Metal 3D Printing vs. Traditional Casting: Comparing Benefits and Use Cases
Metal 3D printing vs. traditional casting is a classic battle of ancient and modern manufacturing technologies. There are multiple additive manufacturing processes for metal 3D printing: directed energy deposition, or DED, binder jetting, and direct metal laser sintering, or DMLS, which we will concentrate on for this comparison.
The differences between casting and DMLS are quite stark, so depending on your application it might be an easy choice regarding which works best for you. Three overarching factors will drive your decision: part design, quantities, and lead times. Continue reading to learn more.
The Basics of Metal 3D Printing and Traditional Casting
First, here’s a high-level oversight at how the two processes work. With casting, liquid metal (or plastic) is poured into a mould containing a cavity that reflects the shape of your final part. Over time, the material cools and solidifies. Once the part has hardened, the mould is removed and the part (or the casting) is available for any finishing options you may require. It’s a rather long process, so be prepared to wait for your parts. More about that later.
In comparison, metal 3D printing builds your part layer-by-layer from a vat of powdered metal. Once the layer is complete, the build drops down into the vat and a new layer of metal powder recoats the surface for the next pass. It uses powerful lasers to melt and grow the part. While it takes a while to build parts—especially large parts—the output is as rugged as those that are cast, achieving nearly 100% density.
Part Geometries for Casting and Metal 3D Printing
Three design-focused issues define some of the differences between the two manufacturing methods: part complexity, accuracy, and part size.
Part Complexity
If your part has simple geometries and doesn’t require additional finishing, you can use casting and (eventually) simply remove the part from the mould. However, parts with complex geometries and intricate design with smaller features are likely to be better suited to 3D printing. The overarching reason for this is that, with casting, it is difficult to get liquid materials to flow through small features built into moulds, which often yields incomplete parts. Meanwhile, 3D printing excels at building out small features, and can be followed by remedial work (post print) to remove the support structures that were needed to start the build.
Both processes require designs with uniform wall thicknesses and radii. Parts with these design qualities will cool more consistently with less shrinkage, have higher dimensional accuracy, and have enhanced mechanical properties. Consistent wall thickness also leads to more efficient use of materials, which can lead to cost savings.
Accuracy
The ability to implement small features in parts for metal 3D printing makes it a better choice for detailed design. Casting can produce parts with small tolerances and a nice surface finish. However, casted parts with complex assembles often need to be made in pieces and brazed together. This extra step opens the door to possible inaccuracies and inconsistencies from the joining process. These parts are also subject to shrinkage as they cool, adding to the imprecision. Casting accuracy is also affected by the material itself, and the temperature of the material being poured into the mould.
Using a digital additive manufacturer gives you the bonus of getting design for manufacturing (DFM) feedback on your CAD model at time of submission. The automated process provides instantaneous feedback on your part and offers a “first pass” at determining if the part is feasible for metal 3D printing. It also serves to remind you that just because something can be 3D-printed in metal, it doesn’t mean you should.
Part Size
Although our biggest metal printers can manufacture parts as large as 400mm x 800mm x 500mm, casting might be a more viable option for larger parts. That said, new printers and metal printing technologies are emerging every year, and continue to push the boundaries of that limitation.
Quantity Considerations for Casting vs. Metal 3D Printing
Metal 3D printing excels at manufacturing low-volume, end-use parts. It does take time to print large parts, but simultaneously printing smaller parts in one batch can speed up production times. Since there is no tooling required, validation runs can also be completed much faster. Casting is the typical go-to if you need parts at production levels, but if you only need a small run of parts, it doesn’t make much sense to go through the time and expense to create a mould (and wait for foundry availability).
Lead Times for Casting vs. Metal 3D Printing
Need a part now? In this situation, casting certainly is not the best solution, especially at lower volumes. It can take more than a year to get parts cast due to capacity issues at foundries, in addition to the time it takes to create a mould. This is also the case even if you already have a mould to work with. With casting, if you’ve accidentally lost or damaged your mould, or need to tweak the design, you’re back at square one. Printed metal parts can be yours in days. Larger parts could take a considerable amount of printing time, but timing is still highly likely to beat that of a cast part.
Applications for Metal 3D Printed Parts vs. Cast Parts
Casting is often used to produce very large parts, such as those for transportation (railway, marine, etc.), construction, machinery, and even some consumer goods. These parts tend to be larger and often thicker. Some examples include engine blocks, bridge components, marine propellers, and turbine blades. These typically do not require a lot of detailed work, so casting is ideal, in this case, is ideal
While metal 3D printing can be used to make large parts (as noted above), it excels at rendering complex geometries, prototyping in production-grade materials, creating functional end-use parts, and even allows you to combine parts that otherwise would have required assembly. Generally speaking, 3D printing can provide smaller parts than casting, with more detail, and much faster.
Quick Comparison
To summarise, here's a quick comparison of the two manufacturing methods:
| Characteristic | Casting | Metal 3D Printing |
|---|---|---|
| Lead Times | Extremely long (potentially more than one year), even if you have an existing mould | Just days for modest-sized parts |
| Production Availability | Limited number of foundries, and they are booked well in advance | Additional printer capacity possible, and technologies are constantly improving |
| Part Changes | Your tool will likely outlive your need for it | Design changes to printed parts can be made and uploaded instantly |
| Start-up Cost | Moulds are expensive to produce | Zero |
| Piece-Part Cost | High at low-quantities, but lower as quantity increases | Lower (does not need tooling), but drops less significantly at high quantities |
| Material Choice | Larger choices | Limited, but growing, list that currently includes most primary choice metals |
Conclusion
While additive manufacturers can always add additional capacity and the technology improves all the time, the number of foundries is available for production is declining, according to a recent issue of Additive Manufacturing. Adding foundries is quite an operation, and for most companies and investors, too expensive and time-consuming.
Interestingly, some companies are using both technologies. Metal moulds can be manufactured via 3D printing and then used for casting, though you must ensure that the design works for a casting environment.
If you have any questions about what process is best to use for your design and situation, you can book a consultation with one of our in-house Applications Engineers at [email protected] or +44 (0) 1952 683047.