بررسی دقیق بهبود فرآیند آهنگری سرد برای یوغ فرمان خودرو با استفاده از روش عناصر محدود سفت و سخت پلاستیک

The steering column in a steering system, one of the main devices of an automobile, is a very important part to attain stability and steady movement of the vehicle. The steering yoke, the core part of steering column is manufactured through various processes, such as hot forging, machining, and assembly by welding. This study proposes a new method for manufacturing an united steering yoke of high manufacturing productivity, improved mechanical properties and low cost through precision cold forging. The rigid–plastic finite-element method for precision cold forging has been used in order to reduce development time and die cost. Practical considerations in the manufacturing stage such as hardness in heat treatment, and coating condition in lubrication have also been investigated.

The forging process is one of the most representative metal forming processes and can be classified into hot and cold forging according to the forming temperature. As the hot forging process is performed at hot working temperature, i.e., above the recrystallization temperature, the work-piece undergoes large plastic deformation and hot forging is usually used for producing the blocker. On the other hand, cold forging is a special type of forging process wherein cold metal is forced to flow plastically under compressive force into a variety of shapes, with several forming steps being used to produce a final part of relatively complex geometry, starting with a slug or billet of simple shape. Some of the advantages provided by this process are: (a) high production rate; (b) excellent dimensional tolerances and surface finish of the forged parts; (c) significant savings in material and machining; (d) higher tensile strengths in the forged part than in the original material, because of strain hardening; (e) favorable grain flow to improve strength. By far the largest area of application of cold forging is the automobile industry [1]. Until now, the steering yoke which is the object of this study, has been manufactured by hot forging or welding of forged head and shaft parts because of technical difficulties (Fig. 1). Thus the hot forged steering yoke can not satisfy the required accuracy, and also involves economical loss and increase of the process number due to secondary machining being unavoidable [2].In this paper, however, the precision cold forging process for the steering yoke of an automobile has been analyzed by using a rigid–plastic finite-element analysis code, DEFORM-3D. Fig. 2 shows the manufacturing process proposed in this paper. Experiments also have been performed through the optimized process.

A new method for manufacturing a united steering yoke of high manufacturing productivity, improved mechanical properties and low cost through precision cold forging is proposed. The rigid–plastic finite-element method for precision cold forging has been used in order to reduce development time and die cost. The practical considerations in manufacturing stage such as hardness in heat treatment, and coating condition in lubrication have also been investigated. From the results, it is concluded that the basic assumptions and the scheme of the present study are very useful for the precision cold forging process, especially for manufacturing the steering yoke. Moreover the results have been applied successfully in mass production.