Urethane Casting (Vacuum casting) is widely used in various industries for prototyping and low-volume parts manufacturing. During the usual business communication with many engineers, we found that they do not understand clearly how dose Urethane Casting works. Today, in this article, KUSLA will explain everything about urethane casting and the common questions from the engineers who need Urethane Casting Service.
What Is Urethane?
Urethane, also known as polyurethane, is a synthetic polymer that belongs to the family of thermosetting plastics. it is a kind of resin which have similar properties to engineering plastic such as acrylic, polycarbonate, ABS, etc.
What is Urethane Casting or Vacuum Casting?
Urethane casting, also called Vacuum casting, is a process that involves using the master prototype to create a silicone mold in a vacuum state, then Casting Polyurethane and other materials through the silicone mold to clone the same replica as the master prototype. These replicas can test and verify the performance and status of products under different materials and different surface treatments.
Video of the Urethane Casting process as below:
Urethane Casting Materials
Urethane Casting Materials are usually classified by the harness of the resins. they typically range in hardness from 40 shore A (soft resin) to 85 shore D (rigid resin).
Rigid Urethane (Shore D Resins)
Shore D urethane resins are a group of rigid urethanes that provide toughness and durability like engineering plastics. Different hardness shore D urethanes can be comparable to different engineering plastics such as Acrylic, Polycarbonate, ABS, HDPE, and Nylons.
Urethane Elastomers (Shore A Resins)
Shore A Urethane Elastomers are soft materials that provide great flexibility and good tear strength. They have similar physical properties to rubber and can be used for applications where soft rubber materials are needed.
Silicone
Silicones are softer than shore A materials and can be used to create some kinds of parts such as sealing, they are also commonly used to create the molds by which end-use parts are cast.
Physical Properties of Common Urethane Casting Materials
Here we summarize a table to show the Physical properties of Common Urethane Casting Materials in our Urethane Casting services.
| Type name | Hardness | Plastic-like | Color | Flexural Strength | Flexural Modulus | Tensile Strength | Elongation | Heat Deflection Temperature | |
| Rigid Urethane | DPI8150 | 83 Shore D | ABS-like | Black, white, yellow | 100Mpa | 2140Mpa | 85Mpa | 8% | 100℃ |
| PX-520 | 80 Shore D | Polycarbonate -like | Clear | 100Mpa | 2000Mpa | 50Mpa | 10% | 70℃ | |
| DPI6160 | 80 Shore D | High Temperature | Black, white, yellow | 115Mpa | 2100Mpa | 58Mpa | 15% | >200℃ | |
| Urethane Elastomers | DPI8400 | 20-90 Shore A | Rubber-like | Black, white | / | / | 15-180Mpa | 200%-500% | 80℃ |
Vacuum Urethane Casting process steps
Step 1: Create a Master prototype by CNC machining or 3D Printing, CNC machining is preferred if high precision replica is needed for Urethane Casting prototypes.
Step 2: Make a silicone mold in a vacuum environment, pour liquid silicone over the master prototype, and let it cure. The mold is usually split into two halves for easy removal of the cast part.
Step 3: Cast Urethane resin, The mixed urethane material is poured into the mold cavity and cured to form the parts.
Step 4: Open The Mold, Once the Urethane material has cured, the mold is opened and the cast urethane part is carefully removed.
Step 5: Post Finishing, the cast part usually needs post finishings such as trimming, sanding, painting, or other surface treatments.
Urethane Casting Machines
A vacuum urethane casting machine is used for mixing, casting, and curing. Operators control parameters like pressure and temperature. The machines are of different sizes and can work with various materials. Some common machines are as below:
- Renishaw 5/01 PLC: Handles molds up to 530 x 450 x 420 mm
- SLM VCM 04: For molds up to 750 x 750 x 900 mm.
- MCP 5/01: Suitable for parts up to 400 x 400 x 400 mm. Offers larger models.
- Scott AM 1000: Handles molds up to 500 x 450 x 425 mm.
- Multistation CSV 340: Capable of molds up to 340 x 340 x 435 mm.
Advantages of Urethane Casting
High precision: Urethane casting can duplicate all details of the master prototype made by CNC machining including the accurate dimensions and surface quality.
Short lead time: urethane casting prototypes can be made within a few days for low-volume production which can significantly save the time of the product development.
Cost saving: Urethane casting uses silicone mold which is a cheap tooling and the Urethane resin material is also cheap compared with what is used in injection molding.
Design flexibility: Silicone mold does not need much draft angle and ok for the undercuts which can give the design more room to be flexible design.
Multiple Material Offerings: Multiple Urethane resin materials can be chosen for different applications, and they can be customed for special colors and other properties.
Excellent Surface Finish: like injection molding, cast urethane parts offer an excellent surface finish because the parts can be colored, textured, and painted.
Applications of Urethane Casting
Rapid Prototyping
Cast urethane is often used to make a small number of prototypes for testing or other evaluations by engineers. This is mainly because of the low cost and fast lead time compared with CNC machining when using a certain quantity.
Low Volume Production
Because urethane casting is a consistent, flexible, and precise manufacturing process, when a project’s volume is low, using hard tooling will be not a cost-effective solution, Urethane casting will be the perfect solution to balance quality and cost in terms of low-volume production.
Urethane Casting VS. Alternatives
Urethane Casting Vs. Injection Molding
Urethane casting is used for low to medium-volume production in a short time. It’s a cost-effective option. In contrast, Injection molding is used for high-volume and consistent production but needs a longer setup time.
Read more about Urethane casting vs injection molding.
Urethane Casting Vs. 3D Printing
Urethane casting can make high-quality parts in small quantities with diverse resins. 3D printing is for rapid prototyping which has lower quality parts with lower quality requirements.
Urethane Casting Vs. CNC Machining
Urethane casting and CNC machining are different production techniques, CNC is better for only 1 or 2 prototypes needed with high precision. Urethane casting can duplicate the CNC master prototype to create more parts which means cost and time saving.
Read more about CNC Machining vs Urethane Casting
Design Guidelines for Urethane Casting
Wall Thicknesses
even the minimum thickness could be 1mm, but if possible, Make the wall thickness between 1.5 mm – 4 mm. Over thick or less thickness causes defects on the final parts like injection molding.
Ribs
add ribs to improve part strength, and make the rib thinner at 60% of wall thickness to avoid shrinkage. And Avoid 90-degree walls which are easy to break.
Radius
Make a radius more than 3mm to improve part strength and be good for silicone tooling lifespan.
Draft Angle
Even the Urethane Casting process is possible to make it without draft angles, but if possible, make 3 degree draft angles which will be better for the lifespan of the silicone mold.
Conclusion
Urethane casting is not an easy job and is very practical for rapid prototyping and low-volume manufacturing. In KUSLA, we have decades experiences of Urethane casting service and make lots of parts for our customers. our advantage is we can make it fast at low cost. contact us today, and you will find it.
FAQs
What is the tolerance of urethane casting prototypes?
When the part size is less than 100mm, the tolerance will be ±0.1mm.
When the part size is over 100mm, the machining accuracy is within ±0.2mm or 0.2% of the dimension.
How much does the urethane casting prototype cost?
the cost will consist of casting cost, silicone mold cost, and master prototype cost, generally, the cost will range from $10 to $200.
Can you insert Metal nuts into the urethane casting prototype?
Yes, Metal nuts can be inserted during the casting process.
What is the lifespan of silicone mold for urethane casting?
The mold can be used for around 20 copies and the storage time is 30 days or it will not be able to use.
