Desktop SLA 3D Printing Speeds Up Injection Molding Innovation

Injection molding is a widely used manufacturing process for plastic products. While traditional CNC metal molds excel in high-volume production, they present significant challenges for small batches: high costs and long lead times. For prototyping and low-volume needs (approximately 10–1,000 units), 3D-printed injection molds offer a time- and cost-efficient alternative. This approach also enables greater flexibility, allowing engineers and designers to test mold designs, make modifications easily, and iterate faster at a fraction of the cost of CNC machining.

Using a stereolithography (SLA) 3D printer—such as the Formlabs Form 3+—to create custom molds is straightforward, combining the benefits of 3D printing with traditional molding techniques. Below is a comprehensive guide to setting up a DIY injection molding system, including essential tools and best practices.

Setting up a DIY plastic molding system requires some initial investment, but the long-term savings in time and cost can justify the effort. Here’s what you’ll need:

• High-performance desktop SLA 3D resin printer: Models like the Formlabs Form 3+ produce precise molds with smooth surface finishes, ensuring high-quality molded parts.
• 3D printing materials capable of withstanding injection molding temperatures and pressures: Recommended resins include:
  • Rigid 10K Resin: An industrial-grade, glass-filled material with high thermal stability (HDT: 218°C @ 0.45 MPa) and stiffness (tensile modulus: 10,000 MPa).
  • High Temp Resin: With a heat deflection temperature of 238°C @ 0.45 MPa, this brittle but heat-resistant material is ideal for high-temperature molding.
  • Grey Pro Resin: Offers lower thermal conductivity, resulting in longer cooling times, but is more durable for extended use.
• Desktop injection molding machine: Options include the Galomb Model-B100, Holipress, Minijector, Morgan, APSX, or Micromolder systems. Automated machines like Babyplast are suitable for small-part production.
• Plastic pellets of your choice
• CAD software for mold design (e.g., Blender)

Note: This method is best suited for small-batch production of small parts. Larger components may still require industrial processes.

Begin by designing mold inserts in CAD software (Blender is used here, but the workflow is similar in other tools):

1. Download a blank mold insert template or design your own.
2. Import both halves of the mold core and your 3D model into the CAD tool.
3. Use Boolean operations to subtract the part geometry from the mold halves, ensuring proper alignment with the injection inlet.
4. Export each mold half for printing.

Select a resin based on your molding requirements:

For optimal results, orient the mold cavity face-up in the slicer (e.g., PreForm) to simplify post-processing and ensure smooth surfaces.

With the 3D-printed mold ready, proceed to injection molding using materials such as:

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

To prevent part adhesion and mold degradation, apply a silicone-based release agent. Follow your machine’s instructions for optimal results.

• Use smaller layer heights (50 or 25 microns) to minimize visible print lines on finished parts.
• Incorporate 2–5° draft angles on vertical surfaces for easier part removal.
• Polish parting lines with fine sandpaper to reduce flash.
• Cool parts faster using a water bath to minimize warping.
• Offset engraved details by at least 1 mm from the surface.
• Add 0.125 mm extra thickness to molds for aluminum frames to ensure sealing under compression.

By combining 3D printing and injection molding, manufacturers can achieve cost-effective, rapid prototyping and small-batch production, accelerating time-to-market for new products.