Deciding Between Plastic Thermoforming and Injection Molding – The Choice is Not Always Obvious

 

Injection Molding vs Plastic Thermoforming - Deciding when the choice is not obvious

Both injection molding and plastic thermoforming have widespread uses in a long list of industries. Each process has some unique features and benefits that are often advantageous for a specific application. In these instances, the choice to manufacture with plastic thermoforming or injection molding may be very obvious. This is most apparent in production volume. Low to mid volume tends to favor thermoforming, while high volume is usually more cost effective with injection molding.

However, a product’s needs and the capabilities of these two processes sometimes overlap. A part’s geometry may seem better suited for injection molding, but in a limited production run, but it may be drastically more cost effective to manufacture it with plastic thermoforming. This is just one example of an application where deciding between injection molding and plastic thermoforming may not be a clear choice. Selecting the right method in these situations requires a deeper appraisal of the features, benefits, and costs associated with each process.

The Clear Choice

As mentioned above, there are some instances when the type and specifications of an application drastically favor one or the other plastic manufacturing process when the choice is between injection molding or plastic thermoforming.

Injection Molding

Injection molding offers the key benefit of cost effectiveness at the mass production scale. When an application requires the production of more than 3,000-5,000 Estimated Annual Usage (EAU) identical parts with uniform wall thicknesses, injection molding often is the clear choice. This can be attributed to a high upfront tooling investment that is gradually offset by a generally low per unit manufacturing cost. The volume range of 3,000 – 5,000 is due to a variation on part cost in respect to part size. Smaller parts are generally cheaper to manufacture than larger.

  • Part production volumes > 3,000- 5,000
  • Uniform part wall thickness required

Plastic Thermoforming

Plastic thermoforming, on the other hand, has a substantially lower tooling investment and a slightly higher per unit Cost comparison for tooling and parts, pressure forming vs. injection moldingmanufacturing cost. This equates to a much lower total part cost at low to moderate part volumes. Plastic thermoforming becomes the clear choice when the volume of manufacturing is less than 3,000 – 5,000 parts per estimated annual usage. This process also has the capability to produce single parts with very large dimensions, whereas the injection molding process is limited to single part sizes of about 4 feet x 4 feet.

  • Single part dimensions > 4’x4’
  • Part production volumes < 3,000 – 5,000 EAU

Considerations When the Process Choice Is Not Clear

If your part or project doesn’t require a uniform wall thickness, large single part dimension, or has a volume requirement that is in the mid thousands, then you have landed in an area where the capabilities of plastic thermoforming and injection molding may overlap, and your process choice is not so obvious.

The good news is that you are now no longer handcuffed to a process that, while cost or size necessary, may not have the most comprehensive scope of benefits that would contribute the greatest to the success of your project.

Here are some points to consider for each process that can be taken advantage of or avoided now that you are free to choose a manufacturing method better suited to your project’s needs.

Plastic Thermoforming:

  • Large single part capability (maximum dimensions approximately 10’ x 18’)
  • Short lead time ( 6-12 weeks )
  • Able to reproduce injection molded level detail
  • Smaller investment in tooling
  • Lower equipment capital investment leads to lower set up and machine time costs
  • Can produce thinner wall parts than injection molding, resulting in weight savings
  • Greater options for part surface finishing (textures, patterns, distortion printing, painting, etc.) that can be accomplished in the mold.
  • Multi material structures for cosmetic and engineering structure options (e.g. Acrylic/ABS)
  • Variable part wall thickness depending on depth of draw
  • Improved cost effectiveness at lower to mid volumes (< 3,000-5,000)
  • Lighter part weight compared to injection molding for most applications
  • Less molded in stress than injection molding
  • Twin sheet capability for hollow parts and added structure

Injection Molding:

  • Longer lead time (22-24 weeks)
  • Large investment in tooling
  • Cost effective at high volumes ( > 3,000 – 5,000)
  • Efficient material use
  • High level of precise part detail
  • Limited single part size capability (maximum dimensions approximately 4’ x 4’)
  • Finished parts often require post processing painting or finishing
  • Greater design freedom on single wall parts

Want More Information?

What you see above is just the tip of the iceberg when it comes to comparing these manufacturing processes. For more information and for assistance in choosing the right process for your project, please contact Productive Plastics and connect with our industry experts and engineers to see how we can put over 62 years of manufacturing experience to work contributing to your project’s success.

 

Please contact Productive Plastics for more information on the thermoforming process
Please download our complimentary thermoforming design guide for more information on the thermoforming process

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