Papers by Keyword: Tube Forming

Abstract: This study presents a numerical analysis of the tube expansion process by conventional tube-end forming versus single point incremental forming (SPIF) using DEFORM. The work includes the assessment of the strain paths within the principal strain space of these processes with respect to the formability limits as well as their evaluation within the equivalent strain versus stress triaxiality space. The results obtained demonstrated that the mechanics of tube flaring process in conventional and incremental forming are substantially different. This analysis of formability in the light of the accumulated equivalent strain and the average stress triaxiality allowed a better understanding of the differences between both processes in terms of the fracture limit strains.

Abstract: Lead or low temperature melting alloys have been sucessfuly utilized as a filling medium in tube forming processes, such as bending and bulging; however, strict lead-free-control plan in industries have prohibited the use of lead in recent years. The authors suggest the use of fiber-reinforced ice (FRI) as an alternative. Fiber of recycled paper was utilized for the preparation of FRIs, and the results of compression tests revealed that the fabricated FRIs exhibit sufficient crushing-strength suitable for use as an alternative for lead-filled media. However, the high density of the fiber in the mixture of fiber and water makes it difficult to fill a tube with the fiber in the pre-freezing process owing to its high vscosity. Therefore, it is useful to examine other strong fibers for FRIs to reduce the ratio of the fiber. In this study, the authors examined glass fibers as reinforcement in FRIs. Compression tests were conducted at various crosshead speeds, and the difference in the stress-strain behaviors of the FRIs with glass fiber and paper-pulp fiber was analyzed.

Abstract: In this paper, the authors discuss process planning for the lateral extrusion of a pipe with a lost core. In this process, maximum longitudinal length of the bulged part is restricted by the balance of the extrusion speed of the material and the lost core. In the free bulging condition, longitudinal length is limited to the pipe radius, because the extrusion speed of the core is slower than that of the pipe material when the longitudinal length of the bulged part is longer. The authors designed a two-stage forming process using the transit shape of a truncated cone to solve this problem. The dimensions of the truncated cone were estimated through trial-and-error using a commercial FEM simulator and considering the stretch effect for wrinkles of the pipe by deformation and traveling of the lost core. Finally, the authors conducted experiments to confirm the design’s validity. As a result, a longer longitudinal length of the bulged part than the pipe radius was successfully obtained.

Abstract: In the last ten years, the automotive sector presents large interest for light alloys tubes for structural and body car parts to reduce CO₂ emissions. Tubes hydroforming is one of the most popular processes to obtain complex parts by using liquids as active part of the dies (i.e. water-or oil-based emulsions) with reduced costs of equipment and machines. However, when elevated temperatures should be used to increase the material formability, hydroforming processes are strongly limited due to the boiling point of liquids. The use of gas at elevated temperature in the so-called Hot Metal Gas Forming process (HMGF) has shown promising capabilities thanks to the increased formability and the possibility to form parts with lower pressures. The paper focuses on a novel experimental set-up to evaluate the tubes formability at high temperatures. Tubes are heated by electric current and air in pressure is used to form the material. Aluminium alloy AA6060 tubes specimens were used to test the experimental equipment and evaluate temperature and pressure ranges able to shape the material.

Abstract: In our previous study, we reduced the slide marks on material surfaces by optimizing the lubricant for push-through bending. In this study, we investigate contact conditions of material deformation in dies during push-through bending. We also attempt to reduce slide marks by investigating the die material, die surface treatment of the die, and roller die set and to clarify the following. Bending deformation and flange wrinkling occur in fixed dies during push-through bending. Sliding between the material and the die begins inside the fixed die. A cemented carbide die is excellent for obtaining ideal surface roughness of the slide marks. Hard metal dies tend to have excellent sliding characteristics. Cold die steel (SKD11) and high-speed steel (SKH51) have almost equal hardness, and their qualities exist harmoniously between the bending member and the die material without the above relationship. When we treat the die surface or use the above dies, roughness of slide marks increases. The die-surface roughnesses in Diamond-Like Carbon (DLC) processing and Toyota Diffusion Coating Process (TD) are minimal, and the surfaces of their bending members are smooth. Furthermore, their efficiency is nearly equal to that of cemented carbide dies without surface treatment. Using a roller die effectively reduces slide marks. However, a roller die contacts the bending member locally, and the contact pressure is higher than with a normal die. Thus, a roller die is inferior to a normal die in its curvature, deformation, and flange wrinkling. The structure of the roller die is most suitable for parts with small curvatures.

Abstract: The push-through bending process can be regarded as a bending mechanism with two fixed diepoints and two movable diepoints, resulting in a total of four points. It can also be regarded as acontinuous four-points bending. As compared to other bending processes, there is severe friction at the contact area betweenthematerial and die in push-through bending. In this paper, we clarify different aspects of lubrication and research excellent lubrication oil in push-through bending. Based on theresultsobtained, it was found that adhesion occursdepending on the lubricant used and the occurring force. It was also confirmed, that olefin is effective as a remedy for oiliness, in case of using a mineral oil-based lubricant. In addition, it was confirmed that excellent lubrication oil could be obtained by increasing the alcohol content and adjusting the content of synthetic ester. This is a good alternative to the more expensive olefin.

Abstract: The cross-section shape change was investigated to determine the effects of proof stress, r value, wall thickness, and cross section in push-through bending of a square extruded pipe. Extruded A6063 aluminium alloy (40×40×2.0 mm) was used in the experiment. The push-through bending machine used has a six-axis NC controller. In this study, a two-dimensional single curvature shape was adopted in order to investigate the fundamental bending properties. A high-proof-stress material with severe bending workability was examined in this experiment to clarify the effect of bending workability on the material properties. Workability was evaluated by examining wrinkles and shape change of the cross section; the change in thickness was also evaluated, as were n and r values. The results are as follows. The high-proof-stress material was bent, resulting in significant cross-section deformation. The size of wrinkles caused by bending increased due to the large bending radius, and the wrinkles produced were deep. The effect of the r value on the cross-section deformation after bending could not be determined. In the present experiment range, the bending limit was determined by the size of wrinkles in internal bending. In A6063-T1, the wall thickness had a significant effect, and the forming limit of the thin-walled material was low. The bending limit was low for A6063-T5, and the effect of the wall thickness was slight. The bending limit of a 60×60mm cross-section piece was considerably lower than that of a 40×40 mm cross-section piece, for the same wall thickness; it was particularly significant in A6063-T5.

Abstract: Low formation loads are desirable in metal stamping industries as it reduces the press capacity of the machine and the tooling cost. In the previous study, the author had successfully developed a 2-stage end formation process of a round tube into a square section having small corner radii. However, the formation load in this process increased linearly with the punch stroke in the 1st stage due to the continuous expansion of the tube end by the conical die. Hence, buckling and cracks occurred at the circular section and the bottom end of the square section respectively when the punch stroke was excessive. In this study, the author proposes a circular die having a conical bottom replacing the conical die for the expansion of the tube end. Although the formation load increases when the tube end is expanded at the conical bottom, the amount of increase becomes small when the tube end reaches the circular section of the die due to its constant diameter. At the circular section, the tube end curls and wraps over the die when the punch stroke is increased. In the 2nd stage, the squaring process is performed with a conical bottom square punch and a taper square die for the two different expanded tubes i.e. the one formed with the conical die and the one formed with the conical bottom circular die. Both Finite Element Method (FEM) simulation and experiment were performed to evaluate these two processes. The distribution of plastic strains, forming loads and product appearances are investigated. With the circular die, the maximum forming loads are successfully reduced by 20% and 33% in the 1st and the 2nd stages respectively in the experiment when compared to the ones formed with the conical die. No buckling and cracks are observed for the tube formed with the circular die.

Abstract: As a response to the recent years’ growing demand for innovation in manufacturing processes towards lightweight design in several industrial sectors, a new process, called Incremental Tube Forming (ITF), and a corresponding machine layout have been developed. ITF is a process to manufacture bent tubes with varying cross-sections. During ITF a tube is clamped in a feeding device, which transports the tube through a spinning tool, where the diameter reduction takes place. This stage is followed by a superposed bending process without suppressing continuous feeding. This combination leads to various advantages such as improved tool life with reduced tool forces and improved product accuracy (e.g. springback behavior), as it is shown in various experimental works. This paper presents a complementary numerical treatment of the process using FEA. For this purpose, a 3D model is constructed using ABAQUS/Explicit, where the tube is modeled with conventional shell elements with uniformly reduced integration to avoid shear and membrane locking (S4R), whereas the spinning rolls are modeled as discrete rigid. With this model, the influences of process parameters, such as diameter reduction ratio and tool geometry, are investigated. This helps not only to gain a deeper understanding of the process but also to interpret already gathered experimental data with better precision and, thus establishing a basis for further improvement and optimization of this fairly new process.

Abstract: The authors have developed a lateral extrusion process with a lost core. The outline of the process is as follows. First, the cavity of a pipe, or a channel material, is filled up with liquid of a low-temperature melting material. The low-temperature melting material is then solidified to become a soluble core of the pipe. The authors call this soluble core the lost core. Next, the material is compressed longitudinally as a composite billet and extruded in the lateral direction. After deformation, the low-temperature melting material is melted and removed. The process can performed in a compression state to control the precise appearance of the product. This study examines a new core material, alumina powder (alumina ball) bonded with wax, as a core material. A mixing methodology for wax and alumina powder is discussed along with the effect of their mixing ratio on the deformation of the pipe.