Introduction: The No‑Man’s Land of Low‑Volume Production

Hi, I’m Barry Zeng, a manufacturing engineer at Shanghai Yunyan Prototype & Mould Manufacture Factory. One of the most common questions I get is: “I need 20–100 custom parts. What’s the best manufacturing method?” Injection molding tooling is too expensive ($5k–50k). CNC machining is affordable per part but slow and wasteful. Two technologies compete in this “sweet spot”: 3D printing (SLA, SLS, MJF) and vacuum casting (silicone mold casting). In this guide, I’ll compare 3D Printing vs Vacuum Casting for 20–100 parts — cost, lead time, material options, accuracy, surface finish, and mechanical properties. I’ll also share a decision matrix and a case study where we switched from vacuum casting to 3D printing and cut lead time by 70%. By the end, you’ll know exactly which technology delivers the best value for your batch size.

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Chapter 1: What Is Vacuum Casting?

Vacuum casting (also called urethane casting or silicone molding) is a low‑volume production process. Steps:

• Step 1: Create a master pattern (usually via SLA 3D printing or CNC).
• Step 2: Cast a silicone mold around the master pattern.
• Step 3: Cut the silicone mold open, remove the master.
• Step 4: Pour polyurethane resin into the silicone mold under vacuum.
• Step 5: Cure, demold, and post‑process.

A single silicone mold typically lasts for 20–50 castings (sometimes up to 100 with careful handling). Vacuum casting produces parts with excellent surface finish (Ra 0.8–1.6 µm) and can use a wide range of polyurethane resins — from ABS‑like to rubber‑like to transparent. For 20–100 parts, vacuum casting has been the traditional “sweet spot” — but 3D printing is catching up.

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Chapter 2: How 3D Printing Competes (SLA, SLS, MJF)

For 20–100 parts, 3D Printing vs Vacuum Casting is now a real debate. Industrial 3D printing technologies have improved dramatically:

• SLA (resin): High detail, smooth surface, but limited material properties. Best for visual prototypes and form‑fit testing.
• SLS (nylon powder): Tough, durable, isotropic. No supports needed. Ideal for functional parts.
• MJF (nylon powder): Similar to SLS but faster and smoother surface. Best for production runs of 50–500 parts.

3D printing requires no tooling, no master pattern, and no silicone mold. You simply upload a CAD file and print. Lead time for 20–100 parts: 3–7 days. Vacuum casting lead time: 7–14 days (master pattern + silicone mold + casting). Speed is a major advantage for 3D printing.

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Chapter 3: Cost Comparison – 20 Parts

Let’s run a real cost example for a typical 50g part (e.g., a small enclosure).

• Vacuum casting: Master pattern (SLA) $200 + silicone mold $150 + casting $15 per part × 20 = $650 total ($32.50/part).
• SLS 3D printing: No tooling. $18 per part × 20 = $360 total ($18/part).
• SLA 3D printing: $12 per part × 20 = $240 total ($12/part).

For 20 parts, 3D printing is 45–60% cheaper than vacuum casting. For 3D Printing vs Vacuum Casting at low volumes, 3D printing wins on cost.

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Chapter 4: Cost Comparison – 100 Parts

• Vacuum casting: Master pattern $200 + silicone mold $150 + casting $15 per part × 100 = $1,850 total ($18.50/part).
• SLS 3D printing: $18 per part × 100 = $1,800 total ($18/part) — nearly identical.
• SLA 3D printing: $12 per part × 100 = $1,200 total ($12/part) — still cheaper.

At 100 parts, the cost gap narrows. SLS is roughly equal to vacuum casting. SLA remains cheaper. For 3D Printing vs Vacuum Casting at 100 parts, 3D printing is still competitive.

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Chapter 5: Material Properties – Where Vacuum Casting Excels

Vacuum casting’s biggest advantage is material variety. Polyurethane resins can mimic:

• ABS (tough, impact‑resistant).
• Polypropylene (flexible, chemical‑resistant).
• Rubber / TPE (Shore A 30–90).
• Clear / optical (transparent).
• Glass‑filled (high stiffness).
• Flame‑retardant (UL94 V‑0).

3D printing materials are more limited. SLA resins are thermosets (brittle). SLS/MJF only offer nylon (PA12, PA11, glass‑filled). If you need rubber‑like parts or specific engineering plastics, vacuum casting may be your only option. For 3D Printing vs Vacuum Casting, material selection often decides the winner.

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Chapter 6: Accuracy and Surface Finish

Both technologies achieve excellent accuracy and surface finish:

• Vacuum casting: ±0.1–0.2 mm. Surface finish Ra 0.8–1.6 µm (smooth, like injection molding).
• SLA: ±0.05–0.1 mm. Surface finish Ra 0.8–1.6 µm (smooth).
• SLS/MJF: ±0.1–0.2 mm. Surface finish Ra 4–12 µm (grainy, but can be smoothed).

For cosmetic parts, SLA and vacuum casting are equivalent. For functional parts where surface finish isn’t critical, SLS/MJF is fine.

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Chapter 7: Lead Time – Speed Matters

Lead time is often the deciding factor in 3D Printing vs Vacuum Casting:

• 3D printing (SLA/SLS/MJF): No tooling. 3–7 days for 20–100 parts.
• Vacuum casting: Master pattern (2–3 days) + silicone mold (1–2 days) + casting (1–3 days) = 4–8 days for first part, then 1–2 days per batch. For 100 parts, total 7–14 days.

If you need parts urgently (e.g., for a trade show or clinical trial), 3D printing is faster. If you have a week of lead time, both work.

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Chapter 8: Case Study – Switching from Vacuum Casting to SLS for 80 Parts

A medical device company needed 80 ergonomic handles (nylon‑like material, functional testing). They initially used vacuum casting: master pattern (SLA) + silicone mold + casting. Lead time: 12 days. Cost: $22/part. We proposed SLS (nylon PA12) — no tooling, no master pattern. Lead time: 4 days. Cost: $18/part. The client switched, saved 8 days and $4/part. The SLS parts passed all functional tests. This case shows that for 3D Printing vs Vacuum Casting, SLS can win on speed and cost for medium batches.

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Chapter 9: Decision Matrix – Which to Choose for 20–100 Parts?

Factor	3D Printing (SLA/SLS/MJF)	Vacuum Casting
Cost (20–100 parts)	Lower ($12–18/part)	Higher ($18–33/part)
Lead time	3–7 days	7–14 days
Material variety	Limited (nylon, resins)	Wide (polyurethane, rubber, clear)
Mechanical properties	Good (isotropic for SLS/MJF)	Excellent (mimics injection molding)
Surface finish	SLA: excellent; SLS: grainy	Excellent
Tooling cost	$0	$350 (master + silicone mold)

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Chapter 10: Summary – Sweet Spot Recommendations

• ☐ Need parts fast (under 7 days)? → 3D printing.
• ☐ Need rubber‑like or transparent parts? → Vacuum casting.
• ☐ Budget is tight for 20 parts? → 3D printing.
• ☐ Need production‑grade mechanical properties? → Vacuum casting (or SLS).
• ☐ Quantity 20–50? → 3D printing (SLA for visual, SLS for functional).
• ☐ Quantity 50–100 and need specific polyurethane? → Vacuum casting.

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Conclusion: Choose Based on Material and Speed

For 20–100 parts, both 3D printing and vacuum casting are viable. 3D Printing vs Vacuum Casting comes down to material requirements and lead time. Need nylon‑like parts fast? Choose SLS. Need rubber, clear, or ABS‑like parts? Vacuum casting is better. We offer both technologies — and we help clients choose the right one. Send me your CAD file, quantity, and material requirements. I’ll provide a free DFM analysis, compare costs, and recommend the best process — within 24 hours. Let’s get your parts made in the sweet spot.

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👇 20–100 Parts: 3D Printing or Vacuum Casting?

Send me your CAD file, quantity, and material needs. I’ll compare 3D printing vs. vacuum casting — cost, lead time, and properties — and provide a free DFM report and quote.

Not sure which process fits your batch? Just say: “Barry, here’s my part and quantity — 3D printing or vacuum casting?” I’ll give you an honest recommendation.

🎯 20–100 Parts — Find Your Sweet Spot 🎯

P.S. Mention “sweet spot guide” when you email, and I’ll send you a cost calculator spreadsheet and a material properties comparison chart.

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Barry Zeng
Senior Manufacturing Engineer, Shanghai Yunyan Prototype & Mould Manufacture Factory
(10+ years helping clients choose between 3D printing and vacuum casting for low‑volume production. Let me help you find the sweet spot.)