There are always more than one way to have your orders of components made, and the vast list of available options can be puzzling. Furthermore, your choices would be the deciding factors for your budget, timeline, and the final product’s performance.
In this article, we will present you a detailed comparison between two of the most prevalent manufacturing methods: CNC machining and die casting. Let’s explore what benefits they offer and how to choose them.
What Is CNC Machining?
How It Works
CNC (Computer Numerical Control) machining is a subtractive manufacturing process: a cutting tool removes material from a solid billet or plate based on precise digital instructions. Multi-axis machines position tools and workpieces to carve complex forms, pockets, and holes. Because it follows a digital model, setup is relatively quick, often just fixturing and toolpath programming, making it ideal for iterative design cycles and custom parts.
What It Excels At
- High Precision: Because of the advanced computation power of modern CNC systems, the mills and lathes can hold tight tolerances for critical features, with excellent positional accuracy and consistency.
- Design flexibility: With the right tool access and strategy, CNC machining produces complex internal features like deep pockets and variable wall thicknesses.
- Effortless Design Changes: Using CNC machining eliminates the concerns for wasted molds and extra costs, as it is totally feasible to cut one geometry today and design a new revised version tomorrow, with no new tooling required.
- Broad material coverage: Melting point is no longer an issue. From soft plastics to aluminum, steel, and copper alloys, CNC handles a wide material portfolio.
Limitations
- Slower for mass production: Each part consumes machine time. As volumes climb, cycle time dominates cost relative to casting.
- Higher unit cost at scale: Without the leverage of tooling, per‑part prices remain higher for large orders compared with die-cast equivalents.
- Subtractive Excess: Parts are carved from solid blocks, producing excessive chips and leading to more waste, especially with expensive metals like titanium, which can be recycled but involves additional energy, cost, and potential material value loss.
What Is Die Casting?
How It Works
Die casting is a manufacturing process used to produce solid metal parts, and it features high-precision processing and reusability unlike traditional sand casting. The die casting process involves forcing molten metal under high pressure into a reusable steel mold, known as a die. This process begins with the creation of the die itself, whose cavity takes the shapes of the desired cast parts. Once the die is complete, molten metal—typically non-ferrous alloys like aluminum, zinc, or magnesium—is injected into it, filling the mold cavity rapidly and then solidifying quickly. After the metal cools, the die opens, and the newly formed casting is ejected.
What It Excels At
- High throughput: Cycle times measured in seconds to minutes make die casting a cornerstone for mass production.
- Complex geometry: Thin walls, ribs, bosses, and integral features are readily formed.
- Attractive surface finish: As-cast surfaces are often smooth enough to reduce post-processing; coatings and paints adhere well.
- Efficient material use: Runners and gates can be recycled, which means there’s less inherent waste than machining from solid stock.
Limitations
- Upfront tooling cost: Designing and building steel dies requires significant capital and lead time.
- Material constraints: Ferrous alloys and high-melting-point metals aren’t typical.
- Hard engineering change: Design changes post-tooling can be expensive; large revisions may require die rework or new inserts.
Making the Choice: Cost and Hybrid Strategy
Cost Factors of Die Casting and CNC Machining
The decision between CNC machining and die casting fundamentally hinges on a trade-off between upfront investment and long-term unit cost. CNC machining avoids significant initial tooling expenses but results in a higher cost per part due to its slower, more labor-intensive process. Die casting, in contrast, requires a substantial upfront investment in hardened steel molds (tooling) to achieve a very low marginal cost per part during high-volume production.
This economic dynamic basically makes the choice self-explanatory. For prototyping, low-volume runs, or any case where a design is still being refined, CNC machining is the better choice. Its flexibility makes it ideal for rapid iteration and testing, in addition to offering a broader selection of engineering materials.
Once a design is finalized and annual production volumes are high enough to justify the initial tooling cost, die casting becomes the most economical option. To illustrate, if a CNC part costs $50, while die casting requires an $80,000 tooling investment with a $10 part cost, the break-even point falls around 2,000 units. It should be noted, however, that this is a basic example that excludes many factors, and real-world cost analyses are typically far more complicated
Considering a Hybrid Strategy
Up until this part, we have been regarding both casting and machining as separate techniques. However, it is entirely possible for both of them to work in collaboration.
CNC machining is perfect for bridge production, supplying parts for market testing or early sales while the permanent die-casting molds are being manufactured. A best-practice strategy is to validate a design with CNC parts before committing to the cost of casting tooling. Furthermore, it is common practice to subject die-cast parts to selective CNC post-machining and finishing processes to achieve critical tolerances on features like sealing surfaces, bearing bores, or threaded holes. This approach leverages the cost and geometric advantages of die casting for the main part while employing CNC machining to achieve precision where it is needed.
Making the Choice: Geometry, Materials, and Quality Control
Geometry Considerations
Each process offers distinct advantages for shaping a part. Die casting excels at producing thin, uniform walls reinforced by ribs, a geometry that is challenging and time-consuming to machine. It can also form certain undercuts using side actions in the mold, though this adds complexity and cost.
Conversely, CNC machining handles varying wall thicknesses and deep pockets with ease but is constrained by the physical reach and diameter of the cutting tool, making very thin walls or tiny internal radii difficult. It can access undercuts through multi-axis movements and produces high-quality, precise threads directly.
Material Selection and Performance
CNC machining offers unparalleled material flexibility, capable of processing a vast portfolio of metals, from various plastics and aluminum to high-strength steels, stainless steels, and temperature-resistant alloys like titanium. This makes it indispensable for applications demanding specific mechanical properties, corrosion resistance, or biocompatibility.
In contrast, die casting is specialized in metal casting for non-ferrous materials, primarily aluminum, zinc, and magnesium. These are selected for their excellent castability, fluidity, and strong strength-to-weight ratios, making them ideal for lightweight, high-volume components.
Quality Control
In terms of quality, the two processes excel in different areas, but both are generally precise and advanced owing to modern science. CNC machining is superb for achieving tight geometric tolerances and complex structures directly from a digital file, making it the benchmark for precision components. Die casting, once the process parameters are optimized and the mold is perfected, delivers outstanding part-to-part repeatability across very high production volumes. While its as-cast tolerances are generally wider than CNC’s, it produces highly consistent forms with excellent surface cosmetics.
Making the Choice: Sustainability
What are often missed in the cost calculation are the recyclability and sustainability of the processing methods. From a sustainability perspective, both processes have recyclable material streams but differ in their waste generation. CNC is a subtractive process, generating chips (swarf) as waste. While these chips are fully recyclable, the process involves inherent material loss, especially for metals with higher melting points.
Die casting is more material-efficient in its primary operation, as the runners and sprues (excess material from the injection channels) can be remelted and reused directly within the foundry, leading to very high material utilization rates. Both processes significantly benefit from closed-loop recycling systems, contributing to a reduced overall environmental footprint.
Conclusion
To return to the question at hand, you would arrive at the conclusion that there is no universal winner, as die casting and CNC machining have their own advantages in different fields of production. CNC machining is the choice for agility, precision, and low-volume production, while die casting excels at high-volume, cost-effective manufacturing of complex geometries.
Remember to base your decision on production volume, design stability, and functional requirements. By carefully weighing these factors, you can confidently select the most efficient and cost-effective manufacturing path for your application.
Frequently Asked Questions
For an order of a medium volume of parts, which process is more suitable?
Although we mentioned “low volume” and “high volume” many times throughout the article, they are never some numbers picked from a fixed range. To analyze the break-even point and find the best approach to your needs, the parts’ designs and complexity are the priorities.
A simpler part might be cheaper to CNC machine, while a complex part would justify the die casting tooling cost sooner. If you have an order of parts and are uncertain about it, try getting in touch with industrial experts, as it will provide you with more professional insights.
Beyond recycling metal, are there other sustainability factors to consider between these processes?
Yes, energy consumption should also be taken into account. CNC machining, especially for hard metals, can be very energy-intensive per part, as the machine tool and cooling systems run for the entire cycle time. Die casting has a high initial energy cost to create the mold and melt the metal, but its very fast cycle times can lead to a lower energy cost per part at high volumes. The “greener” option depends heavily on the production volume and the specific energy mix of the manufacturer.