In the industrial plastic injection molding process, maintaining consistent finished product quality is a major challenge. The two most common technical defects that drive up the defect rate (NG rate) are warpage and flash. To resolve them thoroughly, technicians must understand the exact interaction between temperature, pressure, and mold design.
How to overcome warpage defects caused by uneven shrinkage
Warpage is the dimensional deformation of a product after it leaves the mold, usually caused by internal stress arising from an uneven cooling process.
– Primary causes:
• Temperature variance: Different areas inside the mold cavity have varying cooling rates, causing the plastic to shrink out of sync.
• Plastic wall design: Inconsistent product wall thickness leads to thicker sections cooling slower and shrinking more than thinner sections.
• Improper injection parameters: Holding pressure is too low or cooling time is too short.
– Solutions:
• Optimize the cooling system: Position cooling water channels surrounding areas with high heat accumulation. Maintaining a stable mold temperature is the key to reducing internal stress.
• Adjust machine parameters: Increase holding time and injection pressure to ensure the plastic is packed tightly into the mold cavity, compensating for the amount of plastic that shrinks upon cooling.
• Improve design (DFM): Prioritize designing a uniform wall thickness. For large components, add reinforcing ribs to help shape and prevent deformation.
Solutions to eliminate flash defects at the parting line
Flash is thin, excess plastic that appears at the gaps of the mold, most commonly seen along the parting line or at the positions of the ejector pins.
– Primary causes:
• Weak machine clamping force: When the plastic injection pressure exceeds the clamping force of the molding machine, the two mold halves are pushed slightly open, allowing plastic to overflow.
• Damaged or worn mold: After long periods of operation, the parting line surface is no longer perfectly flush due to friction or impacts.
• Low plastic viscosity: Excessive melting temperatures make the plastic too fluid, allowing it to easily seep into micro gaps (under 0.02mm).
– Solutions:
• Control clamping force and pressure: Increase the clamping force of the industrial plastic injection molding machine to match the mold cavity surface area. Concurrently, reduce the injection speed during the final stage to avoid a sudden spike in peak pressure.
• Periodic mold maintenance: Thoroughly clean the parting line surface after every shift. If any dents or wear are detected, execute laser welding and machining to restore a flush, airtight seal.
• Lower the plastic temperature: Adjust and lower the temperature across the heating bands of the cylinder to increase viscosity, making it harder for the plastic to overflow into unwanted locations.
Resolving defects in industrial plastic injection molding requires patience to test and fine-tune each minor parameter. By combining periodic mold maintenance with optimized machine operation workflows, businesses can elevate product quality and minimize production costs.
At Zeng Hsing, with our modern system of 91 injection machines and an experienced technical team, we always strictly control operational parameters to completely eliminate warpage or flash conditions. This is our definitive commitment to delivering engineering plastic products with the highest precision and consistent quality for every partner.
ZENG HSING VIET NAM
Address: Unit 03-08, Canary Plaza, Binh Duong Boulevard, Binh Hoa Ward, Thuan An City, Binh Duong Province, Vietnam.
Phone: (+84) 0355 846 965 (Mr. Nghia) – (+84) 0362 476 478 (Mr. Nam)
Email: nghia_duong@zenghsing.com.vn or nam_vu@zenghsing.com.vn
Website: zenghsing.vn
