Investigating the deterioration of non-isotropic TWB sheets under the hydroforming process

Master's Thesis in Mechanical Engineering (applied design orientation)

Abstract

Investigation of the deterioration of non-isotropic TWB sheets under the hydroforming process

In this research, the plasticity and deterioration of TWBs in both same-sex and non-homosexual groups have been investigated. During the research, four different metals of aluminum alloys 6111-T4, 5083-H18, 5083-O and dual-phase steel DP590 and two spherical tensile tests and uniaxial simple tensile tests were used. Then we have investigated the new forming method called hydroforming on non-homogeneous TWBs. In all the modeling done, the Abaqus finite element software and the form-limiting model have been used to predict the deterioration of the sheets, and the behavior of the base sheets has been assumed to be non-isotropic. Since the study of the formation of non-homogeneous TWBs is very complicated compared to homogeneous TWBs, and the deformation and collapse of the base sheets are less predictable in them, therefore, in this research, we focus more on non-homogeneous TWBs and the results are expected to be very significant.

Introduction

In recent years, the demand for weight reduction as well as the use of metal sheets with high resistance such as aluminum, magnesium and iron alloys, due to environmental and economic reasons, is constantly increasing. This demand can be clearly seen in the automotive and aerospace industries. Automobile factories try to build cars with reduced fuel consumption and pollution, which is sometimes required by law. In addition to the savings that result from less fuel consumption, another factor is considered for lighter devices, and that is the reduction of damage to the environment. Balancing the environment is becoming more difficult day by day, and this is due to the use of new technologies without considering their environmental costs.

The possibility of having a diverse distribution both in terms of materials and geometric properties in a part can provide optimal distribution of materials in that part and cause a significant reduction in weight and cost. For example, a sheet with non-uniform loading conditions can be made of two parts, each of which has a different thickness or material, so that the thicker (stronger) part is placed in the area with more loading and the thinner (weaker) part in the area with less loading. [1] TWBs as a type of [2] TMBs have been used in the automotive industry for about two decades, but this technology has rarely been used in the aerospace industry. Therefore, the aerospace industry can also use the advantages of this technology like the automobile industry. Among the applications of TWB in the automobile industry, the following can be mentioned: main chassis, panels around the body, front and rear bumpers, reinforcements inside the doors, first and second pillars, rails under the engine, car floor, wheel housing and so on. One of the applications of TWB in the aviation industry is the construction of aircraft shells, pilot inspection hatches, etc. pointed out. The main idea of ??the TWB concept was found from the fact that the sheets [3] used in the production of various parts, both for air and ground applications, may have different thicknesses, materials, and smooth surfaces. Therefore, TWB is a way to connect these heterogeneous sheets. A typical TWB consists of a number of sheets that may be different in terms of mechanical properties, thickness and surface coating, and are welded together before forming. When a TWB is created, the designer is able to use sheets of different strengths where the desired properties are desired. This process of welding and forming sheet parts will allow us great flexibility in product design, structural strength and improvement of the impact behavior of that product. In addition, significant savings in the final weight (due to the reduction of reinforcements and reduction of overlaps during assembly spot welding), the total price, tools and equipment required, assembly and loading, construction costs (due to the reduction of tension molds, reduction of spot welding at the bottom of the hand) and reducing the discarding of sheets) and at the same time, the strength of the structure will be maintained due to the increase in strength [4] during laser, wire and friction welding, and along with that, the dimensional accuracy and corrosion resistance will increase.Weight reduction due to the use of TWB in the automotive industry is usually estimated between 6-11%. Optimum distribution of materials in aerial structures is even more important than automobile manufacturing because it not only reduces the weight of the parts themselves, but also causes the use of smaller wings and smaller engines. which will ultimately cause a significant reduction in overall weight. In addition, TWB technology will eliminate the need for machining aluminum parts and reduce the amount of material and energy required for machining. High-strength aluminum alloy [5], which is widely used in the production of structures in the aerospace industry, does not have the ability to be welded and is very sensitive to high welding temperatures. This high temperature affects the thermal behavior of aluminum alloy deposits and disturbs their microstructure. Another point is the difficulty of self-welding of heterogeneous alloys, which limits the flexibility of TWB. Most of the sheets used in TWB, due to extrusion [6] or rolling [7], have non-isotropic properties in the sheet plane, so that the sheet strength is different in the direction of rolling and perpendicular to it. This non-isotropy will be very effective in forming later in a way that it is very effective in the shape of the yield surface and strain distribution during forming. For this reason, it is very important to consider the non-isotropy of the base metals and the weld line and the heat-affected region [8], as well as the rolling direction relative to the weld line and loading. In addition to that, in the construction of TWBs, the two sheets used may be different in terms of type and thickness, and this makes both the welding process and the forming process very difficult due to the stress concentration.

The importance of forming metals with the help of fluid pressure is increasing significantly in recent years, and this is due to the many advantages of this method compared to other common methods. These advantages include: better shaping and malleability, improving surface smoothness, improving structural strength, the ability to shape models and complex geometries, uniform distribution of torque, reduction of parts and tools to perform the process, and as a result, less operation and cost, less secondary operations, less waste, price reduction, especially in asymmetric objects, reduction of spring return [9]. But this method also has disadvantages, which include: long cycle time for each part, need for expensive devices, and lack of basic knowledge for designing the process and tools. Therefore, according to the information mentioned above, the use of this method in the forming of TWBs can be evaluated as a potential for increasing the forming height.

The ductility test in TWBs is influenced by various parameters such as material flow phenomenon [10], material flow control, stress and strain distribution, relative thickness of two sheets and the spring return behavior of each sheet. Therefore, the spherical tensile test [11] will be used as one of the two-dimensional tests on TWBs in this research, and by means of it, the place and time of the first deterioration [12] will be investigated. In order to estimate the final limit of forming in each forming process, a deterioration criterion is needed, which is obtained directly from the experiment or by using existing analytical equations, this final limit is predicted. If any of these methods are used, the beginning and progress of the first deterioration can be predicted by comparing the criterion with what happens in the modeling. Therefore, in this research, we will first investigate the deterioration of TWBs by using a laboratory standard known as FLD and geometric modeling of samples of TWBs with the stipulation that the sheets used are of the same type. As mentioned, more accurate modeling of different areas of TWB as a structure and application of accurate metallurgical and mechanical properties will improve predictions. Therefore, in this research, in order to confirm the applied finite element method, we will first examine homogeneous TWBs with three different types of welding modeling, and then by changing the yield hypothesis from isotropic to non-isotropic for the base plates, we will evaluate its effect on the prediction accuracy in the modeling. Then, according to the point of reference about non-homogeneous TWBs whose deformation is slightly different than homogeneous samples, we will evaluate non-homogeneous samples from different base metals from the homogeneous metals used in the group of homogeneous TWBs, the behavior of the spherical tensile test in non-homogeneous TWBs. Finally, according to the potentials mentioned in the hydroforming method, we will examine the effect of this method on the formation of non-homogeneous TWBs.