Volumes of production

The process is applicable to high-volume production runs that are comparable with injection molding or extrusion.

Unit price vs. capital investment

Reduced cycle time and usage of materials lowers the cost significantly compared with traditional injection molding. However, the process requires investment in specific equipment that costs more than that used for conventional injection molding.

Speed

The manufacturers maintain there is a 15 percent to 35 percent improvement in cycle times compared with conventional injection molding of thermoplastics.

Surface

The use of the gas creates parts with increased flatness and with less potential to warp.

Types/complexity of shape

The process offers the ability to create finer details and thinner wall thickness than conventional injection molding or extrusion.

Scale

The size of components that can be produced typically ranges from something the size of a latch pin weighing a fraction of an ounce to a large automotive part weighing several pounds. Typically the wall thickness of MuCell^® parts is less than 1/8 inch, 1/10 inch for talc-filled PP.

Tolerances

±1/250 inch.

Relevant materials

A range of thermoplastics, of which engineering plastics such as PA, PBT, PEEK, and PET are known to perform better. Materials often perform better when filled with fillers such as glass fibers.

Typical products

Most of the key applications for this process are currently based on automotive components because of the reduced weight of the molded parts. Applications for base plates for power tools have been implemented, where nylon filled with glass fibers replaces metals while maintaining the flatness needed in this type of application.

Similar methods

Gas-assisted injection molding (p.201).

Sustainability issues

Material consumption is significantly reduced due to the expansion of the foam, which in turn decreases the weight of the component. The viscosity of the material is less, thus speeding up cycle times and making efficient use of energy.

Further information

www.trexel.com

Insert Molding

Product	Stanley DynaGrip Pro screwdriver
Designer	Stanley in-house design
Materials	the handle is made of four layers—the first is nylon, followed by two layers of different colored polypropylene, and finally a thermoplastic elastomer (TPE) grip
Manufacturer	Stanley Tools
Country	UK
Date	1998

Insert molding is a branch of multicomponent molding (also called two-shot molding), which is a method of combining different plastics in the course of only a single manufacturing process. Insert molding refers to the stage of the process where parts (made from a variety of materials, including metal, ceramic, and plastics) are inserted to increase strength in the plastic component. Injection molding (see p.196) is the dominant element in this method of manufacture, with the inserts being placed in the mold prior to the injection of plastics.

Multicomponent insert molding using injection molding exists in two forms. In the first method, known as rotary transfer, two materials are injected into the same mold cavity with the mold having been rotated. The second method, commonly referred to as “robot transfer,” involves a component being produced first and only afterward being transferred to another mold for a second material to be added.

This screwdriver consists of four layers of plastic molded over the metal shank: the first, blue molding can be seen at the end of the handle; the shiny black area is the second layer; the yellow graphics are the third; finally, the black grip.

There are also other forms of insert molding that, instead of injection molding, use compression (p.174), contact (p.152), and rotational (p.137) molding.

–  Allows a range of differing physical and tactile properties to be incorporated into a single component.

–  Reduced labor costs for assembly.

–  Can add a whole range of increased functionalities.

–  High tooling costs.

–  Requires an advanced degree of knowledge on how to combine the various materials, and on subsequent design considerations such as shrinkage and the stresses of one material over another.