Comparison of Constitutive Models for predicting the formability of SS 304 by tubular hydroforming process

Finite Element (FE) simulation of sheet/tube forming precision depends mainly on the accuracy of the constitutive modeling. The present paper aim is to compare the constitutive models to fit the stress-strain curves. The accurate deformation behavior of the SS 304 tubes depends on the constitutive modeling of hardening behavior. Deformation data of the tensile specimens cut from tubular sample were collected by conducting Uniaxial tensile tests (UTT) at three different rolling directions. Five constitutive relationships were then recognized by fitting the true stress and strain data with the constitutive models of Hollomon, Power, Krupowsky, Voce and Ghosh, and the fitting accuracy were analyzed and compared. Effects of hardening models on Forming Limit Curves (FLC), pressure loading and bulge height of the hydroformed tube were then studied. The obtained FLC from the simulations were compared with experimental FLC to predict the accuracy of the hardening models.

Exceptional Mechanical Properties and Heat Resistance of Photocurable Bismaleimide Ink for 3D Printing

Photosensitive resins used in three-dimensional (3D) printing are characterized by high forming precision and fast processing speed; however, they often possess poor mechanical properties and heat resistance. In this study, we report a photocurable bismaleimide ink with excellent comprehensive performance for stereolithography (SLA) 3D printing. First, the main chain of bismaleimide with an amino group (BDM) was synthesized, and then, the glycidyl methacrylate was grafted to the amino group to obtain the bismaleimide oligomer with an unsaturated double bond. The oligomers were combined with reaction diluents and photo-initiators to form photocurable inks that can be used for SLA 3D printing. The viscosity and curing behavior of the inks were studied, and the mechanical properties and heat resistance were tested. The tensile strength of 3D-printed samples based on BDM inks could reach 72.6 MPa (166% of that of commercial inks), glass transition temperature could reach 155 °C (205% of that of commercial inks), and energy storage modulus was 3625 MPa at 35 °C (327% of that of commercial inks). The maximum values of T-5%, T-50%, and Tmax of the 3D samples printed by BDM inks reached 351.5, 449.6, and 451.9 °C, respectively. These photocured BDM inks can be used to produce complex structural components and models with excellent mechanical and thermal properties, such as car parts, building models, and pipes.

Experimental and numerical investigation of the effect of holes on the springback in cold roll forming of UHSS

Ultra-high strength steel (UHSS) pre-notched sections are getting growing popularity in the automotive industry with the development of automotive lightweight. However, the springback of UHSS products is large, and the existence of holes also has an effect on the springback. Accurate prediction of springback of UHSS pre-notched products in cold roll forming ( CRF ) is a key issue to be solved. In this paper, the effect of holes on the springback of UHSS in CRF is discussed by simulation and experiment. The finite element model of pre-notched car threshold was constructed, and its accuracy was validated by continuous CRF experiment. The mathematical model of variable elastic modulus determined by tensile tests of martensite (MS) 1300 was applied in finite element model. The accuracy of springback was improved by 15% in the hole region by using variable elastic modulus . Several forming schemes were designed to research the effect of different features on the springback in the hole region. The results show that the existence of holes reduces the springback and the effect is different at different positions of the car threshold. The springback in the hole region decreases with the increase of the number of stands, the strip thickness and the hole diameter, and with the decrease of the distance between stands and the distance between holes. This study provides a help for reducing the influence of holes on the springback and improving the forming precision of pre-notched sections in the actual production of CRF.

An automatic compensation method for improving forming precision of multi-layer multi-bead component

Wire and arc additive manufacturing (WAAM) is a promising technology for manufacturing large-sized metal components. However, the material shortage region (MSR) at the edge of each slicing layer can influence the forming precision and surface flatness of components. To solve these problems, this paper proposes a shape follow-up edge cycle compensation (SECC) method and model for predicting the weld width and weld height to improve the efficiency of the WAAM process. First, the prediction model was used to determine the weld width and weld height for various welding parameters. The predicted width was then used to obtain the optimal overlap distance, and the filling path of each layer was generated. The same weld height was used for slicing of the 3D model and the tool path compensation cycle was generated. Second, the influence of the MSR on the morphology of multi-layer multi-bead (MLMB) components was analyzed. The MSR results in a height difference between the edge height and the middle height of every deposited layer, and the height difference increases as more layers are added and the height of the component increases. Furthermore, the influence of the MSR gradually extends from the edge to the middle, such that the upper surface presents a parabolic shape. Finally, a mathematical model was established to determine the height difference based on the area of the MSR. When the height difference reaches the weld height, an edge compensation weld is added to eliminate the height difference. Our experimental results show that the proposed forming control strategy improves forming precision and surface flatness. The method is highly feasible and can be applied to a wide range of WAAM applications.

Human-machine-environment information fusion and control compensation strategy for large optical mirror processing system

Large optical mirrors require an ultra-precise machining equipment, and a high level of surface-forming precision must be achieved. However, optical mirror processing systems (OMPSs) are susceptible to human behaviors, mechanical structural errors, and processing environments. The factors that affect quality include artificially formulated processes, slurry choice, joint friction, force-induced deformation, ambient temperature, and vibration interference. These factors can lead to a decrease in the accuracy of an OMPS. To study the influence of disturbances in the human-machine-environment (HME) on the OMPS, it is necessary to conduct a fusion analysis of the related factors. A parameter analysis is first conducted on the HME factors that influence the accuracy of OMPS. Then, the factors that influence the accuracy most significantly are determined. Subsequently, with the influencing factors as input parameters, and the output forces of the computer-controlled optical surface (CCOS) grinding system as the output parameters, the HME influencing factors are fused through a BP neural network optimized using a genetic algorithm, and the result is compared with that resulting from the original BP neural network fusion. Finally, according to the results of the fusion, environmental control of the processing system is performed, and the feedforward PD control compensation measures are established for the joint friction. An experimental analysis is also conducted to verify the effect of the information fusion and error compensation on the accuracy of the OMPS.

Effects of On-Line Vortex Cooling on the Microstructure and Mechanical Properties of Wire Arc Additively Manufactured Al-Mg Alloy

A novel on-line vortex cooling powered by low-cost compressed air was proposed to reduce common defects such as low forming precision, coarse grains, and pores caused by heat accumulation in the Wire Arc Additive Manufacturing (WAAM) of aluminum alloy. The impacts of interlayer cooling (IC), substrate cooling (SC), on-line cooling (OL), and natural cooling (NC) processes were compared on the morphology, microstructure, and mechanical properties of as-deposited walls, revealing that the OL process significantly lowers the interlayer temperature and improves forming precision. The high cooling rate produced by the OL process reduced the absorption of hydrogen in the molten pool, lowering porosity. Furthermore, the grains are refined due to the developed undercooling. However, the high cooling rate enhanced the segregation potential of Mg element and raised the content of the β phase. Conclusively, the maximum tensile strength, elongation, and microhardness of the as-deposited wall are achieved via the OL process, and the fine-grain strengthening mechanism plays an important role in improving mechanical properties. The OL process is cheaper and poses a significant effect; it is highly suitable for the additive manufacturing of complex components compared with other forced cooling processes.

Finite Element Simulation, Analysis and Research on the Influence of 3D Printing Parameters on Forming Precision

Background: 3D printing technology is an emerging technology based on additive ideas. Desktop-level 3D printers molded by Fused Deposition Modeling (FDM) are widely used. However, their printing accuracy is relatively low accompanied by severe warpage, which limits its application scope and fields. Therefore, analysis of the cause of warpage in the printing process and optimization, has important practical significance for promoting the application of FDM printers. Methods: The goal of this work is to improve the forming precision of 3D prints, through the finite element analysis software ANSYS, utilizing the life and death component innovation and coupling the temperature field and stress field of printing speed, one of the key factors affecting the forming precision. After the calculation and analysis, the following conclusions can be drawn: In testing with other conditions unchanged, when the printing speed is gradually increased, the accuracy of the print is improved first and then decreased. This method provides a new way to analyze the influence of other factors on the forming accuracy and also provides a new way to get the best print parameters under the combined action of many factors. We reviewed several patents related to 3D printing, its optimization, formulations, precision and accuracy in respective field. Results: So, to achieve the best results, layer thickness has great influence on the molding precision. Finally, the results were obtained by finite element analysis, finding the best printing accuracy of the print parameters and verifying them by conducting actual printing. Conclusion: The research shows that the thickness of the layer has the greatest influence on the printing accuracy in the process parameters studied.

Directly Writing Patterning of Conductive Material by High Voltage Induced Weak Electric Arc Machining (HV-μEAM)

An additive manufacturing (AM) method for the deposition of metallic layer in micron scale on monocrystalline silicon wafer surface by high voltage induced weak electric arc machining (HV-μEAM) has been proposed. The process characteristics of HV-μEAM are analyzed to fulfil the metal material deposition. The influence of the processing parameters on the deposition effect were studied with copper as additive electrode material. Using the optimal parameters, a number of complex trajectory deposition experiments have been carried out and a QD character-type deposition layer with a height of 139.09 μm has been obtained. The deposition has good continuity and high forming precision. It is proven that the new method is achievable and efficient for patterning metallic materials in the micro- and nano-scale on the silicon substrates surface.

Research on Contact State and Its Effect on Forming Precision in Uniform-Contact Stretch Forming Based on Loading at Multi-Position

Uniform-contact stretch forming based on loading at multi-position (UC-SF) was designed to substitute for conventional stretch forming (C-SF) in the manufacturing of qualified three-dimensional surface parts of a specified shape. Since the integral rigid clamps are replaced by discrete clamps, the sheet metal can be bent in a transverse direction (perpendicular to the stretching direction), and the sheet metal can be automatically warped to the die surface during the loading process. In this paper, finite element numerical simulations were performed to research the contact state evolution and its effect on forming precision by two kinds of loading modes (UC-SF and C-SF). The evolutions of contact state for spherical and saddle-shaped parts were analyzed in different steps, and the results reflect that, in UC-SF, the contact region of curved surface parts is gradually extended in a long strip, and the effective formed regions of the final parts can be in contact with the die surface. However, in C-SF, it is difficult for the final parts to be completely in contact with the die surface, especially spherical parts of a large curvature. Moreover, it is found that the noncontact region of the saddle-shaped part is susceptible to wrinkling in C-SF. Conversely, in UC-SF, the sheet metal can be constrained by contact with a die surface, such that the noncontact region and wrinkle defect disappear and high-precision parts are formed. Finally, stretch forming experiments were carried out and the perfect curved surface part was formed; thus, the experimental results verify the feasibility and effectiveness of UC-SF.