self-regulating melt valves for polymer processing david kazmer may 12, 2005 national plastics...
TRANSCRIPT
Self-RegulatingMelt Valves forPolymer Processing
David KazmerMay 12, 2005
National Plastics Center
Agenda
• Introduction– Vision– Design
• Validation– Steady State Behavior– Consistency– Flexibility– Clamp Tonnage Reduction
• Current Status
Conventional Molding
BarrelHeaters
Reciprocating Screw
Check valveInjectionCylinder
ClampingCylinder
Operator Interface
Stationary PlatenMoving PlatenMold
Pellets
PolymerMelt
Process ControllerHydraulic
Power Supply
Clamping Unit Injection Unit
Tie Rods
Uneven processing inconventional molding
Vision forInjection 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
BarrelHeaters
Reciprocating Screw
Check valveInjectionCylinder
ClampingCylinder
Operator Interface
Stationary PlatenMoving PlatenMold
Pellets
PolymerMelt
Process ControllerHydraulic
Power Supply
Clamping Unit Injection Unit
Tie Rods
Complete process control for each gate…
…without pressure transducersor closed loop controllers
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
1002
2
annulus
cylinder
annulus
cylinder
R
R
A
AI
Valve Function
• No sensor or controller needed!
• Valve adjusts to reject input variation– Outlet pressure proportional to control force– Pin position determined by inlet pressure and
required pressure drop
Fco
ntro
l
time
Pou
t
time
Pin
time
Valve Deployment
• Advantages– Multi-axis melt control without
cavity pressure transducers!– Compact with low actuation forces
• Disadvantages– Hot runner required
Provides flexibility,consistency, and
productivity
Performance Analysis:Flow Vectors
Annular flow provideslow shear rates & pressures
Performance Analysis:Effect of Position
0
2
4
6
8
10
12
14
16
18
0 0.5 1 1.5 2 2.5 3
Pin Position (mm)
Pre
ssu
re d
rop
(M
Pa
)
Q=1cc/secQ=5cc/secQ=25cc/sec
Pin will hover near 1mmwith very fast response.
Performance Analysis:Effect of Size
0
2
4
6
8
10
12
0 2 4 6 8 10 12
Valve Outer Diameter (mm)
Pre
ssu
re D
rop
(M
Pa
)
2.5 mm
5 mm 10 mm
5.4
690
P
Higher melt flow withslightly larger valves
Performance Analysis:Open Loop Error
-80
-60
-40
-20
0
20
40
60
80
0 5 10 15 20 25 30
Flow rate (cc/s) @ nominal pin position
Fo
rce
(N
)
Fpressure
Fshear
Fresultant
Open loop error ~10N
Correctable error of 1-2%
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
0
5
10
15
20
25
30
35
40
0 2 4 6 8 10
Cylinder Air Pressure (V)
Mel
t P
ress
ure
(MP
a)
Cavity 1, Hyd=400, Air=50
Cavity 1, Hyd=800, Air=50
Cavity 1, Hyd=400, Air=85
Cavity 1, Hyd=800, Air=85
Saturated melt pressure
Melt pressureproportional to
air pressure
Melt Pressure vs.Part Weight
0
1
2
3
4
5
6
7
8
9
0 10 20 30 40 50
Melt Pressure (MPa)
Par
t W
eigh
t (g
)
Cavity 1, 430F Melt
Cavity 2, 430F Melt
Cavity 1, 460F Melt
Cavity 2, 460F Melt
Flow in thick section Flow in thin section
Part weights adjustedwith air pressure
Consistency Study:Design of Experiments
X1 X2 X3 X4 X5 X6 X7 X8Run
NumberMelt
TempMold Temp
Inj Pres
Inj Velocity
Pack Pres
Pack Time
Valve2 Setting
Valve2 Cycle
1 -1 -1 -1 -1 -1 -1 -1 -12 -1 -1 1 -1 1 1 1 -13 -1 -1 -1 1 1 1 -1 14 -1 -1 1 1 -1 -1 1 15 -1 1 -1 1 -1 1 1 -16 -1 1 1 1 1 -1 -1 -17 -1 1 -1 -1 1 -1 1 18 -1 1 1 -1 -1 1 -1 19 1 -1 -1 1 1 -1 1 -110 1 -1 1 1 -1 1 -1 -111 1 -1 -1 -1 -1 1 1 112 1 -1 1 -1 1 -1 -1 113 1 1 -1 -1 1 1 -1 -114 1 1 1 -1 -1 -1 1 -115 1 1 -1 1 -1 -1 -1 116 1 1 1 1 1 1 1 1
Most significantparametersinvestigated
Process Sensitivities
Conventional Weight
7.1
7.2
7.3
7.4
7.5
7.6
7.7
7.8
Conventional W
eig
ht
Conventional Valve Gating
Open Loop Weight
7.7
7.8
7.9
8
8.1
8.2
8.3
8.4
Open L
oop W
eig
ht
Open LoopMelt Valve
Machine sensitivitygreatly reduced
Intra-run variation (whiskers)greatly reduced
Short and Long RunConsistency
Processing RelativeVariable Variance Valve Gates Open Loop Closed Loop Valve Gates Open Loop Closed LoopMelt Temp 0.0025 0.1479 0.0240 0.0487 5.47E-05 1.44E-06 5.92E-06Mold Temp 0.0025 0.0812 -0.0082 0.0319 1.65E-05 1.66E-07 2.54E-06Inj Pres 0.0025 0.0308 0.0065 0.0109 2.37E-06 1.06E-07 2.99E-07Inj Velocity 0.0025 0.0000 -0.0211 -0.0818 1.66E-12 1.11E-06 1.67E-05Pack Pres 0.0025 0.2667 0.0158 0.0176 1.78E-04 6.21E-07 7.72E-07Pack Time 0.0025 0.1348 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
VariancesSensitivities
m
jj
jxdx
dyy
1
2Short and long run
consistencygreatly increased
Quality Distributions
-2 -1.5 -1 -0.5 0 0.5 1 1.5 2
Valve Gates
Open Loop
Closed Loop
Flexibility Example
• Use mold inserts to make differentcavities
• Use pressurevalve to controlweights & size
Control Actions
0
20
40
60
80
100
120
0 5 10 15 20 25 30
Time (min)
Ca
vity
Pre
ssu
re S
etti
ng
(%).
0
0.5
1
1.5
2
2.5
Pro
cess
Ca
pab
ility
Ind
ex,
Cp
k.
Big Part
Small Part
Process Capability
The valve settings wereoptimized within 30 minutes,
no retooling
Small Cavity Part Weights
6.08
6.09
6.1
6.11
6.12
6.13
6.14
6.15
0 5 10 15 20 25 30
Time (min)
Litt
le P
art
We
igh
t (g
)
0
0.5
1
1.5
2
2.5
Pro
cess
Ca
pa
bili
ty In
de
x, C
pk.
Small parts acceptable bythird trial, optimal in
sixth trial
Large CavityPart Weights
7.7
7.8
7.9
8
8.1
8.2
8.3
8.4
0 5 10 15 20 25 30
Time (min)
Big
Pa
rt W
eig
ht (
g)
0
0.5
1
1.5
2
2.5
Pro
cess
Ca
pab
ility
Ind
ex,
Cp
k.
Large parts acceptable insecond trial, optimal
in sixth trial
Pressure ProfilePhasing
• 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 ProfilePhasing
Pre
ssur
e
Time
Pre
ssur
e
Time
Black curve offset fromgreen curve by 2 seconds.
Clamp Tonnage vs.Cycle Time
20
25
30
35
40
45
50
24.5 25 25.5 26 26.5 27 27.5
Cycle Time (sec)
To
nn
ag
e
10% increase in cycletime allows 50% reduction
in machine tonnage!
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