Transcript Extrusion of Sections with Varying Thickness Through Pocket Dies

Extrusion of Sections with
Varying Thickness Through
Pocket Dies
Authors: D.Lesniak, W.Libura
Received: 31 August 2006
Published: November 2007
Presented By: Brad Elmer
Date: 19 September 2007
Background

Al market based on:
 Complicated
shapes
 Highest possible quality
Appropriate shape
 Dimensional tolerances
 Surface quality
 Homogenous structure
 Uniform mechanical properties

Background

Metal flow through the die must be as
uniform as possible

Especially a problem on profiles with
varying thickness
 Non-uniform
metal flow
 High velocity gradient in die opening
Solution

Correctly designed pocket die
 Controls
metal flow
 Enhances product quality
Purpose

“…to determine the influence of the pocket
die geometry on the metal flow during
extrusion of sections with varying
thickness and consequently on its
geometrical stability and surface quality”

Mechanical properties of cross sections
Extrusion force measured for all dies

Method
Profile 1 is wall thickness ratio g1/g2=6:2
Profile 2 is wall thickness ratio g1/g2=12:2
Metal Flow Test

Goal: “…check pocket dies geometry on the
formation of cracks and geometrical stability of
extrudate.”
Metal Flow Test
Flat die and different pocket dies
 W2 was varied


1mm pocket A
 3mm pocket B
 7mm pocket C
Results Profile 1
Results Profile 2
Results


Lessens dead zones
Symmetry zones result in uniform flow
Results
Shape stability Test
Results
Flat die: material flows faster at thick part
 “…application of two large pockets at the
thin profile part leads to faster metal exit
speed…”
 Can bend the other way

Results
Results
Results

Flat die: inhomogeneous material flow
 Creates
velocity gradient
 Unbeneficial state of stresses in orifice
 Tensile stresses responsible

B good quality
 Most
beneficial state of stresses
 Homogeneous meterial flow
Extrusion force Test
Indirect extrusion ram pressure = p = Yf ex (ex is from Johnson eqn)
and where Yf is found using the the ideal true strain e = ln rx
In direct extrusion, difficult to predict the chamber/billet interactive
friction, so use the shear yield strength ( about Yf /2 ) to estimate the
chamber wall shear force as
pf p Do2/4 = Yf p Do L/2
giving
pf = 2 Yf L / Do
and where pf = additional pressure to overcome wall friction force
Total ram pressure becomes
p = Yf (ex + 2L / Do )
Results Profile 1
Results Profile 2
Results
Results
Micro properties Test
Conclusions
References