What is Injection Molding:

Injection Molding is a manufacturing process for producing parts in large volume. It is most typically used in mass-production processes where the same part is being created thousands or even millions of times in succession.

Injection Molding Machine
Why Use Injection Molding:

The principal advantage of injection molding is the ability to scale production en masse. Once the initial costs have been paid the price per unit during injection molded manufacturing is extremely low. The price also tends to drop drastically as more parts are produced. Other advantages include the following:

Injection Molding produces low scrap rates relative to traditional manufacturing processes like CNC machining which cut away substantial percentages of an original plastic block or sheet. This however can be a negative relative to additive manufacturing processes like 3D printing that have even lower scrap rates. Note: waste plastic from injection molding manufacturing typically comes consistently from four areas: the sprue, the runners, the gate locations, and any overflow material that leaks out of the part cavity itself (a condition called “flash”).


A sprue is simply the channel that guides molten plastic from the nozzle of the injection molding machine to the entry point for the entire injection mold tool. It is a separate part from the mold tool itself. A runner is a system of channels that meet up with the sprue, typically within or as part of the mold tool, that guides the molten plastic into the part cavities within the mold tool. There are two principal categories of runners (hot and cold) which you can read about here. Lastly, the gate is the part of the channel after the runner that leads directly into the part cavity. After an injection mold cycle (typically only seconds long) the entirety of the molten plastic will cool leaving solid plastic in the sprue, runners, gates, part cavities themselves, as well as a little bit of overflow potentially on the edges of the parts (if the seal isn’t 100% right).

Thermoset material, such as an epoxy resin that cures once exposed to air, is a material that cures and would burn after curing if one attempt is made to melt it. Thermoplastic material by contrast, is a plastic material that can be melted, cool and solidify, and then be melted again without burning. With thermoplastic materials the material can be recycled are used again. Sometimes this happens right on the factory floor. They grind up the sprues/runners and any reject parts. Then they add that material back into the raw material that goes into the injection molding press. This material is referred to as "re-grind". Typically, quality control departments will limit the amount of regrind that is allowed to be placed back into the press. (Some performance properties of the plastic can degrade as it is molded over and over). Or, if they have a lot of it, a factory can sell this re-grind to some other factory who can use it. Typically regrind material is used for low-quality parts that don't need high performance properties.

Injection Molding is very repeatable. That is, the second part you produce is going to be practically identical to the first one etc. This is a wonderful characteristic when trying to produce brand consistency and part reliability in high volume production.Injection_molding_plastic prototypes design and engineering firm

What Is The Downside To Injection Molding:

Up front costs tend to be very high due to design, testing, and tooling requirements. If you are going to produce parts in high volumes you want to make sure you get the design right the first time. That is more complicated than you might think. Getting the design right includes:

Designing and then prototyping the part itself to specification
Initial prototype development is typically completed on a 3D printer and often in a different material (such as ABS plastic) than the final part will be constructed in
Designing an injection mold tool for an initial production round
Typically generating 300-1000 injection molded prototypes in the production material requires the developon mold tool prior to mass-production in an injection mold manufacturing plant.

Potentially negative aspects of injection molding include the following:

Two of the major disadvantages to injection molding are the high tooling costs and large required lead times. Tooling is almost a project in and of itself and only one phase of the entire injection molding process. Before you can produce an injection molded part you first have to design and prototype a part (probably via CNC or 3D printing), then you have to design and prototype a mold tool that can produce replicas of the part in volume. Lastly, and typically after extensive testing in both of the aforementio