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Analysis and optimization of terminal crimping dynamic characteristics based on HyperWorks

Introduction

at present, harness products have been widely considered as a large category of products with broad development prospects. Therefore, as an important equipment for wire harness end processing, the development prospect of terminal crimping machine is very broad

at present, there are manual crimping pliers, mechanical (flywheel) terminal crimping machines, pneumatic terminal crimping machines, hydraulic terminal crimping machines and fully automatic wire harness machines in the domestic market. Manual, pneumatic and hydraulic terminal crimping machines can only meet the needs of small factories or individuals with a daily output of less than a few thousand. Mechanical (flywheel) terminal crimping machines have unstable performance, high noise and bloated appearance, while fully automatic wire harness machines are only suitable for those large wire harness enterprises, but there is no suitable choice for small and medium-sized enterprises with a daily output of about 30000-50000. In order to overcome the gap in the current market, it is necessary to develop terminal crimping equipment suitable for small and medium-sized enterprises, which is low-cost, efficient and energy-saving, easy to operate, safe and reliable, to meet the needs of this group. We take this as our goal, as a new design starting point, that is, the starting point of innovation

1 finite element numerical simulation of terminal crimping machine

Optistruct, a structural analysis and optimization tool included in HyperMesh, is the most mature and widely used optimization software today. Its excellent optimization technology can provide a complete and feasible solution for the optimization goal of products. Optistruct has a fast and accurate linear finite element solver, and has strong and efficient concept optimization and detail optimization capabilities, Yes, Craig mackiewicz, the industrial design manager of Altair company, said at the annual meeting of the American Association of industrial designers held in Austin on August 13 (1) 6: "We consider using other materials in various stages of design. The optimization process can optimize the static, modal and buckling analysis. The effective optimization algorithm allows hundreds of design variables and responses in the large model.

1.1 solid model simplification

the terminal crimping machine is composed of several parts, and each part is composed of several parts and small parts. When establishing the finite element model, these complex It is impossible to take all factors into account and make the mass matrix and stiffness matrix of the finite element model completely consistent with the reality. Therefore, it is necessary to effectively simplify the solid model of the terminal crimper. When simplifying, the simplified model of the terminal crimping machine should be established according to the analysis type and purpose, and only some leading factors should be considered. The principles are as follows:

1) bosses, screw holes, pin holes, rounded corners, etc. of unimportant structures should be ignored

2) for some auxiliary equipment, mass blocks can be added at relevant positions

3) parts such as outer casing and baffle plate, which are only 1.5mm thick, have little impact on the mass matrix and stiffness matrix of the model, and can also be ignored. The simplified model is shown in Figure 1

Figure 1 simplified model of terminal crimping machine

1.2 establishment of finite element model

in order to better reflect the actual situation, three-dimensional solid elements are selected to describe the structure of terminal crimping machine body. In finite element analysis, there are two kinds of three-dimensional solid elements: hexahedral element and tetrahedral element. Because the hexahedral unit requires regular structure when dividing, and the terminal crimping machine is a complex component, it is difficult to divide the hexahedral body, and there is no software that can automatically divide the hexahedral body with ideal quality. When using tetrahedral elements to analyze three-dimensional structures, the element division is very flexible, which can approach more complex geometric shapes, and the automatic division function of tetrahedral structures in various software has been quite mature. Therefore, in this paper, HyperMesh is used to generate tetrahedral 3D solid elements

since the materials of all parts and components of the terminal crimping machine are different, the materials of the base, left and right side plates and so on are Q235A, which have tended to be more humanized services, the materials of the bearing seat and lock nut are 45, and the materials of the crimping spindle are 40gr, so their elastic modulus and Poisson's ratio are different, so the parameters of the established materials are shown in Table 1: Table 1 table of material parameters of the main parts of the terminal crimping machine

in addition, Load simulation is an important part of structural finite element analysis, which is directly related to the authenticity of the calculation results. The load on the frame is: 1) the self weight of the frame. The self weight of the frame can be regarded as the uniformly distributed load distributed to the corresponding nodes of the structure, and can also be applied in the way of density and gravitational acceleration. This paper uses the solver of the software to apply density and gravitational acceleration to the frame model, reflecting the influence of gravity. 2) The maximum working load of the terminal crimping machine. Under the action of the theoretical maximum load of 24.5kn, the auxiliary plate of the bottom plate bears the vertical downward force, and the average surface pressure is 2.2MPa. The side plate of the fuselage is subject to bending stress because it is connected with the body up and down. In the finite element method, the internal or external forces are transmitted by the joints, and the load items in the overall stiffness equation are joint loads. Therefore, when the element is subjected to uniformly distributed load or other non nodal loads, it must be shifted to the node, that is, the non nodal load must be converted into the equivalent concentrated load acting on the node

after referring to the above material table and pre adding the mass blocks of various auxiliary equipment, in order to approximate the actual installation of the terminal crimping machine, all the three degrees of freedom of the unit nodes in contact with the bottom plate and the ground are constrained

2 side plate optimization process

2.1 side plate size optimization (determine the thickness of the side plate)

give the design space, and load forces and constraints according to the actual situation. The optimization problem is described as follows:

Objective: minimum volume

constraint: according to the accuracy of the crimping terminal required, the maximum displacement in the Y direction of the point participating in the pressing is required to be 0.1 mm

design variable: thickness of the side plate

part shape design space is shown in Figure 3:

Figure 3 part shape design space

size optimization result

after optimization, The displacement in the Y direction at the pressing position meets the requirements:

Figure 4 the displacement in the Y direction at the pressing position after optimization

Figure 5 the stress diagram after optimization

Figure 6 check the optimized side plate thickness

from Figure 6, it can be seen that the final optimized structure of the side plate thickness is 1.29e+01mm

2.2 topology optimization of side plate (determine the shape of side plate)

the optimization problem is described as follows:

design objective: minimum volume

constraint: the maximum displacement in the Y direction of the point participating in the pressure is 0.1mm

design variables: material distribution in space (the thickness of side plate is tentatively determined as 15mm)

2.3 three dimensional graphics modification

according to the optimized results and considering the actual installation location on site, Regenerate the three-dimensional graphics as follows

after optimization and before optimization

Figure 10. Regenerate the three-dimensional graphics

2.4 check

for the generated graphics, re analyze whether the maximum displacement in the Y direction of the point participating in the pressing position is less than 0.1mm

Figure 11. Deformation of the optimized part under the same conditions

Figure 12. Displacement in the Y direction of the pressing position

it can be seen from the above figure that the displacement in the Y direction of the pressing position is 9.059e-02, Meet the requirements

therefore, the parts designed based on the results of the size optimization and topology optimization of the side plate fully meet the requirements

3 finite element modal analysis of the frame

the motor speed of the crimping machine is R/min, so the working frequency of the motor is Hz, and the fastest working frequency of the terminal crimping machine is 120 times/min, so the working frequency of the press is Hz. In fact, the natural frequencies of each stage of the terminal crimping machine frame are far greater than the working frequency, so the optimization of the dynamic performance of the terminal crimping machine is to improve its natural frequency as much as possible, Make it further away from the working frequency of the terminal crimping machine and the frequent working frequency of the motor

evaluation conditions for modal analysis of terminal crimping machine:

1) the elastic modal frequency of terminal crimping machine should avoid the frequent working frequency of motor

2) the low order natural frequency of the terminal crimping machine should avoid its own working frequency

3) the vibration mode of the structure should be as smooth as possible to avoid sudden changes

carry out modal analysis on the whole machine, and get the first four natural frequencies (Figure 3) and the corresponding vibration modes of each order (Table 2). The gray line in the legend is the initial outline:

first order mode, second order mode, third order mode, fourth order mode

Figure 13 diagram of the first four vibration modes of the frame

from the above vibration mode analysis, we can see that: 1) the frame structure not only has bending deformation in the front, rear, left and right directions in the low order mode, Moreover, there is overall distortion, which will not only affect the working accuracy of the terminal crimping machine, but also aggravate the wear of the connection position between components; 2) The increase of local mechanism stiffness may increase the natural frequency of the whole frame structure, and the chance of local distortion should be reduced; 3) The distortion and deformation of the tail of the frame structure are relatively severe, and the structural stiffness of the tail is relatively insufficient, resulting in an increase in the probability of the maximum deformation at the upper end of the whole machine, which needs to be further strengthened

4 optimization of frame structure

in order to strengthen the modal performance of the overall structure of the terminal crimping machine, it is decided to make the following improvements:

1) in order to reduce the probability that the oil taken due to local distortion should be highly thin lake oil without impurities and dust, and the natural frequency of the overall structure should occur, the suspended part of the rear transmission part of the terminal crimping machine should be reconnected with the body for reinforcement

2) in the fourth mode, the upper rear end of the side plate is directly embedded in the transmission parts, so a bearing plate is redesigned at the weakest position of the upper rear end of the two side plates, so as to reduce the occurrence of local distortion

3) for the auxiliary structure, try to install it in the middle of the side plate of the fuselage, which can also strengthen the structural rigidity

4) if possible, try to increase the table height of the bottom plate to increase the contact area with the side plate

5 conclusion

from the results of optimization, the frequency of the improved structure is significantly higher than that of the previous one, and the maximum relative deformation is greatly reduced, and the first-order natural frequency is increased by 295hz on the original basis. It shows that the overall dynamic performance of the mechanism is indeed improved through early analysis and later optimization. So far, the design of the terminal crimping machine has been basically completed. After the production process, its performance has been tested, and all performance indicators have met the design requirements. At present, the product has been successfully put on the market. If the design is poor, it will bring direct economic benefits to the enterprise

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