Custom Urethane Cast Parts - Prototype Urethane Casting
With urethane casting, you can create parts and whole models at a low cost and high quality due to the elimination of metal molds. Runsom Precision is one of the prominent urethane casting manufacturers, and our urethane casting process uses master models and silicone molds built by CNC machining or 3D printing to offer high-quality short-run parts up to 30 inches in length. The finished dimensions of a urethane cast part are affected by part geometry, casting materials, and the accuracy of the master model. Generally, shrinkage is expected to be +0.15%.
What Is Urethane Casting?
Urethane casting, also known as vacuum casting or polyurethane casting, is a versatile manufacturing technology to create complicated end-use engineering parts in polyurethane resins and cast nylon for short-runs or low-mid volume production. This casting urethane process is similar to injection molding but it uses a soft mold instead of metal. Thus, urethane casting is less expensive than injection molding, particularly for low-volume production at shorter lead times.
Parts produced by urethane casting are generally not as strong as injection-molded parts, but have a high-standard surface finish. These high-quality components can be manufactured to extremely tight tolerances and require minimal secondary processing.
Urethane Casting Process
Urethane casting may also be referred to as vacuum casting or polyurethane molding. However, adopting the vacuum procedure to make urethane parts is not always necessary. To put it simply, the urethane casting process can be simplified into the following steps:
Place the master mold in a container of liquid silicone to form a negative mold.
Cut the fully cured silicone mold in half and remove the master mold.
Fill a silicone mold with urethane, and let it cure to create a casting. Before processing, the silicone mold can be reused about 20 times.
Vacuum casting may be an ideal choice when a newly developed product needs to do functional testing or components needs to be fabricated in a small series or small batches. The most essential prerequisite for production is a master pattern model or a prototype, which can be duplicated with polyurethane casting. To know more about this process, you can follow the steps listed below:
In most cases, use techniques such as CNC machining or Stereolithography 3D printing to manufacture a positive master mold, so follow the various stages of this manufacturing process.
Depending on the desired finish on the part in the series, the part is cleaned, sanded, and/or polished.
The master part is placed in a tool, usually made of wood, and silicone is poured around it.
There requires a pause for a while to let the silicone harden, and then remove the wooden tool that surrounds the silicone.
The mold is then cut into several parts according to the pre-determined parting line, and the master is gently taken out.
The resin casting process takes place in a vacuum chamber in which the mold is closed and placed.
The mold filled with still liquid silicone is then placed in an oven and will follow a baking cycle depending on the nature of the resin and the type of cast.
Then, the operator can then remove the polyurethane resin part from the tool. The part is then deburred and goes through quality control.
In most cases, plastic parts are produced by injection molding. However, this process is only available for a certain quantity of parts due to the relatively large workload and related high costs.
Technical Specifications for Urethane Casting
Up to 50 parts in 10 days or less, depending on the part complexity and quantity.
±0.15mm/100mm, with the highest precision up to ±0.05 mm.
Maximum Part Dimensions
The vacuum chamber's dimensions (1900 x 900 x 750 mm) and the product's maximum volume (10 liters) determine the mold's size limitation.
A minimum wall thickness of 0.75 mm is necessary for filling the mold properly. A wall thickness of 1.5mm～2.5mm is recommended.
Service Life of the Silicone Mold
Typical quantities are up to 20-25 copies per mold (depending on the casting materials and the mold's complexity).
Surface Finish & Textures
Textured, colored, painted, coated, clear polished, insert, and over-molding can be obtained. Custom finishes are available for request.
Tolerances for Urethane Casting
|0.5 – 6.00 mm||± 0.10 mm|
|6.00 – 30.00 mm||± 0.20 mm|
|30.00 – 120.00 mm||± 0.30 mm|
|120.00 – 400.00 mm||± 0.50 mm|
|400.00 – 1000.00 mm||± 0.80 mm|
Note: In general, a shrinkage rate of 0.15 % in size should be anticipated.
Cast Silicone Materials
Silicone has multiple use cases - It is not only used for creating casting tools, but it is also a great material for making parts due to its durability, flexibility, resistance to tearing, and ability to withstand high temperatures. It is easy to clean and can attain varying levels of softness ranging from Shore A 10 to an intermediate hardness of Shore A 60. Due to its properties, silicone casting is perfect for crafting soft touch housings, surgical models, medical devices, kitchen accessories, props, and numerous other objects.
Shore A 10 (TC-5005 or equiv.)
Shore A 20-30 (TC-5130 or equiv.)
Shore A 30-40 (TC-5140 or equiv.)
Shore A 40-50 (TC-5150 or equiv.)
Shore A 50-60 (Smooth‑Sil™ 960 or equiv.)
Color Options for Urethane
By adding pigments, polyurethanes can be mixed to produce different hues. The urethane typically has a natural color ranging from amber to milky white. However, Runsom has developed clear urethane choices that are intended to be transparent. The following are the color choices offered by us:
- Natural (unpigmented)
- Clear (colorless)
Surface Finishes for Urethane Cast Parts
The smooth, satiny texture of the parts results from the matte bead-blasting of the master pattern. Thus, transparent and translucent components with this finish will look frosted. The use of matte finishes confers benefits for frequently touched areas, as the visibility of fingerprints is reduced.
Semi-gloss finishes are characterized by some sheen, but not as much as high-gloss finishes. They fall between high-gloss and matte and leave a smooth, effortless-to-clean surface.
Creating a highly reflective, glossy finish requires polishing the master pattern before making the mold. The high gloss with a lot of sheen, provides the greatest degree of transparency for transparent components. High gloss finishes are handy for lenses, cosmetic models, and cleanable surfaces.
Before creating soft tooling, the master pattern is textured using paint and manual techniques. This improves grip and reduces scuff marks, especially on high-use surfaces like handles.
Runsom Precision offers post-processing services such as secondary finishing and painting options.
Why Choose Runsom for Casting Urethane Parts?
1. Expertise and quality assurance
We deliver high-quality urethane casting services quickly by combining industry expertise with the latest tools and technologies.
2. Extensive post-processing options
We also offer a variety of finishing services, including machining, media blasting, painting, and more.
3. Instant quotes and no MOQ
We don't require a minimum order quantity or dollar value for our urethane casting services and provide accurate quotes in 24 hours or less for most projects.
4. Comprehensive support for customers
We provide detailed design for manufacturing support and can make patterns for clients. We also offer video files showcasing production steps for remote clients.
Urethane Casting VS Injection Molding
Urethane casting and injection molding are similar processes in which identical plastic casts can be made from similar materials. However, compared to urethane casting which adopts gravity to fill the mold, injection molding uses pressurized nozzles to push molten plastic into the mold cavity.
There are the major factors you need to consider when making decisions between urethane casting and injection molding.
- Initial cost - Injection molds can be significantly more costly than urethane casts because they are made of metal. This makes the system more of an investment and better suited for long-term, mass batch production. Urethane casting moulds are much more cost-effective for one-off designs, pre-production prototypes, or short runs helping you save money upfront.
- Material cost - Injection molds require highly costly production-grade plastic, such as Acetal, PVC, ABS, and LPDE, which makes urethane a preferable material for prototypes and small batch jobs.
- Per-piece cost - Typically, urethane casting will have a higher cost per piece than injection molding. This is because each mold can only produce a few pieces. On the other hand, the higher output of injection molding makes its cost greatly reduced. This reduces prior higher expenses such as materials and tools. As a result, injection molding is typically a cost-effective method for long-term production, while urethane is more suitable for prototypes due to its lower upfront costs and shorter lead times
The process of making molds for injection molding is time-consuming, sometimes even taking months, greatly increasing delivery time. Typically, the molds are 3D metal printed to try and speed up the process. Instead, urethane silicone molds are much easier to make. Often, they can be made with a 3D printer, a CNC machine, or even by hand, helping to reduce lead times and facilitate your product to market.
Urethane molding can be used for one to hundreds of pieces of prototypes, bridges, and low-volume manufacturing.
Injection molding is most often used for large-scale production of hundreds to tens of thousands of units of prototypes or bridges.
Tolerance of the urethane cast part is +/- 0.010″ for the first inch and +/-.005″ for every inch thereafter. Similarly, injection molded parts tolerances are +/.005″ for the first inch and +/-.002″ for every inch thereafter.
Advantages of Urethane Casting
The main advantages of using urethane casting are listed below:
1. Perfect for rapid prototypes
Your product can be optimized before taking it to the market by functional testing, saving time and money on new product development while shortening the product design prototyping stage. Once your product moves to higher yields, you can switch to another process.
3. Flexible for designs with detailed features
You can build models with complex details and have more freedom in design. This is perfect for custom props and model making. You can even make sharp corners on the inside, which can be difficult to achieve with other processes.
5. Security and reliability
Urethane castings can be FDA certificated, making sense for products used in medical, pharmaceutical, and food processing industries.
7. High accuracy and superior surface finish
Urethane casting is especially beneficial for producing low quantities of parts. It is also useful for first-run production parts, as it enables completion weeks before production tooling is ready.
2. A wide range of shapes and finishes
There is a wide range of finishes cured by urethane casting ranging from very hard to impressively flexible, and they can be added with tints to realize color change. This means your urethane cast parts can be personalized depending on your applications.
4. Fast delivery for low-volume production
Urethane casting creates high-quality end-use parts with precise details. This process has the added benefit of eliminating air bubbles, thereby creating a more seamless and detailed outcome.
6. Versatile cast urethane materials
Urethane casting resins are versatile materials for different applications, including colored, flame retardant, food-grade, and transparent resins.
8. Affordability for silicone molds
The cheap molds used in urethane casting cuts down on the need for costly and time-consuming metal tooling, ideal for producing high-quality prototypes and low volumes of parts.
Disadvantages of Urethane Casting
Urethane casting also has some drawbacks. The following factors you should take into account carefully before making a decision.
1. The casting urethane process can be challenging to achieve your exact requirements. This includes color matching, which can be challenging to get quite right.
2. Even if urethane cast parts can be painted, the final finish you want might not quite match your expectation. It may chip and scratch, exposing the underlying surface. It also means you have to pay extra for labor and materials.
3. The heat from the chemical reaction of the resin draws the water out of the mold, which may lead to breakage on your molds when they suffer a few moldings. But you can spray it with mold release agents after five castings to make it firmer.
Products and Applications Of Urethane Casting
Casting with urethane allows precise and targeted small-batch production as a result of a broad array of materials and surface finishing options available in this process. The casting process is used if plastic casts or rubber parts are required to be of high quality. Commonly used urethane cast parts are:
Functional models and testing
Exhibition and Design models
Components with various colors
Spare parts with high complexity
Pilot production before mass production
Pre-series for the first marketing
The urethane method has a wide range of applications and is a common technique used in virtually every industry, from low-volume or pre-series technical components to post-production of vintage car components, or to samples for customer presentations at trade exhibitions. The areas of applications using urethane casting generally include:
1. Low-Volume Production
Urethane casting is ideal for producing high-quality plastic prototypes quickly and cost-effectively, especially when volumes are low and traditional tooling isn't justified. Our rapid prototyping services enable the creation of custom, complex parts in small batches more efficiently.
3. Engineering Testing
Urethane casting with affordable tooling makes engineering verification and design changes simple and economical. This also allows for functional testing before mass production and obtaining necessary certifications.
2. Aesthetic Models
The urethane cast parts can be produced in a variety of colors, textures, and finishes for cohesive aesthetics. To decide on the best color for a final product, create a silicone mold to produce multiple castings, each with different designs, for internal discussion during meetings.
4. Advanced Prototyping
Urethane cast parts are perfect for consumer testing and user evaluations due to their functionality and quality finish. The casting process allows for quick changes to be made for further testing or market launch.
Urethane Casting FAQs
The process of Urethane Casting involves using an SLA printer to create a "master pattern," which is then used to make a mold of silicone gel. This mold is then used to produce identical parts using urethane. The production of parts requires tooling, a master pattern, and the use of urethane material.
When compared to creating an injection molding mold, creating a urethane casting mold is more cost-efficient. While complex injection molds can spend tens of thousands of dollars, the process of constructing a urethane casting mold typically costs only hundreds or thousands of dollars.
In contrast to Urethane Casting, Injection Molding uses pressurized nozzles filled with molten plastic to fill molds. These molds are designed to cool quickly and eject parts promptly, which allows for high-volume production runs with consistent part quality.
To create parts using Urethane Casting, the process involves pouring or injecting polyurethane resins and additives into a silicone mold. This method is typically used for low to medium production volume and uses silicone or “soft” molds.
Urethane casting allows for varying wall thicknesses, which is an advantage over injection molding. However, it's important to have a minimum wall thickness of 0.020” to 0.050” for most designs to ensure accuracy and a complete fill.
When comparing urethane casting with 3D printing, the material quality and performance are the key differentiators. Urethane casting presents superior materials that closely replicate those present in commercial products, thereby enabling high performance. Moreover, urethane cast parts exhibit improved finish and fit. Thus, if you prioritize material quality and appearance, you should consider urethane casting.
The primary factor that determines the selection of urethane casting or injection molding is the quantity of production required. For small quantities, such as less than 50 pieces, urethane casting is a great option as it offers production-grade parts. On the other hand, injection molding has higher upfront tooling costs which may not be ideal for low-quantity runs. Usually, customers opt for urethane casting to test and refine their design before investing in an injection molding tool.