When producing metal parts, the manufacturing process is important. Die casting and CNC machining are two main options, but they produce parts in different ways. This article will talk about their differences in design, production, cost, and precision to help you choose the right one for your project.
How Die Casting Works
Die casting is a metal manufacturing process. It injects molten metal into molds and forms parts with specific shapes. The molds used in die casting are usually made of high-strength steel. They can also be reused multiple times.
During production, the metal will be heated and melted. Then it will be injected into the mold in a die-casting machine. It can fill the mold and replicate the mold’s designed structure. When the metal cools and solidifies, the mold will be opened to remove the part. Excess material such as the sprue and overflow will be removed as well.
According to how the metal is melted and injected, it is mainly divided into hot-chamber die casting and cold-chamber die casting. Hot-chamber die casting machines have a furnace inside. It can keep the metal molten, while in cold-chamber die casting, the melted metal should be injected into a separate injection chamber before filling the mold.
How CNC Machining Works
CNC machining produces parts by removing material. Before producing, you need to make a digital model of the part.
The tool’s movement direction, speed, and cutting depth are controlled. During machining, the part is fixed on the machine, and the cutting tools gradually cut away the material. The machine can follow the programmed path, remove the extra materials, and cut the part into the designed size and shape.
The whole process is controlled by computer programs, so this process can be automatically repeated. This can keep the consistency of the parts. When changing the design, you only need to update the digital model and machining program instead of making a new physical mold.
Die Casting vs CNC Machining Comparison
Manufacturing Capability
Die casting and CNC machining make metal parts differently, so they are different in part manufacturing capabilities. Die casting shapes parts through molds. It fills the molds with melted metal. If you want to produce thin-walled structures, smooth surfaces, and relatively complex shapes at once, die casting is a good choice.
However, since the metal must flow inside the mold and the part must be removed after cooling, die casting has limits on sharp corners, deep undercuts, and certain internal structures.
CNC machining shapes parts by cutting solid material. It is not restricted by mold design, so you can choose CNC machining to achieve sharper edges, deeper features, and more complex structures. But for complex metal parts, CNC machining may need more steps and longer processing time.
Part Geometry
Die casting is suitable for making parts with complex shapes, thin walls, and larger internal cavities. The mold can produce the whole structure at once, so it will cut down on material removal.
However, some structures are hard to make with die casting, such as sharp corners, deep undercuts, and complex internal shapes. You need to use cores, inserts, or other complex mold components when producing these parts.
CNC machining can produce these special structures. For parts with thick walls or uneven shapes, CNC machining can finish well. But if you are producing large cavities or complex-shaped parts, it needs to remove a lot of material. This can increase machining time and produce more waste.
Material Usage
During die casting, most of the material will be made into the part of the final piece. Only the gates, runners, and overflow areas may have some extra material, which can usually be recycled.
CNC machining usually uses a larger block of metal and cuts away the unwanted parts. This will produce many metal shavings and result in higher material loss. However, CNC is less influenced by the type of material. It does not have to control the melted metal flows and solidification.
Production Speed
Production speed is mainly influenced by the preparation time beforehand and the actual processing time. Before mass production, die casting requires mold design, manufacturing, and testing. These usually can take several weeks. The exact timeline is related to the complexity of the mold.
But if your mold is ready, production of die casting can be very fast. A single casting cycle can take only a few seconds to tens of seconds. This is related to the casting part’s size, weight, and the type of equipment.
CNC machining does not need a physical mold, so the preparation time is short. After the program is done, machining can start right away. But the processing time for a single part is usually longer than die casting. Its processing time is related to the material, size, and structural complexity.
Surface Finish
Die casting replicates the appearance of parts through the surface of the mold, so the surface of the parts is usually consistent after demolding. The surface roughness of die casting is around Ra 1.6–6.3 μm. It can change according to the material, mold design, and die casting process.
CNC machining makes the parts by cutting with tools. The final surface finish can be adjusted by changing machining parameters. Its surface roughness is about Ra 3.2 μm. Fine machining or polishing can make the surface smoother, and the surface roughness can reach around Ra 0.4 μm.
Both CNC machining and die casting can also undergo extra surface treatments. You can use painting, powder coating, plating, or anodizing. The final surface finish can be influenced by the manufacturing method as well as the material, process parameters, and mold design.
Accuracy
Die casting can produce stable and consistent sizes or dimensions through a well-designed mold. However, metals shrink as they cool and solidify, so the final size may be smaller. Generally, standard die casting tolerance is about ±0.1 mm per 25 mm (±0.004 inch per inch). It can be influenced by the material and part size.
CNC machining production has higher production precision. Standard CNC machining tolerance is around ±0.025 mm(±0.001 inch), and with special processes, it can be more precise. However, the actual accuracy may also change according to the machine, tool wear, and material.
If moderate precision is enough and you need higher volumes, die casting is more suitable.
Applications
CNC machining and die casting are used in different industries and fields such as electronics, consumer goods, automotive, and industrial equipment. They are used for producing different types of parts.
If you are planning to make metal housings and structural components, die casting is better. It is suitable for stable mass production.
CNC machining produces high-precision parts, prototypes, jigs and fixtures, as well as components with complex shapes. It is widely used in medical equipment, aerospace, and machinery manufacturing.
For long, constant-cross-section steel components made in high volumes—such as warehouse-rack uprights—a roll forming line for rack uprights is generally more suitable than either die casting or CNC machining because it continuously forms coil into repeatable profiles with less material waste.
Die Casting vs CNC Machining Comparison Table
| Comparison Factor | Die Casting | CNC Machining |
| Process | Uses molds to form parts with molten metal | Uses cutting tools to remove material |
| Design Capability | Suitable for thin walls, complex shapes, and integrated structures | Suitable for sharp edges, deep features, and flexible designs |
| Material Usage | Less waste | More waste |
| Production Volume | Suitable for high-volume production after tooling | Suitable for low-volume production and prototypes |
| Speed | Slower setup but faster cycle time in mass production | Faster setup but longer processing time per part |
| Accuracy | Around ±0.1 mm per 25 mm (±0.004 inch per inch) | Around ±0.025 mm (±0.001 inch) |
| Main Advantage | Lower unit cost for large quantities | High flexibility without mold investment |
FAQ
Can Die Casting and CNC Machining Be Used Together?
Yes, they are often used together. Parts can be produced by die casting to form the main body. Then CNC machining makes higher dimensional accuracy or special shapes. Hybrid manufacturing is cost-effective.
When to Switch from CNC Machining to Die Casting?
For production under 1,000 pieces, CNC machining is more cost-effective. When it reaches 1,000–5,000 pieces, you can choose hybrid manufacturing. When production hits 5,000–10,000 pieces, die casting is more economical. Beyond 10,000 pieces, the per-unit price of die casting is much lower.
Are Design Changes Needed When Switching to Die Casting?
Yes. When changing to die casting, the design usually needs to think about how the metal flows in the mold. You can add draft angles, optimize wall thickness, reduce sharp corners, and design proper ribs to improve filling and cooling.
Is CNC Machining More Suitable for the Product Development Stage?
Yes, CNC machining does not need a new mold to modify the design, so it is generally suitable for the product development stage. You can adjust the digital model and produce updated parts quickly. For prototypes, low-volume production, or parts that require design changes, custom CNC machining services offer greater flexibility without the need for a new mold.
Can the Design Be Modified After the Die Casting Mold Is Completed?
The design can be changed after the mold is completed, but it need to modify the mold. It is related to the location of the changes. You need to make a design review in advance.
Final Thoughts
CNC machining and die casting are different in many areas. You can choose the suitable one according to your part design, production volume, cost requirements, and long-term manufacturing plans. If you are looking for a professional die casting or metal machining supplier, feel free to contact us for more information.