Volumes of production
There are small injection molders that produce simple components of 5,000 units or less. However, the minimum quantity is generally accepted to be 10,000 units.
Unit price vs. capital investment
The investment cost for machinery and design planning is high. However, the overall cost is lower in comparison with traditional techniques due to a reduction in storage, assembly costs, transportation of components, and use of materials.
Surface
The steel mold allows for surfaces that range from spark eroded to highly glossy. The location of ejector pins in the mold needs to be considered when designing a part as they will leave a small indented circle. Parting lines where the various parts of the mold come together also need to be considered.
Types/complexity of shape
If production volumes are particularly high multishot injection molding can be used to form highly complex parts. However, elements like undercuts, variable wall thicknesses, inserts, and threads significantly add to the cost of tooling.
Scale
Micro-injection molding is a specialist area and certain manufacturers specialize in parts that are often less than 1/25 inch. For large-scale products like garden chairs it is worth considering gas-assisted injection molding or, for large wall thicknesses, reaction injection molding (RIM).
Tolerances
±1/250 inch.
Relevant materials
The process is suited to the thermoplastics family, but consideration needs to be given to the compatibility of various types when mixing them in a component.
Typical products
Medical and healthcare; automotive; telecommunications; electronics; appliances; cosmetics.
Similar methods
For other methods that combine materials see over-mold decoration (p.214), insert molding (p.206), and in-mold decoration (p.212).
Sustainability issues
As all parts are produced in one process, energy use is very efficient and transportation between locations for additional manufacturing is eliminated. However, it is very difficult to separate materials in multimaterial components, which makes them problematic to recycle. Therefore, consideration should be given to reducing the number of material types.
Further information
www.mgstech.com
www.fiskars.com
In-Mold Decoration
Product |
Demonstration sample masks |
Materials |
The process has optimum effect on PBT plastic |
Manufacturer |
IDT Systems |
Country |
UK |
Shown left are demonstration masks produced by IDT Systems to illustrate the depth of penetration that is possible with this system. These particular samples are made from PBT plastic with a translucent film.
As the name implies, this is not a method of production as such, but, rather, in-mold decoration was developed as an economical way of adding decorative surfaces to injection-molded plastic parts. It offers a way of eliminating the necessity of having to print directly onto a part in a separate, post-forming process. This manufacturing technique is becoming more and more important with the growing market for electronic products, which makes increasing use of graphics for keypads, product branding, and the personalizing of portable consumer products.
The process begins with the printing of the graphic onto a polycarbonate or polyester film, known as a “foil.” Depending on the shape of the component to be molded, the foil is fed on a ribbon into the mold (or is cut and individually inserted, if the part is curved). The process is also suitable for shapes with compound curves, but in this case the foil needs to be molded to shape before being inserted into the mold.
One of the uses for in-mold decoration is as an alternative to spraying or molding parts in specific colors. It is a way of applying color to products to ensure consistency between moldings in different materials, where exact color matches are hard to achieve. An example of the use of this process can be found in the back and front moldings of a cell phone, where the back is molded in one material and the front in another.
– Cost-effective to customize parts and provide customer differentiation without retooling.
– Allows for virtually any color, image, and even surface texture to be added as a skin.
– Equally suited to short and long production runs.
– Films can be used to offer surfaces that are scratch-, chemical-, and abrasion-resistant.
– Incurs additional molding costs because of the complexity of the mold required to accommodate a film or foil.