الفهرس 
FORMULATION OF DIFFERENT THEORETICAL SOLUTIONSOnly 14 pages are availabe for public view
 |  | from | 173 |  |  |
| | | from | 173 | | |
Abstract
The aim of the present investigation is to study
some factors affecting Impact Extrusion proeess. These
faetors are, the effect of slug thickness, reduction
percent, shear factor, and the eftect ot lubrication
on the product quality. The literat~ related to the
process has been critically reviewed with special
reference to lead.
The theoretical solutions to the probl~ have
been surveyed and three models using Upper-Bound-
theorem (2-zone, 3-zone and 4-zone) are presented.
The flow characteristics of lead and the friction
conditions under study have been established experimentally
using the ring compression test teehnique
as a testing method. A sub-press especially
designed and constructed ineorporating load cell
together with the different sets of tools required
for extrusion were used to perform the experimental
work. Extrusion was carried out on a 250 KN b.,y’draulic
press’ of maximum downward speed of 70 mm/see.
The theoretical and experimental results and
discussions in the present work led to the foll~wing
conclusions:
(1) In the range of reduction used in the present
work (80-95%), the 4-zone model was found to - ii -
describe closer to the detormational behaviour
of impact extrusion than the 2-zone and 3-zone
models during the steady state extrusion range.
(2) During the non-steady state extrusion range,
the 4-zone model failed to deecribe the defol’mational
behaviour of impact extrusion while
the 2-zone and 3-zone models were more descriptive
in this aspect.
(3) In the case of steady state extrusion, using any
of the proposed models, the Upper-Bound solution
(as an energy minimization technique) indicate
that the shear pressure plays the main
role in the determination of the total pressure.
While in the case of non-steady state extrusion,
the frictional pressure plays that role.
(4) The use of lubricant prevents the pressure
welding of the dead metal zone with the rest ot
the extruded cup so that it can separate. In
the dry condition, the dead metal zone welds to
the deformed cup and therefore no separation
(5)
takes place.
The deviation of the 2-zone and 3-sone models
from the experimental results in the non-steady
state extrusion is mainly attributed to th.tr
shortage in considering the contribution of the
dead metal zone.(6) Prevention of cavitation was achieved successfully
through the application of the equation proposed
by Avitzur concerning the design of extrusion
tools.
(7) Sound extrusion products can be obtained when
the shear tactor is relatively high. Kateria1
t10w with lubricants of low shear tactor was
tound to be random andLLncontroDab1e.
(8) Decreasing the extrusion reduetion percent improves
the product quality.