Here’s an interesting discussion over at the Shapeways blog about a recent chart published that compares “total cost” vs “demand” for 3D printing vs injection molding — with some additional details from Shapeways about what this chart fails to model:
A recent blog post by 3sourceful compared the cost of manufacturing two items using Shapeways 3D printing and Protomold to make injection molded parts.
“In this case, we prices out two different parts. One, a very small bracket (~1cm^3) and one a larger jig (~50 cm^3). To compare, we obtained quotes from Shapeways and Protomold. And for simplicity, we just assume the cheapest material from each. We then plotted out the total cost of production for different quantities. As we would expect, the tooling costs of the molds resulted in 3D printing being cheaper at lower quantities in both cases. But, in the case of the larger part, the cost of the 3D printing material meant that over 100 units, Protomold became the cheaper solution. Where, for the smaller part, 3D printing was cost effective over 1000 units.”
This is great for a simple equation for comparing the cost of a simple part required in bulk like their bracket, but if there is any level of complexity in the part or strict tolerances, the price to injection mold is likely to quickly increase, where as the price to 3D print would likely stay the same or may actually be reduced if the complexity is in the form of meshed or perforated features. The larger item might not have taken advantage of the density discount on Shapeways that can dramatically reduce the cost of large parts.
The comparison does not take into account the upfront investment required along with cost to warehouse and distribute the injection molded parts with the liability of predicting sales and holding inventory that may not sell. Customization and/or fast iteration is also an incredibly powerful advantage of 3D printing not so easily posible with injection molded parts. If you want to make 1000 components that are very similar but not the same, the cost to 3D print remains the same where as with injection molding you will need to invest in 1000 different molds, or at the very least, 1000 different mold inserts which would then need to be manually changed out after each part is manufactured.
Same too with fast iteration, if you want to modify your design in any way to optimize your design there is no additional cost or delay with 3D printing where as with injection molding you would need to retool in most instances, adding greater cost that would need to then be amortized across the sale of your product.
The post title rightly sums up the equation cost = f(size, quantity, technology) + a whole lot more, where the ‘whole lot more’ is just as important as the rest of the equation.