F.H. Osman

Upper-bound analysis for the automation of open-die forging

Abstract The automation of open-die forging systems can be attractive for small batch manufacture of medium-size parts where they can compete against a number of machining processes. The introduction of new manufacturing systems and the associated work-in-progress minimization technique prompts a consideration of the use of open-die forging for incremental profiling and shaping processes. In order to develop an automated open-die forging process it is essential to be able to predict the shape changes occurring at each step. Therefore a general computerized methodology is proposed for small batch manufacture via a theoretical model, producing rapid predictions of metal flow for continuing incremental deformation. This paper reviews the open-die forging process in this context as a part of a computer-controlled robotics flexible forging system for the economic production of small-batch quantities. The metal flow in open-die forging is analyzed through a number of upper-bound solutions and the basis of an on-line analytical modeling system, together with experimental correlation and a planning system, is presented to produce bar profile features.

Non-conventional cold extrusion

Abstract In recent years new extrusion processes have been developed for non axisymmetric shapes and with a variety of tool geometry, among them radial extrusion, rotary forming, non-axisymmetric extrusion etc. In this paper two “non-conventional” cold extrusion processes are investigated; radial extrusion using a circular punch and backward extrusion with the punch of square cross section. Experiments have been conducted in order to determine the basic process parameters. Furthermore, an Upper Bound solution for load prediction in radial extrusion have been developed which shows relatively good agreement with the experiment.

Forging of complex geometries with differential heating

Abstract An investigation of a new forming method for the production of complex profiles is presented. The deformation is effected by the use of simple tools in a flashless type operation where local heating is applied to the billet surface or volume, thus allowing deformation to occur where material yield stress is lowest. The mode of deformation created by the local variation in the material flow stress is complicated and can only be idealised by the use of visioplasticity techniques. Experiments using split billets and integrated aluminium/plasticine billets showed that in the flow of softer material is predominant.

Preform Design for Forging Rotationally Symmetric Parts

Abstract This paper describes an upper bound modelling based technique to design preforms for forging of rotationally symmetric parts. A reversing algorithm which results in improved metal flow in the final stages of filling the cavity is applied to the precision forging of bevel gears. The predicted preform has a simple rotationally symmetrical profile which accommodates the simultaneous filling of the gear teeth. Experimental results show that the preform designed by this technique requires less energy in the final stages of the forging.

Some observations on contact stress measurement by pin load cell in bulk metal forming

Abstract The information on the intensity and distribution of the contact stresses in bulk metal forming operations is essential both for the die design and for the process analyst. As the theoretical and numerical methods for the contact stress determination have some analytical constraints a number of experimental methods have been developed. One of them is the pin load cell technique which has been applied in different metal forming operations. In this paper some problems related to the measurement of normal contact stress are presented. The focus is placed on the problem of initial pin position relative to the die surface. Experimental investigations were carried out in order to determine the influence of the axial pin position on the measured contact stress values. The process studied was that of simple upsetting of cylindrical specimens. It has been shown that the axial pin position 0.15mm above the die surface prior to the defonnation gives the most realistic results.

Forging process modeller ― A feasibility study

Summary The paper describes a system of programs which have been brought together to form a coherent functional modeller for use in the design of a forging process sequence. The basic elements of the system are data acquisition, data preparation, forging process plasticity analysis (UBET), die stress analysis (FEM) and solid modelling of the forging and dies. The system is designed so that it will link into other relevant CAD and plasticity analysis packages.

Application of 'UREAD' for the Energy Dissipation in Engineering Structures

A concept based upon Equal Channel Angular Extrusion (ECAE) is developed and introduced in the form of a Universal Re-usable Energy Absorption Device ‘UREAD’. In impact situations the device utilises the energy required to extrude deformable materials through the shear planes of a set of intersecting channels and hence provides the means to protect engineering structures. The impact force is absorbed through the resistance of a deformable material and the energy is dissipated through an operational stroke. This paper examines the use of this new concept under dynamic loading. The device performance and usability during dynamic impacts are tested in a landing frame type experiment where the effectiveness of the technique in reducing impact loads and energy are also examined.

Analysis of Cavity Tool Stresses in Channel Angular Extrusion

The Channel Angular Extrusion (CAE) technique is a process, in which a deformable solid material is led to yielding through the intersection of inclined channels. Compared to classic plastic deformation, the process is technically simple but the material experiences, instantly, large plastic deformation. The deformation occurs locally and high internal stresses develop during the process. In most cases the process is used for grain size refinement. Equal Channel Angular Extrusion (ECAE) is a special case where the intersecting channels are of equal cross sections. In this paper, an analytical study of the internal stresses and those developed along CAE tools is presented. A deformation model is introduced for the general process of channel extrusion in which the intersecting channels are not necessarily equal. The procedure splits the material at the intersection of the channels into two zones; one causes the deformation while the other remains rigid. The analysis is also applied to the particular case of ECAE, and the results are compared with those obtained from a finite element analysis and the overall experimental pressure.

FEM Simulation Study for Rapid Preforming of Axisymmetrical Forging by Differential Heating

Feasibility of generating differential metal flow to obtain axi-symmetric protrusions on a billet by flat-die differential heating was studied. Results showed that heating arrangement influenced temperature field and deformation behaviour. FEM simulation to achieve anticipated preform geometry generally requires a series of trial and error approaches that are rather time consuming. Aiming at providing guides for more accurately determining the heating conditions, this paper suggests a useful method in presenting the FEM simulation results. It also sheds light on the heating effectiveness in generating differential flow of material

The upper bound method

Limit analysis has been proposed as a means of obtaining solutions to many otherwise intractable metal-forming problems. In its complete form, this approach seeks to establish two expressions for forming loads, one (a so-called lower bound) which is definitely an underestimate and the other (a so-called upper bound) which is an overestimate. Since it is generally sufficient to ensure that the calculated load for a forming operation is indeed sufficient to perform the operation, then interest naturally centres on the upper bound technique. If used correctly, realistic overestimates are obtained.