DIY Injection Molding: How to Form Plastic Parts In-House with 3D Printed Molds

Posted by FIT THAI on April 21, 2026

Plastic injection molding is a widely used manufacturing process—in fact, most plastic products in today's world are produced using plastic injection molding. While it is an ideal technique for mass production, metal molds machined with traditional CNC are very costly and have long lead times, making them unsuitable for low-volume production.
For prototyping and low-volume production (about 10-1000 pieces), 3D-printed plastic injection molds are an efficient choice in terms of both time and cost. They also make the production process more agile, allowing engineers and designers to easily test mold designs, make adjustments, and iterate improvements more quickly, at a significantly lower cost than traditional CNC machining.
Creating custom molds with a stereolithography (SLA) 3D printer like the Form 3+ is easy and convenient, allowing you to leverage both 3D printing and traditional molding techniques together.
In this guide, we will walk you through the steps of DIY injection molding and share all the tools and tips necessary to implement plastic injection molding in-house using molds printed with a 3D printer.

What you need for DIY injection molding.

Building a DIY plastic molding kit requires some investment. Both money and time are needed to source the right equipment and to learn how to use that equipment proficiently. However, these costs are often still lower than the cost of a single metal mold. Therefore, once you get started, the time and cost savings in the long run can easily offset the initial effort.

The Form 3 SLA 3D printer placed next to the Holipress desktop injection molding machine.

What you will need to get started includes:

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

Materials for 3D printing that can withstand the temperatures and pressures encountered in molds during the injection molding process. We recommend the following materials for Formlabs' SLA printers:

Rigid 10K Resin is an industrial-grade material with a high glass content, providing solutions that can accommodate a variety of shapes and more injection molding processes. It has an HDT of 218°C @ 0.45 MPa and a tensile modulus of 10,000 MPa, making it exceptionally strong, rigid, and thermally stable.

High Temp Resin has a heat distortion temperature (HDT) of 238°C @ 0.45 MPa, making it suitable for injection molding. This material is more brittle but recommended for materials that require high heat for molding and helps reduce cooling time.

Grey Pro Resin has a lower thermal conductivity than High Temp Resin or Rigid Resin, which means it takes longer to cool down, but it is softer and can be used for hundreds of cycles.

Desktop injection molding machines, such as the Galomb Model-B100 or Holipress, currently have several models on the market at various price points. Many low-cost machines use manually driven pistons, while higher-priced machines use screw or pneumatic systems. Some of our customers also recommend systems from Minijector, Morgan, APSX, or Micromolder. Desktop automatic injection molding machines, such as products from Babyplast, are also a good option for producing small parts in large quantities.

Plastic pellets according to the type you want to use.

CAD software you are comfortable with for designing mold parts, such as Blender, which can be downloaded for free.

Before deciding to purchase, evaluate the injection molding machine to ensure it meets your production needs. For large workpieces, industrial processes are still necessary. This DIY injection molding is best suited for producing small parts in low quantities.

Molds printed with Formlabs' 3D printer and the encapsulated parts produced using this DIY injection molding process.

Step-by-step DIY injection molding.

Design the mold in CAD.

First, choose the CAD software you want to use for designing the mold parts. In this example, we will use Blender, which is open-source software, but the overall workflow will be quite similar in other CAD software.

Download the blank mold insert design files that you will use to create the injection mold. These designs can be easily resized to fit most injection molding machines and mold frames. Additionally, you can design your own mold parts using the cavity diagrams of the main mold frame.

Import both sides of the mold core and the 3D model of the workpiece you want to produce into the CAD software.

In Blender, use the eye icon in the scene explorer to hide the display of one side of the mold. Once your workspace is set up as desired, set both sides of the mold to "wire" display mode under the Object menu as shown in the example image below.

Now you can align your mold. Make sure the object (workpiece) completely overlaps with the inlet of the molten plastic during the injection molding process. Use orthographic mode by pressing "toggle perspective/ortho" to make alignment easier.

Hide the display of the active mold core side and open the other side. Repeat the same steps to ensure that the object overlaps completely with the inlet of the mold core on the other side. Once the object is properly aligned, you are ready to remove the overlapping area of the object using the "boolean difference" function in Blender.

Select the first half of the object, then choose the boolean option in the Modifiers menu, select the object to cut out, and ensure that you have selected the "difference" operation. Then click Apply to execute the command and repeat the same steps for the other side. The result should resemble the sample image below. If you encounter issues at this stage, a tutorial on adding interlocking parts to your design may be helpful.

Now that your mold is ready for printing, export each half, ensuring that you have selected the "Selection Only" option in Blender's exporter.

Print the mold with a 3D printer

When printing molds with a 3D printer, it is important to choose materials that can withstand the temperatures and pressures that occur in the mold during the injection molding process.

Based on internal testing and case studies from our customers, we recommend selecting resins for 3D printing based on the criteria in the table below, where three stars indicate high performance and one star indicates lower performance.

เกณฑ์	High Temp Resin	Grey Pro Resin	Rigid 10K Resin
High molding temperature	★★★	★	★★
Shorten cooling time	★★★	★	★★
High pressure	★	★★	★★★
Increase production cycles for complex shapes	★	★★	★★★

Setting up the print job takes only a few seconds in PreForm, which is the print preparation software for Formlabs' professional 3D printers. If your mold design requires support structures for printing, position half of the mold in PreForm with the cavity facing up. This will make the post-printing process easier and help achieve a high-quality surface on the workpiece.

Depending on the shape and size, you can print multiple molds simultaneously on the build platform to enhance printing efficiency.

Injection molding of plastic parts

Now that you have designed and printed the mold with a 3D printer, you can use it to inject mold parts with a desktop plastic injection molding machine.

You have a variety of materials available for injection molding, which Formlabs and our customers have tested with 3D printed molds:

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

Before selecting a material, consider the desired properties of the workpiece and the capabilities of your injection molding machine. Then, follow the specific guidelines of the injection molding machine to produce the workpiece quickly and efficiently.

This depends on the material used for injection molding. The adhesion of the workpiece to the mold may cause the mold to deteriorate during the removal of the workpiece, especially with flexible materials like TPU or TPE. Using a mold release agent is a good way to help separate the workpiece from the mold easily. Silicone-based release agents can be used with Formlabs Grey Pro Resin, High Temp Resin, and Rigid 10K Resin.

If you have further questions about the workflow, be sure to check out the FAQ article: Injection Molding With 3D Printed Molds.

Tips for designers looking to try DIY injection molding.

When designing a mold, consider both what can be successfully printed with a 3D printer and what can be successfully molded with injection molding.

Guidelines for DIY injection molding may vary depending on the design and quantity you need, but the following tips will help increase your chances of success.

To reduce the visibility of layer lines on the final part, print the mold with a smaller layer thickness (50 or 25 microns per layer instead of the default 100 microns), keeping in mind that this setting will increase printing time.

Adding a draft angle of about 2 to 5 degrees on surfaces perpendicular to the direction of part removal will make it easier to demold the part and reduce wear on the mold.

You can sand the split-plane surface with fine sandpaper to reduce flash.

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

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

If designing for an aluminum mold frame, add an additional thickness of 0.125 millimeters to the back of the mold plate to compensate for pressure and ensure a complete seal.

Revolutionizing molds with 3D printing

3D printing and injection molding are often seen as opposing processes, but in reality, you don’t always have to choose one over the other. By directly printing parts with 3D technology or using 3D printed molds for injection molding in prototyping and low-volume production, you can leverage the advantages of both technologies together. This approach can make your manufacturing process more efficient in terms of time and cost, allowing you to bring products to market faster.

Want to learn more about injection molding with 3D printed molds? Download our white paper for a detailed guide on using 3D molds in the injection molding process, along with real case studies from Braskem, Holimaker, and Novus Applications.