Study on Double-Curvature Metal Plates Sequential Forming with Heat-Assisted Incremental Bending Based on Minimum Energy Method

With the development of the shipbuilding, chemical engineering, and military industry, the demand for bending the metal plates with large curvature is increasing dramatically. Take the shipbuilding as an example, the line heating method is widely applied. However, this traditional method has significant disadvantages. In order to improve the manufacturing efficiency and precision, a novel method called incremental bending has been presented by our team, which is based on the minimum energy principle and model-less control method. However, due to the limited formability of the metal plates at room temperature, the bending curvature of the plates during the incremental bending process cannot meet the requirements of the shipbuilding industry. Researches show that heating can reduce springback and improve the metal formability effectively. So here in this paper, a new method called heat-assisted incremental bending is presented. In this method, the metal plate is supported by several supporting pillars and the punch moves according to the loading trajectory, which is calculated by minimum energy method. In addition, the induction heating system is applied to heat the plates at the punching positions. The bending process continues step by step until the metal plate achieves the designed shape finally. During this study, the springback behavior of the metal plates during the heat-assisted incremental bending process was investigated based on theory, numerical simulation, and experiment. Then, the metal plates with large single curvature and variable curvature were deformed based on the novel thermal-mechanical coupled metal forming process. The experimental results show this new forming process can better control the springback behavior of the metal plates and achieve the objective metal plates with lager curvature with higher processing efficiency and accuracy.

A comparative study on the regeneration performance of traditional heating and heat localization methods

In this paper, we propose the minimum energy control input based on Hamiltonian strategy for the motor-table system. The energy equation of the motor-table system contains of the input energy, dissipation energy, potential energy and output energy, and includes electrical and mechanical energies. The methods of the minimum control effort (MCE), minimum input energy control (MIEC), minimum dissipation energy control (MDEC) and trapezoidal trajectory energy control are compared for the motor-table system. From the numerical results, we can find that the MIEC and MDEC approaches can obtain the same minimum input energy. Traditionally, the MCE approach was regarded as the minimum energy control in the previous study. However, we have demonstrated that the MCE approach is not the minimum energy control in this paper.

Changes in food quality and microbial composition of Russian sturgeon (Acipenser gueldenstaedti) fillets treated with low temperature vacuum heating method during storage at 4 °C

To simplify the complex calculation process of the optimal injection transformer turn ratio, a minimum error energy method is proposed in this article. According to the structure of multipulse rectifiers, the injection waveform when the rectifier without harmonics is analyzed, and the relationship between the input voltage and the injection voltage is studied. According to the relationship, the minimum error energy method is researched. To prove the accuracy of the minimum error energy method and improve the harmonic suppression ability of multipulse rectifiers, an improvable hybrid harmonic suppression method is proposed. Based on the structure of the proposed hybrid method, the optimal injection transformer turn ratio is calculated, respectively, by the minimum THD of input voltages and the minimum error energy method. The results show that the proposed minimum error energy method accurately solves the optimal turn ratio of the injection transformer with reduced computation. The proposed harmonic reduction method effectively suppresses the harmonics of the input side, which is suitable for high-power quality requirements.

Experimental study of springback behavior in incremental bending process

In the shipbuilding industry, the traditional manufacturing method for the complicated ship hull metal plates is line heating method, which is not only labor intensive but also inefficient. Considerable efforts have been taken to develop the new automated manufacturing processes at a reasonable quality, efficiency and price during the last few decades. This paper presents a novel flexible forming process called incremental bending to achieve complicated plates. In this method, the initial metal plate is supported by some rotatable hydraulic cylinders and the punches move according to the given path, which is decided by minimum energy method and springback compensation method, to achieve the final plate. Taking one variable curved metal plate as one example, this paper investigates the formability of this novel process based on experiment and numerical simulation. During the numerical simulation, the implicit method is used and the gravity of the plate is considered mainly for the automatic positioning of the plate during each springback process. Results show that the incremental bending process can achieve variable curved metal plates with good accuracy, high efficiency, and relatively small punch load. In comparison with the existing methods, the new process has greater potentiality in the ship hull manufacturing industry.

Thermal performance and energy characteristic analysis of multiple renewable energy complementary heat pump system

Sheet Metal Bending is a common process used in many heavy industry sectors such as shipbuilding. The traditional method is the so-called line heating, which is not only labor intensive but also inefficient and error-prone. This paper presents a new incremental bending method based on minimum energy principle. In this method, the steel blank is supported by an array of hydraulic cylinders with rotary head. This ensures the blank being properly lifted regardless of its shape and size. First, the incremental punching trajectory is generated based on the minimum energy principle. Assuming that the blank can be approximated by a number of strips and each strip is supported at its end. Then the strip can be described by a simply supported beam. According to the minimum energy principle, the punch location will be at where the error between the current shape and desired shape is maximum. Upon obtaining the punch location, the bending of the strip is also computed completing one incremental step. The new method is tested in a custom build incremental bending machine. Based on the experiment results, the method is successfully used in sheet metal bending. Comparing to the existing methods, the new method has a number of advantages, including simple, fast and highly energy efficient.

A thermo-elastic contact problem of functionally graded materials (FGMs) rotating brake disk with different pure brake pad areas under temperature dependent material properties is solved by Finite Element Method (FEM). The properties of brake disk change gradually from metal to ceramic by power-law distribution along the radial direction from the inner to the outer surface. Areas of the pure pad are changing while the vertical force is constant. The ratio of brake pad thickness to FGMs brake disk thickness is assumed 0.66. Two sources of thermal loads are considered: (1) Heat generation between the pad and brake disk due to contact friction, and (2) External thermal load due to a constant temperature at inner and outer surfaces. Mechanical responses of FGMs disk are compared with several pad contact areas. The results for temperature-dependent and temperature-independent material properties are investigated and presented. The results show that the absolute value of the shear stress in temperature-dependent material can be greater than that for temperature-independent material. The radial stress for some specific grading index (n = 1.5) is compressive near the inner surface for double contact while it is tensile for a single contact. It is concluded that the radial strain for some specific value of grading index (n = 1) is lower than other FGMs and pure double side contact brake disks.

Additive Manufacturing (AM) presents a revolutionary potential to produce complex components that are challenging to fabricate through traditional methods such as machining, welding or casting, often requiring sophisticated skills and extensive knowledge. Four major Japanese nuclear power plant suppliers have collaboratively launched a national project supported of the Ministry of Economy, Trade and Industry (METI) together data on AM materials. This project consists of three steps: verification of qualification testing methods for AM material manufacturing processes, acquisition of basic material characteristic data for additive manufactured sample, and confirmation of product verification methods using mock-ups. In step 2 of this project, data was collected on the temperature dependence of the material properties of additive manufacturing samples made from 316L stainless steel using laser powder bed fusion (L-PBF) and laser wire energy deposition (LW-DED). L-PBF was produced using four different batches of powder, equipment, and post-heat treatment conditions. The evaluation samples underwent two types of post-heat treatments: solution annealing (SA) and hot isostatic pressing (HIP) combined with solution annealing (HIP+SA). For the LW-DED additive manufacturing samples, tests were conducted in two conditions: as-built and SA. The tests on material properties evaluated the mean coefficient of thermal expansion, Young’s modulus, Poisson’s ratio, and thermal conductivity. It has been confirmed that the temperature dependence of material properties shows the same trend even in samples manufactured in different batches. Differences in Young’s modulus and Poisson’s ratio were observed based on the manufacturing direction, but no significant differences were found in the mean coefficient of thermal expansion and thermal conductivity, indicating that they are largely unaffected by the manufacturing direction.

Combined with the deformation characteristics of flexible retaining structure, the horizontal displacement calculation method of loess fill slope supported by frame prestressed anchors is proposed. Based on the minimum potential energy method, the analytical solution of horizontal displacement of slope under self-weight and additional load is derived, and the influence of soil parameters and supporting structure parameters on displacement is analyzed. The proposed calculation method is applied to a practical engineering and compared with the numerical simulation, which shows that the method is reasonable and reliable. The minimum potential energy method is clear in concept and simple in solving the horizontal displacement of loess fill slope supported by frame prestressed anchors. The calculation method proposed in this paper can be applied to the structural optimization design of loess fill slope supported by frame prestressed anchors, and further enrich the displacement calculation theory of slope supported by flexible retaining structure.

Three-dimensional sheet metal forming is one of the biggest challenges in the shipbuilding industry. The forming quality of the traditionally applied line heating method depends entirely on the skills of the technicians. Moreover, this approach is inefficient and error-prone. This calls for a need to develop new forming technologies that are easy to control and more efficient. In this paper, a novel forming method called heat-assisted incremental bending is presented. The minimum energy loading path of bidirectional curvature sheet along the direction of Gaussian curvature is adapted to deform the sheet metals with a convex shape surface. Besides, the auxiliary heating method and the auxiliary supporting are exclusively included in the forming process to improve the formability and accuracy. In this study, the convex-shaped sheet metal with large curvature is obtained along the two loading trajectories in two principal curvature directions, respectively. Results proved that using the minimum energy loading trajectory and including the auxiliary supports and heating can reduce the forming force to the greatest extent and effectively reduce the number of stamping points, thus improving the sheet metal forming efficiency and forming accuracy.

Given the lack of accurate and reliable discrete element simulation parameters to study the interactions between soft soil and soil casting components after ginseng land cultivation in Northeast China and the design of ginseng land-specific borders, this paper calibrates the relevant model parameters of ginseng soil using the Hertz–Mindlin with JKR contact model in EDEM to standardize the contact parameters between soil particles and between soil and Q235 steel in soft soil after cultivation in ginseng land. Taking the soil particle accumulation angle as the response value, a Box–Behnken design (BBD) was introduced to establish a regression model for the soil accumulation angle; the surface energy, static friction coefficient, rolling friction coefficient, and coefficient of restoration parameters were obtained, respectively, through the optimization of the model, at which time, the simulated value of the soil accumulation angle was 37°, which is a 4% relative error to the actual measured accumulation angle of 35.5°. Taking the sliding friction angle of the soil on the Q235 steel plate as the response value, the regression model of the soil sliding friction angle was obtained based on the BBD. The static friction factor, rolling friction factor, and coefficient of restitution between the soil particles and the Q235 steel were obtained, respectively. Based on the combination of these parameters, the simulated value of the sliding friction angle was 32.2°, which is a 2% relative error to the measured accumulation angle of 31.5°. To verify the accuracy of the optimized simulation parameters, field and simulation tests of soil-throwing components were conducted. The results show that the maximum relative error between the measured value and the simulation value is 5.6% and 3.4%. The error is within an acceptable range, and the simulation test and field test soil-throwing effects are the same, which verifies the accuracy and reliability of the reference soil parameter calibration. The results of the study can be used for discrete element simulation analysis of the interaction between ginseng loam and touchdown components and their structural optimization.

The feasibility of using microwave energy to dry and fire pre-cured geopolymers was experimentally demonstrated, and supported by analysis of published microwave dielectric data for geopolymers. Dielectric loss tangents and half power microwave absorption depths were calculated from published room temperature dielectric constant and loss values of various geopolymer compositions. The published data indicated that geopolymers would heat at room temperature with microwave energy. Several laboratory experiments were performed to test the heating behavior of sodium and potassium based geopolymer compositions. Experiments demonstrated more vigorous microwave heating with sodium geopolymers than with potassium geopolymers. Both compositions were dried in less than 10 minutes with pure microwave heating. Further heating with pure microwave energy resulted in non-uniform, rapid heating, or “thermal runaway”, with localized melting of the geopolymer. Hybrid microwave heating with susceptors resulted in uniformly fired geopolymers, without melting. INTRODUCTION Interest in geopolymers has accelerated in recent years due to their possible use in structural applications, dentistry, and hazardous waste stabilization, while maintaining a trivial environmental impact compared to traditional building materials. Many useful geopolymer compositions are fabricated by low temperature chemical reaction based curing processes. Some recent research has been reported for using microwave energy to enhance curing and drying . Other research has focused on high temperature firing of geopolymers, which can develop stronger glass-ceramic materials. In situations where heat is required, as in drying and firing, microwave energy provides an energy efficient alternative in place of conventional heating. Traditional radiant heating methods rely on thermal conduction to deliver heat throughout a material. Microwaves generate heat throughout the volume of the material, allowing faster, more uniform heating to occur. Volumetric microwave heating helps to overcome sluggish endothermic phase transitions, such as evaporation of water or decomposition of kaolin to metakaolin through the loss of hydroxides. Both drying and dehydration occur in the firing of geopolymers. In traditional heating, these reactions often require slow heating, as the endothermic reaction prevents heat from progressing into the product until the reaction completes first at the surface. Microwaves can generate heat throughout the part despite an endotherm. When microwave energy is the sole source of heat, a material that absorbs microwave energy will heat volumetrically, but cool from the surface. This situation creates an “inverse temperature profile” in which the sample is warmer inside and cooler at the surface during heating. This is opposite of traditional radiant heating where the material will be cooler in the center. In some materials, the inverse temperature profile can lead to thermal runaway – where the hotter center heats better than the cooler surface, and in turn heats better in the microwave. The thermal runaway can lead to molten centers with unfired surfaces. The most practical way to prevent thermal runaway is through hybrid microwave heating. Hybrid heating combines a radiant heat source with microwave energy, providing a uniform temperature profile throughout the sample as heat is generated at the interior while heat conducts from the exterior. This combination results in a uniform temperature profile and in turn improved properties. Two types of hybrid heating are susceptors, and Microwave Assist Technology (MAT). Susceptors function like wireless microwave heating elements, efficiently converting microwave energy into heat. When used with insulation thermal packages, susceptors can be used to fire ceramics even in standard kitchen microwaves. MAT is based on traditional kilns and uses gas or electric radiant heat, which is controlled independently of the microwave energy. MAT generally requires less microwave power, which reduces equipment costs and simplifies scale-up. Dielectric Properties The effectiveness of microwave heating for materials is generally determined by the dielectric properties at the microwave frequency. Two values represent the dielectric properties of a material, dielectric constant, e’, and dielectric loss, e”. Dielectric constant represents the ability for ions and dipoles within a material to polarize in response to an alternating electric field, and also determines the wavelength of the microwave energy within the material. The dielectric loss represents the degree to which an alternating field is converted to heat energy. From these two values can be derived the loss tangent, tan δ, and the half-power depth. A loss tangent between 0.01 and 1 generally indicates that a material will heat well with microwave energy. Below 0.01, materials tend to be microwave transparent, while above 1 materials become reflective. The half power depth measures the distance at which 50% of the microwave energy passing through a material is dissipated. The equations for loss tangent (1) and half power depth (2) are expressed below. In equation 2, DHP is the half power depth, c is the speed of light, ω is the angular frequency (2πf), and eo is the permittivity of free space.