Self-Regulating Melt Valves for Polymer Processing David Kazmer May 12, 2005 National Plastics Center.

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