Nature of friction in extrusion process and its effect on material flow

Abstract

This investigation focuses on simulation of the extrusion process and in particular the effect of the initial billet temperature on friction and its consequences on material ow. The simulation is compared with data obtained from an experimental extrusion press. All the simulations are performed with the implicit nite element codes FORGE2 and FORGE3. The effect of the initial billet temperature on the deformation zone pattern and its consequent effect on friction using both numerical simulation and experimental work are presented. A comparison with experiments is made to assess the relative importance of some extrusion parameters in the extrusion process and to ensure that the numerical discretisation provided a true simulation of the process. A speci c functional relationship to directly measure interfacial friction under conditions approaching those encountered in the quasi-static deformation process is described. The results revealed that the friction factor increases with increase in initial billet temperature and varies from 0 . 65 at 300°C to a 0 . 91 at 450°C after reaching the peak pressure. The dead metal zone is observed to vary in form and has a greater volume at high temperatures. The increase in friction results in an increase of initial extrusion load. The nite element program appears to predict all the major characteristics of the ow observed macroscopically. MST/5520The authors are in Bournemouth University,

Identification of a friction model for the bearing channel of hot aluminium extrusion dies by using ball-on-disc tests

“…In the current research, choked dies with 15' die angle were used to apply contact pressure to the extrudates and full sticking friction was observed in all the DAE tests 5 conducted in the present research. In the manuscript, the correlation between the length of the extrudates and bearing area has been explained:…”

“…These tests were designed with highlighted friction sensitivity indicated by extrudate lengths, and the lubricants can be evaluated and the global friction coefficient or factor on the workpiece/tooling interface can be determined quantitatively with the aid of FE simulations. On the other hand, the friction coefficients/factors over the container wall can be estimated based on the friction effects on the extrusion load [4,5]. Table 1 shows a summary of the friction test results obtained from extrusion friction tests.…”

“…It was found that many practical problems in the hot extrusion industry, such as wear of the extrusion dies [1][2][3][4], surface quality of the extruded profiles [5], die lines and pick up [6] etc., are related to the strong adhesion between the hot aluminium and the die due to strong chemical and atomic interactions between hot aluminium and steel, which is the main reason for the excessively high friction observed during hot aluminium extrusion [1][2][3]7]. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 3 In the past years, efforts have been made to study the tribological phenomenon of the extrusion process and the developed friction testing techniques can be classified as three different groups, namely, field tests; simulative tests (or physical simulation tests) and tribological tests.…”

Characteristics of the Friction Between Aluminium and Steel at Elevated Temperatures During Ball-on-Disc Tests

“…The experimental approach was mostly taken to determine the friction coefficient at the billet/container interface from the difference in extrusion force due to a change in friction force at this interface during extrusion [6][7][8]. Using a similar approach, Flitta and Sheppard [9] revealed the dependence of friction coefficient at the billet/ container interface on temperature during the aluminium extrusion process at elevated temperatures. A change in friction coefficient from essentially sliding friction to nearly sticking friction was found, when the billet temperature was increased from 300 to 450°C.…”

Material flow during the extrusion of simple and complex cross-sections using FEM

“…The occurrences of material flow during the extrusion process have been the focus of much interest in aluminium alloys in general [3][4][5][6][7][8] but has been most often limited to rod extrusions. The influence of section geometry on the deformation zone is difficult to establish, unlike axisymmetric rod extrusion where the circumferential strain is essentially zero, the introduction of a third dimensional strain requires more careful interpretation.…”