12 Key Factors to Decide Between Casting and CNC Machining: A Complete Guide for Custom Metal Parts

Meta Description: Choosing between die casting and CNC machining for custom metal components? This comprehensive guide compares 12 critical factors—cost, tolerance, volume, and more—to help engineers and procurement managers make the optimal manufacturing decision.

When sourcing custom metal parts, one decision can make or break your project's budget, timeline, and performance: Should you choose die casting or CNC machining? As a leading custom die casting manufacturer serving US, European, and Australian markets, we regularly help clients navigate this critical choice. Both processes deliver high-quality precision components, but they excel in different scenarios.

This guide breaks down the 12 key factors you must evaluate when selecting between die casting vs CNC machining for your next project.

Die Casting thrives in high-volume production (10,000+ parts). While initial tooling costs are higher, the per-unit cost drops dramatically as volume increases. Once the mold is created, each cycle produces a near-net-shape part in seconds.

CNC Machining offers competitive pricing for low to medium volumes (1-10,000 parts). Without expensive tooling, it's ideal for prototypes, bridge production, or specialty components where demand is limited.

Best Practice: Use CNC machining for volumes under 5,000 units. Consider die casting for runs exceeding 10,000 pieces to amortize tooling costs.

Die Casting excels at producing complex geometries with internal features, thin walls (as low as 0.8mm), and intricate surface details in a single operation. Features like ribs, bosses, and holes can be cast directly into the part.

CNC Machining struggles with extreme complexity, as each feature requires additional programming and machining time. Deep cavities and undercuts are particularly challenging and expensive.

Best Practice: For complex housings, enclosures, or parts with integrated features, precision die casting often delivers superior results at lower cost.

Die Casting primarily works with non-ferrous alloys: aluminum (A380, ADC12), zinc (Zamak 3, Zamak 5), and magnesium. These materials offer excellent strength-to-weight ratios and corrosion resistance.

CNC Machining handles virtually any material: aluminum, steel, stainless steel, titanium, brass, plastics, and exotic alloys. If your application requires specific material certifications or high-hardness metals, machining may be mandatory.

Best Practice: For aluminum or zinc components, aluminum die casting provides excellent mechanical properties. For hardened steel or titanium, CNC machining is your only option.

CNC Machining delivers superior precision (±0.025mm or tighter) with exceptional repeatability. It's the gold standard for parts requiring tight tolerances.

Die Casting achieves good accuracy (±0.1mm typical) but may require secondary machining for critical dimensions. Modern precision die casting can achieve ±0.05mm for specific features.

Best Practice: Specify CNC machining for tolerance-critical features. Use die casting for general dimensions and machine only mating surfaces or bores post-casting.

Die Casting produces excellent as-cast finishes (Ra 1.6-3.2 µm) suitable for most applications. Textures and logos can be molded directly into the part surface.

CNC Machining leaves visible tool marks (Ra 0.8-6.3 µm depending on operation) that may require additional finishing. However, it can achieve mirror-like finishes with proper  techniques.

Best Practice: For cosmetic consumer products, die casting surface finish often meets requirements out-of-tool. For optical components or sealing surfaces, CNC machining provides better control.

CNC Machining offers rapid turnaround—parts in days, not weeks. No tooling fabrication means you can iterate designs quickly, perfect for prototyping.

Die Casting requires tooling lead time (4-12 weeks for mold design, machining, and testing). However, once production begins, cycle times are mere seconds.

Best Practice: Start with CNC machining for prototypes to validate design, then transition to die casting for production to optimize long-term costs.

Total Cost of Ownership: While die casting tooling represents significant upfront investment, the per-part cost at 50,000 units can be 60-80% lower than machining.

Best Practice: Calculate your cost per part at projected lifetime volume, not just initial production run.

Die Casting is optimized for small to medium parts (0.05kg to 5kg typical). Very large castings face equipment limitations and quality challenges.

CNC Machining handles an extremely wide range—from tiny medical implants to massive aerospace components (up to 2,000mm+).

Best Practice: For handheld devices, automotive components, or electronic housings under 10kg, die casting is ideal. For larger structural parts, consider machining.

CNC Machining offers unmatched flexibility. Simply modify the CAD file and reprogram— no physical tooling changes required. Perfect for evolving designs.

Die Casting involves hardened steel molds. Design changes require weld modifications or even new tooling inserts, costing thousands and adding weeks.

Best Practice: Freeze your design before die casting mold fabrication. Use machining during the development phase when changes are likely.

Die Casting produces parts with excellent structural integrity and consistent material properties throughout. The process creates a fine-grain structure with good fatigue resistance.

CNC Machining can sometimes introduce residual stresses during material removal, especially with aggressive cuts. However, it starts with homogenous billet material.

Best Practice: For pressure vessels or load-bearing components, high-pressure die casting provides reliable, isotropic strength properties.

Die Casting generates minimal material waste (excess material is remelted) and has lower energy consumption per part at high volumes. Most cast alloys are highly recyclable.

CNC Machining produces significant chips and scrap (often 50-90% of original billet), requiring energy-intensive recycling. However, it uses less energy for very small batches.

Best Practice: For sustainable manufacturing, aluminum die casting offers excellent recyclability and waste reduction at scale.

Die Casting often requires single-source partnership due to tooling ownership. This simplifies supply chain management but creates dependency.

CNC Machining allows multi-sourcing since programs can be shared across suppliers, reducing supply chain risk.

Best Practice: Partner with an integrated manufacturer offering both die casting and CNC machining services for maximum flexibility and risk mitigation.

Smart manufacturers don't always choose one process. Many premium components use die casting for near-net shape followed by CNC machining for critical features—combining the best of both worlds.

At F&Q-Tech, we specialize in custom die casting services with in-house precision machining capabilities. Our state-of-the-art facility produces aluminum and zinc die cast components for aerospace, automotive, medical, and industrial clients across the USA, Europe, and Australia.

Ready to optimize your manufacturing process? Upload your CAD drawings today for a complimentary Design for Manufacturability (DFM) review and quote comparison between casting and machining approaches.

      Q: Can die casting achieve the same tolerances as CNC machining?

      A: For most features, no. However, precision die casting can achieve ±0.05mm, with machining reserved for critical surfaces.

      Q: Is CNC machining always more expensive?

      A: Not at low volumes. For 1-1,000 parts, machining is typically more cost-effective due to avoided tooling costs.

      Q: What is the minimum order quantity for die casting?

      A: Economically viable around 5,000 units to justify tooling investment, though we accommodate smaller runs for strategic projects.

      Q: Can you combine both processes?

      A: Absolutely. Casting followed by machining is common for high-volume precision parts requiring tight tolerances on specific features.