The 1st gear is an important part of the motorcycle drive system, as shown. The outer surface of the part is an involute tooth, the inner hole is a spline tooth, and there are four shaped teeth on each end. The material is 20CrMoT, i surface carburizing and quenching treatment. The key of the forming process is the precise volume forming of the claws at both ends. For this purpose, computer numerical simulation analysis is carried out, and the forming process is optimized by using the best volume forming analysis software DEFORM3D.
2Three-dimensional geometric modeling and technical processing Through the technical process analysis of the part structure, the closed-type warm-finishing forming process is used, and the forging piece is refined. As shown, the eight shaped claws at both ends are directly formed by warm precision forging, no longer carried out. Any mechanical cutting process. The involute profiles of the spline teeth and the outer circle of the inner bore are obtained by subsequent machining. In the volume forming process, the rigid-plastic finite element numerical simulation technique is adopted because the elastic deformation of the blank is much smaller than its plastic deformation.
2.1 Mold and Blank Geometric Model In volume forming, the surfaces of the mold and the blank are generally composed of curved surfaces. The DEFORM3D software does not have a three-dimensional modeling function. For this purpose, a special CAD geometric modeling software Pro/E is used to complete the geometric model of the mold and the blank. When molding, the blanks and molds should be on the same axis and converted into STEL files, read through the relevant interface of DEFORM, and analyze the deformation process. The 3D geometric model is shown. The blank size is 34.5mm36.2mm.
2.2 Mold surface description The mold stiffness is much larger than the blank. In the numerical simulation, the mold is a rigid body. Therefore, the description of the mold is mainly the processing of the mold surface information. There are four commonly used parsing formats, point cloud formats, parameter surface formats, and grid formats. In the mold surface description method, the analytical format has a lot of limitations; the point cloud format relies on a large number of spatial data points, which not only has difficulty in data collection, but also has large storage capacity and low computational efficiency; the parameter surface format has good reliability and high efficiency, but There is still no uniform data standard, which affects the compatibility of the contact solution algorithm; the grid format is similar to the finite element mesh, and the mold surface is approximated by a triangle or a quadrilateral, so that any complex surface can be described without limitation, including vertical surfaces and large Curvature surfaces, grid methods are the most widely used. This paper uses a grid format to describe the cavity of the gear shaping precision forming mold.
2.3 Contact Search and Contact Constraint Contact Point Search is important for volumetric forming such dynamic contact problems. Using a simple, practical, and reliable main flapping algorithm, the mold is defined as the main surface, and the deformed body is the slave surface. In the contact search process, slave nodes on the surface are not allowed to penetrate the main surface, while the master node on the main surface is allowed to penetrate the slave surface, so contact search only needs to be performed between the slave node and the master surface.
The contact gap band is set to 0.0001 mm. When the blank node falls within the gap band, the blank is considered to be in physical contact with the mold, and a contact constraint treatment is required.
During the forming process, as the billet continues to deform, some of the boundary nodes in the free state may be constrained by contact with the mold. This constraint is reflected in the contact mold and the blank to meet the non-penetration constraint, that is, the contact point must It slides tangentially along the surface of the mold and is rubbed by the interface, so it cannot penetrate into the mold. On the other hand, as the deformation progresses, the nodes that originally contact the surface of the mold may become free nodes from the surface of the mold, and the interface constraints are removed for the demolded nodes, that is, the sliding constraints and the interface friction are released.
The direct constraint processing method based on iterative solution is used to track the motion trajectory. Once the contact occurs, the motion constraints (and normal pressure and tangential friction) required for the contact are directly applied to the contact node as boundary conditions.
2.4 Friction model The constant friction constraint treatment is to use the friction work generated by the contact surface of the unit as a correction to the energy functional, and the interface friction effect is reflected in the form of friction functional, which is more used in numerical simulation of volume forming.
The normal friction model is:
Fz=mk where: fz friction m friction factor, m = 0.3k yield stress 2.5 parameter selection forming temperature: 820! Forming speed: 16mm/s; maximum displacement of upper mold: 100mm; forming material: 20CrMoTi.
3 Numerical simulation and result analysis The finite element mesh is used to divide the blank by the tetrahedral element. The geometrical dimensions of the part are not large, but the deformation is large. In order to ensure the accuracy of the simulation calculation, the mesh distortion is delayed and the unit is finely divided. Due to the asymmetry of the formed parts, the overall model was taken for simulation analysis.
The equivalent stress at the end of the part forming is as shown. The maximum value of the equivalent stress is at the flash edge of the part. The higher the flash, the greater the stress, thus preventing the flow of the material, causing the metal to fill the mold cavity, etc. The force is also large at the root of the root of the part, and the smaller the fillet, the greater the stress. At the same time too small a radius of the fillet, there will be folding defects.
The load curve of the forming process is roughly divided into four stages: in the first stage, the deformation force rapidly rises from 0 to about 250 kN from the time the upper mold contacts the billet to the complete contact with the billet; the second stage begins with the upper mold completely contacting the billet. Until the upsetting of the cylindrical part is basically completed, the deformation resistance remains basically unchanged in the larger stroke, increasing from 250 kN to about 450 kN; the third stage, the basic forming of the claw and the final forming of the cylinder, the stroke Not much, the deformation resistance increases rapidly, from 450kN to 850kN; the fourth stage, the final stage of formation, the stroke is small, the deformation resistance increases sharply, from 850kN to 2200kN, which is slightly lower than the theoretical calculation value of 2500kN.
4 Process experimental research According to the simulation analysis results, the blank size of the blank is 34.5mm36.2mm, and the maximum deformation resistance is 2200kN. Under the given process parameters, no defects are formed in the part forming. To this end, a simple forming mold was fabricated, and a process experiment was carried out on a 3150 kN hydraulic press. The results were in agreement with numerical simulations to produce formed parts.
5 Conclusion Using DEFORM3D finite element analysis software to simulate metal flow law and force energy relationship, can effectively help designers optimize process parameters and mold design, reduce the pre-development cost of molds, reduce the workload of designers, and thus help shorten The design and development cycle of the mold. On the basis of simulation analysis, this project carried out mold design and processing and manufacturing, using combined convex and concave mold structure and electric spark reset repair processing, which improved the actual service life of the mold and achieved good economic and social benefits.
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