The demand for low-volume custom parts in various industries has led to a rise in urethane casting. In 2022, a whopping 25.78 million metric tons of polyurethane were sold globally, and experts predict this number will shoot up to 31.27 million tons by 2030 (Statista).
This cost-effective method is an excellent alternative to traditional techniques like injection molding. If you are into creating prototypes, short-run productions, or specialized components, urethane casting is the way to go!
This guide will provide all the essential information to understand how to cast urethane, from its process to picking suitable materials. We have also rounded up some pros and cons and explained how this method differs from injection molding.
What Is the Urethane Casting Method?
Urethane casting, or vacuum casting, is a manufacturing process often used to make custom parts in small quantities. It is an economical alternative to methods like injection molding and is widely used for prototyping, short production runs, and artistic projects.
What Is the Cast Urethane Process?
Here is a step-by-step guide for the cast urethane process:
Step 1: Make a Master Model
This is like the blueprint for your final parts. You can create it in a few ways:
●3D Printing
3D printing builds your model layer by layer. It is a great option for complex shapes; however, it might need some smoothing afterward.
●CNC Machining
CNC machining carves your model out of a block of material. This method is very precise, but it is slower and more expensive than 3D printing.
Step 2: Build a Mold
To make the mold:
●Place the master model in a box and secure it with glue.
●Use dowel pins to clear the holes in your design during molding.
●Remove the air bubbles from the silicone rubber before pouring it into the two layers to form the mold.
Once cured in the oven at 40°C, the mold perfectly captures the master model’s details and is ready for urethane casting.
Step 3: Casting with Urethane Resin
With the mold prepared, you can now create the urethane parts. Prepare the polyurethane resin, preheat it to about 40°C before use, mix the two components of the resin in the correct proportion, then stir and deaerate it thoroughly under vacuum for 50-60 seconds.
Once everything is poured, place the mold in an oven for curing. It is where the urethane resin hardens, transforming it into your desired design. In this step, you can adjust the hardness and rigidity of the part by controlling factors such as the heating time.
The properties of the urethane parts can be similar to ABS, PC, PMMA, soft rubber, etc.
Step 4: Finishing Touches
Once the casting is complete, remove the part from the mold and inspect it carefully. Remove any extra material left from the mold and give it a smooth finish.
Lastly, you can sandblast the part to get a matte surface or paint it in any color you like for that perfect look. Also, through electroplating, you can get a mirror-like finish.
What Material Is Used for Urethane Casting Mold?
The material used for urethane casting mold is usually silicone. It is a flexible mold material ideal for urethane casting due to heat resistance. Silicone is easy for part removal and reusable for replicas in prototyping and small series.
What Are the Advantages and Limitations of Urethane Casting?
Advantages
● You can create working prototypes at a lower cost, compared to mass production with injection molding. It enables you to test the market before committing to full-scale manufacturing.
● Offers high-quality, production-grade parts for smaller batch runs.
● Captures intricate details and sharp internal corners, making it perfect for creating custom models and props.
● Minimal shrinkage (0.15%) compared to other casting methods.
Disadvantages
● Getting consistent colors can be difficult, and painted finishes might give you a different look than you want.
● The curing process of urethane resin can wear down the mold because it pulls out moisture.
What Are the Differences Between Urethane Casting and Injection Molding?
● Mold Material and Cost
- Urethane casting uses relatively inexpensive and quicker-to-produce silicone molds.
- Injection molding requires expensive, highly durable steel or aluminum molds that take longer to manufacture.
● Production Volume
- Urethane casting is used for prototypes and low-volume production, 1 to 100 parts per day.
- Injection molding is best suited for medium to high-volume production, with hundreds to thousands of parts per run.
● Project Cost
- The urethane casting cost per project can range from a few hundred to thousand dollars.
- On the other hand, injection molding is expensive and costs around $12,000 on average.
● Turnaround Time
- Urethane casting has faster turnaround times (often weeks) because mold creation is less complicated.
- It takes months for injection molding to complete a production run due to the complexity of the mold and the production process.
● Tooling Costs
- Urethane casting uses relatively inexpensive silicone molds.
- Injection molding requires expensive, durable steel or aluminum molds.
● Design Complexity
- Urethane casting offers more flexibility for intricate designs with undercuts and sharp corners.
- Injection molding may require design modifications for features like undercuts due to mold limitations.
Conclusion
The urethane casting process may appear to be complex. However, that’s not the case! Following the procedure and using the proper materials is a pretty simple way to bring your ideas to life.
It allows you to create prototypes, small productions, and intricate parts with fast turnaround times. This versatile and economical process is perfect for designers, entrepreneurs, and hobbyists.
By going through the guide, we hope you have found the information you need to explore the ins and outs of the cast urethane process, the materials used, and how it can benefit you.
