Glass fiber issues
>The impact of glass fiber orientation on product shrinkage
>Solutions for deformation of glass fiber products
>Long glass fiber characteristics-LGF
>Moldflow long glass fiber analysis
Stress issues
>Stress definition and measurement
>Moldflow stress judgment index
>Stress improvement cases
Effect of glass fiber orientation on product shrinkage
Without glass fiber: shrinkage in flow direction is greater than shrinkage in direction perpendicular to flow
With glass fiber: shrinkage in direction perpendicular to flow is greater than shrinkage in flow direction

 

Effect of glass fiber orientation on product shrinkage

 

Case Study on Solution to Deformation of Fiberglass Products
Case - Fuel tank cap parts (ultrasonic welding)
Material: PA66+35% GF Rhodia
Problem: Excessive deformation

 

Deformation

 

Improved glass fiber orientation

 

Improvement plan - deformation

 

Glass fiber orientation

 

Advantages of long glass fiber
>Stable performance at different temperatures
>Good formability - easy flow/thin-walled parts design
>Small warping
>Lightweighting of automobiles - plastic instead of steel

 

Definition of long glass fiber
>Definition: aspect ratio>10mm
>Easy to be broken after passing through screw and gate
>New injection molding method-length of glass fiber depends on processing process

 

Effect of glass fiber length on warpage

 

Glass fiber length is measured according to Owens Corning method. Other methods will produce different results.
Improvement Cases
>Use Moldflow to improve instrument panel frame deformation

 

Product name: Instrument panel frame
Product size: 1450mm*475mm*470mm
Basic thickness of product: 2.0mm
Thickness of airbag area: 3.3mm
Product weight: 4100g
Plastic material: PP+20% LGF, Ticona
Background: This product is a structural part with no appearance requirements. Subsequent foaming treatment.
Technical difficulties: This product uses long glass fiber material, and deformation of product must be controlled to avoid affecting subsequent process.
Improvement case
This product has 11 hot runners in overseas CKD sample. After mold flow analysis, it is determined that 7 hot runners of this product can meet requirements. (This figure shows optimized runner system and cooling system)

 

Plastic material description

 

Product flow status

 

In the early stage of the project, follow conventional dashboard method to ensure product filling balance and fill the entire product from middle to all directions
Product deformation

 

After analysis, process edge (Rum off edge) of product is deformed in a wavy shape. During actual mold trial, process edge (Rum 0ff edge) of this product is wavy. This deformation affects subsequent foaming process, and customer does not accept this deformation.
Fiber orientation

 

Moldflow analyzed fiber orientation and found that fiber orientation on process edge (Run off edge) was chaotic, causing product to deform in a wavy shape. It is recommended to improve orientation to improve deformation.
Comparison of product flow states
From perspective of improving fiber orientation, according to 7-point glue injection scheme, try to open sequence valve in one direction in sequence. Flow pattern starts from one side of dashboard and moves to the other direction.

 

Glass fiber orientation

 

After adjusting valve gate opening sequence, it was found that fiber orientation on process side (Run off side) was single and uniform.
Product deformation
In deformation results, process edge (Run off edge) of this solution deforms evenly, actual sample deforms in a single direction, and there is no wavy deformation. Subsequent foaming molding process is good and has been recognized by customers.

 

New version of Moldflow long glass fiber analysis technology
New fiberglass model
Newly added short fiberglass model Reduced Strain Closure (RSC)
Newly added long fiberglass model Anisotropic Rotary Diffusion (ARD-RSC)
Key features
"Reduced Strain Closure (RSC)
>Patented by Delphi Corporation, Illinois, USA
>Autodesk has exclusive rights to use this patent
>Compared to original default fiberglass model, RSC has a wider core and slower fiberglass orientation changes
>Adaptable to 3D, DD and Midplane mesh models
ARD-RSC model can well predict long glass fiber
Prediction results of ARD-RSC model are closer to actual data

 

Long Glass Fiber Fracture Analysis
Overview
Predict impact of long glass fiber fracture during flow on product performance
Key Points
Calculate fracture probability of long glass fibers
Show distribution of glass fibers in product after fracture
Limitations
This analysis cannot be applied to 3D thermoset materials
Long glass fiber fracture model - evolution of glass fiber length

 

Distribution of long glass fibers over time

Distribution of long glass fibers in space

 

Fiber orientation analysis process

 

Select fiber-containing material

 

Set fiber length

 

Select fiber orientation analysis type

 

Long glass fiber distribution prediction

 

2. Stress issues
> Stress definition and measurement
> Moldflow stress judgment index
> Stress improvement case
Explanation of residual stress concept
Residual stress refers to sum of various stresses that remain in product after injection molded part is ejected from mold. It is generally believed that residual stress includes flow residual stress and thermal residual stress
Flow residual stress
Flow residual stress is shear stress during filling and flow of molten plastic. If this shear stress is too large or unevenly distributed, it will cause dimensional changes, molecular chain breakage, excessive local residual stress, and reduced product strength

 

Explanation of concept of thermal residual stress
Residual thermal stress
It is internal stress caused by uneven shrinkage of product, which not only affects mechanical and optical properties of product, but also determines final geometric shape of product to a large extent.

 

Measurement of residual stress
If plastic product is transparent, magnitude and distribution of residual stress can be observed by different degrees of light transmittance. Following pictures are light transmittance photos of transparent parts, and dark areas are areas with relatively high stress.

 

Principle of residual stress measurement
Due to difference in shear stress during flow process, molecules in places with large shear stress are more arranged along flow direction, resulting in a higher degree of crystallization. Difference in degree of crystallization will lead to a difference in light transmittance, thus reflecting different brightness of luster
In areas with high crystallinity, molecules are arranged more closely compared with other parts, and interaction between molecules is increased, resulting in an increase in density, rigidity and strength. This uneven physical and mechanical properties leads to residual internal stress in product after molding.

 

Residual stress solution
Provide corresponding solutions for causes of residual stress
1) Reduce flow stress value
Common methods: reduce injection speed, appropriately increase processing temperature, increase mold temperature, improve product structure, increase gate size and quantity, etc.
2) Reduce thermal stress value
Common methods: improve product structure, adjust product wall thickness, optimize mold cooling system design, maintain uniform mold temperature, etc.
Residual stress defect analysis and optimization
Residual stress defects are usually manifested as
·Stress marks
·Cracks, insufficient strength, skin peeling (electroplating, coating products)
·Birefringence of optical products

 

Stress mark Moldflow application index
Stress mark problem

Analysis results: Time to reach ejection temperature
Boss freezes first, and bottom freezes later, generating stress at joint. When stress is large enough, stress marks will be generated.

 

Analysis results: Volume shrinkage
The greater volume shrinkage difference, the more likely stress marks will appear on product surface

 

Analysis results: Volume shrinkage (3D)
The greater volume shrinkage difference, the more likely stress marks will appear on product surface

 

Analysis results: Residual stress
The greater residual stress difference, the more obvious stress mark

 

Cracking, insufficient strength

Analysis results: Residual stress distribution
Residual stress distribution

 

Maximum shear stress

 

Optical product birefringence
Birefringence may cause serious product defects
Blurred imaging
Ghosting

 

Poor chemical properties
Moldflow analysis
Refractive index change
Phase difference

 

Mobile phone
Material: PC

Case study of crack defects
Crack research experiment

 

Shrinkage deformation, determine conditions to avoid cracks

 

Improved Boss column strength

 

Flow front temperature
Hysteresis of flow makes the two bosses at fracture lower in temperature than the two bosses on opposite side. Temperature difference will increase shrinkage stress during cooling process.

 

Volume shrinkage
Difference in volume shrinkage at boss column position is greater

 

Stress distribution
There is stress concentration at the root of boss position, but two bosses that are broken have thicker flesh at root, so strength is better.

 

Left picture shows stress distribution of original solution, and right picture shows stress distribution under uniform cooling conditions. Uniform cooling reduces stress concentration at root of Boss column.

 

Maximum stress and distribution of two solutions are similar. Thickened Boss solution has a more uniform stress distribution and strength of stress position is enhanced, which is conducive to improving cracking problem

 

Stress distribution - Improvement results
Improvement effect comparison

 

Product cracking
Inflatable valve
Partial residual stress concentration in product, cracking after being stressed

 

Improve product cracking - inflation valve
Adjust molding process to improve participating stress - appropriately reduce processing temperature, mold temperature, and reduce holding pressure value, thereby reducing thermal stress

 

Electroplating cracking and peeling
Residual stress has a great impact on electroplating or painting processes. Generally tested with glacial acetic acid

 

Electroplating parts improvement case

 

 

Residual stress improvement case
Product: Electronic device Up housing
Material: PC+ABS
Mold type: Two-plate mold cold runner
Problem: Stress marks, cannot be solved by adjusting machine

 

Product thickness distribution

 

Problem Analysis

 

Actual product problems

 

 

Improved effect
Stress marks are resolved

 

Mold trial results
Stress marks were completely improved