Casting vs Machining: Which One Is Right for Your Metal Part?

When it comes to manufacturing metal parts, there’s no one-size-fits-all solution. When engineers start planning how to turn a metal design into a finished part, they face a key question: should they use casting or machining? Both casting and machining have helped builders make parts for generations. Casting has roots that go back over 6,000 years while machining has grown rapidly since the mid-20th century.

If you’re designing a metal component and wondering which process fits your project best, this guide will walk you through the key differences, pros and cons, and use cases of each process. You’ll leave with a clear understanding of how to choose between casting and machining—or even combine both methods.

What is Machining?

Machining refers to a set of subtractive processes. A technician loads a solid block of metal, called stock, into a computer numerical control (CNC) machine. The operator then runs a digital program that tells the machine where to move cutting tools. The machine trims away metal layer by layer until the part matches the digital drawing.

• Typical Equipment: CNC milling machines, CNC lathes, drilling centers.
• Volume Range: From a single prototype to a few thousand parts.
• Common Materials: Aluminum, steel, brass, plastics.

Pros and Cons of CNC Machining

Let’s take a closer look at the strengths and weaknesses of CNC machining:

Pros of CNC Machining	Cons of CNC Machining
Engineers can go from CAD model to a finished part in hours.	Material removal and tool wear add cost.
Machined parts come off the machine ready or with little work.	CNC removes more metal, creating chips and scrap.
No special tooling is required beyond standard fixtures.	Per-part cost remains relatively high as volume increases.
Machining can achieve tight tolerances (often ±0.01 mm).	Deep internal channels can be hard to reach.
Changing designs requires only a program update, not a new mold.	Multiple tool changes add to cycle time.
Most metal grades and engineering plastics are machinable.	Machine work envelope limits the maximum part size.

What is Casting?

Casting is a manufacturing process where metal is melted and poured into a mold. Once the metal cools and solidifies, the mold is removed, and the part is ready for use (or further finishing, if needed). The mold often carries the term “die” when metal sheets or high-pressure methods are used.

• Casting Techniques: Die casting, sand casting, gravity die casting, investment casting, permanent mold casting, centrifugal casting.
• Volume Range: Cost-effective at medium to high volume.
• Common Materials: Aluminum alloys, zinc alloys, magnesium, cast iron, bronze.

Pros and Cons of Casting

Here’s a quick overview of what makes casting a good—or not-so-good—choice depending on your project:

Pros of Casting	Cons of Casting
Foundries spread the mold cost over many parts.	Foundries need time to design and build the molds.
Casting can embed features that would be hard to machine.	Flash and parting lines demand cleaning.
Casting can form internal cavities in one go.	Poor fill or cooling can cause defects and waste.
Foundries work with aluminum, steel, copper, and more.	Parts may require extra machining to meet tight tolerances.
Cast bulk can offer consistent strength.	Cast parts often need grinding or polishing.
Automated pour and cooling reduce operator time.	Shrinkage and warping can cause variations.

Direct Comparison: Casting vs. Machining

When you weigh casting and machining side by side, the choice often comes down to volume, precision, part geometry, and cost.

The diagram below summarizes the main factors to consider for each process:

Factor	Casting	Machining
Shape Complexity	Excellent for deep cavities and overhangs	Limited by tool access and cutting geometry
Material Usage	Near-net-shape, minimal scrap	Subtractive, generates chips
Precision & Tolerances	±0.5–1.5 mm (as-cast)	±0.01–0.1 mm (CNC machining)
Surface Finish	Often rough (Ra 3.2–6.3 μm)	Smooth (Ra 0.2–1.6 μm)
Lead Time	Longer mold prep, faster high-volume runs	Fast for prototypes, slower for large batches
Cost per Part	Low at scale, high initial tooling cost	Higher per part, low setup cost
Design Flexibility	Low (mold changes are expensive and slow)	High (easy to update CAM programs)
Typical Materials	Metals (iron, aluminum, bronze)	Metals, plastics, composites
Toolwear	Minimal (mold lasts thousands of cycles before maintenance)	Continuous (tools wear and require replacement)
Best for	Mass production of complex shapes	Precision parts, small batches, prototypes

Material Options

• Casting Materials
  • Metals: iron, steel, aluminum, copper alloys
  • Non-metals: epoxy, concrete, plaster for specialty molds
• Machining Materials
  • Metals: aluminum, brass, steel, titanium
  • Polymers: POM, PMMA, PC, PP
  • Composites: carbon fiber, fiberglass
  • Ceramics and woods with specialized tooling

CNC machining offers broader material compatibility, including exotic alloys and composite materials. Casting is more material-efficient but limited by what materials can be melted and poured.

Volume and Cost Considerations

Volume often drives the decision between machining and casting. We can summarize cost behavior over production quantity:

Production Volume	Machining Cost per Part	Casting Cost per Part
1 to 100 units	Low setup cost; moderate unit cost	High per-part cost; high tooling amortization
100 to 1,000 units	Moderate set-up cost, stable per-part cost	High tooling cost, lower per-part cost
1,000 to 10,000 units	Rising tool wear increases cost	Economies of scale lower overall cost
Above 10,000 units	High machine time and tool cost	Low incremental cost, highly economical

Many manufacturers make the mistake of focusing only on per-part cost. But that’s short-sighted. Consider the total cost of ownership, including:

• Lead time
• Tooling and setup
• Design changes
• Scrap and rework
• Downtime or delays

Machining might seem more expensive per part, but if it saves weeks of delays or prevents expensive die rework, it could ultimately be the more cost-effective choice.

Surface Quality and Tolerances

Casting and machining deliver different surface finishes and dimensional precision:

Criterion	Machining	Casting
Surface Finish	Smooth (Ra < 1.6 µm)	Sand: rough (Ra > 6.3 µm); Die: smooth (Ra ~ 3.2 µm)
Tolerance Capability	Tighter than ± 0.01 mm	Die: ± 0.1 mm; Sand: ± 0.5 mm
Post-Process Needs	Minimal (possible polishing)	Grinding, shot-blasting, machining

When you need hair-fine tolerances or mirror-smooth surfaces, machining has the edge. Casting can approach those levels only with extra finishing work.

Which Process Should You Choose?

The best choice depends on your goals, timeline, and budget.

Choose Casting if:

• You need to produce thousands of identical parts.
• Your part has internal features or complex shapes.
• You want to minimize per-unit cost for large batches.
• Slight variations in precision are acceptable.

Choose CNC Machining if:

• You’re making prototypes or a limited number of parts.
• Your project demands tight tolerances or fine finishes.
• You want to skip the mold design process.
• You may need to adjust the design quickly.

In some cases, manufacturers use both processes together. Regarding how to combine the two technologies, a separate introduction will be given below.

Design Factors to Consider

Before selecting a process, think beyond cost. Consider these design and engineering factors:

• Time-to-market
• Required tolerances
• Mechanical properties
• Surface finish
• Thermal or environmental resistance
• Size and weight

When to Combine Casting and Machining

Some parts benefit from both methods. This combined approach, often called “machined casting,” uses casting to form the basic shape and then CNC machining to finish critical areas. The hybrid process can deliver complex parts with tight tolerances at a lower cost than pure machining.

1. You might prototype a part using CNC machining, finalize the design, and then move to die casting once the design is locked.
2. You may cast a rough shape and then machine specific features (such as holes, threads, or sealing surfaces) to meet tighter specifications.

This hybrid workflow suits parts that need a complex outer profile or internal cavity but also demand precise flat faces or holes. The combined method can reduce material waste, shorten cycle times, and cut per-part cost when compared to full CNC production.

Conclusion

Every manufacturing method has its strengths and weaknesses. The key is to understand what you need most—speed, cost-efficiency, precision, or flexibility—and choose the method that fits your specific situation. Many successful projects combine the two by casting near-net shapes and then using CNC machines for critical features.

Whether you decide on casting, machining, or a hybrid approach, be sure to partner with experienced suppliers who can guide you through material selection, process parameters, and quality checks.

Need Help Making the Right Choice?

Need help choosing between casting and machining? Upload your CAD file today and get a fast quote. Whether you’re testing a new idea or scaling to full production, BOYI TECHNOLOGY here to help you make the right manufacturing decision.