evaluating cavity pressure variations effect on process window€¦ · evaluating cavity pressure...
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Evaluating Cavity Pressure Variations Effect on Process WindowEric BowersoxLab ManagerBeaumont [email protected]| (814) 899-6390
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• The most capable product to be reproduced repeatedly over time is a part that is single cavity and single gated.
Background• The goal of a multi-cavity mold is to have a tool that provides a platform where a
stable/robust process can produce nearly identical parts in each of the cavitiesA Stable Robust ProcessA Robust Process Window
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3. D.O.E.
2. Holding Pressure Experiment
1. Guess / Experience
• Process Window
Process Window Evaluation
Effect of Cavity Pressure on Dimension
1.7231.7241.7251.7261.7271.7281.7291.7301.7311.7321.7331.7341.7351.7361.7371.738
3500 4000 4500 5000 5500 6000 6500
Cavity Pressure
Pa
rt D
iam
ete
r D
ime
ns
ion
s
(In
ch
es
)
USL
LSL
NOM
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FLASH
SHORT
1.7231.7241.7251.7261.7271.7281.7291.7301.7311.7321.7331.7341.7351.7361.7371.738
3500 4000 4500 5000 5500 6000 6500
Cavity Pressure
Effect of Cavity Pressure on Diameter DimensionUSL
LSL
NOM
Adjusting +/- 250 psi = flash or short shots
S # CP-A CP-B1 3000
(short)4500
2 4000 55003 5000 6500
(flash )
Process Window Development
Data courtesy of Suhas Kulkarni
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Critical Dimension
8.78.7258.75
8.7758.8
8.8258.85
8.8758.9
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Cavity ID
mm
8.85 +/-0.025 mm
87651211109
123413141516
Process Window Evaluation
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ResearchArtificially balanced
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Equipment Utilized
• Part volume = 8.51 cm3 (1.49 mm nominal wall thickness)
• Runner volume = 3.32 cm3 (sprue, runner, gates)
• Model 9211 force sensors (Kistler Instrument Corporation)Cavity 1B Cavity 2B Post Gate
Sensors
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Geometrically Balanced Runner vs. Rheologically Controlled Runner
Process UtilizedMold = 8-Cavity Next Gen
Material = PC/ABS
• Fullest Cavity is 95% full• Even Filling Pattern
Does This Matter?• Decrease in Fill Volume
• Increase Fill Volume by 6%
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• Is the impact of rheological variations eliminated during packing?Question
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Packing Pressure• Post Gate Cavity Pressure Comparison
• 4,000 psi pack pressure
Rheologically ControlledGeometrically Balanced
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Packing Pressure (4,000 psi)Geometrically Balanced Rheologically Controlled
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Packing Pressure• Post Gate Cavity Pressure Comparison
• 6,000 psi pack pressure
Rheologically ControlledGeometrically Balanced
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Packing Pressure (6,000 psi)Geometrically Balanced Rheologically Controlled
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Packing Pressure• Post Gate Cavity Pressure Comparison
• 8,000 psi pack pressure
Rheologically ControlledGeometrically Balanced
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Packing Pressure (8,000 psi)Geometrically Balanced Rheologically Controlled
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Lab Demonstration• Results of this study of a Rheologically Controlled Runner System
• Process window increased by 100%• Reduced variation in peak cavity pressures by 97%• Reduced cavity pressure integral variation by 81%• Reduced gate freeze time by 6% due to uniform gate seal• Increased pressure available to the cavity by 50%• Increased shot volume by 6%• Shear imbalance reduction of 20%
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Critical Dimension
8.78.7258.75
8.7758.8
8.8258.85
8.8758.9
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Cavity ID
mm
8.85 +/-0.025 mm
87651211109
123413141516
Industry Example 1
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87651211109
123413141516
Critical Dimension
8.78.7258.75
8.7758.8
8.8258.85
8.8758.9
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Cavity ID
mm
• Identify Flow Groups.1A
1D 1C
1B2A 3A 4A 4B 3B 2B
2D 3D 4D 4C 3C 2C
8.85 +/-0.025 mm
Industry Example 1
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Critical Dimension
8.78.725
8.758.775
8.88.825
8.858.875
8.9
1A (9) 1B (8) 1C (1) 1D (16) 2A (10) 2B (7) 2C (2) 2D (15) 3A (11) 3B (6) 3C (3) 3D (14) 4A (12) 4B (5) 4C (4) 4D (13)
Cavity ID
mm
87654321
910111213141516
1A
1D 1C
1B2A 3A 4A 4B 3B 2B
2D 3D 4C 3C 2C4D
Flow Group ID
8.85 +/-0.025 mm
Industry Example 1
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1A
1D 1C
1B2A 3A 4A 4B 3B 2B
2D 3D 4D 4C 3C 2C
• Dimensional Variations vs. Short Shot Analysis
01234567
1A (9) 1B (8) 1C (1) 1D (16) 2A (10) 2B (7) 2C (2) 2D (15) 3A (11) 3B (6) 3C (3) 3D (14) 4A (12) 4B (5) 4C (4) 4D (13)
Part
Wei
ght (
g)
Flow Group (Cavity ID)
5 Step Process Short Shot Analysis
Critical Dimension
8.78.725
8.758.775
8.88.825
8.858.875
8.9
1A (9) 1B (8) 1C (1) 1D (16) 2A (10) 2B (7) 2C (2) 2D (15) 3A (11) 3B (6) 3C (3) 3D (14) 4A (12) 4B (5) 4C (4) 4D (13)
Cavity ID
mm
Industry Example 1
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Multi-Defect Analysis- Use the mold maintenance and part quality data to create a history plot.
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- Apply Flow Groups to troubleshoot and identify root causes / corrective actions.
Multi-Defect Analysis
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Effective Melt Temperature
Concentricity
Conv
entio
nal
Rheo
logi
cal
Cont
rol
Conventional Rheological Control
Avg. ∆T = 38.3°F
Avg. ∆T = 4.8°F
Industry Example 2• Cavity Pressure & Temperature Development Comparison
− 4 Cavity, Acetal (POM) Gear
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• 4-cavity gear mold; fairly uniform wall thickness• Material = Acetal (POM)• DSC data = Latent Heat of Fusion is an indicator of percent crystallinity
Sample1st Heat ΔHf
(J/g)
3A-3B 155.6
4A-4B 164.4
Delta 3-4 8.8
1A-1B 161.5
2A-2B 159.1
Delta 1-2 2.4
Conv
entio
nal
Rheo
logi
cal C
ontr
ol
Industry Example 2
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• Even with the artificial fill balance:• Higher temperature material still flowing to the inside cavities• Intra-cavity imbalances
Temperature distribution @ 95% full
Intra-cavity imbalanceArtificially balanced runners (Ø0.102” vs. Ø0.094”)
Artificial Balancing Cold Runner Systems
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• Over 400 psi difference
• Remember…the magnitude is severely under predicted!
• Even with the artificial fill balance:• Pack pressure differences exist between the inside and outside cavities
Pressure distribution at 1.9 seconds
Artificially balanced runners (Ø0.102” vs. Ø0.094”)
Artificial Balancing Cold Runner Systems
8,910psi 8,500psi
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Different temperature, viscosities, pressures = DIFFERENT PARTS!
• 500-1,300 psi difference
• Remember…the magnitude is severely under predicted!
• Artificial balancing provides a fill balance only!
Pressure distribution at 3.7 seconds
Artificially balanced runners (Ø0.102” vs. Ø0.094”)
Artificial Balancing Cold Runner Systems
1,932psi 667psi
• Even with the artificial fill balance:• Pack pressure differences exist between the inside and outside cavities