Overmolding
Process > Injection
| Overmolding | ||
Multicomponent injection or overinjection is a process by which a material, which can be a hard or soft polymer with a material (typically a rigid plastic known as a substrate), is overinjected. If properly selected, the over-injected polymer and its injection process conditions form a strong bond with the substrate material. The use of glues, adhesives or mechanical additives (screws) is no longer required to achieve an optimal bond between the two materials. This technique can be carried out in two ways, starting from the placement of the substrate as an insert in the mold and injecting the second material or simply, carrying out the injection of the substrate and the subsequent, overinjection of the second material using the same mold and two injection machines. The main advantage of employing injection molding using the debonded insert is that conventional injection machines can be used and a robot attached. On the other hand, the multicomponent molding carried out in the same stage requires two injection machines in which two different polymers will melt and inject, towards the same mold. The importance of this is to reduce cycle times and labor costs. |  | |
| Adhesion mechanisms | ||
The level of adhesion achieved will be a function of the combination of the materials, however, it must be borne in mind that this approach does not ensure good adhesion, since this will always depend on the process parameters used in each stage. When reference is made to The adhesion mechanisms produced in the union of these materials are observed that there are various types or models, such as: mechanical adhesion, electrical adhesion, diffusion, thermodynamic adsorption, chemical bonds and cohesion, among others. The diffusion refers to the fact that the adhesive force is due to the interdiffusion produced between the surface molecules of the superinjected materials. On the other hand, the mechanical anchoring is the oldest proposal. This model attributes the adhesion to the penetration of the polymer into the pores, surface irregularities and roughness of the substrate. The proposal states that the greater the rugosity, the more active contact sites that benefit accession will be increased. |  | |
| Additional factors that affect adhesion | ||
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