Jay S. Gunasekera

Development of a neural network model for a cold rolling process

Abstract This paper describes the development of a neural network model for the flat rolling process. This neural network was based on the backpropagation paradigm. A nonlinear mathematical model based on the slab method was developed to guide and supervise the learning procedures. A near-optimal neural network structure was determined by using a development process that emphasized second-order derivative information. The application of this process yielded improvements in the learning errors, prediction errors, and training times. A robust and accurate model was obtained as a result of this process.

Extrusion through controlled strain rate dies

The workability of a material during deformation processing is determined by (a) the die geometry which, in turn, determines the flow field during deformation, and, (b) the inherent workability of the material under the imposed processing conditions of strain rate and temperature. Most common alloys have good inherent workability and can be successfully formed over wide ranges of temperature and strain rate. Products can be successfully formed from these alloys even with dies which impose large variations in strain rate during deformation. However, many of the new alloys and composites can be deformed only in very narrow processing regimes, and control of the strain rate during deformation of such materials becomes important. For example, extrusion of a whisker-reinforced aluminum alloy composite is possible only when the strain rate is controlled to within one order of magnitude. This paper describes the development of a method for obtaining preliminary shapes of controlled strain rate extrusion dies, a special case being the constant strain rate die. The theoretical basis for such die design processes is presented, followed by some examples of die geometries. Since this design procedure ignores the material flow properties, the designed die shapes must be verified using the finite element method or physical modeling. Results of simulations with the program ALPID are also presented.

3D flow analysis inside shear and streamlined extrusion dies for feeder plate design

Abstract The extrusion process is one of the commonly used metals forming processes. In this paper, shear dies with a feeder plate are analyzed using a 3D metal forming simulation package — MSC/SuperForge. This package uses the finite-volume analysis method. Twelve simulations using different die shapes (streamlined, shear and shear with feeder plate) for producing a complex shaped product — I-shape — were performed. The results indicated that shear dies with feeder plates can have the same flow characteristics and better surface finish as compared to streamlined dies, which are more difficult to design and manufacture for aluminum extrusions. It is shown that the MSC/SuperForge package using the finite-volume method provides results very close to those obtained from a validated analysis package. However, the simulation time using MSC/SuperForge was almost half the time consumed by the other package in performing identical simulations using the same computer. Moreover, the finite-volume technique used in MSC/SuperForge eliminates the remeshing problems that make simulating a metal-forming process with severe deformation, such as the extrusion process using a shear die, so difficult.

Use of UBET for design of flash gap in closed-die forging

Abstract An upper bound elemental technique (UBET) has been proposed for the design of the flash gap in closed-die forging operations of axisymmetric shapes. The developed method has been applied to analyze the forging load, die-cavity filling, and effective strain and strain rate distributions in axisymmetric closed-die forging with a rib-web type of cavity. The forging process has been superimposed with two sub-stages called the extrusion and the back-fill stages. The total die load required for extrusion and back fill are calculated separately and a maximum allowable extrusion gap is proposed for a given percentage die-fill. FEM simulations have been carried out with different die geometries and the results are in good agreement with UBET predictions.

The effects of temperature on the machining of metals

The machining behaviors of metals at various workpiece temperatures are studied by the milling operation. Cutting power was recorded; tool life, chip size, surface finish and the microstructures of chips were examined.

An upper bound elemental technique approach to the process design of axisymmetric forging by forward and backward simulation

Abstract Upper bound element technique (UBET) is used to simulate axisymmetric forging and to determine the optimum intermediate shapes using backward simulation. The lowest energy rate is the key issue in achieving the optimal intermediate shape as well as the backward simulation of the process. The two simulations (forward and backward) were tested with different profiles of disks and two cases are presented here. The present method was validated using finite element method (FEM) by forward simulation. As results show, this technique improves the capability of the simulation tool and provides results within a short period of time compared to the FEM.

Analysis of Rolling

Summary To simulate a given manufacturing process, it is imperative to have a proper knowledge of material behaviour under processing conditions. Material behaviour in a gives process depends on a number of factors such as strain, strain-rate, microstructure and temperature. For hot working processes, strain-rate and temperature are the important parameters for modelling material behaviour. This paper presents an improved methodology for simulating rolling. The well-tried slab method for plane rolling can be enhanced by including constitutive equations which take into account strain, strain-rate, temperature and stability criteria. The complete mathematical and material model incorporated in the enhanced slab method can thereby reveal regions in which the material remains stable during deformation and allows achievement of the maximum efficiency of working without fracture. This enhanced slab method can therefore be used by the manufacturing engineer to check whether the process is going to lie in the most efficient and stable region and, if not, how to change the rolling mill parameters accordingly. Examples of the use of the enhanced slab method are presented, together with some comparisons with experimental results. The slab method is also useful for providing a rapid technique of solution on which to base more accurate finite element solutions.

Design of Profile Ring Rolling by Backward Simulation Using Upper Bound Element Technique (UBET)

Abstract The upper bound element technique (UBET) is used to determine the optimum intermediate shape for profile ring rolling using backward simulation. The lowest energy rate is the key issue in achieving the optimal intermediate shape as well as the backward simulation of the process. The plastic flow of material in ring rolling is assumed to be a sequence of successive closed-die forging processes. The ring is divided into features, which provide an approximated profile consisting of a number of rectangular elements. The simulation of the profile ring rolling was tested with different profiles of rolls, and two such cases are presented here. The present method was validated using an experimental radial ring rolling mill designed and fabricated in the Dept. of Mechanical Engineering at Ohio University for the investigation of both cold and hot ring rolling processes. As the results show, this technique is capable of solving the backward simulation of profile ring rolling problems in a much shorter time compared to the finite element method (FEM), which cannot easily simulate profile ring rolling. Moreover, as an engineering tool, this approach can be applied effectively to the profile ring rolling process and can serve as a useful tool in industrial applications.

Extrusion of Non-Circular Sections Through Shaped Dies

Summary Hot extrusion of high strength aluminium alloys into various sections is conventionally undertaken using flat-faced dies. This practice has a limitation on the extrusion speed due to high local temperatures withing the product which can result in hot shortness. Shaped extrusion dies have been used in the extrusion of steels, super-alloys and titanium alloys into fairly simple sections, such as elliptic-shaped preforms used for forging of turbine blades. The area of application for lubricated extrusion using smooth shaped extrusion dies has been limited in the past due to the complexity and the high cost of die design and manufacture. The recent advances in the use of computers in Engineering design and manufacture (i.e. CAD/CAM) have opened up new avenues for such applications. This paper presents some theoretical and experimental work carried on the analysis of extrusion through shaped dies. A new upper hound solution is proposed for the solution of three-dimensional metal flow through extrusion dies having circular entry shapes and regular polygonal exit shapes. The optimum die profiles new generated by the computer, and are used to produce Engineering drawings or NC tapes for the machining of electrodes and subsequent electro-discharge machining of dies.

Development of utility programs for a cold drawing process

Abstract Utility programs were developed for a cold draw process of hollow sections to determine proper hot-rolled tube size, die and mandrel geometries, processing parameters, expected final product dimensions, mechanical properties and drawing forces. The utility programs were separated into three parts: geometrical design, finite element analysis and special pre- and post-processing. The geometrical design program determines hot-rolled tube size, number of passes, die and mandrel geometries and processing parameters. A special purpose pre-processing program interfaces the geometrical design program with the ABAQUS finite element analysis program. The ABAQUS program was employed to determine metal flow, strains and stresses. A special post-processing program calculates final product dimensions, mechanical properties and drawing force from the analysis results.