Die Casting vs CNC Machining: How to Choose the Right Process for Your Metal Part

Die casting and CNC machining are both excellent manufacturing processes for metal parts — but they solve different problems, and choosing the wrong one significantly affects your cost, lead time, and part quality. The choice is not always obvious, and the right answer depends on your volume, geometry, tolerance requirements, and where you are in the product development cycle.

This guide compares die casting and CNC machining across every dimension that matters for the manufacturing decision so you can make the right call for your specific part.

How Each Process Works — A Quick Comparison

CNC machining is a subtractive process: material is removed from a solid block of metal by cutting tools under computer control. It starts with material and takes away what is not needed. Die casting is a net-shape process: molten metal is injected under high pressure into a precision steel die and solidifies into the near-final shape with minimal subsequent material removal needed.

This fundamental difference — subtractive vs net-shape — determines most of the trade-offs between the two processes.

Head-to-Head Comparison

When CNC Machining Is the Right Choice

CNC machining is clearly the right choice in these situations:

• Prototyping and low volume: At quantities below 500–1,000 parts, the absence of tooling cost makes CNC machining significantly cheaper total-cost than die casting. You can also change the design between batches without retooling.
• High-precision critical features: Tolerances tighter than ±0.05mm, precision bores for bearing fits, and thread forms are all difficult or impossible to achieve in an as-cast die casting. These features are machined regardless — on a casting, that means a hybrid process.
• Material requirements outside die casting alloys: If your part is steel, ステンレス鋼, titanium, brass, or a specific aluminum alloy not available as a die cast grade, CNC machining is the only option.
• Complex internal features: Internal channels, undercuts, and passages that cannot be captured by a two-part die are impossible in die casting without add-ons — CNC machining handles them directly.

When Die Casting Is the Right Choice

Die casting becomes the correct process choice when:

• Volume above 5,000–10,000 units: The cycle time advantage of die casting (seconds per part vs minutes for CNC) and the low labor content per part drive per-unit cost far below what machining can achieve at volume.
• Complex net-shape geometry: Die casting can produce thin walls, integral ribs, complex external geometry, and embedded features in a single shot — geometry that would require significant CNC machining time to reproduce.
• Housing and enclosure parts: Consumer electronics housings, automotive components, and industrial enclosures are classic die casting applications — complex shapes, medium tolerance, high volume, aluminum or zinc alloy.
• Part consolidation: A single die casting can replace an assembly of several machined parts, reducing assembly labor, part count, and potential failure points.

The Hybrid Approach — Die Casting Plus CNC Machining

Many production parts use both processes. A die-cast aluminum housing provides the net-shape external geometry, wall structure, and overall form cheaply at volume. CNC加工 then refines the critical features — precision bores, sealing faces, threaded holes, and tight-tolerance interfaces — to the dimensional accuracy die casting alone cannot achieve.

This hybrid approach is the standard production method for automotive powertrain components, precision instrument housings, and motor housings. If you find yourself with a complex part at high volume with critical precision features, consider die casting as the primary process with a CNC secondary operation rather than machining the entire part.

よくある質問

At what production volume does die casting become cheaper than CNC machining?

The break-even volume depends heavily on part complexity, size, and the specific die cost. As a rough guide for a medium-complexity aluminum part (die cost ~$20,000): die casting becomes more economical than CNC machining at approximately 3,000–8,000 units. The more complex the part and the lower the CNC machining time per unit, the higher the break-even volume.

Can I use the same design for both CNC machining and die casting?

Rarely without modification. Die casting requires draft angles (typically 1°–3° on all walls), minimum wall thickness constraints, no sharp internal corners, and specific design rules for gates and vents that do not apply to machined parts. Switching from machining to die casting typically requires a design review and likely some redesign to meet die casting DFM requirements.

What is the best material for a structural housing part produced by die casting?

Aluminum ADC12 (also known as A383 in the US) is the most common die casting alloy for structural housings — good fluidity for thin-wall casting, adequate mechanical properties, and good corrosion resistance. For lightweight critical-strength applications, aluminum A380 is a step up in mechanical properties. Zinc alloys are preferred for very thin walls and high-detail parts where dimensional accuracy is paramount.