تجزیه و تحلیل عناصر محدود درباره بهبود فرایند شکل گیری چندگانه مورد موتور یک اتومبیل

Generally, an automobile has about 10 motors for actuators that are equipped with a cooling pan, air-conditioner, and door lock system. The shape of the motor-case is directly related to the noise and vibration of the components, so various forming processes such as deep-drawing, multi-step, and multi-forming, were developed to get higher accuracy and productivity. The multi-forming process is used in this study because it has the best productivity compared with the other forming methods. The simulation technique of motor-case forming was developed to reduce the developing time and trial-error. The manufacturing processes of a motor-case consist of plate blanking, forming, and sizing. This study is focused on the core design of the multi-forming process. The blanked plate and forming dies are modeled to two- and three-dimension and analyzed by the finite element method using a commercial software DEFORM which is based on the elastic–plastic finite element theory. Two kinds of core, a circle and an ellipse, have been designed. Because of the springback effect, the roundness of the elliptic core is better than that of the circular core. The same rule is applied to the diameter ranges (20–40 mm) and yield strength levels (175–240 MPa) of low carbon steel.

Recently, small motors are mostly used for the power parts of automobiles such as the cooling fan, the air-conditioner, and the door-lock system, in order to improve driver conveniences. When the form accuracy of the motor-case worsens, the motor rotates discontinuously due to a change in the magnetic force and vibration that occurs in the motor. Eventually, the motor's vibration will significantly influence the overall vibration and noise of the automobile. Thus, motor manufacturers strictly manage the form tolerance of motor-cases. The maximum tolerance in the diameter of a motor-case is 0.2 mm for a motor-case with an 80 mm diameter. In the early stages, motor-cases were formed by a deep-drawing method using a press machine. Afterwards, the method developed into a multi-stage forming method. In the multi-forming of motor-cases, the power part driven by cams is arranged in the circumferential direction of a core, the steel plate is formed in the shape of a cylinder and both ends are fixed by a puzzle lock method as shown in Fig. 1. In the multi-forming, the thickness of the motor-case is very small compared with the cylinder diameter, and therefore elastic deformation as well as plastic deformation takes place dominantly during forming, resulting in the occurrence of springback [1]. Accordingly, elastic deformation should also be taken into account in the forming analysis of the motor-case [2]. Research on the characteristics of springback have been conducted since the 1940s. However, the existing research [3], [4], [5] and [6] has been focused on the springback and residual stress of products in general plate forming processes, and no studies can be found on the springback characteristics of the multi-forming processes. Therefore, finite element analysis of the forming process of the motor-case has been performed to determine the optimal core shape which is suitable for obtaining the best roundness of the case.

A finite element analysis has been carried out on the multi-forming process for automobile motor-cases to determine optimal core forms with the best roundness. DEFORM 2D was employed to find optimal core sections, and the three dimen- sional analysis was also performed with the optimized core and the complex shape of the initial plate. The analysis results come to the following conclusions. 1. An optimal elliptic core, whose size was decreased by 3.99% in the vertical direction and increased by 0.55% in the hori- zontal direction when compared with the final product, was obtained. 2. The suggested elliptic core can be applied to products with radius ranges of 20–40 mm and material ranges of 175–240 MPa of yield strength