Bi-material or bi-component injection molding is a process based on the injection of two thermoplastics to form parts in two materials. The materials used can be the same or different, depending on the functionality of the parts and the requirements set.
Generally, the same material is used to obtain a part in two colors, while the use of different materials is due to the fact that the components of the part have a different function. At OSF we have extensive experience in this type of manufacturing, having worked on several bi-material injection projects combining a rigid thermoplastic (PP, PP with fiber or talc, ASA-PC) with an elastomeric thermoplastic with a soft "rubber" feel (SEBS, EPDM).
The choice of materials to be combined is crucial, as they must have a compatible chemical base; otherwise there may be debonding problems that make it impossible for the part to function properly.
Mold design expertise is key to bi-material injection molding, as is the right injection molding machine technology.
There are several techniques for manufacturing molds, depending on the type of part. OSF works with the following injection techniques and technologies:
- Part transfer injection: in this case, the machine has two injection units. Using a robotic or manual system, the part to be overmolded is moved into the cavity where the second material is injected. A single mold is created in which the two materials are injected. OSF operates two 50Tn machines with this technology.
- Injection in two steps: Injection is performed in two different machines and two independent molds are produced. First, the first part of the part is injected on one machine, and then the other part is overmolded on a second machine. In this case, standard injection molding machines can be used.
Bi-material injection has many advantages:
- It can produce multicolor designs and combine rigid and soft materials.
- It allows the reinforcement of parts with a soft touch, making the interior rigid to give it
consistency. - Provides sealing or waterproofing of rigid parts when combined with an elastomer.
- Reduces investment in molds by reducing the number of parts in an assembly.
- Allows production optimization by working with a single mold.
At OSF, we study our customer's customized project to propose the materials and technology that meet their needs.