Urethane casting or vacuum casting is an increasingly popular and cost-effective manufacturing technique renowned for its ability to produce intricate, high-quality, and resilient components. This article offers an in-depth examination of urethane casting, encompassing its process, materials, molds, and advantages. Furthermore, we will explore its diverse applications and compare it with 3D printing to assist you in determining the optimal method for your production needs. Catering to both seasoned professionals and industry newcomers, this extensive guide provides invaluable insights into the potential benefits of urethane casting prototypes for your future projects.

What is urethane casting?

Urethane casting (vacuum casting) involves creating a product prototype (master) using 3D printing or CNC machining, then producing a silicone mold in a vacuum environment. The casting material undergoes degassing, stirring, preheating, and pouring under vacuum conditions, followed by a secondary curing process at 60-80℃ for 2-3 hours in a temperature-controlled chamber. This technique is ideal for the new product development phase and small-scale (10-200 units) sample production. Silicone molds offer excellent flexibility, enabling the creation of urethane-casting prototypes with complex structures, intricate patterns, and even negative draft angles. This process boasts a short production cycle and high product quality.

What is the process of urethane casting?

Step 1: Create the master

Duplicate quality depends on master quality. Apply textures or other treatments to the SLA 3D printed or CNC machined master's surface to simulate the product's final details. The silicone mold accurately replicates the master's details and textures, ensuring consistency between the duplicate and the prototype.

Step 2: Create the silicone mold

The mold, made of liquid silicone, is also known as an RTV mold. Silicone boasts excellent chemical stability, self-releasing properties, and flexibility, minimizing shrinkage and effectively transferring part details from the master to the mold. The silicone mold creation process includes:

(1) Apply tape to flat areas around the master for easy demolding and establishing the parting surface of the final mold.

(2) Suspend the master in a box, positioning rods on the part to set up pouring gates and vent holes.

(3) Pour silicone into the box, vacuum, then cure it in an oven at 40℃ for 8-16 hours, depending on the mold's volume.

(4) Remove the box and rods from the silicone, then extract the master, form a cavity, and finish the mold.

Step 3: Vacuum casting

(1) Preheat the silicone mold in an oven at 60-70℃.

(2) Select an appropriate release agent before assembly and apply it properly to prevent sticking and surface defects.

(3) Prepare polyurethane (PU), preheat it to around 40°C, mix both components in the correct ratio, stir thoroughly, and degas under vacuum for 50-60 seconds.

(4) Pour the PU material into the mold in a vacuum chamber, then cure it again in an oven. The average curing time is about 1 hour.

(5) After curing, remove the cast part from the silicone mold.

Repeat this process to produce more duplicates.


What material is used for urethane casting?

The material for urethane casting is polyurethane, PU in short. The material properties can be ABS-like, PP-like, PA-like, PE-like, PMMA/PC-like transparent parts, soft rubber parts (40-90 shore A), high-temperature resistant parts (150°C), flame-retardant materials, etc.


What mold is for urethane casting?

The mold for urethane casting is silicone mold. The silicone material is usually domestic, imported, transparent or special silicone. 

Speedy production

With a master in hand, a silicone mold can be created within 24 hours, facilitating casting and product replication.

Effortless demolding

The silicone mold's flexibility and elasticity allow for the easy removal of complex structures and deeply grooved parts after casting, eliminating the need for increased draft angles and simplifying mold design.

Precise replication

Room-temperature vulcanized silicone rubber boasts excellent simulation and an extremely low shrinkage rate (about 0.3%), enabling the swift production of 20-30 identical products using silicone molds.

However, the mold lacks resistance to acids, alkalis, and aging, resulting in a limited lifespan. The mold surface may display imperfections such as traces, streaks, or roughness, and the product's precision is lower compared to CNC machining.

Benefits of urethane casting

1. Rapid production time

Products can be created in just a few days, cutting the production time by 90% compared to traditional injection molding processes (60-90 days).

2. Cost-effective low-volume production

A single silicone mold lasts 20-30 shots, providing high production efficiency and lower manufacturing costs.

3. Superior detail replication

Silicone molds can craft complex structures and intricate patterns, capturing the product's surface details and precisely reproducing the fine features of the original master.

4. Integrated molding

Silicone mold production enables integrated molding for conventional injection-molded products, resulting in enhanced overall strength.

5. Pre-embedding and secondary casting capabilities

The silicone mold process supports pre-embedding and secondary casting, such as rubber encapsulation for air vents and pre-embedded metal inserts.

Applications of urethane casting

1. Small-batch production

Silicone molding excels in creating small quantities of high-quality plastic prototypes quickly and economically, particularly when steel mold production isn't warranted.

2. Functional testing

The urethane casting process and affordable silicone molds streamline engineering verification and design adjustments, making it especially suitable for functional testing before product releases.

3. Aesthetic evaluation

Urethane casting prototypes can act as a comprehensive set of aesthetic models. If unsure about the ideal design for a product, generate a silicone mold and create 10-15 replicas with varying colors and textures to encourage internal design team discussions.

4. Marketing demonstrations

Small batch replicas are optimal for consumer evaluations. By showcasing models at exhibitions or sharing product photos in advance through promotional materials and official websites, you can generate pre-launch interest and attract potential customers or implement product enhancements.

Urethane casting vs 3D printing

Urethane casting and 3D printing are both popular methods for prototyping and low-volume production. How to choose between them?

Ideal for creating multiple replicas with the same mold, urethane casting is cost-effective for high-quality, low to medium-volume production. It can produce parts with a variety of colors, textures, and materials. But it requires a longer setup time due to mold creation.

3D printing is a quick, flexible, and precise process tailored for prototyping and limited batch production. It is suitable for one-off production runs or highly customized parts. It allows for complex geometries and structures that may be difficult to achieve with urethane casting. 3D printing enjoys faster setup time compared to vacuum casting, as no mold is required.