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 Distribution1

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 / Kinematic2. Melt Delivery3. Air Evacuation (Venting)4. Cooling5. 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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