Hammer Forging Research Articles

Microstructure and mechanical properties of hammer-forging assisted wire-arc directed energy deposition AZ91 alloy

ABSTRACT With the development of lightweight aerospace equipment, magnesium alloys are receiving increasing attention. Wire-arc directed energy deposition (Wire-arc DED) is a highly promising manufacturing method for magnesium alloy parts, but its development has been severely restricted by the problems of coarse grain size and low mechanical properties. To address these issues, a hammer-forging assisted Wire-arc DED technology for magnesium alloy AZ91 is proposed. The effects of interlayer hammer-forging and synchronous hammer-forging on macrostructure, microstructure and mechanical properties of the Wire-arc DED samples are compared, and the microstructure evolution and performance enhancement mechanism are discussed. The results show that the maximum plastic deformation caused by hammer forging reaches 11.7%. Hammer forging can significantly refine grains, and the average grain size decreases from 27.7 μm to 13.5 μm. Synchronous hammer-forging is better than interlayer hammer-forging in terms of performance enhancement, the UTS reaches 301.8 MPa, an increase of 10.9%, which is comparable to that of traditional forged parts, mainly attributed to the grain refinement and increased dislocation density.

Optimal energy distribution in hydraulic hammer forging for minimizing total energy and forging load

Hammer forging is an important manufacturing technology in heavy industry to produce high stiffness product. Forging using mechanical press produces the product by controlling the distance between dies whereas the hydraulic hammer forging utilizes the energy given by the sum of hydraulic energy and potential energy of die, and the product is then produced through several blows. The energy at each blow is conventionally determined through the trial-and-error method. The process to produce the product is simple and the response of hammer foundations and anvil is mainly discussed in the literature, but the optimal energy distribution to successfully produce the product is rarely discussed. In this paper, the optimal energy distribution in hydraulic hammer forging is determined using numerical simulation coupled with design optimization technique. To determine the optimal energy distribution through the process, multi-objective design optimization for minimizing both the total energy and the maximum forging load is performed. High dimensional accuracy is generally required in the forged product, and the underfill is handled as the design constraint. The numerical simulation in hydraulic hammer forging is computationally so expensive that sequential approximate optimization that response surface is repeatedly constructed and optimized is adopted to identify the pareto-frontier between the total energy and the maximum forging load. It is clarified through the numerical result that the total energy is drastically reduced without the underfill in comparison with the conventional one. The experiment is also conducted to examine the proposed approach.

Exceptional Microscale Plasticity in Amorphous Aluminum Oxide at Room Temperature.

Oxide glasses are an elementary group of materials in modern society, but brittleness limits their wider usability at room temperature. As an exception to the rule, amorphous aluminum oxide (a-Al2 O3 ) is a rare diatomic glassy material exhibiting significant nanoscale plasticity at room temperature. Here, it is shown experimentally that the room temperature plasticity of a-Al2 O3 extends to the microscale and high strain rates using in situ micropillar compression. All tested a-Al2 O3 micropillars deform without fracture at up to 50% strain via a combined mechanism of viscous creep and shear band slip propagation. Large-scale molecular dynamics simulations align with the main experimental observations and verify the plasticity mechanism at the atomic scale. The experimental strain rates reach magnitudes typical for impact loading scenarios, such as hammer forging, with strain rates up to the order of 1 000 s-1 , and the total a-Al2 O3 sample volume exhibiting significant low-temperature plasticity without fracture is expanded by 5 orders of magnitude from previous observations. The discovery is consistent with the theoretical prediction that the plasticity observed in a-Al2 O3 can extend to macroscopic bulk scale and suggests that amorphous oxides show significant potential to be used as light, high-strength, and damage-tolerant engineering materials.

An automatic thermo-mechanical testing apparatus for metal forming applications

Dynamic testing of materials is necessary to model high-speed forming processes (e.g. hammer forging, blanking, forming, etc.) and crash/impact behaviour of structures, amongst others. The most common machines to perform medium to high-speed tests are the servo-hydraulic high-speed tensile and compression machines and the Hopkinson bars. The paper analyses the use of a newly-developed laboratory testing facility, named the Automatic Thermo-Mechanical Tester (ATMT). This testing machine is equipped with a pneumatically accelerated Direct Impact Drop Hammer (DIDH), a furnace and automatised robotic arm, capable of characterising materials at intermediate strain rates, ranging from 100 to 300 s−1 in combination with temperatures up to 1350 °C. The hammer has been designed and constructed to conduct a variety of material characterisation tests, such as, upsetting or plane strain compression tests as well as component tests for validation purposes. The DIDH allows testing standard compression specimens at average strain rates in the order of 100 s−1 that decrease progressively until the it is fully stopped. It is, in combination with universal testing machines and Hopkinson bar systems, particularly suitable for experimental validation of loading-rate dependant material models. Compression tests were conducted with different hammer impact velocities generating a variety of strain rates at varying temperatures on S235JR structural steel, OFHC copper and wrought Inconel 625 nickel-based superalloy to assess the potential of the novel apparatus. A detailed finite element numerical study of the system was performed to assess several aspects such as the effect of the specimen geometry or its capability as an intermediate testing device, simulating a simplified system and the full Direct Impact Drop Hammer apparatus.

The Analysis of Deformability, Structure and Properties of AZ61 Cast Magnesium Alloy in a New Hammer Forging Process for Aircraft Mounts.

This article presents the analysis of the deformability, structure and properties of the AZ61 cast magnesium alloy on the example of a new forging process of aircraft mount forgings. It was assumed that their production process would be based on drop forging on a die hammer. Two geometries of preforms, differing in forging degree, were used as the billet for the forging process. It was assumed that using a cast, unformed preform positively affects the deformability of hard-deformable magnesium alloys and flow kinematics during their forging and reduces the number of operations necessary to obtain the correct product. Numerical analysis of the proposed new technology was carried out using DEFORM 3D v.11, a commercial program dedicated to analyzing metal forming processes. The simulations were performed in the conditions of spatial strain, considering the full thermomechanical analysis. The obtained results of numerical tests confirmed the possibility of forming the forgings of aviation mounts from the AZ61 cast magnesium alloy with the proposed technology. They also allowed us to obtain information about the kinematics of the material flow during forming and process parameters, such as strain intensity distribution, temperatures, Cockcroft–Latham criterion and forming energy. The proposed forging process on a die hammer was verified in industrial conditions. The manufactured forgings of aircraft mounts made of AZ61 magnesium alloy were subjected to qualitative tests in terms of their structure, conductivity and mechanical properties.

Metallurgical Analysis of different processing technologies on tensile behavior of GH4169 superalloy

By the measurement of tensile property and microstructure observation, the different effect of 1MJ counter-blow hammer forging and 800MN die forging on the disc were investigated. In order to obtain final forging temperature, hot compression tests under 920~1030°C at 0.08 true strain were performed on GH4169 superalloy. The results showed that at the same processing parameter, ASTM 10 grain and granular δ were obtained by count-blow hammer forging, UTS is 1563Mpa; ASTM 8 grain and needle-like δ phase segregation were obtained by die forging, UTS is 1408Mpa. According to evolution of microstructure under isothermal compression, in one case that final forging temperature of count-blow hammer is about 1000°C, while it is 930°C under die forging. The microstructure of the forging is strongly related to the fabrication process, increase the preheating temperature of the die as much as possible, increase the pressing rate, excellent mechanical property can be obtained by die forging.

Theoretical and experimental investigations of mechanical vibrations of hot hammer forging

The characterization of mechanical vibrations in a hammer forging process is a tremendously important parameter for machine design and production engineering. The dynamic response of a forging hammer to the reaction forces is affected by material behaviour, time, spring-damper system and foundation. In this research firstly, the effect of mass ratio and coefficient of restitution on the forging efficiency were theoretical characterized. The interesting influence of anvil initial velocity on the forging efficiency is also analytically presented. The mechanical vibrations of a LASCO HO U-315 hammer were experimentally investigated. Two steel grades a S355 and a 42CrMo4 were used to forge trial parts. The velocity of the ram and acceleration of the anvil during a hot die forging process were measured using a laser velocity meter type LSV-2000-45. The influences of forging time, coefficient of restitution, energy loss and time interval (delay) between blows on the efficiency of the forging process were examined. The energy loss before die contact was determined to be approximately 10%. The investigations also showed that a variation of the time interval between blows within the usual range has no effect on the intensity of the vibrations of the anvil nor on the energy loss of the hammer. The dependence of the free damped vibrations of the anvil on machine stiffness, damper coefficient and mass of machine has been confirmed. Additionally, the loss of energy due to hammer movement as well as the free damped mechanical vibrations of the anvil were theoretically analysed in order to verify the experimental findings. Theoretical analysis showed an anvil initial velocity of approximately 0.2 m/s results in a 4% increase of forging efficiency. A good agreement between the experimental and theoretical results was observed.

Analysis of a New Process of Forging a 2017A Aluminum Alloy Connecting Rod

Abstract The paper presents the results of a theoretical analysis of a new process of hammer forging of a connecting rod and the technology currently used. In the industry at present connecting rods are forged from extruded rods. The new forging technology assumes the use of a workpiece in the form of a cast preform. For the calculations, it has been assumed that the billet material will be a Ø30 × 148 mm rod and a cast preform. Two variants of preforms have been modeled, from which products of the assumed geometry with different degree of strain are obtained. Calculations were made using the finite element method (FEM) in the Deform 3D program. The input material was 2017A aluminum alloy in the form of rods and sand cast preforms. On the basis of the conducted research, it was found that the use of cast preforms reduces material waste by about 80% in relation to the technology of forging from the bar and reduces the energy consumption of the process by about 75%. Both geometrical variants of the forging preforms ensure obtaining a forging with the assumed shape and dimensions, although forging from the forging preform with a smaller degree of strain seems to be a safer variant in terms of the possibility of cracking of the material. This is supported by the lower strain and normalized Cockcroft–Latham integral values.

Elucidation of Mechanism Underlying Workpiece Jump in Hammer Forging

During the process of drop hammer forging, workpieces sometimes jump after strikes. The present research investigates the mechanism of the workpiece jump by means of experiments and numerical simulations. In the experiments, workpieces were struck by vertical symmetrical flat dies or vertical asymmetrical dies. A high-speed camera was used to measure the workpiece deformation, the position of workpieces during jumping and the position of the dies. Strain of lower dies and structures of the hammer were measured by strain gauges. Vibration of the antirattler under the hammer, elastic vibration of lower dies and structures of the hammer, and contact area between workpieces and dies were analyzed by numerical simulations. The results indicate that workpieces jump by adhesive force between workpieces and dies, and by elastic vibration of lower dies and structures of the hammer.

Monitoring of a Hammer Forging Testing Machine for High-Speed Material Characterization

Dynamic testing of materials is necessary to model high-speed forming processes (i.e. hammer forging, blanking) and crash/impact behavior of structures, among others. The most common machines to perform medium to high-speed tests are the servo-hydraulic high-speed tensile and compression machines and the Hopkinson bars. The paper analyses the possibility to use a laboratory forging hammer for the characterization of materials at medium and high strain rates. For this, an automatized forging hammer has been constructed which is accelerated with a pneumatic cylinder and is able to speed up the upper anvil up to 5 m/s. This forging testing machine can be employed to perform a variety of material characterization tests, such as, uniaxial upsetting tests, plane strain compression tests as well as crash tests. To ensure the correctness of the experimental results obtained from tests performed in this home-developed laboratory facility, it is essential to verify and validate the acquired data. With this aim, copper cylindrical specimens have been deformed at different speeds. A high-speed camera has been employed to monitor real specimen strains using DIC and a load cell has been also utilized to measure the force applied during deformation. In order to obtain valid material rheological results, force data obtained from the load cell has been combined with DIC strain data to draw reference flow curves. Analogous stress-strain values have been calculated analytically using both techniques independently, solely high-speed camera data, on the one hand, and only load-cell data, on the other hand. A comparison of results has been performed and discussed in order to select the best monitoring technique to implement in the laboratory forging hammer.

Investigation of the Hammer Forging Process of Large-Sized Turbine Blades of Stainless Steel

Investigations of the rheological properties and the formation of the structure of stainless steel were performed. A computer model of the process of hammer forging of the turbine blades made of stainless steel 1.3 m long in the package Deform-3D was developed , with the help of which the necessary coefficients and parameters are determined to ensure maximum convergence of the calculated and experimental process data. The obtained data were used to create a mathematical model for stamping a large-sized turbine blade made of stainless steel with a length of 2.1 m. Mathematical modeling of the processes of stamping and distorting of a large-sized blade in the software package Deform-3D has been performed. The influence of process parameters on the stress-strain state (SSS), forming, temperature field in the forging at various stages of stamping. Determined temperature and deformation modes of stamping, the need for additional heating and optimal forgings geometry by stamping.

Microstructural Characterization and Mechanical Properties of Ti-6Al-4V Alloy Subjected to Dynamic Plastic Deformation Achieved by Multipass Hammer Forging with Different Forging Temperatures

Dynamic plastic deformation (DPD) achieved by multipass hammer forging is one of the most important metal forming operations to create the excellent materials properties. By using the integrated approaches of optical microscope and scanning electron microscope, the forging temperature effects on the multipass hammer forging process and the forged properties of Ti-6Al-4V alloy were evaluated and the forging samples were controlled with a total height reduction of 50% by multipass strikes from 925°C to 1025°C. The results indicate that the forging temperature has a significant effect on morphology and the volume fraction of primary α phase, and the microstructural homogeneity is enhanced after multipass hammer forging. The alloy slip possibility and strain rates could be improved by multipass strikes, but the marginal efficiency decreases with the increased forging temperature. Besides, a forging process with an initial forging temperature a bit above β transformation and finishing the forging a little below the β transformation is suggested to balance the forging deformation resistance and forged mechanical properties.

Effect of Forging on Microstructure, Mechanical Properties and Acoustic Emission Characteristics of Al Alloy (2014): 10 wt.% SiCp Composite

In this paper a systematic study has been undertaken to study the effect of forging on microstructure, mechanical properties and acoustic emission (AE) characteristics of Al alloy (2014)—10 wt.% SiC metal-matrix composites. Hammer forging was carried out at a temperature of 470 °C in an open die, with a deformation ratio of 3.5:1. Microstructural analyses were carried out at three different positions of forged billet. Significant material flow was observed in the sample taken from the sides of the forged billet, but no appreciable material flow was observed at the center of the forged billet. The microstructural characterization showed that forging resulted in cracking of SiC particles in Al alloy (2014)—10 wt.% SiC composite. The AE results during forging showed an increase in AE signal intensity during the initial yielding period and a subsequent decrease in the intensity of AE signals with sudden burst at the end of the forging. The plastic deformation at room temperature was less ductile in nature but at high temperature, appreciable ductility was observed. The FESEM micrographs of fracture surfaces of the tensile specimens showed appreciable clustering of SiC particles during plastic deformation both at room and high temperature.

Studying the Machinability of Tin-Bearing Free-Cutting Steel

The machinability of 0.2% Sn free-cutting steel produced by vacuum melting and hot shaping under pressure using the method of hammer forging has been studied. The distribution of elements (Sn, S, Mn) in the steel has been investigated by secondary ion mass spectrometry (SIMS). It has been established that the doping with tin appreciably increases the machinability index of the free-cutting steel to kv = 1.72. The effect of S and Mn segregation with the formation of manganese sulfide MnS precipitates has been revealed. Tin in the form of fine particles is uniformly distributed in crystalline grains and along their boundaries and segregates on MnS particles. In the process of cutting, low-melting tin particles are melted to initiate the Rehbinder effect (liquid-metal embrittlement), thus embrittling the steel. Moreover, tin has a lubricating effect at the point of contact between the cutter and the machined surface. All these effects improve the machinability of tin-bearing free-cutting steel.

Microstructure and properties of thermomechanically treated and bake hardened AISI 4340 steel

Abstract In the present work, response of AISI 4340 steel towards high temperature thermomechanical treatment (HTMT) and bake hardening (BH) studied. During HTMT, steel was austenitized to 1100°C and plastically deformed up to 30% with the help of rolling and immediately quenched in water, followed by tempering at 310±5°C for 2 hours. Optical microstructure, toughness and tensile strength, hardness were evaluated and compared with conventionally hardened and tempered (CHT) steel samples. Observations of HTMT process clarified no alterations in hardness, but a significant improvement in UTS in comparison to CHT samples. Charpy V-Notch (CVN) impact toughness drastically decreased in HTMT samples. Impact toughness of HTMT samples was 13 Joules, but 199 Joules for CHT samples. In HTMT samples, effect of deformation source on process investigated and found that rolling is an effective in improving properties than hammer forging. In addition, significant isotropic properties developed in the case of rolling, compared to hammer forging. Effect of amount of deformation studied; observed 30% deformation was the optimum deformation to achieve the best properties. During bake hardening (BH) flat tensile AISI 4340 steel specimens were pre-strained to 2% and baked at 170°C for 20 minutes a headed with uniaxial tensile testing in which there was no improvement in yield strength after bake hardening observed. This might be because of the low amount of pre-straining or may be the lack of availability of interstitial atoms near to the dislocations generated during pre-straining. Bake hardened specimens were tested at different strain rates; it was observed that yield strength decreases with increasing strain rate, while UTS remains unaffected. FESEM images showed no significant structural changes.

Indentation Mechanism in Rotary Hammer Forging Process: Analytical and Numerical Approach

Rotary hammer forging process is getting popular since it has many advantages comparing to the conventional forging process. The mechanism of the movement in term of orbital motion of the conical upper die become concern of this research. This article present the three stages of the modelling of the rotary hammer forging. The first stage is the development of the orbital motion of the conical upper die. Three-dimensional CAD model of the conical upper die was developed to determine the orbital motion as a function of the four parameters: Nutation, Precession, Spin and Rocking-Die mechanism. A reasonably accurate design of the conical upper die and the workpiece had been developed based on motion because of interaction of conical upper die and upper part of workpiece geometries. The behaviour of orbital motion with any active combination of those four parameters was observed. The second stage was the development of the conical upper die with the specific feature in order to generate a product with an unsymmetrical shape of upper part of the product. The sequence and mechanism of the formation of the upper part of product were generated. The third stage was the analysis of the stress strain state during the formation of the upper part of the workpiece. An elastic-plastic, dynamic analysis of 3D rotary hammer forging mechanism with the concern at the workpiece and their interaction with a model of dies have been performed. Verification of the indentation mechanism of the rotary hammer forging had been done by validating the result with the existing experimental results.

Contact stress and temperature during air-stamp hammer upsetting of a circular cylinder

Air-stamp hammer forging is a traditional hot-forging method. This method is mostly used based on the operator’s skill and not on the measurement of the contact stress condition. In this study, we measured the contact pressure and friction on the tool surface during the upsetting of a circular cylinder of hot steel using an air-stamp hammer. For the upsetting process, we installed friction sensors that could detect the pressure and friction stress on the tool surface on the flat die. A tool surface temperature sensor with a thin thermocouple was also installed 0.3 mm under the tool surface. During the upsetting process, the pressure near the center increased with the increase in the ratio between the diameter and the height. The friction was higher at greater distances from the center than it was near the center. We investigated the relationship between the pressure and friction distributions at the end of the stamping when the material had a high diameter-to-height ratio; this relationship was compared using elemental analysis. The results show that the contact-stress behavior observed during hot forging was similar to that observed in cold forging without a lubricant. The tool surface temperature rapidly increased during stamping but also increased when the tool surface had barely touched the workpiece. The data obtained about the pressure and friction behavior will be useful for designing new forging processes, and the information about the effects of stress and temperature on the tool surface will be useful for investigating tool wear.

New Technologies for Producing Bicycle Hub Forging

The paper presents the results of research on two new forging processes for producing bicycle hub forgings in a three-slide forging press. The first process is related to producing a forging with an axial cavity by flashless forging. The other one concerns the production of a forging from a tube billet. The potential benefits offered by these two new forging processes compared to the conventional hammer forging method for producing hubs are discussed. The designed processes are verified theoretically via numerical simulations. The first of the proposed processes is also subjected to experimental verification. The results demonstrate that the new technologies allow obtaining good quality products. A comparison is made between material and energy consumption in the two analyzed processes and in conventional hammer forging. It is found that the application of the forging process in a three-slide forging press leads to a considerable decrease in manufacturing costs.

A New Cross Wedge Rolling Process for Producing Rail Axles

Rail axles are large-size parts produced in large batches. Currently, these parts are produced by metal forming techniques such as rotary forging, open die forging with hydraulic presses and open die hammer forging (minimum ram weight: 3 Mg). Nevertheless, not only are the above methods far from being efficient, they also lack accuracy (open die forging). As a result, new techniques for producing rail axles are constantly developed. One of such alternative techniques is based on the use of cross wedge rolling (CWR), which is the subject of the present study. An innovative roll design for producing rail axles by CWR is proposed. The rolls are provided with three pairs of wedge tools that act simultaneously on the workpiece and form the part in one revolution of the rolls, i.e., during 20 s. The numerical modelling of a CWR process with the proposed roll design reveals that the solution can be used to produce railway axles with the desired geometry. This technique, however, requires relatively high loads and torques. To decrease the force parameters, the forming process was modified and ran in two operations. The first operation consists in forming the central step of the workpiece while the other one involves the formation of steps on the ends of the workpiece. The results of the new simulation show a significant decrease in the loads and torques, which is caused, among others, by reducing the nominal diameter of the rolls from 1600 mm to 1200 mm. The numerical findings can be used to design a rolling mill for producing rail axles.

Introduction of materials modelling into metal forming simulation

Materials data have been an integral part of metal forming simulation. The essential data for such simulations are wide ranging, from physical and thermophysical properties to rheological properties as well as phase transformation kinetics. This paper reviews our development of material models over the past two decades, by which many of the material properties needed for forming simulation can be calculated. These models have been implemented into computer software, JMatPro®, and the calculated property data can now be easily transferred to CAE tools for the simulation of metal processing. A case study is presented here on the simulation of the hammer forging process of a 30CrMo4 steel using software Forge®. The simulated results demonstrate good agreement with experimental observations. Merging alloy design and processing design into one design loop now becomes a possibility.