Main Types of Rubber-Coated Injection Molding Molds
Rubber-coated injection molding molds are key equipment for realizing the integrated molding of two or more materials (usually hard plastics and soft rubber or different plastics), and are widely used in electronics, automotive, medical, daily necessities and other fields. Its core principle is to make different materials closely combine through one or more injections, which has both structural strength, elasticity, anti-slip and other functions. According to the differences in rubber coating technology, structural design and application scenarios, rubber-coated injection molding molds can be divided into the following main types.
Two-Color Injection Rubber-Coated Molds
Two-color injection rubber-coated molds are one of the most common types, which realize the sequential injection and rubber coating of two materials through a rotating worktable or a moving core. The mold usually includes two independent cavities and a set of shared cores, and is produced by a horizontal two-color injection molding machine.
Structural Features
The mold is divided into two stations, A and B. Station A completes the first injection of hard plastic (such as ABS, PC) to form the base part; after the worktable rotates 180°, station B performs rubber coating of soft materials (such as TPE, TPU) on the base part. The positioning accuracy of the two cavities is extremely high, and the positioning error is usually controlled within ±0.01mm through the precise cooperation of guide pillars and bushings to ensure that the rubber coating layer fits perfectly with the base part.
Application Scenarios
It is suitable for products with relatively simple structures and high requirements for rubber coating accuracy, such as mobile phone cases (hard shells with soft rubber borders), tool handles (PP base parts with TPE anti-slip layers), baby tableware (PP bodies with silicone anti-scald edges), etc. Its advantage is high production efficiency, one-time molding without secondary assembly, and the material bonding strength can reach more than 20N/cm.
Secondary Injection Rubber-Coated Molds
Secondary injection rubber-coated molds adopt a step-by-step molding process. First, hard base parts are produced through ordinary injection molds, and then the base parts are put into rubber-coated molds for the second injection to realize the wrapping of soft materials. Different from two-color molds, secondary injection requires manual or robotic transfer of base parts, and the mold structure is divided into independent base part molds and rubber-coated molds.
Structural Features
The cavity of the rubber-coated mold must completely match the shape of the base part, and is usually equipped with positioning pins or buckle structures to prevent the base part from shifting during secondary injection. The surface of the cavity will be designed with a clearance of 0.02-0.05mm to avoid crushing the base part during rubber coating, and at the same time reserve a rubber coating thickness space of 0.1-0.3mm. For complex structures, the mold may be equipped with ejector pins or sliders to facilitate the placement of base parts and the removal of finished products.
Application Scenarios
It is suitable for products with complex structures of base parts and rubber coating layers and poor material compatibility, such as automobile door handles (ABS base parts with TPV sealing layers), electric toothbrush handles (PP base parts with silicone anti-slip patterns), medical device grips (PC base parts with TPE antibacterial layers), etc. The advantage of secondary injection is high flexibility, and the process parameters of the two injections can be adjusted separately, which is especially suitable for small-batch and multi-variety production.
Insert Injection Molding Rubber-Coated Molds (Insert Rubber-Coated Molds)
Insert rubber-coated molds are used to pre-place metal or hard plastic inserts into the mold cavity, and the soft material is wrapped around the inserts through injection molding to form composite structure products. Inserts usually need to be surface treated (such as sandblasting, pickling) to enhance the bonding force with the rubber coating material.
Structural Features
The mold is equipped with a precise insert positioning mechanism, such as positioning holes, magnetic devices or mechanical fixtures, to ensure that the insert does not shift during injection molding. For slender inserts (such as metal shafts), the mold will be designed with a support structure to prevent the insert from bending due to injection pressure. The position of the feed port of the rubber-coated cavity needs to avoid the stress point of the insert to prevent the insert from deforming due to high pressure.
Application Scenarios
It is widely used in products that need to have both metal strength and plastic elasticity, such as wire plugs (copper pin inserts with PVC insulation layers), hydraulic pipe joints (metal cores with rubber sealing layers), tool blade handles (steel sheet inserts with PP+TPR composite layers), etc. The bonding strength between the insert and the rubber coating material mainly depends on mechanical interlocking, which can usually reach a pull-off force of 15-30N.
