Showing papers on "Forging published in 2009"

The Flow Behavior and Microstructural Evolution of Ti-5Al-5Mo-5V-3Cr during Subtransus Isothermal Forging

Abstract: High-strength metastable β alloys, for example, Ti-5Al-5Mo-5V-3Cr, have replaced steel as the material of choice for large components, such as the main truck beam on the latest generation of airframes. The production of these components is carried out by hot near-net-shape forging, during which process variable control is essential to achieve the desired microstructural condition and subsequent mechanical properties. The flow behavior and microstructural evolution during subtransus isothermal forging of Ti-5Al-5Mo-5V-3Cr has been investigated for two different starting microstructures and analysis has incorporated previously published results. The flow behavior, irrespective of initial microstructural condition, is found to be very similar at strains ≥0.35. It is thought that this is due to a common microstructural state being reached, where dynamic recovery of the β phase is the dominating deformation mechanism. At strains <0.35, the flow behavior is believed to be dominated by the morphology and volume fraction of the α phase. Small globular α particles are thought to have little effect on the flow behavior, while the observed flow softening is directly linked to the fragmentation of acicular α precipitates.

Effect of initial microstructure on plastic flow behaviour during isothermal forging of Ti-10V-2Fe-3Al

Abstract: The plastic flow behaviour and microstructural development during isothermal forging was determined for near beta alloy Ti–10V–2Fe–3Al. Two different initial microstructures were employed: (i) a beta forged billet with a large prior beta grain size with Widmanstatten alpha platelets; and (ii) an alpha–beta forged billet with prior globular primary alpha. The beta forged condition exhibited a peak stress followed by intense flow softening, which is attributed to the break up of the Widmanstatten alpha platelets. Evidence suggests that peak hardening at low strains is due to dislocation pile-ups at alpha platelet/subgrain beta interfaces and subsequent flow softening is attributed to the transmission of beta phase through the alpha platelets. A strain rate ‘jump’ test investigation provided sufficient evidence to suggest that there is a transition from dislocation dominant deformation mechanisms at high strains rates to diffusional dominant deformation at low strain rates in Ti–10V–2Fe–3Al during forging.

Texture heterogeneities in alpha/alpha titanium forging analysed by EBSD-relation to fatigue crack propagation.

Abstract: Summary The microstructure and the local texture of a large IMI 834 forging were characterized using the Electron Back Scattered Diffraction (EBSD) technique. Crystallographic domains called macrozones and formed by a majority of primary αp grains with their axes in nearly the same direction were found. They had a band-like structure, parallel to the axial direction of the forging. The influence of these macrozones on the cold dwell-fatigue properties was studied. Several samples were tested under cold dwell-fatigue conditions. The crack initiation and the short-distance propagation region optically matched a bright region that contained numerous quasi-cleavage facets. The analysis of the EBSD measurements showed that this bright region was enclosed within a sharp textured region with axes at less than 30° from the loading axis. The crystallographic features of the crack nucleation site and the crack propagation path were also analysed.

Comparison between cold rotary forging and conventional forging

Abstract: Cold rotary forging is an innovative incremental metal forming process, which is obviously different from the conventional forging process in many aspects, such as the metal flow, degree of inhomogeneous deformation of workpiece and force and power parameters. In the current work, a 3D elastic-plastic dynamic explicit FE model of cold rotary forging of a cylindrical workpiece is developed under the ABAQUS software environment and its validity has been verified by the experiment. Based on the reliable 3D FE model, the cold rotary forging and conventional forging process are simulated and their difference in the forming process has been thoroughly clarified. The research results may help to understand the cold rotary forging process better. Furthermore, they provide valuable guidelines for further theoretical analysis and experimental studies on the cold rotary forging process.

Ultrafine grain formation in face centered cubic metals during severe plastic deformation

Abstract: The evolution mechanisms of new high-angle boundaries as well as ultrafine grains at large strains were studied by means of multidirectional forging (MDF) of pure copper at low temperature and aluminum alloy at high temperature, where dynamic recovery operates as a main restoration process. The structural changes can be characterized by the evolution of deformation bands such as microshear or kink bands at moderate strains. Multidirectional forging accelerates the evolution of many mutually crossing microshear or kink bands developed in various directions. The misorientations between (sub)grains increased gradually with increasing cumulative strain, finally leading to the development of a new fine-grained structure. The dynamic grain formation can be resulted from in situ or continuous dynamic recrystallization which is discussed in detail.

Microstructure and mechanical properties of TA15 titanium alloy under multi-step local loading forming

Abstract: In this paper six different local loading processes were proposed to study the effects of local loading conditions (temperature, deformation degree, loading pass, heats, cooling modes and heat treatment) on the microstructure and mechanical properties of TA15 titanium alloy workpieces including room and high temperature tensile properties, impact property, fracture toughness and high temperature duration property. It is found that it is better to finish the local loading forming in one heating time, if multi-fire forging needed the optimal forging technique as follows: adopting conventional forging (950 °C) at first and then following near-beta forging to control the proportion of the equiaxed primary α phase and the transformed β phase, allocating deformation degree of each loading pass rationally and using WQ cooling mode. Thus the workpiece with good compositive mechanical properties can be obtained.

Forging of the AA6061/23 vol.%Al2O3p composite: Effects on microstructure and tensile properties

Abstract: The use of aluminium-based particulate reinforced MMCs for automotive components and aircraft structures have been shown to be highly advantageous over their unreinforced alloys, due to their high specific strength and stiffness and superior wear resistance in a wide temperature range. The aim of this paper was to evaluate the effect of the hot forging process on the microstructure and tensile properties (at room and high temperature) of a MMC based on the aluminium alloys AA2618 reinforced with 20 vol.% of alumina particles (Al2O3p). Microstructural analyses of the as-cast and heat-treated composite showed large grain size of the aluminium alloy matrix and a quite non-homogeneous distribution of the reinforcing particles. The forging process led to an evident grain refinement, while it did not lead to significant variations in the size and distribution of the reinforcement particles. Regarding the effect of the forging process on the mechanical properties, it induced a slight increase in hardness, tensile strength, elastic modulus and an evident increase in tensile elongation. SEM analyses of the fracture surfaces of the tensile specimens showed substantially similar morphologies for the as-cast and forged composites, both at room and high temperature. The mechanism of damage was mainly decohesion at the matrix–particle interface.

Ultrafine-grained steel fabricated using warm multiaxial forging: Microstructure and mechanical properties

Abstract: Grain refinement of bulk metals using severe plastic deformation (SPD) is a popular approach to improve both strength and toughness. In this paper, grain refinement of steel processed by warm multiaxial forging (MAF) and its mechanical behavior has been investigated. Coarse-grained, plain low carbon steel was deformed using MAF at 500 °C. Microstructural evolution is characterized using electron backscattered diffraction and mechanical behavior has been studied. Fraction of low angle grain boundaries (LAB) is observed to increase with strain up to total engineering strain of 1.3 thereafter it starts decreasing whereas, high angle grain boundaries showed just the opposite trend. It appears that initially grain subdivision takes place with imposition of strain thereby increasing the fraction of LAB. After a critical strain these LAB transforms into the high angle boundaries (HAB). The initial coarser grains of average 30 μm size subdivided into grains of the size finer than 0.5 μm. This has been confirmed by TEM micrographs. Improved tensile strengths and hardness values are obtained after warm MAF.

Simulation of 42CrMo steel billet upsetting and its defects analyses during forming process based on the software DEFORM-3D

Abstract: In order to study the plastic deformation characteristics of 42CrMo steel in upsetting process and find out the feasibility of using computer simulation to analyze and research the upsetting process of the 42CrMo billet, by means of commercial and professional plastic forming software DEFORM-3D, the forging process of 42CrMo billet was simulated. It is concluded that (1) the changes of the temperatures, stresses and strains at the different regions of the billet were simulated during the entire forging process, (2) based on the stress and strain distributions of the forged billet, the forming defects analyze was proceeded and it is concluded that some forging defects or flaw may occur near the head surface or around the side edge during the plastic deformation process.

An optimization method for radial forging process using ANN and Taguchi method

Abstract: In this study, the artificial neural network (ANN) and the Taguchi method are employed to optimize the radial force and strain inhomogeneity in radial forging process. The finite element analysis of the process verified by the microhardness test (to confirm the predicted strain distribution) and the experimental forging load published by the previous researcher are used to predict the strain distribution in the final product and the radial force. At first, a combination of process parameters are selected by orthogonal array for numerical experimenting by Taguchi method and then simulated by FEM. Then the optimum conditions are predicted via the Taguchi method. After that, by using the FEM results, an ANN model was trained and the optimum conditions are predicted by means of ANN (using genetic algorithm as global optimization procedure) and compared with those achieved by the Taguchi method. The optimum conditions are verified by FEM, and good agreement is found between the two sets of results.

Dimension measurement of hot large forgings with a novel time-of-flight system

Abstract: The dimension measurement of hot large forgings is necessary for process control and product quality. However, the conventional technique in forging plants leads to a high scrap rate of raw materials. In order to reduce the waste and increase the productivity, this paper presents a novel measurement technique based on the pulsed time-of-flight (TOF) laser radar to measure the dimensions of hot large forgings. The system consists of a TOF, a scanning device of the two-degree-of-freedom (2-dof) spherical parallel mechanism (SPM), and two motors. Then, its measuring principle and the SPM are described. A special data-processing method is developed to extract the dimensions and the shape of a large forging by scanning for a few times. The laboratory experiments indicate that the shape and dimensions such as the diameter and length can be achieved by virtue of the TOF system. The dimension measurement in a forging plant is also conducted to verify the effectiveness of the presented system.

Forming of metallic glass by rapid capacitor discharge

Abstract: An apparatus and method of uniformly heating, rheologically softening, and thermoplastically forming metallic glasses rapidly into a net shape using a rapid capacitor discharge forming (RCDF) tool are provided. The RCDF method utilizes the discharge of electrical energy stored in a capacitor to uniformly and rapidly heat a sample or charge of metallic glass alloy to a predetermined “process temperature” between the glass transition temperature of the amorphous material and the equilibrium melting point of the alloy in a time scale of several milliseconds or less. Once the sample is uniformly heated such that the entire sample block has a sufficiently low process viscosity it may be shaped into high quality amorphous bulk articles via any number of techniques including, for example, injection molding, dynamic forging, stamp forging, and blow molding in a time frame of less than 1 second.

Integral impeller processing method

Abstract: The invention discloses an integral impeller processing method for processing an integral impeller through a five-axle number control machine tool. The method comprises the following steps: S1. turning the basic shape of a revolving body on a forging material; S2. performing rough milling to a flow channel part; S3. performing semi finishing to the flow channel part; S4. performing fine finishing to blades; and S5. performing back chipping to the rounding part. The invention ensures that the processing path on the surfaces of the blades can meet the requirement of geometric accuracy, also ensures the processing quality and has high processing efficiency and stable quality.