Showing papers on "Forging published in 2000"

Instability criteria for hot deformation of materials

Abstract: Forming and forging processes are among the oldest and most important materials related technologies. New materials technologies centre on the development and widespread use of thermomechan...

Application of neural network and FEM for metal forming processes

Abstract: This paper proposes a new technique to apply the artificial neural network in metal forming processes. A three-layer neural network is used and a back propagation algorithm is employed to train the network. It is determined by applying the ability of function approximation of the neural network to the initial billets which satisfy the minimum of incomplete filling in the die cavity. The die geometry for cylindrical pulley is designed to satisfy the design conditions of the final product. The proposed schemes have been successfully adapted to find the initial billet size for axisymmetric rib-web product and to design the die geometry for cylindrical pulley. The neural network may reduce the number of finite element simulation for designing the die of forging products and further it is usefully applied to multi-stage process planning.

The effects of forging and rolling on microstructure in O+BCC TiAlNb alloys

Abstract: The effects of hot upset forging and hot pack rolling on microstructure of orthorhombic (O)+body-centered cubic (BCC) TiAlNb alloys was investigated. The starting materials were melted ingots of nominal compositions: Ti25Al25Nb(at.%), Ti23Al27Nb(at.%), and Ti12Al38Nb(at.%). Smaller cigar-shaped Ti25Al25Nb ingots were examined to understand the effect of rolling preheat treatment on microstructure. It was found that super-transus preheat treatment results in large prior BCC grains and surface edge cracking. For larger castings, forging and rolling procedures were carried out after heating the materials between 932–1000°C. These temperatures were below the BCC-transus temperature for Ti23Al27Nb and Ti25Al25Nb and above the transus for Ti12Al38Nb. This resulted in a significantly larger grain size for the as-processed Ti12Al38Nb compared with the other two alloys. The Ti25Al25Nb alloy required the greatest forging and rolling loads, while the fully-BCC Ti12Al38Nb alloy exhibited the best workability and required the lowest forging and rolling loads. This was related to the alloys’ aluminum contents and O-phase volume fractions. Sub-transus processing of the near Ti2AlNb alloys proved to be a viable technique for obtaining homogeneous microstructures containing fine O and BCC phases and lacking large prior BCC grains, which can be detrimental to the mechanical performance.

Cleavage initiation in Ti-V-N and V-N microalloyed ferritic-pearlitic forging steels

Abstract: The effects of silicon (053 and 105 wt%) and titanium (<0002 and 0022 wt%) on microstructure and mechanical properties of vanadium microalloyed medium carbon steels heat treated after rolling to simulate the thermal cycle of hot forging have been determined using room temperature tensile tests, impact tests, optical microscopy and scanning electron microscopy (SEM) Silicon was found to increase strength values whilst titanium had a strong refining action on prior austenite grain size Room temperature Charpy ‘U’ notch impact energies were all on the lower shelf; ductile–brittle transition temperatures, determined from fracture appearance in Hounsfield impact tests, ranged from 100 to 145°C, scaling with material strength Initiation in the Charpy tests was by microcracking of coarse (Ti,V)(C,N)-containing single or multi-phase inclusions except in the low strength, titanium-free case when the absence of a completely continuous grain boundary ferrite layer allowed matrix microstructure initiation by interfacing pearlite colonies to occur

Residual stress prediction and determination in 7010 aluminum alloy forgings

Abstract: Precipitation-hardened aluminum alloys gain their high strength through heat treatment involving a severe quenching operation, which can have the adverse effect of in- troducing residual stresses. The finite element code ABAQUS is used to simulate the quenching of aluminum alloy 7010 in an attempt to predict the residual stress distribution that de- velops in simple shapes. The rate of heat transfer from the material is determined using the finite element method to pre- dict the heat transfer coefficient from surface cooling curves achieved experimentally. The flow stress of the material is as- sumed to be strain rate dependent and to behave in a perfectly plastic manner. The predicted residual stress magnitudes and directions are compared to values determined using the hole- drilling strain gage method and the X-ray diffraction technique. KEY WORDS—residual stress, aluminum alloy, forging, solu- tion heat treatment

Microstructural evolution of Inconel* 718 during ingot breakdown: process modelling and validation

Abstract: A computer model is presented that describes microstructural evolution during the ingot breakdown of nickel base superalloy Inconel 718 via the open die cogging operation. To support the development of the model, a compression testing programme has been carried out which covers the ranges of temperatures, strains, and strain rates experienced during thermomechanical processing. Analysis of the flow curves has allowed the identification of the regimes in which the various deformation mechanisms take place. Logic based rules have been incorporated into the model, and this has allowed predictions of the microstructural evolution to be made. Where possible, the results have been compared with the available experimental data and it is shown that theory and experiment are in reasonable agreement. A number of computational experiments have been carried out, to study the effects of changing the forging procedure.

Processing of titanium-alloy billet for improved ultrasonic inspectability

Abstract: A starting workpiece of a titanium-base alloy having a temperature-composition phase diagram with a beta region and an alpha-beta region separated by a beta transus temperature is processed by first forging the starting workpiece at a first temperature in the beta region to form a billet, thereafter second forging the billet at a second temperature in the alpha-beta region, thereafter third forging the billet at a third temperature in the beta region, thereafter fourth forging the billet at a fourth temperature in the alpha-beta region so that the step of fourth forging accomplishes a reduction in cross-sectional area of from about 5 to about 40 percent, and thereafter ultrasonic testing the billet. The beta-region third forging step combined with a relatively small reduction during the alpha-beta-region fourth forging step produce a microstructure that is conducive to ultrasonic inspection with minimal interference from noise.

Microstructure optimization in design of forging processes

Abstract: A new approach based on sensitivity analysis for optimizing the microstructure development during the forging processes is proposed in this work. The analytical sensitivities of the recrystallization volume fraction and dynamically recrystalized grain size with respect to the design variables are derived. The mean grain size in each finite element is introduced so that the complex recrystallization mechanics, such as no recrystallization, partial recrystallization and complete recrystallization are all considered. The objective is to minimize a function describing the variance of mean grain size and the average value of mean grain size in the whole final product. Two constraints are imposed on die underfill and excessive material waste. Two different kinds of design variables are considered, including state parameter (initial shape of billet) and process parameter (die velocity). The optimization scheme is demonstrated with the design of a turbine disk made of Waspaloy in non-isothermal forging process. The optimal initial shape of billet and the die velocity are obtained.

High performance forged aluminum connecting rod and method of making the same

Abstract: An improved high performance aluminum connecting rod and a method of manufacturing such a connecting rod which is capable of carrying particularly high compressive loads with a substantially reduced deformation resulting from such high compressive loads in high performance engines. The connecting rod is made of an extruded bar stock forging made of an aluminum alloy material which is forged and machined to make the connecting rod. The connecting rod has a substantially increased compressive yield strength as well as a substantially increased tensile yield strength. This increase in the compressive yield strength of the connecting rod effectively prevents bending of the connecting rod beam, elongation of the wrist pin bore, and a marked deterioration in the roundness of the bearing housing bore.

Study of workability limits of porous materials under different upsetting conditions by compressible rigid plastic finite element method

Abstract: Workability limits must be considered when designing powder metallurgy (PM) forging processes. This research successfully applied the general upsetting experiment method to the deformation of porous materials. Based on the plastic theory of porous materials, the compressible rigid plastic finite element method is used to simulate the deformation processes of cold upsetting of disks and rings for porous metal materials with a full account of contact friction boundary conditions, the height-to-diameter ratio, the initial relative density, and the die and workpiece geometry. Furthermore, a successful analysis of the cold forging process results in the prediction of the stress, the strain, and the density field. By coupling with the ductile fracture criterion, which is a strain-based criterion obtained by Lee and Kuhn, possible defects leading to material failure have been checked. This research reveals that larger height to diameter and a lesser friction factor can delay the local strain locus to intersect with the Lee and Kuhn’s fracture line and restrain formation of the surface crack. Meanwhile, it reveals that the initial relative density has only a very small influence on the strain to fracture in compression, and it shows the forming behavior of the ring and disk with the curved die. According to Lee and Kuhn’s results, the calculated results agree well with the experimental results.

Bar or wire product for use in cold forging and method for producing the same

Abstract: A bar or wire product for use in cold forging, characterized in that it comprises a steel having the chemical composition, in mass %: C: 0.1 to 0.65 %, Si: 0.01 to 0.5 %, Mn: 0.2 to 1.7 %, S: 0.001 to 0.15 %, Al: 0.015 to 0.1 %, B: 0.0005 to 0.007%, P: 0.035 % or less, N: 0.01 % or less, O: 0.003 % or less and balance: Fe and inevitable impurities, and it has, in the region from the surface thereof to the depth of the radius thereof x 0.15, a structure wherein ferrite accounts for 10 area % or less and the balance is substantially one or more of martensite, bainite and pearlite, and the average hardness in the region from the depth of the radius thereof x 0.5 to the center thereof is less than that of the surface layer thereof by 20 or more of HV; and a method for producing the bar or wire product. The bar or wire product is excellent in the ductility after spheroidizing and thus allows the prevention of occurrence of cracks in a steel product during cold forging, which has conventionally been a problem in manufacturing structural parts for a machine by cold forging.