How 3D Printing Has Made Low-Run Injection Molding Possible

In the past, creating a die for low-run injection molding was prohibitively expensive. The progression of 3D printing technology has resulted in the creation of efficient and affordable molds that are suitable for the production of fewer than 100 units. Read on to learn more about 3D printed molds for low-run manufacturing.

What Is Injection Molding?

Injection molding is a manufacturing process that involves injecting thermoplastics into a premade mold or die. Once the plastic has cooled, the mold is opened, and the part is ejected. The mold can then be re-used to make another part.

Automated injection molding can be used to create high volumes of identical plastic parts for a low price per unit. Although there is a high start-up cost associated with creating the molds, this cost is non-recurring and is often balanced by the high production rate.

Low-Run Injection Molding

Injection molds are usually made with CNC machining; this creates a durable metal mold that can produce thousands of identical units. Because the cost of machining a unique injection mold can cost anywhere between $10,000 and $100,000, low runs are often prohibitively expensive. Items are usually only made with injection molding if they can be reproduced and sold in mass.

A low run for an injection molding machine is typically less than 100 units. In order to make a production run of this size affordable, the mold must be able to be produced efficiently and for a significantly lower cost. Many engineers turn to 3D printing as a flexible way to meet these production requirements.

The Benefits Of 3D Printed Injection Molds

For normal injection molding, the most important quality of the die is durability and wear resistance. The mold must be able to reproduce an identical product thousands of times. Low-run injection molding doesn't come with this requirement; the mold only has to produce 100 units. Instead, the main concern is the quality of the design and the surface finish of the final product.

3D printing technologies like SLA printing or Material Jetting are particularly well-suited to producing low-run injection molds. These technologies can create dies with a high level of accuracy and a reasonable level of durability. 3D printed molds can be created far more quickly than those made with CNC machining, resulting in the shorter lead times that are necessary for low-run production.

Another benefit of 3D printing an injection mold is the ease at which an engineer can make changes to their design. Printing a new mold is exceptionally affordable; engineers can make slight modifications to the original template or even reproduce the same mold for an additional manufacturing run.

3D printed molds are best suited for the creation of small items less than 150 millimeters across (see example). The larger the item, the more difficult it is to create a durable mold that will withstand the production of 100 units.

Standard Configurations For 3D Printed Molds

Most 3D printed molds are made to be used with aluminum frames. The frame provides additional support and keeps the mold from warping under the heat and pressure associated with the molding process. Engineers should consider the size and placement of the frame in their initial design.

Occasionally, stand-alone molds are created which do not require aluminum supports. These molds often feature intricate cooling channels and design elements. However, these molds are typically more expensive to make and will warp if used extensively.

Designing An Injection Mold For 3D Printing

3D printed injection molds need to follow many of the same design requirements as normal injection molds. Engineers should also take the following elements into consideration. For more information on design for 3D printing, refer to the 3D Hubs Engineering Guide.

• Materials - Because injection molding is an industrial application, standard 3D printing materials may not be suitable. Choose durable materials with high-temperature resistance and a good level of surface detail.
• Support structures - Most 3D printing processes require the use of support structures. Make sure that these structures do not touch the inner faces of the mold; this will ensure that the final product has a smooth finish.
• Air vents - Including shallow air vents roughly 0.05 millimeters deep from the edge of the cavity to the edge of the mold will let air escape during the injection process.
• Reinforcements - For molds that will be used more than 20 times, consider including channels where metal rods can be embedded into the design. This will reinforce the mold and greatly increase its lifespan.

Designing Parts For Injection Molding

The same rules should be followed when designing a product for injection molding, regardless of the size of the manufacturing run. For more information on designing parts for injection molding, please refer to the 3D Hubs Engineering Guide.

• Maintain uniform wall thickness while keeping walls and features as thin as possible.
• Instead of increasing wall thickness, use ribs and gussets to add additional support.
• Include draft angles of 2 degrees or more to allow for smooth removal of the finished product.

For more information on designing low-run injection molds, refer to the 3D Hubs Knowledge Base. 3D Hubs also offers engineering guides for both injection molding and 3D printing.

3D Hubs offers affordable online manufacturing solutions for 3D printing, injection molding, CNC machining, and sheet metal fabrication. Upload any design to generate an instant injection molding quote and preview the manufacturing process.