Two-color molding, a core integrated molding process, is widely used in high-end manufacturing like automotive, electronics and 3C digital industries, thanks to its flexible material combination and high product integration. Through one mold clamping and two injections, it achieves seamless bonding of two materials or colors, simplifying production while enhancing product stability and appearance. This paper summarizes the technical essentials, application requirements and industry trends of three types of two-color molds based on practical production, providing practical references.
Two-color molds realize cavity switching via rotary (rack-and-pinion, hydraulic servo turntable) or slide-type structures, enabling two injections with one clamping. The industry-recognized molding cycle is 20-50 seconds, with dynamic positioning accuracy up to 0.02mm. Key lies in thermal isolation design and material shrinkage compensation to ensure stable bonding and dimensional consistency.
Temperature Control: Independent mold temperature controllers maintain dual-cavity temperature difference within 3℃; hot runners and cooling channels are spaced no less than 3mm, insulated with ceramic fiber.
Bonding Enhancement: Mechanical interlocking (dovetail grooves, barbs) and in-mold plasma treatment improve bonding strength significantly.
Ejection System: Ejector pins avoid appearance and bonding areas; the second shot steel is 2-3 HRC units harder than the first to prevent wear.
Following "thermal matching + shrinkage compatibility", common combinations include PP+TPE (automotive, shrinkage 0.5%-1.2%), ABS+PC (electronics, shrinkage difference ≤0.7%), and PC+TPE (3C digital, glass transition temperature difference ≤20℃). Cavity size compensation or transition layer optimization is needed for large shrinkage differences.
Applications: Interior parts (steering wheels, dashboard frames), exterior parts (headlight lenses, bumper trims), functional parts (seals, buttons).
Requirements: Temperature resistance (-40℃ to 80℃), impact resistance, bonding surface shear force ≥80% of material strength, large part deformation ≤1.5mm.
Key Parameters: Cooling channel coverage ≥90%, inlet-outlet temperature difference ≤5℃.
Applications: Connectors, sensor housings, switch panels.
Requirements: Insulation (breakdown voltage ≥15kV/mm), dimensional accuracy ±0.005mm, abrasion resistance (50 alcohol wipes with no damage).
Key Parameters: Injection pressure 80-100MPa, holding pressure 80-100bar, second shot speed 30-50mm/s.
Applications: Mobile phone middle frames, earphone housings, charger interfaces.
Requirements: Thin-wall molding (0.8-2.0mm), no flow marks/color differences, adhesion ≥8N/cm (ASTM D903 standard).
Key Parameters: 16-cavity design, single-shift capacity ≥50,000 pieces, mold change time ≤30 minutes.
Moldflow simulation predicts filling defects; 3D printed cores enable 48-hour rapid prototyping (≤30 pieces); insert-type molds for small-batch trial production (delivery in 3-5 days).
Design focus: 0.1-0.2mm step for clamping force, exhaust groove width 0.015-0.02mm.
Core equipment: CNC machining centers, EDM, with part processing accuracy up to 0.003mm.
Heat treatment: Cavity hardness HRC 50-55; rotary mechanism wear-resistant treatment; guide sleeve interference 0.005-0.008mm.
Assembly standard: Dynamic clearance ≥0.3mm; rotary mechanism no-load test ≥10,000 times without jamming.
Online inspection: Vision systems detect burrs/color differences (accuracy 0.01mm); key dimensions laser-scanned every 2 hours (deviation ≤0.03mm).
Traceability: Unique QR codes link raw material batches and process parameters; first-piece inspection + in-process sampling (every 500 pieces).
Increased use of bio-based plastics and recycled materials; mold production energy consumption reduced by over 25%; cooling water recycling rate ≥90%.
MES systems optimize scheduling (OEE ≥85%); digital twin simulates molding; collaborative robots reduce manual intervention by 70%.
Multi-color/material integration (≥3 colors) and functional structure integration (e.g., molding + metal embedding); mold reuse rate ≥70%; product launch cycle shortened by 30%.
The success of two-color molds for automotive, electronics and 3C digital products relies on precise structural design, scientific material combination and standardized production control. Injection molding factories should base on dynamic precision control and thermal isolation technology, follow intelligent and sustainable trends to optimize mold life and efficiency. In the future, with higher requirements for product integration and environmental protection, two-color molds will develop towards higher precision, more complex structures and greener materials, supporting high-end manufacturing upgrading.
