Billet Shape Research Articles

Microstructure optimization in design of forging processes

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.

三次元面取り制御装置の開発

When cutting up billets with hot saw, it is unavoidable for cut chips to develop into burr around billets edge. It is often that billets are cut slantwise with saw distorted owing to the increase in cutting resistance with operation. It has been therefore tried to cut edge 2-dimensionaly for burr free. This method, however, has such problems as partially removed burr. The authors have been successful in developing a 3-dimensinal control system for cutting the edge of not only round but also rectangular billet faces even with slantwise faces and no limit in shape of billets. The system has features that the equipment measures the gradient of billet faces and cross section profile and these data are used to extract the edge coordinate of billets face having no burr. An optical 3-D shape measuring system is used to measure the gradient and also optical range finder to measure the profile. The optical measuring system has good feature to measure billet shape with little influence by the condition of billet surface. As a result of the off-line test in which edge of round and rectangular billet faces were cut, the system has shown good effects as follows: (1) The rate of not removed burr is 0%. (2) It attains, with probability of more than 90%, that scatter of cut edge width is within 1mm.

On the nonexistence of certain ideal forming operations for extrusion and drawing dies

It is shown that an ideal forming operation for an extrusion or drawing die shrinks not only the cross-sectional area but also the perimeter. It follows that for any billet shape there are product cross-sections which can be produced by extrusion or drawing dies but not by ideal forming operations.

Spraying the Perfect Billet

In the billet spray-forming process, billet shape and positioning strongly influence billet solidification and consequently end-product quality. Therefore, the ability to produce a billet of a desired shape and position is very important. Shape and positioning of a steady-state billet surface depend, through an averaging procedure, on the atomizer scanner angle function. This paper approaches the problem of how to stably reconstruct the atomizer scanner angle function from a given set of ideal billet shapes. Mathematical features which make a billet shape ideal are discussed. A nonconstrictive subclass of billet surfaces possessing these features is investigated. An algorithm is developed for calculating the scanner angle function which produces the perfect billet, and finally numerical results are presented.

Effect of shell on the change in shape of a porous billet during isostatic pressing. 2. Main results

Isostatic pressing of porous ceramic material in a container is considered. Simulation of the process is based on flow theory with smooth potential. It is aimed at studying the shape change phenomenon. The effect of various factors including initial density and dimensions as well as rheological characteristics is considered. When the ceramic material approaches a rigidly-plastic condition and container material flow is controlled by a linear viscous mechanism shape change is more marked.

Effect of a shell on the change in shape of a porous billet during isostatic pressing. 1. stress deviator with isostatic pressing

Isostatic compaction of a porous billet in an incompressible container is considered. The behavior of the container as well as the matrix phase of a porous billet is assumed to be described by power law equations. Macroscopic deformation of a billet is controlled by flow theory for a compressible body with a smooth potential. It is established that the stressed state in a billet is not isostatic.

Modeling of Billet Shape in Spray Forming Process

A numerical method is presented to predict and analyze the shape of a growing billet produced from the forming which is a fairly new near-net shape manufacturing process. It is important to understand the mechanism of billet growing because one can obtain a billet with the desired final shape without secondary operations by accurate control of the billet shape, and it can also serve as a base for heat transfer and deformation analysis. The shape of a growing billet is determined by the flow rate of the alloy melt, the mode of nozzle scanning which is due to cam profile, the initial positio of the spray nozzle, scanning angle, and the withdrawal speed of the substrate. In the present study, a theoretical model is first established to predict the shape of the billet and next the effects of the most dominent processing conditions, such as withdrawal speed of the substrate and the cam profile, on the shape of the growing billet are studied. Process conditions are obtained to produce a billet with uniform diameter and flat top surface, and an ASP30 high speed steel billet is manufactured using the same process conditions established from the simulation.imulation.

Coupled Thermo-Deformation Analysis of Strain-Rate Dependent Materials with Work Hardening

The finite element formulation of the coupled analysis of plastic deformation and heat conduction is studied for the numerical analysis during the metal forming process at elevated temperatures. As an extension of previous studies, a method of estimating equivalent plastic strain during the steady-state forming process is proposed in the present study, which is applicable to both strain- and strain-rate-dependent materials. As an example of numerical calculation, the coupled heat and deformation analysis for an axisymmetric steady state dieless drawing is performed. The distribution of temperature, plastic strain-rate, equivalent plastic strain and the change of billet shape during dieless drawing are calculated. The obtained results are in good agreement with experimental data. The influence of the work-hardening exponent on deformation and the distribution of temperature is also discussed.

Coupled thermo-deformation analysis of strain-rate dependent materials with work-hardening.

The finite element formulation of the coupled analysis of plastic deformation and heat conduction is studied for the numerical analysis during the metal forming process at elevated temperatures. As an extension of previous studies, a method of estimating equivalent plastic strain during the steady-state forming process is proposed in the present study, which is applicable to both strain and strain-rate dependent materials. As an example of numerical calculation, the coupled heat and deformation analysis for an axisymmetric steady state dieless drawing is performed. The distribution of temperature, plastic strain rate, equivalent plastic strain and the change of billet shape during dieless drawing are calculated. The obtained results are in good agreement with experimental data. The influence of the work-hardening exponent on deformation and the distribution of temperature is also discussed.

A Study of Buckling in Upsetting by Use of Finite Element Method

To observe the fundamental characteristics of buckling in upsetting, annealed and hardened aluminium billets of circular and square cross sections were simply compressed under lubricated and restricted end conditions. Billets with a rectangular cross section were also compressed in a die which realized plane strain upsetting. The buckling distortion after a given reduction in height increased gradually with initial height/diameter (or height/width) ratio, and when the ratio reached a critical value, which usually dropped in the range between 1.5 and 2.0, the degree of buckling increased sharply. When the experimental critical ratios were compared with those calculated by the existing formulae, only qualitative agreements were obtained, i.e., larger n-value resulted in higher critical ratio. In order to simulate the buckling deformation, the rigid-plastic finite element method was used. A slight skew was given to the plane-strain upsetting model to represent the initial distortion of billet shape. It was confirmed that almost the same distorted grid as the experimental one could be obtained by FEM simulation if a proper combination of friction coefficient and the initial distortion were assumed, and that the distortion decreased with increasing friction coefficient and decreasing initial distortion. The relationship between critical height/width ratio against n-value agreed quantitatively well with the experimental results.

Influence of friction on the prediction of forces, pressure distributions and properties in upset forging

The axial compression of solid cylinders with initially equal height and diameter between flat parallel platens is examined. A finite-element method is used to predict the platen forces, the pressure distribution, and the strain and hardness distributions within the billet, for various levels of interface shear stress. The theoretical predictions of pressure distribution indicate that a simple friction-hill does not occur for this billet shape; a number of different distributions are found, dependent on the boundary conditions. Two distinct modes of flow are identified, again dependent on the boundary conditions. Experiments with commercially pure aluminium cylinders show good correlation with the predictions for unlubricated aluminium and for aluminium lubricated by a thin film of lead.

Detecting and eliminating collisions in NC machining

When a 3D object is milled from a billet by a cutting assembly (tool and an associated cutting head), a common hazard, particularly if the cutting is under numerical control, is that this assembly may collide with (foul) the partly cut billet. Fouling may be detected and eliminated by simulating the changing billet shape and the moving cutting assembly: fouling is detected when billet and cutting assembly models occupy the same model space. The principal method of removing fouling is to modify the billet by removing those parts that would subsequently foul. Alternatively, the cutter assembly may be modified by fitting a longer tool, whose length is calculated to lift the cutter assembly above any part of the billet causing fouling. For premodifying billets, the program records the parts of the billet causing fouling and calculates a cutter path to remove these. Since this preliminary cut may itself cause fouling, the program is applied recursively to the initial toolpath and subsequent defouling toolpaths until a final toolpath is reached that does not cause fouling. These preliminary toolpaths are then executed in the reverse order of their generation. The method assumes that the final shape has a single height above every point of its base, and is therefore limited to shapes that do not have undercutting.

連続鋳造ビレットの鋳造組織と偏析について

The macro structure and the segregation of continuously cast carbon steel billets with 80 to 250mm square and 260×370mm in section were investigated. The results were summarized as follows.1. The length of columnar crystal and the thickness of central segregated zone are increased, and the central porosity and segregation become worse, with increase of superheated casting temperature.2. The absolute thickness of central segregated zone is increased with increase of the section of square billet, but its relative value to billet thickness is decreased. The type of V segregation is changed from single V line to multi V line, in the case of high superheat temperature.3. The type of V segregation is changed from V line to V zone and the central segregation disappear, when the billet shape is changed to rectangular.4. The maximum positive segregation ratios of Mn and C are 1.3 and 1.8 respectively, which are obtained by the analysis of specimen with 3 mm in dia and 3 mm in depth taken from the central segregated zone high carbon billet with 160 mm square in section.5. The length of columnar crystal and the width of central segregated zone are increased in the order 0.3%C, 0.1%C and 0.6%C steel under the same condition of super heated casting temperature.6. The mechanism of formation of equiaxed dendrite and V segregation are discussed.