Vacuum casting parts are polyurethane resin components produced using silicone molds under vacuum pressure, reaching ±0.1 mm per 30 mm tolerance and Ra 1.6–3.2 µm surface finish in 10–20 days. More than 20 resin grades simulate the full range of common production thermoplastics.
This guide is for engineers and designers evaluating whether vacuum casting will produce the specific part they need — at the spec, finish, and material they require. It covers the material options for each part type, the tolerances you can rely on, the finish grades you can specify, and the design rules that determine whether your part will cast cleanly.
Every section answers one question: will this process produce the part you have in mind?
What Vacuum Casting Parts Are Made From
Vacuum casting parts are made from polyurethane resin, not the same polymers used in production injection molding. Each resin grade is formulated to simulate a specific production thermoplastic in appearance, rigidity, and mechanical behavior.
Rigid Resin Grades
The three most common rigid grades are ABS-like, PC-like, and nylon-like resins. ABS-like resin delivers good impact resistance and is the standard choice for enclosures, covers, and housings. PC-like resin is transparent or translucent, making it the correct choice for lenses, windows, and light guides. Nylon-like and glass-filled-nylon-like grades offer higher heat resistance and fatigue performance, which suits automotive clips, brackets, and structural inserts.
Based on thousands of vacuum casting orders processed over 12 years, ABS-like and PC/ABS-like resins together account for the majority of material specifications we receive from electronics and appliance clients. Most buyers specify these two grades for first-run builds and refine the material at DVT stage.
Flexible and Specialty Resin Grades
TPE-like resins cover Shore A 30–80 hardness, covering everything from soft grips to firm seals. Rubber-like grades deliver high elongation for gaskets and flexible covers. Fire-retardant grades meet UL94 V-0 for electronic enclosures. ISO 10993-compliant grades support skin-contact medical device applications.
| Resin Type | Simulates | Key Properties | Best Part Types | Industries |
|---|---|---|---|---|
| ABS-like | Production ABS | Rigid, impact-resistant | Enclosures, housings | Electronics, appliance |
| PC-like (clear) | Polycarbonate | Transparent, tough | Lenses, light guides | Automotive, consumer |
| PC/ABS-like | PC/ABS blend | Rigid, paintable | UI panels, covers | Electronics |
| Nylon-like | PA6/PA66 | Fatigue-resistant | Clips, brackets | Automotive |
| PP-like | Polypropylene | Flexible, snap-fit | Living-hinge covers | Consumer goods |
| TPE-like | Thermoplastic elastomer | Shore A 30–80 | Grips, seals | Medical, consumer |
| FR resin | UL94 V-0 ABS | Flame retardant | Electronic enclosures | Electronics |
Tolerances for Vacuum Casting Parts
Vacuum casting parts achieve ±0.1 mm per 30 mm on critical features, with a minimum of ±0.5 mm on overall dimensions, following ISO 2768 Coarse as the standard reference. The master model’s accuracy sets the tolerance ceiling for every part cast from it.
Standard Tolerance Guidelines
For non-critical features, ±0.25 mm is the practical working tolerance for most cast parts. A CNC-machined master model achieves tighter tolerances than an SLA-printed master. For parts where assembly clearance is critical — mating features, snap-fit interfaces, lid-to-housing gaps — specifying a CNC master at quotation stage prevents rework.
Tight tolerances add cost and extend lead time. Specify tight tolerances only on features that directly affect assembly or function. Apply standard tolerances everywhere else.
Tolerance by Feature Type
| Feature Type | Standard Tolerance | Tight Tolerance |
|---|---|---|
| Linear dimension (<100 mm) | ±0.25 mm | ±0.1 mm |
| Linear dimension (>100 mm) | ±0.5 mm | ±0.2–0.3 mm |
| Hole diameter | ±0.2 mm | ±0.1 mm |
| Wall thickness | ±0.15–0.2 mm | ±0.1 mm |
Parts above 300 mm in any dimension accumulate tolerance. Plan for ±0.5 mm on overall length for large housings and allow corresponding assembly clearance.
Surface Finish Options for Vacuum Casting Parts
Vacuum casting parts come off the mold at Ra 1.6–3.2 µm when cast from a CNC-machined master. Parts cast from SLA masters are slightly rougher — Ra 2.0–4.0 µm — because the master’s layer lines transfer to the mold surface.
As-Cast and Base Finishes
As a minimum, all vacuum cast parts have gates and risers removed and parting lines cleaned. This is standard — not an optional post-process. The degree of manual cleanup varies by resin grade, part geometry, and intended use. For structural B-surface parts, as-cast with parting line cleanup is sufficient. For A-surface visual parts, light sanding to Ra 1.6 µm prepares the part for painting.
Post-Processing Finish Options
Available post-processing options for vacuum cast parts include:
- Wet spray painting — high-gloss, satin, or matte; any Pantone or RAL color; multi-coat primer and top coat for production-level appearance
- Clear lacquer — improves optical clarity on clear PC-like parts; adds UV and scratch protection
- Vacuum metallizing — chrome or brushed metal appearance on rigid resin grades; used for lens bezels and decorative trim
- Soft-touch rubber coating — applied over selected areas for grip feel; popular on medical and consumer device housings
- Silk-screen printing — logos, labels, and interface markings; registered to part geometry
- Dyeing — color through the resin body; suitable for small features and flexible grades
Post-processing to Class A painted finish adds 20–40% to part cost and 2–5 days to lead time. Specify your finish class at quotation stage to get an accurate all-in price.
Types of Parts Made with Vacuum Casting
Vacuum casting produces a wide range of part categories. Each category has a standard material specification, typical wall thickness, and preferred finish level.
Enclosures, Housings, and Panels
Product enclosures, control panel covers, display bezels, and UI housings are the most common vacuum casting part type. ABS-like or PC/ABS-like resin is the standard material. Wall thickness of 2.0–4.0 mm gives structural rigidity with clean demolding. Class A painted finish with Pantone-matched color is achievable at 10–100 unit batch sizes.
In our experience handling electronics and appliance prototype projects, enclosure parts are where vacuum casting consistently delivers the highest visual fidelity to the production intent. For more on how this works in practice, see how we apply vacuum casting to sound, light, and electronic prototype development.
Automotive and Functional Components
Vent ducts, door trim inserts, console covers, clip brackets, and lens assemblies are common automotive vacuum casting applications. Nylon-like and ABS-like grades are standard for structural components. Mating features for assembly with metal brackets require tight tolerances — ±0.1 mm on hole diameters and locating pins. Lens surfaces with vacuum metallizing replicate production chrome appearance at EVT and DVT stages.
For examples of how vacuum cast parts fit into appliance and product development builds, the appliance prototype design workflow covers typical part specifications and batch sizes used at each development stage.
Medical, Flexible, and Overmold Parts
Medical device enclosures, ergonomic grip covers, flexible seals, and co-cast overmold assemblies cover the flexible end of the resin range. ISO 10993-compliant resins are required for any part that contacts skin or mucous membranes. Document this requirement at the quotation stage — not during DFM.
TPE-like grades support two-shot overmold simulation: a rigid substrate is cast first, then a flexible overmold is co-cast in the same mold set. This produces grip and soft-touch assemblies that test the two-component design before committing to production tooling.
Design Rules That Determine Part Quality
Good vacuum cast parts start with a design that respects the process limits. These rules apply before the master model is made — changes after tooling starts cost time and money.
Geometry Rules for Clean Fill and Demold
Follow these geometry rules for rigid resin parts:
- Minimum wall thickness: 1.5 mm for rigid resins; 0.75 mm for flexible grades
- Draft angles: ≥0.5° on all vertical faces; ≥1° on textured surfaces
- Uniform wall thickness — avoid abrupt transitions from thin (<2 mm) to thick (>4 mm) in the same section
- Internal corner radius: ≥0.5 mm — sharp corners stress the silicone on demold and create stress concentrations in the part
After reviewing hundreds of first-run mold failures, wall thickness below 1.5 mm accounts for the majority of incomplete-fill defects. Both are preventable at the design stage.
Feature Size and Text Rules
Specific feature size rules that affect cast part quality:
- Minimum hole diameter: 1.5 mm — smaller holes distort during demold in rigid resins
- Engraved text: ≥0.25 mm depth at a minimum 1.5 mm font height
- Ribs: width ≤60% of adjacent wall thickness — thicker ribs cause sink on the opposite face
- Undercuts: handled by mold flex for moderate geometries; deep undercuts require mold slides
For CNC machining of master models that require tighter base tolerances before molding, CNC-machined master models for tighter vacuum casting part tolerances covers Yanmee’s machining capabilities and how they affect casting accuracy.
How Vacuum Casting Parts Compare to CNC and Injection Molded Parts
Vacuum casting parts occupy a specific position in the manufacturing method range. They are not interchangeable with CNC-machined parts or injection-molded parts — each method has a different best-use zone.
| Factor | Vacuum Casting Parts | CNC Machined Parts | Injection Molded Parts |
|---|---|---|---|
| Tooling cost | $200–$1,000 | None | $10,000–$100,000 |
| Lead time | 10–20 days | 5–10 days | 4–12 weeks |
| Minimum quantity | 1 | 1 | 500+ |
| Surface finish | Ra 1.6–3.2 µm (Class A with post-process) | Ra 0.8–1.6 µm | Ra 0.4–1.6 µm |
| Material range | PU resin simulations | True thermoplastics + metals | True thermoplastics |
| Best for | 5–200 parts, complex geometry | 1–10 parts, tight tolerance | 500+ committed production |
Vacuum casting delivers the best cost-per-part for complex-geometry production-appearance parts at 5–200 unit quantities. CNC machining delivers better dimensional accuracy for one-off precision parts. Injection molding delivers the lowest per-part cost at production scale.
When your project moves past 300–500 parts and the design is confirmed, moving from vacuum cast parts to injection mold tooling is the logical next step. The dimensional data from your casting runs translates directly into the mold design.
Frequently Asked Questions
Q1: What materials are available for vacuum casting parts?
Vacuum casting parts use polyurethane resin in over 20 grades that simulate common thermoplastics. The available categories include ABS-like, PC-like, PC/ABS-like, nylon-like, PP-like, TPE-like (Shore A 30–80), rubber-like, fire-retardant (UL94 V-0), and ISO 10993-compliant grades for medical applications. Each grade is formulated to replicate the mechanical properties, surface feel, and appearance of its production thermoplastic equivalent.
Q2: What tolerances can vacuum casting parts achieve?
Vacuum casting parts achieve ±0.1 mm per 30 mm on critical features, with a practical minimum of ±0.25 mm for non-critical dimensions, following ISO 2768 Coarse. CNC-machined masters produce tighter base tolerances than SLA masters. For parts above 300 mm, plan for ±0.5 mm on overall length. Specify tight tolerances only on features that affect assembly fit — applying them across all dimensions increases cost and lead time.
Q3: What surface finishes are available for vacuum cast parts?
As-cast surface finish from a CNC-machined master is Ra 1.6–3.2 µm after parting line cleanup. Post-processing options include wet spray painting in any Pantone or RAL color (gloss, satin, or matte), clear lacquer, vacuum metallizing for chrome or brushed metal, soft-touch rubber coating, silk-screen printing, and through-body dyeing. Post-processing to Class A adds 20–40% to part cost and 2–5 days to lead time.
Q4: What types of parts can be made with vacuum casting?
The most common vacuum casting part types are product enclosures and housings, UI panels, display bezels, automotive trim components, lens assemblies, bracket clips, medical device enclosures, ergonomic grips, flexible seals, and co-cast overmold assemblies. The process works for any geometry that can be demolded from a two-part silicone mold, including moderate undercuts. Draft angles of ≥0.5° and wall thickness ≥1.5 mm are the primary design requirements for clean parts.
Q5: Can vacuum casting parts be used as functional components?
Yes, within the mechanical limits of polyurethane resin. Vacuum cast parts in ABS-like, nylon-like, and PC-like grades are suitable for assembly validation, fit and function testing, drop testing, regulatory submission samples, and pre-launch market runs. They are thermoset polymers, so they do not match all mechanical properties of production thermoplastics under high sustained stress or elevated temperatures above 80–100°C. For applications within those limits, they perform as functional pre-production components.
Specify the Right Part, Material, and Finish from the Start
Vacuum casting parts deliver production-level appearance at prototype-level cost — when the material, tolerance, and finish are specified correctly at the quotation stage. Use ABS-like or PC/ABS-like resin for enclosures and panels, nylon-like grades for structural clips and brackets, and TPE-like grades for grips and seals. Request Class A painted finish when the part goes in front of buyers or regulators — and specify it at quotation, not after the mold is cut.
The global vacuum casting market reached USD 3.82 billion in 2024, growing to USD 6.77 billion by 2035. That growth reflects how much product teams rely on cast parts for development speed.
Submit your part file to Yanmee’s vacuum casting service for a free DFM review and material recommendation. The engineering team reviews files within 24 hours.