Urethane casting from independent shops
The bridge between a 3D-printed prototype and a full injection-molded production run. A silicone tool is cast off a machined or 3D-printed master, then used to vacuum-cast urethane resins that look and feel like production plastic, roughly 10 to 200 parts per tool at a fraction of hard-tooling cost. Upload your part and hear back from independent shops with tooling and per-part pricing.
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How OpenSpindle works
We tap our partner network. You get the best-match quote.
Upload your part and we tap our network of partner shops to get you a competitive, all-in quote that is the best match for the job.
One upload
A CAD file or a sketch. That is the whole ask on your end.
Your best-match quote
Sourced from the partner shops set up for your exact part.
All-in, on your timeline
Machining, finishing, and shipping detailed to your turnaround.
Cast resins our shops run
Two-part polyurethane systems are formulated to mimic the look, feel, and mechanical behavior of common production plastics and rubbers. Filled and flame-retardant grades are available, and shops can also cast clear and translucent parts. If your target material is not here, ask when you request a quote.
ABS-like urethane
Rigid, impact-resistant housings
PP-like urethane
Living hinges, snap-fits, flexible parts
PC-like urethane
Impact-resistant, semi-clear housings
Clear / acrylic-like urethane
Water-clear covers, lenses, light pipes
Rubber / elastomer
Shore 30A to 90A seals, grips, overmolds
Glass-filled urethane
Stiffer, more heat-resistant grade
Design rules
How to design for Urethane Casting
Cast urethane parts come off a flexible silicone tool, so the design rules lean similar to injection molding but with looser tolerances and a shorter tool life.
| Design rule | Typical spec | Why |
|---|---|---|
| Nominal wall thickness | 0.060 to 0.150 in | Uniform walls cast and cure evenly. |
| Minimum wall thickness | 0.040 in | Thinner walls risk incomplete fill or fragility once demolded. |
| Draft angle | 1 to 2 degrees per side | Flexible silicone forgives less draft than steel, but draft still eases clean release. |
| General tolerance | +/- 0.010 in or +/- 0.003 in/in, whichever is greater | Resin shrinkage and the flexible tool make it looser than machined or steel-molded tolerances. |
| Silicone tool life | ~20 to 25 parts per mold | The tool degrades and tears at parting lines and undercuts; a new tool is recast off the same master. |
| Maximum part size | Bounded by the vacuum casting chamber | Large parts may need to be cast in sections and bonded, or split across multiple tools. |
Exact numbers depend on the resin system and the shop's casting chamber. Send your part and a shop confirms wall, draft, and tolerance for the cast resin you pick.
Tooling
Silicone tooling and process options
Urethane casting trades hard tooling for a soft silicone mold, which is what makes it fast and cheap for a low-volume run. These are the tooling choices shops weigh.
Tooling and cavity layout
- Master pattern
- The mold is copied off a master made by SLA/DLP resin 3D printing or CNC machining, typically finished and painted to the target cosmetic quality before the silicone is poured around it.
- Silicone (RTV) tool
- Liquid room-temperature-vulcanizing silicone is poured around the master and cured, then cut open along a parting line to pull the master and leave a two-half cavity for casting.
- Single-cavity mold
- One cavity per tool, the default for prototype and low-volume runs where turnaround matters more than throughput.
- Multi-cavity / parallel molds
- Several silicone tools cast in parallel off the same reusable master to run a bigger order or a tighter deadline, since each tool is cheap relative to the master.
Casting process and materials
- Vacuum casting
- The resin is mixed and poured or injected under vacuum to pull out air bubbles, then cured in the mold, producing dense parts free of voids.
- Two-part polyurethane resins
- Cast resins are formulated to mimic ABS, PP, PC, clear acrylic, and rubber-like elastomers, and can be dyed to match a target color.
- Overmolding / multi-shot casting
- A rigid cast part can be recast in a second, softer resin for a grip or seal, similar in concept to overmolding in injection molding.
Tool life and lead time
- Silicone tool life
- A single silicone mold typically yields on the order of 20 to 25 parts before it degrades, after which a new tool is recast off the same master.
- Turnaround
- A master plus first silicone tool and initial cast parts usually lands in about 1 to 3 weeks, faster than cutting a production steel mold.
Process comparison
Urethane casting vs other processes
Urethane casting fills the gap between a printed prototype and a production mold. When your volume, timeline, or material points elsewhere, here is the better-fit process.
| Process | Best for | Typical volume | Choose it over Urethane Casting when |
|---|---|---|---|
| Injection Molding | High-volume production | 1,000+ | You are past a few hundred parts and want the lowest per-part cost and true production resin. A steel or aluminum tool amortizes once volume climbs into the thousands. |
| 3D Printing | One-offs, fastest turnaround | 1 to 50 | You need parts today and can accept as-printed finish and strength. Urethane casting takes longer to set up a tool but delivers more production-like resins and surface quality. |
| CNC Machining | Metal or tightest tolerances | 1 to 500 | The part needs to be metal, or needs a tolerance tighter than a flexible silicone tool can hold. Casting suits plastic-like geometry where machining would be slow or costly. |
Applications
Industries we serve
Urethane casting shops on OpenSpindle support everything from consumer product bridge runs and trade-show samples to low-volume medical and robotics housings.
More on OpenSpindle
Need a different process?
Get a quote for these capabilities too.
Designing for this process
What actually changes your quote
Not a definition of urethane casting. The design and sourcing choices that move your tooling cost, per-part price, and lead time.
Size the run to a tool, not a guess
One silicone tool lasts roughly 20 to 25 casts before it needs replacing. If you need more parts than that, plan for the shop to cast a second tool off the same master rather than pushing a worn mold past its life and risking part quality.
Pick the resin for the job, not just the look
Cast urethanes are formulated to mimic ABS, PP, PC, clear acrylic, or rubber, each with different stiffness, impact resistance, and heat tolerance. Tell the shop what the part needs to do (drop test, flex, chemical exposure) and let them match a resin, not just a color.
Finish the master, not the cast part
The silicone tool is a direct copy of the master, so any sink, print lines, or surface texture on the master transfers to every part cast from it. Sand, polish, or paint the master to the finish you want before it goes into the silicone.
Use it as a bridge, not a permanent solution
Urethane casting is most valuable for the gap between a printed prototype and a production mold: trade-show samples, user testing, a bridge run while a steel tool is cut. If your volume settles in the thousands, price out injection molding against your ongoing casting cost.
Questions
Frequently asked questions
Urethane casting, also called vacuum casting, makes production-like plastic parts from a silicone mold instead of a machined steel tool. A master pattern (usually 3D printed or CNC machined) is used to cast a silicone tool, then two-part polyurethane resin is poured or injected under vacuum into that tool and cured. It is the standard way to get tens to a couple hundred parts that look and feel molded without paying for hard tooling.
Get urethane casting quotes
Upload your part once and compare silicone tooling and per-part pricing for low-volume cast urethane runs from independent shops.
STEP · STL · IGES · DWG · DXF · PDF · and more
Uploads are secure & confidential