How to identify and solve glass fiber molding and stress problems in Moldflow

1. How to identify and solve glass fiber molding and stress problems in Moldflow 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

2. 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

3. Improved glass fiber orientation Improvement plan - deformation

4. 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

5. 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

6. 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

7. 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 Plastic material: PP+20% LGF, Ticona 1. Melt density 0.8239 g/cu.cm 7.Minimum material temperature 215 deg.C 2. Solid density 1.0276 g/cu.cm 8. Maximum material temperature 240 deg.C 3. Ejection temperature 87 deg.C 9.Minimum mold temperature 40 deg.C 4. Recommended mold 55 deg.C 10.Maximum mold temperature 71 deg.C temperature 5. Recommended material 230 deg.C 11. Maximum shear rate allowed 1000 L/s temperature 00 6. Cracking material temperature 250 deg.C 12. Maximum shear force allowed 0.25 MPa Product flow status

8. 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

9. 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

10. 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

11. >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

12. Distribution of long glass fibers over time Distribution of long glass fibers in space

13. Fiber orientation analysis process Select fiber-containing material

14. Set fiber length Select fiber orientation analysis type

15. 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

16. 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.

17. 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

18. Stress mark Moldflow application index Stress mark problem Stress Moldflow application Improvement direction Moldflow analysis results mark index Freezing time Difference in freezing time between ribs, bosses 1) Frozen layer fraction difference and bottom surfaces is controlled within a certain 2)Time to reach ejection range temperature Temperature gradient The smaller temperature gradient, the less Bulk temperature obvious stress mark Volume shrinkage The smaller and more uniform volume shrinkage Volumetric shrinkage value, the less obvious stress mark Residual stress The larger the residual stress difference, the more Stress in first principal obvious stress mark direction 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.

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

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

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

22. Cracking, insufficient strength Insufficient Moldflow standard Improvement direction Moldflow analysis results cracking indicators strength Residual stress The smaller the better 1) Stress in first principal direction (mainly brittle materials without fillers) 2) Stress, Mises-Hencky (mainly brittle materials without fillers) Shear stress Do not exceed allowable Shear stress value of material Weld lines The larger angle, the farther Weld lines away from stress area Analysis results: Residual stress distribution Residual stress distribution Maximum shear stress

23. Optical product birefringence Birefringence may cause serious product defects Blurred imaging Ghosting Poor chemical properties Moldflow analysis Refractive index change Phase difference

24. Mobile phone Material: PC Packing pressure (MPa) Small Big Shrinkage/warpage Big Small Risk of cracks Low High Case study of crack defects Crack research experiment Shrinkage deformation, determine conditions to avoid cracks

25. 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.

26. 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

27. 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

28. Stress distribution - Improvement results Improvement effect comparison Product cracking Inflatable valve Partial residual stress concentration in product, cracking after being stressed

29. 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

30. 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

31. Product thickness distribution Problem Analysis

32. Actual product problems

33. Improved effect Stress marks are resolved Mold trial results Stress marks were completely improved