Effect of glass fiber orientation on product shrinkage:
Without glass fiber: Shrinkage in flow direction is greater than shrinkage perpendicular to flow direction;
With glass fiber: Shrinkage perpendicular to flow direction is greater than shrinkage in flow direction.

 

Effect of glass fiber orientation on product shrinkage

 

Case Studies on Fiberglass Product Deformation Solutions
Fiberglass orientation

 

Advantages of long glass fiber: Stable performance at different temperatures; Good formability – easy to flow/design for thin-walled parts; Minimal warpage; Lightweight automotive components – replacing steel with plastic.

 

Case Study - Fuel Tank Cap Parts (Ultrasonic Welding)
Material: PA66 + 35% GF Rhodia
Problem: Excessive Deformation

 

Definition of Long Glass Fiber: Aspect ratio > 10mm. Easily broken by screw and gate.
New Injection Molding Method – Glass Fiber Length Depends on Processing.

 

Deformation

 

Influence of Fiberglass Length on Warpage
Fiberglass length was measured using Owens Corning method. Other methods will produce different results.

 

Case Study:
Application of Moldflow to Improve Instrument Panel Frame Deformation
Product Name: Instrument Panel Body Frame
Product Dimensions: 1450mm*475mm*470mm
Basic Thickness: 2.0mm
Airbag Area Thickness: 3.3mm
Product Weight: 4100g
Plastic Material: PP + 20% LGF, Ticona
Background: This product is a structural component with no appearance requirements. Subsequent foaming processing is required.
Technical Challenges: This product uses long glass fiber materials; deformation must be controlled to avoid affecting subsequent processes.

 

Improved fiberglass orientation

 

Improvement Case
Imported CKD sample of this product had 11 hot runner points. After mold flow analysis, it was determined that 7 hot runner points in this product would meet requirements. (This diagram illustrates optimized runner system and cooling system.)

 

Plastic Material Description

 

Improvement Plan - Deformation

 

Product Flow Status

 

In initial stage of project, standard dashboard procedure was followed to ensure balanced product filling, with the entire product being filled from center outwards in all directions.
Product Deformation

 

Analysis revealed that run-off edge of product was exhibiting wavy deformation. During actual mold testing, run-off edge of this product displayed a wavy shape. This deformation affects subsequent foaming processes, and customer does not accept this deformation.
Fiber Orientation
Moldflow analysis revealed that fiber orientation at run-off edge was disordered, causing product to deform in a wavy shape. It was recommended to improve orientation to mitigate deformation.

 

Product Flow Pattern Comparison
From perspective of improving fiber orientation, following a 7-point glue injection scheme, we attempted a sequential valve opening method from one direction. This involved a flow pattern starting from one side of dashboard and moving to the other.

 

Fiberglass Orientation
After adjusting valve gate opening sequence, it was found that fiber orientation on process edge (run off edge) was uniform and singular.

 

Product Deformation
In deformation results, process edge (run-off edge) of this solution deformed uniformly, actual sample deformed in a single direction, and no wavy deformation occurred. Subsequent foaming and molding process was good, approved by the customer.

 

New version of Moldflow long glass fiber analysis technology
ARD-RSC model can predict long glass fibers very well.
Predictions of ARD-RSC model are closer to actual data.

 

Long glass fiber fracture analysis
Fracture model of long glass fibers - evolution of glass fiber length

 

Distribution of long glass fibers over time

 

Spatial distribution of long glass fibers

 

Fiber Orientation Analysis Workflow

 

Choose fiber-containing materials

 

Set fiber length

 

Select fiber orientation analysis type

 

Prediction of long glass fiber distribution

 

II. Stress Problems
Explanation of Residual Stress Concept
Residual stress refers to sum of various unrelaxed stresses remaining in molded part after demolding. It is generally considered to include flow residual stress and thermal residual stress.
Flow residual stress is shear stress generated during flow of molten plastic. If this shear stress is too high or unevenly distributed, it can cause dimensional changes, molecular chain breakage, excessive localized residual stress, and decreased product strength.

 

Explanation of the concept of residual thermal stress
Residual thermal stress is internal stress generated by uneven shrinkage of a product. It not only affects mechanical and optical properties of product, but also largely determines its final geometry.

 

Measurement of Residual Stress
If plastic product is transparent, magnitude and distribution of residual stress can be observed by varying degree of light transmission. Following images are translucent photographs of transparent parts; darker areas represent regions with higher stress.

 

Residual Stress Measurement Principle
Due to differences in shear stress during flow, molecules align more along flow direction in areas of higher shear stress, leading to increased crystallinity. This difference in crystallinity results in variations in light transmittance, thus producing different levels of gloss.
In areas of high crystallinity, molecules are more tightly packed compared to other parts, increasing intermolecular forces and thus increasing density, rigidity, and strength. This non-uniformity in physical and mechanical properties leads to residual internal stress in product after molding.

 

Residual Stress Solutions
Addressing causes of residual stress, we provide corresponding solutions.
1) Reducing Flow Stress Values
Common methods include: reducing injection speed, appropriately increasing processing temperature, raising mold temperature, improving product structure, and increasing gate size and number, etc.
2) Reducing Thermal Stress Values
Common methods include: improving product structure, adjusting product wall thickness, optimizing mold cooling system design, and maintaining uniform mold temperature, etc.
Residual stress defects analysis and optimization
Residual stress defects typically manifest as: stress marks; cracking, insufficient strength, and peeling (electroplated and coated products); birefringence in optical products.

 

Moldflow Application Indicators for Stress Marks
Stress Mark Problems

Analysis Results: Time to Reach Top Temperature
Boss freezes first, followed by bottom, creating stress at joint. When stress is sufficiently high, stress marks will form.

 

Analysis Results: Volume Shrinkage
The greater difference in volume shrinkage, the more likely stress marks will be generated on product surface.

 

Analysis Results: Volume Shrinkage (3D)
The greater difference in volume shrinkage, the more likely stress marks will be generated on product surface.

 

Analysis Results: Residual Stress
The greater residual stress difference, the more obvious stress marks.

 

Cracking and Insufficient Strength Issues

Analysis results: Residual stress distribution

 

Maximum shear stress

 

Birefringence in optical products.
Birefringence can lead to serious product defects: blurred images, ghosting, and poor chemical properties.
Moldflow analysis: refractive index changes, phase difference.

 

Case Study of Crack Defects
Mobile Phone
Material: PC

Crack Study Experiment

 

Shrinkage deformation, determining conditions to avoid cracks
Based on analysis and inspection, confirmed

 

Improved Boss Pillar Strength: There is slight stagnation in two Boss Pillars. Stagnation effect will be amplified when material temperature is low and firing rate is slow.

 

Temperature at flow front: Sluggish flow causes two bosses at fracture point to be cooler than two bosses on opposite side. Large temperature difference increases contraction stress during cooling process.

 

Volume shrinkage: Difference in volume shrinkage at boss column position increases.

 

Stress distribution: There is stress concentration at base of both bosses, but two bosses that are broken have more flesh at base, so they are stronger.

 

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

 

Maximum stress and distribution of two schemes are similar. Thickened Boss column results in a more uniform stress distribution and increased strength at stress points, which helps improve cracking issues.

 

Stress Distribution Improvement Results
Comparison of Improvement Effects

 

Product cracking
Inflation valve; localized residual stress concentration in product, leading to cracking after being subjected to force.

 

Product cracking improvement – air inlet valve
Adjusting molding process to improve stress participation – appropriately reducing processing temperature and mold temperature, and reducing holding pressure value, thereby reducing thermal stress.

 

Cracking and peeling of electroplated layers
Residual stress has a significant impact on electroplating or painting processes; it is generally tested using glacial acetic acid.

 

Case Study on Improvement of Electroplated Parts

 

 

Case Study on Residual Stress Improvement
Product: Electronic component upholstery
Material: PC+ABS
Mold Type: Two-plate mold with cold runner
Problem: Stress marks, which cannot be resolved by adjusting machine.

 

Product thickness distribution

 

Improvement Measures

Improvement effect: Stress marks are resolved.

 

Actual product issue

 

Trial mold results: Stress marks were completely improved.