evaluating cavity pressure variations effect on process window€¦ · evaluating cavity pressure...

Evaluating Cavity Pressure Variations Effect on Process WindowEric BowersoxLab ManagerBeaumont [email protected]| (814) 899-6390

• 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

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

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

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

ResearchArtificially balanced

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

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%

• Is the impact of rheological variations eliminated during packing?Question

Packing Pressure• Post Gate Cavity Pressure Comparison

• 4,000 psi pack pressure

Rheologically ControlledGeometrically Balanced

Packing Pressure (4,000 psi)Geometrically Balanced Rheologically Controlled

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%

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

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

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

1A

1D 1C

1B2A 3A 4A 4B 3B 2B

2D 3D 4D 4C 3C 2C

• Dimensional Variations vs. Short Shot Analysis

01234567


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


Cavity ID

mm

Industry Example 1

Multi-Defect Analysis- Use the mold maintenance and part quality data to create a history plot.

- Apply Flow Groups to troubleshoot and identify root causes / corrective actions.

Multi-Defect Analysis

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

• 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

Thank You for Your Time

Eric Bowersox, [email protected], 814-899-6390 Ext. 153

Bonus Material

Eric Bowersox, [email protected], 814-899-6390 Ext. 153

• 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

• 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”)


8,910psi 8,500psi

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”)


1,932psi 667psi

• Even with the artificial fill balance:• Pack pressure differences exist between the inside and outside cavities

evaluating cavity pressure variations effect on process window€¦ · evaluating cavity pressure...

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