Metal 3D Printing vs. Casting vs. CNC: Which is Better?

As metal 3D printing gains popularity throughout the manufacturing industry, many are beginning to wonder whether it’ll become the preferred choice above traditional methods, such as casting and CNC machining.

This article compares metal 3D printing with casting and CNC machining to determine which, if any, is the best method to choose.

Read more: Metal 3D Printing vs. Traditional Manufacturing: Which Should You Choose?

Metal 3D Printing vs. Casting

In basic terms, casting is the manufacturing process where a liquid material is deposited into a mould of the desired shape then left to solidify. It’s a traditional method of manufacturing that dates back to the middle ages. We’ve compared casting with metal 3D printing based on several factors.

Size

When producing large parts, casting would be the method to choose. Generally, traditional manufacturing methods are much better at producing larger parts. This is because 3D printed parts must be printed within a controlled environment and are limited to the size of the printer´s build volume.

However, innovations within additive manufacturing could mean the size of parts produced by 3D printing could increase in time. Direct energy deposition (DED) is a 3D printing process that can print larger parts. Due to the use of a robotic arm, a DED printer isn’t limited to a specific part size. This could mean if a large, complex part is required, metal 3D printing could meet this need.

Cost

Cost is often the biggest crunch point when deciding whether to use traditional manufacturing or metal 3D printing. One variable will affect this answer — the number of parts required.

Casting would be the cheaper option when producing many parts. If your order size is smaller and has more complex requirements, then metal 3D printing would be the more cost-effective route.

This is because casting benefits from higher economies of scale. As the quantity of parts increases, the fixed cost of producing a casting mould – which can be very expensive – can be allocated across many parts. With metal 3D printing variable costs are the main cost drivers, meaning the unit cost is not as dependent on the production quantities.

Lead Times

If time is of the essence, then metal 3D printing is the fastest method out of the two for small batch production. The overall process is much quicker, as 3D printing requires less set-up time and no special tooling is required to produce a part.  

Casting involves a number of pre-production tasks, whereas 3D printing only requires a 3D model being uploaded to the printer. In addition to this, there are typically more post-process steps involved with casting to achieve the desired material density requirements.

Complexity

Metal 3D printing excels in printing complex parts with fine details that are often challenging to achieve using casting methods. Moreover, LPBF (Laser Powder Bed Fusion) 3D printing provides a superior surface finish resolution compared to casting.

Therefore, you need to consider the types of parts you’re producing. Metal 3D printing would be better suited to smaller parts with intricate features, such as nozzles, small impellers or parts requiring lightweight structures. Casting is more suitable for larger parts where metal can more easily flow to all sections of the mold.

Mechanical Properties

Finally, you’ll need to consider the mechanical properties required for your parts. The mechanical properties achieved through metal 3D printing vary depending on the printing technology used. Parts produced using LPBF generally outperform casted parts, thanks to their higher densities and reduced risk of internal voids. However, it’s worth noting that practically any metal material can be cast, whereas the portfolio of materials for 3D printing is still limited.  

Metal 3D Printing vs. CNC Machining

CNC machining is when automated cutters remove material from a solid block of material to achieve the final shape. It’s one of the most popular traditional manufacturing methods, as it offers repeatability and can be used with a wide range of materials.

Before we compare metal 3D printing with CNC machining, many of the advantages and disadvantages will be similar to casting, as CNC machining and casting are both types of traditional manufacturing.

Size

Similarly to casting, CNC machining can be a suitable option for producing large parts. This is because it requires less of a controlled environment than 3D printing and there’s a wide range of machine sizes available, in addition to lathes and milling machines capable of producing very large parts. 

Cost 

The overall price depends on the number of parts produced. 3D printing will be the more cost-effective option for small production batches, especially if there is a degree of design variation involved. As that quantity increases, CNC machining becomes a cheaper option in terms of unit cost. When comparing the three methods, casting would be the most suitable method for the largest quantities.

*Highly dependent on part geometry             

Credit: Hubs

It’s also worth noting the waste involved in each process here, as waste material usually comes at an expense. CNC machining is a subtractive manufacturing process, meaning the material is cut away to achieve a final part, resulting in a large amount of material waste. 

However, metal 3D printing only uses the amount of material needed to create a part and any excess can usually be recycled into the next build. As the world becomes increasingly invested in sustainability, this could be a determining factor for some businesses.

Lead Times

In general CNC machining is slower for producing smaller production batches compared to metal 3D printing. This is because more setup time is required and depending on the hardness of the working material, the cutting process may take longer. On the other hand, metal 3D printing prints the entire part in a single run and the hardness of the material is not a determining factor of the production process.

Similar to 3D printing, CNC machining uses a digital file to create a part. However, unlike 3D printing, the machining operations need to be programmed into the CNC machine for each production run, which can take a lot of time. 

The main benefit of CNC machining is that the final machined part usually only needs post-process heat treating. In contrast, 3D printing may require post-process machining to achieve the desired tolerances on certain features.

Although CNC machining is generally quicker than casting for lower production volumes, casting can be a more productive method for higher volume production.

Complexity

Metal 3D printing is still the best method when producing intricate parts with fine features. Not only this, but metal 3D printing can also produce lightweight structures and internal cavity profiles that would be impossible to produce using CNC machining.

However, CNC machining still offers superior dimensional accuracy – capable of achieving tolerance of +/-0.001mm – which is significantly better than both casting and metal 3D printing. For this reason, both casted and printed parts often undergo post-process machining to achieve design specification requirements.

Mechanical Properties

LPBF 3D printed parts commonly display superior isotropic characteristics when compared to parts produced through CNC machining. This improved isotropy can be attributed to the consistent shape and distribution of the powder raw material utilized in 3D printing. Conversely, CNC machining, which utilizes forged bar stock as the working material, often yields denser parts that may exhibit potential anisotropic behaviour due to the grain structure of the starting material.

Which Method Is Better?

There’s no clear winner when comparing metal 3D printing with casting and CNC. Each technique has several pros and cons that need to be addressed concerning the task at hand.

However, we can apply a few general rules:

• Metal 3D printing: The best method for creating complex parts with intricate geometries on a smaller production scale.

• CNC machining: Can create precision parts on a larger scale, but is limited in its ability to create very complex parts.
• Casting: The best method for producing simple or complex parts in large volumes, but at the expense of high investment costs and long lead times.

The direct relationship between complexity and quantity is shown on the graph below.

Credit: Hubs

There’s no method that always comes out above another. To progress in the future, the idea is that traditional manufacturing techniques and metal 3D printing will complement each other, filling gaps where the other falls short. 

When considering your project, it’s crucial to think about the quantity, complexity, cost and time to help you decide on the best method.

Is Metal 3D Printing the Future?

In our guide, we unpack the topic of metal 3D printing, focusing on the technologies, applications and processes, as well as discuss whether it’s the future for the manufacturing industry. 

To join the debate, click the link below to download the guide and gain more insight.