Injection Molding has been the primary means of producing large quantities of plastic parts for nearly 100 years. 3D Printing has been a means of prototyping for only about 30 years. But they are beginning to overlap. And there are many reasons that 3D Printing is starting to become a better alternative to injection molding.
Iteration
The key advantage of production 3D Printing is that it does not require molds. A design can be changed simply by changing a CAD design. This means that companies can produce several versions of the same physical product at scale and test how they sell. This is much how internet companies test different versions of a website to see how they perform. The ability to iterate without setting a part into stone, allows companies to test products, and make changes based on customer needs. It also allows companies to have many variations of the same product made without extra cost in order to address different customer niches.
Scalablility
3D Printing is able to produce hundreds of thousands of parts at a cost similar to injection molding. But it is also able to produce just a few parts at a price that is much less than injection molding. This means that a company company can make 10 pieces of a product, test market those, and then make 100 pieces. Then a 1000, then 10,000. 3D Printing is very scalable. So a small business can start with small production runs and then scale up to whatever the demand for the product is. This means that no cost is ever wasted. The parts can be made as needed without much need for warehousing or inventory or any kind.
Design Freedom
The way most 3D printing printing processes work, especially FDM, there are far fewer constraints on geometry than with molding. Parts can be made thick with a hollow honeycomb interior so that they are stronger than molded parts. Holes can be cut that curve through the parts, again impossible with injection molding. Something as simple as a solid 2 inch cube is impossible to produce with injection molding. But is simple and very affordable with 3D Printing. Another large advantage of 3D printing is the precise control of the surface of the part. 3D Printed parts can have a texture applied to them while they are being made. So the texture is basically free to add to the part.
Cost
There is a common misconception that 3D Printing is far more expensive than injection molding. This may have been true 5 years ago. But it is no longer. At Slant 3D we find that on average we can produce up to 20-50,000 parts or more before a mold becomes more economical than 3D printing. This is not only because of the cost of the mold. But the cost of warehousing and wasted product. Generally 10% of the cost of a final product is in the inventory. And often 10-20% of all inventory is just not sold. Since production 3D Printing allows parts to be made on demand it is possible to produce parts only as needed. So less warehousing is needed and there is never unsold inventory. In some cased Slant 3D will only produce parts for a client once those parts are sold, so there is never any inventory or wasted product.
The fact that production 3D printing is reaching a point where is is simply more efficient to produce parts with than injection molding, and give companies the ability to better address product problems makes is very compelling compared to molding. There is also the fact that the design freedom of 3D printing allows businesses to address individual niches very affordably. So even though 3D printing can't yet make the Millions of parts that molding can, the necessity for that volume may not be necessary. Why sell 1 million of a single product when you can sell 1000, of 100 different products that each customer would like better. 3D Printing very likely will drive the market away from injection molding. The high up front cost and lack of flexibility will simply become to expensive.