From Prototype to Production — Selecting the Right Injection Molded Materials
“If it ain’t broke, don’t fix it.” Are you following this rule by choosing the same materials for your injection molded products just because they worked well in the past? It’s understandable, but selecting the right injection molded material is a critical yet challenging task due to numerous options. However, this approach may not always be the best choice. To select the best injection molded material, product designers have to thoroughly understand the material properties and consider the specific application needs. Let’s dive into these further in this article about thermoplastic materials.

Thermoplastic Materials Classified According to Molecular Structure

Thermoplastic materials can be classified based on their molecular structure into two main categories: amorphous plastics and semi-crystalline plastics.
1. Amorphous Plastics: These plastics have a disordered molecular structure both in molten and solid states. When cooled from a molten state, they transition from a rubbery state to a glassy state below their glass transition temperature. Common examples include PC, PPO, ABS, PMMA, PVC, and PEI.
 
2. Semi-crystalline Plastics: These have a partially ordered molecular structure in their solid state, forming crystalline regions that are denser and more tightly packed. The degree of crystallinity depends on the molecular structure and molding conditions. Examples include POM, PET, PBT, PA, PPS, and PEEK.

Characteristics of Amorphous and Semi-crystalline Plastics

Plastic Classification Material Characteristics Amorphous Plastics Semi-crystalline Plastics Molecular Structure Common Plastics Specific Gravity Tensile Strength Tensile Modulus Ductility Impact Resistance Maximum Service Temperature Shrinkage and Warpage Flowability Chemical Resistance Wear Resistance Creep Resistance Hardness Transparency Effect of Glass Fiber Reinforcement PC, PPO, ABS, PMMA, PVC, PEI Lower Lower Lower Higher Higher Lower Lower Lower Lower Lower Lower Lower Higher Lower POM, PET, PBT, PA, PPS, PEEK Higher Higher Higher Lower Lower Higher Higher Higher Higher Higher Higher Higher Lower Higher

Applications of Common Thermoplastic Materials

1. General-purpose Plastics: These have lower mechanical properties and are used for non-structural applications due to their ease of molding and low cost. Examples include PE, PP, EEA, and PVC, which are widely used in films, pipes, footwear, containers, and packaging materials.
 
2. Standard Engineering Plastics: These materials have moderate mechanical properties and are used in engineering for non-load-bearing applications. Examples include PS, HIPS, ABS, AAS, ACS, MBS, AS, and PMMA, commonly used for housings and casings.
3. Structural Engineering Plastics: These have higher mechanical properties and are used for structural components that bear significant loads. Examples include PA, PPO, POM, PC, PBT, and PET, widely used in various housings and structural components.
 
4. High-temperature Engineering Plastics: These maintain high mechanical properties under high temperatures and are used in applications such as automotive engine parts, oil pump covers, and high-temperature electrical connectors. Examples include PI, PPS, PSF, PAS, and PAR.
5. Plastic Alloys: These are high-performance, functional, and specialized materials created by blending or grafting different plastics, such as PC/ABS, PC/PBT, and PC/PMMA. They are used in automotive, electronics, precision instruments, office equipment, packaging, and construction materials, enhancing performance while reducing costs.
6. Thermoplastic Elastomers (TPE): These materials exhibit properties between rubber and plastic, offering elasticity and easy processability. They are used in automotive, electronics, electrical, construction, engineering, and daily-use products like sheaths, tubing, cables, gaskets, parts, footwear, and adhesives.
7. Modified Plastics: These are enhanced by adding additives, fillers, and reinforcements like glass fibers, conductive fibers, flame retardants, impact modifiers, and stabilizers to improve specific properties such as flame resistance, mechanical strength, impact resistance, high-temperature resistance, wear resistance, and conductivity. An example is Fiberglass Reinforced Plastics (FRP), a high-strength, high-performance material used in automotive, machinery, electronics and ships, offering a lightweight, rust-free, cost-effective alternative to traditional metals.

Pros and Cons of Common Thermoplastic Materials

Explores the pros and cons of several common thermoplastic materials, providing valuable insights for material selection. Below is a detailed analysis of these materials.
Injection MoldedMaterials Advantages Disadvantages Non-flammable, weather-resistant, geometrically stable, highly resistant to oxidizers, reducers, and strong acids Corroded by concentrated sulfuric acid, nitric acid, and alkali, poor flow characteristics, poor processability Excellent geometric stability, superior insulation properties, transparency, electrical insulation, and good limiting oxygen index Strongly oxidized by corrosion, corroded by concentrated sulfuric acid and nitric acid, and can swell and deform in some organic solvents Moderate mechanical properties, easy to print and electroplate, good flow, high dimensional stability, good comprehensive characteristics Susceptible to solvent-induced stress cracking, poor weather resistance, cannot withstand high loads Excellent optical properties and weather resis - tance (such as UV resistance) Low impact strength, poor wear resistance, poor fatigue resistance High surface hardness, good rigidity, good wear resistance, excellent friction properties, good fatigue resistance Not resistant to high temperatures, poor thermal stability, poor acid resistance High impact strength, high stability, high gloss, flame retardant, anti-pollution, good dimensional stability Glass strength low, prone to stress cracking, poor resistance to acid and alkali, easy to print, poor dimensional stability Good mechanical strength and rigidity, excellent wear resistance and lubricity Poor dimensional accuracy, high thermal expan - sion and water absorption, poor wear resistance, poor aging resistance, poor light aging resistance One of the toughest engineering thermoplastics, excellent chemical stability, mechanical strength, electrical insulation properties High crystallization shrinkage rate, poor dimen - sional stability, poor moisture and thermal resistance Good mechanical properties, high temperature resistance, chemical resistance, good wear resistance Poor high-temperature resistance, easy aging Combines the excellent properties of PC and PBT, with high strength, toughness, and heat resistance, good dimensional stability / Combines the rigidity of PC and the toughness of ABS, with good impact resistance and heat resistance, good dimensional stability / PVC PS ABS PMMA POM PC PA PBT PPO PC/PBT PC/ABS

Work with Engineering Experts

Material properties can significantly impact component design, including wall thickness, rib thickness, screw hole dimensions, and more. With over 20 years of experience, RPWORLD provides comprehensive manufacturing solutions to help you navigate these complexities and optimize your product design, and MORE BENEFITS:
1. Expert Guidance: Our engineers help you select the best materials and design for your application, ensuring optimal performance and cost-efficiency. Thermoplastics share similar properties, but differences can make one material more suitable than another based on your specific requirements.
 
2. Advanced Injection Molding: quipped with state-of-the-art presses and robot arms, our facility produces high-quality parts using 100+ engineering-grade plastics. We handle production runs from 100 to 100,000+ pieces.
 
3. Rapid Prototyping and Production: Our on-demand services can accelerate your product development by up to 80%, delivering parts in as fast as 7 days.
As we all know that this is a pocket-sized guide that lists specific material properties to help you choose the right materials for your injection molded parts. Contact Us now to get additional guidance.