Which should you choose when producing component parts?
When selecting a manufacturing process for metal components, two of the most common options are die casting and CNC machining. Both processes produce high-quality parts, but they differ significantly in terms of cost, precision, production volume, material options and mechanical properties.
The right choice depends on your application, production requirements and budget.
Die Casting
Die casting is best suited to medium and high-volume production where consistent quality and low unit costs are priorities. The process can produce complex components with thin walls and integrated features that would require multiple operations using other manufacturing methods.
Advantages
- Low unit cost for large production runs
- Excellent repeatability
- Complex geometries can be produced in a single operation
- Thin walls and intricate features are achievable
- Good surface finish
- Fast production cycle times
- Minimal material waste
Limitations
- High tooling costs
- Less economical for low-volume production
- Limited to castable alloys
- Internal porosity can occur
- Tight tolerances may require secondary machining
CNC Machining
CNC machining offers exceptional precision and flexibility, making it well suited to prototypes, custom components and production runs where tight tolerances or a broad choice of materials are required. Components are machined from solid stock, allowing high mechanical strength and excellent dimensional accuracy.
Advantages
- Extremely high dimensional accuracy
- Excellent surface finishes
- Wide range of materials
- No expensive tooling
- Ideal for design changes
- Stronger material properties because components are machined from wrought stock
- Suitable for low and medium production volumes
Limitations
- Higher cost per part
- Longer machining times
- More material waste
- Complex internal cavities may be impractical
- Production speed is slower than die casting
Comparison
| Feature | Die Casting | CNC Machining |
|---|---|---|
| Initial tooling cost | High | Very low |
| Cost per component | Very low at volume | Higher |
| Best production volumes | Thousands to millions | One-offs to several thousand |
| Dimensional accuracy | Good | Excellent |
| Surface finish | Very good | Excellent |
| Material waste | Low | Higher |
| Design flexibility | Limited once tooling exists | Very high |
| Lead time | Longer initially | Short |
| Material choices | Aluminium, zinc and magnesium alloys | Almost any machinable metal or plastic |
| Mechanical strength | Good | Excellent |
| Complex internal features | Excellent | Limited by cutting tool access |
Production Volumes
Production volume is often the deciding factor when choosing between the two processes.
Die Casting
Die casting becomes increasingly cost-effective as production volumes rise. Although the initial investment in tooling is significant, the cost per component falls substantially over larger production runs. It is commonly used for automotive parts, electrical enclosures, consumer products and industrial components where thousands of identical parts are required.
CNC Machining
CNC machining is generally the better choice for prototypes, low-volume production and bespoke components. Without the need for dedicated tooling, parts can be manufactured quickly and design changes can be implemented with minimal additional cost.
Accuracy
CNC machining generally offers tighter tolerances than die casting.
Typical tolerances include:
- Die casting: ±0.1 to ±0.25 mm, depending on component size and alloy
- CNC machining: ±0.01 to ±0.05 mm, with even tighter tolerances achievable for critical features
Many die cast components undergo secondary CNC machining to produce precision bores, sealing faces, bearing locations or threaded holes.
Material Properties
A key difference between the two processes is the way the material is formed.
Die cast components are created from molten metal, allowing complex geometries but with the possibility of small amounts of internal porosity. For many applications this has little practical impact, but it can influence strength or pressure-tightness in demanding environments.
CNC machined components are produced from wrought material such as rolled, forged or extruded stock. This provides a more uniform grain structure and often delivers higher mechanical strength and improved fatigue resistance.
Design Complexity
Die casting excels at producing components with:
- Thin walls
- Internal ribs
- Bosses
- Mounting features
- Complex external shapes
- Integrated design features
Many of these features would require multiple machining operations if produced using CNC machining.
CNC machining remains highly versatile but is constrained by cutting tool access. Deep cavities, undercuts and enclosed internal features can increase machining time or require alternative manufacturing methods.
Cost Considerations
The cost profile of each process differs considerably.
Die casting requires a significant upfront investment in tooling, but delivers very low unit costs once production volumes increase.
CNC machining has minimal setup costs, making it economical for prototypes and smaller production runs. However, because each component requires machining time, the unit cost remains relatively constant regardless of batch size.
Surface Finish
Both manufacturing methods produce high-quality components, although the resulting surface characteristics differ.
Die casting provides a smooth, consistent finish directly from the mould and is well suited to cosmetic components.
CNC machining produces precision-machined surfaces with excellent flatness and dimensional control.
Both processes can be complemented with secondary finishes such as anodising, powder coating, painting or plating.
Typical Applications
Die Casting
- Automotive housings
- Heat sinks
- Electrical enclosures
- LED lighting components
- Consumer electronics
- Industrial equipment
CNC Machining
- Aerospace components
- Medical devices
- Precision engineering
- Robotics
- Scientific instruments
- Bespoke machinery
- Prototype parts
Combining Die Casting and CNC Machining
Many manufacturers use both processes to achieve the optimum balance of cost and performance. A component can be die cast to produce its overall geometry before critical features such as bearing seats, sealing faces, precision bores and threaded holes are CNC machined. This approach combines the efficiency of die casting with the accuracy of CNC machining.
Choosing the Right Process
The most suitable manufacturing method depends on the application’s priorities.
| Choose die casting when you need: | Choose CNC machining when you need: |
|---|---|
| High production volumes | Prototypes or low-volume production |
| Low unit costs | Tight dimensional tolerances |
| Complex component geometries | High-strength components |
| Excellent repeatability | Design flexibility |
| Good cosmetic finishes | Access to a wider range of materials |
For many engineering applications, the most effective solution is a combination of both processes, using die casting for the primary component shape and CNC machining for precision-critical features. This approach delivers an excellent balance of manufacturing efficiency, accuracy and overall cost.
