Injection Molding

How Plastic Injection Molding Works

01 Part & Mold Design

A design analysis is highly recommended to optimize your tool and part designs for manufacturability. This process often uncovers issues that need to be fixed, such as inadequate draft, thick-to-thin wall transitions and poorly-designed bosses. These problems should be resolved before tool construction begins. Gating, cooling and venting are also important considerations during tool design.

02 The Molding Process

Plastic pellets are placed in a heated chamber, where they melt. The two halves of the mold are tightly clamped together. The molten plastic is injected under high pressure into the closed mold cavity through the runner and gate system. The amount of material and pressure is precisely calculated so the resin fills the mold completely. Cooling channels built into the mold help to cool it quickly. The part is then ejected.

03 Post-Processing

As a first step, any runners or flashing are trimmed from the freshly-molded parts. If inserts were not placed in-mold, they can be heat staked into the plastic to make it easier to assemble with other components. They may also be ultrasonically welded to other parts. Injection molded parts may be painted and are often pad printed or laser marked to add labels and instructions.

Advantages & Disadvantages of Injection Molding

Advantages

High-Volume Production

Injection molding is extremely efficient for producing large quantities of identical parts, with cycle times that can be as short as a few seconds.
Low Cost Per Part

For large production runs, the cost per unit is very low, making it ideal for mass manufacturing.
Low Labor Costs

Injection molding is highly automated, requiring only one operator to manage multiple machines, which significantly reduces labor costs.
Design Flexibility

Injection molding enables you to create complex and intricate designs with fine details.
Precision & Consistency

Injection molding produces parts with tight tolerances and a high degree of consistency from one part to the next.

Disadvantages

High Tooling Costs

The cost of creating the custom mold can be very high, sometimes reaching tens or hundreds of thousands of dollars, making it impractical for small production runs.
Long Lead Times

The design and manufacturing of the mold can take weeks or even months. Once production starts, the cycle time for each part can be lengthy, depending on its size, thickness, and complexity.
Design Limitations

Parts must be designed with the molding process in mind. Features like undercuts and sharp corners can be difficult or expensive to produce, and uniform wall thickness is generally required.
Part Size Limitations

While there is no theoretical limit to the size, very large parts require enormous, expensive machines and molds, and can be prone to issues like warpage and uneven cooling.

Is Injection Molding a Good Fit for Your Application?

Injection molding is one of the most common manufacturing methods in the world. Its versatility means it has found a home in many industries.

Medical

Injection molded components are commonly used in surgical tools, including scalpel handles, forceps and clamps. They are also found in knee and hip joints and dental implants. Finally, injection molded components are used in medical instruments like MRI machines.

Automotive

Injection molding’s versatility and the durability of the parts it produces mean they’re found just about everywhere in the interiors and exteriors of today’s automobiles: Bumpers, dashboards, cup holders, wheel covers, mirror housings, for example.

Electronics

Look for injection molded parts in device casings and enclosures, housings for computers and related equipment, electrical switches, battery enclosures and connectors for networking cables.

Case Studies Block

Specialty Molding Options

Fathom offers multiple options for more complex injection molding needs:

Multi-Cavity Molding

We can mold multiple parts in a single tool, depending on their size. This is especially valuable if you need a lot of small parts produced quickly.

Family Molds

A special type of multi-cavity tool that enables you to produce several types of similar parts (such as right and left sides or the top and bottom of a product) using a single tool.

Insert Molding

A metal part, such as a threaded component that will accept a screw, is placed into the tool. Plastic is then molded around it. In some cases, inserts are “hot staked” into the parts after they are molded. Inserts are often used in parts that will become part of a larger assembly.

Overmolding

A part is first molded using rigid plastic. A softer material is then molded over the top of it so that the finished part is easier and more comfortable to hold. Overmolding is done in a single tool using an automated two-step bi-molding process. It’s a complex process that requires a team of experienced injection molding technicians to get it right.

Two-Shot Molding

We build bi-injection rotary tools that enable two-shot molding – a process where two materials are molded together in a single cycle.