Urethane Vacuum Casting

CreateProto, on the leading edge of vacuum casting technology, can create silicone rubber molds producing urethane cast parts quickly and accurately. Cast urethane through this process is ideal to test pre-production parts, functionality, and design verification.

Fast Short-Run Production Option: Small Batch Plastic Prototypes

CreateProto’s vacuum casting technology offers a wide variety of materials to facilitate the creation of cast urethane parts, typically for functional test, pre-production evaluation and low volume production. Cast urethane parts are quick and inexpensive without the need to invest any metal tooling when quantities are only dozens of short runs, and can be delivered within weeks in most instances.

Vacuum casting (also known as polyurethane casting) can be used to closely simulate final injection molded parts or finished products. Generally, molds are made from silicone rubber and use a CNC or SLA part as a master pattern. These molds duplicate details and textures and give consistent finishes from one part to the next. You can get production-like results including mechanical traits, colors, and finishes.

With 20 years’ experience, Createproto’s specialist team provides excellent vacuum casting service for low volume plastic prototypes, and helps you striking the right balance between high-quality, end-use parts and production lead-time. Find more information about our vacuum casting processes, you can request a quote there.

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Making Master Pattens for Urethane Casting

The quality of the casting parts is determined by the quality of master pattern, and most of the common masters are machined by CNC when you need to hold tight tolerance such as +/-0.05mm. In addition, we also will consider making the master by SLA for those parts with complicated structures. CNC machine takes longer time and costs more to make the master, while SLA can produce the masters faster, and can ensure the assembly features to form correctly and accurately.

The quantity of the masters is based on the total quantity of casting parts required at last. If the casting quantity is only several pieces, then one master will be enough, while if the quantity is over 30 pieces, in considering the delivery time, we will make 1-2 masters so we can make more silicone molds to do the casting parts faster.

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When the requirement of a client comes to high tolerance, glossy finish or even optically clear parts, the master pattern will be manufactured with CNC machine which is characterized with high specification precision machining and high-quality surface finish.

The professionally polished parts will be glossy finish and optical clarity. Meanwhile, we also can paint parts surface for texture or satin effect to simulate the final mold texture of the product. The silicone molds will copy the details and textures from the original master, so the casting parts will come out the same as the master without any extra finish on the surface.

Silicone Rubber Mold Making

The silicone rubber mold (also known as RTV mold) is created based on a master pattern. The chemical stability, self-releasing properties and flexibility of silicone rubber are excellent that it gives minimal shrinkage and carries fine details effectively from master to mold.

The lifetime of the silicone mold is directly related to the complexity of the casting part. Generally, it outputs 12-15 pieces before degradation. If the structure of the part is simple, one mold might be able to cast 20 parts; while if the part requires high quality such as the clear complicated part, one mold can only make 12 or even 10 casting parts.

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Steps to Creating a Silicone Rubber Mold

  • The master needs to be stuck with some thin films to make the mold easier to be cut, which will act as a seam for the final mold.
  • The master model is suspended in a box with the gates and vents attached; risers are put on the part to allow air to escape from the final mold.
  • Silicone is poured around the master and vacuum is used to remove all air. This then is cured in an oven, at a temperature of 40℃. It generally takes 8-16 hours depending on the volume of the mold.
  • Once the silicone rubber has cured, the box and risers are removed; as the master is removed from the silicone to form a cavity, a silicone rubber mould is made.

Polyurethane Casting Process Detail

Polyurethane casting can accurately match clients’ specification, no matter in color, texture and glossy finish, insert and over molding, or even optically clear.

CreateProto standardized operational procedures assure accurate part replication and consistent mechanical properties. Our casting technicians control all operational parameters: mixing, de-gassing, stirring, preheating, casting and de-molding, allowing for near-perfect copies of the master pattern to be created, and providing a standard tolerance on ± 0.15mm/100mm, with the highest precision able to reach ± 0.05 mm.

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CreateProto Urethane Vacuum Casting 10

Steps to Urethane Casting Process

  • First-phase preparation, the silicone mold is placed in an oven and heated to 60°C-70°C.
  • Assemble the mold before casting the polyurethane. Choosing right mold-release agent (and using it properly) is very important to avoid stickiness and surface defects.
  • Prepare the polyurethane resins to preheat it to about 40°C before use. Mix two-component resins in exact proportions, and then fully stir and degas for 50-60 seconds under vacuum.
  • The resin is poured into the mold inside the vacuum chamber under computer control, and cured again in the oven. Average cure time: 1-3 hours for small parts and 3-6 hours for big parts.
  • Remove the resin part from the silicone mold after cured. Remove the gates and vents; leave an exact copy of the original.
  • Prepare to repeat this cycle.

Create Cast Urethane Parts With A Wide Variety Of Resin Materials

Urethane resins are polymers with a wide range of properties, strengths, and uses. Urethanes can be rigid, elastomeric, colored, clear, painted, and coated. Materials are mainly developed to mimic common production plastics.

CreateProto offers various materials to meet your applications, including Hei-Cast from Japan and Axson from France. Materials with certain properties are similar to engineering production plastics, such as ABS, PMMA, PC, PP, PA, and so on. Casting parts can be varied from transparent, translucent to colored and from soft rubber to hard plastic. Various materials contain those impact resistant, high temperature resistant (120℃) or fire resistant (UL94-V0), and glass filled resins and different hardness silicone.

The possibilities of cast urethane are endless, and it proves to be a perfect low volume solution.

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CreateProto Urethane Vacuum Casting 12

Polyurethane Vacuum Casting Applications

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Low Volume Manufacturing / Short Production Runs

The vacuum casting is perfect for high quality plastic prototypes. When volumes do not justify investment in injection molding and short run production parts, it can complete weeks before production tooling is ready. Our advanced manufacturing services help you to create custom and complex production parts in low volumes faster than traditional tooling and molding.

Engineering Verification / Functional Testing

The urethane casting process and relatively inexpensive tooling involved make it easy and economical for any necessary engineering verification and design changes. Additionally, these would be used to do functional test before testing the mass production products and issue report or even get any certification approval.

Aesthetic Models / Color & Texture Studies

The casting part can be a full set aesthetic model with various colors, textures and finishes under the same design idea. If having no idea about what color would be the most suitable for a product, you can make a silicone mold to produce 10-15 castings and paint each with your design colors and textures to discuss internally during meeting among design departments or even management meetings.

Marketing Ready / Display Models

End-user functionality and a high-quality finish makes urethane cast parts ideal for consumer testing and user evaluation. The application of the cast urethane process means that changes can be quickly made for either further testing or market launch. At any trade shows or exhibitions, you can display several modeled pieces to clients who are interested. Urethane molding are also needed for photos in preparing the company brochure or being posted on the official website to more potential clients.