When it comes to plastic parts, is thermoforming, injection molding or reaction injection molding better? Each of these methods of plastics manufacturing has its benefits; and the ideal one for a given product depends on a number of factors, including the size and shape of the part, the size of the run itself and timing. Here’s a brief overview of each process, its advantages and what parts you may want to consider for each.
In thermoforming, a 3D mold is created from aluminum. A flat sheet of plastic – typically available in a range of material finishes, colors and thicknesses – is heated until it becomes pliable. From there, the plastic is either pressure formed or vacuum formed. In pressure forming, the plastic sheet is pressed against a 3D mold by vacuuming out the air between the sheet and the mold, and applying air pressure above the plastic sheet. In vacuum forming, the plastic is pressed around a single mold, and the air is suctioned out.
- Time: Thermoforming has a fast turnaround time (time to market can be weeks instead of months).
- Cost: The creation of a thermoforming mold generally costs less than an injection-molding one.
- Size: Thermoforming can create very large parts.
- Appearance: Thermoforming has a high-quality finish out of the mold, and can be easily painted if desired (unlike injection molding and RIM, which typically require painting).
- Recyclability: Thermoforming produces fully recyclable products and byproducts.
- Durability: There is zero residual stress in a molded part, leading to superior impact performance.
- Point-of-purchase displays
- Multi-part medical devices and lab equipment
- Industrial and outdoor equipment enclosures, bezels, housings and covers
- Dunnage material trays or pallets
- Fitness and office equipment
Injection molding and Reaction Injection molding
Injection molding begins with a double-sided 3D mold made from steel, aluminum or a beryllium-copper alloy. Thermoplastic pellets, which are available in a range of materials and colors, are heated until they liquify and then injected into the mold, under extreme pressure, which can leave a molded part with residual stress.
In reaction injection molding, two liquid raw materials (polylol and isocyanate) are mixed and injected into a heated mold. When the liquid touches the heated mold, its chemicals react and expand to fill the mold’s cavity. Reaction injection-molded parts have a very thick wall and can be used to encapsulate products.
- Cost: The per-piece production cost for injection molding is generally less expensive than with thermoforming.
- Variance: Unlike thermoforming, reaction injection molding allows for variable thickness within a single part.
- Detail: Injection molding can produce small, intricate parts.
- Automotive parts
- Electronic parts
- Bottle caps, lids and small containers
- Small appliance parts
- Small plastic goods and accessories
If you’re still not sure which process is best for you, reach out to a trusted plastics manufacturer.