Analysis and Simulation of the hottest assembly mo

Analysis and Simulation of assembly model

in the assembly process, there are many interactions between parts, from simple contact to friction to tension/pressure/torque action. In addition, there are many ways and methods to assemble parts. Fasteners (such as bolts, studs, screws and pins) can be used for connection, as well as spot welding, riveting and bonding

the mathematical model can clearly show various contour characteristics of components, which will help users understand more easily how multiple parts are assembled together and how different parts interact in a complex assembly model

modeling is one of the most critical steps in assembly simulation, because it means quickly determining the position of all parts and accurately defining the interaction between any two contact parts. Then, automatic detection tools play a role in the pre/post-processing of the simulation system, such as femap, which is a visual tool to determine which parts are in contact and provide all contact conditions. The "visualization" here can show that the forging of 12%cr waste rotor is changed into the surface to surface contact of consumable electrode, and it can also show the contact and cooperation relationship between parts and components. By referring to an appropriate attribute definition, femap can ultimately simplify various connection methods as general linear contact or bonding. This simplified process can be automatically completed when performing contact detection, or added when the existing definition can be easily and changed. In addition, new contacts can be manually defined from scratch. The contact condition can be applied to the geometric model before lattice, and also to solid parts or hollow shell parts themselves

Figure 1 general connection lattice model

Figure 2 NX NASTRAN bonding model

linear contact

for the numerical simulation of surface contact problems, harsh solutions generally require a nonlinear method to represent contact and other potential nonlinear problems, such as large deformation problems and material properties that may change nonlinearly with environmental conditions. However, if the surface contact can be controlled within a limited range (small deflection and "linear" material), then "linear contact" is an absolutely simpler solution on the basis of ensuring the accuracy of simulation results

for example, the NX NASTRAN solver adopts the technical scheme of linear static analysis for the calculation of surface to surface contact, and uses the same technical method to search and detect the interaction between assembly contact surfaces. Therefore, users can use NX NASTRAN to conduct complex motion simulation such as sliding analysis with friction resistance

bonding connection

bonding can be used to assemble parts, no matter whether these parts are made of the same material or different materials, as long as these parts share the same connection interface

Figure 3 model of bonding contact（ σ Max = 50500 lbf/in 2)

different results of linear contact and bonding

of course, users sometimes need to accurately select the corresponding assembly model to make it leave a different impression on this kind of material, so as to more accurately represent the real situation. The user's choice of bonding rather than linear contact will completely change the load distribution of the model and the assembly contact results in the model

for example, for a simple assembly model of lifting lug and lifting lug pin, if linear contact and bonding connection are selected respectively, in the linear contact analysis results, the force between them will only occur on one side of the contact surface between lifting lug and pin shaft, and there will be an untouched "notch" space on the other side. Using the bonding model, a completely different stress distribution is obtained

Figure 4 model of linear contact（ σ Max = 78800 lbf/in 2)

spot welding and fasteners

NX NASTRAN, the suggestions for assembling parts and overhauling this method are also included in the legislative plan. Spot welding and fastener connection are generally modeled by a connection unit, which can connect two surfaces, units or points. The grids of the connected surfaces are not required to be consistent, which gives greater free space when assembling different parts. Generally speaking, the stiffness of the connection unit depends on the diameter, length (such as non spot welding) and material properties of the weldment

bolted connection

when the parts to be assembled are connected with bolts, the torque generated when tightening the bolts will become the preload of the bolt shaft. Usually, the ideal situation is to analyze the bolt according to the preload that has been set or generated, but this isolated preload situation may have little practical application value, and the user may also want to obtain the stress analysis results. In the traditional finite element analysis, the equivalent thermal load is used in the modeling process of bolt preload. The result obtained by this method is only an approximate result. In fact, the assembly model containing multiple bolts also requires the calculation of the interaction between these bolts. Nx NASTRAN can solve these problems automatically and simply, because the bolt itself is represented as a beam element model, and the bolt preload is used at the end

Figure 5 bolt preload assembly model

increasingly simple assembly analysis

finite element analysts can now more easily obtain functional characteristics such as linear contact, bonding and other connection methods. Technological advances have advanced the availability of this feature and ensured its accuracy. With the support of pre/post-processing tools for modeling and visualization, the task of establishing assembly models and conducting simulation analysis has now become very simple. (end)