Injection Molding | Aero-Plastics

Aero-Plastics specializes in injection molding projects such as insert molding and other value-added services. We offer injection molding PEEK, Ultem and other high-performance engineered resins, plus commodity resins such as polypropylene, polyethylene, polystyrene, ABS, and nylons.

As veterans in high-performance polymers and engineered resins, you can rely on us to provide expert guidance on materials. All of our tooling is built to Class 103, 102, and 101 industry standards.

What is Injection Molding and How Does It Work?

Injection molding is a manufacturing method in which molten material — commonly a thermoplastic or polymer– is injected into a mold in order to produce a part.

A heated barrel mixes the desired material and injects it into a mold cavity. When it cools, it hardens to the shape of the cavity, creating the desired product. Molds are usually designed by an engineer or industrial designer, who then further refines the mold with precision machining.

Use cases for injection molding vary widely; it can be used to manufacture molds and parts from tiny components to large automotive parts.

Injection Molding Machines

Injection molding machines consist of two units: a clamping unit and an injection unit.

The clamping unit is used to open and close a die in the machine, and to eject the final product.
The two methods for the injection unit are a straight-hydraulic, in which a hydraulic cylinder opens and closes the mold, or a toggle.

Toggle clamping uses the injection unit to melt the material, then inject it into a mold. In a process called metering, a screw then rotates to gather melted material from the hopper, until enough is accumulated to begin the injection process. The machine controls the injection speed via the rotation of the screw.

Injection Molding Machine | Aero-Plastics

The Advantages of Injection Molding

Manufacturers typically turn to injection molding to produce a large volume of a particular part, for several main reasons:

  • Low scrap rates: Compared to traditional manufacturing processes (i.e. CNC machining), injection molding results in minimal scrap rates. Waste from the injection molding process comes from the sprue, runners, gate locations, and overflow material (also called flash).
  • Consistent & repeatable: The molds used for injection molding offer one of the strongest guarantees that parts will match the original. This lends to brand consistency and part reliability.
  • Easily scalable production: Injection molding is a perfect solution for scaling large volume production, due to the simplicity and consistency of the process.
  • Low price per unit: After setup costs are paid off, the price per unit of products manufactured via injection modeling drops steeply, and remains extremely low. The more parts produced, the lower the individual cost.

What Plastics & Resins Are Used in Injection Molding?

Aero-Plastics has the ability to mold nearly all engineered resigns, including:

  • Polypropylene
  • Polyethylene
  • Acrylonitrile Butadiene Styrene (ABS)
  • Polycarbonates
  • Nylon
  • PEEK
  • Ultem

Important Factors to Consider for Injection Molding


Before selecting injection molding as your production method, it’s important to first determine how many parts need to be produced in order to make it cost-effective. You may do this by figuring out how many parts it will take to break even on the project, and building in a conservative margin.


Injection mold production requires a significant up-front cost, in order to prepare the mold and manufacturing setup. However, this subsequently ensures a low production cost after that initial investment is paid off.

Part and Tool Design

If a part is to be produced by injection molding, this must be considered in its design — this includes simplifying its geometry and number of components as much as possible. The mold should be designed with a goal of minimizing the risk of defects during the production process.


For injection molding, it’s prudent to minimize cycle time as much as possible. The more time you can cut from the cycle, the more money you’ll save.

It also helps to keep assembly simple — the more parts required in the setup, the higher the cost.

Aero-Plastics’ Injection Molding Tolerance Objectives

Injection molding tolerances, listed below, are directly related to the material to be molded; part size and part geometry. We review parts and tolerances on a case-by-case basis during quoting, and use a Design for Manufacture process to align your project goal to our manufacturing methods.

We want you to achieve the best value possible — so our experts work with you on these tolerance objectives. Over-specified tolerances can increase project costs, and we understand how to minimize them without sacrificing product quality.

For tight tolerance parts, we can combine molding with post-mold machining operations. We’re on the Boeing QPL for all types and classes of molded parts, and an approved molder on the D14426 for BAC 5321 class II injection molded parts.

Our molding tolerance objectives:

  • The material used dictates the tolerances that can be maintained.
  • Size and part geometry influence the tolerances.
  • Aero-Plastics reviews all injection molded quotes to ensure the part quality and objectives can be delivered.
  • Aero-Plastics uses a Design for Manufacture process to attain part quality.
  • In cases of very tight tolerances, we can use post-molding machining processes.

Frequently Asked Questions about Injection Molding

How much does injection molding cost?

While injection molding has a significant up-front cost, it quickly turns into one of the most cost-effective methods of manufacturing parts.

We’d love to give you a quote. Use this simple form, and we’ll respond within 1 business day.

Our mantra — “Driven by Dependability” — is founded on our adherence to our quality system, and remains the leading reason our customers keep coming back.

How do I design for injection molding?

We address the most important design concerns for injection molding projects above, in the Important Factors to Consider for Injection Molding section. Below are more helpful guidelines:

  • Materials should be specified and acknowledged by both parties early in the design process. This allows us to purchase large quantities of specific resins at major discounts, which we pass on to clients.
  • Designers should avoid sink marks in injection-molded parts. The recommended maximum wall thickness at the base of a rib or boss is less than 50-60% that of the perpendicular face wall.
  • Designers should take care to include steel safe areas in injection-molded parts. Tight tolerances such as snap fits, alignment features, and interlocking parts increase the risk of production error, because they’re difficult to replicate. Steel safe areas are designed with enough clearance to allow a molder to easily machine away steel in order to tighten up the clearances after initial test shots are molded.
  • Gate location is critical and should be specified and agreed upon by the designer, molder, and manufacturer. It affects appearance, warpage, tolerances, surface finish, wall thickness, and more.

Which polymers is injection molding used for?

The most common polymers and thermoplastics used for injection molding are acrylonitrile butadiene styrene, polyethylene, polycarbonate, polyamide (nylon), high impact polystyrene, and polypropylene.

What is custom injection molding?

Your project’s level of complexity is what determines the level of “customization” it requires — in other words, the level of engineering and design support required, analysis needed, and number of process technologies required.

While cheaper methods make for a quicker time to market, custom injection molding takes more care with part design, material selection, mold design, and process control in order to achieve more consistent and accurate end products.

Can metal be injection molded?

Yes. Injection molding can be used to manufacture metal parts, by a process called metal injection molding (MIM), in which metal powder is mixed with plastic and molded. The plastic is subsequently removed, and the remaining part sintered.

MIM allows us to produce intricate parts in a wide range of metals, including steel, stainless steel, and high-temperature alloys.

Mold Isometric | Aero-Plastics
Mold End Elevation | Aero-Plastics
Mold Cross Section| Aero-Plastics
Mold Finished Product | Aero-Plastics
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