Injection molding is a widely utilized manufacturing process that involves injecting molding material into a metal mold to produce parts and products. This process is highly suitable for the production of large quantities of complex, high-precision, and highly repeatable components. As the process requires heating polymers to a molten state and maintaining that state until they are injected into the mold, careful consideration and equipment capable of handling liquid polymers are necessary.
Well-known polymers such as polypropylene, polyethylene, and even nylon are relatively easy to handle in this process. Not only do they melt at relatively low temperatures (between 150-175°C), but they are also quite manageable in their liquid form since they do not release any corrosive gaseous effluents. Additionally, they exhibit very predictable melt flow and shrinkage, which means that parts can be developed quickly using off-the-shelf indicators typically provided by raw material suppliers.
High-heat thermoplastic structures:
High-temperature thermoplastics (as all polymers) comprise two molecular structures:
- Amorphous (random order)
- Crystalline (specific order)
| Amorphous |
Semi-crystalline |
1. Strength, stiffness
2. Isotropic dimensional stability
3. Toughness and impact resistance
4. Clarity
5. Good surface appearance |
1. Chemical resistance
2. Wear resistance
3. Lower ductility and impact strength
4. Opaque
5. Low stiffness and creep resistance at high temperatures
6. Poor dimensional stability |
High temperature plastics vs metals:
High-temperature thermoplastics, with a continuous operating temperature above 150°C, owe their essential performance qualities, such as heat resistance, durability, stability, and mechanical strength, to their high-temperature resistance.
- wear and chemical resistance.
- weight savings in many applications (e.g., automotive).
The table below provides a concise overview of the benefits and drawbacks of using high-temperature thermoplastics as a replacement for metals, highlighting their temperature resilience, weight advantages, and corrosion resistance, alongside their lower strength, potential for creep, and cost implications.
| Advantages Over Metals |
Disadvantages Over Metals |
1. Low density
2. Good noise and vibration damping
3. Electrical and thermal insulation or adjustable conductivity
4. Good chemical and corrosion resistance
5. Increased design freedom
6. Adaptable to high volume production processes
7. Adaptable to property modification for specific applications |
1. Greater thermal expansion
2. Poorer creep resistance
3. Lower thermal resistance
4. Susceptible to UV, moisture, and oxidation
5. Not considered to be a vapor barrier
6. Lower mechanical properties
7. Plastic parts generally must be redesigned over metal parts |
