Die casting excels in high-volume, complex shapes but has lower precision. CNC machining is precise and versatile for prototypes and lower volumes. Die casting uses molten metal in molds, while CNC subtracts material from solid blocks.  Choose die casting for mass production, CNC for accuracy and flexibility.

By comparing both procedures along with their fundamental parameters, you can find the better option. Therefore, this article provides in-depth details of die-casting vs. CNC machining.

Die-Casting: Overview and Benefits

The manufacturers melt selected metals according to their melting temperature. For example, they melt zinc at 385°C and aluminum at 660°C. Then the next step, die-casting, happens.

This method feeds molten metal into a permanent mold under 10–175 MPa pressure. Runners flow this metal, and risers collect their residues.

Molten metal solidifies, taking 5–30 seconds and enabling ejection at 200–300°C. You must know each cycle is complete in 15- 60 seconds.

Looking at its rapid production ability, you can complete large batches with die-casting up to 10–100x faster than CNC machining.

Applications of die-casting

Die-casting helps in producing complex parts. For instance, it can make engine blocks from aluminum along with 1.5 mm walls. Also, this method provides durability and heat resistance.

Electronic parts cast zinc to make their thin-walled enclosure much lighter. Furthermore, aerospace applications use magnesium for the purpose of cutting weight around 30% and increasing fuel efficiency.

Die-casting Processes

1.   High-pressure die-casting (HPDC):

Generally, HPDC works under 10–175 MPa pressure. It injects metal at 10–50 m/s speed. This process perfectly produces stated aluminum parts for electronics or automotive. It can add thin walls (1.5–5 mm).

2.   Low-pressure Die-casting (LPDC):

Manufacturers use 0.3–1.5 MPa pressure while operating LPDC. In this process, the mold-filling process is very slow to avoid defects. It works better for great depth around 5–15 mm parts (wheel hubs). They also provide certain strength and durability.

3.   Gravity Die-Casting:

The method employs gravity to fill the mold, which is preheated to 150–300°C. It can produce very simple aluminum parts with fine surfaces at affordable prices.

Types of Alloys and Properties

Die-casting Tooling Process

Manufacturers create dies that are 10 times stronger using steel (H13 grade) to resist the effect of  50,000–1,000,000 cycles. They can cost 10,000–200,000 depending on the design, alloy, or other factors. Besides, their key aspects include:

• They use a clamping force of around 100–5,000 tons (according to part size).
• Per cycle takes 15–60 seconds (depending on part cooling).
• Their ejection force can be around 5–20% of clamping force.

Limitations of die-casting

• An X-ray inspection is needed to check porosity because air pockets can form up to 1–2 mm deep.
• Use 1–3° draft angles for part removal.
• The maximum part size can be up to 600 mm due to die costs.

CNC Machining: Overview and Benefits

CNC (Computer Numerical Control) machining uses computer-aided techniques. This technology gets guidance from computers to cut shapes and convert raw metal into sharply defined parts.

You know, in die-casting, hot metal goes in and a solid shape comes out. Conversely, CNC machining uses cutting tools to remove material (metals, plastics, and composites) layer by layer.

However, this procedure is suitable for fewer custom parts, prototypes, and low- to medium-kind orders (1–1,000 units)

CNC Programming Process

CNC machining uses a tool that is held by a spindle. This tool cut the raw material on worktable. The drive motor gets MCU signals and moves the spindle accordingly. Meanwhile, the feedback device confirms correctness.

CNC Machining Operations

CNC machines operate three common tasks:

• ミーリング
• ターニング
• 掘削

ミーリング

Manufacturers use spinning tools (500–15,000 RPM) in milling. They cut up flat and curved shapes. For instance, they use a 10 mm carbide end mill. That helps cut aluminum alloys at 2,000 RPM for making engine brackets.

ターニング

A rotating spindle secures the workpiece where it rotates it up to 3,000 RPM). Meantime, cutting tools or stationary rotate along the spindle axis and give a cylindrical (screw or pipe) shape to the material.

掘削

The drilling process needs to make holes in parts. Usually, manufacturers use drill bits (1–25 mm diameter) at speeds of 500–1,500 RPM. For example, they make holes in plastic housing using bits of 5 mm.

Examples of CNC Machined Parts

CNC machining takes 3 hours to produce a prototype for a 100 mm aluminum robot joint. This part can provide up to 0.02 mm accuracy.

In medical implants, manufacturers polish cobalt-chrome knee replacements to Ra 0.4 µm. That allows it to move smoothly.

Aerospace titanium turbine blades stand up against 800°C. These parts are made using 5-axis CNC mills with 0.01 mm precision.

Types of CNC Machines and Capabilities

3-axis CNC mills

It contains three primary axes (X, Y, Z). That moves left-right, front-back and up-down. Despite its limited movement capabilities, it can manage parts about 600 mm long. 3 axes make 3D shapes for parts like gearboxes with ±0.05 mm accuracy.

5-axis CNC mills

This machine tilts and rotates tools. These tools can cut very difficult shapes (e.g., turbine blades) in one setup. You can get ±0.02 mm stated parts.

CNC lathes

This kind of CNC machine specializes in round parts. It can grip materials up to 300 mm wide. Using it, you can cut threads as fine as 0.5 mm pitch.

Tooling in CNC Machining

Manufacturers make CNC cutting tools, usually with carbide (lasts 200–400 minutes). The other tool’s material can be high-speed steel (HSS, 100–200 minutes) or ceramics (for high heat).

Also, you can increase the lifespan of these tools by using several coatings like titanium nitride (TiN). Coating layers make the tool 50% faster, and do not let it wear. For instance, coated drill bits are capable of making 500 holes in stainless steel at 0.2 mm per spin.

Tool holders use hydraulic force (up to 200 bar). These force clamp tools tightly, minimizing vibrations during cutting.

Materials for CNC Machining

Limitations of CNC Machining:

• CNC machining removes material slowly.
• Its feed rates typically range from 0.1 to 0.5 mm/tooth, which is, therefore, inefficient for large orders.
• Cutting materials at high speed causes tool wear.
• It can be challenging for CNC to obtain complex geometries with deep features (e.g., depth-to-width ratios >5:1).

Comparison of die-casting and CNC Machining

1.   Material Properties Comparison

As we have discovered, both the technique of die-casting and CNC use different materials. This means they have unique properties. For example, a common die-cast alloy is aluminum A380. This alloy comes with a tensile strength of around 310 MPa and a yield strength of up to 159 MPa.

Likewise, CNC machines use Aluminum 6061. That offers 310 MPa tensile strength and 276 MPa yield strength.

2.   Tolerance Comparison

You can get tolerances around 0.004 inches (0.1 mm) for small parts via die-casting. However, material shrinkage and cooling effects increase tolerances with part size.

Conversely, CNC machining gives very tight tolerances, often below 0.001 inches (0.025 mm). This means it can work well when strictly conforming to a pattern.

However, getting accurate outputs demands higher costs. If you want to achieve a 0.003-inch (0.075 mm) tolerance, it might cost 100 units. Meanwhile, a 0.0005-inch (0.012 mm) tolerance could triple it. This is because of increased machining time, tool wear, and quality control measures.

3.   Cost Analysis

Die-casting includes initial setups and tooling. That is why it costs around $5,000–$50,000. However, it reduces each unit cost ($1–$5 per part) for a big order.

CNC machining does not claim tooling costs. Its production cost depended on material selection and design complexity level.

4.   Lead Time Comparison

Tooling setup of die casting takes 4–8 weeks before initiating the process. However, once these tools are ready, they can produce large batches quickly.

There is no tooling delay in CNC machining. This process can make prototypes within 1–3 days. Additionally, batch production takes 5–10 days according to design complexity.

5.   Part Complexities

die-casting can handle simple to moderate complexity levels of designs. It supports thin walls and integrated features like ribs. This process struggles while making deep cuts, sharp internal corners, and lengthy stated parts.

CNC machines can work on deeper designs and complex geometries. This process is slower, which is why it increases the cost of large batches.

6.   Environmental Impact Comparison

There is less material waste during casting operations, but leftover material is not always 100% recyclable. This is because of oxidation and impurities. Also, mold fabrication uses significant energy.

The CNC machining process produces more scrap. In particular, you can reuse metal chips. However, its cooling agent impacts the environment. This can be reduced up to 50% using modern filtration systems.

Decision Matrix for Choosing the Right Process

Design Considerations for die-casting and CNC Machining

Design Rules for die-casting

die-casting needs draft angles. These angles make the ejection process smoother. You can calculate the draft angle using formulas.

Formulas incorporate alloy-specific constants, typically 1°–3° per side. Its calculation is also affected by the material and part complexity.

Additionally, wall thickness can also vary. For example, aluminum can be used 1–1.5 mm, and zinc can be used 0.5–1 mm. Thickness confirms proper flow and repels defects.

Moreover, the main job of fillets and radii is to reduce stress concentration and increase mold life.

Design Considerations for CNC Machining

Generally, CNC machining designs do not need draft angles. They can make sharp internal corners and vertical walls. Their design option can include T-slots, dovetails, and deep pockets. That contain higher depth-to-width ratios.

Consider tool access because deep cavities need longer ones. That can also increase vibration and not provide accurate results. In addition, fixturing supports stability during machining.

Use of Simulation Software

You can use simulation tools to polish the design’s performance further. These tools make diecasting mold flow and CNC tool paths as functional as possible. It also helps in identifying defects like porosity in die-casting and chatter in machining.

Collaboration Between Designers and Engineers

Try to communicate with designers early. Confirm your requirements to produce cost-effective and manufacturable parts. This step also prevents several modifications and production issues.

結論

The die-casting option is good to use for large production. It produces parts faster at a low rate but is not efficient for precision results. Conversely, CNC machining uses multiple materials and provides high accuracy. However, this technique is slow and costly.

Both processes have different pros and cons. The selection totally depends on what types of material or products you are producing.