Forging Stage Research Articles

The evolution of the compaction process and the deformed state of porous blanks during their hot forging in the open die

The article presents the results of the study of the evolution of the deformed state of the workpieces, the energetic parameters of the process and the distribution of porosity over the volume of the forging at all stages of hot forging of porous powder forgings in an open die. Modeling of the process was carried out using the finite element method using the DEFORM 2D/3D software complex. As a result of the simulation, it was found that at the initial stage of the process, the blank is mainly compacted with minimal radial flow of the material. Noticeable flow of metal into the groove groove area begins only when the forging material reaches an average relative density exceeding 90%. A significantly different nature of the distribution of axial er and radial ez deformations over the volume of the forging was noted. A zone with increased levels of values of axial deformations is formed in the central layer of the forging, equidistant from the upper and lower surfaces of the die cavity, and the values of radial deformations decrease with distance from the zone bordering the free side surface of the workpiece in the radial (to-center) direction. The minimum values of ez and er appear in the upper and lower angular stagnant zones of the forging. It is shown that the graph of the dependence of the deformation force on the displacement of the punch is marked by the presence of at least three characteristic sections due to the relationship between the processes of compaction and forging shape change at each stage of the process.

Analysis of the Effect of the Elongation Operation on the Welding of Internal Metallurgical Discontinuities.

This article discusses the results of our research into the effect of elongation on the welding of internal metallurgical discontinuities for two different geometrical shapes of a model feedstock of a selected magnesium alloy. Model discontinuities, specifically those of the metallurgical void type, were placed in various local zones of the modelled feedstock to check the influence of their location on their welding. The numerical modelling was carried out using the Forge®NxT2.1 application based on the finite element method. The results of the numerical tests were verified in laboratory conditions using the Gleeble simulator of metallurgical processes. Based on this research, it was found that the geometric shape of the feedstock material and the location of internal metallurgical discontinuities have a significant impact on the welding of discontinuities. The optimal values of the main process parameters of the elongation operation in flat dies were also determined for use in individual forging stages in order to eliminate internal metallurgical discontinuities. On the basis of the numerical studies carried out and their verification under laboratory conditions, it was concluded that a relative draft equal to 35% should be applied to weld the metallurgical discontinuities, which would result in a favorable hydrostatic pressure distribution within the discontinuities.

Application of processing maps and numerical modelling for identification of parameters and limitations of hot forging process of 80MnSi8-6 steel

The processing maps developed by dynamic material modelling (DMM) method are now widely used in the design of hot forming processes. However, this applies to those processes that are relatively fast or are carried out under isothermal conditions, when it is possible to maintain the deformation parameters within the processing window. In the case of multi-stage free forging, the temperature successively decreases during subsequent operations and is increased during inter-process reheating. Under such conditions, processing maps in direct form are not applicable. The proposed solution is to implement the data obtained by the DMM method into calculations carried out by the finite element method (FEM). This approach leads to obtain the distributions of DMM parameters in the volume of the feedstock at successive forging stages. Selected results of a combined DMM/FEM analysis of a multi-stage hot forging process of 80MnSi8-6 steel are presented. The starting data for the analysis were the flow curves of this material, determined from compression tests. The processing maps were developed and processing windows were determined. The results of the DMM analysis were verified by microstructure observations. Data from the DMM analysis were implemented into QForm software using LUA scripts. An integrated FEM/DMM numerical analysis of the process of a multi-step hot free forging of an example product was performed. The geometry of the tools and a sequence of operations were developed. The distributions of the DMM parameters and the hot deformation activation energy in the forging volume after successive forging sequences were analyzed.

Cylindrical Billet Size Optimization for Hot Closed-Die Forging of the Upper Ball Joint

Three-dimensional finite element modeling (FEM) has been carried out using QForm software on the hot forging operation of the upper ball joint, involving the process of roughing and finishing. The material used is SNCM8 commercial alloy steel. This paper aims to optimize the initial billet size to achieve a final forged product without any defects. To accomplish this task, it was necessary to determine the initial optimum billet size by calculating the mass ratio. It is more practical to reduce the length of the initial billet and keep the diameter constant. The initial billet size was obtained by FE simulation by varying the five cases of mass ratio. The minimum dimension of the initial billet, which filled the die cavity without defects, was selected for the tryout experiments. The experimental results supported the FEM results and indicated that the optimum size was ∅48x152.88 mm, which may reduce material waste by 17.65%. Additionally, the forging load during the forging process was investigated. The actual forging load was slightly higher than the experimental one. The forging load showed a maximum error about 10.13%. Finite element simulation by QForm V10.1.6. software is recommended as an efficient tool for predicting the hot deformation behavior of the material during several stages of hot forging, which can save material costs and the cost of trials, leading to enhancements in the manufacturing process.

Direct Powder Forging—A New Approach for near Net Shape Processing of Titanium Powders

This study investigates direct powder forging (DPF) as a new approach for near-net-shape processing of titanium alloys using a coarse particle size distribution (PSD) between 90 and 250 μm. This route was utilised to takes advantage of DPF’s enclosed nature to make near-net-shape components with conventional forging equipment, making it attractive and viable even for reactive powder such as titanium. In this study, the uncompacted Ti-6Al-4V ELI powder was sealed under vacuum in a stainless-steel canister and hot forged in air to produce a fully dense titanium femoral stem. After the final forging stage, the excess material in the flash region was cut, which efficiently released the canister, revealing the forged part with minimal surface contamination. The as-forged microstructure comprises coarse β grains with a martensitic structure. The subsequent annealing was able to generate a fine and homogenous lamellar microstructure with mechanical properties that respects the surgical implant standard, showing that DPF offers significant potential for forged titanium parts. Therefore, the DPF process provides a suitable alternative to produce titanium components using basic equipment, making it more available to the industry.

Evolution of γ′ Precipitation During the Early Stages of Industrial Forging of a Nickel-Based Superalloy

A sample of the Ni-based superalloy AD730 was heat treated at a supersolvus temperature (1160 °C) then slowly cooled through the solvus temperature (1110 °C) at 10 °C/hr down to 1080 °C, i.e., a rate representative of the cooling conditions of an industrial-scale billet undergoing controlled cooling. The γ′ precipitate distribution which forms during this cooling was investigated, and a mix of continuous and discontinuous precipitation was found. The discontinuous γ′ precipitates were imaged using 3D tomography, and were shown to present very different sizes, morphologies, and aspect ratios when observed in different 2D imaging planes. The interaction between different populations of γ′ precipitate and recrystallization was investigated, and it was found that the discontinuous precipitates present more of a barrier to recrystallization than the continuous ones. This has been explained based on the different inter-precipitate spacings observed for the two populations. In addition to these γ′ precipitates which form during slow cooling, a fine and dense distribution of approximately spherical γ′ precipitates was found to form dynamically, during subsequent subsolvus forging, within unrecrystallized grains.

Computer and physical modeling of multiple isothermal forging of EK61 superalloy

Studies on the process of multiple isothermal forging of high-temperature nickel-based EK61 superalloy using computer simulation in the DEFORM-3D software package in a three-dimensional formulation and a comparison with experimental data were carried out. Based on the simulation results, it is shown that with each subsequent stage of forging, the maximum strain values become higher, and the strain differences in the central and peripheral regions become smaller. Such a strain distribution leads to the formation of a homogeneous ultrafine-grained (UFG) microstructure. The initial coarse-grained microstructure is gradually transformed into a fine-grained microduplex type microstructure at 0.77Tmelt and with a further decrease in the processing temperature to 0.73Tmelt, it is transformed into a submicroduplex type (γ + δ) UFG microstructure.

Provision of allowance for the root and connecting rod necks and balancing of the forgings of the crankshaft of a heavy-duty vehicle

The article discusses the requirements for balancing crankshafts. The unbalanced mass of the crankshaft after machining should be oriented in a certain angular sector, which ensures the removal of material in the opposite phase along the end surface of the counterweights. The existing calculation methods provide the specified imbalance conditions only at the design stage of the crankshaft forging by sorting through combinations of geometric accuracy indicators within the fields of their tolerances with simultaneous calculation of the position of the unbalanced mass. The method provides the design position of the unbalanced mass, but does not extend to the forging manufacturing process. The article considers the practice of machining production of changing the position of the machining base, which ensures the redistribution of masses. unprocessed elements of counterweights and the hit of an unbalanced mass in a given angular sector. Changing the position of the processing base completely redistributes the allowance for the root and connecting rod necks, which is not taken into account in the process of hot volumetric stamping of crankshaft forgings. The article presents a calculation scheme that allows taking into account changes in the position of the machining base, as well as mathematical dependencies that allow, according to measurements from the extreme trunnions of the crankshaft forging, to simulate the distribution of the allowance for the root and connecting rod necks from the machining base. Mathematical dependencies allow you to select the value of the adjustment displacements of the stamping equipment and ensure that there is an allowance for all angular phases of the main and connecting rod necks of the crankshaft forging.

Deformation Heating and Temperature Changes in a Near-β Titanium Alloy during β-Processed Forging

We investigated the temperature increase caused by heat generation from plastic deformation during β-processed forging in a near-β titanium alloy, Ti-17 alloy (Ti-5Al-2Sn-2Zr-4Cr-4Mo, wt%), by inserting thermocouples into large workpieces (100 mm in diameter and 50 mm in height). The workpiece was initially heated and held at 1193 K (920 °C) in the single-β region. It was subsequently forged between hot dies in surrounding heaters at a compression percentage of 75% at strain rates of 0.05 and 0.5 s−1 at 1023–1123 K in the (α + β) region. At 0.05 s−1, the temperature logarithmically increased by 39 K in 28 s for 1023 K; it increased by 30 K in 28 s for 1073 K. However, at 0.5 s−1, the material temperature increased, in 3 s, beyond or close to the β-transus temperature during forging at 1023 and 1073 K. In addition, as the forging temperature decreased, the increase in material temperature moderated, resulting in a difference of 27 K in the last forging stage, between the conditions of 1023 and 1073 K. This would reduce the temperature difference effect on microstructure formation during β-processed forging.

Justification of the Application of Resource-Saving Technology for the Restoration of Metal-Intensive Rear Semi-Axles of Trucks Using Hot Plastic Deformation

The article is devoted to the substantiation of technological foundations for the restoration of extremely worn-out, metal-consuming, and resource-consuming parts, in a method consisting of applying a compensating metal wear with subsequent plastic deformation. Currently, there are no technologies for their restoration in a repair facility that guarantee the resilience of the factory product. The proposed technological process of repair consists of butt welding onto the end of the spline semi-axle shank, compensating for the wear of the metal, the volume of which takes into account the losses resulting from the wear of the slots, as well as allowances for their machining. In the example of forging the axle shaft of a truck’s driving axle, the regularities of the plastic flow of metal during part deformation in the stamp are revealed. In the process of hot volumetric upsetting of long cylindrical parts with a variable diameter, it is important to know the possible directions of metal movements, as well as the energy-power characteristics of the process at various stages of forging. The evaluation criteria of the level of perfection of the technology were indicators of resource conservation and efficiency of the recovery route. The technological direction of the conducted research was analyzed, step by step, from the standpoint of saving repair materials and energy resources. The results of theoretical studies are crucial in the design of die tooling, for the manufacture of blanks, when restoring the rear axle shafts of trucks with pressure. Production tests carried out on the models, obtained as a result of mathematical processing of experimental data, confirmed the reliability of the experimental information. The introduction of the proposed set of repair equipment for the restoration of semi-axles will allow the formation of additional production in the region for the recycling of worn-out metal-intensive steel parts of agricultural machinery.

Analysis of an automotive coil spring fracture

Failure analysis of a coil spring which failed prematurely during service was carried out using optical and scanning electron microscopy, hardness testing, metallography and optical emission spectroscopy. Indentation marks, which described a helical pattern along the spring wire, were identified in the spring wire below the protective paint. By analyzing the manufacturing process, which included a radial forging stage, it was established that these indentation marks were due to a crack in the forging hammer. One of these marks propagated fatigue cracks, which is confirmed by the presence of ratchet marks on the fracture surface. Observation of a notch at the crack origin, followed by fatigue mechanism and intergranular cracking implies that some sort of stress concentration might have facilitated crack growth and led to failure. It is suggested that radial forging should be carried out by recommended procedures and the status of the forging hammers should be checked before each major run. Careful inspection of the surface after forging must also be carried out to assure product quality and avoid premature failure.

FINITE ELEMENT ANALYSIS OF CHROMIUM AND MOLYBDENUM ALLOYED STEEL BILLETS FORGED ON MULTI STEP PROCESS USING SIMUFACT FORMING

ABSTRACT Simufact Forming covers the complete spectrum of working on forming technologies like rolling, forging, and sheet metal forming. In this paper, finite element comparative analysis was performed on two chromium- and molybdenum-alloyed steel billets, namely 42CrMo4 and 16CrMo4 alloyed steels, using multi-step forming process of hot closed die forging process using Simufact Forming software. 42CrMo4 alloy steel is most commonly used in making of automobile components, and 16CrMo4 alloyed steels are commonly utilised in the area of ship building, airplanes, etc. While working with these materials, with the help of forging process, lot of stresses, strains and temperatures will develop. In this paper, three state variables, namely effective plastic strain, equivalent stress and temperature, for two materials at the end of multi-step forming processes like chamfering, preforming and final forging stages are evaluated and compared. In cooling process, the initial temperature of billet is maintained at 1250°C for both materials. Finally, comparative analysis of two alloyed steel billets was done by considering three-state variables.

Microstructural and mechanical response of ZK60 magnesium alloy subjected to radial forging

Radial forging (RF) is an economical manufacturing forging process, in which four dies arranged radially around the workpiece simultaneously act on the workpiece with high-frequency radial movement. In this study, a ZK60 magnesium alloy step-shaft bar was processed under different accumulated strains by RF at 350 °C. The deformation behavior, microstructure evolution, and mechanical responses of this bar were systematically investigated via numerical simulations and experiments. At the early deformation stage of forging, the material undergoes pronounced grain refinement but an inhomogeneous grain structure is formed due to the strain gradient along the radial direction. The grains in different radial parts were gradually refined by increasing the RF pass, resulting in a bimodal grained structure comprising coarse (∼14.1 μm) and fine (∼2.3 μm) grains. With the RF pass increased, the initial micro-size β-phases were gradually crushed and dissolved into the matrix mostly, eventually evolving to form a higher area fraction of nano-sized Zn2Zr spheroidal particles uniformly distributed through the grain interior. The texture changed as the RF strain increased, with the c-axes of most of the deformed grains rotating in the RD. Additionally, excellent mechanical properties including higher values of tensile strengths and ductility were attained after the three RFed passes, compared to the as-received sample.

Effect of Friction Time on the Mechanical and Microstructural Properties of AA6061 Joints by Continuous Drive Friction Welding

Friction welding is becoming a viable replacement of conventional joining methods. Continuous Drive Friction Welding (CDFW) is a type of friction welding used to join rods, tubes and similar shapes. Usually, the process contains a friction stage and a forging stage and the process parameters would be ticked accordingly. AA6061 is an Mg and Si aluminum alloy that is widely used in many industries. This research investigates the effect of friction time on the mechanical properties of AA6061 joints made with CDFW and the relation to the microstructure of the material and thermal profiles. It was found that AA6061 does not require a forging stage where solid joints are obtained without forging and did not fracture within the welding zones. Also, it was concluded that the process parameters are to be tailored in a way that produces a specific type of grain structure within the welding areas.

Multi-objective optimization of high carbon steel (EN-31) and low carbon steel (SAE-1020) using Grey Taguchi method in rotary friction stir welding

PurposeNowadays, a rotary friction welding method is accepted in many industries, particularly for joining dissimilar materials as a mass production process. It is due to advantages like less material waste, low production time and low energy expenditure. The effect of the change in carbon contents in steel is studied experimentally in the rotary friction welding process, and a statistical model is developed. The Grey Taguchi method gives the single parameters optimization for all output responses. The paper aims to discuss these issues.Design/methodology/approachAn experimental setup was designed and produced to achieve the multi-response in single optimum parameters through Grey relational analysis. A continuous/direct drive rotary friction welding process is chosen in which transition from friction to the forging stage can be achieved automatically by applying a break. In this experimentation, high carbon and low carbon work-pieces with different carbon percentage were welded with rotary friction welding. Response tensile strength and micro-hardness of the design of the experiment are used to analyze the results.FindingsThe optimization of parameters has been performed with Grey relational analysis, and optimum parameters are friction pressure 40 kg/cm2, forging pressure 100 kg/cm2 and speed 1,120 rpm. GRA optimum parameters give 56.04 and 82.16 percent improvement in Tensile strength and micro-hardness, respectively.Practical implicationsHigh carbon steel (En-31) and low carbon steel (SAE-1020) are used in so many industrial applications. These materials are mostly used in the process like manufacturing, metallurgy, machinery, agricultural, etc. These practical applications have brought forward definite and notable economic benefits.Originality/valueIt provides a new framework to investigate the problems where multiple input machining variables and various output responses are obtained in single optimized parameters.

Heading process design of titanium alloy dental screws

This study is to investigate the effects of the process parameters on the heading load and metal flow pattern during heading processes of titanium alloy dental screws. The flow stresses of titanium alloy Ti-6Al-4V at different forming temperatures and strain rates are obtained by compression tests. A heading process composed of two stages of shaft extrusion and head forging is proposed. The material flow pattern of the billet inside the die is analyzed using the finite element analyses. The effects of the upper die stroke and forming speed on the heading loads and product shapes are discussed. On the other hand, die stress analysis inside the punch and lower die are also investigated.

Microstructure evolution and mechanical properties of AZ80 magnesium alloy during high-pass multi-directional forging

Abstract Severe plastic deformation (SPD) was carried out on AZ80 alloy by high-pass multi-directional forging (MDF). Results showed that AZ80 alloy was effectively refined through MDF, and average grain size was refined to 0.73 µm after 24 passes of forging. Its tensile strength, yield strength and elongation reached 333.8 MPa, 233.7 MPa and 17.8%, respectively, which were 1.22 times, 1.35 times and 2.54 times of those before the forging. When the MDF was less than 6 passes, the coarse grains were mechanically divided and refined, and a small amount of recrystallized grains appeared in the deformation band and its cross zone. When the MDF was more than 6 passes, grain division, recrystallization nucleation and grain growth occurred simultaneously, the microstructure refinement was slowed, and the uniformity was improved continuously. The heating between forging passes mainly caused restoration in the early forging, and the static recrystallization refinement in the middle of forging. In the later stage of forging, the grain growth caused by static recrystallization and the grain refinement caused by the deformation canceled out, and the microstructure no longer continued to refine with the increase of the forging pass.

Controlling Flow Instability in Straight Spur Gear Forging Using Numerical Simulation and Response Surface Method

Workability domain without the onset of flow instability was developed by numerical simulation and response surface method (RSM) for complex-shaped straight spur gear forging. The processing map of AZ31B alloys was calculated from flow stress curves and then integrated with the finite element model to simulate the distribution of flow instability in the straight spur gear undergoing isothermal forging process. Occurrence of flow instability depends on forging temperature, punch velocity and billet reduction. Taking forging temperature and punch velocity as design variables, while billet reduction as response variable, RSM of workability domain was established. Analysis of variance indicates that forging temperature is the most significant factor determining the appearance of flow instability in the forged gear. Flow instability is easier to take place at lower temperatures of 250 and 300 °C in the early stage of forging but at higher temperatures of 350 and 400 °C in the later stage of forging, which is attributed to different deformation mechanisms and dynamic recrystallization behaviors at different temperatures or deformation levels. Meanwhile, increasing punch velocity further reduces the workability of the forged gear. Four different processing paths were chosen to carry out the gear forging trials. Visual observations and metallographic examinations demonstrate that the developed workability domain contributes to optimization of forging parameters.

Stress relaxation behaviour in IN718 nickel based superalloy during ageing heat treatments

Designing microstructure of components made from Inconel 718 nickel based superalloy (IN718) with tailored mechanical properties for high temperature applications, require sequential thermo-mechanical processing. This often includes straining and annealing at solution annealing temperature (i.e. ≈ 980°C) followed by water quenching and subsequent aging heat treatments at lower temperatures. In addition to the microstructure development (i.e. precipitation) the aging heat treatment partially relieve the residual stresses generated at previous stages of forging and water quenching, however the stress field will not be completely relaxed.In this study, a series of experiments were conducted on round tensile specimens made from IN718 bar to investigate tensile stress relaxation behaviours at elevated temperatures used for aging heat treatments. The stress relaxation curves obtained can be described by a hyperbolic function with a non-zero asymptotic stress (σ∞), which seems to be proportional to the initially applied stress (σ0) for a fixed temperature. This behaviour is investigated at temperatures between 620°C and 770°C that is a temperature range used in industry to perform the aging heat treatments to obtain microstructures with tailored mechanical properties. It has been shown that the σ∞/ σ0 ratio has decreased rapidly with increasing temperature at this range. The relaxation behaviour has been assessed numerically and an empirical relationship has been defined for each temperature that can be used for modelling purposes.

Design and hot forging manufacturing of non-circular spur bevel gear

Non-circular spur bevel gear (NCSB-gear) is a kind of special spur bevel gear which can perform variable speed ratio transmission. It can achieve several special functions which cannot be realized by circular spur bevel gear (CSB-gear), such as the skid resistance function in automobile differential mechanism. However, NCSB-gear is quite difficult to be designed and manufactured because of its complicated shape and specific transmitting characteristic. In this research, a new design method of NCSB-gear based on vectorial coordinate transmission is proposed to simplify the calculation process of tooth profile, and a NCSB-gear pair which is used in automobile differential is designed. Then, a new hot forging process is proposed to manufacture the driven NCSB-gear, and a pre-forging stage is arranged in this hot forging process so as to pre-allocate the material according to the shape features of the driven NCSB-gear, which is benefit for metal flowing in final forging stage. Several 3D FE simulation models of hot forging process of the driven NCSB-gear with or without pre-forging stage are developed, and the metal flowing, effective strain distribution and temperature distribution are comprehensively investigated and compared. Based on the FE simulation results, several experiments of hot forging process of the driven NCSB-gear are carried out. The results show that, the hot forging process with pre-forging stage can obviously improve the rationality of metal flowing, the homogeneity of the effective strain distribution on NCSB-gear, and the homogeneity of temperature distribution on NCSB-gear and the gear-tooth die. Furthermore, the experiment results are consistent well with the simulation results, and a fully filled NCSB-gear part is obtained by using the hot forging process with pre-forging stage, which confirms that this hot forging process of NCSB-gear is reliable.