T.A. Dean

A practical computer-aided approach to mould design for axisymmetric forging die cavities

Abstract This paper reviews existing guidelines for the design of mould impressions and discusses previous computer-aided approaches. A critical assessment shows these proposals to be inadequate for design by numerical methods and two new mould design rules are suggested. These are implemented in a computer program based on a Tektronix 4052 microcomputer and designs obtained from the computer are compared with those obtained by previous methods and also shapes collected from industry. Built inside the program are interactive routines which enable the user to modify the designs produced by the program alone, if they are not suitable for a particular purpose.

An analysis of the forging of spur gear forms

Abstract Forging spur gear forms in completely closed cavity dies is investigated by means of an upper bound analysis. A velocity field comprising three unit deformation regions is proposed. The tooth regions are approximated by prismatic rectangular sections. The effects of root diameter, number of teeth and workpiece/die interface friction, on flow and forging pressures, are determined. Forging pressure without friction is independent of root diameter but increases with the number of teeth. In the presence of friction forging pressure increases with reducing root diameter.

The quality of hot forged spur gear forms. Part I: Mechanical and metallurgical properties

This paper describes the effects of pre-heating and post-forging cooling methods on the properties of complete spur gear forms. It is shown that atmosphere control during heating and minimum exposure to air after forging are necessary for a satisfactory surface finish and adequate tooth hardnesses to be obtained. The effect of carbon loss at the surface of gears was overcome by forging carburized billets. These could be quenched immediately after removal from the forging die to obtain desirable levels of hardness. The design of a jig for impact testing gear teeth in situ is described. The impact strength of completely forged gear teeth was found to be about 30% greater than that of those machined from rolled bar or pre-forged blanks. The strength is independent of the degree of deformation during forging, within the range investigated.

Computer aids to data preparation for cost estimation

Abstract This paper describes an interactive computer programme, implemented on a 64K mini-computer, a size which is within the purchasing capability of most drop forges, to aid the process of preparing data for cost estimation and preform die design for forging on hammers. The programme utilises Interactive -MODCON [1], a CAM system developed for machining finish forging dies, as an input facility to describe the geometry of forged shapes. Provided with an input file describing the geometry of the forging, the programme can be executed to obtain data such as the weight, cross sectional areas, plan area, mean thickness, centre of gravity, perimeter of the forged shape. Based upon these data, essential information required for cost estimation and preform die design is provided using the built-in design rules. The information includes amount of flash, flash geometry, mass distribution curve, forging energy and load, hammer size, minimum preform operations and bar size.

The application of upper bound analyses to real situations—A comparison of flash and flashless forging

Abstract This paper describes the application of a heuristic method in which calculations using upper bound analyses are combined with experimental results to produce an indication of frictional behaviour and the effects of work hardening and strain-rate sensitivity in practical forging situations. It also demonstrates that considerable load reductions are achievable by eliminating flash from two types of forging considered.

An examination of some aspects of warm forging production

Abstract The information presented in this paper is some results from a broad investigation into the warm forging process. A comparison of the properties of four different component shapes forged at 800°C, 1000°C and 1200°C is made. The effects of several lubricants on forging at 800°C are examined and experiences with various tool steels presented.

A new energy method analysis of plastic distortion in plane strain compression

Abstract This paper describes the use of a realistic admissible velocity field for the analysis of plane strain compression of workpieces in the presence of boundary friction. The velocity field is derived from displacement functions written in the form of trigonometric series. The coefficients of terms in the series defining the velocity field are obtained from considerations of volume constancy and minimisation of the energy function. The method is applied to rigid-plastic materials deformed in non-steady-states between flat rigid tools with an assumed friction factor m at the interfaces. Both loads and distortion at free surfaces are analysed, for various forging conditions. This analytical approach appears to have application to a range of non-steady-state or steady-state processes in which non-uniform deformation results in bulged free surfaces.

The quality of hot forged spur gear forms. Part II: Tooth form accuracy

Abstract An examination of requirements for the manufacture by Electro-Discharge Machining of dies for hot forging spur gear forms is presented. The effects of post-forging thermal contraction on tooth profile is analysed for a variety of gear geometries. Gears hot forged, hot forged and ground, and machined directly from blanks are graded on the International Standard Classification system. It is concluded that the forging process offers a cheap means for producing a heat-treated gear form, requiring only a grinding or shaving operation to be serviceable.

Computer aided design and machining of fuller dies for forging hammers

Abstract In this paper, the structure of an interactive computer programme to aid fuller design and machining, implemented on a 64K multi-user minicomputer, is discussed. Common fuller geometries and processes and the design methods adopted in the programme are elaborated. Provided with appropriate input data, the programme can be used for designing fuller cavities required for preforming operations. The outputs include dimensioned hard copies of fuller cavities and tapes for direct NC machining fuller cavities or electrodes for subsequent spark erosion. The principles used for the NC tape generation are described and examples of output given also. This programme forms part of a system for the CAD of complete hammer die blocks.

Extrusion forging high speed steels

Abstract Experiments have been performed to determine the effects of temperature and deformation speed on the extrusion pressure for two high speed steels, at various reductions. The effects of flow stress and friction are separated and experimental extrusion pressures compared with theoretical values. Examination of the products shows that cracking can arise at certain combinations of speed and temperature. The optimum conditions for extrusion are found to be high deformation speed and a preheat temperature of about 800°C.