Although 3D printing, also known as additive manufacturing, has emerged as increasingly important manufacturing strategy, it cannot replace traditional manufacturing of parts through injection molding, or other mass manufacturing means. As Dr. Mark Cotteleer, Deloitte Services, summed up, "Additive manufacturing is not a pancea. There is no reason to view it as a universal replacement for traditional manufacturing methods. [However,] we do see it as important within the constellation of manufacturing methods that businesses can deploy in pursuit of performance, innovation, and growth." (Source: 2014 SIMT Additive Manufacturing Symposium)
The question is: when does it make sense from a business perspective to employ 3D printing vs. other manufacturing methods? Said another way: at what volumes is at advantageous to 3D print parts?
To answer this question we compared the costs of 3D printed parts, with the average cost to produce the same exact part via injection molding. In order to make a true apples-to-apples comparison, we selected Selective Laser Sintering (SLS) durable white nylon, which has very similar material properties to the polyamide nylon used in injection molding.
The sample part we used was a fairly simple bracket with holes, which was designed for end-use and therefore needed to be durable. Nylon, which is a robust material, was a good fit here.
Given this part and the nylon material, we wanted to find the breakeven at which injection molding was more economical than 3D printing, on a cost per unit basis.
In order to do that, we uploaded the 3D CAD file to Xometry's automated quoting engine, which provides instant quotes for SLS in various quantities. For a quantity of 2, the cost was $72.95, or $36.48 per unit:
Next, we compared that with the average costs to manufacturing the same part via injection molding, and plotted the results:
As industrial 3D printing technology continues to improve and manufacturing capacity increases, the costs for building 3D printed parts has decreased. Specifically, Selective Laser Sintering has emerged an economical method for manufacturing end-use parts in low volumes. In this case, an order of 1 bracket cost just $41. That price also decreased with scale – 10 parts were $33 each.
Since injection molding requires both setup fees and tooling costs, low-volume production is often cost-prohibitive. In this instance, injection molding at a quantity of 10 units ($405 per part) was more than ten times as expensive as producing the same part using SLS ($33).
In this example, the breakeven point was 130 units, where both 3D printing and injection molding were the same cost per unit. All things created equal, if the order quantity were greater than 130, injection molding should be selected here.
3D printing and injection molding are not competing, but rather complementary ways of manufacturing. For example, a business may use SLS for rapid prototyping and low-volume production, and then switch to injection molding once the volume of parts is above a certain threshold.
The ability to produce a just-in-time quantity of parts, in a short amount of time, is where 3D printing shines. Compare that with injection molding, which is typically used in mass manufacturing – i.e. producing hundreds, if not thousands, of parts inexpensively.
Although cost per unit is an important figure, there are several hidden costs that managers should also take into consideration when making manufacturing decisions: 1) time required to manufacture and receive parts, 2) potential inventory costs, and 3) having the option or flexibility to quickly change product design. All of these play a factor in manufacturing selection, and vary on a case by basis.