How to Customize Injection Molding

Injection Molding

Plastic injection molding remains the most versatile of plastic molding processes. A comprehensive range of injection molding machinery exists in differing tonnages or pressure ratings, and common material choices include multiple plastic resins and a broad range of additives used to alter the physical properties of final parts. Based on machine type and material choice, injection molding can produce items ranging from large automobile parts to small precision medical components.

While fabricating steel molds for plastic injection molding is expensive, this cost is offset by the low cost-per-part offered by the process. Low part cost, design flexibility, a variety of material and finishing options, and expansive customization techniques have made injection molding one of the most popular manufacturing processes available for engineers.

The standard injection molding manufacturing process follows these steps:

• Plastic is heated to its melting point.
• The melted plastic is injected into the mold with a nozzle until all cavities are filled.
• The mold is cooled, creating a finished part.
• The finished part is ejected from the mold automatically using pins.

How to choose Material  for Plastic Injection Molding

Selecting the appropriate resin for a design is critical for the ultimate functionality of the final part. Recent advancements in polymer science have produced a comprehensive range of plastic resins that can facilitate a wide variety of mechanical and aesthetic properties in molded parts.

There are five factors to consider when choosing a plastic resin:

1. The aesthetic appearance of the part (color, texture, transparency)

2. The strength, stress, and flexibility/rigidity requirements of the part

3. Required resistances (temperature, chemical, weather, etc.)

4. Regulatory requirements (FDA, RoHS, REACH, NSF)

5. Part service life

With so many materials available, resin sourcing can be confusing. Working with an experienced injection molding provider ensures you’ll get the correct resin for your design.

How to fabricate Molds for Plastic Injection Molding

Constructing the molds used for plastic injection molding is the most time-consuming and expensive part of the process. These tools require a great deal of precision and specialized consideration by talented design engineers and toolmakers. An error in the mold could result in thousands of parts being ruined. As such, quality control and careful testing before full production are critical to project success.

While mold-making is the most expensive step in the plastic injection molding process, a quality precision mold will last for many years and can potentially facilitate the creation of millions of products. When creating a mold, there are multiple variables to consider, including:

• Core metal. Most high-volume molds are fabricated from stainless steel. The steel can be machined and fabricated to facilitate close tolerances and complex geometries, but still lasts for many years. At The Rodon Group, we still use many stainless steel molds that were created decades ago.

• Required cavities. Mold cavitations should be maximized to support higher efficiency during production. Also, using one mold per part in a multi-cavity tool typically facilitates uptime and high precision, while family molds tend to require significant maintenance and produce inferior parts.

• Mold base. A mold base is required to hold all mold cavities, components, and inserts in place during manufacturing. The cost of a mold base can vary wildly depending on customization requirements, size, and material.

• Machining. A variety of machining capabilities will be required to implement necessary customizations into the mold, such as cavities, cooling lines, cores, and ejectors.

• Complexity. More complex part designs will increase the ultimate cost of constructing a mold.

Plastic Injection Molding Costs

The start-up costs associated with plastic injection molding can vary wildly based on the complexity of the design. The injection mold itself is typically a significant investment—even more so if the design requires tight tolerances, intricate geometries, or if the mold has multiple cavities. Other factors that may influence overall costs include:

• Resin type
• Part size
• Cycle times

Ultimately, the costs of plastic injection molding scale downward as volume scales upward. This is why plastic injection molding is considered a high-volume process—the set-up costs are often too prohibitive for small and medium production runs.