The forging process, in comparison with machining processes, has advantageous characteristics such as the improvement of mechanical properties for the component, mass production capability and saving of raw material. On the other hand, the process is disadvantageous in that a special devoted die set to the each component is needed. Recently, in the forging industry, large forging parts tend to be ordered in small volumes. In case that huge equipment and the required special die to fit in with the equipment raises the cost of production. Therefore, the development of an incremental forging process, which utilizes a rather small equipment and more universal tools instead of a special die, is currently carried out in many applications.
Most research works on incremental forging processes have been focused on the manufacturing of shaft parts having a smaller diameter than an initial diameter of its raw material by radial forging process. The kind of products manufactured by this process is somewhat limited. On the other hand, if radial forging and axial forging can be done simultaneously, incremental forging of a shaft part having a flange of apparently larger diameter than its raw material is possible, hence parts of more diverse shapes can be produced.
In this dissertation, a radial-axial incremental forging process to produce shaft parts with flange has been developed. For the development of the radial-axial incremental forging process, a new incremental method of three-dimensional forged part manufacturing has been proposed and the process design, the machine design and production, and the process itself have been subjected to verification for practical applicability. At the same time, to analyze flow properties and formability of the proposed process, Automatic Expansion of Domain (AED), which is a new method of setting the analysis domain in finite element analysis, has been proposed and by applying the AED scheme to both radial and axial incremental forging the effectiveness of this method is reviewed. The influences of the process parameters on the flow as well as on the formability are also analyzed by introducing the finite element analysis using AED scheme.
The main characteristics of the radial-axial incremental forging are; a three-dimensional part can be obtained from a raw material having smaller outer dimensions than the final product and this product is made homogeneous by repeating the radial-axial forging process. This forging method is composed of two primary forming operations which are the combination of radial and axial incremental forging processes and, in addition, the notching, fishtail modification operations. A radial-axial incremental forging mechanism has been designed and fabricated to realize this radial-axial incremental forging process and to examine the process property.
To analyze the flow characteristics of the radial-axial incremental forging process and its formability, the AED technique in the analysis domain has been proposed. In the shaft forging process most part of the shape tends to be deformed in the tangential region of the die. The ADE technique is applied to analysis of a domain out of the total analytic domain automatically selected by a specific criterion where deformation is concentrated, then the analytic domain is gradually expanded as the incremental forging process is repeated. The proposed AED technique has been confirmed to be an efficient analytic method first by analyzing a two-dimensional plane-strain incremental forging process deriving an adequate measure as well as a criterion for AED applications. Analyzing the three-dimensional radial and axial incremental forging processes, the efficiency of AED method has also been verified and the influences of process parameters on the flow characteristics and the formability of this process have been studied.
A finite element analysis has been carried out to study the influences of the process parameters on the flow characteristics and the formability has been carried out to develop an optimal incremental forging process. The process parameters include the path schedule, compression rate and the feeding rate for the finite element analysis. The analysis has shown that the material gets more homogeneous when forged by several small compression rates than by a single high-rate compression rate.
Various three-dimensional axial forging products have been manufactured to prove the validity and applicability of the proposed radial-axial incremental forging process. From the result of the three-dimensional axial forging experiment, it has been shown that the radial-axial incremental forging process enables the manufacture of a desired shaft part having a larger diameter as compared with its raw material. The notching operation and the fishtail modification operation are found to be effective and essential intermediate operations in forming a shaft part having a detailed flange. It has been thus shown that the proposed process enables the manufacture of various flanged shaft parts by introducing the proposed radial-axial incremental forging process. It has been also confirmed that the use of AED technique greatly facilitates the computation for the forging of long shaft-like parts in the finite element analysis for the optimal design of the process.
