Die Casting vs CNC Machining

Die Casting vs CNC Machining for Aluminum Parts

Category: Casting & Forming Reading time: 7 min Meta description: Aluminum die casting vs CNC machining — compare cost, quality, lead time, and minimum order quantities. A practical guide to choosing the right process. URL: /blog/die-casting-vs-cnc-machining/ Tags: die-casting, cnc, aluminum, comparison, manufacturing

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Aluminum is the most versatile engineering metal. But how should you produce your aluminum parts — by die casting or CNC machining?

The answer depends on quantity, geometry, and budget. This guide compares both processes so you can make the right call.

Process Overview

Die Casting: Molten aluminum is injected into a steel mold (die) under high pressure. The die opens once the part solidifies, and the cycle repeats. High volume, high upfront cost, low per-part cost.

CNC Machining: A block of aluminum is cut to shape using computer-controlled cutting tools. No tooling cost, moderate per-part cost, excellent accuracy.

Cost Comparison

Scenario 1: Small Bracket (100×80×30mm, 50% machined volume removed)

	Die Casting	CNC Machining
Tooling cost	$8,000-20,000	$0 (CAM programming included)
Per part (qty 100)	Too high — tooling amortizes poorly	$25-40/part
Per part (qty 1,000)	$8-20/part + tooling	$12-25/part
Per part (qty 10,000)	$3-5/part + tooling	$8-12/part
Per part (qty 100,000)	$1-3/part + tooling	N/A (impractical)

Break-Even Analysis

The cross-over point where die casting becomes cheaper than CNC is typically between 500-2,000 units, depending on part complexity.

Part Complexity	Break-Even Quantity
Simple (2D bracket)	2,000-5,000 units
Moderate (enclosure with ribs)	1,000-3,000 units
Complex (multi-function housing)	500-1,500 units
Very complex (thin-walled, deep features)	300-800 units

Quality Comparison

Factor	Die Casting	CNC Machining
Dimensional tolerance	±0.1mm (standard) ±0.05mm (precision)	±0.025mm (standard) ±0.005mm (precision)
Surface finish (as-produced)	Ra 1.0-3.2µm	Ra 0.8-3.2µm
Mechanical properties	Good (slightly lower than wrought)	Excellent (uses wrought material)
Porosity	Possible (can be managed)	None
Wall thickness	1.5mm minimum (0.8mm possible)	0.5mm minimum (with care)
Threads/secondary ops	Must be machined after casting	Can be machined direct

When to Choose Each

Choose Die Casting When:

1. Quantity is high (> 2,000 units for simple parts, > 500 for complex)
2. Part geometry suits casting (thin walls, complex features, internal cavities)
3. You have the budget for tooling ($8,000-50,000)
4. Production will continue for years (tooling amortized over long runs)
5. You need consistency across millions of parts

Choose CNC Machining When:

1. Quantity is low (< 500-1,000 units)
2. You need tight tolerances (±0.025mm or better)
3. You can't afford upfront tooling cost
4. Design is still changing (no tooling commitment)
5. Part is simple (not justifying the complexity of die design)

Hybrid Approach

For many projects, a hybrid approach works best:

Phase 1: CNC for market launch — CNC machine the first 500-2,000 parts while die tooling is being built. This gets your product to market weeks faster.

Phase 2: Die casting for volume — Once the die is ready, transition production to die casting. Use the CNC program for secondary machining of critical surfaces.

Summary

Factor	Die Casting Wins	CNC Machining Wins
Quantity	2,000+	< 1,000
Tolerance	±0.1mm or looser	±0.05mm or tighter
Time to first part	6-10 weeks (tooling)	3-10 business days
Unit cost (high volume)	Very low ($1-5/part)	Moderate ($8-25/part)
Unit cost (low volume)	Very high (tooling)	Moderate
Surface finish	Good	Excellent
Design flexibility	Changes = new tooling	Changes = new program (free)
Material choice	Die-cast alloys only	All grades

Get a Quote

Need aluminum parts? Submit your design to app.moldkey.com/quote and get quotes for both processes so you can compare directly.