Final Forming Research Articles

Friction Modelling for Tube Hydroforming Processes-A Numerical and Experimental Study with Different Viscosity Lubricants.

The final quality of sheet and tube metal–formed components strongly depends on the tribology and friction conditions between the tools and the material to be formed. Furthermore, it has been recently demonstrated that friction is the numerical input parameter that has the biggest effect in the numerical models used for feasibility studies and process design. For these reasons, industrial dedicated software packages have introduced friction laws which are dependent on sliding velocity, contact pressure and sometimes strain suffered by the sheet, and currently, temperature dependency is being implemented as it has also a major effect on friction. In this work, three lubricants having different viscosity have been characterized using the tube-sliding test. The final aim of the study is to fit friction laws that are contact pressure and sliding velocity dependent for their use in tube hydroforming modeling. The tests performed at various contact pressures and velocities have demonstrated that viscosity has a major effect on friction. Experimental hydroforming tests using the three different lubricants have corroborated the importance of the lubricant in the final forming of a triangular shape. The measurement of the axial forces and the final principal strains of the formed tubes have shown the importance of using advanced friction laws to properly model the hydroforming process using the finite element modeling.

Evolution of Microstructure and Mechanical Properties of Al-Zn-Mg-Cu Alloy by Extrusion and Heat Treatment

Herein, composite extrusion deformation and heat treatment process at various temperatures were studied on a new type of Al-Zn-Mg-Cu alloy billet. The influence of pre-deformation and the final forming of extrusion and heat treatment of annular channel corner extrusion on the microstructure evolution and mechanical properties were explored. The results show that the extrusion process could further refine the structure and break the coarse θ phase. The grains can be refined again after the deformed sample was treated by solution-aging treatment. At the same time, a fine, dispersed second phase is precipitated around the fine recrystallized grains. This is the main reason for the increase in alloy elongation and tensile strength. The best heat treatment process parameters for the formed cup-shaped structure are 480 °C × 1 h solid solution and 120 °C × 24 h aging. The strengthening of the alloy mainly includes three mechanisms: fine grain strengthening, precipitation strengthening, and dispersion strengthening.

The Process Design and Rapid Superplastic Forming of Industrial AA5083 for a Fender with a Negative Angle in a Small Batch

A front automobile fender with a negative angle was trial produced via rapid superplastic forming (SPF) technology. The tensile test of industrial AA5083 was carried out at elevated temperatures, and the results showed that the maximum elongation was 242% at 480 °C/0.001 s−1. A rigid-plastic constitutive model of the SPF process was established. Initial dies of preforming and final forming were designed. The finite element method (FEM) was used to simulate the forming process and predict the thickness distribution of different areas. Furthermore, the dies were optimized to make the thickness distribution uniform. In the final structure, the maximum thinning ratio decreased from 83.2% to 63% due to the optimized design of the forming dies. The front automobile fender was then successfully fabricated by the preforming process and final forming process at 480 °C. A thickness measurement was carried out, and the minimum thickness of the preforming structure was 2.17 mm at the transverse tank, while that of the final structure was 2.49 mm near the edge of the lamp orifice. The average grain size grew from 20 to 35 μm. The grain growth led to the reduction of mechanical properties. Compared with the mechanical properties of the initial material, the maximum decrease in tensile strength for the material after superplastic forming was 5.78%, and that of elongation was 18.5%.

Accumulative traction-hoisting construction technology of a semi-rigid steel batten cable dome

A new structure called a steel-batten cable dome (SBCD) is proposed in this study. By replacing flexible ridge cables to semi-rigid steel battens, this structure is provided with the characteristics of good integrity and large local stiffness to support heavy rigid roofing systems. In addition to avoid installing large amount of temporary stent, the accumulative traction-hoisting construction technology (ATHC) was present, with the feathers of few brackets, small lifting force, and high efficiency of tensioning. Moreover, the modified NDFEM form-finding method is introduced to simulate the construction process of ATHC. The results show that the SBCD model and the conventional cable dome (CCD) model both experienced the traction-hoisting stage, the adjustment stage, and the rigid stage to build sufficient stiffness to withstand external load, with their overall shapes changing from “ω” to “m”, and finally reach their designed states. Total stresses of the steel battens are within 85 MPa before final forming and 250 MPa after construction, which ensures the stable state for the steel batten grid and the elastic state of the entire structure. Furthermore, ATHC can be applied for both SBCDs and CCDs, while a SBCD could be simplified to a similar CCD to optimize the calculation efficiency.

Precise Forming of Complex Magnesium Alloy Components Based on Finite Element Method and Quantitative Preforming Design

To solve the difficulties associated with integral precise extrusion forming for complex components of magnesium alloy, Deform-3D finite element simulation software was used to conduct numerical analyses for the forming process. Different extrusion schemes were used for determining the overall extrusion difficulties associated with special-shaped thin-walled complex components of magnesium alloy. The effects of a preformed blank on the filling and formation of folding defects in the forming process were studied. Based on the principle of minimum energy in the process of plastic deformation and the law of least resistance, volume predistribution and equal distance flow quantitative compensation methods were put forward. These methods were used to optimize the size and structure of the preform, forming a uniform material flow distribution. They also enabled one to manifest a uniform material flow velocity distribution, reduce the forming load, and avoid the creation of folding and filling defects during the final forming, for the realization of an efficient and reliable preform optimization design for magnesium alloy profiled complex components. The results obtained from a forming test, microstructure and mechanical properties test showed that the mechanical properties of the extruded component all met the service indexes. This design method can provide a theoretical reference for preforming design of profiled complex components.

Transverse and longitudinal flexural properties of unidirectional carbon fiber composites interleaved with hierarchical Aramid pulp micro/nano-fibers

Unidirectional carbon fiber reinforced polymer (UD-CFRP) composites designed for ultimate tensile strength and stiffness along the fiber direction are vulnerable in the transverse direction. In this study, UD-CFRPs were reinforced in the transverse direction using sparsely distributed hierarchical Aramid pulp (AP) micro/nano-fibers between 2 and 8 g per square meter (gsm) per ply interface. Those AP micro/nano-fibers, a few hundred microns in length, effectively formed an ultra-thin interleaving layer around 20 μm in thickness between carbon fiber plies. Flexural properties along and perpendicular to continuous carbon fiber direction were measured under three-point-bending (3-P-B) to determine the toughening effects of AP. Flexural loads in both longitudinal and transverse directions have been enhanced by 30% and over 100% respectively from those randomly distributed AP micro/nano-fibers with diameters varied from a few hundred nanometers to 10 μm. Even slight increase in the elastic modulus of AP-toughened CFRP along the fiber direction was observed. Total fracture energy absorption, initial cracking and final fracture loads were measured and compared, indicating AP micro/nano-fibers have contributed to the high strength, high toughness and high modulus characteristics of AP-interleaved UD-CFRPs. Details on toughening mechanisms were revealed from SEM and cross-section optical microscopy examinations. Comparisons of unreinforced UD-CFRP and AP-toughened UD-CFRP showed the hierarchical AP micro/nano-fibers indeed played an important role in composite microstructure design and property optimization. The ultra-thin interleaved AP veil around 20 μm in thickness can be conveniently incorporated into pre-preg fabrication so that the extra interleaving step can be eliminated, i.e. the toughened pre-pregs can be used as normal pre-pregs in the final composite forming.

Research on the plastic fluidity of high-strength steel 22MnB5 based on the thermal-mechanical-fluid multi-filed coupling

The effects of technological parameters such as pre-deformation, strain rate, and final forming temperature on the formability of high-strength steel 22MnB5 were studied. Firstly, the finite element model of thermal-mechanical-fluid coupling was established by finite element simulation software ABAQUS. Secondly, the simulation and experiment of the pure hydraulic bulging with the forming temperature are 20, 100, 300, 500, and 700 °C and were carried out, respectively. Finally, by setting the technological parameters such as the cavity pressure loading rate (2, 4, 6, 8, and10 MPa/s) and final forming temperature T (20, 100, 300, 500, and 700 °C), the numerical simulation and the experiment of the coupling of the initial room temperature pre-deformation and high-temperature final forming were studied, and the optimal combination of process parameters was optimized by making the bulging height as the objective function at the end of the forming process. Keeping the cavity pressure loading rate is invariable; the bulging height difference between the two processes is 12.02, 20.43, 26.18, 33.20, and 39.39 mm, respectively, when the temperature is 300 °C. Keeping the final forming temperature is invariable; when the cavity pressure loading rate is 8 MPa/s and the temperature is 300 °C, the difference of the bulging height difference between the hot hydraulic bulging and room temperature hydraulic bulging is maximum, the largest value is 2.17 mm. Taking the bulging height as the criteria of material forming performance, the combination of the final forming temperature of 300 °C and the cavity pressure loading rate of 8 MPa/s is optimum. Finally, the whole coupling process is divided into three stages, and by using the form of structuring sectionalized constitutive equation, the influence law of the dual action of work hardening and softening on the deformation and fluidity of the material in the compound-forming process is analyzed from the perspective of the evolution law of microstructure.

Influence of 1st Step Shape on the Formability of Circular Truncated Cone Stretch Forming in Two-Step Forming

The formability of steel sheets must be improved to form complicated car parts. Multistep forming is one way of improving the formability. The shape after preforming could influence the formability in the main step of multistep forming. However, no relationship has been reported between the shape after preforming and the final shape in the case of stretch forming. In this study, circular truncated cones were formed by two-step forming consisting of preforming and main forming, with combinations of various shapes after preforming and final shapes in order to investigate the effect of the shape after preforming on the forming limit in final forming. The results show that the forming limit height in main forming is affected by the preforming shape. In addition, the forming limit height in main forming is determined by the central cross sectional line length of the shape after preforming.

Contact mechanism between dissimilar materials under plastic deformation

The description of the new contact mechanism between dissimilar materials during joint plastic deformation is proposed in this paper. To analyze the process of joint deformation of composite material layers, a multi-stage analytical model was developed based on the study of the contact interaction between the surfaces of the materials to be bonded using the slip line method. When mathematical simulation of the process of joint deformation of dissimilar materials, the influence of the geometrical surface profile of a harder layer of a composite, as a more significant factor, was estimated. For the entire range of influence of the investigated geometrical surface profile of a harder material of a composite, the final forming and stress state parameters in its intermediate zone were determined. To verify the analytical model, computer simulation of the process of joint deformation of composite material layers by the finite element method in two-dimensional formulation was carried out. The comparison of both solutions has confirmed the adequacy of the results obtained in the mathematical simulation. The theoretical model can be used in the development of bonding mechanisms between dissimilar materials, in the development of manufacturing technologies of new clad composite materials, as well as in the analysis and improvement of the existing manufacturing technologies of clad composite materials.

Effect of inter-annealing between two stages of extrusion on the microstructure and mechanical property for spray deposited Al–Cu–Li alloy 2195

The spray deposited alloys need to be first extruded to reduce porosity, and then the extrusion is conducted again for final profile forming. It is required to carry out an inter-annealing between the two stages of extrusion. In this study, billets after the first extrusion were annealed with different parameters, and the effect of annealing process on the microstructure was investigated. Then the annealed billets were extruded again to obtain the extruded plates. The role of inter-annealing processes on the properties of extruded plates was investigated through microstructure characterization and mechanical properties testing. The results show that the inter-annealing processes increase the width of extrusion fibers and lead to static recrystallization in the extruded billets. The <100>//ED texture in extruded billets increases obviously after the inter-annealing due to the static recrystallization. The solubility of the secondary particles can be increased with the inter-annealing temperature and holding time, which thus enhances the effect of solution strengthening. The billets annealed with higher temperature and longer time exhibit stronger deformation resistance owing to the high solution strengthening effect. After the second extrusion, the texture of <211>//ED is introduced into the extruded plates, which causes apparent anisotropy of mechanical properties. The plates extruded by the billets with different inter-annealing parameters have similar microstructures, which thus results in similar mechanical properties. However, after solution and aging treatments, the extruded plate with inter-annealing at high temperature for a long time shows significant performance degradation, which results from the severe grains coarsening.

Investigation of forming process of the third-generation automotive medium-Mn steel part with large-fractioned metastable austenite for high formability

With the increasing requirement of lightweight and safety of automotive industry, the third-generation automotive medium-Mn (TAMM) steel with large-fractioned metastable austenite has been newly developed in order to enhance the strength and guarantee the formability. In this paper, the effect of plastic deformation condition, such as strain direction and strain rate, on mechanical properties and microstructure of TAMM steel is firstly investigated. The results show that the TAMM steel holds isotropic characteristic and the effect of strain direction and strain rate on mechanical properties can be neglected. Furthermore, the two-step forming process of TAMM steel is studied step by step to understand the effect of pre-forming on final forming. On the one hand, the martensitic transformation and work hardening during pre-deformation increase the strength but decrease the uniformity of mechanical properties, which decreases the final formability. On the other hand, with the increase of pre-strain, the enhanced yield strength, lengthened yield platform and undulating work hardening rate during final forming increase the probability of the crack. The simulated and experimented results prove that one-step forming process is suitable for the TAMM steel part with complex shape because the TRIP effect during one-step forming contributes to high plasticity.

The Theory of Accounting in the Context of Modern Paradigm of Scientific Knowledge

Accounting as a practical activity was being developed during millennia but the final forming of accounting science is impossible without the development of its modern theory, which is correspondent to the requirements of scientific doctrines of the 21st century. The existing theory, in many cases, is not good at all and, in general, it is the set of technical approaches of realization of double record. The results of economic investigations of the world level show the impossibility of modern accounting science to fulfill its functions because of its conservative character and it was not changed during many years. All these investigations have a direct impact on economy and show that the understanding of the basic postulates changes and the stress is made on psychological and social aspects and avoiding of material ruling.

유한요소해석을 이용한 브레이크 챔버 헤드 판재 성형에 관한 연구

In this study, the sheet metal forming process of the brake chamber head, which had a complex shape compared to the conventional head part, was investigated using finite element (FE) analysis. In order to prevent the forming failures such as necking and fracture, the multi-stage forming process was introduced. The forming process consisted of three steps: (1) first drawing, (2) second drawing, (3) final forming. Experimental and FE simulated results of the brake chamber head were compared, and the results showed that the required characteristics of the straightness and the wall thickness at each location were satisfied.

An experimental investigation of parameters effect on laser forming of Al6061-T6 sheets

Laser forming, which is categorized as a thermal forming process, is used in forming and bending of metallic and non-metallic sheets. Laser beam irradiation causes a localized temperature increase and a localized mechanical strength decrease. In this article, the effects of four process parameters, comprising laser power, scan velocity, the number of scan passes, and sheet thickness, on laser forming of Al6061-T6 sheets are studied. A design of experiment, including response surface methodology, is carried out to limit the experimental runs and costs and to identify the parameter effects on the bending angle of the sheet. Experiment results show that bending angle increases due to the decrease of scan velocity and sheet thickness. In addition, laser power and number of scan passes have a direct relation with a final sheet forming.

Cross wedge rolling and bi-directional forging of preforms for crankshafts

Preforming is an essential step in flashless forging processes. This paper describes the development of a four stage process chain for flashless forging of a two cylinder crankshaft with pin and flange. The process consists of cross wedge rolling, lateral extrusion, bi-directional forging and final forming, with cross wedge rolling being the essential step. The finite-element-analysis (FEA) performed with the software Forge 3 and experimental tests are executed with different process parameters, like billet and tool temperature, rolling velocity and steel. To reduce process steps, like lateral extrusion, a direct combination of cross wedge rolling and bi-directional forging is analysed with FEA-software Forge 3 for a one cylinder crankshaft without pin and flange. The one cylinder crankshaft is selected to reduce development effort. The results of the FEA give suitable forming angles α for cross wedge rolling and several geometric parameters for a modification of the bi-directional tool.

육면체 요소 재구성을 통한 개방형 사다리꼴이 성형된 판재의 탄성 거동 균질화에 대한 연구

The current collector for the molten carbonate fuel cell (MCFC) which has sheared protrusions is manufactured by the three-stage forming process that integrates slitting, preforming and final forming. Due to the repetition of sheared protrusions, an effective simulation method is required to predict the mechanical behavior. In the current study, a sheet with sheared protrusions was assumed to be an orthotropic plate, which has the same length, width and height. FEM simulations were conducted to evaluate the homogenized properties of the current collector, which has 4 (longitudinal direction) x 4 (transverse direction) sheared protrusions. The simulation model was constructed using hexahedral mesh coarsening. From the verification examples, it was found that the proposed simulation method was efficient within reasonable accuracy. The calculated homogenized properties can be applied to the design of a stack for molten carbonate fuel cells and the prediction of mechanical behavior for other applications.

An approach to triangular induction heating in final precision forming of thick steel plates

An automatic high-frequency (HF) induction-heating (IH)-based triangular heating process was introduced in order to investigate the influence of designing heating patterns on the permanent deformation behavior of an SS400 thick plate. Temperature distribution and permanent plate deformation during triangular heating were predicted based on electromagnetic–thermal and thermal–structural analyses, respectively. Both analytical and experimental permanent deformation values obtained by zigzag-type triangular heating were significantly higher than those by fan-shaped triangular heating, presumably because of the different temperature gradient along the thickness. Proper design of triangular heating pattern appeared to be the most important factor in determining the final shape of the thick plate. All predicted results were in good agreement with the experimentally observed permanent deformation.

Rutherford cable made of single-core MgB2 wires

A flexible Rutherford cable stranded from twelve single-core MgB2 wires has been made. Individual MgB2/Ti/Cu/Monel strands of the cable were prepared by wire drawing down to an outer diameter of 300 μm. The strands were wound into the rectangular Rutherford-type cable with the aid of a back-twist cabling machine. The transposition length of the cable, shaped into the final overall dimensions of 0.54 mm × 2 mm, is 20 mm. In order to analyse the electrical and mechanical properties, short specimens of a heat-treated reference sample (as-drawn wire), wire strand extracted from the cable, as well as Rutherford cable specimens were prepared and measured. It was found that final cold forming of the cable by a rolling die increased the critical current density of individual strands by 65% in comparison to drawn ones. Consequently, the critical current of the Rutherford cable is considerably higher than the 12Ic of the reference sample. Bending stress applied to the Rutherford cable has shown that critical current degradation starts below a diameter of 35 mm, which suggests using the cable for the construction of small-scale windings and applications where low bending diameters are required.

Theoretical analysis of the combined radial-reverse extrusion parts with flange

This article describes the mathematical model of the process combined radial-reverse part extrusion type of glass with a flange for identifying energy-power parameters of the process and explore the gradual and the final forming of the billet. It shows a comparative analysis of the phase-forming patterns based on the proposed computational scheme, finite element modeling and experimental data.

가상모델로부터 산출된 응력 등가정하중을 이용한 금속 성형품 및 단조품의 형상최적설계

본 논문은 응력 등가정하중을 이용하여 금속제조공정에서 원하는 성형품과 단조품의 최종형상을 얻기 위한 형상최적화 방법을 제안한다. 성형품의 최종형상은 블랭크의 형상에 따라 달라지고 단조품의 최종형상은 빌렛의 형상에 따라 달라진다. 따라서 원하는 형상의 제품을 얻기 위해 구조최적화방법 중형상최적화방법을 적용하였다. 금속성형 공정은 비선형 동적해석을 수행하므로 등가정하중법을 이용한다. 등가정하중법 중 가상모델을 이용한 응력 등가정하중은 등가정하중을 산출하는 새로운 방법으로 재료 특성의 가치를 재정의하여 응력 등가정하중을 계산한다. 본 논문에 포함된 예제를 통해 원하는 제품의 최종형상을 얻기 위한 최적의 블랭크 및 빌렛 형상을 도출하여 제안한 방법의 유용성을 검증한다.