Common Plastic Resins for Injection Molding
Plastic injection molding is a manufacturing process that enables the production of large volumes of identical parts. It is considered to be one of the fastest, most efficient production methods for plastic parts used in the industrial sector today. It is typically used in projects that require the production of thousands, or even millions of parts through repeatable processes.
There are several advantages to utilizing injection molding techniques, such as:
- A high rate of repeatability. Each produced part will be essentially identical to other parts in the run.
- Low per-unit costs. While injection molding does require an upfront investment, once the operation is underway it offers a very low per-unit cost, as well as economies of scale for larger orders.
- Low scrap rates. Injection molding tends to leave very little waste behind, making it one of the most efficient manufacturing processes available today.
Common Plastic Resins
There are multiple plastic resins that manufacturers use within their injection molding operations. Six of the most common plastic resins on the market today include:
Acrylonitrile butadiene styrene (ABS) is a thermoplastic material that merges the strength of acrylonitrile and styrene with the resilience of polybutadiene rubber. ABS can be easily molded at a reasonable cost.
ABS has a reputation as an all-purpose injection molding material. It is strong and sturdy, highly impact-resistant, and easily machinable to achieve a pristine appearance. It is found an expansive range of consumer goods, including but not limited to:
- Exterior and interior automobile trim
- Golf clubs
- Musical instruments
Celcon—also commonly known by variations such as acetal, polyoxymethylene (POM), polyacetal, or polyformaldehyde—is a synthetic thermoplastic formed on a molecular level by the condensation of two alcohol molecules with an aldehyde molecule.
Celcon offers several advantages for manufacturing projects, such as exceptional toughness, good creep resistance, and low moisture absorption. It is often used in parts that are designed to come into contact with other surfaces. Common Celcon applications include:
- Toy parts
- Automotive gears and bearings
- Food and beverage equipment
- Electrical components
This exceptionally flexible thermoplastic material encompasses a range of available compounds that vary in quality and cost. Polypropylene has a reputation for offering a high deformation threshold—in other words, it can be twisted, bent, or reshaped without breaking. Due to its flexibility, manufacturers often utilize polypropylene as a living hinge material for products such as bottle caps and container lids.
The nylon commonly used in injection molding operations is reinforced with glass fibers for additional tensile strength. Typically the amount of added glass fibers does not exceed 40%.
Glass-filled nylon boasts higher strength and resistance to heat than both ABS and polycarbonate thermoplastics. Its innate heat resistance makes it a highly suitable material for kitchen applications, such as ovens. It is also highly resistant to electric current, making it a great choice for electrical applications where insulation is a must.
High-impact polystyrene (HIPS) is a thermoplastic polymer with exceptional machinability and unsurpassed aesthetic attributes. It is popular for use in printed products, such as displays, posters, retail packaging, and graphics arts applications. Manufacturers also use HIPS for TV and audio-visual (A/V) equipment, bicycle trailers, hot and cold Thermos bottles, and electronic components.
Low-density polyethylene is the most flexible kind of polyethylene on the market today. It is highly cost-effective to produce, weather-resistant, and has high impact strength characteristics. It is found in a wide range of everyday consumer goods, as well as specialized equipment. Some common LDPE applications include:
- Food containers
- Food service and storage
- Consumer goods
- Industrial parts
- Medical products
What to Consider When Choosing a Material
When selecting a source material for an injection molding project, it is important to consider the following factors:
- Impact strength. Will your application be subjected to high-impact forces? Which resins are known to be highly impact-resistant?
- Tensile strength. Will tensile forces be periodically or consistently acting on your final product? Which resins can successfully withstand your expected load without being torn apart?
- Heat deflection. Will your end product be subjected to high temperatures? Will it require a strong insulating performance? Which options make the most sense for heat deflection/insulation?
- Water absorption. Will the application be involved in a high-moisture environment, or need to resist water absorption day in and day out? Which resins can provide the best water-resistant properties?
- Financial considerations. Which resins offer the most cost-effective solution for your particular project? Which ones will ensure that your end products are maximized for durability and functionality?
Material Selection Help From Darter Plastics
There are certainly many options for injection molding source materials on the market today, and many factors to weigh for each project. If you’d like to learn more about the pros and cons of each injection molding material, or want to explore the injection molding process further, reach out to our team of experts at Darter Plastics today.