DIY Injection Molding: How to mold plastic parts in-house using 3D printed molds.

Posted by FIT THAI on February 24, 2026

Injection molding is a widely used manufacturing process; in fact, most plastic products in the world today are produced using injection molding. While this method is ideally suited for high-volume production needs, traditional CNC-machined metal molds are very expensive and pose a significant obstacle, and they also involve long production times for low-volume manufacturing.

For prototyping and low-volume production (approximately 10-1000 pieces), 3D-printed injection molds are a time- and cost-effective solution. They also enable a more agile manufacturing approach, allowing engineers and designers to easily test, modify, and iterate mold designs more quickly, all at a lower cost than traditional multi-stage CNC milling.

Creating custom molds using a stereolithography (SLA) 3D printer like the Form 3+ is easy and convenient, allowing you to take advantage of both the benefits of 3D printing and traditional molding techniques simultaneously.

In this guide, we'll walk you through the process of DIY injection molding and share all the tools and tips you need to implement the plastic injection molding process within your organization using 3D printed molds.

For detailed guidelines, design recommendations, and real-world case studies, please download our white paper.

What you need for a DIY injection molding process.

Creating a DIY plastic molding kit requires some investment. Both money and time are needed to acquire the right equipment and to train to become proficient. However, these costs are often still less than the cost of a single metal mold. Therefore, once you're fully operational, the long-term savings in time and cost will easily outweigh the initial effort.

The Form 3 SLA 3D printer is placed next to the Holipress benchtop extrusion machine.

Here's what you need to get started:

High-performance desktop SLA resin 3D printers, such as Formlabs' Form 3+, can produce molds with high precision, sharp detail, and smooth surfaces, resulting in high-quality injection molded parts. Beyond custom plastic molding, SLA 3D printers are also valuable assets for prototyping and other applications throughout the product development process.

For 3D printing, we recommend materials that can withstand the temperatures and pressures applied to the mold during the injection molding process. The following materials are recommended for Formlabs SLA 3D printers:

Rigid 10K Resin is a high-glass fiber reinforced industrial-grade material that provides a wider range of geometries and injection molding processes. With a heat-induced deflection temperature (HDT) of 218°C @ 0.45 MPa and a tensile modulus of 10,000 MPa, it offers exceptional strength, rigidity, and thermal stability.

High-temperature resin has a warping temperature under heat of 238°C @ 0.45 MPa, making it suitable for injection molding applications. This material is more brittle but is recommended for materials requiring high molding temperatures and helps reduce cooling times.

Grey Pro Resin has a lower thermal conductivity than High Temp Resin or Rigid Resin, resulting in a longer cooling time, but it is softer and can withstand hundreds of production cycles.

Benchtop injection molding machines such as the Galomb Model-B100 or Holipress are currently available in a wide range of prices. Many budget-friendly models use hand-driven pistons, while more expensive models utilize screw or pneumatic systems. Some of our customers also recommend systems from Minijector, Morgan, APSX, or Micromolder. Benchtop automated injection molding machines, such as those from Babyplast, are also a good option for high-volume production of small parts.

Plastic pellets according to the type you require.

Use your preferred CAD software for designing mold inserts, such as Blender, which is available for free download.

Before making a purchase, carefully evaluate the injection molding machine to match your production needs. For large parts, industrial processes are still necessary. This custom injection molding technique is best suited for producing small parts in small quantities.

The mold is 3D printed with a Formlabs printer, and the encapsulated component is produced using a DIY injection molding process.

DIY Injection Molding: Step-by-Step

1. Design the mold using CAD software.
First, choose a CAD program you're comfortable with to design the mold insert. In this example, we'll use the open-source Blender, but the overall workflow is quite similar in other CAD programs.

Download blank mold insert design files. You will use these files to create your injection mold drawings. Furthermore, these drawings can be easily scaled to accommodate most injection molding machines and mold frames. Alternatively, you can design your own mold inserts based on cavity diagrams of master mold frames.

Import both sides of the mold core and the 3D design file of the part you want to produce into your CAD software.

In Blender, use the eye icon in the Scene Explorer window to hide half of the mold first. Once you've arranged your workspace as desired, set the display type for both sides of the mold to "wire" under the Object menu, as shown in the example below.

Now you can position your mold. Ensure the workpiece completely intersects with the molten plastic entrance during the injection molding process. Use orthographic mode, which can be enabled via the “toggle perspective/ortho” command, to simplify this step.

Hide the visibility of the currently active side of the mold axis, then reveal the visibility of the other side. Repeat this process to ensure the workpiece completely cuts through half of the other mold axis entrance. Once you've aligned the workpieces, you're ready to remove the intersecting area using Blender's "boolean difference" function.

Select the first half of the object, then choose the Boolean option under the Modifiers menu. Select the object you want to use for cutting and ensure the “difference” action is selected. Press Apply to confirm the command, and repeat the same process on the other side. The result should look similar to the example below. If you get stuck on this step, a tutorial on adding interlocking components to your design may be helpful.

Your mold is now ready for printing. Export each half of the mold file, making sure to check the “Selection Only” box in Blender’s Exporter window.

2. Print the mold using a 3D printer.
When 3D printing molds, it is crucial to select a material that can withstand the temperatures and pressures applied to the mold during the injection molding process.

Based on our internal testing and customer case studies, we recommend selecting 3D printing resins based on the criteria in the table below. Three stars indicate very high performance, while one star means the resin is less efficient.

criterion	High Temperature Resin	Grey Pro Resin	Rigid 10K Resin
High molding temperature	★★★	★	★★
The cooling period is shorter.	★★★	★	★★
High pressure	★	★★	★★★
Increase the production cycle quantity for complex shapes.	★	★★	★★★

Setting up your print job in PreForm, Formlabs' professional 3D printer print preparation software, takes only a few seconds. If your mold requires support structures for printing, orient each mold half in PreForm with the cavity facing upwards. This simplifies post-processing and helps achieve a high-quality surface finish on the molded part.

Depending on the geometry and size of the printing plate, you can print multiple plates simultaneously on the same build platform to improve printing efficiency.

3. Injection molding of plastic parts.
Once you have designed and printed the mold using a 3D printer, you can then use it to mold the finished part on your desktop injection molding machine.

You have a wide variety of materials to choose from for injection molding. Formlabs and our customers have tested the following materials with 3D printed injection molds:

LDPE
PP
PA
PE
TPE
TPU
PLA
ABS
ASA
HDPE
EVA
PS
POM

Consider the required properties of your part and the capabilities of your injection molding machine before you decide on a material. Then, simply follow the specific instructions for your injection molding machine to produce your part quickly and efficiently.

Depending on the material injected, adhesion of the part to the mold may cause mold degradation during removal, especially with flexible 3D printed materials such as TPU or TPE. Using a mold release agent is a good way to help separate the part from the mold. Silicone-based mold release agents are compatible with Formlabs' Grey Pro Resin, High Temp Resin, and Rigid 10K Resin.

If you have further questions about the process, please see our Frequently Asked Questions (FAQ) article: Injection Molding With 3D Printed Molds.

Tips for designers who want to try DIY injection molding.

When designing your mold, consider both what can be successfully 3D printed and what can be successfully injection molded.

The exact approach for DIY (Do It Yourself) injection molding will vary depending on the part design and production volume you desire, but the following tips and techniques will help increase your success rate.

To reduce the blurring of layer lines on the finished product, print the plate with a lower layer height (50 or 25 microns per layer instead of the standard 100 microns). Please note that this will increase the printing time.

Adding a draft angle of approximately two to five degrees to the surface perpendicular to the part removal direction will facilitate easier part removal and reduce mold wear.

You can sand split-plane surfaces with fine-grit sandpaper to reduce excess flash.

Consider using a water bath to help cool the workpiece more quickly and reduce warping.

Embossed and engraved details should be offset from the surface by at least 1 millimeter.

If designed for use with aluminum mold frames, add 0.125 millimeters of thickness to the back of the mold plate to compensate for compression and ensure a complete seal.

For complete workflow instructions and other best practices, please download our white paper.

Overcoming the limitations of traditional molds through 3D printing.

3D printing and injection molding are often perceived as contradictory, but in reality, one doesn't necessarily have to replace the other. By directly printing parts with a 3D printer or using 3D-printed molds for injection molding in prototyping and low-volume production, you can leverage the advantages of both technologies. This can make your manufacturing process more time- and cost-effective, and help you get to market faster.

Want to learn more about 3D printed mold injection molding? Download our white paper for a detailed guide to using 3D printed molds in injection molding processes and explore real-world case studies with Braskem, Holimaker, and Novus Applications.