When comes to a project, engineers always want to know which process is better for Urethane casting vs injection molding, this is because Urethane casting and injection molding can be both used for low-volume manufacturing plastic parts. This blog will help to compare these two processes in terms of all the factors of a project such as volumes, cost, lead time, and design considerations including material, precision, wall thickness, and more.
What is urethane casting?
Urethane casting creates plastic parts by pouring liquid urethane into a mold cavity which is typically made from a soft material such as silicone. the liquid urethane is cured with the mold in a heated chamber to form the part.
To understand clearly the Urethane casting process, you can find more details in our blog: Urethane Casting Process: A Complete Guide.
What is injection molding?
Injection molding makes plastic products by injecting molten plastic material into the cavities of a mold which is made from steel. the molten plastic material rapidly cools down in the mold and forms the plastic parts. it’s an ideal process for large-scale manufacturing operations.
Comparison of urethane casting vs injection molding
Mold
The mold for urethane casting is made of soft materials such as silicone while the mold for injection molding is made of metal such as steel or aluminum which is much more durable than silicone.
The mold for urethane casting is created based on a master pattern which is made by CNC machining or 3D Printing, Use liquid silicone surrounding the entire master pattern to cure and set, then form the mold. The Mold for injection molding is made from CNC machining and electric discharge machining (EDM) on a proper size metal block directly.
Lead time
When comparing the lead times of these two processes, we need to compare two factors mold making lead time and plastic part making time.
The time of Mold making for injection molding takes from 4 weeks to 2 months, it is much longer than that of urethane casting which only takes from one to two weeks. The time for plastic part making by injection molding takes only a few seconds, it is much shorter than that of urethane casting which needs hours to cure the urethane material.
Cost
the cost of these two processes both include mold cost and part cost.
the mold cost of injection molding costs ranges from $2000 to $100000 depending on the complexity of the mold. in contrast, the mold cost of urethane casting is much cheaper which only ranges from $100 to $1000.
Regarding the part cost, Urethane molding part costs range from $20 to $100. while injection molding costs range from $1 to $10. this is because urethane molding is a much more labor-intensive process, while injection molding can be more automated.
But, for the machine investment of these two processes, the Injection molding machine costs much more than the urethane casting machine.
Volumes
Urethane casting is commonly used for prototyping and low-volume manufacturing from 1 to 100 parts. Injection molding can be used for both low-volume and high-volume production from 100 to 100,000 parts by using different steels with different hardness.
Design flexibility
Urethane casting parts have more design flexibility such as undercuts, and small draft angles than injection molding parts design. this is because Urethane casting uses flexible silicone molds which can accommodate undercuts and draft angles more easily.
Mold Lifespan
Urethane casting mold lasts between 10 to 25 runs due to the soft silicone material. it will lose part quality if over runs. when you need more parts over 25 pieces, you need to make more silicone molds. In contrast, Injection molding mold made of aluminum or steel can last between 1,000 to 100,000 shots with good maintenance conditions.
Design Considerations of urethane casting vs injection molding
When we compare urethane casting and injection molding, we also need to know the part design according to the requirements of these two processes so that you can choose the right one for your project.
Part materials
Urethane casting uses polyurethanes which simulate the injection mold grade production plastic with different hardness. while Injection molding uses the actual production of plastic materials with wider choices. they both can make custom-colored or textured parts.
Precision
Injection molding parts have better precision because of the hard steel mold. injection molding part tolerance start at +/.004”(0.1mm) for the first inch, and +/-.002”(0.05mm) for every inch afterwards. While, Urethane casting parts tolerance starts at +/-.01”(0.25mm) for the first inch, and +/-.005”(0.125mm) for every inch afterwards.
Wall Thicknesses
The wall thickness of Urethane casting parts is generally between 1 mm (0.04 inches) and 5 mm (0.20 inches). While the wall thickness of injection molding parts is generally between 0.5mm to 4mm.
Pros and Cons of urethane casting and injection molding
Here we summarize a table for you to understand the pros and cons of urethane casting and injection molding, and then you can find how to choose for your project.
| Urethane Casting | Injection Molding | |
| Best used for | Rapid prototypes and manufacturing Low volume of less than 100 pieces | 1. mass production 2. Low volume from 100 pieces to 1000 pieces 3. Prototypes need the same materials as mass production |
| Pros | 1. Cost is cheap when the volume of the part is less than 100 pieces. 2. Fast to get the parts | 1. High efficiency to make parts when the volume is high 2. High precision of the part’s dimension 3. Pieces come out ready for use. |
| Cons | 1. Need much time for setting up for every part 2. Mold lifetime is short and needs replacement 3. Parts require post-finishing such as polishing and trimming. | 1. Mold cost is high 2. Mold-making time is long |
How to Get the Molded Parts You Need?
Urethane casting and injection molding are both manufacturing processes that require expertise and investments. KUSLA engineers can help you choose the right process for your projects and help you save your costs with high-quality molded parts. Contact us or find out more about KUSLA Urethane Casting Service and Injection Molding Prototyping Service.
You may also interested in other plastic parts manufacturing process comparisons
FAQs
Is casting cheaper than injection molding?
Not really. this depends on the volume of your project. for part cost, casting is more expensive than injection molding due to more labor costs. for mold cost, casting is cheaper than injection molding.
How to choose between urethane casting and injection molding?
you should check with a professional rapid prototyping and manufacturing supplier as KUSLA, we will provide feedback based on your project needs.
