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Injection molding is ubiquitous as a manufacturing process—in fact, the majority of plastic products in the world today are manufactured by injection molding. While it is an ideal technique for large-scale production needs, traditional CNC machined metal molds have prohibitive high costs and long lead times for low-volume production.
For prototyping and low-volume production (approximately 10-1000 parts), 3D printed injection molds provide a time- and cost-efficient solution. They also enable a more agile manufacturing approach, allowing engineers and designers to test mold designs, easily modify them, and then continue to iterate on their designs much faster, while being orders of magnitude cheaper than traditional CNC machining.
Creating custom molds using a stereolithography (SLA) 3D printer, like the Form 3+, is simple and convenient, allowing you to leverage the benefits of both 3D printing and traditional molding techniques.
In this guide, we’ll walk you through the process of DIY injection molding and share all the tools and tips necessary to utilize plastic injection molding in-house using 3D printed molds.
For detailed guidelines, design recommendations, and real-life case studies, download our white paper.
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Download our white paper for guidelines for using 3D printed molds in the injection molding process to lower costs and lead time and see real-life case studies with Braskem, Holimaker, and Novus Applications.
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Building a setup for DIY plastic molding does require some investment. It takes both money and time to acquire the right equipment and to master using it. However, these costs are in many cases still lower than the cost of a single metal mold, so the eventual time and cost savings, once you’re up and running, will easily offset the initial effort.
The Form 3 SLA 3D printer next to a Holipress desktop injection molder.
Here’s what you’ll need to get started:
A high-performance desktop SLA 3D resin printer, like the Formlabs’ Form 3+. The Form 3+ can produce accurate molds with crisp features, and a smooth surface finish that will yield high-quality final molded parts. Beyond DIY plastic molding, an SLA 3D printer is also a valuable asset for prototyping and other applications throughout product development.
A 3D printing material that can withstand the temperature and pressure on the mold during the injection molding process. We recommend the following materials for Formlabs SLA 3D printers:
Rigid 10K Resin is an industrial-grade, highly glass-filled material, which provides a solution that can cope with a wider variety of geometries and injection molding processes. It has an HDT of 218°C @ 0.45 MPa and a tensile modulus of 10,000 MPa, making it strong, extremely stiff, and thermally stable.
High Temp Resin offers a heat deflection temperature is 238 °C @ 0.45 MPa that is suitable for injection molding. This material is more brittle, but is recommended for materials with a high molding temperature and to reduce cooling time.
Grey Pro Resin has a lower thermal conductivity than High Temp Resin or Rigid Resin, which leads to a longer cooling time, but it is softer and can wear hundreds of cycles.
A benchtop injection-molding machine, such as the Galomb Model-B100 or the Holipress. There are a number of benchtop injection molders on the market that vary in cost. Many of the lower cost molders use a hand-driven plunger, while some of the more expensive units use a screw or pneumatic system. Some of our customers have recommended systems from Minijector, Morgan, APSX, or Micromolder as well. Desktop automated molders such as the product line from Babyplast are good alternatives for mass production of small parts.
Plastic pellets of your choice
A CAD software tool of your preference to design the mold insert, such as Blender, which you can download for free.
Before purchase, make sure to evaluate the injection molder carefully against your production requirements. For large parts, industrial processes will still be necessary. This DIY injection molding technique is best optimized for producing small parts at low volumes.
A Formlabs 3D-printed mold, and encapsulated component, made using this DIY injection molding process.
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First, pick the CAD software tool of your preference to design the mold insert. We’ll use the open-source Blender, but the workflow should be fairly similar in any other CAD software.
Download the blank mold insert design files—you’ll use them to create your injection mold design. The designs can also be easily scaled to accommodate most injection molders and mold frames. Alternatively, you can also design your own mold insert for the using the cavity diagrams of the master mold frames.
Import both mold halves of the mold core and the 3D design you’d like to produce into your CAD tool.
In Blender, use the eye icon in the scene explorer to toggle off one half of the mold. Once your workspace is set up to your liking, set both halves of the mold to the “wire” draw type under the Object menu, as in the image below.
Now, you can position your mold. Ensure that the object fully intersects with the inlet for the molten plastic during the injection molding process. Use orthographic mode, engaged via “toggle perspective/ortho,” to make this more straightforward.
Turn the visibility of your current mold core off, and turn the other side on. Repeat the process to ensure that the object fully intersects with the inlet of the other half of the mold core. With your object lined up, you’re ready to subtract the area of two intersecting objects by using the “boolean difference” function in Blender.
Select the first half of your object, and choose the boolean option under the Modifiers Menu. Select the object you’re cutting, and make sure that the “difference” operation is selected. Apply the operator, and do the same for the other side. It should look something like the image below. If you get stuck here, this tutorial on adding interlocking components to a design may be helpful.
Your mold is now ready for printing. Export each half, making sure to check the “Selection Only” box in the Blender exporter.
To 3D print the mold, it’s essential to pick a material that can withstand the temperature and pressure on the mold during the injection molding process.
Based on internal testing and case studies with our customers, we suggest to choose the 3D printing resin based on the criteria from the table below. Three stars means the resin is highly effective, one star is less effective.
CriteriaHigh Temp ResinGrey Pro ResinRigid 10K ResinHigh molding temperature★★★★★★Shorter cooling time★★★★★★High pressure★★★★★★Increase cycle number for complex geometries★★★★★★Setting up the print only takes a few seconds in PreForm, the print preparation software for Formlabs professional 3D printers. If your mold design requires support structures for printing, make sure to orient the mold halves in PreForm so that the cavity faces up. This will simplify post-processing and ensure a high-quality surface for your molded parts.
Depending on the geometry and the size, multiple molds can be printed at once on a build platform to increase printing efficiency.
Now that you’ve designed and 3D printed your mold, you can mold the parts on your benchtop plastic 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:
Consider the desired properties of your object and the capabilities of your injection molder before you make your choice. From there, simply follow the bespoke instructions on your injection molder to quickly and efficiently produce your parts.
Depending on the injected material, adhesion of the part to the mold can cause deterioration of the mold during extraction, in particular with flexible 3D printing materials such as TPUs or TPEs. Using a mold release agent is a good solution to help separate the part from the mold. Silicone mold release agents are compatible with Formlabs Grey Pro Resin, High Temp Resin, and Rigid 10K Resin.
If you have more questions about the workflow, make make sure to check our article FAQ: Injection Molding With 3D Printed Molds.
When designing your mold, consider what will 3D print successfully, as well as what will mold successfully.
The exact approach to DIY injection molding will vary based on your desired design and volume, but these tips and tricks will help increase your success rate.
To reduce the visibility of print lines on the finished part, print the mold with a smaller layer height (50 or 25 microns per layer instead of the default 100). Note that this increases print time.
Adding two to five degrees of draft on surfaces perpendicular to the direction of pull will allow the part to be removed more easily and will minimize degradation of the mold.
You can polish split-plane surfaces with fine-grit sandpaper to reduce flash.
Consider using a water bath to more rapidly cool your part and reduce warping.
Embossed and engraved details should be offset from the surface by at least 1 mm.
If designing for an aluminum mold frame, add .125 mm of extra thickness to the back of the mold plates to account for compression forces and to ensure a complete seal.
For the complete process workflow and other best practices, download our white paper.
White Paper
Interested in other applications of 3D printed molds? Download our white paper that also covers thermoforming and casting with elastomers.
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The conversation around 3D printing and injection molding is often oppositional, but it’s not always a question of one versus the other. By directly 3D printing parts or using 3D printed molds for injection molding for prototyping and low-volume production, you can leverage the benefits of both technologies. This will make your manufacturing process more time- and cost-efficient and allow you to bring products to the market faster.
Want to learn more about injection molding with 3D printed molds? Download our white paper for detailed guidelines for using 3D printed molds in the injection molding process and see real-life case studies with Braskem, Holimaker, and Novus Applications.
Download the White Paper
Plastic components are used in many industries. From automotive to home appliances and medical devices, components in a variety of plastics are used to protect, enhance and build a huge range of products.
With its reliable, high-quality performance, injection molding is one of the most common processes used to produce plastic components. Indeed, the compound annual growth rate (CAGR) of the injection molded plastics market is expected to increase by 4.6% up to 2028.
Yet, despite its ability to produce high numbers of plastic components quickly, the injection molding process must be tightly controlled to maintain the quality of the final parts. This article will explain how injection molding works and how experienced manufacturers control the process to produce the best quality plastic components. We'll cover:
Injection molding is a complex manufacturing process. Using a specialized hydraulic or electric machine, the process melts, injects and sets plastic into the shape of a metal mold that’s fitted into the machine.
Plastic injection molding is the most widely used components manufacturing process for a variety of reasons, including:
This cost-effectiveness, efficient production time and component quality are just some of the reasons why many industries choose to use injection molded parts for their products.
As well as the fact that plastic injection molding process can be optimized to have a lower carbon impact. Find out more in our guide, Design for Sustainability: Optimizing Plastic Injection Molding Processes.
The injection molding cycle includes many parameters which need to be tightly controlled to ensure the overall quality of the plastic components produced. Understanding the process and parameters in some depth will help manufacturers to identify plastic components producers who can provide the quality and consistency they need.
Before the actual process begins, it’s key that the right thermoplastics and plastic injection molds are selected or created, as these are the essential elements that create and form the final components. Indeed, to make the right selection, manufacturers need to consider how the thermoplastic and mold interact together, as certain types of plastics might not be suitable for particular mold designs.
Each mold tool is made up of two parts: the mold cavity and the core. The mold cavity is a fixed part that the plastic is injected into, and the core is a moving part that fits into the cavity to help form the component’s final shape. Depending on requirements, mold tools can be designed to produce multiple or complex components. The repeated high pressures and temperatures that mold tools are put under mean they are typically made from steel or aluminum.
Due to the high level of design and quality of materials involved, developing mold tools is a long and expensive process. Hence, before creating a final bespoke mold, it’s recommended that tools are created, prototyped and tested using computer aided design (CAD) and 3D printing technology. These tools can be used to digitally develop or create a prototype mold that can then be tested in the machine with the chosen thermoplastic.
Learn more about how 3D printing can complement the injection molding process.
Testing the tool with the right thermoplastic is key to ensuring that the final component has the right properties. Each thermoplastic offers different characteristics, temperature and pressure resistances due to their molecular structure. Plastics with an ordered molecular structure are called semi-crystalline and those with a looser structure are known as amorphous plastics.
Each plastic’s mechanical properties will make them appropriate for use in certain molds and components. The most common thermoplastics used in injection molding and their characteristics include:
The final thermoplastic selection will depend on the characteristics that manufacturers need from their final component and the design of the mold tool. For example, if a manufacturer needs a lightweight part with electrical properties, then PC will be appropriate, but only if the mold doesn’t need to operate above 275°F (135°C) or at very high pressures, which the plastic won’t be able to resist.
Once the right thermoplastic and mold have been tested and selected, the injection molding process can begin.
Injection molding machines can be powered by either hydraulics or electricity. Increasingly, Essentra is replacing its hydraulic machines with electric-powered injection molding machines, showing significant cost and energy savings.
Injection molding machines consist of a feeder or ‘hopper’ at the top of the machine; a long, cylindrical heated barrel, which a large injection screw sits in; a gate, which sits at the end of the barrel; and the chosen mold tool, which the gate is connected to.
To start the process, raw plastic pellets of the thermoplastic material are fed into the hopper at the top of the machine. This could be virgin material, like plastic resin, or recycled plastic materials. As the screw turns, these plastic pellets are fed gradually into the barrel of the machine. The turning of the screw and the heat from the barrel gradually warm and melt the thermoplastic to melting point until it turns to a molten material.
Maintaining the right temperatures within this part of the process is key to ensuring the plastic can be injected efficiently and the final plastic part formed accurately for the injection molding project.
Once the melted plastic reaches the end of the barrel, the gate (which controls the injection of plastic) closes and the screw moves back. This draws through a set amount of plastic and builds up the pressure in the reciprocating screw ready for injection. At the same time, the mold halves close together and are held under high pressure, known as clamp pressure.
Injection pressure and clamp pressure must be balanced to ensure the part forms correctly and that no plastic escapes the tool during injection. Once the right pressure in the tool and screw is reached, the gate opens, the screw moves forward, and the molten plastic is injected into the mold.
Once most of the plastic is injected into the mold, it is held under pressure for a set period. This is known as ‘holding time’ and can range from milliseconds to minutes depending on the type of thermoplastic and complexity of the part. This holding time is key to ensuring that the plastic packs out the tool and is formed correctly.
After the holding phase, the screw draws back, releasing pressure and allowing the part to cool in the mold and the plastic solidifies. This is known as ‘cooling time’, it can also range from a few seconds to some minutes and ensures that the component sets correctly before being ejected and finished on the production line.
After the holding and cooling times have passed and the part is mostly formed, ejector pins or plates eject the parts from the tool. These drop into a compartment or onto a conveyor belt at the bottom of the machine. In some cases, finishing processes such as polishing, dying or removing excess plastic (known as spurs) may be required, which can be completed by other machinery or operators. Once these processes are complete, the components will be ready to be packed up and distributed to manufacturers.
At Essentra, injection molding is a key production process. As part of our ESG strategy, we are optimizing our plastic injection molding processes, including replacing old hydraulic machines with electric machinery.
We continue to invest in material innovation and have a new Centre Of Excellence at our UK headquarters, which will help us to test and develop new materials that will in turn enable us to offer even more sustainable product ranges globally for our customers.
Our team of experts are on hand to help you create consistent, high quality parts for your next project. With over 45,000 molds to choose from and custom solutions available, we can deliver the parts you need. As well as plastic parts, we also have a range of metal components manufactured using hot chamber die casting.
Free CADs are available for most solutions, which you can download. You can also request free samples (some exclusions apply) to make sure you’ve chosen the right product for what you need. Same day dispatch for sample requests received by 4pm.
If you’re not quite sure which solution will work best for your application, our experts are always happy to advise you.
Request your samples or download free CADs now.
Questions?
Email us at sales@essentracomponents.com or speak to one of our experts for further information on the ideal solution for your application 800-847-0486.
Are you interested in learning more about Prototype Injection Molding? Contact us today to secure an expert consultation!