Most plastic resins today are thermoplastics which allow excellent performance for most applications. Amafas also offers thermoset resins for high temperature, high dielectric, or optimum burn/smoke applications. See the table below for a full overview of these materials.
Thermoplastics soften when heated and become more fluid as additional heat is applied. The curing process is completely reversible as no chemical bonding takes place. This characteristic allows thermoplastics to be remolded and recycled without negatively affecting the material’s physical properties.
Thermoset plastics contain polymers that cross-link together during the curing process to form an irreversible chemical bond. The cross-linking process eliminates the risk of the product remelting when heat is applied, making thermosets ideal for high-heat applications such as electronics and appliances.
Features and Benefits
There are multiple thermoplastic resins that offer various performance benefits, but most materials commonly offer high strength, shrink-resistance, and easy bendability. Depending on the resin, thermoplastics can serve low-stress applications such as plastic bags or high-stress mechanical parts.
Thermoset plastics significantly improve the material’s mechanical properties, providing enhances chemical resistance, heat resistance and structural integrity.
Most molding machines operate using the same principles. Plastic pellets are loaded into a funnel-shaped hopper, which then feed into a screw that is inside a barrel. The turning of the screw moves/mixes the plastic from the hopper toward the mold in use. Heaters on the barrel add heat to the plastic until it melts inside the barrel. To inject the melted plastic, the screw is pushed toward the mold using hydraulics, or electric motors, pushing the molten plastic into the mold at high pressures. The plastic compresses as it moves through the runners and gate into the mold. The plastic expands once inside the mold cavity filling even the smallest feature of the molded part. The plastic then cools inside the mold which opens when the part has cooled enough to be handled. The entire process is computer controlled, producing consistent high-quality parts.
The tonnage of the machine is often used to describe the size of the part that can be molded, because it is a critical part of the process. The high pressure used during the process of injection tries to push the mold open. The clamping tonnage keeps the mold closed and sealed during injection. Typically, the mold is clamped with 3X to 5X the amount of force generated by the high-pressure injection. This ensures that the mold remains firmly clamped and does not open which might result in flash around the edges or sealoffs.
At AMFAS, we also address the shot size of the machine being used. Many suppliers do not review this, which results in an inferior product. Also, all plastics degrade quickly at high temperatures, burning and becoming brittle. They may discolor as well. We ensure that the shot size is 30-60% of the machine capacity to insure our parts are of the highest quality and that the plastic resin has not been degraded during the molding process.
OvermoldingIn several applications, we combine the strength and durability of machined metals with the cost-effective use of overmolded plastics. Transfer molding, or overmolding, is typically more labor intensive than operating an unattended injection molding machine but has advantages when plastics can be used for less critical areas of the component design. The use of overmolding in a plumbing application uses brass for the mechanical functionality and adds a threaded fitting which would be expensive if fabricated by other means. Amfas has also overmolded clear plastics with opaque resin for lighting applications that provide a clear lens in a single integrated piece.
Insert MoldingMany applications can be found which use molded inserts for screw threads for strength or metal inserts to improve wear surfaces when plastic may not provide the durability required. The resulting product is a single piece with the insert encapsulated by the plastic.
Reaction Injection MoldingReaction injection molding (RIM) is a special molding technique in which two or more plastics are chemically bonded to a polymer prior to being injected into the mold. RIM can streamline the fabrication process and reduce the need for secondary tooling. RIM lends itself to larger component manufacturing, having a relatively high strength-to-wight ratio, complex designs, and smooth finishes.
Thermoforming is the process where a plastic sheet is heated to a pliable forming temperature, it is then stretched over or into a single-sided mold, and then holds in place for cooling. The movement of the pliable plastic material around the single mold can be accomplished from pressure, a vacuum, or by mechanical means. Thin-gauge thermoforming is used primarily for cups, containers, lids, trays, and other products for various industries. Thick-gauge thermoforming can include parts such as door panels, appliance liners, and vehicle beds.
The plastic extrusion process involves melting plastic material, forcing it into a die to shape it into a continuous profile, and then cutting to length. The process is ideal for applications in which a final product has a constant cross-section.