One of the most exciting aspects of the rise of additive manufacturing is its potential to drastically lower the costs for rapid prototyping and low-volume orders. I say “potential” because this is only true if the part you’re manufacturing takes advantage of the “complexity paradox” that can make 3D printing so cost effective.
What is the complexity paradox? Well, in traditional subtractive manufacturing, the more complex your part is, the more expensive. That’s because you’re starting with a solid block of material and cutting away from it, and the more you have to cut away from it (i.e., the more complex it is), the more work it is for the machine and the higher the price. So a solid block with a hole in it is a lot easier to manufacture than a solid block that has features like pocketing and ribs for removing weight, since each of those pockets needs to be cut out from the material. Because the price for 3D printing only increases with the amount of material being used, those pockets represent less material that needs to be printed, reducing the price of the part. Added complexity can actually lower your costs, which is why 3D printing can serve as a wonderful alternative for complex pieces.
There’s a common mistake I see companies make when they decide to dip their toes into the world of 3D printing. This mistake is typically made by larger organizations that have heard 3D printing can reduce costs for their low-volume parts, so they put together a team to investigate additive manufacturing and assess the price differential. The problem is that they come in with a design that has absolutely no modifications from the CNC version of the part. In other words, rather than designing a part specifically for additive manufacturing, they’re using the exact same CAD file they’ve used in the past. The original part was often designed for as little subtraction as possible, which drove down the cost of CNC machining but will drive up the cost for 3D printing. Remember: the more material that’s used in 3D printing, the more expensive the part is and the longer it takes to build.
What these companies should be doing is modifying their designs to the strengths of the 3D printing process being investigated. This will not only allow you to take advantage of the complexity paradox, but the part will be much lighter, which in many cases improves the performance of an overall product.
When calculating the price differential between CNC machining and 3D printing, it helps to look at the bigger picture. Consider that CNC machining is more cost effective when you manufacture many parts at once. The per-unit cost for manufacturing 1,000 parts, therefore, is much, much lower than if you were to manufacture only five parts. But if you manufacture 1,000 parts for a product that doesn’t sell at high volume, you have to then store those parts, and storage is expensive. With 3D printing, on the other hand, the per-unit cost for printing parts on demand (“Just in Time”) may be cheaper than the cost of storage and potential scrap due to obsolescence. Therefore, you’re able to keep much lower volumes in storage and then only manufacture new parts when your supply gets low. This not only lowers storage costs, but requires less risk on the part of the company in case it’s not able to sell out its inventory.
Is 3D printing less expensive than subtractive manufacturing? It all depends on whether you approach it with a fresh perspective and keen understanding of how to design parts for the technology. Simply uploading a CAD file and making a 1:1 comparison will leave you with the impression that it is more, not less, expensive. But if you design your part so that it takes advantage of the complexity paradox and match it with the right 3D printing technology, then you’ll find additive manufacturing can be a viable alternative that can save you money.