One of the most important decisions you’ll make is selecting the appropriate injection molding materials for your part. Material selection significantly influences your product’s performance, durability, and cost. In this guide, we explore the most common materials, their strengths, molding temperatures, common applications, and other important properties. By the end of this guide, you’ll be able to make an informed decision for your project.
Before Making a Selection
- Environmental Impact: In recent years, environmental considerations have become paramount. Biodegradable and recycled materials are gaining prominence in the manufacturing industry. Materials like biodegradable PLA (Polylactic Acid) and recycled plastics offer eco-friendly alternatives, reducing the carbon footprint of injection molding processes.
- Material Cost and Availability: The cost and availability of materials can significantly impact your project. Some high-performance materials might be expensive, while others are more cost-effective but might be tougher to get. Balancing material costs with the desired product characteristics is crucial for a budget-conscious decision.
- Regulatory Compliance: Different industries and regions have specific regulations regarding the materials used in products. You probably have experienced this in your industry. This is especially important with food, healthcare, and children’s products. Ensuring that the selected material complies with relevant regulations and standards is essential to avoid legal complications.
- Post-Processing Capabilities: Are you painting, plating, or surface finishing your parts? Some materials are more conducive to these processes, ensuring your final product meets aesthetic and functionality expectations.
- Real World Application: It’s important to consider the properties of potential injection molding materials like strengths, weaknesses, heat resistance, tensile strength, and even its heat deflection temperatures (HDT). HDT is the temperature range at which a material will deform under a specific load before failure. In the end, these properties will easily help you decide which material is best for your part.
Common Injection Molding Materials
Polyethylene (PE)
Polyethylene is a thermoplastic polymer known for its excellent chemical resistance, low cost, and ease of processing. Melt temperatures start around 375 F, but generally have a wide range from there. PE is categorized into different types based on its density. Low-density polyethylene (LDPE), high-density polyethylene (HDPE), and ultra-high-molecular-weight polyethylene (UHMWPE).
- Strengths: PE offers good tensile strength and impact resistance, especially in its high-density form. Polyethylene’s flexibility and ease of molding make it an ideal choice for applications requiring intricate shapes and contours. It also has food grades available.
- Weaknesses: While PE is known for its flexibility it has relatively poor resistance to UV radiation, which can cause it to degrade and lose mechanical properties when exposed to sunlight for extended periods. In high-temperature environments, PE is susceptible to creep and may soften and lose its strength over time.
- Common Applications: Packaging materials, plastic bags, containers, toys, and pipes.
- Heat Resistance: PE offers moderate heat resistance, maintaining its structural integrity at lower temperatures but is not recommended for high heat applications.
- Heat Deflection Temperature: 140°F – 185°F
- Tensile Strength: 1900 – 4500 psi
Polypropylene (PP)
Polypropylene is a versatile thermoplastic known for its excellent chemical resistance. It has a melt temperature from 320°F to 464°F, making it suitable for both low and high-volume production processes.
- Strengths: PP exhibits high tensile strength, stiffness, and good impact resistance. In addition to its durability, polypropylene’s resistance to moisture and chemicals makes it suitable for products exposed to harsh environmental conditions.
- Weaknesses: PP is susceptible to environmental stress cracking, especially when exposed to certain chemicals or harsh high-heat environments. Exposure to sunlight long term can also cause color fading and reduced mechanical properties.
- Common Applications: Automotive components, medical devices, packaging, and consumer goods.
- Heat Resistance: PP offers moderate heat resistance, maintaining its structural integrity at lower temperatures.
- Heat Deflection Temperature: 158°F – 212°F
- Tensile Strength: 4,500 – 18,500 psi
Polystyrene (PS)
Polystyrene is a widely used thermoplastic with a melt temperature typically around 356°F to 464°F. This ensures efficient processing inside the injection molding equipment. It is known for its transparency, ease of molding, and affordability. PS can be categorized into two main types: general-purpose polystyrene (GPPS) and high-impact polystyrene (HIPS). PS is prone to cracking instead of deforming.
- Strengths: PS has moderate tensile strength and impact resistance, with HIPS being tougher than GPPS. It’s also very lightweight in nature and has excellent insulation properties.
- Weaknesses: PS, especially in its high-heat form, is relatively brittle and lacks high impact resistance. It is also sensitive to certain solvents, which can cause surface damage and deformation, limiting its use in chemical environments. Lastly, it is not biodegradable and can contribute to environmental concerns if not properly recycled.
- Common Applications: Disposable cutlery, packaging materials, toys, and electronics housings.
- Heat Resistance: PS has moderate heat resistance but it may soften or deform in higher temperature environments.
- Heat Deflection Temperature: 185°F – 212°F
- Tensile Strength: 5,000 – 7,500 psi
Polyvinyl Chloride (PVC)
Polyvinyl chloride is a thermoplastic polymer known for its excellent chemical resistance and flame retardancy. It’s typical molding temperature ranges from 320°F to 410°F, allowing for the production of a wide range of products.
- Strengths: PVC offers good tensile strength and durability. Apart from its chemical resistance, PVC also has flame retardant properties.
- Weaknesses: PVC can be relatively brittle, especially at lower temperatures, which affects its impact resistance. However, at higher temperatures PVC can soften and lose its structural integrity. It also emits toxic fumes when burned, making it less desirable in fire-prone environments. Lastly, like PS, PVC is not biodegradable and as a result can pose environmental concerns during recycling.
- Common Applications: Pipes, cable insulation, automotive parts, and medical tubing.
- Heat Resistance: PVC has good heat resistance, retaining its properties in environments with slightly elevated temperatures.
- Heat Deflection Temperature: 129.2°F – 167°F
- Tensile Strength: 10,000 – 12,000 psi
Acrylonitrile Butadiene Styrene (ABS)
ABS is a thermoplastic polymer known for its exceptional impact resistance, toughness, and dimensional stability. It has a molding temperature around 410°F to 527°F, which ensures proper flow and mold filling during injection molding.
- Strengths: ABS exhibits excellent impact resistance, making it ideal for products subjected to mechanical stress. Additionally, it possesses excellent moldability, allowing for intricate designs and complex shapes in manufactured products.
- Weaknesses: ABS can degrade over time when exposed to sunlight and may not be suitable for outdoor applications without proper UV protection. It also has a relatively low heat resistance, which can limit its use in high-temperature environments.
- Common Applications: Automotive components, electronics housings, toys, and consumer appliances.
- Heat Resistance: ABS offers good heat resistance, retaining its properties at moderate temperatures.
- Heat Deflection Temperature: 190.4°F – 212°F
- Tensile Strength: 5,000 – 7,500
Polyethylene Terephthalate (PET)
PET is a strong, lightweight thermoplastic with a relatively high melt temperature, typically around 500°F to 554°F. Although these melt temperatures are achievable on most molding machines, the molds themselves often require running at temperatures above 212 degrees F. Hot oil temperature controllers may be required when using injection molding materials like this.
- Strengths: PET offers high tensile strength, stiffness, and excellent resistance to wear and abrasion. PET’s recyclability and ability to retain its mechanical properties after recycling contribute to its eco-friendly reputation.
- Weaknesses: While strong and lightweight, PET can be prone to scratching, impacting its visual appeal over time. Additionally, PET can absorb odors and flavors, which can affect the taste and smell of products stored in PET containers. While PET is recyclable, its recycling process can be energy-intensive, impacting its overall environmental footprint.
- Common Applications: Beverage bottles, food packaging, fibers, and engineering resins.
- Heat Resistance: PET has good heat resistance, maintaining its properties at high temperatures but not extreme temperatures.
- Heat Deflection Temperature: 149°F – 239°F
- Tensile Strength: 7,000 – 23,000 psi
Polycarbonate (PC) High Heat
Polycarbonate is a transparent thermoplastic known for its exceptional impact resistance, optical clarity, and high-temperature resistance. PC should reach a molding temperature around 518°F to 608°F, ensuring the material flows smoothly into the mold cavities.
- Strengths: PC offers outstanding impact resistance, making it suitable for products requiring high durability. It also has exceptional UV resistance, making it ideal for outdoor applications where sun exposure is expected.
- Weaknesses: PC can be prone to scratching, requiring additional surface treatments for improved durability. It is also sensitive to certain chemicals and exposure to them will cause degradation over time.
- Common Applications: Eyewear lenses, automotive components, electronic enclosures, and medical devices.
- Heat Resistance: PC has excellent heat resistance overall, retaining most of its properties at high temperatures.
- Heat Deflection Temperature: 266°F – 374°F
- Tensile Strength: 9,000 – 23,000 psi
Nylon (Polyamide)
Nylon, also known as polyamide, is a popular thermoplastic renowned for its high strength, toughness, and excellent wear resistance. The molding temperature typically ranges from 446°F to 572°F, depending on the specific type of nylon being processed.
- Strengths: Nylon offers exceptional tensile strength and impact resistance, making it ideal for parts subjected to mechanical stress. Its self-lubricating properties reduce friction and wear, making it valuable in applications that require smooth operation and longevity.
- Weaknesses: Nylon absorbs moisture which can lead to dimensional changes and reduced mechanical properties, especially in high humidity. Also, like PE, nylon components can be prone to creep under sustained loads, affecting their long-term dimensional stability. Lastly, the production of nylon involves the use of non-renewable resources, impacting its overall environmental sustainability.
- Common Applications: Gears, bearings, bushings, and structural components in automotive and aerospace industries.
- Heat Resistance: Nylon exhibits good heat resistance and maintains its properties at elevated temperatures.
- Heat Deflection Temperature: 140°F – 374°F
- Tensile Strength: 6,000 – 24,000 psi
Polymethyl Methacrylate (PMMA) - Acrylic
PMMA, commonly known as acrylic, is a transparent thermoplastic known for its optical clarity, UV resistance, and weatherability. Its molding temperature is on the lower end when compared to other injection molding materials. Typically molded around 464°F to 518°F, this allows it to be processed in a variety of molding machines.
- Strengths: Acrylic offers moderate strength and excellent optical properties, making it a preferred choice for transparent applications. Apart from its optical clarity, it can be easily polished, ensuring clear and scratch-free surfaces.
- Weaknesses: When compared to other plastics on our list, Acrylic is relatively brittle, making it susceptible to scratches, cracking, and chipping from impacts or stress. It is also prone to yellowing over time when exposed to UV radiation, impacting its optical clarity and suitability for outdoor applications without proper UV protection.
- Common Applications: Display panels, lighting fixtures, lenses, and decorative items.
- Heat Resistance: Acrylic has moderate heat resistance and may soften at higher temperatures.
- Heat Deflection Temperature: 158°F – 230°F
- Tensile Strength: 2,800 – 10,900 psi
Polyoxymethylene (POM) - Acetal
POM, also known as acetal, is a high-performance engineering thermoplastic with excellent dimensional stability and low friction. Its molding temperature ranges from 347°F to 410°F. This is critical to achieve desired flow consistency during injection molding.
- Strengths: Acetal offers high tensile strength, stiffness, and excellent resistance to wear and chemicals. It also has a low friction coefficient and excellent dimensional stability. Making it suitable for applications requiring precise movements and minimal wear.
- Weaknesses: Acetal like Nylon, absorbs moisture which can lead to dimensional changes and reduced mechanical properties, especially in high humidity conditions. It also has a relatively high coefficient of linear thermal expansion, which can pose challenges in applications requiring tight dimensional tolerances over a wide temperature range. Lastly, Acetal production involves the use of formaldehyde, a potentially hazardous substance, raising environmental and health concerns during manufacturing processes.
- Common Applications: Gears, bushings, valves, and conveyor belts.
- Heat Resistance: Acetal has good heat resistance, maintaining its properties at moderately high temperatures.
- Heat Deflection Temperature: 230°F – 341.6°F
- Tensile Strength: 6,000 – 22,000 psi
Polybutylene Terephthalate (PBT)
PBT is another commonly used thermoplastic for injection molding. Its molding temperature range is 428°F to 500°F, allowing for efficient processing in various injection molding machines.
- Strengths: PBT is known for its excellent electrical insulating properties, high strength, and resistance to abrasion and chemicals.
- Weaknesses: PBT also absorbs moisture, which can lead to dimensional changes and reduced mechanical properties, especially in high humidity conditions. This can also affect its electrical properties. PBT does not have as high impact resistance as some other moldable plastics, making it less suitable for applications requiring excellent toughness. Lastly, its processing may release hazardous substances, posing environmental concerns during manufacturing processes.
- Common Applications: Electrical connectors, automotive parts, and various industrial components requiring high-performance characteristics.
- Heat Resistance: PBT has good heat resistance overall. It can take prolonged exposure to temperatures without significant loss of its mechanical or electrical properties.
- Heat Deflection Temperature: 122°F – 302°F
- Tensile Strength: 6,000 – 13,000 psi
Polyphenylene Sulfide (PPS)
PPS is a high-performance thermoplastic known for its exceptional chemical resistance, flame retardancy, and high-temperature stability. It has a molding temperature around 536°F to 626°F. Although these melt temperatures are achievable on most molding machines, the molds themselves often require running at temperatures above 212 degrees F. Hot oil temperature controllers may be required.
- Strengths: PPS offers high tensile strength, excellent dimensional stability, high temperature resistance, and resistance to chemicals. It’s ideal for applications in aggressive chemical environments where durability is crucial.
- Weaknesses: PPS can be prone to degradation under high-stress conditions, leading to reduced mechanical properties. It can also be relatively expensive compared to other thermoplastics, impacting its cost-effectiveness for certain projects. PPS materials often require specialized processing techniques and high molding temperatures, which can add complexity to manufacturing processes. Lastly, the production and disposal of PPS can pose challenges, requiring proper waste management practices.
- Common Applications: Automotive components, electrical connectors, and industrial filters.
- Heat Resistance: PPS exhibits outstanding heat resistance, retaining its properties at high temperatures.
- Heat Deflection Temperature: 212°F – 320°F
- Tensile Strength: 14,000 – 28,000 psi
Making Your Final Decision
Selecting the right injection molding materials can make or break your injection molding project. As you can see, each material has its unique properties, advantages, and limitations. Remember, the material you choose not only impacts the performance of the final product but also manufacturing costs and the environment.
If you’re unsure what material is best, contact us to consult with one of our material experts. We’ll ensure you choose the most suitable material that aligns with your project goals and other requirements. With the right material and proper molding technique, you can create high-quality, durable products that meet or exceed your expectations.
