Key Technical Analysis for Injection Mold Design and Molding of Complex Flat Plastic Parts
Complex flat plastic parts (e.g., thin-walled enclosures, decorative panels, electronic covers) present challenges such as warpage, short shots, and visible weld lines due to their large projected area, minimal thickness, and asymmetric geometry. This article systematically examines critical technical aspects from mold design, material selection, and process control perspectives.
I. Core Elements of Mold Design
Runner and Gating System
Balanced Multi-Point Gating: Use 3-5 pin or fan gates to ensure uniform melt filling. For a 300mm×200mm flat part, gate spacing should be ≤80mm to prevent pressure loss at flow ends.
Runner Optimization: Main runner diameter: 6-8mm; branch runners: 4-5mm; gate thickness: 50%-80% of wall thickness (typically 0.6-1.0mm).
Venting and Cooling Systems
Stepped Venting: Vent depths of 0.015-0.025mm at melt convergence points and cavity ends, with total vent area comprising 20%-30% of the parting surface area.
Conformal Cooling Channels: Position 8-12mm from cavity surface, spacing ≤2.5× channel diameter, mold temperature variation within ±3°C.
Ejection and Structural Reinforcement
Distributed Ejection System: Use φ2-3mm ejector pins spaced ≤40mm, combined with air-assisted ejection to prevent whitening or deformation.
Enhanced Mold Rigidity: Increase support pillars and angled braces; plate thickness 20%-30% greater than standard molds to withstand high injection pressure (≥100MPa).
II. Material Selection and Process Control
Low-Shrinkage Material Preference
Select glass-fiber-reinforced PP/ABS (shrinkage: 0.2%-0.5%) or crystalline materials (e.g., PA+30% GF) to minimize warpage from anisotropic shrinkage.
Injection Process Parameters
High-Speed/High-Pressure Filling: Injection speed: 200-400mm/s to reduce melt front cooling time; holding pressure: 80%-90% of injection pressure.
Segmented Mold Temperature Control: Adopt variotherm technology (e.g., chillers + induction heating), mold temperature: 80-100°C during filling, 40-60°C during cooling.
Weld Line and Orientation Control
Predict weld line locations via CAE analysis; install vents or heating elements in critical areas.
Utilize sequential valve gating to adjust fiber orientation and enhance structural strength.
III. Case Study and Data Validation
An electronics enclosure (400mm×300mm×1.5mm, ABS+PC material) achieved a higher yield through:
Mold Optimization: 8-point hot runner + zoned cooling (12 independent loops), warpage reduced from 1.2mm to 0.3mm.
Process Adjustment: Variotherm process (30℃→90℃→50℃), fill time shortened from 1.8s to 1.2s.
Quality Metrics: Flatness ≤0.5mm, weld line strength ≥85% of base material strength.
IV. Trends and Challenges
Intelligent Molds: Integrated pressure/temperature sensors for real-time parameter adjustment.
Microcellular Foam Molding: Supercritical fluid (SCF) technology to reduce weight and internal stress.
Challenges: Flow resistance in ultra-thin walls (<0.8mm), necessitating high-fluidity materials (e.g., LCP).
Conclusion
Successful production of complex flat parts relies on synergistic optimization of mold, material, and process. Balanced runner design, precise temperature control, and low-shrinkage materials significantly improve flatness and mechanical properties. Future advancements require integrating digital simulation and intelligent control for efficient molding of ultra-thin structures.
