Open-die Forging Research Articles

Towards microstructure control in forging and rolling: combining AI with process models for closed-loop property control

Abstract Metal forming processes like open-die forging or hot rolling are well-established for the production of key components in various industries. Nevertheless, the control of the final microstructure and hence mechanical properties is not yet common. To achieve this, the authors propose and discuss a control concept based on reinforcement learning, fast process models (FPM) and an “operator in the loop” approach. The concept is explained and tested using deviating initial ingot temperatures as idealized process disruptions. RL algorithms are trained for both processes and transferred into the controllers that are connected to a simulative environment based on FPM. Within this framework, the online adaption is possible in ∼2 s in rolling and 4–6 s in forging. This highlights the concepts suitability to be used for property control in hot metal forming.

Modeling of equivalent strain in 2D cross-sections of open die forged components using neural networks

Open die forging is one of the oldest manufacturing methods known to remove defects in the ingot resulting from the casting process. The improved properties of the final component are highly dependent on the strain distribution. Although sinusoidal equations and empirical formulations have been already used to estimate the strain, they have been applied only to the core of the workpiece. In this work, a novel approach is presented to model the equivalent strain distribution in 2D cross-sections, in the direction of the press, of open die forged components using neural networks. The proposed method efficiently combines a parametric sinusoidal function with a neural network to learn the complex relationships between the process parameters and the resulting local strain. The neural network is trained on a dataset of finite element (FE) simulations of rectangular geometries that cover a wide range of aspect ratios, bite ratios, and height reductions. The presented methodology with near real-time prediction capabilities shows good agreement with FE results. Moreover, the parametric function captures the characteristic pattern of the strain distribution and reveals certain physical relationships affecting the deformation of the material. These patterns are later examined by analyzing the parameters identified in the parametric sinusoidal function.

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.

Studies of forging on the aluminium-sea sand composites

The goal of this research was to determine the impact of cold forging on the mechanical characteristics and microstructure of Al MMCs at various sea sand percentages and forging deformations. The wettability of sea sand was improved by applying an electroless coating just before the stir-casting procedure. Using the stir casting technique, a composite material of Al6061 and sea sand was fabricated at several percentages of sea sand in weight, such as 2, 4, and 6%. In addition, open-die forging in cold settings was studied to learn more about the deformation characteristics of Al6061-sea sand composite. Composites were tested for density, porosity, microstructure, macrostructure, and hardness. The behaviour of microstructures was studied with an optical microscope. Brinell hardness readings taken according to ASTM E-10 were used to characterize the composite. The stir casting method was used to investigate and analyse the samples characteristics. More sea sand particles are distributed throughout the matrix as the composite’s density decreases. Increases in porosity are associated with an increase in reinforcement percentage, as this leads to more matrix-reinforcement surface contact and hence more porosity. The hardness diminishes with an increase in the proportion of sea sand particles. The mechanical qualities of the composite were enhanced by an oxide compound found on the sea sand. Evidence suggests that forging enhances mechanical and microstructure qualities.

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.

Review of Hydro-Pneumatic Accumulator Models for the Study of the Energy Efficiency of Hydraulic Systems

This review article deals with hydro-pneumatic accumulators (HPAs) charged with nitrogen. The focus is on HPA models used in the study of the energy efficiency of hydraulic systems. Hydraulic circuits with HPA are presented along with their various applications for delivering the required volume of fluid, maintaining the required pressure, ensuring safe operation, safety stop, leak compensation, fluid volume change compensation, pulsation damping, and pressure shock absorption. A general regenerative hydraulic system and a general hybrid hydraulic system are also presented. The review focuses primarily on HPA computational, dynamic, and simulation models. Basic HPA calculation parameters and computational models of energy storage and thermodynamic cycle are presented. Various computational and dynamic models of HPA have been defined, such as the thermodynamic model, simulation model, dynamic model, pulsation damper model, and shock pulse damper model. Research projects that have used HPA in industrial hydraulic systems are reviewed, such as those maintaining operating pressure in an industrial 80 MN open-die hydraulic forging press and acting as a shock pulse absorber in the lifting and levelling module of a tracked mobile robotic bricklaying system. The development of energy storage technology in HPA from various sources is now a global challenge.

Miniaturised experimental simulation of open-die forging

This study presents a novel experimental set-up for laboratory-scale simulation of cogging and open-die forging processes during ingot-to-billet conversion of advanced engineering alloys. The experimental set-up is designed to be cost-effective, employing a remotely operated manipulator assembly constructed from readily available “off-the-shelf” components used in conjunction with a conventional uni-axial load-frame - equipment that is available in most materials testing laboratories. Small test-bars of C101 copper alloy were subjected to multi-stroke cogging operations with intermittent rotation at ambient and elevated temperatures (20–600 °C). Prior to forging, the as-received material underwent heat treatments to coarsen the starting grain structure, and to help demonstrate the capability of the apparatus to achieve grain refinement via recrystallisation (dynamic and static) and recovery processes within the deformed material. The resulting microstructural evolution and mechanical property changes of the forged material have been investigated using light microscopy (LM), Vickers hardness (HV) testing, and electron backscatter diffraction (EBSD). The deformed C101 alloy exhibited measurable grain refinement after forging at elevated temperatures, thus demonstrating the effectiveness of the designed miniaturised open-die forging set-up.

A Study Utilizing Numerical Simulation and Experimental Analysis to Predict and Optimize Flange-Forming Force in Open-Die Forging of C45 Billet Tubes

Open-die forging holds a pivotal role in shaping machine parts within industrial applications. This study focuses on the assessment of stress–strain curves for C45 material at different elevated temperatures and strain rates through numerical simulations employing the finite element method (FEM). Specifically, the research investigates how the flow curve of materials at elevated temperatures and individual strain rates impacts the forming force during the flange forming of C45 billet tubes. By comparing the simulation results with experimental data on the flange-forming force, this study observes that optimal outcomes arise when considering both elevated temperature and strain rates in the flow curve of materials. The study then conducts simulations for C45 billet tubes with varying upsetting ratios (H0/D0), (S0/D0), and the punch’s pitch angle (α), aiming to address optimization challenges related to the flange-forming force. Consequently, a mathematical model is developed to represent the relationship between the flange-forming force and geometric parameters (H0/D0, S0/D0, and α). This model accurately predicts the forming force under various flange-forming conditions, demonstrating high precision with a maximum error of 4.26% compared with the experimental results. This study significantly contributes to the advancement of flange-forming technology in open-die forging through numerical simulation, enabling the optimization of the flange-forming force and the selection of appropriate equipment. These findings pave the way for more effective and efficient industrial processes, fostering innovation and progress in the field.

Effect of forging sequence and heat treatment on microstructure of high-duty power-plant shaft made of Cr-Mo ultra-high strength steel

The paper presents results of modeling and testing of a heavy weight part made of Cr-Mo, which was V-modified ultra-high strength steel grade AISI 4140, processed through a novel open-die forging schedule and two alternative routes of two-stage heat treatment cycles designed to meet requirements of high-duty components for energy sector. Taking advantage of unconventional forging conditions based on assumption of large feed and reduction ratios and the modification of chemical composition better control of austenite grain was achieved to minimize abnormal grain growth and/or strain uniformity problems. With aid of Finite Element Modeling of multi-stage sequence of upsetting and cogging strain distribution was optimized so as to minimize strain fluctuations on the length to range 2.2?2.7,and correlated with microstructure produced at every major stage on the large cross-sections of the shaft. Designed with aid of finite element method processing cycles was verified in full-scale physical modeling with use of 16 ton forging ingot, including two alternative quenching strategies: oil vs. water spray and air. Examination of material in as-forged, normalized and heat-treated condition was carried out to observe response of hot-worked material and the effect of cooling conditions on microstructure during final heat treatment. As observed, employing large feed ratios on cogging and varied cooling allowed suppress detrimental effect of inevitable abnormal grain growth which resulted in 1-2 ASTM grain in as-forged conditions to reach 6 ASTM in normalized and 8/9 ASTM after quenching in oil and water spray, respectively, which allows producing after tempering, correspondingly, 44?48 and 85?122 J/cm2 V-notch impact strength in the critical area of the forged shaft.

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.

Influence of Forging Parameters on Microstructure and Properties of En AW-6082 Alloy

Aluminum alloys are widely used in automotive industry due to their low density and good corrosion resistance. This category includes alloys based on AlSiMg which are suitable for load bearing parts operating under higher temperatures. This paper deals with analysis of influence of deformation parameters and heat treatment on structure and mechanical properties of EN AW-6082 (AlSi1MgMn) alloy manufactured by horizontal cast module technology. Casted rods were used as a billet, which was formed to defined height by hot open-die forging. Subsequently the precipitation hardening was used as heat treatment. Changes in microstructure were evaluated based on the metallographic analyzes performed by light optical microscopy and scanning electron microscopy using an energy dispersive X-ray spectrometry and electron backscatter diffraction. Mechanical properties were determined by uniaxial tensile test and hardness testing. The results showed, that due to the process parameters, no significant structural changes were observed in the surface layer of forging. However, microstructure is significantly inhomogeneous in the core due to the dynamic softening processes. Mechanical properties are increasing which is significantly influenced by the type and distribution of precipitates emerging during the artificial aging.

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.

Numerical evaluation of forging process designs of a hybrid co-extruded demonstrator consisting of steel and aluminium.

Multi-material solutions represent a promising approach for the production of load-optimised parts. The combination of material-specific advantages of different materials in a single component allows the fulfilment of conflicting requirements e.g. high performance and low weight. Fabrication of hybrid components is challenging due to the dissimilar properties of the individual materials and requires the development of suitable manufacturing technologies. The present paper deals with the simulation-based design of a forming process for the production of a suspension control arm consisting of steel and aluminium. With the focus on material flow, two forming concepts, open-die and closed-die forging, were investigated, in order to ensure the required material distribution similar to the final part. In addition, a tool analysis was carried out to avoid thermo-mechanical overload of the tool system. It was found that the required material distribution can be achieved with both forming concepts. However, a closed-die forging concept is not suitable because of the high stresses in the forging dies exceed the tool steel’s strength.

Subsurface Crack Initiation and Propagation in an Open Dieforged High Strength Steel: A Microstructural Analysis

This paper presents an experimental investigation with the objective to determine the root causes for the cracking of a large size bar made of a medium carbon low alloy steel after open die forging and heat treatments operations. The cracks were observed below the surface during the machining step. In order to understand the mechanisms of crack initiation and propagation, micro-CT tomography and scanning electron microscope (SEM) were employed. Microstructural damage analysis revealed oxidation of different alloying elements, more specifically manganese, chromium and silicon. The presence of defects in the form of cavities and porosities were also observed at the grain boundaries. Some of the above defects were observed along the crack path, while others were on both sides of the cracks without any connection to them and finally, a third group completely isolated from any crack. The characteristics of the defects were thoroughly analyzed and it was found that the crack initiation could be attributed principally to the porosities/cavities formed during solidification. The analysis also showed that crack propagation occurred during solidification and/or forging and heat treatment steps.

Cost-affordable and qualified powder metallurgy metastable beta titanium alloy by designing short-process consolidation and processing

Short-time processing route has been designed to manufacture cost-affordable and high-quality powder metallurgy (PM) metastable β titanium alloy, containing rapid powder consolidation (modified thermomechanical pressing), one-step thermomechanical processing (simple open die uniaxial hot forging by industrial press) and fast heat treatment (one-step annealing at various temperatures for only one hour). Based on comprehensive microstructure characterizations and mechanical property examinations, underlying microstructural evolution mechanism and microstructure-property relationship of the produced alloys were uncovered and elucidated thoroughly. Homogeneous macrostructure and fine-grain microstructure without undissolved particles and large pores are obtained for the alloy after thermomechanical powder consolidation as a result of the concurrent effect of external deformation and high-temperature diffusion. One-step open-die forging is verified to produce full-dense and sound PM alloy pancake with large-scale and high strength. Attributed to the harmonious concurrence of hierarchical α precipitation and heterogeneous grain structure, synergistic strength-ductility combinations are achieved for the alloy after specific processing and heat treatment with the tensile strength and strain at failure values of 1386.5 MPa/7.3% and 1252.3 MPa/9.0%, respectively. These strength-ductility combinations are comparable and/or even better than other metastable β titanium alloys prepared by some PM and ingot metallurgy approaches with relatively high cost and time consumption.

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.

An analytical cost estimation model for the design of axisymmetric components with open-die forging technology

Open-die forging is a manufacturing process commonly used for realising simple shaped components with high mechanical performances and limited capability in terms of production volume. To date, an analytical model for estimating the costs of components manufactured with this technology is still an open issue. The paper aims to define an analytical model for cost estimation of axisymmetric components manufactured by open-die forging technology. The model is grounded on the analysis of geometrical features available at the design stage providing a detailed cost breakdown in relation to all the process phases and the raw material. The model allows predicting product cost, linking geometrical features and cost items, to carry out design-to-cost actions oriented to the reduction of manufacturing cost. The model is mainly conceived for design engineers, cost engineers and buyers, respectively, for improving the product design, the manufacturing process and the supply chain. Cost model and related schemas for collecting equations and data are presented, including the approach for sizing the raw material and a set of rules for modelling the related cost. Finally, analytic equations for modelling the cost of the whole forging process (i.e. billet cutting, heating, pre-smoothing, smoothing, upsetting, max-shoulder cogging, necking and shoulders cogging) are reported. The cost model has been tested on eight cylindrical parts such as discs and shafts with different shapes, dimensions and materials. Two forge masters have been involved in the testing phase. The absolute average deviation between the actual and estimated costs is approximately 4% for raw material and 21% for the process. The absolute average deviation on the total cost (raw material and manufacturing process) is approximately 5%.

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