Transcript Slide 1

Self-Regulating
Melt Valves for
Polymer Processing
David Kazmer
May 12, 2005
National Plastics Center
Agenda
• Introduction
– Vision
– Design
• Validation
– Steady State Behavior
– Consistency
– Flexibility
– Clamp Tonnage Reduction
• Current Status
Conventional Molding
Stationary Platen
Moving Platen
Clamping
Cylinder
Tie Rods
Mold
Operator Interface
Check valve
Pellets
Reciprocating
Screw
Polymer
Melt
Injection
Cylinder
Barrel
Heaters
Uneven processing in
conventional molding
Process Controller
Clamping Unit
Injection Unit
Hydraulic
Power Supply
Vision for
Injection Molding
• Decouple the mold from the molding
machine
– To increase supply chain productivity
• Decouple the gates from each other
– To increase part design flexibility
– To increase manufacturing flexibility
– To increase molded part consistency
• Decouple filling from the packing
– Increased molded part quality
Enabler:
Self-Regulating Valves
Stationary Platen
Moving Platen
Clamping
Cylinder
Tie Rods
Mold
Operator Interface
Check valve
Pellets
Reciprocating
Screw
Polymer
Melt
Injection
Cylinder
Barrel
Complete
process control
Heaters
for each gate…
…without pressure transducers
or closed loop controllers
Process Controller
Clamping Unit
Injection Unit
Hydraulic
Power Supply
Valve Design
• Self-regulating valve
– Two significant forces:
• Top: control force
• Bottom: pressure force
• Forces must balance
– Pin moves to
equilibrium position
• Melt pressure is proportional to control force
– Intensification factor related to valve design
I
Acylinder
Aannulus

2
Rcylinder
2
annulus
R
 100
Valve Function
• No sensor or controller needed!
• Valve adjusts to reject input variation
Fcontrol
– Outlet pressure proportional to control force
– Pin position determined by inlet pressure and
required pressure drop
Pin
time
Pout
time
time
Valve Deployment
• Advantages
– Multi-axis melt control without
cavity pressure transducers!
– Compact with low actuation forces
Provides flexibility,
consistency, and
productivity
• Disadvantages
– Hot runner required
Performance Analysis:
Flow Vectors
Annular flow provides
low shear rates & pressures
Performance Analysis:
Effect of Position
18
Q=1cc/sec
Q=5cc/sec
Q=25cc/sec
16
Pressure drop (MPa)
14
12
10
8
6
4
Pin will hover near 1mm
with very fast response.
2
0
0
0.5
1
1.5
Pin Position (mm)
2
2.5
3
Performance Analysis:
Effect of Size
P 
690
 4.5
12
 2.5 mm
Pressure Drop (MPa)
10
8
Higher melt flow with
slightly larger valves
 10 mm
 5 mm
6
4
2
0
0
2
4
6
8
Valve Outer Diameter (mm)
10
12
Performance Analysis:
Open Loop Error
80
Fpressure
Fshear
60
Fresultant
40
Force (N)
20
0
0
5
10
15
20
25
30
-20
Open loop error ~10N
-40
-60
Correctable error of 1-2%
-80
Flow rate (cc/s) @ nominal pin position
Agenda
• Introduction
– Vision
– Design
• Validation
– Steady State Behavior
– Consistency
– Flexibility
– Clamp Tonnage Reduction
• Conclusions
Validation
• All validation performed with a
two cavity hot runner mold
– Mold Masters Lts (Georgetown, Ontario)
• Mold produced binder separators
– 1.8 mm thick by 300 mm long
– 10 g weight
• Three control schemes investigated
– Convention molding
– Open loop control
– Closed loop control with pressure feedback
Air Pressure vs.
Melt Pressure
40
Cavity 1, Hyd=400, Air=50
Cavity 1, Hyd=800, Air=50
35
Cavity 1, Hyd=400, Air=85
Melt Pressure (MPa)
30
Cavity 1, Hyd=800, Air=85
25
20
Saturated melt pressure
15
Melt pressure
proportional to
air pressure
10
5
0
0
2
4
6
Cylinder Air Pressure (V)
8
10
Melt Pressure vs.
Part Weight
9
Flow in thick section
Flow in thin section
8
7
Part Weight (g)
6
5
4
3
Cavity 1, 430F Melt
Cavity 2, 430F Melt
2
Cavity 1, 460F Melt
1
Cavity 2, 460F Melt
0
0
10
20
30
Melt Pressure (MPa)
40
Part weights adjusted
with air pressure
50
Consistency Study:
Design of Experiments
Run
Number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
X1
Melt
Temp
-1
-1
-1
-1
-1
-1
-1
-1
1
1
1
1
1
1
1
1
X2
Mold
Temp
-1
-1
-1
-1
1
1
1
1
-1
-1
-1
-1
1
1
1
1
X3
Inj
Pres
-1
1
-1
1
-1
1
-1
1
-1
1
-1
1
-1
1
-1
1
X4
X5
X6
Inj
Pack
Pack
Velocity
Pres
Time
-1
-1
-1
-1
1
1
1
1
1
1
-1
-1
1
-1
1
1
1
-1
-1
1
-1
-1
-1
1
1
1
-1
Most
1
-1 significant
1
parameters
-1
-1
1
-1
1
-1
investigated
-1
1
1
-1
-1
-1
1
-1
-1
1
1
1
X7
Valve2
Setting
-1
1
-1
1
1
-1
1
-1
1
-1
1
-1
-1
1
-1
1
X8
Valve2
Cycle
-1
-1
1
1
-1
-1
1
1
-1
-1
1
1
-1
-1
1
1
Process Sensitivities
8.4
7.7
8.3
7.6
8.2
Open Loop Weight
7.8
7.5
7.4
Machine sensitivity
greatly reduced
Open Loop Weight
8.1
8
7.3
7.9
7.2
7.8
Intra-run variation (whiskers)
greatly reduced
Conventional
Valve Gating
el
t
Te
m
w
Lo
el
t
gh
M
w
w
w
gh
gh
gh
gh
gh Lo w
Lo
Lo
Hi
Lo
Hi
Hi
Hi
Hi
Hi
p
s
p
e
y
s
p
s
p
e
y
s
t
t
i
e
e
i
e
e
m
m
m
em em j Pr
em
oc
Pr
Ti
Pr
oc
Pr
Ti
T
Te d T
el
tT
el
k
k
nj
In
ck
ck
d
lt
l
I
V
c
c
l
V
el
a
a
e
o
j
o
j
M
P
P
M
M
In
Pa
Pa
M
In
w
Lo
p
Lo
Te
w
m
M
p
ol
H
d
Te ig h
M
m
ol
p
d
Te Low
m
p
Hi
In
gh
jP
re
s
In
Lo
jP
w
re
In
s
jV
Hi
el
oc gh
In
i
ty
jV
L
el
oc ow
i
t
y
Pa
Hi
ck
gh
Pr
e
Pa
s
ck
Lo
w
Pr
e
Pa
s
H
ck
ig
h
T
Pa ime
ck
Lo
Ti
w
m
e
Hi
gh
7.7
7.1
M
Conventional Weight
Conventional Weight
Open Loop
Melt Valve
Short and Long Run
Consistency
Short and long run
consistency
greatly increased
m
dy 2
  
 xj
y
dx
j 1
j
Processing
Variable
Melt Temp
Mold Temp
Inj Pres
Inj Velocity
Pack Pres
Pack Time
Relative
Variance
0.0025
0.0025
0.0025
0.0025
0.0025
0.0025
Valve Gates
0.1479
0.0812
0.0308
0.0000
0.2667
0.1348
Sensitivities
Variances
Open Loop
Closed Loop Valve Gates Open Loop
Closed Loop
0.0240
0.0487
5.47E-05
1.44E-06
5.92E-06
-0.0082
0.0319
1.65E-05
1.66E-07
2.54E-06
0.0065
0.0109
2.37E-06
1.06E-07
2.99E-07
-0.0211
-0.0818
1.66E-12
1.11E-06
1.67E-05
0.0158
0.0176
1.78E-04
6.21E-07
7.72E-07
0.0826
0.0589
4.55E-05
1.71E-05
8.67E-06
Estimated long run standard deviations (g)
0.0172
0.0045
0.0059
Estimated short term standard deviations (g)
0.0096
0.0039
0.0078
Estimated total standard deviations (g)
0.0197
0.0060
0.0098
Relative process capability, Cp
1.000
3.806
2.915
Quality Distributions
Valve Gates
Open Loop
Closed Loop
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
Flexibility Example
• Use mold inserts to
make different
cavities
• Use pressure
valve to control
weights & size
Control Actions
The valve settings were
optimized within 30 minutes,
no retooling
100


2


80
2.5

1.5

60
1
40
Big Part
20
0.5
Small Part
Process Capability
0
0
0
5
10
15
Time (min)
20
25
30
Process Capability Index, Cpk.
Cavity Pressure Setting (%).
120
Small Cavity
Part Weights





2.5

6.14
Little Part Weight (g)
2
6.13
1.5
6.12
6.11
1
6.1
0.5
6.09
6.08
0
0
5
10
15
Time (min)
20
25
30
Process Capability Index, Cpk.
6.15
Small parts acceptable by
third trial, optimal in
sixth trial
Large Cavity
Part Weights





2.5

8.3
Big Part Weight (g)
2
8.2
1.5
8.1
8
1
7.9
0.5
7.8
7.7
0
0
5
10
15
Time (min)
20
25
30
Process Capability Index, Cpk.
8.4
Large parts acceptable in
second trial, optimal
in sixth trial
Pressure Profile
Phasing
• The processing of each cavity may be
slightly offset in time
• By offsetting pressures, the moment of
maximum clamp force is offset
• Slight extensions in cycle time can yield
drastic reductions in clamp tonnage
Pressure Profile
Phasing
Pressure
Black curve offset from
green curve by 2 seconds.
Time
Clamp Tonnage vs.
Cycle Time
50

10% increase in cycle
time allows 50% reduction
in machine tonnage!
45

Tonnage
40

35

30
25
20
24.5

25
25.5
26
Cycle Time (sec)
26.5
27
27.5
Current Status
• Intellectual property
– UML has filed a utility application
– Licenses under consideration
• Technology
– Being validated for extrusion
• Extrusion of multi-layer nano-composites
– New designs under development
• Valve gating
• Multiple materials