Establishment of finite element model for forming process scheme of spur gear

The numerical simulation analysis is based on the assumption of rigid plastic finite element model. Properly combine and simplify the die structure, complete the three-dimensional solid modeling with CATIA software, convert it into STL file, export it, and then import DEFORM-3D software to establish the finite element model. Divide the 1 / 23 unit of die and spur gear blank for simulation analysis. The main simulation parameters are set as follows:

① Material selection: the material of spur gear is the most commonly used low-carbon alloy gear steel 20CrMnTi, which corresponds to American brand material aisi-4120 [70-2200f (20-1200c)] in DEFORM-3D material library. When the ring blank of spur gear is cold extruded to form tooth shaped parts, the metal blank of spur gear has large plastic deformation, the elastic deformation of formed parts can be relatively ignored, and the material can be regarded as rigid plastic material.

② Definition of temperature and press speed: cold extrusion forming is carried out at room temperature. The straight cylindrical gear blank does not need heating, and the die does not need preheating. The straight cylindrical gear blank and die temperature are set to room temperature of 20 ℃. By default, the lower die remains fixed, and the extrusion speed of the upper die is defined as 20mm / s.

③ Local mesh refinement: when the ring blank of spur gear is cold extruded to form the inner and outer teeth, the large deformation area of spur gear blank is concentrated in the annular area corresponding to the diameter of outer tooth top circle and tooth root circle. Local mesh refinement of this annular area can not only improve the accuracy and accuracy of simulation, but also greatly shorten the calculation time. Firstly, the blank of spur gear is automatically divided into 80000 meshes by finite element software, and then the outer tooth forming ring area of spur gear blank is refined.

④ Constraint boundary: both the spur gear blank and the die model are axisymmetric rotating bodies. When the spur gear blank is extruded, it is in an axisymmetric stress state, so it can be divided into 1 / 23 of the die and spur gear blank to complete the fine simulation. The blank of spur gear is a plastic body. The boundary between the two sections needs to be defined as the boundary of plastic deformation zone and rigid zone.

⑤ Definition of volume compensation and mesh redrawing: when the tooth profile of spur gear blank is formed, severe deformation is easy to produce mesh distortion, and volume loss will occur in the iterative calculation process. Volume compensation and re meshing are required for calculation.

⑥ Definition of contact and friction: the forming process scheme 2 and scheme 3 adopt the continuous extrusion method of “part pressing part” to form the external teeth. The contact relationship is complex. It is necessary to correctly set the contact relationship between the two spur gear blanks and the upper and lower dies, as well as the contact relationship between the two spur gear blanks, otherwise the iterative operation cannot be carried out, resulting in non convergence of the operation.

The type of shear friction is selected for the contact friction between the spur gear blank and the die during cold extrusion. The friction factor of the cold extruded spur gear blank is generally set to 0.12 after lubrication. The contact and friction definition settings and their effects are shown in the figure.

⑦ Step definition: select the constant stroke control incremental step. Generally, the single step is set to 1 / 3 ~ 1 / 10 of the minimum grid element size of spur gear blank. The minimum mesh size of spur gear blank is 0.462mm, the step size is set to 0.1mm, and it is saved every 10 steps.

According to the three cold extrusion process schemes designed above, the ideal rigid plastic finite element model is established respectively.

Scroll to Top