CNC Machining vs Injection Molding: Your Ultimate Process Selection Guide

Estimated reading time: 8 minutes

Key Takeaways

• CNC machining is ideal for prototypes, low-volume production (under 500 units), and complex parts requiring tight tolerances (±0.025mm) or exotic materials
• Injection molding is cost-effective for high-volume production (over 1,000 units) of identical parts, especially with standard polymers
• The break-even point between CNC and injection molding typically occurs around 500-1,000 units due to mold costs
• Hybrid approaches (CNC for prototyping and mold making, then injection molding for mass production) offer the best of both worlds
• Material selection is critical: CNC handles exotics like PEEK and titanium, while molding excels with ABS, nylon, and polypropylene

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• Breaking Down the Basics: How CNC and Injection Molding Work
• CNC vs Plastic Injection Molding: Material Showdown
• CNC vs Vacuum Casting: Prototyping Face-Off
• CNC vs Die Casting: Metal’s Heavyweight Bout
• CNC Machining vs Mold Making: The Hidden Symbiosis
• What Really Drives Your CNC vs Molding Choice?
• When to Choose CNC Machining or Injection Molding
• Real-World Wins: CNC vs Molding in Action
• The Future: Smarter, Faster, Greener
• Your CNC vs Injection Molding Checklist

Breaking Down the Basics: How CNC and Injection Molding Work

CNC Machining: Precision Through Subtraction
Imagine sculpting a statue from marble. CNC works similarly—just digitally. It carves metals or plastics from solid blocks using computer-guided tools. You get millimeter-perfect parts fast. Perfect for CNC rapid prototyping services or complex aerospace brackets.

Key perks? Near-zero tooling costs and tolerances tighter than ±0.025mm. Need 10 titanium sensors by Friday? CNC delivers.

Injection Molding: Mass Production’s Powerhouse
Think of a waffle iron squeezing batter. Injection molding injects molten plastic/metal into custom molds. Once cooled, you pop out identical parts. Ideal for 10,000+ smartphone cases.

The catch? Molds cost thousands upfront. But per-part prices plummet at scale. Your breakeven? Around 1,000 units.

CNC vs Plastic Injection Molding: Material Showdown

Problem: You’re torn between exotic plastics and budget-friendly volumes.

Solution: Match materials to your goals.

• CNC loves exotics: Machining handles PEEK, Ultem, or carbon-fiber blends. Medical implants? CNC’s your ally. Learn about material selection for custom aluminum CNC parts
• Molding masters standards: ABS, nylon, or polypropylene shine here. Plus, less waste (just 1-5% vs CNC’s 30% scrap).

Pro tip: “Designing for molding? Avoid undercuts. They trap parts in molds,” says SyBridge’s lead engineer.

CNC vs Vacuum Casting: Prototyping Face-Off

Problem: Need 50 urethane prototypes for user testing?

Solution: Vacuum casting uses silicone molds (often CNC-made!) for soft, visual models. But CNC? It creates functional parts. Like drone arms surviving real-world stress.

Case study: Tesla uses CNC-machined vacuum molds for dashboard prototypes. Cuts iteration time 65%.

CNC vs Die Casting: Metal’s Heavyweight Bout

Problem: Mass-producing aluminum housings without breaking the bank.

Solution:

• Die casting injects molten metal under pressure. Perfect for 50,000+ engine blocks. Fast, cheap per unit.
• CNC tackles tough alloys like titanium. Or precision gears needing ±0.01mm accuracy.

Data point: Ford die-casts 90% of transmission cases. But CNC machines turbocharger vanes.

CNC Machining vs Mold Making: The Hidden Symbiosis

Problem: You need molds—but outsourcing delays you 8 weeks.

Solution: CNC makes those molds. Steel or aluminum blocks become cavity-perfect tools in days. Then, injection molding scales.

Real talk: 78% of mold shops use CNC. It’s faster than EDM or hand carving.

What Really Drives Your CNC vs Molding Choice?

Here’s your decision blueprint:

Volume & Cost: The Break-Even Math

• Under 500 units? CNC wins. Understand CNC machining costs for low-volume projects
• Over 1,000 units? Molding slashes per-part prices 60-80%.

Reminds me of a client who wasted $22K molding 300 units. CNC would’ve saved $15K.

Lead Time & Iteration

• CNC: Revise designs in hours. New code = new part.
• Molding: Mold changes add weeks. Budget $500-$5K per tweak.

Design Complexity

• CNC: Makes 5-axis contours, zero draft angles.
• Molding: Needs 1-3° drafts for easy ejection. Uniform walls prevent warping.

When to Choose CNC Machining or Injection Molding

Pick CNC when you need:

• ✅ Prototypes in <72 hours
• ✅ Volumes under 500
• ✅ Exotic metals/plastics (e.g., aerospace titanium)
• ✅ Tolerances tighter than human hair (±0.025mm)

Pick injection molding when you need:

• ✅ 1,000+ identical parts
• ✅ Costs under $1/unit at scale
• ✅ Polymer/elastomer components (e.g., medical device housings)
• ✅ Surface finishes like polished marble

Hybrid hero move: CNC a prototype → CNC the mold → injection mold 10,000 units. Best of both worlds.

Real-World Wins: CNC vs Molding in Action

Automotive:

• Die casting: 100,000+ aluminum wheel hubs (cost: $4.20/unit)
• CNC: Custom titanium exhaust flanges (precision CNC machining for automotive parts) (2-week lead time)

Aerospace:

• CNC: Boeing’s wing brackets (CNC machining for aerospace parts) from Inconel. Survives 1,200°C.

Consumer Tech:

• Vacuum casting: 200 silicone Apple Watch bands (user trials)
• Injection molding: Final versions at $0.83/unit

The Future: Smarter, Faster, Greener

CNC’s next gen:

• AI predicting tool wear. Cuts machining time 40%.
• Hybrid 3D printing/CNC: Complex parts in one setup.

Molding’s evolution:

• Bioplastics from algae. Cuts carbon footprint 75%.
• Digital twins simulating mold fills. Zero physical trials.

Your CNC vs Injection Molding Checklist

CNC machining vs injection molding isn’t either/or—it’s when. Use this cheat sheet:

1. Volume <500? → CNC ✅
2. Tighter than ±0.05mm? → CNC ✅
3. Design unstable? → CNC ✅
4. Volume >1,000? → Molding ✅
5. Scaling proven designs? → Hybrid ✅ (CNC mold + molding)

“Start with CNC prototypes. Validate. Then mold at scale,” advises Xometry’s production chief.

Your next steps:

• <100 parts? Upload your CAD to QDJ-prototype’s CNC platform
• >1,000 units? Request a molding quote via SyBridge
• Still unsure? Download our Process Selector Tool

Got questions? We tackle top FAQs like “Can CNC make molds?” and “When is die casting better?” in our companion guide.