process for refilling keyhole. The Design of Experiment (DOE) was used to optimize the TFSSW process parameters. A hat shape forming test was performed using a patchwork blank manufactured with the optimal process parameters to investigate validity of applying HFQ. Formed hat shape part was sequentially heat treated with artificial aging (T6) condition. The hardness of the weld zone was measured to confirm a drop of mechanical property in comparison with the conventional cold forming, which shows the validity of HFQ application to patchwork blank using TFSSW.

Prepreg compression molding (PCM) is well known for its high productivity among the manufacturing processes for carbon fiber reinforced plastic (CFRP) products. However, the disadvantages of CFRP products manufactured by the PCM process are related to defects involving micro grooves and voids. The purpose of this study is to develop a vacuum-assisted prepreg compression molding (VA-PCM) process to prevent these defects. To verify the application of the VA-PCM process, the mechanical properties of small-scaled specimens fabricated by the VA-PCM process were compared with the mechanical properties of specimens fabricated by the PCM process. The tests related to surface roughness, void content, tensile, and three-point bending were performed to evaluate the mechanical properties, including elastic modulus, tensile strength, bending stiffness, and energy absorption. Finally, automotive roof panels produced by each process were evaluated by a bending test to validate the VA-PCM process.

In this study, we design an integrated manufacturing process for Al6061 alloy bolts to fasten offshore platforms. The proposed scheme includes the theoretical design and numerical study for the heading, trimming, and thread-rolling process. For the theoretical design, the initial rod diameter and the penetration depth (PD) in the thread-rolling process are calculated according to thread standards and geometric relation. The dimensions of the initial workpiece for the heading process are obtained using the volume constancy law. Considering process limitations to predict the defects, the number of stages is set, and the preform is then determined using the design rule in the heading process. Based on the theoretical design, finite-element (FE)-analysis is conducted. In order to predict the defects and fracture phenomena, the ductile fracture criterion was applied during the heading and trimming processes. The Taguchi method is used to optimize the trimming and thread-rolling process with the set of design parameters, such as the PD, transfer velocity, and revolutions per minute in the thread-rolling process, and the blade radius (BR), land width, and stop distance in the trimming process, respectively. Results show that the PD and BR have the most significant effect on the dimensional accuracy and forming load. To validate the proposed design, the aluminum alloy bolt-forming experiment is performed. We obtain the sound Al6061 alloy M12 hexagonal bolt shaped with highdimensional accuracy. Therefore, this research provides valuable guidelines for the design of the integrated forming process in actual bolt production.

Abstract—This paper deals with finite element analysis to know the thickness and diameter reduction of a single pipe. The tube forming process begins with a straight pre-cutting tube. There are many variables in the pipe bending process. In particular, there is a difference in the accuracy of the bend depending on the shape of the mandrel. Through this analysis, we want to find the part where the reduction direction of the mandrel drastically occurs. In this process, the more the number of mandrill, the better the reduction in diameter. Also, it was concluded that the movement speed of the pressure die should be controlled to reduce the thickness.

Background: Sevoflurane and desflurane are widely used in balanced anaesthesia in combination with opioid analgesics. The opioid remifentanil is frequently chosen because of its extremely rapid pharmacokinetics. However, intraoperative high-dose remifentanil is associated with increased postoperative pain and rescue analgesic use owing to acute tolerance and opioid-induced hyperalgesia. This study aimed to compare intraoperative remifentanil requirements during equiminimum alveolar concentration (MAC) sevoflurane and desflurane anaesthesia via surgical pleth index-guided remifentanil administration. Methods: Eighty-two subjects undergoing laparoscopic cholecystectomy were randomly allocated to two groups receiving either sevoflurane (n = 40) or desflurane (n = 42). Anaesthesia was maintained with the assigned inhaled anaesthetics and remifentanil. End-tidal anaesthetic concentration was maintained at age-corrected 1.0 MAC, and remifentanil infusion was continuously adjusted to achieve a surgical pleth index of 20-50. Mean remifentanil infusion rate, which was the primary outcome of the study, was calculated as the total infused remifentanil dose per kg body weight per minute of total operative time. Results: Mean remifentanil infusion rate [mean (standard deviation)] was significantly higher in the sevoflurane group than in the desflurane group [0.192 (0.064) vs. 0.099 (0.033) mu g kg(-1) min(-1); difference, 0.093 (95% confidence interval, 0.071-0.115); P< 0.001]. Conclusions: During equi-MAC anaesthesia of 1.0 MAC, sevoflurane and desflurane did not show similar intraoperative remifentanil consumption under surgical pleth index-guided opioid administration. Further studies using other monitors with different measuring mechanisms are warranted to determine the cause of this difference.

Recently, carbon fiber reinforced thermo-plastic (CFRTP) has been used widely in a number of composite applications owing to the growing concerns about reducing energy consumption and protecting the environment. Various attempts have also been made to apply CFRTP to automotive parts in place of metal alloys because of the superior mechanical properties and being lightweight. Generally, CFRTP is applied to automotive parts with metal alloys because of the high material price. Therefore, research has been conducted on the multi-material forming process to reduce the process price. However, it is difficult to predict the formability of multi-materials and to design the shape of a CFRTP part because there is little research on the design and formability prediction of multi-materials. The aim of this study is to develop the B-pillar on automobile reinforced with CFRTP. Since the B-pillar is deformed simultaneously with CFRTP and DP780, the following study is required. First, a shape optimization analysis was performed to design the B-pillar reinforcement using CFRTP. The determined shape of the B-pillar reinforcement was used to determine the thickness of the product that satisfied the bending stiffness of the conventional product. Next, the friction coefficient at the interface between DP780 and CFRTP was measured for a multi-material forming analysis. The problems that occurred during forming process were analyzed through a multi-material forming analysis. Finally, the developed product was manufactured through the same method as in the analysis, and any problems were evaluated and analyzed.

The purpose of this study is to investigate the failure mode dependent the load bearing characteristics of the mechanical clinching under the mixed mode loading condition. The joint strength of the mechanical clinched joint was determined by the geometrical interlocking shape parameters, such as the neck thickness and undercut. The load bearing tests under the pure normal and shear mode loading condition were carried out to investigate the influence of the geometrical interlocking shape parameters on the failure mode of the mechanical clinching and its joint strength by analytical approach. The Arcan test apparatus was modified to realize the mixed mode loading condition on the cross-tension specimen. For each angular positions(α=0,15,30,45,60,75,90° ), the failure mode and strength of the mechanical clinched joint was evaluated by the cross tension specimen with the modified Arcan test apparatus. Based on the experimental result, an analytical expression was derived to describe the joint failure criterion under the mixed mode loading condition.

Carbon-fiber-reinforced thermoplastic (CFRTP) laminate undergoes large deformations and slip between each layer during the prepreg compression forming (PCF) process. Particularly, the formability of CFRTPs varies for each layer as a result of the temperature difference during heat transfer between tool and laminate because of the viscosity of resin. These behaviors affect the final product quality and may create related defects such as wrinkling, and delamination. The objective of this study is to predict the defects by using the finite element method (FEM) considering the heat transfer according to the forming temperature. The bias extension were performed to measure the shrar properties (which are dependent on temperature) at 150°C, 170°C, and 190°C. In addition, the heat transfer coefficient between tool and laminate was measured using the inverse analysis method. The effect of tool temperature on formability of CFRTP prepreg was investigated by FE analysis of the hemispherical punch drawing test. To verify the reliability of the FE analysis, hemispherical punch drawing experiments were performed under the same conditions as those of the FE analysis. The deformed shear angle of CFRTP specimens in the experiment were compared with simulation results. Finally, the temperatures were evaluated to investigate the effects of temperature variation caused by heat transfer.

In this study, a hot multi-point forming process was proposed. The hot multi-point forming die can form the various curved surface by controlling the height of each punch. In addition, the cooling system was installed inside each punch and can be selectively used as a punch or a cooling nozzle. Therefore, efficient hot forming and cooling of the thick plate is possible. However, in manufacturing plant, there has not been sufficient fundamental research on hot multi-point forming process with cooling system. In this study, the hot forming and cooing performance of the hot multi-point forming process according to punch arrangement and forming curvature conditions was evaluated through FE-analysis. As a result of FE-analysis, a punch arrangement design suitable for the target curvature is required in consideration of the shape error and the cooling rate.

Porthole extrusion process is a very effective metal forming process to produce aluminum profiles with hollow sections. The structure of porthole extrusion die is very complex. In this process, the billet is divided by porthole bridge, and then the divided billet is welded in the welding chamber. The welding pressure in the welding chamber is very important. The higher welding pressure improves the quality of the aluminum profiles. Therefore, the objective of this study is to develop a new porthole extrusion die for improving the welding pressure in the welding chamber by using numerical analysis. The effectiveness of the new porthole extrusion die was verified by using numerical analysis. Through numerical analysis, the welding pressures in the welding chamber between the new porthole die and the conventional porthole die were compared with each other.