what lies below the surface of your molded parts?
TRANSCRIPT
What Lies Below the Surface of Your Molded Parts?
Plastics Manufacturers Strength:• Throughput Efficiency• Focus has been on Lean Manufacturing Principals• New Work Cells
• Improving Plant Layouts
• Streamlining the Process from Molded Part to Loading the Truck
Reve
nue
/ ft2
2008 Present
Plastics Manufacturers Weakness:• Development and Commissioning New Projects• Grass Roots Approach• hurry up, make mistakes, try something else • just find away to get this part to meet specification• we’ll figure out how to make money at it on the backside
Concept Mold Design
Part & Mold Commissioning
Product Design Launch Production CIP
So you followed all of the design guidelines and scientific molding procedures and you still ended up with part variations.What could possibly be going wrong?
Identical runner lengths
Identical channel radius
Identical gate geometry
Identical cavity sizes
II. Rheological Variations (η )
I. Mold Steel Variations (l, r)
Why is New Mold Commissioning Such a Challenge?• Plastic Rheology is Not Well Understood• Shear-induced imbalances• Shrink & Warp characteristics• Cooling and thermodynamics• Regional pressure variations• Amorphous and Semi-crystalline materials
• Plastic is a Non-Newtonian Material– Viscosity is affected by Shear Rate and Temperature– As shear rate increases, viscosity decreases – As temperature increases, viscosity decreases
The Science Behind Non-Uniform Rheology
• Highest Shear Rate is just inside the frozen layer– Shear-thinning and Shear-heating
reduce viscosity in these laminates
Single Cavity Disk Mold:• Rivering flow front• Gas trap created
Influence on melt front advancement profile
Melt Property Distribution
1
1
3 4
3 4 34
1
2
2
3 4
2
1
2 2
1
2
Conventional Runner
More than just a “filling imbalance”...
Temperature differences result in shrink variations
* Forces process technician to increase cooling time and use mold as a cooling fixture to minimize difference between
part
Result = Increase Cycle Time
180° F
100° F
Volumetric: Mold Design (Cooling)
)( TLL
At ejection:
Linear Shrinkage:
Effect of Regional Pressure Differences
Center packs under higher pressure = possible dome warp
ΔP at End of Fill
ΔP Thick Part55 mPa
40 mPa
ΔP Thin Part70 mPa
25 mPa
55 Mpa
40 Mpa
x
Must also consider processing effects
Can this be processed out?
Packing profile can be ramped
Orientation-Induced Shrink: Flow Types
• Linear– Polymers oriented in direction of flow
• Extensional– Expanding flow front (center-gated disk)– Dependent on part thickness and processing
• Polymers oriented in the extensional or radial direction
• Transient– Flow direction changes during mold filling
4-cavity moldLID
Cav. 1= o.k.
Cav. 4= o.k.
Cav. 3= not o.k.
Cav. 2= not o.k.
Hot runner nozzle
Cold runner withtunnel gate 3x
Warp in Cavities 2 & 3
Warp in Cavities 1 & 4
Different filling pattern change orientation and shrinkage
• Be careful of putting too much faith in simulation output. Put it through a reality check with your understanding of plastic flow.
Intersection Options
Solution: Patented In-Mold Rheological Control Systems
– Two Rotation Types:• Single-Axis Symmetry• Multi-Axis Symmetry
• Continually manage the melt properties within the runner system through strategic repositioning of the high sheared laminates
Single-Axis Multi-Axis
Naturally “Imbalanced” + Intra-Cavity Control
Solution: Patented In-Mold Rheological Control Systems
Melt Rotation: Intra-Cavity Control, ConcentricityMold Layout Effective Melt Temperature Concentricity
Con
vent
iona
lM
elt R
otat
ion
Conventional Melt Rotation
Avg. ∆T = 39.3°F
Avg. ∆T = 4.8°F
1. Structural / Kinematic
2. Melt Delivery
3. Air Evacuation (Venting)
4. Cooling
5. Ejection
Engineering for SuccessSystems of the mold:
Cooling Strategies
What is the heat capacity of the material?
What is the thermal diffusivity?
How conductive is the mold steel?
Is there turbulent flow?
Cooling System:
Will the improvements be measurable?
The Challenge:• Learn what is needed to Engineer for Success• We can be good program managers, exceptional engineers, and good stewards of our companies•Identify areas for improvement•Seek out the appropriate training courses that will help everyone in the
organization Engineer for Success
Course 1:
“Mold Start-up, Debug & Qualification”
Course 3:
“Injection Molding & Root Cause Analysis for QC/QA”
Course 5:
“Mold Design for Project Engineers”
Course 7:
“Understanding & Applying Flow Simulation”
“Teaching you to Think From the Plastic’s Perspective... From Design through Production”
Course 2:
“Hot & Cold Runner Systems”
Course 4:
“Understanding Shrink & Warp”
Course 6:
“Plastic Flow & Design Essentials for Mold Makers/Designers”
Benefits:• Improve Competitiveness on the Global Stage
• Improve Customer Satisfaction
• Reduce Mold Commissioning Time and Costs
• Produce Higher Quality Parts at a Lower Cost
Next Steps:• Sharpen the Saw•Identify areas for improvements within your
organization•Seek out appropriate training courses that will
improve your ability to Engineer for success•Apply what is learned•Measure Results•Repeat
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