Volumes of production
High-volume production process, typically above 100,000 units.
Unit price vs. capital investment
An economical process when compared with manual assembly of the different materials.
Speed
Depends on the product. Thin-walled products cool very quickly, but the type of plastic and overall component design are also important factors.
Surface
Depends on the molding process used, but is comparable to injection molding (see p.196) but, in with insert molding, surface materials may be introduced that can enhance the finish, for example the extra grip on a toothbrush handle.
Types/complexity of shape
Since this type of insert molding is based on injection molding, the same possibilities and restrictions apply, although the shape of the insert itself will partly dictate the shapes achievable.
Scale
It is possible to achieve products of greatly varying size depending on the type of injection molding used.
Tolerances
Can be very high, because injection molding can achieve tolerances of ±1/250 inch.
Relevant materials
Any combination of materials, including thermoplastic and thermoset polymers. Depending on the combination of materials, different layers may bond chemically to varying degrees. However, thermosets and thermoplastic elastomers (TPEs), for example, generally do not provide a chemical bond.
Typical products
One of the key features of combining different materials is that you are able to bring together multiple functions in a single component. For instance, it is possible to have movable joints and decorative features over a flexible yet strong core, without the additional assembly costs. Typical products that are made through this process include toothbrushes, screwdrivers, razors, and housings (of, for example, power tools with rubber grips).
Similar methods
In-mold decoration (p.212).
Sustainability issues
This process can eliminate the need for several stages of production and subsequent energy use by reducing everything into one single step in one location, making the most efficient use of transportation and energy. However, recycling becomes more difficult when two or more materials are combined, as they need to be separated before they can be reprocessed.
Further information
www.engel.info
www.bpf.co.uk
www.mckechnie.co.uk
Multishot Injection Molding
Product |
Garden secateurs |
Materials |
Thermoplastic Elastomer (TPE) grip, polypropylene handle, steel blades |
Manufacturer |
Fiskars |
Country |
Finland |
The cutaway of these secateurs show how the gray TPE is injection molded within the black PP handle.
In contrast to traditional injection molding where each component is produced separately as a single piece, multishot injection molding makes it possible to mold several pieces and assemble them in a single cycle, resulting in a finished product in just one run. The process even allows for products with moving parts such as caps, handles, and hinges to be created within the same molding cycle. Generally, the manufacture of a product with several components can be a lengthy process that requires each piece to be molded separately, often in different locations, along with an additional manual assembly to complete production. Multishot injection molding makes production a lot less messy by eliminating all these secondary processes and incorporating them into one, which in turn significantly reduces lead time as well as costs.
As with anything simple, a great deal of setup is required in order to maximize the process. Every aspect must be considered, from how the combination of materials will react with one another to the type of machine that should be used. The design of the molding process is very creative because of the flexibility of the machine processing. The designers examine several different ways of making a part as there is no single solution. Some methods may offer cost savings while others may allow for flexibility in designing parts.
A multishot injection molding machine is automated and consists of robotic arms that are controlled by a computer and move the component from one mold cavity to another.
– Reduced production time.
– Reduced unit costs.
– Multicomponent part produced in single cycles.
– Up to four different materials can be molded in one cycle.
– A variety of functional/decorative features, including graphics, text, and grips, can be applied during the process
– Needs a great deal of production planning.
– It is likely that the original design will require some alterations before it is suitable for manufacture.
– The robot sometimes has difficulty picking up and placing complex components, which can result in moldings being dropped and misplaced.