Andrzej Rosochowski

Rapid tooling: the state of the art

Abstract Producing tooling directly from CAD models is regarded as an important method of reducing the cost and time to market for new products. This paper describes the role of rapid prototyping technology in increasing the speed of tooling development. A comprehensive review of examples of rapid tooling indicates a major shift in tooling practice. This new trend in manufacturing based on rapid prototyping and rapid tooling has already had a dramatic impact on the engineering environment.

Numerical and physical modelling of plastic deformation in 2-turn equal channel angular extrusion

A new process of 2-turn equal channel angular extrusion (ECAE) was simulated by finite element method with a view to providing an insight into the mechanics of the process. The stress results obtained gave indication of expected forces and tool contact stresses. Plastic flow sensitivity analysis, with respect to geometrical features of the die, enabled process and tool design guidelines to be formulated. Two methods of increasing productivity of 2-turn ECAE were presented and simulated using finite element method. Physical modelling experiments with wax billets validated the results of numerical simulation and also gave indication of possible problems with the real process.

Simulation of wrinkling in sheet metal forming

Abstract Wrinkling of conical cups was simulated using the finite element method (FEM) and verified experimentally. Two different FEM codes: static-explicit ITAS3D and dynamic-explicit ABAQUS/Explicit were used in numerical simulations. It was found that several parameters could affect results of wrinkling simulation. Most important was the initial shape of the finite element mesh. General difficulties in simulation were reported for both FEM codes, dynamic and static. Stamping of conical cups was conducted using an anisotropic steel sheet to establish a reference frame for the validation of numerical results.

Micromilling: material microstructure effects

Abstract Micromilling is one of the technologies that is currently widely used for the production of microcomponents and tooling inserts. To improve the quality and surface finish of machined microstructures the factors affecting the process dynamic stability should be studied systematically. This paper investigates the machining response of a metallurgically and mechanically modified material. The results of micromilling workpieces of an Al 5000 series alloy with different grain microstructures are reported. In particular, the machining response of three Al 5083 workpieces whose microstructure was modified through a severe plastic deformation was studied when milling thin features in microcomponents. The effects of the material microstructure on the resulting part quality and surface integrity are discussed and conclusions made about its importance in micromilling. The investigation has shown that through a refinement of material microstructure it is possible to improve significantly the surface integrity of the microcomponents and tooling cavities produced by micromilling.

Double-Billet Incremental ECAP

Batch SPD processes have a limited scope for being used on an industrial scale. More feasible are continuous processes among which the new SPD process of Incremental ECAP (IECAP) is an attractive option. In this paper, a double-billet version of I-ECAP, which doubles process productivity, is presented. The concept of the process is first checked using the finite element (FE) method. FE simulation results are the basis for the design of an experimental rig. Trials of nanostructuring of 10x10x200 Al 1070 billets are carried out with the forces on the reciprocating die and the feeder measured. Metallurgical samples after 4 and 8 passes of I-ECAP (route BC) are investigated using TEM. Tensile properties after 8 passes are established. All these results show that the new SPD process of I-ECAP gives the results comparable to those obtained by a classical batch ECAP with the added capability of dealing with much longer (possibly infinite) billets.

Processing Metals by Severe Plastic Deformation

Severe plastic deformation (SPD) is used to convert traditional coarse grain metals and alloys into ultrafine-grained (UFG) materials. UFG materials possess a number of improved mechanical and physical properties which destine them for a wide commercial use. However, any attempt to use SPD technology commercially requires a better insight into the mechanics and practicality of SPD processes. This paper looks into historical development of SPD processes and focuses on such aspects of SPD as material flow, role of hydrostatic pressure, friction, geometry of tools, billet and feeding considerations, technical feasibility, etc. The discussion of these topics sets a background for decisions concerning further research and commercialisation of SPD.

Incremental equal channel angular pressing for grain refinement

Creating a small amount of ultrafine grained metals by severe plastic deformation, for example using equal channel angular pressing, is possible in many research laboratories. However, industrial production of these materials is lagging behind because of the lack of industrially viable severe plastic deformation processes. One attempt to change this situation is based on the concept of incremental equal channel angular pressing developed by the University of Strathclyde and Warsaw University of Technology. The paper describes the path the researchers took to develop the process starting from finite element simulation, through tool design and process implementation, to material characterisation. Examples of various process configurations, which enable obtaining UFG bars, plates and sheets are given and possible future developments discussed.

Effect of secondary yielding on nett-shape forming

Abstract Nett-shape forming requires better understanding of the phenomena affecting component accuracy. Some of these are subtle or not fully recognised and are, therefore, being disregarded. This paper reveals secondary yielding in some cold bulk metal forming operations. Secondary yielding of a component results from unloading by punch removal and die contraction. The process of closed-die upsetting of a cylindrical workpiece is examined. The theoretical analysis of this process explains the notion of secondary yielding. The main factors affecting secondary yielding are the flow stress of the workpiece material and the elastic properties of both the workpiece and the die. Secondary yielding refers to the plastic flow of material during the unloading cycle and, therefore, affects the final dimensions of the workpiece. The present analysis, which has been carried out in terms of the elastic strains of both the workpiece and the die, enables formulation of the die compensation procedure for this case. It appears that the die compensation procedure used for processes which involve secondary yielding is different from that for processes characterised by purely elastic unloading.

FEM Simulation of Incremental Shear

A popular way of producing ultrafine grained metals on a laboratory scale is severe plastic deformation. This paper introduces a new severe plastic deformation process of incremental shear. A finite element method simulation is carried out for various tool geometries and process kinematics. It has been established that for the successful realisation of the process the inner radius of the channel as well as the feeding increment should be approximately 30% of the billet thickness. The angle at which the reciprocating die works the material can be 30°. When compared to equal channel angular pressing, incremental shear shows basic similarities in the mode of material flow and a few technological advantages which make it an attractive alternative to the known severe plastic deformation processes. The most promising characteristic of incremental shear is the possibility of processing very long billets in a continuous way which makes the process more industrially relevant.

Secondary yielding of forged components due to unloading

Abstract Secondary yielding of the workpiece material is a new phenomenon recently recognised, which can occur in some bulk metal forming operations. It is caused by contracting dies as a result of unloading. Since secondary yielding involves dimensional changes of the workpiece, it becomes one of the factors which should be taken into account when attempting net-shape forming. This paper contains a comprehensive study of secondary yielding. A simplified theoretical model will serve as a means of explaining the notion of secondary yielding. It will also be used to predict dimensional changes of the workpiece. Experimental verification of these results will be presented. Observed discrepancies will be rectified by an improved analysis using the finite element technique and thoroughly discussed.