SLIDE 1
Mark Richman and Jayant Khambekar Mechanical Engineering Department Metal Processing Institute Worcester Polytechnic Institute
A Balanced Die Method to Reduce Ejection Forces
SLIDE 2 Outline of Presentation
- Overview of the Balanced Die
– overview of compaction-to-ejection process – description of the balanced die method
– qualitative effects (intuitive)
- Brief description of the ejection model
- Results: Prediction of ejection forces
– unchanging radial pressure – increasing radial pressure – qualitative comparison to experimental results
SLIDE 3 Reduced by the Balanced Die
Overview: Compaction to Ejection
Compaction Springback Ejection
Axial Pressures Radial Pressures Radial Pressures Frictional Stresses Added Frictional Stresses Axial Pressures Radial Expansion Radial Pressures
Elasticity Solution of 3 Misfit Cylinders
SLIDE 4
The Balanced Die
upper punch cylindrical piston die carrier die wall metal powder rubber sleeve core rod lower punch L h
SLIDE 5
Balancing Pressure
R Ro Ri H
σ
Pressure σ exerted by rubber sleeve
SLIDE 6
Radial Interfaces
Ri Ro R CENTER LINE CORE ROD POWDER DIE WALL
L
SLIDE 7
Radial Interfaces
CENTER LINE CORE ROD COMPACT DIE WALL
H
SLIDE 8
Radial Interfaces
CENTER LINE CORE ROD COMPACT DIE WALL
H
SLIDE 9
Radial Interfaces
CENTER LINE CORE ROD COMPACT DIE WALL
σ H
SLIDE 10
Radial Interfaces
CENTER LINE CORE ROD COMPACT DIE WALL
σ H
SLIDE 11
Radial Interfaces
CENTER LINE CORE ROD COMPACT DIE WALL
σ H
SLIDE 12 fi= µiRi( σi + αeP ) fo= µoRo( σo + αeP )
radial pressures developed after springback
Friction Forces :
Ejection Force Balance in the Compact
fi fo fo fi P+dP P P+dP P Ri Ro dz
( )
i
f R R dz dP +
) ( 2
2 2
z
αP αP
radial pressures due to Poisson effect
SLIDE 13 Physical Parameter Values
Focus on NC 100 iron powder with no lubricants (Holownia [1996]) Geometric parameters
Inside radius of Compact (Ri): 8 mm Outside radius of Compact (Ro): 16 mm Outside radius of die (R): 19 mm Fill height (L): 40 mm Compact height (H): 20 mm
Material properties
3.245 g/cm3
7.82 g/cm3
Friction coefficients
µi = µo 0.1
Elastic properties
Compact- E= 55GPa, ν=.315 Die and Core rod- E= 200GPa ν=.3 Rubber Sleeve- E=.778MPa ν=.48
SLIDE 14 Ejection Force vs. Compaction Height for Constant External Pressure
Compacted Height H/L
0.50 0.52 0.54 0.56 0.58 0.60
Ejection Force (kN)
20 40 60 80 100
=0
50 100 150 200
SLIDE 15 Varying External Pressure
σ σ H Axial strain in sleeve:
ε = (H-h)/h
Cylindrical piston Rubber Sleeve
h L
Powder
SLIDE 16 Radial Pressure Exerted by Sleeve vs. Axial Strain
Axial Strain
- 0.30
- 0.25
- 0.20
- 0.15
- 0.10
- 0.05
0.00
External Radial Pressure
50 100 150 200
Elastic Properties of the Rubber Sleeve: E = .778 MPa ν = .48
SLIDE 17 Ejection Force vs. Compaction Height for Increasing External Pressure
Compacted Height H/L
0.50 0.52 0.54 0.56 0.58 0.60
Ejection Force (kN)
20 40 60 80 100 h/L=.6 .7 .65
unbalanced die
103 kN 11.9% 36.9% 91.4%
SLIDE 18 Ejection Force vs. Compaction Height for Increasing External Pressure
Compacted Height H/L
0.50 0.52 0.54 0.56 0.58 0.60
Ejection Force (kN)
5 10 15 20 25 .71 .7 h/L=.69
98.2% 91.4% 77.7%
Sensitivity to small differences in initial sleeve height:
SLIDE 19 Qualitative Comparison to Experimental Results
Total Load (kN)
100 200 300
Ejection Force (kN)
4 8 12 16 20 24 28 .71 .7 h/L=.69
Current Model:
Total Load (kN)
100 150 200 250 300 350 400
Ejection Force (kN)
1 2 3 4 5 6 7
Holownia [1996]:
SLIDE 20 Compaction Loads
Compacted Height H/L
0.5 0.6 0.7 0.8 0.9 1.0
Total Load (kN)
50 100 150 200 250 300 350 h/L=.71 .7 .69 unbalanced die
208.5 kN 49.4%
SLIDE 21 Summary of Results
- When the balancing pressure is unchanged throughout
compaction:
– significant decreases in required ejection force – but…ejection force always increases with increasing compaction
- When balancing pressure increases due to increasing
axial strain in the rubber sleeve:
– significant decreases in required ejection force – and….ejection force can decrease with increasing compaction
- requires proper choice of initial sleeve height
– decrease in ejection force is much greater than the increase in required compaction load
SLIDE 22
Thank You for Your Attention
