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Injection Molding vs Thermoforming

Plastic Thermoforming Process vs. Injection Molding – How to Choose?

Injection molding and the plastic thermoforming process both 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 have been easily made in years past. However, as advances in manufacturing technology continue to evolve, the area where a product’s needs and the capabilities of plastic thermoforming and injection molding overlap is increasing. Selecting the right method in these situations requires a deeper appraisal of the features, benefits, and costs associated with each process.
  • What is Plastic Thermoforming?

    Plastic thermoforming is a manufacturing process used to create 3D formed plastic parts. The process begins by applying heat to a sheet of formulated thermoplastic. The now pliable thermoplastic is then stretched onto a temperature controlled mold to conform to a desired three-dimensional shape or part. This is accomplished through the application of either vacuum or positive pressure (vacuum forming or pressure forming). Once the part has been formed in the mold, it is then removed and any excess material is trimmed to exact design specifications. Secondary operations, if required, such as painting, silk screening, additional assembly, or attachment point bonding are accomplished to complete a finished part.
  • What is Injection Molding?

    Injection molding is a process that uses thermoplastic material in a heated resin form to produce 3 dimensional parts. Two sided and highly engineered injection mold tools are clamped together to form a 3D cavity of the desired part shape. The tool is then fed with melted plastic material into the cavity. The material is then allowed to cool to a solid state in the shape of the intended part design. The molded part is then ejected from the tool and any secondary finishing, such as surface painting, is applied to produce the finished part.

Comparing Plastic Thermoforming and Injection Molding

The choice to manufacture with plastic thermoforming or injection molding may at time 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. This is due primarily to differences in tooling complexity and cost between the two processes. 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, 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.

Plastic Thermoforming Key Points

  • Fast part processing and lead times (~ 6-12 weeks)
  • Complex part geometry and large size capability with little impact on lead time and cost
  • Significantly lower tooling cost than injection molding
  • Able to reproduce the same level of part detail as injection molding
  • Ideal for part runs from ~250 – 5,000 EAU (estimated annual usage)
  • Parts are produced with less internal stress than injection molding

Injection Molding Key Points

  • Ideal for small parts and large annual production volumes ( 3-5k / year or greater)
  • Large tooling investment - A double sided 3D mold is required
  • Extended lead times due to two sided mold construction and auxiliary requirements (~ 24 weeks)
  • Highly detailed and consistent part repeatability
  • Large capital investment
  • Controlled wall thickness and two sided part geometry

Product Development Cycle

The combination of tooling and production time provides a measure of comparison. For thermoforming (pressure forming), the typical tooling time is 0-8 weeks, and first production typically happens within 2 weeks of that. With injection molding, tooling usually takes 12-16 weeks with up to four more weeks for production. If time-to-market is an important consideration, thermoforming may be the preferred manufacturing technology
Product Development Cycle Thermoforming vs Injection Molding

Part Cost Comparison

Total Part Cost Injection Molding vs Plastic Thermoforming
The cost comparison chart uses the total aggregate cost of parts and tooling for a large plastic part. Total part cost is substatially lower for thermoforming below about 3,000 - 5,000 parts but beyond this volume, injection molding per part cost is typically more competitive. This is driven primarily by the difference in tooling costs between each processes.

Compare More Benefits and Key Manufacturing Data of Plastic Thermoforming and Injection Molding Processes

Above are just a few statistics and comparisons for plastic thermoforming and injection molding. Choosing the right plastic manufacturing process that fits your project’s unique manufacturing needs can be daunting. That’s why Productive Plastics has developed this comparison and selection guide for plastic thermoforming and injection molding processes. Inside you’ll find additional information that is valuable to manufacturing decision makers, design engineers and every member of an original equipment manufacturer (OEM) project team.

Click here to download Productive Plastics’ Plastic Thermoforming & Injection Molding Manufacturing Process Comparison and Selection Guide (PDF) now.

Injection Molding Comparison Guide

Download a FREE Injection Molding vs. Thermoforming Comparison and Conversion Guide from Productive Plastics.

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