How To Create 3D-Printed Molds for Casting

For full transparency, buying a 3D printer, especially a fairly good one, can be expensive. The molds often need a little extra post-processing work, like sanding or sealing, to get the best quality, and sometimes the surface of a 3D-printed mold isn't as smooth as what you’d get from traditional methods. 

Also, 3D-printed molds might not last as long as traditionally made ones, especially under high stress or temperatures. However, the only real aspect where traditional mold-making techniques beat 3D printing ones is the size of the molds you can make. With 3D printing, the mold’s size is restricted by the size of your 3D printer. 

As long as you know what you’re doing, it’s quite simple to make 3D-printed molds for casting, so we prepared some step-by-step instructions for you. 

1. Design a CAD Model

The first step is to design your mold using CAD (computer-aided design) software and create a 3D digital model of what you want to cast. Some popular CAD software options are Autodesk Fusion®, SolidWorks®, and Tinkercad®. Make sure you’ve got all the details down, including draft angles and parting lines to help you easily remove the final object from the mold. 

You’ll also want to check the wall thickness to ensure the mold is strong enough for the casting material. You might want to include extra features like channels for pouring the material (runners or sprues) and vents to let air escape. Our top tips for this step are to keep the design simple, go for symmetrical designs, and avoid filled objects within hollow spaces.

2. Determine if the Model Is Hollow or Solid

You then have to decide if your model will be hollow or solid because the casting process is slightly different for each. Hollow models are slightly more complicated because they require an internal structure that needs to be removed after casting. Solid models don’t need internal support so are generally easier to make. If you’re making a solid model, you can skip ahead to step 4.

3. Generate the Inside Structure for the Hollow Model

For hollow models, you’ll need to create an internal structure inside the mold. Your final piece will have a hole somewhere that’s large enough to allow the removal of the supporting material when the cured resin is stretched. You can make the solid block inside your hollow model using CAD software. Align this block within the hollow space, then add support pieces to keep the structure in place during casting (you’ll have to remove this later). This step basically ensures that the final cast doesn’t lose its shape when the mold is removed. An example is below:

4. Generate a Solid Block Around the Model

To create a block around your model that will form the outer walls of the mold, you’ll need to make it watertight (if it isn’t already solid — if it is, go ahead and skip this step). Design a larger block around it to make sure the model is centered; the model should be surrounded by the block, with space between it and the block’s inner walls. Then combine the block and model into one object. Congratulations! You now have the block that will define the shape and size of your final cast.

5. Split the Block Into Two or More Pieces, Depending on the Design

If you have a really complex model, you might need to split the block into two or more pieces to allow for easy removal after casting. Think about where it would be best to make the split so that it will make the process easier without damage. For example, if your model is ball-shaped, you’ll need at least one split along the middle so that you can easily pull the sections apart. 

The splits will need to give you access to the inside of the model so that you don’t end up squishing or damaging it. Our top tip in this section is to avoid making wedges or shapes that would make the block difficult to remove. For smaller, simpler designs, you can likely skip this step.

6. Embed the Model Into Solid Blocks

Next, put your model inside the split blocks sideways so that it’s centered. This will ensure you get equal coverage on both sides when the blocks are put together. Make sure that the blocks fit snugly around the model when you bring them together and that you add alignment pins to help guide the mold halves together for a perfect fit. 

You should also add a central channel to pour the material into, and this should be wide enough for the resin to flow smoothly, and prevent blockage, or air bubbles from forming. We recommend designing a chamber for extra resin that sits on top of the mold; gravity will help pull it down into the mold, and you can make it as big or small as you like to hold the exact amount of resin you need.

7. Start the 3D Printing

This is the fun part, you can now start printing your mold. Make sure your 3D printer is ready, properly calibrated, and with the right material loaded, whether it’s pouring resin into the chamber or adding a spool of filament. Check that the printer bed is clean and level and that the printhead or extruder isn’t obstructed in any way. Use slicing software to prep your design for printing. This software tells the printer how to build the mold layer by layer (or one “slice” at a time), and gives it precise instructions on things like layer height, infill density, and print speed. When you’re done, hit print and keep an eye on the process to catch any issues early on.

8. Use the Printed Mold and Pour the Silicone to Start the Casting Process

Once the mold is printed (and you’ve taken a few moments to admire your handiwork), it’s time to form the actual cast inside your 3D-printed mold. Mix the silicone according to the instructions on the pack, and pour it into the mold. Do this slowly and evenly from one end, allowing the silicone to properly fill the cavities, and taking care to avoid air bubbles. If bubbles do form, gently tapping or shaking the mold should get rid of them. 

If air bubbles are the bane of your life, you can always get a vacuum chamber or a pressure pot designed especially for silicone casting to remove air bubbles easily. Allow the silicone to fully harden—the silicone’s instructions will tell you how long this will take—before you carefully remove the mold. If you have splits, you can separate the halves; otherwise, you can flex the mold to release the cast.

9. Trim the Excess Parts

After the cast has cured and been removed from the mold, trim away any excess material that might have leaked out or formed around the edges with an appropriate tool, like a hobby knife or scissors. Do this slowly and carefully so you don’t accidentally cut into the actual cast.

What Are the Advantages of 3D-Printed Molds for Casting?

The use of 3D printing for casting molds has a wide range of advantages, including:

1. 3D printing offers unparalleled design freedom, allowing the creation of intricate, thin-walled geometries in a single step without the need for additional tools. 
2. 3D printing offers significant cost advantages. The requirements are minimal: a digital file, printing material, and a 3D printer. 3D printing eliminates the need for additional equipment and labor. 
3. 3D printing patterns follow an automated process, enabling rapid production. Patterns can be printed in a matter of hours or days. Moreover, if a pattern does not meet requirements or needs modifications, digital designs can be easily adjusted and reprinted, reducing turnaround time.
4. 3D printing minimizes raw material consumption and reduces waste generation. It only uses the necessary material to create the final printed pattern.
5. By utilizing digital files and 3D printing, the need for physical model inventory is eliminated. Instead of storing and managing physical molds, new patterns can be quickly and cost-effectively 3D-printed on demand.

What Is the Disadvantage of 3D-Printed Molds for Casting?

While there are many benefits that 3D printers can bring to the mold-making industry, there are also some disadvantages to consider:

1. Investing in a 3D printer, especially larger-scale models, can require a significant upfront investment. 
2. 3D-printed molds often require additional post-processing and finishing steps to achieve the desired mold quality. This may involve sanding, sealing, or applying surface treatments.
3. The durability and lifespan of 3D-printed molds may be inferior to those produced using traditional methods. Depending on the materials and printing techniques employed, 3D-printed molds can be more susceptible to wear, deformation, or degradation when exposed to the stresses and temperatures associated with casting processes.
4. The size of 3D-printed molds can be limited by the build volume of the 3D printer. If a larger mold is required for casting large parts, it may need to be printed in multiple sections and assembled.
5. 3D-printed molds may not always achieve the same level of surface finish and texture as molds produced through traditional methods like machining or mold making. Depending on the 3D printing technology used and the resolution of the printer, the resulting mold surface may exhibit visible layer lines or roughness.

What Is a Mold for Casting?

3D molds for casting are essentially shapes or forms made using 3D printing technology. They are then used to create objects by pouring liquid materials like metal, plastic, or silicone into them (kind of like those ice trays that can create ice cubes in the shape of fruit or animals). Once the material hardens, the mold is removed to reveal the final product. 

Why 3D Printed Mold Is Cheaper?

A 3D-printed mold is often considered cheaper compared to traditional mold-making methods for several reasons. Traditional mold-making processes typically require the production of complex and expensive tooling, such as CNC-machined molds. These tools can be costly to design, manufacture, and maintain. In contrast, 3D printing eliminates the need for tooling. The mold can be directly printed from a digital file, significantly reducing tooling costs. Design iterations with 3D printing are much simpler and more cost-effective. Changes can be made directly in the digital file, and the updated mold can be quickly printed without the need for new tools or extensive manual labor. Additionally, 3D printing allows for on-demand production for which molds can be printed as needed.

What Are Other Types of Casting

Metal casting processes utilize various types of molds made from different materials to meet the specific requirements of the metal being cast. The name of the casting process often corresponds to the type of mold used. Some other common metal casting methods include:

1. Sand Casting: This involves creating molds using a combination of sand with a bonding agent, typically clay. The mold is created by compacting the sand around a pattern and creating a channel or gate for pouring the molten metal. After the mold solidifies, the pattern is removed, and the metal is poured into the cavity. Once cooled, the sand mold is broken away, revealing the final part. Sand can often be recycled for additional molds, making sand casting a cost-effective method. It is widely used, accounting for approximately 60% of all metal castings, and is suitable for a range of applications, including heavy steel foundry applications.
2. Investment Casting: The term "investment" refers to the process of encasing or surrounding the pattern with a material, usually wax or refractory material. The wax pattern is coated with a ceramic slurry, forming a mold. The wax is then melted and burned away, leaving behind a cavity that is subsequently filled with molten metal. Investment casting is commonly known as "lost-wax casting" and is widely used in the jewelry industry due to its ability to create intricate and detailed parts.
3. Plaster Casting: Plaster casting is similar to sand casting, but instead of sand, the mold is made of plaster. This method is often used for producing small parts such as valves, gears, and fittings. However, plaster casting cannot be utilized for ferrous materials such as steel. Plaster molds are more unstable than sand molds, and the longer cooling time limits production volumes.
4. Die Casting: In die casting, molten metal is injected into a mold under high pressure. This process is commonly used for producing engine blocks and ship propellers. Die casting is predominantly used with non-ferrous materials like aluminum, pewter, tin, or copper. Die-cast molds are durable and resilient, making them ideal for industries requiring high-volume production of small to medium-sized castings.

Copyright and Trademark Notices

1. Fusion®, Tinkercad®, and AutoCAD® are trademarks of Autodesk, Inc., and/or its subsidiaries and/or affiliates, in the United States
2. SolidWorks® is a registered trademark of Dassault Systèmes SolidWorks Corp
3. Rhino3D® is a registered trademark of Robert McNeel & Associates

Disclaimer

The content appearing on this webpage is for informational purposes only. Xometry makes no representation or warranty of any kind, be it expressed or implied, as to the accuracy, completeness, or validity of the information. Any performance parameters, geometric tolerances, specific design features, quality and types of materials, or processes should not be inferred to represent what will be delivered by third-party suppliers or manufacturers through Xometry’s network. Buyers seeking quotes for parts are responsible for defining the specific requirements for those parts. Please refer to our terms and conditions for more information.