3D Printing VS Injection Molding: Manufacturing Solid Objects

Is 3D printing better than injection molding?  This is a common question we get at Slant 3D.  The answer is it really depends on what parts you are trying to make. Your project details including your deadlines, the product you are printing, and how the product is being used are all valuable pieces of information we can use to help decipher whether 3D printing is the right option for you.  One of the key pieces of information that we need to determine this is whether or not your product is an enclosed body.

An enclosed body in 3D printing means that the design has a closed print chamber. This means there is no airflow that runs through the product and it is virtually solid.  3D printing is exceptionally good at making products with enclosed bodies like a solid cube. On the other hand, injection molding physically cannot make a solid cube that is about two inches small.

Small solid objects cannot be made with injection molding because the material would shrink once created. With injection molding, you would have to fill up a solid cube with melted plastic and once it starts to cool, a solid object would shrink and deform.

​The sample brick made with injection molding (Figure 2) demonstrates this occurrence. You can see where the shrinkage is happening because the cube is a solid body. If you go any larger than 2 inches the shrinkage is going to be worse.  This does not happen with 3D printing. 3D printing can make fully enclosed bodies that are solid all the way through.​

Often when using injection molding, solid cubes are laid out flat and then molded together via heat. This process is very similar to origami; you take a two dimensional paper and then fold it to create something three dimensional. With injection molding, you create a flat mold then bring the separate pieces together to make your product three dimensional. Injection molding tries to avoid product redesigns by putting a cavity on the back side of the product.  Again this still doesn’t compare to 3D printing because a fully solid cube has all six sides covered with no holes.  

Creating solid objects with injection molding usually takes longer because of this multi-step process.  However with 3D printing, you can print a solid cube directly off the printer and send it out as is.

Another option with 3D printing is to also fill your product with infill.  The reason for this is because it has the durability of a solid object but it is more cost effective because it uses less plastic.  Inside the product would look like a honeycomb pattern that is able to maintain excellent structural integrity but also be light weight and use less material. Injection molding cannot do this. ​

So if you have a solid part, we suggest that 3D printing is probably the right direction for you.  With 3D printing your product can be ready to ship directly off the printer rather than having a multi-step manufacturing process.  With 3D printing there is also no need to redesign your product in order to prevent deformation because that issue is no one that 3D printing has.  We are going to continue the conversation about 3D Printing versus Injection Molding in future blogs to come so make sure you are following Slant 3D on social media to see when we post our next blog post on the topic. ​