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3D Printed Injection Mold: All You Need to Know

Picture of Yuanyuan Chen
by Yuanyuan Chen
Mar 21, 2020
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3D printing meets injection molding. Find out why 3D printed injection molds exist and how you can make one.

3D Printed Injection Mold

Molding the Future

The general injection molding process
The general injection molding process (Source: tronicarts via YouTube)

To understand what a 3D printed injection mold is, let’s start with regular injection molding.

Injection molding is one of the most common manufacturing processes in the plastic industry. Essentially, molten plastic is injected into a mold cavity, it hardens as it cools, and then the mold is opened and the plastic pieces taken out.

Injection molding is primarily used in mass production because of its high upfront costs from design, tests, and tooling. Of course, the unit price drops dramatically the more parts that are produced, which is why it’s worth using injection molding for mass production.

Why 3D Printing?

Injection molds themselves are blocks with cavities that determine the shapes of the products being made. Molds are traditionally designed and produced via computer numerically controlled (CNC) milling machinery, which is quite expensive.

Since molds are usually made out of metals such as steel and aluminum, they’re very difficult to alter once produced.  Therefore, 3D printing injection molds offers a cheap and flexible alternative.

Let’s have a look at how to actually print a 3D injection mold, some pros and cons, new developments in 3D printing injection molds, and finally some tips for printing on your own.

Note: Though 3D printing injection molds is within the reach of most hobbyist makers, actually using them may require more than the standard amount of effort and equipment. Of course, there’s always the possibility of using a professional 3D printing service. To find the best price and provider for your needs, check out Craftcloud, the 3D printing and price comparison service from All3DP.

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3D Printed Injection Mold

How to Print

The process of 3D printing an injection mold
The process of 3D printing an injection mold (Source: Athlone Institute of Technology)

Process

3D printing injection molds is similar to how you print other 3D printed objects:

  1. The injection molds are designed with CAD software, such as AutoCAD or Fusion 360.
  2. The design is saved in the STL file format and sliced into G-code.
  3. The molds are printed, layer by layer, with a 3D printer.
  4. Molds are fitted into metallic frames and ready for injection molding.

Real World Example

An example of a 3D printed injection mold, produced and used by the Athlone Institute of Technology, features in the image above. Their mold was designed to produce a 3D version of the college’s logo. The whole process took less than a day and the cost was negligible.

You can find more details on how to 3D print injection molds in our article 3D Printed Molds: A Simple DIY Guide.

Materials

Now that we’ve covered the basic process of how to 3D print injection molds, let’s have a look at what materials you can use.

Generally speaking, you’ll want something that has high strength and stiffness to withstand the pressure generated during injection. Also, it will need to have high temperature resistance.

Here are a few common materials used for 3D printed injection molds:

  • PETG (polyethylene terephthalate)
  • ABS (acrylonitrile butadiene styrene)
  • Nylon (a.k.a. polyamide)
  • PP (polypropylene)
  • TPE (thermoplastic elastomers)
  • POM (polyoxymethylene, a.k.a. Delrin or acetal)

3D printing injection molds can be done with SLA, FDM, material jetting, and SLS. That said, since high dimensional accuracy and smooth surfaces are ideal for injection molds, SLA is the preferred 3D printing method to produce injection molds.

There is one thing you should know about the metal frames and their role in injection molds. The frames provide support against the pressure and heat generated during injection molding. Because metal frames can be used universally, it’s only the molds that need to be 3D printed, so altering designs is easy and flexible. However, in the case that the entire mold is 3D printed, more material and a longer printing time is required.

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3D Printed Injection Mold

Pros & Cons

3D printing injection molds have their advantages and disadvantages
3D printing injection molds have their advantages and disadvantages (Source: All3DP)

3D printing is a great option to produce injection molds, but it also has its drawbacks. Let’s go over the main advantages and disadvantages.

Pros

  • Low cost: The traditional way to produce injection molds is very expensive and time consuming, requiring precise machinery and expertise from mold makers. 3D printing, on the other hand, is a much cheaper way to make molds. It’s reported that 3D printed molds can save up to 80% of costs compared to conventional techniques.
  • Flexibility and efficiency: 3D printing significantly reduces design and production time. Anyone who has experience with 3D printing can print a mold, and if you aren’t happy with it, you can simply tweak the design and print another one.
  • Low-volume production suitability: As we discussed earlier, the injection molds made from conventional methods, such as CNC milling, have a very high initial cost. For this reason, they’re only considered viable when the production volume is large enough. On the other hand, 3D printed molds are much cheaper to make, and without that initial high upfront cost, low- to medium-volume production is best done with 3D printed molds.

Cons

  • Longer production time: Because plastic has a lower thermal conductivity compared to metal, 3D printed plastic molds take longer to produce products, prolonging the overall production time and reducing the rate of production.
  • Shrinkage: Like many other 3D printed objects, 3D printed injection molds can suffer from shrinkage when cooling, a common problem in 3D printing. This can pose issues when precise dimensions are required.
  • Weaker structural integrity: Most 3D printed molds are made of plastic, which cannot withstand high temperature and pressure for long periods of time. This causes 3D printed injection molds to have degradation at the gate and weld line.

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3D Printed Injection Mold

Cutting-Edge Research

3D printed metallic injection molds
3D printed metallic injection molds (Source: Addy Machinery via YouTube)

Now that we know about the pros and cons of 3D printing injection molds, let’s take a look at some of the most recent developments are in the field.

Surface Coating

3D printed injection molds tend to degrade under high temperature and pressure. Improving surface integrity with a protective coating is a way to prevent heat degradation. Depositing a layer of metal, metal nitrates, ceramic, and oxides on the surface of 3D printed injection molds can enhance their heat and tear resistance.

Thermal Conductive Composites

Thermal conductivity is a measure of an object’s ability to conduct heat. Metals have better thermal conductivity than plastics. In other words, metals can be heated or cooled quicker than plastics.

Because 3D printed injection molds have a longer heating and cooling phase than those produced with CNC, they also have a longer cycle time. When fewer products can be produced in any given period, the production cost increases compared to traditional metallic molds.

To solve this issue, thermal conductive additives are included in mold materials to improve the injection process. For instance, boron nitride can be added to ABS and iron particles to epoxy resin.

Metallic Injection Molds

Metal has better thermal conductivity than plastic, so why not 3D print metallic injection molds? With recent developments in metal 3D printing, this is now possible. That said, 3D printing metal is still far more expensive than with plastic, so upfront costs will still be high.

You can find more information about this process in our article on direct metal laser sintering (DMLS).

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3D Printed Injection Mold

Printing Tips

Get started 3D printing your own injection molds
Get started 3D printing your own injection molds (Source: All3DP)

Before you start printing injection molds yourself, here are some helpful tips to consider:

  • Number of prints: Make sure you know how many units you want to make! Remember, 3D printed injection molds are only for low-volume manufacturing (30 to 100 runs, depending on the mold). So if you’re thinking of making thousands of units, you might need to consider a conventional mold.
  • Adding a draft angle: Right angles make the injection molded parts hard to get out of the mold, so try adding a 2-degree draft angle to make the object easier to slide out.
  • Using a printing service: Don’t forget there’s always the printing service route, which can help you design and print molds to your exact specifications without you lifting a finger. For the widest range of materials and technologies, check out Craftcloud, the 3D printing and price comparison service from All3DP.

(Lead image source: Rosti)

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License: The text of "3D Printed Injection Mold: All You Need to Know" by All3DP is licensed under a Creative Commons Attribution 4.0 International License.

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