Vacuum Casting Vietnam – Silicone Molds, Low-Volume PU

Technical summary: Vacuum casting (casting in silicone molds under vacuum) is a low-volume production method in which an RTV silicone mold replicates a master pattern, then two-part PU resin is poured inside a vacuum chamber to eliminate air bubbles. CT3D offers a complete vacuum casting service in Vietnam: 3D printing or CNC machining of the master pattern, mold making, casting, post-processing and dimensional inspection. It is the right choice when you need from a few dozen to a few hundred parts with near injection-molded appearance, without investing in steel tooling yet.

Our vacuum casting service is built for engineers and product teams who need real-looking, functional plastic parts in small batches: pilot runs, certification samples, trade-show sets or spare parts. Below you will find how the process works, what the parts can and cannot do, design rules that keep the mold alive longer, a comparison with 3D printing and injection molding, and what to send us for a fast quote.

Key Facts at a Glance

Parameter	CT3D vacuum casting
Typical batch size	Around 10–300 parts per design
Master pattern	SLA 3D printing at 25–100 micron layers, tolerance ±0.05–0.1 mm; or 3/4/5-axis CNC milling
Mold life	Approximately 15–20 casts per silicone mold; more molds are made from the same master for larger runs
Casting resins	Two-part PU simulating ABS, PP, PC and rubber; hardness from soft Shore A to rigid Shore D; clear grades
Color and finish	Color-through, clear, gloss, matte or textured; painting and screen printing after casting
Special features	Insert molding of nuts and metal parts; overmolding of soft layers (after DFM approval)
Files accepted	STEP, STL, OBJ, 3MF – or a 2D drawing or physical sample for reverse engineering
Delivery	Nationwide transit within Vietnam takes 1–3 days after completion; international shipping available

When Should You Choose Vacuum Casting Instead of Injection Molding?

Every product development cycle has a gap between one-off prototypes (rapid prototyping) and mass production with injection molds. Steel tooling is expensive, takes a long time to build and is very difficult to modify while the design is still changing. On the other hand, printing parts one by one makes it hard to achieve consistent surface finish and color as quantities grow. Vacuum casting fills exactly that gap, acting as bridge tooling.

Three signs that your project is a good fit for this method:

• You need around 10–300 parts per design, for example a sample batch for customers, a pilot run for market testing, or a set of parts for certification.
• The design is not yet frozen: each revision only requires a new master pattern and silicone mold, at far lower cost than modifying a steel mold.
• Appearance requirements are high: smooth surfaces, color-through casting, clear parts or soft, rubber-like parts.

For a deeper look at the mold-making technique, see our silicone molds page.

How Vacuum Casting Works

1. Master pattern: the part is SLA printed or CNC machined, then sanded and primed to the gloss or texture the final parts should have.
2. Silicone mold: the master is suspended in a mold box with its sprue and vents, and RTV silicone is poured around it and left to cure.
3. Cutting the mold: the cured silicone is cut along the planned parting line and the master is removed, leaving an exact cavity.
4. Vacuum pouring: the two-part PU resin is mixed, degassed and poured into the closed mold inside the vacuum chamber, so air cannot be trapped in the part.
5. Curing and demolding: the part cures under a controlled schedule, then the flexible mold is opened and the part released. The mold is reused for the next cast.
6. Finishing and inspection: gates and flash are trimmed, parts are painted or printed if required, and the first article is measured.

Vacuum Casting Scope of Work and Technical Specifications

CT3D takes on complete turnkey projects or individual process steps, depending on what you supply. The table below summarizes the work items and reference specifications we typically use when planning a project.

Item	Technical details	Notes
Master pattern	SLA 3D printing at 25–100 micron layers, tolerance ±0.05–0.1 mm; or 3/4/5-axis CNC milling	The master is sanded and primed to the required gloss before mold making
RTV silicone mold	Two-piece or multi-piece mold with parting line, sprue and air vents	Mold life depends on geometry and resin type; at CT3D, vacuum casting silicone molds achieve approximately 15–20 casts
Casting resin	Two-part PU simulating ABS, PP, PC and rubber; hardness from soft Shore A to rigid Shore D	Selected according to mechanical and cosmetic requirements
Color and finish	Color-through pigmentation, clear casting, gloss, matte or textured surfaces replicated from the master	Painting and screen printing available after casting
Special features	Insert molding of nuts and metal parts; overmolding of soft layers	DFM approval required first
Lead time	Based on number of mold sections, quantity and post-processing	Quoted per file

Source: CT3D SLA specification sheet; mold life is a general reference value for the silicone casting industry.

Casting Materials and Selection Criteria

The greatest advantage of vacuum casting is the very wide range of polyurethane resins. Rather than asking “which plastic should we use?”, CT3D engineers first ask what conditions the part must withstand, then select the matching resin system.

Rigid Resins Simulating Engineering Plastics

ABS-like PU suits enclosures, box lids and assembly parts that need rigidity. PP-like PU offers better toughness and flexibility, and is used for living hinges and snap-fit features. PC-like PU is typically chosen when clarity and moderate impact strength are needed. Important: these are simulation materials, so their mechanical properties approach – but do not fully replace – the original thermoplastics.

Elastomers

Elastomeric PU resins are classified on the Shore A hardness scale. Low values feel soft, like gaskets or push buttons; high values are closer to caster wheels or anti-slip feet. When designing soft parts, specify the target hardness on your drawing to avoid multiple rounds of trial casting.

Clear and Functional Resins

Clear resins are used for light covers, light pipes and viewing windows. The master pattern surface determines almost all of the part’s transparency, so the master must be polished very carefully. Flame-retardant resins, higher-heat resins and metal-powder-filled resins (for a heavier feel) are also available; their feasibility is checked project by project. For other clear-part options, see clear and transparent parts.

Application requirement	Suggested resin system	Key considerations
Machine housings, box lids, assembly frames	ABS-like PU	Uniform wall thickness, avoid localized thick sections
Hinges, snap-fit parts	PP-like PU	Test the number of flex cycles on a prototype
Gaskets, buttons, soft grips	Shore A elastomeric PU	Specify the target hardness
Light covers, viewing windows	Clear PU	Master pattern needs a mirror polish

This table is for guidance only; the specific resin system is confirmed during DFM review.

Design Guidelines for Vacuum Cast Parts

Vacuum casting is forgiving compared with injection molding, but a few design choices strongly affect part quality and how many good casts each mold delivers. The values below are general industry guidance, not fixed CT3D limits; we confirm them for your part during the DFM review.

Feature	Typical recommendation	Reason
Wall thickness	Keep walls as uniform as possible; typically a few millimetres for rigid PU	Thin areas fill poorly; thick lumps shrink and warp
Draft	A small draft helps, although flexible silicone tolerates near-vertical walls	Easier demolding and longer mold life
Undercuts	Shallow undercuts release from the flexible mold; deep ones need extra mold pieces	Tearing the silicone shortens mold life
Ribs and bosses	Thinner than the main wall, with fillets at the base	Avoids sink marks and air traps
Inserts	Design pockets that hold nuts or metal parts in position during the pour	Inserts must not move when resin flows in
Text and logos	Raised or engraved detail with enough depth to read after painting	Very shallow detail disappears under primer
Dimensional tolerance	Typically a few tenths of a millimetre per 100 mm, depending on geometry and resin shrinkage	Specify critical dimensions on the drawing so they can be checked

Finishing Options

Finish	How it is achieved	Best for
Color-through	Pigment mixed into the resin before casting	Housings and parts that may be scratched in use
Gloss, matte or texture	Replicated from the master surface into the silicone mold	Cosmetic samples that must look like production parts
Clear	Clear PU cast in a mold taken from a mirror-polished master	Lenses, light covers, viewing windows
Painting	Primer and paint after casting, color matched on request	Exact brand colors, metallic effects
Screen printing and plating	Applied after casting and painting	Logos, markings, decorative metallic parts

The general post-processing options are described on our painting and plating page.

Industry Applications

• Consumer electronics and IoT devices: enclosures for field-test batches, certification samples and trade show display sets.
• Home appliances: knobs, lids and soft-touch handles for ergonomic evaluation with real users.
• Automotive and motorcycles: interior parts, trim and prototype gaskets for assembly checks before production tooling.
• Lighting: lamp shades, lenses and clear-cast light pipes.
• Gifts, crafts and models: replication of small statues, mascots and decorative parts in moderate quantities.

Vacuum Casting vs. 3D Printing vs. Injection Molding

Criteria	3D printing	Vacuum casting	Injection molding
Typical quantity	1 to a few dozen	Around 10–300 per design	Typically thousands and more
Tooling	None	Master pattern + silicone molds	Steel or aluminum mold
Upfront cost	Lowest	Low	High
Design changes	Just edit the file	New master and mold	Costly tool modification
Surface and color	Varies by technology; finishing per part	Near-molded; color-through, clear or textured	Production finish
Materials	Printing resins and powders	PU simulating ABS, PP, PC, rubber	Real thermoplastics
Unit price	Flat regardless of quantity	Falls as the mold cost is shared	Lowest at high volume

If you only need a handful of parts, see industrial 3D printing; if a printed or machined mold is closer to your need, see 3D printed molds and rapid tooling.

Quality Control of Cast Parts

The three typical defect groups in vacuum casting are air bubbles, shrinkage and deviations caused by mold distortion. CT3D controls them at the root cause:

Defect	Common cause	Countermeasure
Surface or internal bubbles	Insufficient degassing, poorly placed vents	Control the vacuum cycle, add air vents
Short shot	Walls too thin, gate far from the area to be filled	Reposition the gate, increase local wall thickness
Warpage, shrinkage	Uneven wall thickness, unstable curing temperature	Propose thickness changes during DFM, stabilize the curing schedule
Flash at the parting line	Mold wear after many casts	Track casting count, replace molds on time

For tight dimensional requirements, CT3D can 3D scan cast parts and generate a deviation color map against the original CAD file. This provides objective confirmation that the batch is within the agreed tolerance, rather than measuring only a few points with calipers. See 3D scanning inspection.

How to Order: From RFQ to Delivery

1. Request for quotation (RFQ): send your STEP, STL, OBJ or 3MF files via our website, Zalo, email or Contact form, along with quantity, color and preferred material.
2. DFM review: our engineers check draft angles, undercuts, wall thickness, parting line and gate locations. Where needed, CT3D suggests minor geometry changes to extend mold life and reduce part defects.
3. Quotation with schedule: costs are split into three parts – master pattern, mold and per-part casting price – so you can calculate your break-even point.
4. Production: printing or CNC machining of the master, surface finishing, silicone pouring, mold cutting, resin pouring in the vacuum chamber and curing.
5. Quality control (QC): first article inspection (FAI), measurement of critical dimensions, color and surface comparison.
6. Delivery: pickup at our workshop or shipment by domestic courier, post or air freight; nationwide transit within Vietnam takes 1–3 days after completion, and international shipping is available.

Why Work with CT3D

• Master and mold in-house: SLA printing at 25–100 micron layers or CNC machining, followed by silicone molding and casting in the same company.
• Transparent pricing: master, mold and per-part prices quoted separately so you can compare options.
• Free DFM review with every quote, including suggestions that extend mold life.
• Reverse engineering available: no CAD file? We can work from a drawing or 3D scan a physical sample.
• Scan-based inspection with deviation color maps when tolerances matter.
• NDA on request, engineering support in English and international shipping.

Frequently Asked Questions (FAQ)

How many parts can one silicone mold produce?

It depends on geometry, material and undercut depth. At CT3D, each vacuum casting silicone mold achieves approximately 15–20 casts; for larger quantities, CT3D makes additional molds from the same master pattern.

Can PU cast parts replace injection-molded parts?

In appearance, they come very close. Mechanically, PU only simulates thermoplastics, so testing on the actual product is needed if the part is subject to load, heat or chemical exposure.

What if I only have a 2D drawing or a physical sample?

CT3D can build the 3D file from your drawing or 3D scan the physical sample for reverse engineering, then produce the master pattern and mold.

How is vacuum casting priced?

The price consists of the master pattern cost, the mold cost and a per-part casting price. Because it depends on size, quantity and material, CT3D quotes based on your file.

What quantities is vacuum casting best for?

Around 10–300 parts per design is the typical range – for example sample batches, pilot runs or certification sets. For a few parts, 3D printing is usually cheaper; for thousands, injection molding becomes more economical.

Can you cast clear or soft rubber-like parts?

Yes. Clear PU is used for light covers and windows, with the master polished to a mirror finish, and elastomeric PU covers soft Shore A hardness ranges for gaskets, buttons and grips.

Can metal inserts or a second soft layer be added?

Yes. Nuts and metal parts can be cast in place, and soft layers can be overmolded, after the design has been approved in the DFM review.

Which file formats should I send?

STEP, STL, OBJ or 3MF files, together with the quantity, color and preferred material. Mark critical dimensions and the target hardness on a drawing if they matter.

Videos from the CT3D Workshop

Watch the video High-Tech 3D Printed Molds produced by CT3D to get a clearer picture of our process and product quality. More videos are available on our YouTube channel Chế Tạo Vlog – CT3D.

Contact CT3D – Send Your Files for a Fast Quote

Whether you have a 3D file, a 2D drawing, photos or just an idea, you can send it to CT3D online (STL, STEP, IGES, OBJ). Our engineers will review your files, advise on process and materials, and send you a quotation with a delivery schedule.

• Email: [email protected] – [email protected]
• Phone / Zalo: +84 975 008 728 (Mr. Thai) – +84 985 936 728 (Mr. Dang) – or use our Contact form
• Head office: Binh Duong, Vietnam.
• Workshops: Ho Chi Minh City, Vietnam.
• Other workshops and drop-off points: Can Tho, Da Nang, Bien Hoa, Ba Ria – Vung Tau, Hanoi, Hai Duong, Hai Phong. Delivery throughout Vietnam and international shipping.
• Website: ct3dgroup.com – in3d.edu.vn

CT3D – 3D design & prototyping: 3D printing, 3D scanning, reverse engineering, silicone mold making, painting and finishing, CNC machining, composite fabrication, and supply of 3D printers and 3D printing resins.