Multi-stage Forging Research Articles

Numerical prediction on microstructure evolution for multi-stage hot forging of micro-alloyed piston

Purpose – The purpose of this paper is to build a flow stress model and microstructure evolution models which can be used to fulfill the multi-physics prediction of hot forging process, in this way the process design can be virtually verified and optimized. This is especially crucial for micro-alloyed steel forging which microstructure determines the component properties, since the downstream quenching is usually not needed. Design/methodology/approach – First, hot compression tests have been completed; second, experimental data are used to build the flow stress model and models for microstructure evolution; third, programming has been finished to integrate the proposed models into the commercial finite element method (FEM) code; fourth, case study is conducted to simulate multi-stage hot forging process of micro-alloyed steel F38MnV piston; and fifth, simulation results are validated by experiment. Findings – First, simulation results in grain size and phase volume fraction are in well agreement with experimental ones; second, the austenite grain is dramatically refined by the dynamic recrystallization in pre-forging process and static recrystallization in the two intervals has no obvious change during the following final forging and cooling above the Ae3 temperature; third, during the cooling process below the Ae3 temperature, ferrite and pearlite transformation begin from the thin skirt to the thick skirt and piston bottom because of different cooling speeds at different areas. Originality/value – First, flow stress model, dynamic recrystallization model, static recrystallization model, austenite grain growth model and phase transformation models are established for a micro-alloyed steel; second, the multi-physics FEM simulation of multi-stage hot forging of industrial piston has been conducted and verified by experiment, which show good agreement.

Process Simplification of Multi-Stage Forging for the Outer Race of a CV Joint

Constant velocity (CV) joint with six inner ball grooves has been conventionally produced by a multi-stage warm forging process that includes forward extrusion, upsetting, backward extrusions, necking, ironing, and sizing. In this study, multi-stage cold forging is presented with four simplified stages of forward extrusion, modified upsetting, backward extrusion, and combined necking–ironing–sizing. A three-dimensional numerical simulation is performed to ensure the appropriateness of the proposed process, and experimental investigations are carried out using spheroidized and phosphophyllite-coated SCr420H billet material. It is shown that the proposed multi-stage cold forging process could be successfully applied to the production of the outer race.

Computer Aided Design of Manufacturing of Anchors and Formulation of the Optimization Task for in Use Properties

Computer aided design of the manufacturing technology for anchors is presented in the paper. Evaluation of applicability of various materials for anchors, as well as analysis of the influence of process parameters on the in use properties of product, were the objectives of the research. In the material part, bainitic steels were considered as an alternative for the commonly used C-Mn steels. Possibility of elimination of the heat treatment was evaluated. Rheological models for the investigated steels were developed and implemented into the finite element code for simulations of drawing and multi stage forging. Criteria for the selection of the best manufacturing chain composed dimensional accuracy, tool life and product properties. Industrial trials were performed for the selected cycle and the efficiency of this cycle was evaluated. Finally, simulations of the in use behaviour of the anchor-concrete joint were performed. On the basis of the simulations the optimization task using strength of the joint as the objective function was formulated

Open Die Forging of Large Shafts with Defects – Physical and Numerical Modelling

The aim and scope of this paper is centered to analyze the influence of the geometry of V-shaped dies on the closure of internal centerline porosity defects in ingots during multistep open-die forging. The investigation is performed with small scale physical models made from lead using V-shaped dies with 90º and 120º and a reference pair of flat parallel platens. Holes drilled through the center of these preforms are produced to mimic centerline porosity in full scale cast ingots and intermediate rotation of the preforms replicate a multi-stage forging sequence under laboratory testing conditions. The presentation is supported by finite element modelling using an in-house developed computer program and the overall investigation shows that better results in closure of centerline defects are obtained with a V-shaped die with 120º die angle.

Austenite Grain Size Evolution in Railway Wheel During Multi-Stage Forging Processes

The knowledge of microstructure evolution of railway wheel during hot forming process is the prerequisite of improving mechanical properties of the final product. In order to investigate the austenite grain size evolution of railway wheel during multi-stage forging process, mathematical models of recrystallization and austenite grain growth were derived firstly by hot compression tests for railway wheel steel CL50D, which then were integrated with a thermal-mechanical finite element model by the developed subroutines. The information about kinetics of recrystallization and grain size distribution during the forging process was obtained by simulation. The predicted results were validated by experiments in an industrial scale, and the average error between the predicted grain sizes and the measured ones is about 5%. The result shows that, under the current railway wheel forging process, the grain size distribution after final forging is inhomogeneous extremely. There is a narrow coarse grain zone between the external part and center of the hub caused by Static recrystallization after final forging. With cooling of 60 s after final forging, the grain size is about 85 μm for the areas near the web surface and 175 μm for center areas of the hub and rim.

Microstructure Evolution of Dynamic Recrystallization of 42CrMo Steel during Multi-Stage Forging by FEM

Different process steps of the workpiece have different effects on the microstructure in the multi-stage forging. In this study, the effect of four different process steps of steering arm on microstructure was studied by FEM. Results have showed that upsetting is beneficial to refine the microstructure as well as finish forging. Especially drawing can make the distribution of microstructure homogeneous while bending has less effect on it. The already-designed forging process for steering arm was reasonable based on the simulation. Eventually, the grain size level of the steering arm was tested as 6.5 based on the conventional standard.

Green alternative processing technology for a spring guide pin of stamping die set

In this research, a multi-stage cold forging process for a spring guide pin of stamping die set is designed through alternative process for sustainable production. Highly energy and material consuming process needs to be converted to an energy saving process. Up to now, a spring guide pin for stamping die set is usually manufactured by machining process in order to achieve dimensional accuracy. However, machining process has some disadvantages such as excessive material loss, low productivity, and poor mechanical properties. In order to overcome these problems, a multi-stage cold forging process is applied to manufacturing spring guide pin for achieving less material loss and higher productivity. Multi-stage forging process requires careful design steps to prevent the defects of the final product. So, the design must consider the material flow during the whole process and the loading limit of the press in order to avoid product defects such as folding and underfilling. To develop multi-stage forging process for spring guide pin the forming load and material flow at each step is analyzed using a commercial finite element code, DEFORM. The guide pin is then manufactured by the developed multistage forging process, and is compared to the simulation results. Also the efficiency of the developed forging process is compared to the machining process. The developed process is a green manufacturing process minimizing material loss, which achieves cost reduction through improved material usage and productivity compared to the more widely used machining process.

Evaluation of environmentally friendly lubricants for cold forging

The authors proposed double-layer-type environmentally friendly lubricants, which were composed of an undercoat, superior in adhering to a material, and an overcoat, superior in reducing the friction between the material and the die. The performance of these lubricants for cold forging was evaluated by the ring compression test, the combined forward rod-backward can extrusion-type friction test and the combined forward conical can-backward straight can extrusion-type friction test. The double-layer-type lubricants showed comparable friction characteristics and anti-pick-up properties to a conversion coating lubricant, when the film thickness and surface treatment before coating were improved. In a practical application by cold multistage forging, the double-layer-type lubricants showed a similar performance to a conversion coating lubricant.

Computer Aided Design of Manufacturing of Fasteners - Selection of the Best Production Chain

Computer aided design of the manufacturing technology for the fasteners is presented the paper. The particular objectives of the work were twofold. The first objective is evaluation of applicability of various materials for fasteners. Analysis of different technological variants is the second objective of the research. In the material part, bainitic steels are considered as an alternative for the commonly used carbon-manganese steels. This is a continuation of [1,2]. Possibility of elimination of the heat treatment was evaluated. Main features of the new generation of bainitic steels are discussed briefly in the paper. Rheological models for all steels investigated in the project were developed. The models were implemented into the finite element code for simulations of drawing and multi stage forging. Simulations of various variants of manufacturing chain were performed and the best alternative was selected. Criteria for the selection composed dimensional accuracy and tool life. Industrial trials were performed for the selected cycle and the efficiency of this cycle was evaluated. Finally, the optimization task was formulated. However, solution of the optimization problem is costly at this stage and improvement of the efficiency of the formulation will be the objective of further research.

Residual stress analysis of the multi-stage forging process of a nickel-based superalloy turbine disc

In order to analyze the multi-stage forging process of a nickel-based GH4169 superalloy (similar to Inconel 718 alloy) aero-engine turbine disc with high efficiency and accuracy, a modified material constitutive law, grid convergence study, and a combined two-dimensional and three-dimensional finite element simulation technology were used to analyze the thermo-mechanical-coupled stress variation during the turbine disc multi-stage forging process with the general-purpose nonlinear finite element software MSC.Marc. The predicted finite element forging residual stresses were tested and verified with the measurement results by the layer removal method; it was found that the constitutive law combined with heat contact properties between dies and material could be used to accurately predict and analyze the turbine disc forging processes. Based on the predicted precise and comprehensive finite element residual stress distributions, the consequent disc anti-fatigue manufacturing technologies could be optimized and improved greatly, which would guarantee the stable manufacturing quality and excellent performance of the aero-engine turbine disc.

Study on Load Control and Optimization of Rotary Forging Method for Heavy and Thick-Walled Container Head by FEM

In this study, the finite element method (FEM) was used to simulate the rotary forging process of a heavy and thick-walled container head, and the problems about load, strain distribution and optimization of rotary forging method were studied. First, five controlling factors of load were defined, which were single reduction amount (δ), reduction rate (ν), thickness of top die (ω), rotary angle (θ) and rotary way (γ) respectively, and their influence degree on load was studied later. Then the influence of γ on strain distribution was investigated. The results indicate δ, ν and ω have a strong influence on load, while θ and γ have a small influence on it; the strain distribution under crossed rotary way which is proposed in this paper is more homogeneous than stepwise rotary way. Based on the research results, a new multi-stage rotary forging method was proposed, by which load and strain distribution could be controlled effectively by means of an optimized combination of the five controlling factors in different forming stages. The simulation results are in good agreement with practical production. This study can provide valuable guidance in load control and process optimization for other similar heavy blind-hole forgings. Keywords: Heavy and thick-walled container head, FEM, Rotary forging method, Load control, Strain distribution

環境対応型冷間鍛造用固体潤滑剤の性能評価

Abstract The authors proposed double-layer-type environmentally friendly lubricants, which were composed of an undercoat, superior in adhering to a material, and an overcoat, superior in reducing the friction between the material and the die. The performance of these lubricants for cold forging was evaluated by the ring compression test, the combined forward rod-backward can extrusion-type friction test and the combined forward conical can-backward straight can extrusion-type friction test. The double-layer-type lubricants showed comparable friction characteristics and anti-pick-up properties to a conversion coating lubricant, when the film thickness and surface treatment before coating were improved. In a practical application by cold multistage forging, the double-layer-type lubricants showed a similar performance to a conversion coating lubricant.

Optimal Design of Pre-Forging for Gear Blank Using BP Neural Network and Genetic Algorithm

The design of pre-forging is very important during multistage forging of producing gear blank. It directly affects the behavior of metal flowing, filled situation of die cavity of finish forging, quality of products and die life. Most designs of pre-forging for gear blank are based on trial and error method. This paper presents a suitable method for practical designation of pre-forging for gear blank by proposing an improved algorithm, which combines Back Propagation Neural Network and Genetic Algorithm. Firstly, the mathematical model between the size parameters of pre-forging and forming force and maximum die stress of finish forging was established by using Back Propagation Neural Network which has the feature of processing highly nonlinear problems. Secondly, the established model was set as the fitness function of Genetic Algorithm. At last, the most superior pre-forging shape and the size parameters were solved by using the Genetic Algorithm with the function of overall situation optimization. These can lead to lower cost and time in the stages of designing pre-forging for gear blank.

A combined approach to determine workpiece-tool-press deflections and tool loads in multistage cold-forging

Press and tool deflections have significant influence on the accuracy of products and tool service life in cold-forging processes. This paper presents a combined experimental–numerical approach to determine the deflections of the workpiece-tool-press (WTP) system and tool loads to improve product accuracy in a multistage cold-forging process. The measurements of deflections of the vertical mechanical press for the determination of the press flexibility matrix were performed in dynamic operating conditions. Numerical modelling of the vertical mechanical press and a multistage forging system was performed in order to evaluate the tool loads, the displacements and the rotations of the entire WTP system. The press flexibility matrix in combination with finite element (FE) model of the press and multistage process enable predictions of the elastic displacements and rotations of the tool and the press ram as well as determination of the evolution of the resultant force in order to design a reliable multistage cold-forging process. By redesigning the time sequences and evolution of the multistage forming operations during the press stroke, the evolution of the resultant force and the torque are optimized. This approach has been successfully applied to improve the prediction of tool loads, WTP deflections and rotations for the production of the automotive starter side plate.

Near Net Shape Forging of CV Joint Outer Race

A CV joint outer race is an important load-supporting part in cars. Its geometry is very complicated. Traditional hot and cold forging methods have their own limitations to produce such a complex shaped part. Therefore, multistage forging may be advantageous to produce this part. The key point of outer race is performing the geometry of ball grooves with negative slope angle. Traditional methods form the ball groove by machining that takes long time and waste many portions of the material. Thus near net shape forging is an attractive option for producing of outer race. In this study, the process sequence in the multistage forging of a CV joint outer race has been investigated by using the rigid plastic finite volume method and forging process sequence is designed which can produce a near net-shape housing without defects within a given press capacity. Finally physical modelling with commercial lead is used to verify the reliability of numerical simulation results.

비축대칭 와셔 캠 볼트의 다단 단조공정 설계를 위한 유한요소 해석

Process design of multi-stage forging for a bolt with nonaxisymmetric washer cam has been studied by using finite element method. For shape complexity of the bolt, it is impossible to manufacture in a single stage forging. To design multi-stage forging for the bolt the forging load and fiber flow of each step have been analyzed by using commercial finite element code DEFORM-3D. Simulated results have been compared with experimental ones. Multi-stage forging process has been designed with four stages. The workpiece should be eccentric shape until third forging stage. And then bolt head and washer of eccentrical shape is created in last stage. As a results, It was predicted that shape of product would be good and effective strain would be uniformly distributed in the product. Also, it was predicted whether defects would exist or not by reviewing the fiber flow.

A new algorithm for reduction of number of press-forming stages in forging processes using numerical optimization and FE simulation

This study presents a new simulation-based technique for the optimum design of a multi-stage forging process aiming at reduction of the number of press-forming stages. This iterative design technique involves response-surface-based numerical optimization and a finite element analysis of the process. The design procedure starts with an initial process design that is deemed too conservative, i.e. allows to arrive at the desired product but involves an excessive number of stages. To obtain a better process design, one stage of the existing multi-stage process is eliminated using numerical optimization in conjunction with an FE simulation. This is repeated by reducing the number of stages one by one until the minimum possible number of stages is reached. This design technique is applied to stage reduction of a three-stage forging process of an axisymmetric aluminum billet. It is confirmed that a new two-stage process design is obtained successfully and the developed design optimization technique showed its effectiveness in reduction of the number of press-forming stages in a multi-stage forming process.

3D FEM simulation of the multi-stage forging process of a gas turbine compressor blade

Abstract Due to the complicated three-dimensional geometry and the non-steady state contact between the workpiece and the die surface, the simulation of blade forging process performed so far has been restricted to two-dimensional plane-strain problems or simplified three-dimensional deformational cases throughout which some simplifications and assumptions are employed. This study attempts to simulate an entire forging process of a gas turbine compressor blade from a cylindrical billet to a complicated product, using 3D rigid-viscoplastic FEM. Simulation successfully predicts a complete load/time diagram and deformed configurations on the preforming stages and the following forging stage. Meanwhile, the distribution of different field-variables, such as strain and temperature, were obtained. On the basis of these results, a change of the original forging stage is recommended. The validity of simulation results was verified through comparisons with industrial trials, which were conducted on the same process parameters as those in the simulation. The simulation results may be effectively applied to other types of three-dimensional turbine blade forging processes.

Process analysis of multistage forging by using finite element method

Much progress in forging technology including low production cost and fast production has allowed an intensive use of forging. Manufacturing companies have especially focused on producing a complex shaped part with a tight dimensional tolerance. Traditional warm and cold forging methods have their own limitations to produce such a complex shaped part; warm forging requires complex system with relatively higher manufacturing cost, while cold forging is not applicable to materials with limited formability. Therefore, multistage forging may be advantageous to produce complex shaped parts. In order to build a multistage forging system, it is necessary to characterize mechanical properties in response to system design parameters such as temperature, forging speed and reduction. For the analysis of formability of multistage forging process, finite element method (FEM) has been used for the process analysis. As a model case, a constant velocity (CV) joint forging process is analyzed by FEM, since CV joint has a complex shape and also its required dimensional tolerances are very tight. A systematic approach to process analysis is established using the FEM for the multistage forging of the CV joint outer race.

3D Rigid-Viscoplastic FEM Simulation of Forging Process of a Gas Turbine Rotor Blade

Analysis of the forging of gas turbine rotor blades is a complex operation because of the complicated three-dimensional geometry and the non-steady state contact between the workpiece and the die surface. As a result, the simulation of blade forging performed so far has been restricted to two-dimensional plane-strain problems or simplified three-dimensional deformational cases throughout which some simplifications and assumptions are employed. In this paper a three-dimensional analysis of the non-isothermal multi-stage forging process of a gas turbine rotor blade from a cylindrical billet to a complicated product is presented, using 3D rigid-viscoplastic FEM. The simulation results of the blade forging processes are summarized in terms of deformed configurations, the material flow net pattern of typical cross-sections, the distribution of different field variables such as strain and stress, and the load-stroke relationships for each operational stage, in this way the forming laws during forging process of a gas turbine rotor blade being revealed. The validity of simulation results has been verified through comparisons with forging tests, which show good agreements with numerical simulation results. The simulation results may be effectively applied to other types of three-dimensional turbine blade forging processes.