P.L.B. Oxley

Allowing for Nose Radius Effects in Predicting the Chip Flow Direction and Cutting Forces in Bar Turning

A model is presented for predicting the chip flow direction and cutting forces for bar turning with nose radius tools. A comparison which is made of predicted and experimental results shows excellent agreement.

A universal slip-line model with non-unique solutions for machining with curled chip formation and a restricted contact tool

Abstract A universal slip-line model and the corresponding hodograph for two-dimensional machining which can account for chip curl and chip back-flow when machining with a restricted contact tool are presented in this paper. Six major slip-line models previously developed for machining are briefly reviewed. It is shown that all the six models are special cases of the universal slip-line model presented in this paper. Dewhurst and Collinss matrix technique for numerically solving slip-line problems is employed in the mathematical modeling of the universal slip-line field. A key equation is given to determine the shape of the initial slip-line. A non-unique solution for machining processes when using restricted contact tools is obtained. The influence of four major input parameters, i.e. (a) hydrostatic pressure (PA) at a point on the intersection line of the shear plane and the work surface to be machined; (b) ratio of the frictional shear stress on the tool rake face to the material shear yield stress (τ/k); (c) ratio of the undeformed chip thickness to the length of the tool land (t1/h); and (d) tool primary rake angle (γ1), upon five major output parameters, i.e. (a) four slip-line field angles ( θ, η 1 , η 2 , ψ ); (b) non-dimensionalized cutting forces (Fc/kt1w and Ft/kt1w); (c) chip thickness (t2); (d) chip up-curl radius (Ru); and (e) chip back-flow angle (ηb), is theoretically established. The issue of the “built-up-edge” produced under certain conditions in machining processes is also studied. It is hoped that the research work of this paper will help in the understanding of the nature and the basic characteristics of machining processes.

Predicting cutting forces in face milling

Abstract It is shown how orthogonal machining theory can be applied to predict the cutting forces in face milling from a knowledge of the work material properties and cutting conditions. Predicted and experimental results are compared.

Allowing for End Cutting Edge Effects in Predicting Forces in Bar Turning with Oblique Machining Conditions

Oblique machining tests are described which were made to determine how the cutting which occurs at the end (secondary) cutting edge in bar turning affects the direction of chip flow and the cutting forces. Normally in developing a predictive machining theory only the cutting action at the side (main) cutting edge is considered, with no account taken of the contribution of the end cutting edge. By introducing the concept of an equivalent cutting edge which in essence combines both the side and end cutting edges it is shown how the influence of the latter can be accounted for in predicting cutting forces.

Analysis and experimental investigation of a simplified burnishing process

A slipline field model of a simplified burnishing process is used to derive equations for estimating the burnishing force, the depth of the burnished layer and the plastic strains in this layer. A detailed comparison is made between predicted and experimental results. An observation of considerable practical interest is the high quality surface finish (low surface roughness) which can be obtained by the burnishing process described.

A slip-line field for plane-strain extrusion of a strain-hardening material

Abstract An experimental method of obtaining flow fields for plane-strain extrusion using printed grids (0.002 in. square) is described, and a slip-line field is constructed by calculating the directions of maximum shear strain-rate from the measured velocity gradients. It is shown that account must be taken in the stress equilibrium equations of variations in flow stress caused by strain-hardening in order to satisfy internal stress consistency and equilibrium of forces.

A strain-hardening slipline field analysis of the plastic deformation observed in a model asperity interaction experiment

Abstract S caled-up model asperity experiments are described in which a hard wedge is indented into and then slid along the surface of a relatively soft material with the resulting plastic deformation measured using printed grids. A slipline field analysis of the deformation occurring once steady-state conditions have been achieved is described. This shows that tensile stresses can exist in a small region of the field when in calculating stresses account is taken in the stress equilibrium equations of variations in flow stress resulting from the strain-hardening properties of the deforming material.This result could be important in considering the viability of processes such as low cycle fatigue and fracture as possible wear mechanisms.

Investigation of experimental flow patterns for plane strain extrusion of hardening materials with slipline field methods

The paper describes a method of obtaining experimental flow patterns in extrusion of aluminium alloys through tapered dies, of constructing slipline meshes from the velocity fields and of carrying out stress analyses with hardening rules based on measured stress-strain relations in compression. The slipline meshes are patched together from local Hencky-Prandtl nets which are perturbed to obtain the best overall match between the computed velocity field and that of the experimental flow pattern, by using an iterative optimization procedure. The extrusion forces computed from the stress fields and from the plastic work are compared with the measured forces and with those predicted by the corresponding solutions for rigid-perfectly plastic material.

An experimentally-determined slip-line field for plane-strain wedge indentation of a strain-hardening material

Abstract PRINTED grids are used to measure the plastic flow in very slow speed plane-strain wedge indentation experiments. Using a radial grid with its centre coinciding with the origin of the indentation it is shown that the necessary condition for the maintenance of geometric similarity during indentation, namely that all elements initially on a given radial line should describe the same trajectory in the unit diagram, is satisfied within experimental accuracy over a wide range of indentation depths. A slip-line field is then constructed using the directions of maximum shear strain increment calculated by making an incremental indentation of an initially square grid printed on a previously-indented specimen. In making a stress analysis of this field it is shown that consistent results can only be obtained if account is taken in the stress equilibrium equations of variations in flow stress with strain.

Strain-hardening extrusion—I. Construction of slip-line fields from experimental flow patterns

Abstract A possible method of solving problems in strain-hardening flows is by perturbation of known perfectly-plastic solutions. It is shown that vertex singularities, which are possessed by most such solutions, are not admissible in steady hardening flows. The structure of regular local solutions, both perfectly-plastic and strain-hardening, is investigated, and it is shown how vertex singularities can be replaced by regular local corner solutions. A scheme for constructing strain-hardening slip-line fields based on experimental flow patterns is described, which uses the maximum shear strain-rate directions calculated from the digitized and smoothed flow pattern to perturb local Hencky-Prandtl nets, which are then patched together in conformity with the topology of the solution to form a complete slip-line field. This method has been implemented in a computer program to construct slip-line fields from flow patterns for extrusion through wedge-shaped dies, and some fields computed by the program are presented.