Closed-die Forging Research Articles

Multi-objective optimization of preforming operation in near-net shape forming of complex forging

The coupler knuckle of railway wagon is a complex forging component with big section change. In this paper, a near-net-shape forming process for coupler knuckle based on closed-die forging without flash was proposed and the preforming operation was designed and optimized. Firstly, the shape and the dimension of the preforging were preliminarily designed based on the geometric features of forged knuckle and the flow characteristics of metal in the forging process, and then a multi-objective optimization approach based on the filling capacity, deformation homogeneity, and damage degree of forgings was established, and the response surface method combined with the finite element simulation was used to obtain the optimum geometric parameters of preforging. In order to verify the effectiveness of the near-net-shape forming process and the optimized results on preform design, forming experiments and measurements were carried out; the analyzed results show that based on the designed preforging, near-net-shape forming process is capable of producing coupler knuckle of high quality and without forming defect.

Investigation of the key process parameters in the hot forming of a shackle

To investigate the impact of the variations of different input parameters in the multi-stage hot forging process of a shackle, an analysis is carried out through numerical simulations of the whole manufacturing process. Due to the complexity of the process and the large number of factors influencing the thermo-mechanical forming process, the investigation is focused on the workpiece positioning, the temperature of the tools, the transportation time and the contact-friction conditions. The analysis is narrowed down to the key stages of the process that are closed-die forging and ram bending. Coupled with experimental measurements, a comparison of forging loads, functional dimensions and shackle geometry is presented. It is shown that the conformation of shackle geometry to the industrial specifications depends mainly on the workpiece positioning and the transportation time. The dispersion measured in the forging load and in the main dimensions can thus be explained and these observations can be used to improve the manufacturing process for shackles.

Optimization of Process Parameters for Closed-die Forging Based on Finite Element Simulation

In this study, finite element software was used to simulate and optimize the process parameters including billet thickness, forging speed, and friction coefficient during closed-die forging. The results show that the mean equivalent strain of the billet gradually increases as the thickness reduces. However, the corners of the billet show certain arcs and the materials are insufficiently filled when the thickness is too small. The higher the die-forging speed is, the more significantly the temperature rises and the more non-uniformly the temperature distributes in the billet. In addition, the mean equivalent strain shows little change when the friction coefficient increased from 0.1 to 0.3, but the strain distribution became more inhomogeneous.

Closed-die Forging Technology and Numerical Simulation of Aluminum Alloy Connecting Rod

Abstract In order to improve quality and reveal the law of precision forging, closed-die forging technology is used in this paper to conduct a numerical analysis of the forming process of aluminum alloy connecting rod by the DEFORM software. Forming effects under different loading modes were acquired, and forming process, blank flow characteristics, stress-strain distribution and load-stroke curve characteristics were analyzed. Study results indicate that the forming effect under the loading mode featuring first movement of lateral punch and then movement of upper and lower punches is good with high quality forge piece and no defect, the closed-die forging technology of aluminum alloy connecting rod is reasonable and feasible. Under a certain deformation velocity and deformation mode, aluminum alloy connecting rod forming load firstly reduces and then increases, the forming load is in direct proportion to deformation velocity. When the forming process is finished, forming load reaches 130T, it accords with the production practice. The study results provide a certain reference for guiding the formulation of closed-die forging production technology of aluminum alloy connecting rods.

Experimental evaluation of wear protection ability of sheet metal die covers in closed-die forging

Wear is the main mechanism that reduces the lifetime of forging dies used in closed die forging. A newly proposed approach to decrease die wear is the concept of protective sheet metal forging die covers, where an inexpensive and easy-to-exchange sheet metal die cover is used to protect forging dies. After this concept has been fundamentally validated by previous studies, the presented work aims to further evaluate the protective effects of this concept regarding wear reduction. First, an application-oriented experiment of the die cover concept on forging dies for producing square flange was conducted. On both the forging dies with and without die covers 100 forging strokes were carried out. The wear depths of both forging dies were then measured and compared. The results indicated that the forging die with die covers has up to 98% less wear than the forging die without die covers. The expected tool life of the forging die with die covers is therefore 600% longer. In addition, the die cover applied in the experiment achieved the service life of 100 forging cycles without being distorted, which reached the maximum service life of the die cover concept so far.

FAST-forge of Diffusion Bonded Dissimilar Titanium Alloys: A Novel Hybrid Processing Approach for Next Generation Near-Net Shape Components

Material reductions, weight savings, design optimisation, and a reduction in the environmental impact can be achieved by improving the performance of near-net shape (NNS) titanium alloy components. The method demonstrated in this paper is to use a solid-state approach, which includes diffusion bonding discrete layers of dissimilar titanium alloy powders (CP-Ti, Ti-6Al-4V and Ti-5Al-5Mo-5V-3Cr) using field-assisted sintering technology (FAST), followed by subsequent forging steps. This article demonstrates the hybrid process route, firstly through small-scale uni-axial compression tests and secondly through closed-die forging of dissimilar titanium alloy FAST preforms into an NNS (near-net shape) component. In order to characterise and simulate the underlying forging behaviour of dissimilar alloy combinations, uni-axial compression tests of FAST cylindrical samples provided flow stress behaviour and the effect of differing alloy volume fractions on the resistance to deformation and hot working behaviour. Despite the mismatch in the magnitude of flow stress between alloys, excellent structural bond integrity is maintained throughout. This is also reflected in the comparatively uncontrolled closed-die forging of the NNS demonstrator components. Microstructural analysis across the dissimilar diffusion bond line was undertaken in the components and finite element modelling software reliably predicts the strain distribution and bond line flow behaviour during the multi-step forging process.

Tensile and Fracture Properties of Commercially Pure Titanium (CP-70) Hemispherical Forgings

Commercially pure (CP-70) titanium is used as the metallic liner for composite overwrapped pressure vessels used in satellite launch vehicles. The metallic liner is fabricated from domes machined out of CP-70 titanium forgings. During the hot closed-die forging of CP-70 domes from billets, the amount of deformation varies location to location, due to the non-uniform flow of material in the die cavity. This non-uniform strain distribution in the hemispherical dome results in microstructural variations along the forging axis which will remain even after annealing. The aim of the present work is to study the tensile properties, impact strength and fracture toughness of CP-70 hemispherical forging in annealed condition from top end to bottom end of domes in radial and circumferential directions with a view to understand the variation in mechanical properties to asses the design margin. Study revealed significant amount of the work-hardening difference within a forged dome even after annealing.

Investigation of applying protective sheet metal die covers for hot forging dies on a cross-forging geometry

Improving tool life is one of the main challenges and research objectives in closed-die forging. One approach, first proposed in (Rosenstock et al. 2015) uses an inexpensive and easy-to-exchange sheet metal die cover, which is placed on the die surface during forging. By using this cover, die wear can be reduced since mechanical and thermal loads mostly affect the die cover instead of the die itself. Numerical and experimental investigations (Wolfgarten et al. 2015; Yu et al. 2016) have proven the general key features of the concept and the positive impact on the lifetime of the forging die. However, these studies have shown that the applicability of the concept and the corresponding lifetime of the die cover are strongly dependent on the investigated die and die cover geometries. For simple 2D die cover geometries, where the die cover can be produced by a simple bending operation, the maximum die cover lifetime of seven forging cycles was achieved. Since these geometries offer low structural stability, the die covers are prone to deformation or folding during forging. Hence, this work investigates the application of die covers in complex geometries. For this purpose, a 3D die cover geometry was proposed that offers higher structural stability and less challenging contact conditions regarding the material flow during forging. The die cover successfully experienced 40 forging cycles without visible distortions or folds. Regarding the thermal loads, the maximum temperature and the temperature amplitude measured in the forging die were reduced by 40 °C. Based on the experimental results, a numerical simulation model was built and validated regarding the temperature evolution and forging forces. The numerical model indicates a significant reduction in the mechanical loads on the dies through the application of the die cover.

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.

NALYSIS OF CLOSED DIE COLD FORGING FOR SPUR GEAR USING THREE DIMENSIONAL SLAB TECHNIQUE

The present study is concerned with upset forging of arbitrarily-shaped prismatic blocks which is characterized by three-dimensional deformation. From the proposed velocity field, the upper-bound load and deformed configuration are determined by minimizing the total power consumption with respect to some chosen parameters; such as the proposed method of analysis in this work can be used for prediction of forging load and deformation in upset forging of arbitrarily-shaped prismatic blocks. Closed-die forging of toothed disk is investigated using the slab method technique The tooth regions are approximated by prismatic rectangular sections. The velocity field comprising three-unit deformation regions is used. A constant frictional stress between work-piece and forging die is assumed. The average punch pressure normalized by the flow stress of the billet material is determined theoretically and compared with the present experimental results The experimental work is carried out on a commercial pure Aluminum (Al 1100) at room temperature The forging process is carried out using one die geometry without using any additional blocker dies. The theoretical predictions of forging pressures and deformation configurations are in good agreement with the experimental results. The experimental work proves that the analysis is good within approximately 36% of error according to many parameters.

Study on closed-die forging technology and numerical simulation of T-junction of high-pressure pipe

Study on closed-die forging technology and numerical simulation of T-junction of high-pressure pipe

Novel Method of Severe Plastic Deformation - Continuous Closed Die Forging: CP Aluminum Case Study

There is a large number of methods for severe plastic deformation (SPD). Multidirectional forging (MDF) is probably one of the most easily scalable for industrial application. In general, two main conditions need to be fulfilled for successful SPD processing: constant sample geometry and application of a quasi-hydrostatic pressure. The first condition is necessary for strain accumulation by repetitive deformation and the second one helps preventing cracking in the specimens with high accumulated strain. However, MDF is not providing quasi-hydrostatic condition in the processed sample. This paper reports a novel method for severe plastic deformation, namely continuous closed die forging (CCDF), which fulfils both requirements for the successful deformation of samples to a very high accumulated strain. Commercially pure aluminum (1050) was processed to a total strain of 24 by CCDF. After processing, the microstructure was refined down to a mean grain size of 0.78 μm. Tensile testing showed good mechanical properties: yield strength and ultimate tensile strength of the ultrafine-grained aluminum were 180 and 226 MPa, respectively. Elongation to rupture was about 18%. The microstructure, microhardness and grain boundary statistics are discussed with regard to the high mechanical properties of the UFG aluminum processed by this novel method.

NEW TREATMENT ROUTE FOR CLOSED-DIE FORGINGS OF STEELS WITH 2.5% MANGANESE

The requirements placed on closed-die-forged parts of advanced steels have been increasing recently. Such forgings demand an innovative approach to both design and heat treatment. It is important to obtain high strength and sufficient ductility in closed-die forgings. High strength, mostly associated with martensitic microstructure, is often to the detriment of ductility. Ductility can be improved by incorporating a certain volume fraction of retained austenite in the resulting microstructure. Among heat treatment processes capable of producing martensite and retained austenite, there is the Q&P process (Quenching and Partitioning). This process is characterized by rapid cooling from the soaking temperature to the quenching temperature, which is between Ms and Mf, and subsequent reheating and holding at the partitioning temperature. Thus, strength levels of more than 2000 MPa combined with more than 10% elongation can be obtained. This experimental programme involved steels with 2.5% manganese. Forgings of these steels were heat treated using an innovative process in order to obtain an ultimate strength of more than 2000 MPa combined with sufficient elongation. Thanks to a higher manganese level, the Mf was depressed as low as 78°C, and therefore quenching was carried out not only in air but also in boiling water. Holding at the partitioning temperature of 180°C, when carbon migrates from super-saturated martensite to retained austenite, took place in a furnace. The effects of heat treatment parameters on the resulting mechanical properties and microstructure evolution in various locations of the forging were studied.

High Temperature Friction and Wear Testing for Closed-Die Steel and Aluminium Forgings

There are several testing methodologies to characterize the friction and wear behavior of coated or special heat treated dies and forging materials for closed-die forgings. In order to measure the friction coefficient, the wear rate, galling or fretting behavior or the effect of lubricants, three different testing types (ring compression testing, a self-made high temperature rotation tribometer and hot torsion friction) are described in detail. To meet the practical requirements, the influencing factors like temperature level, sliding speed, contact pressure and specific surface treatments or coatings have to be varied in proper ranges. The results may contribute to find better friction models for finite element analysis, and consequently to a better prediction of the material flow and other related parameters. By confocal microscopy and a full metallographic investigation, the microstructural changes near the interface are studied, which lead to a better understanding of the wear and degradation mechanisms involved. These findings may help to find out countermeasures for life time improvements of the forging dies.

Numerical simulation of cryogenic cyclic closed-die forging of Cu: hardness distribution, strain maps and microstructural stability

Cyclic closed-die forging (CCDF) appears to be an easy to operate deformation process, which imposes high levels of strain, even on difficult-to-deform materials. However, despite said potential advantages, the CCDF at cryogenic temperatures has not yet been investigated. Copper samples with dimensions of 10mm×10mm×20mm were processed in up to six passes with interpass rotation, enabling the samples to return approximately to their initial dimensions after each pass. The intensity and homogeneity of plastic deformation was evaluated by mapping the Vickers hardness over the entire surface of the sample, and the resulting maps were compared with the strain and stress distribution estimated by FEM numerical simulation. The deformed microstructures were examined by optical and transmission electron microscopy. Cryogenic CCDF has proved to be effective in suppressing the recovery mechanisms of Cu samples, resulting in finer and more heterogeneous strains distribution than those deformed at room temperature. However, long-term observations by TEM have shown that these microstructures are inherently unstable, so that hardness decreases 50% after two years.

Fatigue life improvement of cast ZK60 Mg alloy through low temperature closed-die forging for automotive applications

The influence of low-temperature closed-die forging on the quasi-static and cyclic behaviour of as-cast ZK60 magnesium alloy was investigated. As-cast ZK60 billets were forged at a ram speed of 20 mm/sec and a temperature of 250 °C. While the yield strength of the starting alloy was 139 MPa, the forging process improved the yield strength significantly by ~68% to 234 MPa. Moreover, the stresscontrolled push-pull fatigue tests at the stress amplitudes of 140 MPa to 180 MPa revealed that the fatigue life was enhanced by an order of magnitude. Microstructural analyses besides the texture measurements at different locations of the forged part manifested partial grain refinement and texture modification strengthening mechanisms. It is believed that the fatigue life improvement is achieved in the wake of the grain refinement and the subsequent material strengthening.

Reliability of system for precise cold forging

Abstract The influence of scatter of principal input parameters of the forging system on the dimensional accuracy of product and on the tool life for closed-die forging process is presented in this paper. Scatter of the essential input parameters for the closed-die upsetting process was adjusted to the maximal values that enabled the reliable production of a dimensionally accurate product at optimal tool life. An operating window was created in which exists the maximal scatter of principal input parameters for the closed-die upsetting process that still ensures the desired dimensional accuracy of the product and the optimal tool life. Application of the adjustment of the process input parameters is shown on the example of making an inner race of homokinetic joint from mass production. High productivity in manufacture of elements by cold massive extrusion is often achieved by multiple forming operations that are performed simultaneously on the same press. By redesigning the time sequences of forming operations at multistage forming process of starter barrel during the working stroke the course of the resultant force is optimized.

Improved Microstructure and Mechanical Properties of AZ31–Mg2Si in Situ Composite Fabricated by Cyclic Closed-die Forging

AZ3111.6 wt.% Mg2Si in situ composite was fabricated by conventional casting method. Then cyclic closed-die forging (CCDF) were applied to severely deform the as-cast billets at 450 °C for one, three, and five passes. During multi-pass CCDF processing, both dendritic and eutectic Mg2Si particles are broken up into much smaller ones due to the shear stress inflicted by the matrix. With the increasing of CCDF passes number, finer grain size and more homogeneous distribution of Mg2Si phase are obtained along with notable improvement in both strength and ductility. AZ3111.6 wt.% Mg2Si composite presents tensile strength of 171 MPa and elongation of 2.6% after five CCDF passes as compared to initial 99 MPa and 1.0%.

Parametric Analysis and Optimization of Closed Die Forging of Gear Blank

Objectives: To analyze the effect of change of input parameters on the forging process using industrial component, a gear blank using the technique of FEM. Methods/Statistical analysis: The input parameters of billet shape/size, forging temperature and coefficient of friction between die workpiece interfaces were selected and the simulated experiments were designed using the technique of Response Surface Method (RSM). The simulations were done using Simufact®(MSC Corporation). The results were analyzed on die filling, defects and flash reduction. Findings: The deformation process was observed by defining flow lines and flow particles in the workpiece. The quantitative data from the flow particles gave the standard deviations of all the responses i.e. shear and normal stresses, effective plastic strain, effective stress, effective strain rate, material flow rate, load and die wear. These values were analyzed by using ANOVA and the significant parameters were highlighted. It was concluded that the parameters in the decreasing order of significance were billet size, coefficient of friction and temperature of billet. The graphical results were checked for defects, die filling and flash. Based on the simulated analysis and experimental values, mathematical models have been developed for die wear, effective strain rate and material flow rate with error ranging from 4% to 9%. It was concluded that for a defect free forging, a homogenous deformation and proper material flow with increased die life were important. Application/Improvements: The experimental production runs have shown remarkable improvement in reduction of rejects. The flash has been reduced by 60%, resulting in the saving of material.

New heat treatment process for advanced high-strength steels

Today’s advanced steels are required to possess high strength and ductility. It can be achieved by choosing an appropriate steel chemistry which has a substantial effect on the properties obtained by heat treatment. Mechanical properties influenced the presence of retained austenite in the final structure. Steels of this group typically require complicated heat treatment which places great demands on the equipment used. The present paper introduces new procedures aimed at simplifying the heat treatment of high-strength steels with the use of material-technological modelling.Four experimental steels were made and cast, whose main alloying additions were manganese, silicon, chromium, molybdenum and nickel. The steels were treated using the Q-P process with subsequent interrupted quenching. The resulting structure was a mixture of martensite and retained austenite. Strength levels of more than 2000 MPa combined with 10-15 % elongation were obtained. These properties thus offer potential for the manufacture of intricate closed-die forgings with a reduced weight. Intercritical annealing was obtained structure not only on the basis of martensite, but also with certain proportion of bainitic ferrite and retained austenite.