3D Printing

A guide to using thermoforming, injection molding, or reaction injection molding

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.

Robotic trimming tools are often used in the thermoforming process. Photo courtesy of Ray Products

Thermoforming

The Process

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.

The Advantages

    • 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.

Best for:

  • 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

The Process

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.

The Advantages

      • 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.

Best for:

      • 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.

Ray Products
rayplastics.com
www.rayplastics.com/learn-about-thermoforming/thermoforming-vs-injection-molding/