04 Oct CNC Machining VS 3D Printing
Prototyping is an essential phase in the development of new products. No matter how well your product is designed, there will would always be some revisions to the original design. These revisions are not necessarily caused by errors, but are simply new features that now you are able to see clearly and would like to add to your current product design. There are many processes to choose from when going about making your first prototype, the big question is which processes to use for prototyping. This is a common question we are asked here at MEMA Engineering. In this post I will mainly talk about 3D printing and machining since these two are the most used in prototyping.
CNC stands for computer numerical control, and the two most commonly used CNC’s are CNC milling machines and CNC lathes. CNC machining requires a set of instructions called g-code, which today is mostly written by advanced CAD to CAM software packages. The CNC machine interprets the g-code and uses a number of pre-loaded tools to remove material from the “stock” (stock can be any material: plastic, aluminum, steel, etc.) Since we are removing material, we are not affecting the material properties (in most cases) which is an important factor if you are planning on having a prototype that you can run structural tests on such as tensile, compressive, bending, and thermal. Another key benefit of CNC machining is the precision, giving you tight tolerances. This is important if your product has mating parts, shafts, and bearings.
The down side to machining is that it’s more involved than simply clicking the print button and have it machine a part for you.
PRO: High tolerance parts, unaffected material properties, any surface finish needed
CON: More expensive, design limitation due to tool path and tool diameter
There are various methods for 3D printing; Selective Laser Sintering (SLS), Stereolithography (SLA), Polyjet (J-P), and Fused Deposition Modeling/Fused Filament Fabrication (FDM/FFF). You can 3D print in various materials, such as: plastic, glass, metal, polymers, was, sand/glue, and even edible food such as chocolate. Unlike machining, 3D printing is an additive process and is created by laying down/curing successive layers until the complete part is made. Since it’s placed layer by layer, this results in a poor surface finish. Also, it has no structural benefits or stiffness.
3D printing is still a great process to test out your idea and have a physical prototype in your hands faster. The key benefits are the following: no design restrictions (if you can model it in CAD, then you can print it), closer representation to injection molding, great for seeing aesthetics and complex shapes, print complete assembly as one part, and it is relatively inexpensive.
PRO: faster lead times, inexpensive, no design limitation
CON: Poor surface finish, not accurate/poor tolerances, cannot be used for physical testing
So you’re still wondering which process to use? Simple answer is it really depends on your product. You have to decide what your goals are for the first prototype and what information it is that you’re seeking.
Here is a list of questions to consider:
- Do tolerances matter in this prototype? Are there mating components?
- Would the finished product be a machined part, injection molded or other processes?
- And lastly, what is your budget?