Radial Forging Process Research Articles

Study of the effects of die geometry on deformation in the radial forging process

Radial forging is an open forging process used for reducing the diameters of shafts, tubes, stepped shafts and axels, and creating internal profiles for tubes such as rifling of gun barrels. Usually a mandrel is used inside a tubular workpiece to create internal profile and/or size the internal diameter, but the process can also be performed without a mandrel when workpiece geometry does not allow utilizing it or the internal surface quality is not critical. Moreover, in stepped shafts and tubes, often there is a fillet connecting two different sections. If it is possible to produce that fillet during the forging process, the process could be more cost effective. So, in this paper, four different shapes for the die inlet zone including linear, convex, concave and hybrid surfaces are considered and the effects of die shape on the deformation pattern and quality of radially forged products are studied. In this study, slab method analysis is used to obtain the deformation pattern, pressure distribution and the position of neutral plane in both cases; with mandrel and without it.

Rigid‐plastic finite element analysis of incremental radial forging process using the automatic expansion of domain scheme

The incremental radial forging process employs several tens or hundreds of incremental local strokes, so that the entire process is difficult to analyze due to large computation time and large computer memory. The objective of this work is to propose a new numerical scheme of the finite element method, automatic expansion of domain (AED), to reduce computation time and computer memory. In the AED scheme, an effective analysis domain in each local forging step is defined and then the domain is automatically expanded in accordance with the repeated process. In order to verify the validity of the criterion for the AED scheme and the applicability of the AED scheme, two‐dimensional incremental plane‐strain forging process is first analyzed using the proposed scheme with various criteria and full domain. In addition, three‐dimensional incremental radial forging process is analyzed to verify the applicability of the proposed scheme to a practical incremental forging process.

A Study on the Warping Problems of Thin Flange under the Radial Forging Processes by FEM and Experiments

During metal forging, warping can easily occur on the edge of the thin flange, causing it to fold, affecting the sustainability of the application of the flange. This investigation proposes a chamfer design for the die and the taper design for the ring gap, to eliminate warping. First, the radial forging process of work-hardened materials is simulated, the phenomenon of flange warping is analyzed, and the accuracy of the simulation is experimentally verified. Secondly, the materials, lubricants and the height of the ring gap of the die are set as fixed parameters, and the analytical results for dies with rounded corner, chamfered and a tapered of the ring gap, are compared. The experiments and simulation confirm that the problem of flange warping can be solved effectively. The results are as follows.

Investigation of the influence of various process parameters on the radial forging processes by the finite element method (FEM)

In this study, the finite deformation theory was used to develop a large rigid-plastic deformation finite element program which could simulate the radial forging process of work-hardening materials. First, experiments were carried out to confirm the accuracy of the program. Then we investigated the influence of each parameter on the forging process. The parameters adopted in this study are die corner radius (R), ring gap height (H), friction factor (m), and work-hardening coefficient (n). The effects of parameters on the flange thickness ratio (h/H) and the outer protruding shape ratio (D/D0) are also obtained.

Study of stress development in axi-symmetric products processed by radial forging using a 3-D non-linear finite-element method

A hollow shafts popular axi-symmetric machine elements, are used frequently under severe service conditions such as for automobile transmissions, the shafts of aircraft, and turbine shafts. They are usually manufactured through the radial-forging process. The residual stress in these forged products directly affects the material stability, the resistance to deformation, the accuracy, and the fatigue life of products. In order to extend the operating life of products and satisfy the required quality of operation during customer usage, it is necessary to monitor the residual stresses during the forging operations. As a way to study residual stress formation due to radial forging, a three-dimensional theoretical model was developed using a non-linear finite-element method program. The workpiece used in the calculations was alloy steel MILS 11595 and was assumed to have elasto-plastic behavior during forging. The Coulomb friction law was applied to simulate the contact behavior between the workpiece and the mandrel and between the workpiece and the die. The residual stress distributions in the forged product were calculated and selected results were compared with published experimental data to verify the effectiveness of the developed model.

Development and validation of a finite-element model for multiple-pass radial forging

This paper includes a discussion of the techniques which were used to model multiple-pass radial forging using the finite-element method. The model was used to predict the thermomechanical history of an Alloy 718 workpiece during billet conversion. The techniques which were developed and used to measure the strain and temperature profiles in the forged billet in order to validate the finite-element model are also presented. Results of the model validation show that an axisymmetric approximation of the radial forging process provides reasonable predictions of the billet's thermomechanical history whilst yielding acceptable simulation times.

Application of the finite-element method to the radial forging of large diameter tubes

Previous investigations of large-diameter tube forging using the radial-forging process have been based on highly simplified slab and upper-bound process models. In order to make accurate predictions of the thermal and mechanical history of the workpiece, more detailed models are required. In this paper, a model of the tube-forging process based on the rigid-thermoviscoplastic finite-element method is considered. The results that are presented include the effective strain, strain rates, and temperature distributions in the forged tube. The deformation was found to be uniform but sensitive to the axial feed-rate. Strain rates were found to be sensitive to the axial feed rate and were within the range typical for a mechanical press. Large temperature gradients across the wall thickness were predicted in the tube. These temperature gradients were generated during forging due to contact with the mandrel and are thought to give rise to variation in the mechanical properties in the forged tube.

Thermomechanical simulation of a radial forging process

The thermomechanical behaviour of a radial forging process has been investigated. The slab method was applied to study the mechanics of the process. A one-dimensional heat-transfer equation was used to predict the axial temperature distribution of the workpiece. The analysis has been computerized by taking into account the effects of strain, strain rate and temperature on the flow stress of the material being forged. A contact factor is formulated to consider the actual area of contact between the hammer dies and workpiece. An electrical analogy scheme has been developed to determine the thermal contact resistance which is needed in thermal study. The radial pressure, forging force, forging power and axial workpiece temperature were predicted for selected operating conditions. The model predictions were compared to the on-line measurement data. The comparison indicates that the computer model used in this study is sufficiently accurate for practical purposes.

回転鍛造におけるインコネル７１８の温度変化と変形過程の解析

The radial forging machine SX 55 produced by GFM was installed in Sibukawa Plant, Daido Steel Co., Ltd. in 1986. The main purpose of this machine is to process the heat resistant materials in a fewer heats.A numerical model can be used to simulate different conditions under which the process is to operate. A decision can then made on the most suitable set of conditions.A thermal-mechanical coupled finite element method was applied using a elastoplastic material model to calculate the temperature transition of Inconel 718 deformed with 4 hammers from ingot to billet during several passes.The calculated results indicate that heat-rise caused by the penetration of stresses leads to the critical temperature for cracking due to low ductility in the case of high feeding speed and they are in good accordance with the results of forging trials.A suitable operating schedule obtained by calculations shows the possibilities of controlling the micro-structure of billet during radial forging process.

Design of dies for radial forging of rods and tubes

Radial forging is a unique process for the precision forging of round and tubular components, with or without internal profiles, and for reducing the diameter of ingots and bars. This process is now widely used for the precision forging of bars with round, square, and rectangular cross-sections. Radial-forging machines are also used for producing profiled parts, such as solid or hollow-stepped shafts, and for finishing tubes with cylindrical and conical profiles. The process possesses the capability for the virtually chipless manufacture of rods and tubes to provide a precision-finished product with in excess of 95% material utilization. In addition, the list of materials processed by this method includes tool steels, titanium alloys, beryllium, tungsten, and high-temperature super-alloys. Basically, the hammers in these machines are given rapid periodic motion so that the dies sweep around the part to be formed. Thus, only a small portion of the workpiece is subjected at any moment to the pressures required for plastic deformation, thereby keeping the overall forces on the machines fairly low. The portion of the workpiece in direct contact with the tool thus undergoes intensified local contact stresses. The design of the radial-forging dies greatly influences the process variables, such as forging load, stress distribution on the dies, mental flow during deformation, and surface finish of the forged product. Recently, based on the slab method of analysis, computerized analytical methods have been developed for designing radial-forging dies with straight conical and compound angle entries. The analysis, which takes into account the strain, strain rate and temperature effects on the material, has been applied to a number of selected forging conditions. Results have been found to agree with results of actual forging trials. This paper briefly describes the radial forging process, reviews the practical aspects of die design, and gives a brief summary of the results of the computerized analysis.