Two-color injection molding is widely used in consumer electronics, automotive interiors, and medical devices for one-step molding of complex structures and improved product functionality. However, its defect rate is about 30% higher than single-color injection molding (industry test data) due to dual injection systems, precise mold cavity coordination, and material compatibility control. Mastering defect causes and solutions is key to stable mass production.
Color mixing refers to blurred boundaries and variegated stripes between two materials; chromatic aberration means color deviation from standard samples.
Causes: incomplete nozzle switching, irrational runner design, or overheating of the first material during secondary injection.
Chromatic aberration triggers: mismatched pigment heat resistance/dispersibility, process parameter fluctuations, or uneven mold cavity temperature.
Solutions: self-cleaning nozzles, optimized runner design, ±2℃ cavity temperature control, and real-time colorimeter monitoring.
Insufficient peel strength causes delamination or cracking, critical for structural reliability. Bonding strength must reach ≥25N/cm² for safety components (industry standard).
Causes: high crystallinity, surface contaminants, poor material compatibility, or insufficient secondary injection pressure.
Improvements: surface roughening/activation, compatible material combinations (e.g., PC/ABS and TPE), and optimized packing pressure/time.
Dimensional deviation means out-of-tolerance sizes or misalignment; flash refers to melt overflow from mold joints, affecting assembly and appearance.
Deviation causes: low-precision mold positioning, shrinkage calculation errors, or uneven cooling/shrinking.
Flash causes: insufficient clamping force, mold gaps >0.02mm, or excessive injection pressure/speed.
Controls: high-precision positioning components, accurate shrinkage calculation, and clamping force 1.2× theoretical value.
Bubbles are internal/surface cavities; sink marks are depressions from melt shrinkage, common in thin-wall products (≤1.5mm thickness).
Bubble causes: air entrainment, excessive moisture (>0.2% for hygroscopic materials), or insufficient packing pressure.
Sink mark causes: overheating, slow cooling, irrational gate position, or rapid pressure decay.
Solutions: material pre-drying, optimized gate design, extended packing time, and controlled melt temperature.
Intelligent monitoring (in-mold sensors + AI) reduces defects by ~40% (industry data). Co-injection molds and rotary stack molds optimize material flow and space utilization. Biobased/degradable materials require updated compatibility and process strategies.
Defect control spans mold design, material selection, and process optimization. Intelligent monitoring and precise control will be core solutions for two-color injection molding defects.
