Two-color injection molds (also called dual-color molds or two-shot molding molds) are precision molds based on composite molding technology. They realize integrated optimization of product functions and appearance by injecting and fusing two materials or colors in one mold sequentially. Compared with traditional single-color injection molds, their core advantage is completing multi-material compounding in one molding cycle, which reduces assembly procedures and enhances product structural stability. They have become core equipment in high-end manufacturing sectors like automotive, consumer electronics and medical industries. With the integration of material technology and intelligent manufacturing, two-color injection molds are evolving towards high precision, high efficiency and multi-functional integration, driving innovations in product design and production modes.
The operation of two-color injection molds follows the core logic of "two injections, one molding". First, the first injection unit injects the primary material (usually rigid substrates such as PC/ABS) into the first cavity to form the product base structure. Then, the mold’s rotation or translation mechanism accurately transfers the core with semi-finished products to the second cavity. Finally, the second injection unit injects the secondary material (such as soft TPU or engineering plastics of different colors). The two materials achieve interface fusion in the molten state, and the finished products are ejected once after cooling, without manual intervention throughout the process.
Rotary two-color molds are the most widely used type, realizing core switching via a 180° rotating turntable and suitable for mass production of symmetrical parts like toothbrush handles and mobile phone cases, with production cycles controllable within 20 seconds. Shuttle two-color molds complete cavity switching through horizontal sliding mechanisms, featuring simple structures and low manufacturing costs, ideal for large asymmetric parts such as automotive interior panels. Stacked two-color molds adopt an up-down stacked dual-cavity design, working synchronously with dual injection units. Their production efficiency is 30% higher than that of rotary types, making them suitable for large-scale production of small precision parts.
Cavity layouts must ensure precise alignment after rotation or sliding to avoid interference during two injections. Core surfaces need to meet the molding requirements of both materials, and bonding surfaces should be designed with micro mechanical interlocking structures (such as grooves and bosses) to improve material bonding strength. A shrinkage margin of 0.5%-1% can be reserved for first-shot product dimensions to ensure sealing effects during second-shot molding.
Molds must be equipped with symmetrical guide pillars, guide bushes and precision positioning pins. Turntable positioning errors should be controlled within ≤0.02mm to prevent product flash or misalignment caused by positioning deviations. Guide pillars and bushes of mold bases should be arranged symmetrically in four directions, and side locks should be set on the four sides of the mold center to ensure precise alignment of front and rear molds after rotation.
Two sets of gating systems need independent designs. Second-shot gates should avoid product appearance surfaces, with sub-gates or hot runner systems preferred to reduce cold slugs and waste. Temperature control systems require separate circuit control, and the temperature difference between first-shot and second-shot cavities should be ≤3℃ to prevent poor material bonding or product warpage due to uneven temperatures.
Material selection should follow the "three matching" principles: melting point differences controlled at 20-30℃, melt flow rate (MFR) ratios at 0.8-1.2, and shrinkage rate differences ≤1.5%. During injection, temperature errors should be ≤±2℃, injection pressure control accuracy ±1bar, and holding time dynamically adjusted according to material characteristics to ensure sufficient interface fusion.
In the automotive industry, they are used for car lights (transparent PC lampshades + black PP bases) and interior parts (matte hard plastics + soft touch layers), with interior parts accounting for 35% of applications in mainstream automobile manufacturers. In consumer electronics, they apply to mobile phone cases (PC substrates + TPU non-slip edges) and keyboard keys (ABS keycaps + elastic soft plastics), with boundary precision controllable within 0.03mm. In the medical field, they are used for surgical instrument handles (rigid bodies + non-slip soft plastics) and catheter connectors (PEEK + sealing silicone), reducing defect rates by over 60% compared with traditional processes. In daily necessities, they are adopted for toothbrushes (PP handles + soft rubber grips) and tool handles (rigid bodies + non-slip TPE layers), achieving dual optimization of function and hand feel.
Equipment capable of synchronous molding of 3-4 materials has emerged. Through stacked injection unit layouts, it realizes integrated packaging of metal inserts and various plastics, increasing process integration by 60%.
Industrial internet-based real-time monitoring systems can collect over 160 process parameters, predict weld line positions via machine learning with an accuracy of over 92%, and reduce test mold times by 70%.
The application proportion of bio-based composite materials (such as PLA/PBAT) is increasing year by year, with a degradation rate of over 90%. Composite molding of conductive plastics and insulating materials provides integrated electromagnetic shielding solutions for wearable devices, with shielding effectiveness reaching over 30dB.
Through collaborative innovation in materials, structures and processes, two-color injection molds break the limitations of traditional molding technology. While improving product added value and production efficiency, they promote the transformation of manufacturing towards lean and high-value-added directions. In the future, with continuous breakthroughs in intelligent and material technologies, their application scenarios will be further expanded, becoming core supporting equipment for high-end manufacturing.
