Open-die Forging Process Research Articles

Evaluation of cracking risk of 80MnSi8-6 nanobainitic steel during hot forging in the range of lower temperature limits

Abstract Nanobainitic steels exhibit an exceptional combination of high strength, good plasticity, impact toughness, and wear resistance. They are suitable for the production of large mass components through the open-die forging process. Subsequently, the forgings are air-cooled. An obstacle of this method is the extended time required for the large forgings to undergo a bainitic transformation, making the industrial implementation of this process economically unjustifiable. Nevertheless, nanobainitic steels also allow for the open-die forging of small batches of structural elements with high property requirements. A technological limitation lies in the necessity of performing a series of operations, leading to a prolonged processing time dependent on the shape of the product and the degree of deformation. Therefore, inter-operational reheating is often necessary, incurring costs and time consumption. This is particularly relevant to forgings with a mass ranging from a few to several dozen kilograms, which, due to their low thermal capacity, rapidly dissipate heat to the surroundings and tools. Designing an economical process with a limited number of reheating cycles requires advanced knowledge of material behavior under thermo-mechanical deformation parameters, including boundary conditions where a significant decrease in plasticity occurs and the risk of crack initiation. To obtain this information, a comprehensive analysis of the influence of thermo-mechanical parameters applied during the deformation of nanobainitic steel at relatively low temperatures on the flow characteristics and crack formation was conducted. To achieve this goal, the Digital Image Correlation method, the finite element method modeling considering damage criteria, and the macrostructural evaluation of deformed specimens were employed.

CrystalMind: A surrogate model for predicting 3D models with recrystallization in open-die hot forging including an optimization framework

This work introduces CrystalMind, a surrogate model developed to accurately reconstruct 3D models along with recrystallization induced by the open-die hot forging process. CrystalMind employs two types of data inputs, a 3D Model depicting pre-stroke workpiece geometry, and a forging vector outlining the proposed forging strategy. This forging strategy consists of bite infeed, bite offset, number of offsets and initial position. Moreover, a machine learning architecture with two different units, MLP-based (Multi-Layer Perceptron) and PointNET++-based, was implemented and compared, demonstrating similar performance in terms of recrystallization and deformation errors. However, MLP proved 36 times faster in computational time reaching an average computational time of 5ms pro run. Furthermore, CrystalMind adheres to the volume conservation condition and limits recrystallization error to less than 2% and deformation error to less than 0.1 mm or 0.9% for the test data. Finally, CrystalMind is employed in conjunction with an optimization algorithm, leading to remarkable enhancements in time efficiency. The optimization framework can effectively optimize a forging vector(s) for one, two, or three strokes. For instance, in the case of three strokes, CrystalMind enables the optimization process to be completed within an average of 7 min, a stark contrast to the approximately 2.3 years required when utilizing FEM simulation. Overall, CrystalMind provides fast and accurate predictions of deformed 3D models with corresponding recrystallization per point caused by a forging process, something not to be found in the state of the art so far.

Influence of thermally grown oxides on interfacial friction during hot deformation of large-size forging ingots

High-strength steels are pre-heated in gas-fired furnaces before undergoing the open-die forging process. This process increases thermal oxidation on steel surfaces, affecting the interfacial friction between ingot and anvils during deformation. Two medium carbon high-strength steels with different nickel contents were oxidized, and the mechanical characteristics of oxide layers were investigated by micro and nano-indentation methods. It was found that the formed layers on high nickel steel had lower Young modulus and hardness compared to the steel with lower nickel. Finite element modeling and ring tests were used to assess oxide layers' effect on interfacial friction during deformation. The results demonstrated that oxide layers' formation decreased the interfacial friction and deformation load, acting as lubricants at high temperatures.

Interactions Between Dynamic Softening and Strengthening Mechanisms During Hot Forging of a High-Strength Steel

Open-die forging is a critical step in the manufacture of large numbers of components used in the transportation and energy industries. Dynamic recrystallization, dynamic transformation, and dynamic precipitation take place during the hot deformation process and significantly affect microstructure conditioning, which ultimately influences the service properties of the component. In the present work, using a Gleeble 3800 thermomechanical simulator, the open-die forging of a large-size ingot made of a modified AISI 6140 medium carbon high-strength steel is investigated. Deformation temperatures ranging from 950°C to 1,250°C and strain rates ranging from 0.01 to 1 s−1, representative of the actual process, are considered in the analysis. The generated true stress–true strain curves are used as a basis for the development of a constitutive model predicting the occurrence of softening and strengthening phenomena as a function of thermomechanical conditions. The corresponding activation energy is determined to be about 374 kJ mol−1 and is compared against the values reported in the literature for other high-strength steels. Dynamic recrystallization kinetics is studied using the t50 model, and the influence of temperature and strain rate is quantified and discussed. The interaction between dynamic precipitation and dynamic recrystallization is discussed, and the deformation conditions under which such interactions occur are determined. The thermomechanical results are validated by microstructure examination, including laser confocal microscopy, field emission scanning electron microscopy, transmission electron microscopy, and energy-dispersive spectroscopy. The present study focuses on reproducing the deformation cycle applied during the open-die forging process of a vanadium-containing high-strength steel used in the industry with special attention to the interaction between dynamic recrystallization and precipitation processes.

Effect of Direct Powder Forging Process on the Mechanical Properties and Microstructural of Ti-6Al-4V ELI.

The study of powder metallurgy processing methods for titanium represents a promising avenue that can respond to a growing demand. This work reports the feasibility of direct powder forging (DPF) as a method to process large spherical Ti-6Al-4V powder into wrought products with noteworthy properties and physical characteristics. Direct powder forging is a thermomechanical process that imparts uniaxial loading to an enclosed and uncompacted powder to produce parts of various sizes and shapes. Stainless steel canisters were filled with prealloyed Ti-6Al-4V powder and consolidated through a multi-step open-die forging and rolling process into wrought DPF bars. After DPF, annealing was performed in the upper α+β phase. The results show that full consolidation was achieved and higher mechanical properties than the Ti-6Al-4V grade F-23 requirements in annealed conditions were obtained. The results also show that direct powder forging of spherical titanium powder could produce wrought mill products and exhibit some potential for further investigation for industrial applications.

FINITE ELEMENT SIMULATION OF Ti-6Al-4V BILLET ON OPEN DIE FORGING PROCESS UNDER DIFFERENT TEMPERATURES USING DEFORM-3D

ABSTRACT This paper explains the methodology of developing an open die-forging model using Deform-3D software to simulate the hot forging process on Ti-6Al-4V billet used in aerospace applications. Three-dimensional finite element model of an open die-forging model was designed in the Deform-3D software. To complete the simulation run, it comprises three modules, namely, pre-processing, simulation and post-processing. During pre-processing module, as per open die-forging process setup requirement two dies and one billet has been created using the standard data of forging. Suitable temperature conditions of Ti-6Al-4V material varying from 500°C to 1000°C are applied to billet. After the simulation had run with 100 steps, during post-processing step effective stress and strain, total velocity and displacement, final temperature was recorded. From results, it was observed that with increasing forging temperatures at 500°C, 750°C and 1000°C of hot Ti-6Al-4V billet – effective stress and strain were decreased, total displacement and velocity were decreased and the final temperature was increased. Deform-3D software will be used for finite element simulation to predict the metal flow behaviour effectively, during the forging process.

Prediction of the parameters and the hot open die elongation forging process on an 80 MN hydraulic press

Abstract The main task of the study was to develop and implement predictive control in the hot open die forging process of heavy, large, and hard deformable steel forgings on an 80 MN hydraulic press at the Forged Products Department (FPD) of Celsa Huta Ostrowiec (CHO). The predicted hot flow stresses and the predicted deformation/forging forces as a function of the parameters of the elongation forging process were determined. The predicted parameters of the forging process were included in the dynamic model of the hydraulic forging press. Generalized predictive control (GPC) algorithm of the hot open-die forging process on the hydraulic press was developed. The use of predictive control solved the uncertainty of the hot open forging process, which depends on the dimensions, shapes, and material properties of the forgings, as well as the parameters of the hydraulic press and forging tools.

Practical Study and Finite Element Simulation of Production Process of the Bush of Gearbox of Mercedes-Benz 10-Wheel Truck by Closed Die Forging

Nowadays, the closed die forging process is extensively applied to produce small to medium parts. The parts produced by this method show high strength, impact resistance, and toughness, which is the main advantage of this method compared to casting. Furthermore, the parts produced by this method are considerably close to the final shape of the designed part in terms of appearance compared to the open-die forging process, and the need for secondary operations such as finishing after the subjected process is significantly reduced. The present work investigates the production process with closed die forging of one of the most important parts of the gearbox of Mercedes-Benz 10-wheel truck, which is affected by various mechanical and thermal stresses in its working conditions. Finite element simulation results in ABAQUS software have been applied to analyze experiments for the purpose of evaluating the extent and type of impact of some important process parameters and also compared with the observed practical results. The results indicated that the initial temperature parameter of the workpiece has the highest effect on reducing the flow stress, and consequently, the required maximum force throughout the process. While the other evaluated parameters, i.e., press speed and mold temperature, have a smaller but undeniable impact.

Energy-Saving Hot Open Die Forging Process of Heavy Steel Forgings on an Industrial Hydraulic Forging Press

The study deals with the energy-saving process of hot open die elongation forging of heavy steel forgings on an 80 MN industrial hydraulic forging press. Three innovative energy-saving power supply solutions useful for industrial hydraulic forging presses were analyzsed. The energy-saving power supply of hydraulic forging presses consists in reducing electricity consumption by the electric motor driving the pumps, reducing the noise emitted by pumps and reducing leaks in hydraulic piston cylinders. The predicted forging force as a function of heavy steel forging heights for various deformation temperatures and strain rates was determined. A simulation model of the 80 MN hydraulic forging press is presented, which is useful for determining the time-varying parameters during the forging process. An energy-saving control for the hydraulic forging press based on the forging process parameters’ prediction has been developed. Real-time model predictive control (MPC) was developed based on multiple inputs multiple outputs (MIMO), and global predictive control (GPC). The GPC has been implemented in the control system of an 80 MN industrial hydraulic forging press. The main advantage of this control system is the repeatability of the forging process and minimization of the size deviation of heavy large steel forgings

Optimization of workability technological testing for open-die forging

Developing an open-die forging process for a poor-workability alloy has always been a challenge. This paper presents a rapid method that meets this purpose. A simplified forging test was considered for assessing the limit states of material in open-die forging. It can be employed in industrial forge shops. A V-shaped testing die was designed using finite element (FE) simulation. The V-shape geometry is convenient for strain evaluation. Rectangular blocks will be tested across a wide range of working temperatures. Based on the test results, limit states can be identified. Then friction testing method was optimized. It is also simple comparison test. Both technological tests are suitable for determination of optimized parameters in forging. The risk of material failure can thus be eliminated or minimized.

FAST AND COST EFFICIENT MEASURING OF GEOMETRY AND TEMPERATURE FOR OPEN-DIE FORGING

In open-die forging it is state of the art to use simulation tools for creating forging plans and setpoint values for the forging press and the automated part manipulator. These forging plans define required positions and forces. Therefore, the process can be fully automated. However, even small variations of not considered influence parameters lead to different forging results and thus to a discontinuous process. Influencing factors are, e.g. material parameter deviations, uncertainties in force measurements or variations in the part temperature due to varying environmental conditions. This paper presents an approach for a fully automatic open-die forging process with respect to actual conditions, based on a parallel measurement of the workpiece geometry and temperature and a “process-real-time” adaptation on the controller system. The focus of this work is the development of a measuring strategy and an according sensor setup for the combined temperature and geometry measurement of the workpiece. In addition, the structure, the characteristic features of the components and the beam path of the sensors scanning units are shown. Furthermore, first experimental results for the alignment of the beam path are presented. In the outline, the setup and calibration strategy of the measurement system are stated.

Using design geometrical features to develop an analytical cost estimation method for axisymmetric components in open-die forging

Hot forging is an industrial process where a metal piece is formed through a series of dies which permanently change the shape of the part. Open-die forging is a particular type of hot forging in which the used dies are generally flat and the part to be formed has a simple shape. Manufacturing cost estimation is a well-debated topic, especially for traditional manufacturing technologies. However, only few models are available in scientific literature for the open-die forging process. This lack is due to the complexity of the process, characterized by a low level of automation and a high degree of expertise required to develop the process. The paper proposes an analytical model for the cost estimation of axisymmetric components realized using open die-forging. The model uses as input the geometrical features of the part (e.g. dimensions, shape, material and tolerances), and gives as output: (i) the time required for the process development, (ii) the amount of material needed for the part processing and, (iii) the forging machine size/type, from the cutting of the billet to the piece deformation. Two cylindrical discs have been analysed for validating the proposed cost estimation model. The case studies show that the cost models give an accurate result in terms of cost breakdown, allowing the designer a quick calculation of process costs.

Analytical and numerical modelling of open-die forging process for elliptical cross-section of billet

The present work proposes a novel analytical solution for open-die forging for the billet of elliptical cross-section. From design and evaluation, moreover, from industrial prospective, in order to overcome the limitations and complexities of mathematical modelling for complex shape billets, the numerical simulation technique has also been demonstrated to establish and exploit the potential of commercially available finite element analysis (FEA) software. To start with, testing of fundamental material properties such as tensile and compressive tests have been simulated and validated against experimental data of aluminum alloy such as AA6063-T7 and AA6061, respectively. In a similar manner, the FEA simulation for a closed-die forging process has been carried out and validated against experimental result. Subsequently, a mathematical model for open-die forging having elliptical cross-section of billet has been derived with certain predefined assumptions. The potentials of FEA simulation for different materials such as aluminum alloy (AA6063), mild steel and brass, have also been investigated to justify the proposed analytical solution, which has been noticed to have less than 5% error. The intricacies involved in the simulations along with mathematical modelling have been discussed in detail in the present article.

Hydraulic systems control based on the characteristics of major-motion mechanism for an open-die forging manipulator

In the open-die forging process, the forging manipulator must cooperate closely with the forging press. Terrible working conditions of open-die forging have resulted in significant demand on the hydraulic control systems of the forging manipulator. This article analyzes the characteristics of major-motion hydraulic systems with the aim of proposing a novel hybrid serial–parallel heavy-duty forging manipulator. Kinematic and dynamic models of the major-motion mechanism are developed to investigate the control and comply with performance of hydraulic lifting, pitching, and buffering systems. Simulation shows that the three hydraulic systems are coupled in the position and posture control of the clamp. A separate posture control method based on the characteristic of the major-motion mechanism is designed for the hydraulic systems, and the position tracking performance of the hydraulic systems is studied in a stretching process of a plat-tool.

Analysis of Void Closure during Open Die Forging Process of Large Size Steel Ingots

Large size forged ingots, made of high strength steel, are widely used in aerospace, transport and energy applications. The presence of internal voids in the as-cast ingot may significantly affect the mechanical properties of final products. Thus, such internal defects must be eliminated during first steps of the open die forging process. In this paper, the effect of in-billet void positioning on void closure throughout the ingot breakdown process and specifically the upsetting step in a large ingot size steel is quantitatively investigated. The developed Hansel-Spittel material model for new high strength steel is used in this study. The ingot forging process (3D simulation) was simulated with Forge NxT 1.0® according to existing industrial data. A degree of closure of ten virtual existing voids was evaluated using a semi-analytical void closure model. It is found that the upsetting process is most effective for void closure in core regions and central upper billet including certain areas within the dead metal zone (DMZ). The volumetric strain rate is determined and two types of inertial effects are observed. The dependence of void closure on accumulated equivalent deformation is calculated and discussed in relation to void in-billet locations. The original combination of information from both relative void closure and the volumetric strain rate provides a way to optimize the forging process in terms of void elimination.

Theoretical study on Cold Open Die Forging Process Optimization for Multipass Workability

Cold Workability limits strength enhancement of austenitic materials through cold deformation. The intrinsic workability is the material characteristic whereas state-of-stress workability is governed by nature of applied stress, strain rate and geometry of deformation zone. For Cold Open Die Forging (CODF), multipass workability is essential. In this work, FEM tool FORGE-3 is used to optimize CODF on hydraulic press by analysis of stress-strain profiles and use of Latham-Cockroft damage criterion. Study recommends optimized process parameters, die combinations and pass-schedules.

Mitigation of Barreling Defect in Open Die Forging Process

Mitigation of Barreling Defect in Open Die Forging Process

Optimization of welding thickness on casting-steel surface for production of forging die

There are many drawbacks of traditional mold manufacturing technology, especially for dies used on large-scale hydraulic press, such as poor forging penetration, high difficulty of open die-forging process of modules, inferior hardness after heat treatment, high cost, massive waste of invalid forging dies, and so on. Therefore, a new method of mold making is put forward in this paper, which is to do surface welding on casting-steel. The FEM simulation experiments were done to establish a simplified finite element model of the surface welding mold based on JXZG casting-steel. Then, the thermal cycle curve method was used to simulate the surface welding and tempering process. Meanwhile, the temperature field and residual stress field under different welding thickness were analyzed. The finite element modal of landing gear used in a large civil aircraft was established, and then elastic-plastic finite element method was utilized to simulate the forming process of billet and to analyze the temperature field and residual stress distribution of different time. The results demonstrated that FEM could simulate the actual process of surface welding on casting-steel effectively. The equivalent stress close to welding line decreased when the welding thickness inclined, and then it leveled out when the welding thickness was 15 mm; on contrary, the equivalent stress far from welding line increased when the welding thickness declined and the impact of weld pass on casting-steel matrix enlarged which increased the possibility of defects when the casting-steel was used. In sum, when the impact of welding thickness and the cost of mold making are taken into consideration, 16 mm was chosen as the optimal surface welding thickness under given working conditions of landing gear.

Dynamic Modeling and Analysis of Lifting Mechanism for Forging Manipulator

The kinematic and dynamic behaviors of lifting mechanism for a forging manipulator are investigated. The forward kinematic equations are established. Then, based on the modular approach combined with equivalent dynamic ideal, the dynamic equations are deduced. Moreover, all the equations have been verified by the simulation on a virtual prototype with the ADAMS software and the experiments on a forging manipulator. The results show that the calculated values are well in agreement with the real measurements. Finally, both kinematic and dynamic models are analyzed, and it is found that the force produced by the kinetic energy has very weak effect on the results in comparison with the gravity. The results provide the foundation of gripper’s position control in automatic open-die forging process.

The Numerical Simulation of Conductive Body Forming Process and Mould Design

T2-copper conductive body is a important part used in high voltage switch, it has poor machining process due to the complex shape. Through Deform numerical simulation, conductive body was formed by open-die forging and closed die forging. In the open-die forging simulation，heat transfer coefficient between blank (880°C) and open-die (200°C) is 11, the surrounding environment temperature is 20°C, friction factor is 0.3. The main open-die forging process parameters is: outer draft angle α=6.5°; inner draft angle β＝10°; bridge width b＝5、8、11mm. punching skin and cylindrical blank. Simulation results show that forging can meet the requirement while properly adjusting mould parameters. The main size of closed-die forging working parts is designed according to the conductive body graph, no draft angle and ring blank of external diameter Φ111mm and inside diameter Φ93mm with the same volume of conductive body. The simulation results shows that forging can be formed using open-die forging, and it is difficult to form product by the process of the closed-die forging for ring blank because of the restriction of solid state metal liquidity, many regions of the filling is not sufficient. Open-die forging and casting blank-closed die forging are both used in actual production. The casting blank-closed die forging is a more reasonable forming process compared with the open-die forging as metal volume of distribution is solved, higher utilization rate of material, more simple process in following work and the like. To make it more suitable for practical production, appropriate adjustments of some parameters was made in the mold design process based on the numerical simulation. Keywords: open-die forging; casting blank–closed die forging; numerical simulation