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Simulation support for forming development

Abstract: for more than a decade, forming and connection processes such as undercut connection and punching riveting have been the application objects of finite element calculation. At present, for example, the development of new and complex geometric shapes of semi hollow punch riveting connection, or the need to further develop the connection process such as bite riveting, so that it can be combined with the bonding process, has made a considerable contribution to the development of these technologies

for more than 20 years, the body has been designed with digital technology. The purpose of simulation is to master the processing process and identify the weak links in strain under different types of loads. When manufacturing a single component, as far as its processing process is concerned, the forming process has been paid attention to for a long time. Nowadays, finite element software such as AutoForm and PAM stamp used in sheet metal forming are indispensable, so that the feasibility of new structures can be evaluated before expensive experiments on deep drawing dies, such as possible shrinkage and wrinkling. For more than ten years, forming and connection processes such as undercut connection and punching riveting have been the application objects of finite element calculation. Through the three-dimensional strain state and deformation state to be handled, the forming connection process can be included in the solid forming process. The finite element software used, such as SuPerform and deform, in addition to describing the properties of materials with the theory of elasticity, is often used to describe other physical effects such as temperature effects and structural changes, and is widely used in extrusion processes. Just after the turn of the century, forming connection technology has made important progress on the basis of virtual technology. However, especially when the process development based on experiments is very expensive - for example, the development of a new geometric configuration of half empty punching and riveting turns to the use of finite element tools. This trend will continue with a strong momentum and strongly stimulate the vitality of development

the geometry of the punching and riveting die affects the function of the component

the following three examples show that it may be very time-consuming and expensive to solve the problem without using the finite element method. The geometry of the punching and riveting die has a great influence on the quality of the connection, and thus affects the function of the component. For example, the automobile manufacturer () of BMW Group has clear regulations on the geometry of riveting, and it is difficult to specify the geometry of punching and riveting edge, because dimensional tolerance is inevitable in production technology during punching and riveting. Therefore, there is a problem that needs to be discussed. Whether such tolerance will affect the quality of the connection, such as the side recess or the height of the side recess during riveting

it is impossible to affect only one parameter in actual research, because changing one parameter will lead to changes in other parameters. Therefore, for example, it is difficult to manufacture two kinds of rivets with different edges and the same hardness. Here, simulation technology has obvious advantages, and there is no difficulty in solving this problem, because people can accurately adjust the selected parameters. According to the calculation, the whole forming connection process can be analyzed and the early mechanical separation process of the material can be clarified under the condition of small rivet tip radius. The calculated connection structure can well reflect (describe) the results obtained through the test. On this basis, through digital simulation, the relationship between parameters can be clearly identified at a faster speed, without the tolerance problems caused by the technological process in the laboratory, and the pre standard can be drawn up

the stress in brittle parts can only be analyzed by finite element

as we all know, the edge geometry that can be achieved in production technology deviates from the ideal radius. For the multi-stage forming of semi hollow riveting, the die affects the free flow of workpiece material at the bottom of the rivet. Therefore, it is meaningful to pay attention to the whole process of multi-stage impact, riveting and connecting loads. Because the heat treatment after impact greatly changes the internal stress and cold work hardening state. Therefore, production and riveting can be carried out separately. When reaching the set working condition, in addition to the geometry, the internal stress and cold work hardening state must also be considered, so that the shear condition can be predicted by 3D model, for example, so that the strength eigenvalue and stiffness eigenvalue can be directly predicted

for semi hollow punching and riveting, the geometry of the die is a combination of a series of geometric parameters. When machining brittle materials such as aluminum alloy die castings or magnesium, an important aspect is the tensile stress, which is produced due to local creep on the surface of the blank under the action of the die during the connection process

requirements for smaller cracks (e.g. based on a smaller die depth) and better formed rivet connections (e.g. based on a deeper die depth) are often very different requirements

in the process of connection, controlling the stress in brittle materials can only be achieved by finite element tools. The vault at the bottom of the die supporting the rivet kingpin is used to simplify the geometry and make multiple use of the die for different connection tasks. Therefore, for the purpose of research, only the flat top mold is used here. In order to test the simulation results, it is often necessary to compare the test results. Other edge conditions, such as the stress-strain curve of rivet materials and blank plates, are prerequisites. By using digital simulation, the local tensile stress can be minimized by changing the geometric parameters of the die. The female die optimized in this regard has been adopted on the new BMW X5. The diameter, depth and radius of the concave bottom of the die should be adapted accordingly, so as to minimize the stress in the bottom of the rivet and the casting

the biting riveting process can be well combined with the bonding process

during punching riveting bonding, an air gap will be formed due to the suction effect of the unhardened binder, which may cause corrosion problems in the future use of components. Therefore, sealing is necessary. This is the main reason for developing new undercut riveting. In the process of many tests, the relationship between the digital image of the connection and the geometric parameters of the rivet can lead to the optimization of a connection in many aspects. For example, the optimization of the sharp corner radius of the rivet edge. In this way, a close relationship between the continuous reduction of the side concave of the riveting forming of the biting pressure testing machine, also known as the electronic pressure testing machine, with the increase of the sharp corner radius of the rivet edge is obtained. Therefore, the best values of flat bottom thickness and side recess should be achieved through the adaptation of rivets

compared with semi hollow punching riveting, the average gross profit rate of domestic coated paper with nip riveting is ⑵ The 59% bonding technology has the following advantages: it has good joint use with adhesive (it can avoid typical air gap and better crowding effect); As the top die, the flat anvil has the advantage of low price compared with the forming die; There is no coaxiality requirement (this is an important requirement for bow connecting pliers with large overhang distance); It has good cyclic load intensity and no adjustment cost; Minimum die wear; High process reliability; Simple cleaning and painting; Small equipment operation height (easy access to equipment during connection operation and the achievements of Minnesota team at Cornell University may change the above problems. In a complete structure, the equipment arrangement distance is narrow) and crack free processing of brittle materials. Compared with semi hollow punching riveting, the following limitations should be paid attention to:

◆ small process range (for plates with thinner thickness and the same thickness, the paired matching of thickness is limited)

the two clamps separate and stretch the specimen at a fixed speed

◆ higher connection force and smaller rivet head tensile strength

◆ for brittle materials, a larger edge distance

as a conclusion, when inspecting the formed connection process, The digital description of forming and connecting process is an important tool for effective analysis and optimization. It is especially beneficial for expensive connection processes, such as the development of new rivet geometries. Other possible applications are to verify the key parameters in the connection process and thus carry out reliable hypersensitivity analysis

at present, the influence of adhesive has not been considered in the simulation. In this regard, it remains to be studied. (end)

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