Most plastic products in today's world are produced using the injection molding process. However, producing molds can be very costly and time-consuming. Fortunately, molds do not always need to be machined from metal but can be printed with 3D printers.

Stereolithography (SLA) 3D printing is a more cost-effective option than machining aluminum molds. Parts printed with SLA have a complete dense structure and consistent properties in all directions, and they also have materials with a heat deflection temperature of up to 238°C at 0.45 MPa, meaning that these materials can withstand the heat and pressure of the injection molding process.

Rapid production of 3D-printed injection molds for small quantities.

3D-printed injection molds installed in an aluminum frame, along with finished injection-molded parts.

With affordable professional-grade 3D printers, temperature-resistant materials for 3D printing, and injection molding machines, it is possible to create 3D-printed injection molds in-house to produce functional prototypes and small usable parts from plastic for production. For low-volume production (approximately 10-1000 pieces), 3D-printed injection molds can save time and costs compared to expensive metal molds. They also allow for a more flexible manufacturing process, enabling engineers and designers to easily create mold prototypes, test mold designs, or modify molds, and continuously develop designs with short lead times and low costs.

SLA 3D printing technology is an excellent choice for molding, characterized by smooth surfaces and high precision, which the molds transfer to the final parts, and it also facilitates easier removal of parts from the molds. Parts printed with SLA have chemical adhesion, resulting in full density and consistent properties in all directions, allowing for the creation of functional molds at a quality level that cannot be achieved with FDM technology. Desktop and benchtop SLA printers, such as those produced by Formlabs, simplify the workflow as they are easy to set up, use, and maintain.

Rigid 10K Resin from Formlabs is an industrial-grade material that has a high fiber glass content, making it ideal for use as a mold material in various shapes and conditions of the injection molding process. Rigid 10K Resin has a heat deflection temperature (HDT) of 218°C at 0.45 MPa and a tensile modulus of 10,000 MPa, making it a very strong, highly rigid material with thermal stability that can maintain its shape under pressure and temperature to produce parts with precision.

Rigid 10K Resin is Formlabs' primary material for printing complex molds for injection molding, presented through three case studies in the company's white paper. The IPC industrial technical center in France has researched and printed thousands of parts. The contract manufacturer Multiplus uses this material for low-volume production, and the product development company Novus Applications has injected hundreds of complex screw caps from a single Rigid 10K Resin mold.

High Temp Resin is an alternative material to consider when the pressure and injection forces are not very high, and when Rigid 10K Resin cannot withstand the required temperatures. High Temp Resin has a heat deflection temperature (HDT) of 238°C at 0.45 MPa, the highest among Formlabs' resin materials and one of the highest in the market, allowing it to withstand high molding temperatures and reduce cooling times. The white paper includes a case study example from Braskem, a petrochemical company, which performed 1,500 cycles of injection molding with an insert mold printed with High Temp Resin to produce mask straps. The company printed the insert and installed it within a standard metal mold included in the injection molding system, which is an efficient solution for rapid medium-volume production.

However, High Temp Resin is quite brittle; in the case of very complex shapes, the material may easily warp or crack. For some models, using it for more than ten cycles can be challenging. To address this issue, a French startup named Holimaker has turned to Grey Pro Resin, which has a lower thermal conductivity than High Temp Resin, resulting in longer cooling times but greater flexibility, allowing it to withstand hundreds of cycles

Download our white paper for free to see case study details and learn how to create in-house 3D printed molds for injection molding

Case Study: 3D Printed Injection Molds

Surfaces (Textures) on injection molds printed with 3D from Rigid 10K Resin and on the finished molded parts

Injection molding using 3D printed molds can be applied to a variety of applications. Download our white paper to see 5 real case studies to learn how this hybrid manufacturing process enables on-demand mold production and rapid production of small quantities of thermoplastic parts:

IPC has conducted technical studies on injection molding using 3D printed molds
Multiplus used 3D printed molds made from Rigid 10K Resin for low-volume production
Novus Applications injected hundreds of screw caps using a three-piece mold made from Rigid 10K Resin
Braskem produced 3,000 mask straps within one week using insert molds made from High Temp Resin
Holimaker produces hundreds of technical parts using molds made from Grey Pro Resin and Rigid 10K Resin

Choosing the right resin for 3D printing injection molds.

Injection molds printed with a 3D printer using Formlabs High Temp resin.
Based on internal testing and case studies with our customers, we recommend selecting resins for 3D printing based on the criteria in the table below, where three stars indicate the resin has very high performance, and one star indicates lower performance.

How to inject mold parts using molds printed with 3D Printing.

The complexity of the injection molding process largely depends on the complexity of the part and the structure of the mold. Various thermoplastics can be used for injection molding with 3D printed molds, such as PP, PE, TPE, TPU, POM, or PA. Low-viscosity materials will help reduce pressure and extend the lifespan of the mold. Polypropylene and TPEs are easy to mold and can operate at high cycle counts. In contrast, engineering plastics like PA will support fewer production cycles. Using a release agent will help separate the part from the mold more easily, especially with flexible 3D printing materials like TPU or TPE.

The type of injection molding machine does not significantly influence the process. If you are just starting with injection molding and want to experiment on a budget, using a tabletop injection molding machine, such as Holipress or Galomb Model-B100, may be a good option. Small automatic injection molding equipment, such as the tabletop Micromolder or the hydraulic Babyplast 10/12, is also suitable for producing small parts in high volumes.

Design guidelines for molds printed with 3D Printing.

We recommend following design principles for additive manufacturing, including general principles of injection mold design, such as setting a draft angle of about 2 to 3 degrees, maintaining consistent wall thickness throughout the part, or rounding corners. Here are some useful tips from users and experts, specifically for molds printed from polymers:

To increase size accuracy:

Plan for material stock allowance on the mold for adjustments and surface finishing after production.
Print a set of molds to study size deviations and use this data to adjust the CAD model of the mold.

 

To extend the lifespan of the mold:

Enlarge the flow path (gate) to help reduce pressure within the mold cavity.

If possible, design one side of the mold to be flat and the other side to have details of the part. This will help reduce the chances of misalignment of the mold parts and decrease the risk of flashing.

Add large air vents from the edges of the mold cavity to the edges of the mold to allow air to escape, which will improve material flow into the mold, reduce pressure, and decrease the formation of flash around the gate, resulting in shorter production cycle times.

Avoid overly thin cross-sections: Surface thickness less than 1-2 mm may deform when exposed to heat.

To optimize printing:

Adjust the back of the mold to reduce material usage: Reducing the cross-section in areas not supporting the mold cavity will save resin and reduce the risk of print failure or warping.

Add chamfers to help remove the part from the print bed more easily.

Add centering pins at the corners to help align the two mold pieces.

If you have further questions about the workflow, please check our FAQ article: Injection Molding With 3D Printed Molds, and for the entire process including other best practices, please download our white paper.

3D printed injection molds can accommodate side actions.

3D printed molds: Techniques for prototyping and production

Integrating mold making with desktop 3D printing allows engineers and designers to expand the range of usable materials and take the potential of 3D printers beyond rapid prototyping to actual production levels.

Using molds, dies, and patterns that are 3D printed to enhance the forming and casting processes is often both faster and more cost-effective than CNC machining and is also easier to work with than silicone molds.

In addition to injection molding, 3D printed molds can also be used with the following forming and casting processes:

Thermoforming and Vacuum Forming
Silicone mold making (including overmolding and insert molding)
Vulcanized rubber molding
Jewelry casting
Metal casting

Molds from 3D printing: Techniques for prototyping and production
You can click the link to download our white paper, which contains specific guidelines for each process.

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References

https://formlabs.com/blog/3d-printing-for-injection-molding/