Plastics : Compression Molding - Plastic making procedure -

A manufacturing process where plastic material (usually in powder or sheet form) is placed in an open, heated mold cavity, then compressed with high pressure between two heated mold halves, forcing the material to fill the mold cavity.

 
How compression molding works:

• The plastic is placed in a heated mold
• Heat and pressure is applied to the plastic
• The material softens and flows to fill cavity
• The plastic cools under pressure
• We remove the final product 

Advantages:

• Excellent for high-strength parts
• Low waste production
• Good surface finish
• Can handle complex materials
• Minimal internal stress in parts
• Good for high-volume production
• Works well with fiber reinforcements

Fiber reinforcements are strong fibers (like glass or carbon) added to plastic materials to improve their strength, stiffness, and durability. These fibers are embedded within the plastic to create stronger composite materials.

Disadvantages:

• Slower cycle times than injection molding
• Limited to simpler geometries
• Higher labor costs
• Less precise than injection molding
• Limited undercuts possible
• Material must be precisely measured

Undercuts are features in a molded part that prevent it from being easily removed from the mold, like a hook or lip that extends beyond the main body

Injection molding is a manufacturing process where molten plastic is injected under high pressure into a mold cavity, where it cools and solidifies into the final part shape.It works like squeezing toothpaste into a mold to create plastic products like toys, containers, or car parts.

Common applications:

• Electrical components
• Automotive parts
• Cookware handles
• Buttons
• Dishware
• Circuit breaker housings
• Appliance parts
• Composite panels
• Electrical insulators
• Kitchenware

Materials commonly used for compression molding:

• Thermoset plastics
• Thermoplastics
• Composite materials
• Sheet Molding Compounds (SMC)
• Bulk Molding Compounds (BMC)
• Glass-reinforced plastics

Thermoset Plastics: Plastics that permanently harden when heated and cannot be remelted or reshaped, like electrical outlets or countertops.
Thermoplastics: Plastics that can be repeatedly melted and reshaped when heated, like water bottles or food containers.
Composite Materials: Materials made by combining two or more different materials to create better properties, like fiberglass boats combining plastic resin and glass fibers.
Sheet Molding Compounds (SMC): Ready-to-mold sheets of reinforced polyester material that can be compressed into parts, commonly used for automotive panels.
Bulk Molding Compounds (BMC): Putty-like mixture of resin, reinforcements, and fillers that can be molded into parts, used for electrical components.
Glass-reinforced Plastics: Plastics strengthened by embedding glass fibers within them, like in boat hulls or car bodies.

Key process parameters for compression molding:

• Mold temperature
• Compression pressure
• Cure time
• Material amount
• Heat distribution
• Cooling rate

Cure time is the duration required for a thermoset plastic or resin to fully harden and achieve its final properties through a chemical reaction, typically involving heat, pressure, or other conditions.