Get High-Quality Cast Urethane Parts

Table of Contents

What is Cast Urethane?

Cast urethane is creating a mold from a 3D-printed master pattern and using that mold to form parts from liquid resin materials. The liquid resin solidifies into end-use pieces with exceptional precision, consistency, and speed, making this manufacturing process ideal for low to medium-volume production runs (from 1 to in the 100s), and parts can be made with flexible or rigid parts materials

How Does Cast Urethane work?

At Midwest Prototyping, we use four types of cast urethane molds; box molds, cut molds, 3D-printed molds, and gravity molds. 

Three of the processes we offer follow similar steps.  Our cast urethane specialists take a master pattern, often 3D-printed using stereolithography, and create a frame around the part.  Silicone is poured into the frame around the component.  Then the frame is placed into a pressurized tank where any bubbles are drawn out, and the silicone hardens around the master pattern.  After this, the master pattern is removed from the hardened silicone, which creates the mold.  From this mold, we can create exact replicas of the master pattern.  

What are the advantages to using Cast Urethane?

Whether you need multiple prototypes or are ready to jump into low-volume production, there are many advantages to using Cast Urethane. Cast urethane produces high-quality, precise, and consistent parts. The molds are low-cost and suitable for 20 – 25 reproductions. For larger production orders, we create more molds and maintain low prices for parts produced in the 100s. There is no need for expensive tooling. Cast Urethane is a relatively quick method. Once the CAD files for the master pattern are received, the products will be made and shipped in as little as three to ten days. The design flexibility is similar to injection molding, with a few exceptions. We’ll go into more detail below in the design guidelines section. We also offer a wide range of materials in our cast urethane department. For more information on materials, don’t hesitate to contact one of our solutions managers at solutions@midwestproto.com or call us at 608-437-1400.

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Which types of Cast Urethane molds do you use?

Box Mold

Box molds are our most popular cast urethane mold; creating them is a two-step process.  In step one, the part is placed into the frame with clay on one side.  The cut line is determined by where the clay is placed.  The silicone is poured into the box, and the box is placed into a pressurized tank.  Once the silicone is hardened, it is removed, the box is opened up, and the clay is removed from around the part.  Step two is repeating step one by replacing the clay with silicone.  When this process is finished, the master pattern can be removed, and end-use parts can be created. 

Cut Mold

The part is clued to the gates and vents with cut molds and suspended in the frame. The silicone is poured around the piece, and the frame is placed in the pressurized tank. Once finished, the structure is removed from the material, and the cutlines are determined according to the part location and geometry. Creating a cut mold is one day faster. However, parts need to be simpler to turn out.  

3D Printed Mold

3D-printed molds are printed in-house and can be used for silicone parts.  This is easier to remove the parts and can be re-used forever as long as heat isn’t introduced.  Another advantage to 3D-printed molds is no need for a master pattern.

Gravity Mold

Gravity molds are used for more complex parts—for example, elements with locked-in features. A gravity mold is created much like a cut mold, where the master pattern is suspended in the frame and silicone is poured around it. Once the silicone is set in the pressurized tank, the box can be removed, and cutlines are created around the pieces. This is a very time-consuming process depending on how complicated the part is. The difference between the gravity mold and the cut mold is the gravity mold won’t have gates and vents. The end-use material can be poured into the mold.

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Learn more about designing cast urethane parts.

Visit our post, which discusses best practices for designing parts needing wall thickness, drafts and undercuts, ribs, and more. If you have any questions, don’t hesitate to reach out to one of our Solutions Managers at solutions@midwestproto.com.

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