Plastic Injection Molding

Our custom plastic injection molding consists of six injection molding presses ranging in size from 120T to 1450T. We also cover insert molding and in-mold appliques (decorative films).

In addition to our new plant in Roseville, Mich., Special Tool & Engineering has two vacuum form presses. One of our state-of-the-art presses covers in-mold appliques and our other press handles vinyl and leather wraps. Our assembly operations makes us experts with manual fasteners, heat stake and ultrasonic welding and tape.

Special Tool’s employees are extremely versatile in skilled operations. As an industry-leading company, we have a culture for quality, maintaining aluminum production molds, and creating custom hand built products, ranging from design, constructing and molding.

We have experience with engineering grade resins such as:

  •  Nylons
  •  PP
  •  Polyesters
  •  PE
  •  Acetal
  •  TPO
  •  ABS
  •  TPE
  •  PC
  •  PC+ABS

Advantages of Plastic Injection Molding

There are many advantages to using injection molding. However, it is vital to understand these advantages before deciding whether injection molding is right for your business. These are the advantages to consider:

Reduce Costs: Perhaps the most significant advantage of plastic injection molding is it is quick and affordable. The molding process is speedy, allowing for a high output rate. Increased output will streamline your processes and will enable you to make more money in less time. Once the injection molds have been produced once, countless parts can be created from a single mold. Typically, a new item can be made once every 30 seconds. Also, unlike traditional manufacturing methods, molding reduces the likelihood of sharp edges. The final product is smooth, precise and built precisely to your specifications.

Eliminate Waste and Increase Efficiency: The molding process is so precise that only the required amount of plastic is needed. You won’t have to worry about plastic being thrown out due to a faulty manufacturing run. The molding process is also predictable and you can always recycle excess plastic to minimize waste.

Integrate Design Complexity: Plastic injection molding is ideal for high-production items that must be extremely uniform. Objects with complex designs, such as complicated electrical components, are well suited to the molding process. The original molds are put under a large amount of pressure and heat during the molding process. Therefore, it is feasible to create a mold with a lot of detail and complexity.  

Increase Strength and Material Versatility: Strength is one of the critical factors you should consider when designing a plastic injection molded item. You need to fully brief the designer and let them know if the item should be ridged or malleable. The piece’s strength is vital to determine during the design process to integrate the right number of ribs and gussets. Understanding how the part may be used and the environment in which it may be used is also essential.

Material is also a consideration during the design process. Choosing the right material can provide the proper structure for the item and increase its strength and stability. You also have the flexibility to play around with color. The same mold can be used to create many products of different colors and shades. You can also use other materials with the same mold if you choose. Being meticulous during the design process ensures you get a robust and stable output.

Special Tool and Engineering is a recognized leader in creating high-quality, affordable injection molds. We specialize in helping operators streamline their processes and increase product reliability.


Injection molding can be used to create multi-layered items with multiple materials. The process starts similar to any injection molding process. A steel, aluminum or other material is used to create a mold. The mold is made to not only match the specific component being created, but also to allow for expansion or shrinkage of the specific material being used.

After the first layer is created, a second layer is molded over the first. This layer can be a different color, material or both. Just like single-step injection molding, two-step overmolding is  a fast and efficient process to create in-demand components at high rates of production.

Common Applications

Manufacturers use overmolding to mold two materials together into a single, efficient component. Here are a few common examples of this production method:

  • Automotive steering wheels
  • Hand tools
  • Power tools
  • Phones
  • RFID

Every step needs to be carefully engineered to create a fully finished product at the right dimensions. Overmolding procedures need to take into account the shrinkage of both layers of material to ensure a proper fit.

Benefits of Overmolding

This industrial process is more cost-effective than two separate injection molding stages. By molding the second layer of material directly over the first, the process removes a post-molding fabrication step.

It also creates a more durable product with a longer service life. Post-molding fabrication and installation can create weak points in the component, causing it to break or become compromised with heavy use.

Products with two layers of plastic or other material can be used in a wider range of applications. Mold a seal directly onto a component or create a soft, textured grip on a handle without compromising its rigid structure. Two diverse materials can come together to create a single component with improved qualities and greater areas of use.

Insert Molding

Another two-step process that can save time and improve product efficiency is insert molding. An insert molding production line uses the standard injection molding process, but inserts a fully finished component into the mold.

Similar to overmolding, this process can be used to create a dual-material component for complex tasks. It can also be used to create complex shapes and dimensions that would be difficult in a single injection molding step.

Typical Uses of Insert Molding

Insert molding is used to create precision components, often with two separate materials. Here are some common components that are efficiently produced using this process:

  • Air ducts for automobiles
  • Medical syringes
  • Industrial equipment components
  • Fine mesh filters
  • Hose connectors for vacuums

Filters insert a fine mesh to add a second material to the insert molded product. Hose connectors and air ducts insert a distinctly different shape into the product for a complex component that would otherwise be difficult to create.

Advantages of the Insert Molding Process

Injection molding, overmolding and insert molding all offer distinct advantages for industrial manufacturing. Consider insert molding if you need to create a small, specialized component using injection molding technology. This process allows you to insert a complex part into a small injection mold, creating components like medical syringes at precise design specifications.

This process also allows for faster assembly times for complex parts. Connecting two components during the injection molding process reduces the need for post-injection assembly, similar to overmolding.

Create the components you need at less cost and production time using insert molding. Encapsulating an insert in plastic removes the need to create multiple components and seal them together. The alternative to insert molding in this instance is to create two separate pieces, install the insert and then connect them together. Insert molding removes this post-production task and allows you to save money on your mass-produced injection molded components.

Plastic Injection Molding Gallery


33910 James J. Pompo
Fraser, MI 48026

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Phone: 586-285-5900
Fax: 586-285-5901

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