What Is Vacuum Casting? Uses, Specs & Comparisons | Xometry Pro

Vacuum casting (urethane casting/vacuum duplication) produces prototypes or small-series plastic parts (typically 5 to 50 pieces) with a quality comparable to injection molding. It’s a cost-effective alternative to injection molding, as it does not require expensive steel tooling.

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This method allows the production of aesthetic parts with good mechanical properties and high dimensional accuracy. It is commonly used in industries such as automotive (intake manifolds, exhaust systems, body panels), consumer products (toys, sports equipment), and electronics, particularly for the production of housings, battery casings, and cell holders.

What is Vacuum Casting?

Vacuum casting involves pouring liquid plastic into a silicone mold, then curing it in an oven. A vacuum chamber removes trapped air, ensuring complete cavity filling and bubble-free parts.

The process supports complex shapes, undercuts, and insert overmolding, offering excellent design flexibility. It’s ideal for pre-series parts with appearance and performance close to injection-molded components—a valuable step before mass production.

However, vacuum casting has limits. Manual operation reduces dimensional accuracy, throughput, and repeatability, making it less scalable than automated methods (see how it compares with other manufacturing processes).

Advantages Limitations High design flexibility: supports complex shapes, undercuts, overmolding Manual process: not suited for large-scale production Injection-like quality: good aesthetics, fine details, and mechanical strength Slower than CNC machining or 3D printing Low cost for short runs: no steel tooling required Lower dimensional precision and stability compared to CNC or injection molding Wide material range: rigid/flexible, transparent, RAL-colorable resins Possible visual flaws (e.g., gate marks, release gloss) Multiple finishes available: polishing, painting, metallization

Technical Specifications of Vacuum Casting

Vacuum casting uses a vacuum to evacuate air from the mold, resulting in smooth surface finishes and minimal defects.

Below are general specifications for the process:

Specification Details Materials Select materials based on final use case: rigid (for enclosures), flexible (for seals), or transparent (for visual inspection parts). Pigment resins using RAL shades for visual prototypes. Lead time 10–20 days Design flexibility Take advantage of vacuum casting’s design freedom to test non-uniform wall thicknesses, soft curves, and aesthetic detailing without tooling constraints. Minimum wall thickness Maintain a wall thickness of at least 1.5 mm to ensure full cavity filling and avoid deformation. You can reduce to 0.75 mm in non-load-bearing areas, but expect a higher risk of warping. Undercuts Design undercuts with care. Vacuum casting can demold simple undercuts, but complex ones increase mold wear and risk tearing. Add inserts or use parting lines to simplify. Quantity per mold Typically 1 to 20 parts Surface finish Choose a glossy finish to highlight geometry or a matte texture to reduce reflections—both are achievable without post-processing. Additional options Use insert overmolding to simulate final assemblies or test part fit before investing in injection tooling.

Tolerance values in vacuum casting depend on part dimensions and design complexity. The table below provides example tolerances based on various dimension ranges (the values provided are illustrative):

Dimensions (mm) 0 — 25 25 — 50 50 — 75 75 — 100 100 — 125 125 — 150 Tolerance (mm) ±0.3 ±0.35 ±0.4 ±0.45 ±0.5 ±0.55

Vacuum Casting Compared to Other Manufacturing Processes

The table below compares vacuum casting with other common manufacturing processes—injection molding, 3D printing, and CNC machining—to help you choose the most suitable option based on production needs, materials, lead time, and cost-efficiency.

Vacuum Casting Injection Moulding 3D Printing CNC Machining Description Small batches of detailed parts resembling production quality Mass production of highly detailed plastic parts Rapid prototyping and complex geometries with minimal tooling High-precision parts from metal or plastic, suitable for both prototyping and production Optimal Quantity Range 1 – 100 50 – 1,000,000 1 – 100 1 – 100 Lead Time (available at Xometry) 20 days 38 days 3 days 7 days Maximum Part Size (available at Xometry) × × mm × × mm 900 x 900 x 600 mm x 750 x 600 mm Mould Life 1 – 20 shots 10,000 – 1,000,000 shots – – Material Selection Rigid plastics (ABS-like, PMMA-like, PP-like, PC-like), rubber-like plastics Any thermosets/ thermoplastics Plastics (PLA, ABS, PETG, Nylon, PC, etc.), resins, metals (aluminium, steel, titanium), and composites (carbon-fibre reinforced) Metals (aluminium, steel, titanium, brass), plastics (POM, PTFE, ABS, PC, PMMA, Nylon), and composites Prototyping ⭐⭐ ⭐ ⭐⭐⭐ ⭐⭐⭐ High-Volume Production ⭐ ⭐⭐⭐ ⭐ ⭐⭐ Part Design Complexity ⭐⭐ ⭐⭐⭐ ⭐⭐⭐ ⭐⭐⭐ Standard Surface Finish ⭐⭐⭐ ⭐⭐⭐ ⭐⭐ ⭐⭐⭐ Post-Processing No No Yes Yes Cost of Design Mistakes Low High Low Medium Advantages • Excellent for short production runs and detailed prototypes with fast lead times
• Ideal for creating high-quality surface prototypes, such as robotic components or lenses, making it perfect for professional product demonstrations or exhibition samples where aesthetics are crucial • High repeatability for consistent part quality
• Ideal for large production volumes
• Extensive material options to suit diverse applications
• Ability to meet custom colour requirements, ensuring precise tones • No tooling costs
• Fast iteration
• Great for custom geometries • High precision
• Excellent surface finishes
• Supports diverse materials Disadvantages • Limited mould lifespan, typically up to 20 parts • High upfront investment in mould tooling
• High costs for mould modifications or improvements, particularly if the design is not frozen before mould production
• Limited flexibility for highly complex or intricate designs • Slower production for large batches
• Limited material properties • High cost per part for large volumes
• Slower for intricate designs

Vacuum Casting vs. Injection Molding

Use vacuum casting when you need 5–100 parts with production-like quality but want to avoid the cost and delay of steel tooling. Injection molds can cost €5,000–€50,000+, while vacuum casting only needs a master pattern and silicone mold. It’s ideal for validation, marketing, or pilot runs where fast iteration and low upfront costs matter more than tight tolerances.

Switch to injection molding once your design is final and you’re producing hundreds to millions of parts. It offers high repeatability, precise tolerances, and low part costs at scale—but demands more time, money, and commitment upfront.

Vacuum Casting vs. 3D Printing

3D printing is your go-to for rapid iterations, complex internal features, and single-unit prototyping. It’s fast, tool-free, and works well early in development—especially when functional performance isn’t critical yet.

Vacuum casting comes into play when you need multiple units with production-grade appearance and mechanical properties. It offers better surface finish, material consistency, and can simulate injection-molded parts more closely.

How Vacuum Casting Works

Vacuum casting uses a silicone mold and a vacuum chamber to create detailed plastic or rubber parts with smooth surfaces and minimal defects.

Here’s a step-by-step breakdown of the process:

1. Create a 3D Model

As with most modern manufacturing processes, the first step is to design a 3D model of the part.

• Use CAD software such as AutoCAD, SolidWorks, or CATIA.
• To get optimal results, follow injection molding design rules, including draft angles, uniform wall thickness, and allowances for undercuts.

2. Build the Master Pattern

Produce a master pattern from the 3D model using SLA 3D printing or CNC machining.

• While CNC was traditionally used, it still offers higher dimensional accuracy, especially for pre-series parts.
• 3D printing speeds up prototyping and reduces cost during early design validation.

3. Create the Silicone Mold

Place the master pattern in a casting box along with any cores, inserts, and gating systems.

• Pour liquid silicone over the pattern to capture its geometry and surface details.
• Cure the mold in an oven at 40°C for 8 to 16 hours, depending on its size.
• Once cured, cut the mold open along the parting line to reveal the negative cavity.
• Apply a mold-release agent to prevent sticking and avoid surface flaws.

4. Mix and Pour the Resin

Prepare a two-component polyurethane resin and add any required pigments.

• Preheat the mixture to ~40°C for better flow.
• Install the mold in the vacuum chamber and connect the pouring gates.
• Mix and deaerate the resin under vacuum for 50–60 seconds to remove air bubbles.
• Apply vacuum to the mold so gravity fills the cavity evenly without trapped air.

5. Demold the Parts

Cure the filled mold in an oven for 1 to 4 hours, depending on the material.

Further reading:
Ford F-150 Performance Coils - Advance Auto Parts

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• After curing, remove the hardened part from the mold, then trim gates and perform any needed finishing.
• A single silicone mold typically produces 10 to 20 parts, depending on the geometry and resin used.

Source Your Vacuum Cast Parts at Xometry

Vacuum casting is a versatile and efficient process for producing detailed plastic or rubber parts in low volumes. It’s ideal for prototypes, functional parts, and high-quality presentation models, such as exhibition pieces or customer samples.

At Xometry, you can get a quote for your vacuum cast parts instantly. Simply upload your 3D file to our Instant Quoting Engine, configure your specifications, and receive a quote in seconds—no waiting, no emails, no back-and-forth.

Ready to try vacuum casting for your next prototype?

I find vacuum assisted casting to have better surface finish and
less porosity. Of course melting technique along with the alloys
used will always impact the quality of the castings. 

Jeffrey, I have to agree on the melting technique and alloy but by
vacuum assist, do you mean vacuum assist as like in setting a solid
walled flask on a silicon pad and having the vacuum drawing on the
end of the flask? Or are you referring to using perforated flasks, I
never could get decent results with what I was told was vacuum
assist, (using a conventional flask and sitting it on a silicon pad)I
tried straws, wax web, all sorts of (remedies) however, I swear by
perforated flask vacuum casting.

Was there any mention by Rio as to what system was used? I would
imagine it was a Neutec system or some exotic shielded system, I wish
I could afford one. I have been using the Neutec flask bases and
tapered sprue wax though, very good concept I like the idea of being
able to gently remove the base, and the sprue holder is easy to fit
in a swivel vise. Makes sprueing so easy, Also the material has a
very fast dwell time, so you don’t have to hold the piece in place
while the sticky wax sets. Just for an experiment, I cut part of the
bottom off one of the sprues and used sticky wax to attach it on a
conventional sprue base and cast some Brass findings today on my
large centrifugal, very nice castings. The taper helps keep the mass
and weight down, so think I’ll cut the ball shape down on some bases
and use the Neutec sprue wax for everything just glue it down with
sticky wax. I would like to see or find out about some of the
equipment coming out of Germany and Israel; I have heard some
incredible stories of how thin they can cast pieces. I’ve heard down
to 28 to 30 Ga. Over a 1.5 to 2 sq in. area. I’m sure that will be
the next criteria customers will be looking for before heading for a
developing nation!!

Do you recall in which issue of the Symposium the article was
published?. I certainly miss many technical issues being out in the
middle of the swamps of the Natchez Trace. Of course, I suppose I
could just buy the Symposium books each year (DUH) but then I could
be intelligent and that would scare my friends and family. Not to
mention the few customers I have left (the ones not learning
2nd or 3rd languages) !

Do any Orchidians do “flask less or Paper Flask casting”?. I’m
curious if this is a viable alternative for small, as in very small
shops?

Is Orchidians actually a suitable term or would Orchidites be more
acceptable.

Kenneth Ferrell
Enjoying not having any Tornado warnings today.
(but wait till tomorrow)

    I have to agree on the melting technique and alloy but by
vacuum assist, do you mean vacuum assist as like in setting a
solid walled flask on a silicon pad and having the vacuum drawing
on the end of the flask? Or are you referring to using perforated
flasks, I never could get decent results with what I was told was
vacuum assist, (using a conventional flask and sitting it on a
silicon pad) I tried straws, wax web, all sorts of (remedies)
however, I swear by perforated flask vacuum casting. 

I’m just using a silicon pad and only casting one-offs recently. I
no longer cast commercially. However, I always had good luck with
both wax web or bent rods hung over the side of the flask. Now I’m
just casting into small flasks. I’ve always used hydrogen and oxygen
for torch melting. I seem to get better results with it. I’ve used
the Aurum induction machine (going back a few years) and resistance
melting (Thermotrol and hand held melters). I don’t know why you
didn’t get good results, maybe your investment mix? I’m sure someone
more knowledgeable than me can answer.

    Do you recall in which issue of the Symposium the article was
published?. I certainly miss many technical issues being out in
the middle of the swamps of the Natchez Trace. Of course, I suppose
I could just buy the Symposium books each year (DUH) but then I
could be intelligent and that would scare my friends and family.
Not to mention the few customers I have left  (the ones not
learning 2nd or 3rd languages) ! 

Sherman and the professor enter the WayBack machine… Enter the
year … give or take a year. I’m at the MJSA New York show
looking at vacuum casting machines and reading literature given to me
by a salesman in which microphotographs (from an electron
microscope?) are featured. The photos show the molecular structure,
in a side by side comparison of centrifugally cast and vacuum cast
cross sections. The vacuum cast example is clearly more dense, the
centrifugally cast example exhibiting voids on a microscopic scale.

I remembered the above while looking for the Symposium book. The
only book easily found was from and the did not contain the
I had hoped to find, at least at a quick run through. I
may have been wrong about the source. (grimace) I’m going to go out
on a limb here and state that AJM magazine may have also had an
article about differences in density between vacuum and centrifugally
cast pieces.

I’ll keep looking for the other volumes, but can make no promises.
They may have been loaned out permanently, if you know what I mean…

I have been using the Neutec flask bases and tapered sprue wax
though, very good concept I like the idea of being able to gently
remove the base, and the sprue holder is easy to fit in a swivel
vise. Makes spruing so easy, Also the material has a very fast
dwell time, so you don't have to hold the piece in place while the
sticky wax sets. Just for an experiment, I cut part of the bottom
off one of the sprues and used sticky wax to attach it on a
conventional sprue base and cast some Brass findings today on my
large centrifugal, very nice castings. The taper helps keep the
mass and weight down, so think I'll cut the ball shape down on some
bases and use the Neutec sprue wax for everything just glue it down
with sticky wax. I would like to see or find out about some of the
equipment coming out of Germany and Israel; I have heard some
incredible stories of how thin they can cast pieces. I've heard
down to 28 to 30 Ga. Over a 1.5 to 2 sq in. area. I'm sure that
will be the next criteria customers will be looking for before
heading for a developing nation!! 

Maybe you’re referring to the over-pressure casting machines. Nice
machines!

I’m curious how you melted the brass. I use my old Thermotrol for
casting brass and for casting large thin pieces. I don’t like to
torch melt brass.

    Do any Orchidians do "flask less or Paper Flask casting"?. I'm
curious if this is a viable alternative for small, as in very
small shops? 

I used to used a ringless casting system back in the 80’s when I was
doing a lot of photopolymer burnout. The investment had to be mixed
in a vacuum and only had a 4 minute working time. Came out of the
oven hard as ceramic and required a hydrofluoric acid substitute
(anyone crazy enough to use real hydrofluoric acid?) to dissolve the
investment. Pain in the rear!

Is Orchidians actually a suitable term or would Orchidites be more
acceptable.

Kenneth Ferrell Enjoying not having any Tornado warnings today. (but
wait till tomorrow) 

Tornados always freak me out. One day I found myself looking up into
about a 300 foot vortex opening a few hundred feet above me. The
tornado had just torn up the town just west of us and was easing off.
The clouds can do some truly amazing things (read either awesome or
scary) in tornado weather. Darn tornados sound and feel like a
speeding freight train 3 feet away… If I never see another one
that’s okay with me!

I think Orchidians is more appropriate.

Jeffrey Everett

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