Materials are often specified early in the design process and should be mutually agreed upon by both parties. Sometimes molders may purchase large quantities of specific resins at major discounts.
These discounts can be passed on to customers. For example, if a designer can specify an ABS grade that matches the properties of one purchased in large quantities by a molder, many tens of thousands of dollars can be saved. A designer may discover certain high-performance resins may not be ideally suited for a molder due to viscosity, high glass content or crystallinity. A resin may be chosen for specific physical or chemical-resistance properties but may be very difficult to mold or maintain specified tolerances. Molders should be in agreement with specified resins and overall part requirements, since they will be required to actually mold the parts.
Selecting the appropriate material for plastic injection molding part production is a pivotal consideration. The market offers an expansive array of around 85,000 thermoplastics, encompassing approximately 40 distinct polymer blends or families.
At our disposal, we have a comprehensive selection of 40 resins readily available. Moreover, our expertise extends to aiding in the procurement of non-stock materials, custom colors, specialty resins, and accommodating customer-provided materials.
Thorough insights into each material and their respective families can be garnered from suppliers’ data sheets, design manuals, online resources, and other references. Conducting thorough research in advance is essential. The eventual material choice significantly impacts both the rapid manufacturing process and the performance of the part.
Several key attributes warrant consideration when finalizing material selection:
Durability: Evaluate the material’s resistance to pressure, damage, and wear.
Flexibility: Assess whether the material can bend without fracturing.
Chemical Resistance: Determine if protection against chemical or solvent reactions is necessary.
Tensile Strength: Examine the material’s ability to resist breaking under tension.
Temperature Resistance: Consider exposure to high or low temperatures and potential interactions with other factors or polymers during manufacturing.
Aging: Determine if a specific shelf life requirement exists.
Impact Resistance: Evaluate the material’s capacity to withstand sudden, intense force or shock within a short duration.
Environmental Factors: Factor in external influences like weather, chemicals, or other conditions that could affect the product.
Material Cost: Decide between selecting a premium or equivalent-grade polymer based on cost considerations.
Product Availability: Take into account lead times and availability.
Overmolding: If utilizing two distinct materials, analyze how they interact during the manufacturing process and consider compatibility.
Thoroughly evaluating these attributes ensures an informed and strategic material selection process, which is pivotal for achieving optimal part performance and successful injection molding outcomes. Contact us to leverage our expertise and resources in material selection for your plastic injection molding needs.
Our material selection guide will provide an overview of the materials for injection moulding projects. The features and applications of each material are also discussed in detail.
Elastomers and Synthetic Rubbers
Material selection is an integral part of the injection molding process. It impacts the performance, cost and production time of a project. With such an important decision to make, choosing the right material can be daunting.
ABS
ABS is a widely used thermoplastic material. It is ideal for producing parts with good impact resistance, low cost and high tensile strength. It offers high surface hardness, chemical resistance and toughness. Good heat resistance also makes it ideal for producing parts with a glossy finish, which is often desired in the automotive industry. It gives a high resistance to scratch for outdoor applications. All these features make ABS a very popular choice for injection molding.
Key features: High rigidity • Resistance to scratches • Good strength-to-weight ratio • High weldability
Applications: ABS is widely used in the manufacture of automotive and marine parts
Acrylic (PMMA)
Acrylic (PMMA) is commonly used when optical clarity is a necessity. This thermoplastic offers excellent optical transparency even at very thin wall thicknesses, making it ideal for applications like lenses and face shields. It is a great substitution for glass for outdoor use. Acrylic shows high moldability which can be used to form various different shapes and sizes in injection molding.
Key features: Good abrasion resistance, impact strength and weatherability properties
Applications: It is used in the manufacture of windows, frames, mobile screens etc.
HDPE
HDPE provides excellent impact resistance and chemical resistance. It is an ideal choice for producing parts with excellent toughness and rigidity. HDPE offers high heat resistance and a low coefficient of expansion. Its good temperature stability makes it ideal for applications where parts must retain their shape under extreme temperature changes. It also provides good electrical insulation.
Key features: HDPE is a lightweight, chemical resistant and environmentally friendly material
Applications: It is best used for heavy construction, agriculture and the manufacture of medical products
LDPE
LDPE is a resilient thermoplastic, making it an ideal choice for applications requiring good impact resistance. It also has excellent chemical resistance properties, as well as a melting temperature of 115°C. Its flexibility makes it suitable for intricate shapes requiring high levels of detail and dimensional accuracy. Its low cost also makes it a great choice for the mass production of injection moulded parts.
Key features: Lightweight • Translucent • Resistant to stress
Applications: LDPE is commonly used in food containers, toys, and industrial and medical parts
See the datasheet
Nylon 6 / PA 6
Nylon 6 is a semi-crystalline thermoplastic that offers excellent wear resistance, chemical resistance, and toughness. It can be used in combination with other materials to enhance its properties further. The fibre in the material is tough but gives good elasticity to the product. Nylon 6 is also suitable for applications requiring tight tolerances. It also gives good resistance to wear with good electrical
Key features: Rigid • High strength • Resistant to wear and chemicals
Applications: It is best suited for bearing, gears, and electronic connectors
Nylon 66 / Nylon 6/6
Nylon 66 is a synthetic polyamide that offers excellent strength and toughness, making it suitable for applications with high-impact requirements. It has a high melting temperature of 258°C and a good tensile strength of 85 MPa. However, it shows no resistance against UV rays. With its good sliding property, Nylon 66 makes an excellent choice for many injection molding applications.
Key features: Light weighted • Good mechanical strength • Stiff • Wear resistance
Applications: Nylon 66 / Nylon 6/6 are commonly used in making brushes, tennis strings, surgical sutures
PBT
PBT is a semi-crystalline thermoplastic that offers excellent mechanical strength, rigidity, and heat resistance. It has a high melting point of 215°C which makes it a good choice for injection moldings. PBT shows good chemical resistance. It also offers good dimensional stability and tight tolerances, as it has a low coefficient of expansion. Its good temperature resistance makes it suitable for applications that require parts to maintain their shape under extreme temperature changes.
Key features: Abrasion resistant • Good dimensional stability • Low coefficient of thermal expansion
Applications: PBT is mostly used in gears, bearings and iron handles, motor brackets
PC (Polycarbonate)
PC is a transparent thermoplastic with excellent impact resistance, shatter resistance and stiffness. It also has good chemical resistance properties. PC’s transparency makes it ideal for applications where visibility of the internal parts is required. Its high melting point of 250°C makes it suitable for various engineering processes. It shows high stiffness and high viscosity which makes it suitable for parts requiring high dimensional accuracy and tight tolerances.
Key features: Shatter resistance • Good electrical properties • Transparent • Durable
Applications: It is widely used in medical devices, eyewear, electronics and beverage packaging
PS-ABS Polycarbonate
PS-ABS Polycarbonate Blends are a special type of injection molding material that combines the strength, heat resistance and rigidity of a PC with the flexibility and cost savings of ABS. It is ideal for parts requiring high-temperature stability, good chemical resistance and dimensional accuracy. PS-ABS also offers excellent impact resistance, making it suitable for applications requiring parts that are durable and perform well under shock and vibration.
Key features: High impact strength • Heat resistance • Flexibility
Applications: PS-ABS is suitable to produce parts like keypads, panels, TV frames etc. for the electronics industry
PC-PBT
PC-PBT is a special thermoplastic which combines the high mechanical strength, heat resistance and rigidity of a PBT with the shatter resistance and stiffness of a PC. It is widely used in the manufacture of automotive and aerospace parts as it offers a high strength-to-weight ratio and good chemical resistance. It is also used for parts that require high corrosion resistance.
Key features: Heat and corrosion resistance • Dimensionally good mechanical strength
Applications: This material is mostly used in the manufacture of automotive bumpers and gear cases
PEEK
PEEK is a semi-crystalline thermoplastic offering excellent mechanical strength and stiffness, as well as high temperature resistance. It has a low thermal coefficient of expansion, making it suitable for precision parts with tight tolerances. Its chemical resistance and wear resistance is also very good. PEEK can be used in combination with other materials to enhance its properties further. It shows high resistance to stress cracking and has excellent dimensional stability. Best used for parts where shock and vibration are a concern.
Key features: Chemical and fatigue resistance • High mechanical strength • High chemical resistance
Applications: PEEK is commonly used for medical implants, electric insulations, seals and valves
PEI (Ultem)
PEI (Ultem) is a semi-crystalline thermoplastic offering excellent mechanical strength and stiffness, as well as high temperature resistance. It is one of the most popular materials used in injection molding thanks to its excellent electrical properties. It is also widely used for its exceptional dimensional stability. It boasts superior flame retardant properties and can be used in a variety of applications, from automotive and electronics components to medical equipment and machinery.
Key features: Heat resistance • High dielectric strength • Good stiffness and hardness
Applications: It is used in engine components, temperature sensors, medical devices etc.
PET
PET is another common material used in injection molding. It has excellent mechanical and thermal properties, making it ideal for parts that need to be lightweight and shatter-resistant. PET also has outstanding chemical resistance, so it can withstand exposure to many chemicals without degrading or becoming brittle. Additionally, it has good aesthetic properties – it has a glossy finish and is easy to dye, allowing for parts with vivid colours. Its high melting point requires the molding to be done at a high temperature.
Key features: Flame retardant • Heat, creep and chemical resistant
Applications: PET is used in the making of capacitors, bottles, recording tapes and many other electrical components
PLA
PLA is a bioplastic derived from renewable sources such as cornstarch and sugarcane. It has excellent mechanical properties, making it a great choice for parts that require strength and flexibility. PLA also has good thermal stability, allowing it to remain strong at high temperatures. It has a low melting point of 145 – 160°C. PLA is recyclable and biodegradable, making it a great choice for environmentally friendly manufacturing.
Key features: Biocompatible • High tensile strength • Low glass transition temperature • High flexibility
Applications: PLA is commonly used in plastic films, bottles and medical devices
Polyethylene (PE)
Polyethylene (PE) is a lightweight but tough material that can withstand high impact and has excellent chemical resistance. It is the most widely used plastic in the world
. It is derived from petroleum and shows a good strength-to-weight ratio. It also offers dimensional stability – its parts will retain their shape even when exposed to extreme temperatures or pressure. Polyethylene is also recyclable, making it a great option for many applications.
Key features: Impermeable • Chemical resistant • Exhibits good electrical insulation properties
Applications: This material is commonly used in garbage and grocery bags, packaging films, bottles and food packaging containers
Polypropylene (PP)
PP is a widely used thermoplastic with high strength and excellent elasticity. It can be clear or coloured and is widely used in the manufacture of car parts, electrical components and packaging materials. It has good moisture resistance, making it suitable for use in high-temperature applications, and can be formed into various sizes and shapes through injection molding. It is also resistant to heat, fatigue and electrical insulation.
Key features: Heat, chemical and moisture resistant • Good elasticity • High impact strength
Applications: PP is used in making carpets, clothing and camping equipment for domestic use. Car batteries, bumper and cladding for industrial use
Polystyrene (PS)
PS is a transparent amorphous thermoplastic made from monomer styrene. It is a hard material with high strength, making it suitable for use in a variety of applications. It shows good electrical properties and is resistant to gamma radiation. It can be formed into various sizes and shapes through injection molding, making it a popular choice for household items and other plastic products.
Key features: Transparent • Hard and brittle • Excellent strength
Applications: PS is widely used in the making of disposable cutlery, food containers, plates, bowls etc.
POM / Delrin acetal
POM, also known as Delrin Acetal, is a semi-crystalline thermoplastic with excellent strength and wear resistance. It can be easily formed into different shapes through molding processes and has good chemical resistance properties. POM is often used in industrial applications because of its high tensile strength of 75.8 MPa. It is mostly tough and durable with low moisture absorption properties.
Key features: Wear resistant • Strong and durable • High tensile strength
Applications: This material is generally used in the manufacture of mechanical parts such as pumps, valves and bearings etc.
PPE-PS
PPE-PS blend is a combination of PPE and PS. It offers superior mechanical properties. This allows for improved impact strength and stiffness. It can also be used in applications requiring high temperature resistance as well as electrical insulation. It gives a good surface appearance and is highly ductile. PPE-PS shows a good tensile strength of 50 MPa at room temperature.
Key features: Ductile • Strong • Good flow ability • Impact resistant
Applications: PPE-PS is best used in making valve components, water pumps and various medical devices
PPS
PPS (Polyphenylene Sulfide) is a semi-crystalline thermoplastic with good chemical resistance, high heat deflection and UV light. It has exceptional dimensional stability and can be used in applications requiring good electrical insulation. PPS is highly fire resistant. It has a good tensile strength of up to 80 MPa at room temperature which makes it a popular choice for automotive parts.
Key features: Rigid • UV and chemical resistant • Good dimensional stability
Applications: PPS is mostly used in fuel injection systems, switches, and electronic devices like steam iron and hair dryers
See the datasheet
PSU
PSU (Polysulfone) is a semi-crystalline known for its high-temperature stability. It has excellent electrical insulation, dimensional stability and very good chemical resistance. PSU also offers improved impact strength over other plastics. Its tensile strength can reach up to 80 MPa. PSU is ideal for applications requiring excellent mechanical properties and heat resistance such as automotive parts, electrical components and medical devices.
Key features: Thermal stability • Strong and durable • Chemical and heat resistant
Applications: PSU is mostly used in the automotive, medical and electrical industries, such as electrical insulators and applications
Properties to consider when selecting injection molding materials
There are several important properties to consider for selecting injection molding materials for any plastic product. These include the desired tensile strength, flexural modulus (bending stiffness), Izod impact (toughness), electrical insulation, temperature resistance, chemical resistance, FDA compliance, and cost of the final product.
The first property to consider when selecting injection molding materials is the product’s desired tensile strength. Tensile strength is the resistance to being pulled apart, typically measured in PSI (pounds per square inch). Similarly, another material property to consider is Izod impact (notched) or toughness. The Izod impact test is an ASTM standard method of determining the impact resistance of materials. This is done by swinging an arm into the notched sample, recording the energy required to break the part, which is measured in ft·lb/in2.
Manufacturing Polyurethane Tie StrapAnother property to consider when selecting your plastic material is the material’s flexibility or bending stiffness. Also known as flexural modulus, the material’s stiffness is measured in psi. Next, is electrical insulation properties, or dielectric strength. Typically measured in volts per micrometer (v/mil), to determine how well the plastic part will prevent the flow of electrical charge. While these are accurate for certain standards, sometimes we have to use metric units due to the material info we are given, or doing tests in other standards (ISO or DIN for example).
Chemical resistance is also important because this will determine how well the plastic can resist being degraded by certain chemicals better than others. For example, gasoline will melt polystyrene (basically making napalm), but not polyethylene (which plastic gas cans are made of). Therefore, it is important to identify what the finished product will come in contact with and pick a compatible material. Along this note, FDA compliance is an important factor when dealing with medical or consumer products that must be approved for human contact.
How the injection molding material reacts to heat is important to consider when comparing thermoplastic materials. The thermal properties will determine the max and min working temperature, the melting temperature, and can determine how the material will react in the mold and as it cools. Injection molding pressure and flow rate of material can cause shrinkage and dimensional instability if not chosen carefully.
Lastly, cost is important for obvious reasons and can change in numerous ways, from availability, and material properties, to the use of material additives. If multiple plastic materials will meet your property requirements then cost may be the determining factor to produce your product to your specifications.
When it comes to injection molding, one of the most crucial decisions you’ll make is selecting the right material. This choice significantly influences numerous aspects of your final product and the production involved in its making. Read on to explore a comprehensive understanding of this selection process and learn how to select the right injection molding material that aligns with your product objectives.
The Science of Injection Molding
Injection molding is a highly scientific process that requires a deep understanding of materials and their specific properties. The process typically involves melting plastic pellets and injecting them into a mold under high pressure. Once cooled, the material takes the shape of the mold, creating a precise replica of the intended design.
The choice of material plays a pivotal role in this process due to the unique properties each has, such as melting point, flow rate, and cooling time. These properties significantly impact the overall quality of your final product and, hence, require careful consideration during the material selection process.
Defining the Objectives of Your Injection Molding Project
Before diving into the vast world of materials, it’s essential to define the objectives of your injection molding project clearly. Understanding what you want to achieve with your product guides your material selection.
Consider factors such as your product’s intended function, its environment, and the desired lifespan. If your product frequently experiences extreme temperatures, select a material with a high thermal resistance. If your product needs to be lightweight yet durable, consider high-strength plastics. By defining your objectives upfront, it becomes easier to select a material that fulfills your current needs and anticipates future demands.
Cataloguing the Array of Materials Available for Injection Molding
The injection molding industry boasts a broad spectrum of materials, offering solutions that cater to various needs. From common plastics such as polypropylene to engineering-grade resins such as polycarbonate, the options are numerous.
Each material has unique properties, including strength, flexibility, resistance to heat and chemicals, and cost. More specialized materials, such as glass-filled nylon, offer enhanced properties, including higher tensile strength and rigidity.
Manufacturers can customize many materials by using additives to enhance color, flame retardancy, or other specific attributes. With the myriad of choices available, it is paramount to have a solid understanding of each material and its properties. A thorough understanding of the materials allows you to make an informed decision that will yield a successful product.
Deciphering Material Properties
Deciphering various material properties is essential for the best injection molding project. Key properties include tensile strength, flexural strength, and impact strength. Understanding thermal properties, particularly the heat deflection temperature and melting point.
Additionally, consider the material’s resistance to chemicals and UV radiation if your product faces harsh environments.
Selecting the Appropriate Material Based on Product Functionality
A product’s functionality needs to meet the user’s goals and needs, and selecting the best material for the product assists in this endeavor. This functionality involves a detailed analysis of how to use your product and the various conditions it will experience.
For instance, a kitchen utensil that comes into contact with food and endures high temperatures requires a food-safe, heat-resistant plastic such as polypropylene. On the other hand, a protective helmet needs a material that offers high impact resistance, such as polycarbonate.
It’s also worth considering regulatory requirements that may apply to your product, ensuring the material used complies with all necessary standards. This careful alignment of product functionality and material properties optimizes your final product’s performance, safety, and longevity, leading to a successful injection molding project.
Assessing Material Costs
In addition to the technical properties, cost is another crucial aspect to consider in the material selection process. Material costs vary significantly, from inexpensive, commonly-used plastics, such as polyethylene, to higher-cost, specialized resins. Understanding that the cheapest material may not necessarily be the most cost-effective in the long run is essential.
A material may be inexpensive to purchase, but if it doesn’t align with your product’s functionality and durability requirements, it could lead to product failure and increased costs. Conversely, a more expensive material might provide superior performance and longevity, offsetting its initial higher cost over the product’s lifespan. Plastic injection molding manufacturers such as Polymer Molding consider the initial price and the long-term value when assessing material costs to offer the best product at an affordable price.
Prioritizing Aesthetics in Product Design
While a product’s structural integrity and functionality are paramount, you shouldn’t undermine aesthetics. In the world of product design, the look and feel of a product play a crucial role in its market appeal. The choice of material significantly influences the product’s aesthetic elements, including color, texture, and gloss.
Certain materials, such as polystyrene, are easy to add color and finishes to. Others, like acrylic, offer a high-gloss, transparent look, perfect for products that require a glass-like appearance. Careful consideration of the material’s aesthetic potential enhances the product’s appeal and helps you choose the best material for plastic injection molding.
Environmental Impact of Material Selection
In the era of increasing environmental concerns, you shouldn’t overlook the ecological impact of injection molding material selection. Determining the sustainability of a material involves considering its life cycle from extraction, production, and usage to eventual disposal.
Some materials, such as biodegradable plastics, minimize environmental harm as they break down naturally over time. Other materials are recyclable, reducing waste and the need for new raw materials. Incorporating sustainability into material selection enhances your company’s reputation for social responsibility. Additionally, regulations related to the environmental impact of materials are tightening in many sectors, making it prudent to select materials that anticipate and meet these evolving requirements.
The Impact of Material Choice on the Manufacturing Process
The choice of material for your injection molding project doesn’t just influence the final product—it plays a significant role in the manufacturing process. Materials differ in their melt flow rate, cooling time, and the pressure required for molding, and these factors directly impact the efficiency of the production run.
For instance, materials with a high melt flow rate and quicker cooling time can speed up manufacturing, leading to higher output and potentially lower costs. On the other hand, some materials may require specialized molding techniques or additional processing steps, which could increase the complexity and cost of manufacturing.
Common Mistakes in Material Selection
Avoiding the most common industry mistakes is an essential part of ensuring you make the best choice for your product’s material. One of the most common mistakes in material selection is neglecting to consider the full range of a material’s properties and focusing solely on cost. This neglect leads some manufacturers to select a material that is ill-suited to the product’s functionality or durability requirements.
Another error is failing to consider the material’s impact on manufacturing. Materials behave differently during molding, with varying melt flow rates, cooling times, and pressure needs. Neglecting these aspects leads to inefficiencies in production or unexpected costs.
Additionally, overlooking regulatory requirements or the material’s environmental impact leads to compliance issues and potential reputational damage. Avoid these pitfalls by comprehensively evaluating all relevant factors in material selection.
In conclusion, selecting the right material for your injection molding project is a multifaceted process that requires a deep understanding of the material and its numerous aspects. Avoid common mistakes and examine how the chosen material may affect the final product. Every decision made in the material selection process has a profound impact.
Shrinkage is a characteristic of the polymer used to manufacture the part. The molded part will shrink down in size for up to 24 hours post molding effecting the part geometry. Determining the proper amount of shrinkage to use to design and build the mold is both art and science. Every polymer has a unique shrink rate that must be applied to the 3D part model. Unfortunately, shrink rate information is not always provided by the polymer vendor. In some instances when it is provided, it is typically a wide range. Careful thought must go into selecting the proper shrinkage and it is necessary that the grade of polymer be selected prior to designing the injection mold. A good Plastics Engineer has the experience to help make the best shrinkage decision for your product and polymer.
Material shrinkage can vary with part and mold design; thick walls will shrink more than thin walls, variation in part thickness or geometry will cause differential shrinkage and warping; flow direction will also effect shrinkage especially when using fiber filled polymers.
Shrinkage is also influenced by process conditions. As cavity pressures rise, shrinkage will normally decrease. The mold and melt temperature will also greatly effect shrinkage. Cooler molds will reduce shrinkage while hotter melt temperatures will increase shrinkage.