Bi-Material plastic injection

Bi-material plastic injection, also known as bi-injection, is an advanced method for producing plastic parts. It involves two successive molding stages, each with a different thermoplastic material, to produce a complex plastic part with specific characteristics

This process is commonly used to manufacture parts that meet various criteria such as:

• Inclusion of two different colors.
• Combining two materials with distinct characteristics, such as rigid and flexible zones or using technical and aesthetic materials.
• Creating parts with zones possessing a "grip" effect or a "soft" touch.

Bi-material injection offers the possibility of developing sealing functions by molding seals directly onto the part without additional assembly operations. Additionally, it allows further automation of the manufacturing process by performing all operations on the injection press.

Regarding the molds used in this process, four main categories can be identified:

• Transfer Molds: These molds allow the part to be moved manually or by a robot within the same mold for the second injection.
• Rotary Plate Molds: These molds have a movable part that rotates 180° to place the first molding in the second material's cavity.
• Rotary Base Molds: Similar to rotary plate molds but with an integrated rotation mechanism within the mold itself.
• Gate or Slideback Molds: These molds use a core movement to create the required space for the second injection.

Manufacturing bi-material injection molds requires specific expertise in multi-material plastic injection and plastic overmolding. Managing technical issues such as shrinkage, venting problems, and filling challenges must be taken in account. These molds are generally more mechanically complex, making the scope and adjustments more difficult to achieve.